Use of non-invasive NIRS during a vascular occlusion test to assess dynamic tissue O2 saturation response

Intraoperative Oxygenation and Microcirculatory Changes Following Off-pump Coronary Artery Bypass Grafting: An Exploratory Secondary Analysis of a Randomized Clinical Trial

OBJECTIVES

The effect of perioperative hyperoxia on microcirculation after cardiac surgery remains inconclusive. We evaluated the relationship between intraoperative fractional inspired oxygen and microcirculation after off-pump coronary artery bypass grafting (OPCAB).

DESIGN

Exploratory secondary analysis of a multicenter cluster-randomized trial.

SETTING

Three teaching hospitals.

PARTICIPANTS

Adult patients who underwent OPCAB.

INTERVENTIONS

Seven postoperative microcirculatory parameters, including De Backer scores and the proportion of perfused vessels via sublingual microscopy (from all and small vessels), and thenar muscle tissue oxygenation, occlusion slope, and recovery slope via the vascular occlusion test, were compared between patients receiving 30% and 80% oxygen intraoperatively. Generalized estimating equations were used to account for intracluster correlation.

MEASUREMENTS AND MAIN RESULTS

The analysis included 52 and 51 patients from the 30% and 80% oxygen groups, respectively, for sublingual microscopy and 59 and 53 patients for the vascular occlusion test. Although all microcirculatory parameters were similar between groups, the 80% oxygen group had higher De Backer scores for all vessels (mean, 9.8 ± 2.9 mm-1 vs. 8.7 ± 2.0 mm-1; p = 0.011) and small vessels (4.0 ± 1.8 mm-1 vs. 3.4 ± 1.1 mm-1; p = 0.024) than the 30% oxygen group at the end of surgery. The 80% oxygen group also exhibited greater thenar muscle tissue oxygenation immediately before vascular occlusion (78.4% ± 10.5 vs. 74.0% ± 9.3; p = 0.031) and a higher recovery score (4.1%·s-1 ± 1.7 vs. 3.2%·s-1 ± 1.4; p = 0.001).

CONCLUSIONS

Patients receiving 80% oxygen during OPCAB had significantly better postoperative microcirculatory profiles than those receiving 30% oxygen. These findings highlight the potential for optimizing perioperative oxygenation to improve or mitigate microcirculatory impairment, thereby reducing postoperative complications.

Cardiac arrest and microcirculatory dysfunction: a narrative review

PURPOSE OF REVIEW

This review provides an overview of the role of microcirculation in cardiac arrest and postcardiac arrest syndrome through handheld intravital microscopy and biomarkers. It highlights the importance of microcirculatory dysfunction in postcardiac arrest outcomes and explores potential therapeutic targets.

RECENT FINDINGS

Sublingual microcirculation is impaired in the early stage of postarrest and is potentially associated with increased mortality. Recent work suggests that the proportion of perfused small vessels is predictive of mortality. Microcirculatory impairment is consistently found to be independent of macrohemodynamic parameters. Biomarkers of endothelial cell injury and endothelial glycocalyx degradation are elevated in postarrest settings and may predict mortality and clinical outcomes, warranting further studies. Recent studies of exploratory therapies targeting microcirculation have shown some promise in animal models but still require significant research.

SUMMARY

Although research continues to suggest the important role that microcirculation may play in postcardiac arrest syndrome and cardiac arrest outcomes, the existing studies are still limited to draw any definitive conclusions. Further research is needed to better understand microcirculatory changes and their significance to improve cardiac arrest care and outcomes.

Effects of occlusion pressure on hemodynamic responses recorded by near-infrared spectroscopy across two visits

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (-1959.2 ± 1417.4 vs. -10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. -11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSIslope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

Assessment of microcirculatory alteration by a vascular occlusion test using near-infrared spectroscopy in pediatric cardiac surgery: effect of cardiopulmonary bypass

OBJECTIVES

Cardiopulmonary bypass cause microcirculatory alterations. Near infrared spectroscopic measurement of tissue oxygen saturation and vascular occlusion test are novel technologies for assessing the microcirculatory function of peripheral tissue specifically in patients undergoing cardiac surgery with cardiopulmonary bypass.Our study aimed to evaluate dynamic microcirculatory function using the vascular occlusion testing during cardiac surgery in pediatric patients.

METHODS

120 pediatric patients were scheduled. Children had continuous regional oxygen saturation monitoring using near infrared spectroscopy and vascular occlusion test. Vascular occlusion test was performed five times; before induction (T1), after induction (T2), then during cardiopulmonary bypass with full flow (T3), after the termination of CPB (T4) and after sternum closure (T5).

RESULTS

Basal value was the lowest at T3 and this value was significantly different among measurements (p < 0,01).Values for maximum and minimum tissue oxygen saturation were the lowest at T3 (83,4 and 52,9%).The occlusion slope varied significantly among measurements (p < 0,01).Reperfusion slopes were significantly different among measurements (p < 0,01) with a further progressive decrease in reperfusion slope with duration of cardiopulmonary bypass.

CONCLUSION

Microcirculatory function can assessed using VOT with forearm Near-infrared spectroscopy derived variables during cardiopulmonary bypass in pediatric cardiac surgery. Noninvasive assessment of microcirculatory perfusion during cardiopulmonary bypass can further help evaluate and improve circulatory support techniques.

TRIAL REGISTRATION

The research Project was registered at ClinicalTrials.gov (NCT06191913).

Evaluating the relationship between ocular blood flow and systemic organ blood flow in hemorrhagic shock using a rabbit model

This study aimed to investigate the feasibility of utilizing noninvasive ocular blood flow measurements as potential indicators of systemic circulation in rabbits experiencing hemorrhagic shock. Using Laser speckle flowgraphy, ocular blood flow indices, relative flow volume (RFV), and mean blur rate in the choroidal area (MBR-CH) were assessed in New Zealand White rabbits (n = 10) subjected to controlled blood removal and return. Hemodynamic parameters and biochemical markers were monitored alongside ocular circulation during blood removal and return phases. Additionally, correlations between ocular parameters and systemic indices were examined. The results indicated that RFV and MBR-CH exhibited significant correlations with renal and intestinal blood flows, with stronger correlations observed during blood removal. Additionally, ocular blood flow changes closely mirrored systemic dynamics, suggesting their potential as real-time indicators of shock progression and recovery. These findings indicate that ocular blood flow measurements may serve as real-time indicators of the systemic circulation status during hemorrhagic shock, offering potential insights into shock management and guiding tailored interventions. Thus, noninvasive ocular blood flow evaluation holds promise as an innovative tool for assessing systemic circulation dynamics during hemorrhagic shock.

Assessment of power spectral density of microvascular hemodynamics in skeletal muscles at very low and low-frequency via near-infrared diffuse optical spectroscopies

In this work, we used a hybrid time domain near-infrared spectroscopy (TD-NIRS) and diffuse correlation spectroscopy (DCS) device to retrieve hemoglobin and blood flow oscillations of skeletal muscle microvasculature. We focused on very low (VLF) and low-frequency (LF) oscillations (i.e., frequency lower than 0.145 Hz), that are related to myogenic, neurogenic and endothelial activities. We measured power spectral density (PSD) of blood flow and hemoglobin concentration in four muscles (thenar eminence, plantar fascia, sternocleidomastoid and forearm) of 14 healthy volunteers to highlight possible differences in microvascular hemodynamic oscillations. We observed larger PSDs for blood flow compared to hemoglobin concentration, in particular in case of distal muscles (i.e., thenar eminence and plantar fascia). Finally, we compared the PSDs measured on the thenar eminence of healthy subjects with the ones measured on a septic patient in the intensive care unit: lower power in the endothelial-dependent frequency band, and larger power in the myogenic ones were observed in the septic patient, in accordance with previous works based on laser doppler flowmetry.

Transfusion increased skin blood flow when initially low in volume-resuscitated patients without acute bleeding

Background

Alterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation.

Methods

A prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT.

Results

Overall, SBFBT did not significantly change after RBCT [from 79.8 (4.3-479.4) to 83.4 (4.9-561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3-279.3) vs. 136.3 (6.5-479.4) perfusion units; p < 0.01], mixed or central venous oxygen saturation (62.5 ± 9.2 vs. 67.3% ± 12.0%; p < 0.01) and CVP (8.3 ± 5.1 vs. 10.3 ± 5.6 mmHg; p = 0.03) at baseline than non-responders. SBFBT increased in responders [from 41.3 (4.3-279.3) to 93.1 (9.8-561.6) perfusion units; p < 0.01], and decreased in the non-responders [from 136.3 (6.5-479.4) to 80.0 (4.9-540.8) perfusion units; p < 0.01] after RBCT. Pre-transfusion SBFBT was independently associated with a 20% increase in SBFBT after RBCT. Baseline SBFBT had an area under receiver operator characteristic of 0.73 (95% CI, 0.68-0.83) to predict SBFBT increase; A SBFBT of 73.0 perfusion units (PU) had a sensitivity of 71.4% and a specificity of 70.4% to predict SBFBT increase after RBCT. No significant differences in SBFBT were observed after RBCT in different subgroup analyses.

