Association of the intraoperative peripheral perfusion index with postoperative morbidity and mortality in acute surgical patients: a retrospective observational multicentre cohort study

Assisted Fluid Management and Sublingual Microvascular Flow During High-Risk Abdominal Surgery: A Randomized Controlled Trial

BACKGROUND

Implementation of goal-directed fluid therapy (GDFT) protocols remains low. Protocol compliance among anesthesiologists tends to be suboptimal owing to the high workload and the attention required for implementation. The assisted fluid management (AFM) system is a novel decision support tool designed to help clinicians apply GDFT protocols. This system predicts fluid responsiveness better than anesthesia practitioners do and achieves higher stroke volume (SV) and cardiac index values during surgery. We tested the hypothesis that an AFM-guided GDFT strategy would also be associated with better sublingual microvascular flow compared to a standard GDFT strategy.

METHODS

This bicenter, parallel, 2-arm, prospective, randomized controlled, patient and assessor-blinded, superiority study considered for inclusion all consecutive patients undergoing high-risk abdominal surgery who required an arterial catheter and uncalibrated SV monitoring. Patients having standard GDFT received manual titration of fluid challenges to optimize SV while patients having an AFM-guided GDFT strategy received fluid challenges based on recommendations from the AFM software. In all patients, fluid challenges were standardized and titrated per 250 mL and vasopressors were administered to maintain a mean arterial pressure >70 mm Hg. The primary outcome (average of each patient's intraoperative microvascular flow index (MFI) across 4 intraoperative time points) was analyzed using a Mann-Whitney U test and the treatment effect was estimated with a median difference between groups with a 95% confidence interval estimated using the bootstrap percentile method (with 1000 replications). Secondary outcomes included SV, cardiac index, total amount of fluid, other microcirculatory variables, and postoperative lactate.

RESULTS

A total of 86 patients were enrolled over a 7-month period. The primary outcome was significantly higher in patients with AFM (median [Q1-Q3]: 2.89 [2.84-2.94]) versus those having standard GDFT (2.59 [2.38-2.78] points, median difference 0.30; 95% confidence interval [CI], 0.19-0.49; P < .001). Cardiac index and SVI were higher (3.2 ± 0.5 vs 2.7 ± 0.7 l.min -1 .m -2 ; P = .001 and 42 [35-47] vs 36 [32-43] mL.m -2 ; P = .018) and arterial lactate concentration was lower at the end of the surgery in patients having AFM-guided GDFT (2.1 [1.5-3.1] vs 2.9 [2.1-3.9] mmol.L -1 ; P = .026) than patients having standard GDFT strategy. Patients having AFM received a higher fluid volume but 3 times less norepinephrine than those receiving standard GDFT ( P < .001).

CONCLUSIONS

Use of an AFM-guided GDFT strategy resulted in higher sublingual microvascular flow during surgery compared to use of a standard GDFT strategy. Future trials are necessary to make conclusive recommendations that will change clinical practice.

Prospective Evaluation of the Peripheral Perfusion Index in Assessing the Organ Dysfunction and Prognosis of Adult Patients With Sepsis in the ICU