Conclusion

The skin blood flow is globally unaltered by red blood cell transfusions in non-bleeding critically ill patients after initial resuscitation. However, a lower SBFBT at baseline was associated with a relative increase in skin tissue perfusion after RBCT.

Spatial-Temporal Oxygenation Mapping Using a Near-Infrared Optical Scanner: Towards Peripheral Vascular Imaging

Near-infrared spectroscopy (NIRS)-based peripheral perfusion, or microcirculation, can be used to assess the severity of peripheral vascular dysfunction. A low-cost, portable non-contact near-infrared optical scanner (NIROS) was developed for spatio-temporal mapping of tissue oxygenation and perfusion in tissues. In vivo validation studies were carried out on control subjects (n = 3) to assess the ability of NIROS to measure real-time oxygenation changes in response to an occlusion paradigm on the dorsum of the hand. NIROS captured real-time tissue oxygenation changes with 95% correlation when compared to a commercial device. A feasibility peripheral imaging study was performed in a mouse model (n = 5) of chronic kidney disease (CKD) induced vascular calcification to assess differences in microcirculatory peripheral tissue oxygenation. The tissue oxygenation (in terms of oxy-, deoxy-, and total hemoglobin changes) due to the occlusion paradigm was distinctly different prior to (week-6) and after the onset of vascular calcification (week-12) in the murine tails. Future work will involve extensive studies to correlate these microcirculatory tissue oxygenation changes in the peripheral tail to the vascular calcification in the heart.

Optimal Hyperspectral Band Selection for Tissue Oxygenation Mapping with Generative Adversarial Network

Tissue oxygenation assessment using hyperspectral imaging is an emerging technique for the diagnosis and pre- and post-treatment monitoring of ischemic patients. However, the high spectral resolution of hyperspectral imaging leads to large data sizes and a long imaging time. In this study, we propose a method that utilizes multi-objective evolutionary algorithms to determine the optimal hyperspectral band combination when developing a deep learning model for predicting tissue oxygenation from hyperspectral images. Our results confirm that the deep learning model effectively predicts tissue oxygenation images for various oxygenation states. Moreover, we demonstrate that a high-performance prediction model can be developed using only a small number of spectral bands, indicating the potential for more efficient non-contact tissue oxygenation mapping with the proposed method.Clinical Relevance- The proposed method allows for the non-contact and efficient acquisition of two-dimensional tissue oxygenation information in various oxygenation states.

Tissue Oximetry Changes during Postoperative Dangling in Lower Extremity Free Flap Reconstruction: A Pilot Study

Background: Lower extremity free flap dangling protocols are still widely practiced, despite a paucity of evidence for their use. This pilot study investigates the use of tissue oximetry to provide further insight into the physiological effect of postoperative dangling in lower limb free flap transfer. Methods: Ten patients undergoing lower extremity free flap reconstruction were included in this study. Free flap tissue oxygen saturation (StO₂) was continuously measured using non-invasive near-infrared spectroscopy. Measurements were performed on the free flap and contralateral limb during dangling from postoperative day (POD) 7 until 11, according to the local dangling protocol. Results: StO₂ values measured in the free flap diminished to 70 ± 13.7% during dangling. This minimum StO₂ was reached significantly later, and correspondingly the area under the curve (AUC) was significantly larger on POD 11 compared to the start of the dangling protocol on POD 7, reflecting an improving free flap microvascular reactivity. The dangling slope was equal between the free flap and contralateral leg. The reperfusion slope was significantly flatter on POD 7 compared to the other PODs (p < 0.001). Thereafter, no significant differences between PODs were observed. Patients with a history of smoking had significantly lower tissue oximetry values compared to non-smokers. Conclusions: The application of tissue oximetry during dangling provides further insight into the physiological effect (i.e., changes in microcirculatory function) of the free flap of the reconstructed lower extremity. This information could potentially be useful to either revise or disrupt the use of such dangling protocols.

Effects of percutaneous transluminal angioplasty and associated factors in access hand oxygenation in patients undergoing hemodialysis

In hemodialysis (HD) patients with arteriovenous fistula (AVF), changes in systemic or peripheral tissue circulation occur non-physiologically via the presence of AVF; however, associations between blood flow and tissue oxygenation in the brain and access hand are uncertain. In this study, 85 HD patients with AVF were included and evaluated for changes in flow volume (FV) and regional oxygen saturation (rSO₂) in the brain and hands with AVF before and after percutaneous transluminal angioplasty (PTA). Furthermore, we evaluated the factors that determine access hand rSO₂ without stenosis after PTA. Brachial arterial FV increased after PTA (p < 0.001), and carotid FV decreased (p = 0.008). Access hand rSO₂ significantly decreased after PTA (p < 0.001), but cerebral rSO₂ did not significantly change (p = 0.317). In multivariable linear regression analysis of factors associated with access hand rSO₂, serum creatinine (standardized coefficient: 0.296) and hemoglobin (standardized coefficient: 0.249) were extracted as independent factors for access hand rSO₂. In conclusion, a decrease in access hand oxygenation and maintenance of cerebral oxygenation were observed throughout PTA. To maintain access hand oxygenation, it is important to adequately manage Hb level and maintain muscle mass, in addition to having an AVF with appropriate blood flow.

Microvascular effects of oxygen and carbon dioxide measured by vascular occlusion test in healthy volunteers

BACKGROUND

Changes in near-infrared spectroscopy-derived regional tissue oxygen saturation (StO₂) during a vascular occlusion test (VOT; ischemic provocation of microcirculation by rapid inflation and deflation of a tourniquet) allow estimating peripheral tissue O₂ consumption (desaturation slope; DS), vascular reactivity (recovery slope; RS) and post-ischemic hyperperfusion (AUC-H). The effects of isolated alterations in the inspiratory fraction of O₂ (FiO₂) and changes in expiratory CO₂ remain to be elucidated. Therefore, in this secondary analysis we determined the effects of standardized isolated instances of hypoxia, hyperoxia, hypocapnia and hypercapnia on the VOT-induced StO₂ changes in healthy volunteers (n = 20) to establish reference values for future physiological studies.

METHODS

StO₂ was measured on the thenar muscle. Multiple VOTs were performed in a standardized manner: i.e. at room air (baseline), during hyperoxia (FiO₂ 1.0), mild hypoxia (FiO₂ ≈ 0.11), and after a second baseline, during hypocapnia (end-tidal CO₂ (etCO₂) 2.5-3.0 vol%) and hypercapnia (etCO₂ 7.0-7.5 vol%) at room air. Differences in DS, RS, and AUC-H were tested using repeated-measures ANOVA.

RESULTS

DS and RS remained constant during all applied conditions. AUC-H after hypoxia was smaller compared to hyperoxia (963 %*sec vs hyperoxia 1702 %*sec, P = 0.005), while there was no difference in AUC-H duration between hypoxia and baseline. The StO₂ peak (after tourniquet deflation) during hypoxia was lower compared to baseline and hyperoxia (92 % vs 94 % and 98 %, P < 0.001).

CONCLUSION

We conclude that in healthy volunteers at rest, common situations observed during anesthesia and intensive care such as exposure to hypoxia, hyperoxia, hypocapnia, or hypercapnia, did not affect peripheral tissue O₂ consumption and vascular reactivity as assessed by VOT-induced changes in StO₂. These observations may serve as reference values for future physiological studies.

TRIAL REGISTRATION

This study represents a secondary analysis of an original study which has been registered at ClinicalTrials.gov nr: NCT02561052.

Near Infrared Spectroscopy For Cerebral Hemodynamic Monitoring During Carotid Endarterectomy Under General Anesthesia

Background:

Near infrared spectroscopy (NIRS) is a noninvasive method for continuous monitoring of cerebral oxygenation.

Objective:

To describe the intraoperative behavior of NIRS variables used to evaluate hemodynamic response in patients with atherosclerotic disease undergoing carotid endarterectomy under general anesthesia.

Methods:

Fifteen volunteers with atherosclerotic carotid disease with indications for endarterectomy were evaluated. After selection of patients, carotid stenosis was confirmed by appropriate diagnostic methods. NIRS was used for intraoperative monitoring. The variables total hemoglobin (Hb), oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), and regional oxygen saturation (rSO2) were evaluated at three intraoperative time points: before, during, and after carotid clamping.

Results and Discussion:

Measurements recorded by NIRS showed that, during the first 5 min of clamp time, patients experienced a decline in O2Hb levels, an increase in HHb levels, and a marked decrease in rSO2. Hb remained constant throughout the procedure. At the post-clamping time point, HHb, O2Hb, and rSO2 returned to patterns similar to those observed before clamping.

Conclusion:

NIRS was able to reliably and accurately identify the three stages of carotid endarterectomy and may predict the risk of cerebral hypoxia during carotid clamping under general anesthesia.

Colorectal Surgery in Critically Unwell Patients: A Multidisciplinary Approach

A proportion of patients require critical care support following elective or urgent colorectal procedures. Similarly, critically ill patients in intensive care units may also need colorectal surgery on occasions. This patient population is increasing in some jurisdictions given an aging population and increasing societal expectations. As such, this population often includes elderly, frail patients or patients with significant comorbidities. Careful stratification of operative risks including the need for prolonged intensive care support should be part of the consenting process. In high-risk patients, especially in setting of unplanned surgery, treatment goals should be clearly defined, and appropriate ceiling of care should be established to minimize care that is not in the best interest of the patient. In this article we describe approaches to critically unwell patients requiring colorectal surgery and how a multidisciplinary approach with proactive intensive care involvement can help achieve the best outcomes for these patients.