Background: The peripheral perfusion index (PI) reflects microcirculatory blood flow perfusion and indicates the severity and prognosis of sepsis. Method: The cohort comprised 208 patients admitted to the intensive care unit (ICU) with infection, among which 117 had sepsis. Demographics, medication history, ICU variables, and laboratory indexes were collected. Primary endpoints were in-hospital mortality and 28-day mortality. Secondary endpoints included organ function variables (coagulation function, liver function, renal function, and myocardial injury), lactate concentration, mechanical ventilation time, and length of ICU stay. Univariate and multivariate analyses were conducted to assess the associations between the PI and clinical outcomes. Sensitivity analyses were performed to explore the associations between the PI and organ functions in the sepsis and nonsepsis groups. Result: The PI was negatively associated with in-hospital mortality (odds ratio [OR] 0.29, 95% confidence interval [CI] 0.15 to 0.55), but was not associated with 28-day mortality. The PI was negatively associated with the coagulation markers prothrombin time (PT) (β -0.36, 95% CI -0.59 to 0.13) and activated partial thromboplastin time (APTT) (β -1.08, 95% CI -1.86 to 0.31), and the myocardial injury marker cardiac troponin I (cTnI) (β -2085.48, 95% CI -3892.35 to 278.61) in univariate analysis, and with the PT (β -0.36, 95% CI -0.60 to 0.13) in multivariate analysis. The PI was negatively associated with the lactate concentration (β -0.57, 95% CI -0.95 to 0.19), mechanical ventilation time (β -23.11, 95% CI -36.54 to 9.69), and length of ICU stay (β -1.28, 95% CI -2.01 to 0.55). Sensitivity analyses showed that the PI was significantly associated with coagulation markers (PT and APTT) and a myocardial injury marker (cTnI) in patients with sepsis, suggesting that the associations between the PI and organ function were stronger in the sepsis group than the nonsepsis group. Conclusion: The PI provides new insights for assessing the disease severity, short-term prognosis, and organ function damage in ICU patients with sepsis, laying a theoretical foundation for future research.

Peripheral perfusion index stratifies risk in patients with intraoperative anemia: A multicentre cohort study

STUDY OBJECTIVE

Evidence for red blood cell (RBC) transfusion thresholds in the intraoperative setting is limited, and current perioperative recommendations may not correspond with individual intraoperative physiological demands. Hemodynamics relevant for the decision to transfuse may include peripheral perfusion index (PPI). The objective of this prospective study was to assess the associations of PPI and hemoglobin levels with the risk of postoperative morbidity and mortality.

DESIGN

Multicenter cohort study.

SETTING

Bispebjerg and Hvidovre University Hospitals, Copenhagen, Denmark.

PATIENTS

We included 741 patients who underwent acute high risk abdominal surgery or hip fracture surgery.

INTERVENTIONS

No interventions were carried out.

MEASUREMENTS

Principal values collected included measurements of peripheral perfusion index and hemoglobin values.

METHODS

The study was conducted using prospectively obtained data on adults who underwent emergency high-risk surgery. Subjects were categorized into high vs. low subgroups stratified by pre-defined PPI levels (PPI: > 1.5 vs. < 1.5) and Hb levels (Hb: > 9.7 g/dL vs. < 9.7 g/dL). The study assessed mortality and severe postoperative complications within 90 days.

MAIN RESULTS

We included 741 patients. 90-day mortality was 21% (n = 154), frequency of severe postoperative complications was 31% (n = 231). Patients with both low PPI and low Hb had the highest adjusted odds ratio for both 90-day severe postoperative complications (2.95, [1.62-5.45]) and 90-day mortality (3.13, [1.45-7.11]). A comparison of patients with low PPI and low Hb to those with high PPI and low Hb detected significantly higher 90-day mortality risk in the low PPI and low Hb group (OR 8.6, [1.57-162.10]).

CONCLUSION

High PPI in acute surgical patients who also presents with anemia was associated with a significantly better outcome when compared with patients with both low PPI and anemia. PPI should therefore be further investigated as a potential parameter to guide intraoperative RBC transfusion therapy.

Non-Invasive Hemodynamic Monitoring System Integrating Spectrometry, Photoplethysmography, and Arterial Pressure Measurement Capabilities

Minimally invasive and non-invasive hemodynamic monitoring technologies have recently gained more attention, driven by technological advances and the inherent risk of complications in invasive techniques. In this article, an experimental non-invasive system is presented that effectively combines the capabilities of spectrometry, photoplethysmography (PPG), and arterial pressure measurement. Both time- and wavelength-resolved optical signals from the fingertip are measured under external pressure, which gradually increased above the level of systolic blood pressure. The optical channels measured at 434-731 nm divided into three groups separated by a group of channels with wavelengths approximately between 590 and 630 nm. This group of channels, labeled transition band, is characterized by abrupt changes resulting from a decrease in the absorption coefficient of whole blood. External pressure levels of maximum pulsation showed that shorter wavelengths (<590 nm) probe superficial low-pressure blood vessels, whereas longer wavelengths (>630 nm) probe high-pressure arteries. The results on perfusion indices and DC component level changes showed clear differences between the optical channels, further highlighting the importance of wavelength selection in optical hemodynamic monitoring systems. Altogether, the results demonstrated that the integrated system presented has the potential to extract new hemodynamic information simultaneously from macrocirculation to microcirculation.

Association between peripheral perfusion index and postoperative acute kidney injury in major noncardiac surgery patients receiving continuous vasopressors: a post hoc exploratory analysis of the VEGA-1 trial

BACKGROUND

The peripheral perfusion index is the ratio of pulsatile to nonpulsatile static blood flow obtained by photoplethysmography and reflects peripheral tissue perfusion. We investigated the association between intraoperative perfusion index and postoperative acute kidney injury in patients undergoing major noncardiac surgery and receiving continuous vasopressor infusions.

METHODS

In this exploratory post hoc analysis of a pragmatic, cluster-randomised, multicentre trial, we obtained areas and cumulative times under various thresholds of perfusion index and investigated their association with acute kidney injury in multivariable logistic regression analyses. In secondary analyses, we investigated the association of time-weighted average perfusion index with acute kidney injury. The 30-day mortality was a secondary outcome.

RESULTS

Of 2534 cases included, 8.9% developed postoperative acute kidney injury. Areas and cumulative times under a perfusion index of 3% and 2% were associated with an increased risk of acute kidney injury; the strongest association was observed for area under a perfusion index of 1% (adjusted odds ratio [aOR] 1.32, 95% confidence interval [CI] 1.00-1.74, P=0.050, per 100%∗min increase). Additionally, time-weighted average perfusion index was associated with acute kidney injury (aOR 0.82, 95% CI 0.74-0.91, P<0.001) and 30-day mortality (aOR 0.68, 95% CI 0.49-0.95, P=0.024).

CONCLUSIONS

Larger areas and longer cumulative times under thresholds of perfusion index and lower time-weighted average perfusion index were associated with postoperative acute kidney injury in patients undergoing major noncardiac surgery and receiving continuous vasopressor infusions.

CLINICAL TRIAL REGISTRATION

NCT04789330.

Early peripheral perfusion index predicts 28-day outcome in patients with septic shock

BACKGROUND

To investigate the prognostic value of the peripheral perfusion index (PPI) in patients with septic shock.

METHODS

This prospective cohort study, conducted at the emergency intensive care unit of Peking University People's Hospital, recruited 200 patients with septic shock between January 2023 and August 2023. These patients were divided into survival (n=84) and death (n=116) groups based on 28-day outcomes. Clinical evaluations included laboratory tests and clinical scores, with lactate and PPI values assessed upon admission to the emergency room and at 6 h and 12 h after admission. Risk factors associated with mortality were analyzed using univariate and multivariate Cox regression analyses. Receiver operator characteristic (ROC) curve was used to assess predictive performance. Mortality rates were compared, and Kaplan-Meier survival plots were created.

RESULTS

Compared to the survival group, patients in the death group were older and had more severe liver damage and coagulation dysfunction, necessitating higher norepinephrine doses and increased fluid replacement. Higher lactate levels and lower PPI levels at 0 h, 6 h, and 12 h were observed in the death group. Multivariate Cox regression identified prolonged prothrombin time (PT), decreased 6-h PPI and 12-h PPI as independent risk factors for death. The area under the curves for 6-h PPI and 12-h PPI were 0.802 (95% CI 0.742-0.863, P<0.001) and 0.945 (95% CI 0.915-0.974, P<0.001), respectively, which were superior to Glasgow Coma Scale (GCS), Sequential Organ Failure Assessment (SOFA) scores (0.864 and 0.928). Cumulative mortality in the low PPI groups at 6 h and 12 h was significantly higher than in the high PPI groups (6-h PPI: 77.52% vs. 22.54%; 12-h PPI: 92.04% vs. 13.79%, P<0.001).