Predicting the Need for Renal Replacement Therapy Using a Vascular Occlusion Test and Tissue Oxygen Saturation in Patients in the Early Phase of Multiorgan Dysfunction Syndrome

Background: Acute kidney injury (AKI) is associated with an increased mortality in critically ill patients, especially in patients with multiorgan dysfunction syndrome (MODS). In daily clinical practice, the grading of AKI follows the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. In most cases, a relevant delay occurs frequently between the onset of AKI and detectable changes in creatinine levels as well as clinical symptoms. The aim of the present study was to examine whether a near infrared spectroscopy (NIRS)-based, non-invasive ischemia–reperfusion test (vascular occlusion test (VOT)) together with unprovoked (under resting conditions) tissue oxygen saturation (StO₂) measurements, contain prognostic information in the early stage of MODS regarding the developing need for renal replacement therapy (RRT). Methods: Within a period of 18 months, patients at the medical intensive care unit of a tertiary university hospital with newly developed MODS (≤24 h after diagnosis, APACHE II score ≥20) were included in our study. The VOT occlusion slope (OS) and recovery slope (RS) were recorded in addition to unprovoked StO₂. StO₂ was determined non-invasively in the area of the thenar muscles using a bedside NIRS device. The VOT was carried out by inflating a blood pressure cuff on the upper arm. AKI stages were determined by the changes in creatinine levels, urinary output, and/or the need for RRT according to KDIGO. Results: 56 patients with MODS were included in the study (aged 62.5 ± 14.4 years, 40 men and 16 women, APACHE II score 34.5 ± 6.4). Incidences of the different AKI stages were: no AKI, 16.1% (n = 9); AKI stage I, 19.6% (n = 11); AKI stage II, 25% (n = 14); AKI stage III, 39.3% (n = 22). Thus, 39.3% of the patients (n = 22) developed the need for renal replacement therapy (AKI stage III). These patients had a significantly higher mortality over 28 days (RRT, 72% (n = 16/22) vs. no RRT, 44% (n = 15/34); p = 0.03). The mean unprovoked StO₂ of all patients at baseline was 81.7 ± 11.1%, and did not differ between patients with or without the need for RRT. Patients with RRT showed significantly weaker negative values of the OS (−9.1 ± 3.7 vs. −11.7 ± 4.1%/min, p = 0.01) and lower values for the RS (1.7 ± 0.9 vs. 2.3 ± 1.6%/s, p = 0.02) compared to non-dialysis patients. Consistent with these results, weaker negative values of the OS were found in higher AKI stages (no AKI, −12.7 ± 4.1%/min; AKI stage I, −11.5 ± 3.0%/min; AKI stage II, −11.1 ± 3.3%/min; AKI stage III, −9.1 ± 3.7%/min; p = 0.021). Unprovoked StO₂ did not contain prognostic information regarding the AKI stages. Conclusions: The weaker negative values of the VOT parameter OS are associated with an increased risk of developing AKI and RRT, and increased mortality in the early phase of MODS, while unprovoked StO₂ does not contain prognostic information in that regard.

Microcirculation during surgery

Throughout the long history of surgery, there has been great advancement in the hemodynamic management of surgical patients. Traditionally, hemodynamic management has focused on macrocirculatory monitoring and intervention to maintain appropriate oxygen delivery. However, even after optimization of macro-hemodynamic parameters, microcirculatory dysfunction, which is related to higher postoperative complications, occurs in some patients. Although the clinical significance of microcirculatory dysfunction has been well reported, little is known about interventions to recover microcirculation and prevent microcirculatory dysfunction. This may be at least partly caused by the fact that the feasibility of monitoring tools to evaluate microcirculation is still insufficient for use in routine clinical practice. However, considering recent advancements in these research fields, with more popular use of microcirculation monitoring and more clinical trials, clinicians may better understand and manage microcirculation in surgical patients in the future. In this review, we describe currently available methods for microcirculatory evaluation. The current knowledge on the clinical relevance of microcirculatory alterations has been summarized based on previous studies in various clinical settings. In the latter part, pharmacological and clinical interventions to improve or restore microcirculation are also presented.

Value of peripheral perfusion index to predict acute limb ischaemia in newborns after peripheral artery cannulation

AIMS AND OBJECTIVES

To investigate the feasibility of using peripheral perfusion index (PPI) to monitor acute limb ischaemia (ALI) in newborns after catheterisations.

BACKGROUND

ALI is common complication of neonatal peripheral artery cannulation. It is important to address as soon as the early signs of ALI. PPI could aid in noninvasive evaluation of distal extremity perfusion in an effort to notify risk of potential ischaemic injury from catheterisations.

DESIGN

A nested case-control study.

METHODS

Clinical information of newborns who had been admitted to the Neonatal Intensive Care Unit of Jiangxi Provincial Children's Hospital and had received peripheral artery cannulation from January 2018 to January 2020 was prospectively collected. Transcutaneous blood oxygen saturation (TcSO₂ ), PPI and delta-PPI (ΔPPI1; the difference in PPI values of the two arms. ΔPPI2; difference in the PPI values before and after cannulation) were recorded. We used STROBE checklist as an EQUATOR in this study.

RESULTS

A total of 25 newborns with ALI were included in the study. These were then paired with 100 newborns without ALI. The PPI and TcSO₂ of the cannulated limb were significantly lower in the ALI group than in the non-ALI (NALI) group (p < .05). The area under the receiver-operating characteristic curve was significant for ΔPPI1. The ΔPPI1 had a sensitivity and specificity of 92% and 87%, respectively, for diagnosing ALI. ΔPPI1 greater than 0.315 suggested that the infant was at risk of ALI.

CONCLUSIONS

Monitoring the change in the PPI in newborns after catheterisations helped in the early assessment of ALI.

RELEVANCE TO CLINICAL PRACTICE

Drops in the PPI and TcSO₂ of the cannulated limbs might, to some extent, reflect the possibility of ALI in newborns. ΔPPI1 (the difference in PPI values of the two arms) proved to be a simple, objective parameter to predict the presence of ALI.

Performance Assessment of a Commercial Continuous-Wave Near-Infrared Spectroscopy Tissue Oximeter for Suitability for Use in an International, Multi-Center Clinical Trial

Despite the wide range of clinical and research applications, the reliability of the absolute oxygenation measurements of continuous wave near-infrared spectroscopy sensors is often questioned, partially due to issues of standardization. In this study, we have compared the performances of 13 units of a continuous wave near-infrared spectroscopy device (PortaMon, Artinis Medical Systems, NL) to test their suitability for being used in the HEMOCOVID-19 clinical trial in 10 medical centers around the world. Detailed phantom and in vivo tests were employed to measure the precision and reproducibility of measurements of local blood oxygen saturation and total hemoglobin concentration under different conditions: for different devices used, different operators, for probe repositioning over the same location, and over time (hours/days/months). We have detected systematic differences between devices when measuring phantoms (inter-device variability, <4%), which were larger than the intra-device variability (<1%). This intrinsic variability is in addition to the variability during in vivo measurements on the forearm muscle resulting from errors in probe positioning and intrinsic physiological noise (<9%), which was also larger than the inter-device differences (<3%) during the same test. Lastly, we have tested the reproducibility of the protocol of the HEMOCOVID-19 clinical trial; that is, forearm muscle oxygenation monitoring during vascular occlusion tests over days. Overall, our conclusion is that these devices can be used in multi-center trials but care must be taken to characterize, follow-up, and statistically account for inter-device variability.

Usefulness of a finger-mounted tissue oximeter with near-infrared spectroscopy for evaluating the intestinal oxygenation and viability in rats

PURPOSE

To investigate the utility of the device for evaluating intestinal oxygenation and viability using an animal model.

METHODS

Sprague-Dawley rats underwent laparotomy under general anesthesia, and the blood vessels in the terminal ileum were clamped to create ischemia. We measured the regional tissue oxygenation saturation (rSO2) using an oximeter after 1, 3, and 6 h of vessel clamping. Ischemic tissue damage was assessed using a histological score. The intestine was reperfused after each clamping period, and intestinal rSO2 and survival rate were evaluated.

RESULTS

When reperfusion was performed at 1 and 3 h after ischemia, rSO2 increased after 10 min, and it improved to the same level as for normal intestine after 1 h; all rats survived for 1 week. In contrast, after 6 h of ischemia, rSO2 did not increase after reperfusion, and all animals died within 2 days. The histological scores increased after 1 h of reperfusion, with longer clamping periods.

CONCLUSION

A finger-mounted tissue oximeter could evaluate intestinal ischemia and the viability, which is thus considered to be a promising result for future clinical application.