CONCLUSION

PPI may have value in predicting 28-day mortality in patients with septic shock.

"The peripheral perfusion index discriminates haemodynamic responses to induction of general anaesthesia"

Induction of general anaesthesia is often accompanied by hypotension. Standard haemodynamic monitoring during anaesthesia relies on intermittent blood pressure and heart rate. Continuous monitoring systemic blood pressure requires invasive or advanced modalities creating a barrier for obtaining important information of the circulation. The Peripheral Perfusion Index (PPI) is obtained non-invasively and continuously by standard photoplethysmography. We hypothesized that different patterns of changes in systemic haemodynamics during induction of general anaesthesia would be reflected in the PPI. Continuous values of PPI, stroke volume (SV), cardiac output (CO), and mean arterial pressure (MAP) were evaluated in 107 patients by either minimally invasive or non-invasive means in a mixed population of surgical patients. 2 min after induction of general anaesthesia relative changes of SV, CO, and MAP was compared to the relative changes of PPI. After induction total cohort mean(± st.dev.) MAP, SV, and CO decreased to 65(± 16)%, 74(± 18)%, and 63(± 16)% of baseline values. In the 38 patients where PPI decreased MAP was 57(± 14)%, SV was 63(± 18)%, and CO was 55(± 18)% of baseline values 2 min after induction. In the 69 patients where PPI increased the corresponding values were MAP 70(± 15)%, SV 80(± 16)%, and CO 68(± 17)% (all differences: p < 0,001). During induction of general anaesthesia changes in PPI discriminated between the degrees of reduction in blood pressure and algorithm derived cardiac stroke volume and -output. As such, the PPI has potential to be a simple and non-invasive indicator of the degree of post-induction haemodynamic changes.

Intraoperative blood pressure: could less be more?

Retrospective observational studies have reported a significant association between intraoperative hypotension and postoperative morbidity. However, association does not imply causation, and whether preventing intraoperative hypotension can improve patient outcome remains to be demonstrated. In this issue of the British Journal of Anaesthesia, D'Amico and colleagues meta-analysed 10 prospective randomised trials comparing low (≤60 mm Hg) and higher mean arterial pressure targets during anaesthesia and surgery. They did not observe an increase in postoperative morbidity and mortality in the low target group. In contrast, they reported a statistically significant (but not clinically relevant) reduction in postoperative cardiac arrhythmia and hospital length of stay when targeting mean arterial pressure ≤60 mm Hg. These findings suggest that during most surgical cases, intraoperative hypotension is a marker of the severity, frailty, or both rather than a mediator of postoperative complications.

Associations between clinical interventions and transcutaneous blood gas values in postoperative patients

PURPOSE

Postoperative monitoring of circulation and respiration is pivotal to guide intervention strategies and ensure patient outcomes. Transcutaneous blood gas monitoring (TCM) may allow for noninvasive assessment of changes in cardiopulmonary function after surgery, including a more direct assessment of local micro-perfusion and metabolism. To form the basis for studies assessing the clinical impact of TCM complication detection and goal-directed-therapy, we examined the association between clinical interventions in the postoperative period and changes in transcutaneous blood gasses.

METHODS

Two-hundred adult patients who have had major surgery were enrolled prospectively and monitored with transcutaneous blood gas measurements (oxygen (TcPO2) and carbon dioxide (TcPCO2)) for 2 h in the post anaesthesia care unit, with recording of all clinical interventions. The primary outcome was changes in TcPO2, secondarily TcPCO2, from 5 min before a clinical intervention versus 5 min after, analysed with paired t-test.

RESULTS

Data from 190 patients with 686 interventions were analysed. During clinical interventions, a mean change in TcPO2 of 0.99 mmHg (95% CI-1.79-0.2, p = 0.015) and TcPCO2 of-0.67 mmHg (95% CI 0.36-0.98, p < 0.001) was detected.