Monitoring deep-tissue oxygenation with a millimeter-scale ultrasonic implant

Vascular complications following solid organ transplantation may lead to graft ischemia, dysfunction or loss. Imaging approaches can provide intermittent assessments of graft perfusion, but require highly skilled practitioners and do not directly assess graft oxygenation. Existing systems for monitoring tissue oxygenation are limited by the need for wired connections, the inability to provide real-time data or operation restricted to surface tissues. Here, we present a minimally invasive system to monitor deep-tissue O₂ that reports continuous real-time data from centimeter-scale depths in sheep and up to a 10-cm depth in ex vivo porcine tissue. The system is composed of a millimeter-sized, wireless, ultrasound-powered implantable luminescence O₂ sensor and an external transceiver for bidirectional data transfer, enabling deep-tissue oxygenation monitoring for surgical or critical care indications.

Effects of anesthetics on microvascular reactivity measured by vascular occlusion tests during off-pump coronary artery bypass surgery: a randomized controlled trial

Microvascular function may be modulated by various anesthetics. Desflurane and propofol anesthesia have different effects on microvascular function. However, there are few reports on the effects of sevoflurane and desflurane on microvascular function during cardiac surgery. We compared the effects of sevoflurane and desflurane on microvascular reactivity, as measured by the vascular occlusion tests (VOTs) during off-pump coronary artery bypass (OPCAB) surgery. Patients undergoing OPCAB were eligible for study inclusion. Patients were excluded if they were unsuitable for treatment with volatile agents or the VOT, had renal failure or uncontrolled diabetes, or were pregnant. The enrolled patients were randomized to receive sevoflurane or desflurane during surgery. Tissue oxygen saturation (StO₂) dynamics during the VOT were measured at baseline (pre-anesthesia), pre-anastomosis, post-anastomosis of vessel grafts, and at the end of surgery. Macrohemodynamic variables, arterial blood gas parameters, and in-hospital adverse events were also evaluated. A total of 64 patients (32 in each group) were analyzed. StO₂ dynamics did not differ between the groups. Compared to baseline, StO₂ and the rate of recovery following vascular occlusion decreased at the end of surgery in both groups (adjusted p-value, < 0.001), and no group difference was observed. Macrohemodynamic variables, blood gas analysis results, and the rate of postoperative in-hospital adverse events were similar between the groups. Microvascular reactivity, as measured by the VOT during OPCAB, showed no difference between the sevoflurane and desflurane groups. Also, there were no group differences in macrohemodynamics or the rate of postoperative adverse events. TRIAL REGISTRATION : Clinicaltrials.gov, identifier NCT03209193; registered on July 3, 2017.

Prognostic Value of Tissue Oxygen Saturation Using a Vascular Occlusion Test in Patients in the Early Phase of Multiorgan Dysfunction Syndrome

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is a common disease pattern in intensive care units which is associated with an increased mortality. The aim of this study was to investigate whether a near-infrared spectroscopy (NIRS)-based noninvasive ischemia-reperfusion test (vascular occlusion test) using the parameter of tissue oxygen saturation (StO2) contains prognostic information for patients in the early phase of MODS.

METHODS

Within a period of 18 months between 2010 and 2012, 56 patients who newly developed MODS (≤24 h after diagnosis, Acute Physiology and Chronic Health Evaluation [APACHE] II score ≥20, subgroups: cardiogenic MODS [cMODS] and septic MODS [sMODS]) were included into the study. The StO2 was determined non-invasively in the area of the thenar muscles using a bedside NIRS device, InSpectra Tissue Spectrometer Model 650 (Hutchinson Technology Inc., Hutchinson, MN). The VOT was carried out by inflating a blood pressure cuff on the upper arm 30 mmHg above systolic blood pressure for 5 min. The parameters occlusion slope (OS) and recovery slope (RS) were recorded.

RESULTS

Fifteen patients with cMODS and 41 patients with sMODS were included in the study (age: 62.5 ± 14.4 years, 40 men and 16 women, APACHE II score: 34.6 ± 6.4). Twenty-eight-day-mortality was 55.4% (cMODS: 7 out of 15 patients, sMODS: 24 out of 41 patients). The measurement of StO2 while applying the VOT at baseline showed an OS of -11.7 ± 3.7%/min and an RS of 2.2 ± 1.5%/s. Survivors had significantly better values compared with non-survivors at baseline regarding OS (-12.8 ± 3.5%/min vs. -9.8 ± 3.4%/min; P = 0.016) and RS (2.6 ± 1.7%/s vs. 1.6 ± 1.0%/s; P = 0.022). Receiver-operating characteristic (ROC) curves show that the area under the curve (AUC) for OS was found to be significantly related to 28-day mortality (AUC: 0.7; 95% confidence interval [CI]: 0.56-0.85; P = 0.01). However, using both univariate and multivariate binary logistic regression models, RS was significantly associated with increased 28-day mortality (OR [univariate model]: 1.21 [95% CI: 1.1-1.8]; OR [multivariate model]: 1.23 [95% CI: 1.1-1.3]).

CONCLUSIONS

Impaired values of the VOT-parameters OS and RS are associated with an increased 28-day mortality in patients in the early phase of MODS.

Intravenous lidocaine to prevent endothelial dysfunction after major abdominal surgery: a randomized controlled pilot trial

Background

Major abdominal surgery is associated with endothelial glycocalyx disruption. The anti-inflammatory effects of lidocaine were recently associated with endothelial barrier protection.

Methods

This was a single-centre, parallel group, randomized, controlled, double blind, pilot trial. Forty adult patients scheduled for major abdominal surgery were included between December 2016 and March 2017 in the setting of a University Hospital in Brussels (Belgium); reasons for non-inclusion were planned liver resection and conditions associated to increased risk of local anesthetics systemic toxicity. Patients were randomized to receive either lidocaine by continuous intravenous administration or an equivalent volume of 0.9% saline.

The primary endpoint was the postoperative syndecan-1 concentration (difference between groups). Near-infrared spectroscopy of the thenar eminence in association with the vascular occlusion test, and contemporary analysis of flow-mediated dilation of the brachial artery were the secondary outcomes, along with haemodynamic data. Blood samples and data were collected before surgery (T0), and at 1–3 h (T1) and 24 h (T2) post-surgery.

Results

Syndecan-1 concentration increased significantly post-surgery (P < 0.001), but without any difference between groups. The near-infrared spectroscopy-derived and flow-mediated dilation-derived variables showed minor changes unrelated to group assignment. Compared with the placebo group, the intervention group had a significantly lower peri-operative mean arterial pressure and cardiac index, despite equally conducted goal-directed haemodynamic management. Postoperative lactate concentrations were similar between groups.

Conclusions

Lidocaine failed to have any effect on endothelial function. Since in comparisons to other types of clinical situations, syndecan-1 was only slightly upregulated, endothelial dysfunction after major abdominal surgery might be overestimated.

Trial registration

« ISRCTN Registry » identifier: ISRCTN63417725. Date: 15/06/2020. Retrospectively registered.

Thenar oxygen saturation (StO2) alterations during a spontaneous breathing trial predict extubation failure

Background

Weaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxygenation status has shown promising results in predicting the tolerance to spontaneously breathe in the process of weaning from MV. Our aim was to determine whether changes in skeletal muscle oxygen saturation (StO₂) measured by near-infrared spectroscopy (NIRS) on the thenar eminence during a vascular occlusion test (VOT) can be used to predict extubation failure from mechanical ventilation.

Methods

We prospectively studied 206 adult patients with acute respiratory failure receiving MV for at least 48 h from a 30-bed mixed ICU, who were deemed ready to wean by their physicians. Patients underwent a 30-min spontaneous breathing trial (SBT), and were extubated according to the local protocol. Continuous StO₂ was measured non-invasively on the thenar eminence. A VOT was performed prior to and at 30 min of the SBT (SBT₃₀). The rate of StO₂ deoxygenation (DeO₂), StO₂ reoxygenation (ReO₂) rate and StO₂ hyperemic response to ischemia (H_AUC) were calculated.

Results

Thirty-six of the 206 patients (17%) failed their SBT. The remainder 170 patients (83%) were extubated. Twenty-three of these patients (13.5%) needed reinstitution of MV within 24 h. Reintubated patients displayed a lower H_AUC at baseline, and higher relative changes in their StO₂ deoxygenation rate between baseline and SBT₃₀ (DeO₂ Ratio). A logistic regression-derived StO₂ score, combining baseline StO₂, H_AUC and DeO₂ ratio, showed an AUC of 0.84 (95% CI 0.74–0.91) for prediction of extubation failure.

Conclusions

Extubation failure was associated to baseline and dynamic StO₂ alterations during the SBT. Monitoring StO₂-derived parameters might be useful in predicting extubation outcome.

The vascular occlusion test using multispectral imaging: a validation study : The VASOIMAGE study

Multispectral imaging (MSI) is a new, non-invasive method to continuously measure oxygenation and microcirculatory perfusion, but has limitedly been validated in healthy volunteers. The present study aimed to validate the potential of multispectral imaging in the detection of microcirculatory perfusion disturbances during a vascular occlusion test (VOT). Two consecutive VOT's were performed on healthy volunteers and tissue oxygenation was measured with MSI and near-infrared spectroscopy (NIRS). Correlations between the rate of desaturation, recovery and the hyperemic area under the curve (AUC) measured by MSI and NIRS were calculated. Fifty-eight volunteers were included. The MSI oxygenation curves showed identifiable components of the VOT, including a desaturation and recovery slope and hyperemic area under the curve, similar to those measured with NIRS. The correlation between the rate of desaturation measured by MSI and NIRS was moderate: r = 0.42 (p = 0.001) for the first and r = 0.41 (p = 0.002) for the second test. Our results suggest that non-contact multispectral imaging is able to measure changes in regional oxygenation and deoxygenation during a vascular occlusion test in healthy volunteers. When compared to measurements with NIRS, correlation of results was moderate to weak, most likely reflecting differences in physiology of the regions of interest and measurement technique.

Microvascular responses during reactive hyperemia assessed by near-infrared spectroscopy and arterial stiffness in young, middle-aged, and older women

We investigated the effects of age on microvascular responses during reactive hyperemia and arterial stiffness in 13 young (22 ± 1 years), 12 middle-aged (42 ± 5 years), and 15 older (63 ± 2 years) women. During the vascular occlusion test (VOT), forearm tissue oxygen saturation (StO₂) was measured using near-infrared spectroscopy (NIRS). During reperfusion, the area under the curve (AUC) during hyperemia in young women (1123 ± 208% s) was significantly greater than that in middle-aged (771 ± 445% s, P = 0.024) and older women (619 ± 356% s, P = 0.001) with no differences between middle-aged and older women (P = 0.265). Cardio-ankle vascular index (CAVI) as an indicator of arterial stiffness was assessed using four-limb oscillometry. CAVI significantly increased with age (8.1 ± 0.7 in the older group, 6.0 ± 0.8 in the middle-aged group, and 5.8 ± 0.4 in the young group), with significant differences between older women and women in the other groups (P < 0.001); however, no differences in CAVI between young and middle-aged women (P = 0.484) were found. When the data of all groups were pooled, the AUC or upslope was associated with CAVI or body mass index or mean arterial pressure (all P < 0.05). To conclude, the AUC derived by NIRS measures of StO₂ during the reperfusion phase can be used as one of the evaluations of microvascular function, followed by the development of atherosclerosis in middle-aged and older women.

Tissue oxygen saturation changes and postoperative complications in cardiac surgery: a prospective observational study

Background

Cardiac surgery with extracorporeal circulation (ECC) can induce microvascular dysfunction and tissue hypoperfusion. We hypothesized that the alterations in near-infrared spectroscopy (NIRS)-derived parameters would be associated with post-operative complications in cardiac surgery patients.

Methods

Prospective observational study performed at two University Hospitals. Ninety patients undergoing cardiac surgery with ECC were enrolled. The NIRS sensor was applied on the thenar eminence. A vascular occlusion test (VOT, 3-min ischemia) was performed at baseline (t0), at Intensive Care Unit (ICU) admission (t1), 3 (t2) and 6 (t3) hours later. Baseline tissue oxygen saturation (StO₂), oxygen extraction rate and microvascular reactivity indices were calculated.

Results

In the first hours after cardiac surgery, StO₂ tended to increase (86% [80–89] at T3 versus 82% [79–86] at T0, p = ns), while both tissue oxygen extraction and microvascular reactivity tended to decrease, as indicated by increasing occlusion slope (− 8.1%/min [− 11.2 to − 7] at T3 versus − 11.2%/min [− 13.9 to − 7.9] at T0, p = ns) and decreasing recovery slope (1.9%/sec [1.1–2.9] at T3 versus 3.1%/sec [2.3–3.9] at T0, p = ns). No substantial differences were found in NIRS-derived variables and their changes over time between patients with complications and those without complications.

Conclusions

Peripheral tissue oxygen extraction and microvascular reactivity were reduced during the first hours after cardiac surgery. NIRS-derived parameters were not able to predict complications in this population of cardiac surgery patients.

Assessment of the peripheral microcirculation in patients with and without shock: a pilot study on different methods

Microvascular dysfunction has been associated with adverse outcomes in critically ill patients, and the current concept of hemodynamic incoherence has gained attention. Our objective was to perform a comprehensive analysis of microcirculatory perfusion parameters and to investigate the best variables that could discriminate patients with and without circulatory shock during early intensive care unit (ICU) admission. This prospective observational study comprised a sample of 40 adult patients with and without circulatory shock (n = 20, each) admitted to the ICU within 24 h. Peripheral clinical [capillary refill time (CRT), peripheral perfusion index (PPI), skin-temperature gradient (Tskin-diff)] and laboratory [arterial lactate and base excess (BE)] perfusion parameters, in addition to near-infrared spectroscopy (NIRS)-derived variables were simultaneously assessed. While lactate, BE, CRT, PPI and Tskin-diff did not differ significantly between the groups, shock patients had lower baseline tissue oxygen saturation (StO₂) [81 (76–83) % vs. 86 (76–90) %, p = 0.044], lower StO₂min [50 (47–57) % vs. 55 (53–65)  %, p = 0.038] and lower StO₂max [87 (80–92) % vs. 93 (90–95) %, p = 0.017] than patients without shock. Additionally, dynamic NIRS variables [recovery time (r = 0.56, p = 0.010), descending slope (r = − 0.44, p = 0.05) and ascending slope (r = − 0.54, p = 0.014)] and not static variable [baseline StO₂ (r = − 0.24, p = 0.28)] exhibited a significant correlation with the administered dose of norepinephrine. In our study with critically ill patients assessed within the first twenty-four hours of ICU admission, among the perfusion parameters, only NIRS-derived parameters could discriminate patients with and without shock.

No effect of fitness on brachial or forearm vascular function during acute inflammation in young adults

Acute inflammation is associated with increased risk of cardiovascular events and impaired vasodilatory capacity. Vasodilatory capacity can be measured in different segments of the arterial tree; however, it is unknown if the effects of acute inflammation are vascular segment-specific or if inflammation-induced dysfunction can be attenuated by factors that modulate cardiovascular risk, such as high cardiorespiratory fitness. The purpose of this study was to determine the effect of acute inflammation and fitness on conduit artery, resistance artery, and microvascular function in healthy, young adults. Vascular function was assessed at baseline and 24 h after a typhoid vaccination in 11 low-fit (5 male, 24 yr of age, 34.5 ± 2.9 ml·kg^-1·min^-1 peak O₂ uptake (V̇o_2peak)] and 12 high-fit (7 male, 27 yr of age, 56.4 ± 9.7 ml·kg^-1·min^-1 V̇o_2peak) young adults. Vascular assessments included flow-mediated dilation (FMD) of the brachial artery, forearm reactive hyperemia (RH) via venous occlusion plethysmography, and near-infrared spectroscopy (NIRS) during a 5-min arterial occlusion. Acute inflammation was evident with increases in IL-6 and C-reactive protein (P < 0.01), and mean arterial pressure did not change (P = 0.33). FMD was lower in the high-fit group, yet it was reduced in both groups at 24 h, even after controlling for shear (P < 0.05). No effect of acute inflammation was observed for RH or NIRS (P > 0.05). Acute inflammation had nonuniform effects on vascular function throughout the arterial tree in young adults, and fitness did not alter the vascular response. This suggests that cardiorespiratory fitness may not protect the vasculature during acute inflammation in young adults in the absence of age- or disease-related decline in vascular function.

Continuous monitoring of interstitial tissue oxygen using subcutaneous oxygen microsensors: In vivo characterization in healthy volunteers

Measurements of regional tissue oxygen serve as a proxy to monitor local perfusion and have the potential to guide therapeutic decisions in multiple clinical disciplines. Transcutaneous oximetry (tcpO2) is a commercially available noninvasive technique that uses an electrode to warm underlying skin tissue and measure the resulting oxygen tension at the skin surface. A novel approach is to directly measure interstitial tissue oxygen using subcutaneous oxygen microsensors composed of a biocompatible hydrogel carrier platform with embedded oxygen sensing molecules. After initial injection of the hydrogel into subcutaneous tissue, noninvasive optical measurements of phosphorescence-based emissions at the skin surface are used to sense oxygen in the subcutaneous interstitial space. The object of the present study was to characterize the in vivo performance of subcutaneous microsensors and compare with transcutaneous oximetry (tcpO2). Vascular occlusion tests were performed on the arms of 7 healthy volunteers, with repeated tests occurring 1 to 10 weeks after sensor injection, yielding 95 total tests for analysis. Comparative analysis characterized the response of both devices to decreases in tissue oxygen during occlusion and to increases in tissue oxygen following release of the occlusion. Results indicated: (I) time traces returned by microsensors and tcpO2 were highly correlated, with the median (interquartile range) correlation coefficient of r = 0.93 (0.10); (II) both microsensors and tcpO2 sensed a statistically significant decrease in normalized oxygen during occlusion (p < 0.001 for each device); (III) microsensors detected faster rates change (p < 0.001) and detected overshoot during recovery more frequently (38% vs. 4% of tests); (IV) inter-measurement analysis showed no correlation of baseline values between microsensors and tcpO2 (r = 0.03), but comparison of integrated oxygen dynamics showed similar variation in the normalized response to occlusion between devices (p = 0.06), (V) intra-measurement analysis revealed that microsensors detect greater physiological fluctuations than tcpO2 (p < 0.001) and may provide enhanced sensitivity to processes such as vasomotion. Additionally, the functional response of microsensors was not significantly different across time groupings (per month) post-injection (p = 0.61). Although the compared devices have differences in the mechanisms used to sense oxygen, these findings demonstrate that subcutaneous oxygen microsensors measure changes in interstitial tissue oxygen in human subjects in vivo.