CONCLUSION

Clinical interventions resulted in significant changes in transcutaneous oxygen and carbon dioxide. These findings suggest future studies to assess the clinical value of changes in transcutaneous PO2 and PCO2 in a postoperative setting.

TRIAL REGISTRY

Clinical trial number: NCT04735380.

CLINICAL TRIAL REGISTRY

https://clinicaltrials.gov/ct2/show/NCT04735380.

Association of the perfusion index with postoperative acute kidney injury: a retrospective study

BACKGROUND

Many studies have examined the risk factors for postoperative acute kidney injury (AKI), but few have focused on intraoperative peripheral perfusion index (PPI) that has recently been shown to be associated with postoperative morbidity and mortality. Therefore, this study aimed to evaluate the relationship between intraoperative PPI and postoperative AKI under the hypothesis that lower intraoperative PPI is associated with AKI occurrence.

METHODS

We retrospectively searched electronic medical records to identify patients who underwent surgery at the general surgery department from May 2021 to November 2021. Patient baseline characteristics, pre- and post-operative laboratory test results, comorbidities, intraoperative vital signs, and discharge profiles were obtained from the Institutional Clinical Data Warehouse and VitalDB. Intraoperative PPI was the primary exposure variable, and the primary outcome was postoperative AKI.

RESULTS

Overall, 2,554 patients were identified and 1,586 patients were included in our analysis. According to Kidney Disease Improving Global Outcomes (KDIGO) criteria, postoperative AKI occurred in 123 (7.8%) patients. We found that risks of postoperative AKI increased (odds ratio: 2.00, 95% CI [1.16, 3.44], P = 0.012) when PPI was less than 0.5 for more than 10% of surgery time. Other risk factors for AKI occurrence were male sex, older age, higher American Society of Anesthesiologists physical status, obesity, underlying renal disease, prolonged operation time, transfusion, and emergent operation.

CONCLUSIONS

Low intraoperative PPI was independently associated with postoperative AKI.

Modifications of peripheral perfusion in patients with vasopressor-dependent septic shock treated with polymyxin B-direct hemoperfusion

Abnormal peripheral perfusion (PP) worsens the prognosis of patients with septic shock. Polymyxin B-direct hemoperfusion (PMX-DHP) increases blood pressure and reduces vasopressor doses. However, the modification of PP following administration of PMX-DHP in patients with vasopressor-dependent septic shock have not yet been elucidated. A retrospective exploratory observational study was conducted in patients with septic shock treated with PMX-DHP. Pulse-amplitude index (PAI), vasoactive inotropic score (VIS), and cumulative fluid balance data were extracted at PMX-DHP initiation (T0) and after 24 (T24) and 48 (T48) h. Changes in these data were analyzed in all patients and two subgroups (abnormal PP [PAI < 1] and normal PP [PAI ≥ 1]) based on the PAI at PMX-DHP initiation. Overall, 122 patients (abnormal PP group, n = 67; normal PP group, n = 55) were evaluated. Overall and in the abnormal PP group, PAI increased significantly at T24 and T48 compared with that at T0, with a significant decrease in VIS. Cumulative 24-h fluid balance after PMX-DHP initiation was significantly higher in the abnormal PP group. PMX-DHP may be an effective intervention to improve PP in patients with abnormal PP; however, caution should be exercised as fluid requirements may differ from that of patients with normal PP.

Association between mean arterial pressure and sublingual microcirculation during major non-cardiac surgery: Post hoc analysis of a prospective cohort

OBJECTIVE

To test the hypothesis that there is an association between mean arterial pressure (MAP) and sublingual perfusion during major surgery, and perhaps an identifiable harm threshold.