Effect of assuming constant tissue scattering on measured tissue oxygenation values during tissue ischemia and vascular reperfusion

The purpose of this study was to determine the effects of assuming constant tissue scattering properties on tissue oxygenation measurements during a vascular occlusion test (VOT). Twenty-one subjects (21.8 ± 1.9 yr) completed a VOT [1 min baseline (BL), 5 min of tissue ischemia (TI), and 3 min of vascular reperfusion (VR)]. Absolute concentrations of oxygenated heme (oxy-[heme]), deoxygenated heme (deoxy-[heme]), total heme (total [heme), tissue oxygen saturation (StO2), and heme difference [heme]diff) were measured using frequency domain near-infrared spectroscopy (FD-NIRS) while 1) continuously measuring and incorporating tissue scattering ([Formula: see text]) and 2) assuming scattering remained constant. FD-NIRS measured [Formula: see text] increased during TI at 692 nm ( P < 0.001) and decreased at 834 nm ( P < 0.001). During VR, [Formula: see text] decreased at 692 nm ( P < 0.001) and increased at 834 nm ( P < 0.001). When assuming constant scattering, oxy-[heme] was significantly less at TIpeak ( P < 0.05) while deoxy-[heme] and StO2 were significantly altered at BL, TIpeak, and VRpeak (all P < 0.001). Total [heme] did not change during the VOT. Absolute changes in deoxy-[heme], oxy-[heme], and StO2 in response to TI and VR were significantly exaggerated (all P < 0.001) and the rates of change during TI ( slope 1) and VR ( slope 2) in deoxy-[heme], oxy-[heme], StO2, and [heme]diff were significantly increased (all P < 0.05) when constant tissue scattering was assumed. These findings demonstrate the need for caution when interpreting NIRS data without continuously measuring tissue optical properties. Further, assuming tissue optical properties remain constant may have important consequences to experimental data and clinical conclusions made using NIRS.

NEW & NOTEWORTHY NIRS measurements provide significant experimental and clinical insight. We demonstrate that absolute changes in tissue oxygenation measurements made with NIRS are overestimated and the kinetic responses of NIRS measurements are exaggerated by varying degrees among individuals if tissue scattering characteristics are assumed to remain constant during vascular occlusion tests.

Effects of ischaemic conditioning on tissue oxygen saturation and heart rate variability: an observational study

Objective

Ischaemic conditioning (IC) has organ-protective effects, but its clinical results have been inconsistent. Tissue oxygen saturation (StO₂) and heart rate variability (HRV) reflect peripheral microcirculation and autonomic nervous system activity, but their changes during IC have not been well documented. We assessed StO₂ and HRV during IC in patients undergoing cardiac surgery and healthy volunteers.

Methods

Ten patients undergoing cardiac surgery and 10 healthy male volunteers underwent remote IC (four 5-minute cycles of ischaemia/reperfusion) applied to the upper arm. Changes in StO₂ at the thenar eminence and HRV according to the R-R intervals were recorded during IC.

Results

The lowest StO₂ during ischaemia significantly decreased in patients and significantly increased in volunteers. Among the HRV parameters, the low-frequency domain, which corresponds to sympathetic activity, significantly increased after IC in volunteers but not in patients. Other variables were similar between the groups.

Conclusions

These results suggest that the minimum tissue oxygen content is depleted during ischaemia in patients and preserved in healthy volunteers. Sympathetic nervous activity seems to increase after IC in healthy volunteers but remains unaffected in patients. Thus, IC may act differently between patients undergoing cardiac surgery and healthy subjects.

Assessment of Regional Perfusion and Organ Function: Less and Non-invasive Techniques

Sufficient organ perfusion essentially depends on preserved macro- and micro-circulation. The last two decades brought substantial progress in the development of less and non-invasive monitoring of macro-hemodynamics. However, several recent studies suggest a frequent incoherence of macro- and micro-circulation. Therefore, this review reports on interactions of macro- and micro-circulation as well as on specific regional and micro-circulation. Regarding global micro-circulation the last two decades brought advances in a more systematic approach of clinical examination including capillary refill time, a graded assessment of mottling of the skin and accurate measurement of body surface temperatures. As a kind of link between macro- and microcirculation, a number of biochemical markers can easily be obtained. Among those are central-venous oxygen saturation (S_cvO₂), plasma lactate and the difference between central-venous and arterial CO₂ (cv-a-pCO₂-gap). These inexpensive markers have become part of clinical routine and guideline recommendations. While their potential to replace parameters of macro-circulation such as cardiac output (CO) is limited, they facilitate the interpretation of the adequacy of CO and other macro-circulatory markers. Furthermore, they give additional hints on micro-circulatory impairment. In addition, a number of more sophisticated technical approaches to quantify and visualize micro-circulation including video-microscopy, laser flowmetry, near-infrared spectroscopy (NIRS), and partial oxygen pressure measurement have been introduced within the last 20 years. These technologies have been extensively used for scientific purposes. Moreover, they have been successfully used for educational purposes and to visualize micro-circulatory disturbances during sepsis and other causes of shock. Despite several studies demonstrating the association of these techniques and parameters with outcome, their practical application still is limited. However, future improvements in automated and “online” diagnosis will help to make these technologies more applicable in clinical routine. This approach is promising with regard to several studies which demonstrated the potential to guide therapy in different types of shock. Finally several organs have specific patterns of circulation related to their special anatomy (liver) or their auto-regulatory capacities (brain, kidney). Therefore, this review also discusses specific issues of monitoring liver, brain, and kidney circulation and function.

Association between sublingual microcirculation, tissue perfusion and organ failure in major trauma: A subgroup analysis of a prospective observational study

INTRODUCTION

Previous studies described impaired microvascular perfusion and tissue oxygenation as reliable predictors of Multiple Organ Failure in major trauma. However, this relationship has been incompletely investigated. The objective of this analysis is to further evaluate the association between organ dysfunction and microcirculation after trauma.

MATERIALS AND METHODS

This is a retrospective subgroup analysis on 28 trauma patients enrolled for the Microcirculation DAIly MONitoring in critically ill patients study (NCT 02649088). Patients were divided in two groups according with their Sequential Organ Failure Assessment (SOFA) score at day 4. At admission and every 24 hours, the sublingual microcirculation was evaluated with Sidestream Darkfield Imaging (SDF) and peripheral tissue perfusion was assessed with Near Infrared Spectroscopy (NIRS) and Vascular Occlusion Test (VOT). Simultaneously, hemodynamic, clinical/laboratory parameters and main organ supports were collected.

RESULTS

Median SOFA score at Day 4 was 6.5. Accordingly, patients were divided in two groups: D4-SOFA ≤6.5 and D4-SOFA >6.5. The Length of Stay in Intensive Care was significantly higher in patients with D4-SOFA>6.5 compared to D4-SOFA≤6.5 (p = 0.013). Total Vessel Density of small vessels was significantly lower in patients with high D4-SOFA score at Day 1 (p = 0.002) and Day 2 (p = 0.006) after admission; the Perfused Vessel Density was lower in patients with high D4-SOFA score at Day 1 (p = 0.007) and Day 2 (p = 0.033). At Day 1, NIRS monitoring with VOT showed significantly faster tissue oxygen saturation downslope (p = 0.018) and slower upslope (p = 0.04) in patients with high D4-SOFA.

DISCUSSION

In our cohort of major traumas, sublingual microcirculation and peripheral microvascular reactivity were significantly more impaired early after trauma in those patients who developed more severe organ dysfunctions. Our data would support the hypothesis that restoration of macrocirculation can be dissociated from restoration of peripheral and tissue perfusion, and that microvascular alterations can be associated with organ failure.

Changes in the sublingual microcirculation following aortic surgery under balanced or total intravenous anaesthesia: a prospective observational study

Background

In vascular surgery with aortic cross-clamping, ischemia/reperfusion injury induces systemic haemodynamic and microcirculatory disturbances. Different anaesthetic regimens may have a varying impact on tissue perfusion. The aim of this study was to explore changes in microvascular perfusion in patients undergoing elective open abdominal aortic aneurysm repair under balanced or total intravenous anaesthesia.

Methods

Prospective observational study. Patients undergoing elective open infrarenal abdominal aortic aneurysm repair received balanced (desflurane + remifentanil, n = 20) or total intravenous anaesthesia (TIVA, propofol + remifentanil using target-controlled infusion, n = 20) according to the clinician’s decision. A goal-directed haemodynamic management was applied in all patients. Measurements were obtained before anaesthesia induction (baseline) and at end-surgery and included haemodynamics, arterial/venous blood gases, sublingual microvascular flow and density (incident dark field illumination imaging), peripheral muscle tissue oxygenation and microcirculatory reactivity (thenar near infrared spectroscopy with a vascular occlusion test).

Results

The two groups did not differ for baseline characteristics, mean aortic-clamping time and requirement of vasoactive agents during surgery. Changes in mean arterial pressure, systemic vascular resistance index, haemoglobin and blood lactate levels were similar between the two groups, while the cardiac index increased at end-surgery in patients undergoing balanced anaesthesia. The sublingual microcirculation was globally unaltered in the TIVA group at end-surgery, while patients undergoing balanced anaesthesia showed an increase in the total and perfused small vessel densities (from 16.6 ± 4.2 to 19.1 ± 5.4 mm/mm², p < 0.05). Changes in microvascular density were negatively correlated with changes in the systemic vascular resistance index. The area of reactive hyperaemia during the VOT increased in the balanced anaesthesia group (from 14.8 ± 8.1 to 25.6 ± 14.8%*min, p < 0.05). At end-surgery, the tissue haemoglobin index in the TIVA group was lower than that in the balanced anaesthesia group.

Conclusions

In patients undergoing elective open abdominal aortic aneurysm repair with a goal-directed hemodynamic management, indices of sublingual or peripheral microvascular perfusion/oxygenation were globally preserved with both balanced anaesthesia and TIVA. Patients undergoing balanced anaesthesia showed microvascular recruitment at end-surgery.

Trial registration

NCT03510793, https://www.clinicaltrials.gov, date of registration April 27th 2018, retrospectively registered.

Reliability of microvascular responsiveness measures derived from near-infrared spectroscopy across a variety of ischemic periods in young and older individuals

BACKGROUND

Cardiovascular disease (CVD) is associated with impairments in microvascular responsiveness. Therefore, reliably assessing microvascular function is clinically relevant. Thus, this study aimed to examine the reliability of the near-infrared spectroscopy (NIRS)-derived oxygen saturation (StO₂) reperfusion slope, a measure of microvascular responsiveness, to four different vascular occlusion tests (VOT) of different durations in young and older participants.

METHODS

Eight healthy young (29 ± 5 yr) and seven older (67 ± 4 yr) men participated in four NIRS combined with VOT (NIRS-VOT; 30 s, 1, 3, and 5 min) in the leg microvasculature on two visits separated by 1-2 weeks. Vascular responsiveness was determined by the StO₂ reperfusion slope. The coefficient of variation (CV), repeatability, reliability (ICC), and the limits of agreement (LOA) were calculated for the NIRS-derived reperfusion slopes for each occlusion duration and visit.

RESULTS

CV for the StO₂ reperfusion slope following 30 s, 1, 3 and 5 min of occlusion were 33 ± 29%, 19 ± 21%, 14 ± 12%, and 12 ± 10%, respectively. Repeatability values following 30 s, 1, 3 and 5 min occlusions were 20%, 1%, 4% and 21%, respectively. The ICC for the StO₂ reperfusion slopes for each occlusion duration were 0.29, 0.42, 0.84, and 0.88 following 30 s, 1, 3 and 5 min of occlusion, respectively. LOA values between visit 1 and 2 for occlusions were not different from zero. There were no age-related differences for all variables of the study.

CONCLUSION

NIRS-derived StO₂ reperfusion slope, has good reliability across a range of occlusion durations with the strongest reliability during longer occlusion durations.

Microvascular reactivity monitored with near-infrared spectroscopy is impaired after induction of anaesthesia in cardiac surgery patients: An observational study

BACKGROUND

Induction of anaesthesia causes significant macrohaemodynamic changes, but little is known about its effects on the microcirculation. However, alterations in microvascular perfusion are known to be associated with impaired tissue oxygenation and organ dysfunction. Microvascular reactivity can be assessed with vascular occlusion testing, which evaluates the response of tissue oxygen saturation to transient ischaemia and reperfusion.

OBJECTIVE

The aim of the current study was to evaluate the effects of an opioid-based anaesthesia induction on microvascular reactivity. We hypothesised that despite minimal blood pressure changes, microvascular function would be impaired.

DESIGN

Prospective, observational study.

SETTING

Single-centre, tertiary university teaching hospital, Belgium.

PATIENTS

Thirty-five adult patients scheduled for elective coronary artery bypass grafting surgery.

INTERVENTION

Microvascular reactivity was assessed before and 30 min after anaesthesia induction by means of vascular occlusion testing and near-infrared spectroscopy.

MAIN OUTCOME MEASURES

Tissue oxygen saturations, desaturation rate, recovery time (time from release of cuff to the maximum value) and rate of recovery were determined.

RESULTS

Data are expressed as median (minimum to maximum). Tissue oxygen saturation was higher after induction of anaesthesia [70 (54 to 78) vs. 73 (55 to 94)%, P = 0.015]. Oxygen consumption decreased after induction, appreciable by the higher minimum tissue oxygen saturation [45 (29 to 69) vs. 53 (28 to 81)%, P < 0.001] and the slower desaturation rate [11 (4 to 18) vs. 9 (5 to 16)% min, P < 0.001]. After induction of anaesthesia, recovery times were longer [40 (20 to 120) vs. 48 (24 to 356) s, P = 0.004] and the rate of recovery was lower [114 (12 to 497) vs. 80 (3 to 271)% min, P < 0.001].

CONCLUSION

After induction of anaesthesia, oxygen consumption was decreased. The longer recovery times and slower rates of recovery indicate impaired microvascular reactivity after induction of anaesthesia.

TRIAL REGISTRATION

The research project was registered at ClinicalTrials.gov (NCT02034682).

Cross-section and feasibility study on the non-invasive evaluation of muscle hemodynamic responses in Duchenne muscular dystrophy by using a near-infrared diffuse optical technique

Duchenne muscular dystrophy (DMD) is an X-linked debilitating muscular disease that may decrease nitric oxide (NO) production and lead to functional muscular ischemia. Currently, the 6-minute walk test (6-MWT) and the North Star Ambulatory Assessment (NSAA) are the primary outcome measures in clinical trials, but they are severely limited by the subjective consciousness and mood of patients, and can only be used in older and ambulatory boys. This study proposed using functional near-infrared spectroscopy (fNIRS) to evaluate the dynamic changes in muscle hemodynamic responses (gastrocnemius and forearm muscle) during a 6-MWT and a venous occlusion test (VOT), respectively. Muscle oxygenation of the forearm was evaluated non-invasively before, during and after VOT in all participants (included 30 DMD patients and 30 age-matched healthy controls), while dynamic muscle oxygenation of gastrocnemius muscle during 6-MWT was determined in ambulatory participants (n = 18) and healthy controls (n = 30). The results reveal that impaired muscle oxygenation was observed during 6-MWT in DMD patients that may explain why the DMD patients walked shorter distances than healthy controls. Moreover, the results of VOT implied that worsening muscle function was associated with a lower supply of muscle oxygenation and may provide useful information on the relationship between muscular oxygen consumption and supply for the clinical diagnosis of DMD. Therefore, the method of fNIRS with VOT possesses great potential in future evaluations of DMD patients that implies a good feasibility for clinical application such as for monitoring disease severity of DMD.

Recent advances in bedside microcirculation assessment in critically ill patients

Parameters related to macrocirculation, such as the mean arterial pressure, central venous pressure, cardiac output, mixed venous saturation and central oxygen saturation, are commonly used in the hemodynamic assessment of critically ill patients. However, several studies have shown that there is a dissociation between these parameters and the state of microcirculation in this group of patients. Techniques that allow direct viewing of the microcirculation are not completely disseminated, nor are they incorporated into the clinical management of patients in shock. The numerous techniques developed for microcirculation assessment include clinical assessment (e.g., peripheral perfusion index and temperature gradient), laser Doppler flowmetry, tissue oxygen assessment electrodes, videomicroscopy (orthogonal polarization spectral imaging, sidestream dark field imaging or incident dark field illumination) and near infrared spectroscopy. In the near future, the monitoring and optimization of tissue perfusion by direct viewing and microcirculation assessment may become a goal to be achieved in the hemodynamic resuscitation of critically ill patients.

Postoperative hemodynamic instability and monitoring

PURPOSE OF REVIEW

The purpose of the review is to identify the recently validated minimally invasive or noninvasive monitoring devices used to both monitor and guide resuscitation in the critically ill patients.

RECENT FINDINGS

Recent advances in noninvasive measures of blood pressure, blood flow, and vascular tone have been validated and complement existing minimally invasive and invasive monitoring techniques. These monitoring approaches should be used within the context of a focused physical examination and static vital sign analysis. When available, measurement of urinary output is often included. All studies show that minimally invasive and noninvasive measure of arterial pressure and cardiac output are possible and often remain as accurate as invasive measures. The noninvasive techniques degrade in severe circulatory failure and the use of vasopressor therapy. Importantly, these output parameters form the treatment goals for many goal-directed therapies protocols.

SUMMARY

When coupled with a focused physical examination and functional hemodynamic monitoring analyses, these measures become even more specific at defining volume responsiveness and vasomotor tone and can be used to drive resuscitation strategies.

Skin microcirculatory reactivity assessed using a thermal challenge is decreased in patients with circulatory shock and associated with outcome

Background

Shock states are characterized by impaired tissue perfusion and microcirculatory alterations, which are directly related to outcome. Skin perfusion can be noninvasively evaluated using skin laser Doppler (SLD), which, when coupled with a local thermal challenge, may provide a measure of microcirculatory reactivity. We hypothesized that this microvascular reactivity would be impaired in patients with circulatory shock and would be a marker of severity.