METHODS

This post hoc analysis of a prospective cohort included patients who had elective major non-cardiac surgery with a duration of ≥2 h under general anesthesia. We assessed sublingual microcirculation every 30 min using SDF+ imaging and determined the De Backer score, Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Our primary outcome was the relationship between MAP and sublingual perfusion which was evaluated with linear mixed effects modeling.

RESULTS

A total of 100 patients were included, with MAP ranging between 65 mmHg and 120 mmHg during anesthesia and surgery. Over a range of intraoperative MAPs between 65 and 120 mmHg, there were no meaningful associations between blood pressure and various measures of sublingual perfusion. There were also no meaningful changes in microcirculatory flow over 4.5 h of surgery.

CONCLUSIONS

In patients having elective major non-cardiac surgery with general anesthesia, sublingual microcirculation is well maintained when MAP ranges between 65 and 120 mmHg. It remains possible that sublingual perfusion will be a useful marker of tissue perfusion when MAP is lower than 65 mmHg.

Comparative effects of desflurane and sevoflurane on intraoperative peripheral perfusion index: a retrospective, propensity score matched, cohort study

Desflurane is known to have a larger vasodilatory effect than that of sevoflurane. However, its generalizability and effect size in actual clinical practice are yet to be proven. Patients aged ≥ 18 years who underwent noncardiac surgery under general anesthesia using inhalation anesthetics (desflurane or sevoflurane) were matched 1:1 by propensity score. The mean intraoperative perfusion index (PI) of each patient were compared between the two groups. Propensity score matching of 1680 patients in the study cohort identified 230 pairs of patients. PI was significantly higher in the desflurane group (median of paired difference, 0.45; 95% CI 0.16 to 0.74, p = 0.002). PI durations below 1.0 and 1.5 were significantly longer in the sevoflurane group. Mean arterial pressure (MAP) and durations of low MAP did not differ significantly between the two groups. Generalized linear mixed models revealed that the use of sevoflurane, mean MAP, mean heart rate, age, and duration of anesthesia had significant negative effects (lower PI), whereas mean age-adjusted minimum alveolar concentration of inhalation agent had a positive effect on PI (higher value). Intraoperative PI was significantly higher in patients administered desflurane than sevoflurane. However, the impact of the choice between desflurane and sevoflurane on intraoperative PI in this clinical setting was minimal.

Intraoperative Assessment of Surgical Stress Response Using Nociception Monitor under General Anesthesia and Postoperative Complications: A Narrative Review

We present a narrative review focusing on the new role of nociception monitor in intraoperative anesthetic management. Higher invasiveness of surgery elicits a higher degree of surgical stress responses including neuroendocrine-metabolic and inflammatory-immune responses, which are associated with the occurrence of major postoperative complications. Conversely, anesthetic management mitigates these responses. Furthermore, improper attenuation of nociceptive input and related autonomic effects may induce increased stress response that may adversely influence outcome even in minimally invasive surgeries. The original role of nociception monitor, which is to assess a balance between nociception caused by surgical trauma and anti-nociception due to anesthesia, may allow an assessment of surgical stress response. The goal of this review is to inform healthcare professionals providing anesthetic management that nociception monitors may provide intraoperative data associated with surgical stress responses, and to inspire new research into the effects of nociception monitor-guided anesthesia on postoperative complications.

To identify normovolemia in humans: The stroke volume response to passive leg raising vs. head-down tilt

Volume responsiveness can be evaluated by tilting maneuvers such as head-down tilt (HDT) and passive leg raising (PLR), but the two procedures use different references (HDT the supine position; PLR the semi-recumbent position). We tested whether the two procedures identify "normovolemia" by evaluating the stroke volume (SV) and cardiac output (CO) responses and whether the peripheral perfusion index (PPI) derived from pulse oximetry provides similar information. In randomized order, 10 healthy men were exposed to both HDT and PLR, and evaluations were made also when the subjects fasted. Central cardiovascular variables were derived by pulse contour analysis and changes in central blood volume assessed by thoracic electrical admittance (TEA). During HDT, SV remained stable (fasted 110 ± 16 vs. 109 ± 16 ml; control 113 ± 16 vs. 111 ± 16 ml, p > 0.05) with no change in CO, TEA, PPI, or SV variation (SVV). In contrast during PLR, SV increased (fasted 108 ± 17 vs. 117 ± 17 ml; control 108 ± 18 vs. 117 ± 18 ml, p < 0.05) followed by an increase in TEA (p < 0.05) and CO increased when subjects fasted (6.7 ± 1.5 vs. 7.1 ± 1.5, p = 0.007) with no change in PPI or SVV. In conclusion, SV has a maximal value for rest in supine men, while PLR restores SV as CBV is reduced in a semi-recumbent position and the procedure thereby makes healthy volunteers seem fluid responsive.