Methods

We first evaluated skin blood flow (SBF) using SLD on the forearm and on the palm in 18 healthy volunteers to select the site with maximal response. Measurements were taken at 37 °C (baseline) and repeated at 43 °C. The 43 °C/37 °C SBF ratio was calculated as a measure of microvascular reactivity. We then evaluated the SBF in 29 patients with circulatory shock admitted to a 35-bed department of intensive care and in a confirmatory cohort of 35 patients with circulatory shock.

Results

In the volunteers, baseline SBF was higher in the hand than in the forearm, but the SBF ratio was lower (11.2 [9.4–13.4] vs. 2.0 [1.7–2.6], p < 0.01) so we used the forearm for our patients. Baseline forearm SBF was similar in patients with shock and healthy volunteers, but the SBF ratio was markedly lower in the patients (2.6 [2.0–3.6] vs. 11.2 [9.4–13.4], p < 0.01). Shock survivors had a higher SBF ratio than non-survivors (3.2 [2.2–6.2] vs. 2.3 [1.7–2.8], p < 0.01). These results were confirmed in the second cohort of 35 patients. In multivariable analysis, the APACHE II score and the SBF ratio were independently associated with mortality.

Conclusions

Microcirculatory reactivity is decreased in patients with circulatory shock and has prognostic value. This simple, noninvasive test could help in monitoring the peripheral microcirculation in acutely ill patients.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0393-7) contains supplementary material, which is available to authorized users.

Evaluation for occult sepsis incorporating NIRS and emergency sonography

PURPOSE

We aim to determine whether the combination of regional tissue oxygen saturation (StO₂) measurement using near-infrared spectroscopy (NIRS), inferior vena cava (IVC) collapsibility and ejection fraction (EF) is able to detect occult sepsis.

METHODS

We included adult patients in the emergency department with at least one of the following: fever; any one component of the quick sepsis-related organ function assessment (SOFA) score; heart rate≥100 beats per minute; or white cell count <4.0×10⁹/L or >12.0×10⁹/L. StO₂ parameters, IVC collapsibility and EF were assessed. Primary outcome was composite of admission to intensive care unit, hypotension requiring fluid resuscitation or vasopressor use, and antibiotic escalation.

RESULTS

We included 184 patients with mean age of 55.4years and slight male predominance (51.6%). Increase in temperature (adjusted odds ratio [aOR] 3.05; 95% confidence interval [CI] 1.16 to 8.02), higher white cell counts (aOR 1.10; 95% CI 1.03 to 1.19), increase in time taken to new StO₂ baseline (aOR 1.03; 95% CI 1.01 to 1.06) and reduced EF (aOR 33.9; 95% CI 2.19 to 523.64) had higher odds of achieving the primary outcome.

CONCLUSION

Change in StO₂ and time taken to reach new StO₂ baseline, combined with EF could potentially predict sepsis among patients with infection.

Near-Infrared Spectroscopy and Vascular Occlusion Test for Predicting Clinical Outcome in Pediatric Cardiac Patients: A Prospective Observational Study

OBJECTIVES

This study is designed to determine the feasibility and utility of vascular occlusion test variables as measured by INVOS Medtronic, Dublin, Ireland) in pediatric cardiac patients.

DESIGN

A prospective observational study.

SETTING

A tertiary children's hospital.

PATIENTS

Children less than or equal to 8 years old who were scheduled for elective cardiac surgery under cardiopulmonary bypass.

INTERVENTIONS

A vascular occlusion test (3 min of ischemia and reperfusion) was performed on the calf at three time points: after induction of anesthesia (T0), during cardiopulmonary bypass (T1), and after sternal closure (T2).

MEASUREMENTS AND MAIN RESULTS

Baseline regional tissue hemoglobin oxygen saturation, deoxygenation rate, minimum regional tissue hemoglobin oxygen saturation, and reoxygenation rate were measured using INVOS. Influence of age on variables at each measurement point was also checked using linear regression analysis. Receiver operating characteristics curve analysis was performed to determine the ability of vascular occlusion test variables at T2 to predict the occurrence of major adverse events. Both the deoxygenation and reoxygenation rates were lowest in T1. There was a tendency to decreased regional tissue hemoglobin oxygen saturation in younger patients at T0 (r = 0.37; p < 0.001), T1 (r = 0.33; p < 0.001), and T2 (r = 0.42; p < 0.001) during vascular occlusion. Minimum regional tissue hemoglobin oxygen saturation was correlated with age at T0 (r = 0.51; p < 0.001) and T2 (r = 0.35; p = 0.001). Patients with major adverse events had similar baseline regional tissue hemoglobin oxygen saturation but lower minimum regional tissue hemoglobin oxygen saturation (48.8% ± 19.3% vs 63.3% ± 13.9%; p < 0.001) and higher reoxygenation rate (4.30 ± 3.20 vs 2.57 ± 2.39 %/s; p = 0.008) at T2 compared with those without. The minimum regional tissue hemoglobin oxygen saturation less than 51% after sternal closure could predict the occurrence of major adverse events with a sensitivity of 61.1% and a specificity of 85.4%.

CONCLUSIONS

Vascular occlusion test using INVOS can be applied in children undergoing cardiac surgery. Vascular occlusion test variables are influenced by age and cardiopulmonary bypass. The minimum regional tissue hemoglobin oxygen saturation less than 51% after sternal closure is associated with worse clinical outcomes in pediatric cardiac patients.

Performance comparison of the MOXY and PortaMon near-infrared spectroscopy muscle oximeters at rest and during exercise

The purpose of the study was to compare muscle oxygenation as measured by two portable, wireless near-infrared spectroscopy (NIRS) devices under resting and dynamic conditions. A recently developed low-cost NIRS device (MOXY) was compared against an established PortaMon system that makes use of the spatially resolved spectroscopy algorithm. The influence of increasing external pressure on tissue oxygen saturation index (TSI) indicated that both devices are stable between 2 and 20 mmHg. However, above this pressure, MOXY reports declining TSI values. Analysis of adipose tissue thickness (ATT) and TSI shows a significant, nonlinear difference between devices at rest. The devices report similar TSI (%) values at a low ATT (<7  mm) (PortaMon minus MOXY difference is +1.1±2.8%) with the major subsequent change between the devices occurring between 7 and 10 mm; at ATT values >10  mm the difference remains constant (-14.7±2.8%). The most likely explanation for this difference is the small source-detector separation (2.5 cm) in the MOXY resulting in lower tissue penetration into muscle in subjects with higher ATT. Interday test-retest reliability of resting TSI was evaluated on five separate occasions, with the PortaMon reporting a lower coefficient of variation (1.8% to 2.5% versus 5.7% to 6.2%). In studies on male subjects with low ATT, decreases in the TSI were strongly correlated during isometric exercise, arterial occlusion, and incremental arm crank exercise. However, the MOXY reports a greater dynamic range, particularly during ischemia induced by isometric contraction or occlusion (Δ74.3% versus Δ43.7%; hyperemia MAX-occlusion MIN). This study shows that in this subject group both MOXY and PortaMon produce physiologically credible TSI measures during rest and exercise. However, the absolute values obtained during exercise are generally not comparable between devices unless corrected by physiological calibration following an arterial occlusion.

Microvascular effects of intravenous esmolol in patients with normal cardiac function undergoing postoperative atrial fibrillation: a prospective pilot study in cardiothoracic surgery

BACKGROUND

Postoperative atrial fibrillation (POAF) is commonplace after cardiothoracic surgery. A rate control strategy using short-acting beta blockers is recommended as a first-line therapy in patients without hemodynamic instability. Microcirculatory effects of POAF and esmolol have not yet been investigated. We hypothesized that POAF without hemodynamic instability would induce microvascular dysfunction which could be reversed by intravenous esmolol.

METHODS

Twenty-five cardiothoracic surgical patients with POAF were included in the study. Microcirculation was assessed by peripheral near-infrared spectroscopy (NIRS) in association with a vascular occlusion test (VOT) before esmolol infusion, during incremental doses of esmolol (25, 50, 100, and 200 μg/kg/min), and after a return to sinus rhythm. Esmolol was given to control heart rate to between 60 and 90 beats/min. Regional tissue oxygen saturation variables (StO₂, StO₂ min, StO₂ max, and ∆StO₂) and desaturation/resaturation speeds during VOT were recorded to evaluate the microcirculation.

RESULTS

StO₂ and resaturation speed were significantly improved when POAF returned to sinus rhythm (StO₂ 64% ± 6 versus 67% ± 6, P < 0.01; resaturation speed 0.53%/s (0.42-0.97) versus 0.66%/s (0.51-1.04), P = 0.020). ∆StO₂ was significantly decreased after a return to sinus rhythm (7.9% ± 4.8 versus 6.1% ± 4.7, P = 0.026). During esmolol infusion, we found a significant decrease in both heart rate (P < 0.001) and blood pressure (P < 0.001), and a non-significant dose-dependent increase in StO₂ (P = 0.081) and resaturation speed (P = 0.087).

CONCLUSION

POAF without hemodynamic instability is associated with significant impairment in the microcirculation which could be partially reversed by intravenous esmolol.