Microcirculatory tissue perfusion during general anaesthesia and noncardiac surgery: An observational study using incident dark field imaging with automated video analysis

BACKGROUND

Handheld vital microscopy allows direct observation of red blood cells within the sublingual microcirculation. Automated analysis allows quantifying microcirculatory tissue perfusion variables - including tissue red blood cell perfusion (tRBCp), a functional variable integrating microcirculatory convection and diffusion capacities.

OBJECTIVE

We aimed to describe baseline microcirculatory tissue perfusion in patients presenting for elective noncardiac surgery and test that microcirculatory tissue perfusion is preserved during elective general anaesthesia for noncardiac surgery.

DESIGN

Prospective observational study.

SETTING

University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

PATIENTS

120 elective noncardiac surgery patients (major abdominal, orthopaedic or trauma and minor urologic surgery) and 40 young healthy volunteers.

MAIN OUTCOME MEASURES

We measured sublingual microcirculation using incident dark field imaging with automated analysis at baseline before induction of general anaesthesia, under general anaesthesia before surgical incision and every 30 min during surgery. We used incident the dark field imaging technology with a validated automated analysis software.

RESULTS

A total of 3687 microcirculation video sequences were analysed. Microcirculatory tissue perfusion variables varied substantially between individuals - but ranges were similar between patients and volunteers. Under general anaesthesia before surgical incision, there were no important changes in tRBCp, functional capillary density and capillary haematocrit compared with preinduction baseline. However, total vessel density was higher and red blood cell velocity and the proportion of perfused vessels were lower under general anaesthesia. There were no important changes in any microcirculatory tissue perfusion variables during surgery.

CONCLUSION

In patients presenting for elective noncardiac surgery, baseline microcirculatory tissue perfusion variables vary substantially between individuals - but ranges are similar to those in young healthy volunteers. Microcirculatory tissue perfusion is preserved during general anaesthesia and noncardiac surgery - when macrocirculatory haemodynamics are maintained.

Transcutaneous blood gas monitoring and tissue perfusion during common femoral thromboendarterectomy

BACKGROUND

Improving tissue perfusion can improve clinical outcomes in surgical patients, where monitoring may aid clinicians in detecting adverse conditions and guide interventions. Transcutaneous monitoring (TCM) of oxygen (tcpO₂) and carbon dioxide (tcpCO₂) is a well-proven technology and could potentially serve as a measure of local circulation, perfusion and metabolism, but the clinical use is not thoroughly explored. The purpose of this proof-of-concept study was to investigate whether TCM of blood gasses could detect changes in perfusion during major vascular surgery.

METHODS

Ten patients with peripheral arterial disease scheduled for lower limb major arterial revascularization under general anaesthesia were consecutively included. TcpO₂ and tcpCO₂ were continuously recorded from anaesthesia induction until skin closure with a TCM monitor placed on both legs and the thorax. Peripheral oxygen saturation was kept ≥94% and mean arterial blood pressure ≥65 mmHg. The primary outcomes were changes in tcpO₂ and tcpCO₂ related to arterial clamping and declamping during the procedure and analyzed by paired statistics.

RESULTS

Femoral artery clamping resulted in a significant decrease in tcpO₂ (-2.1 kPa, IQR-4.2; -0.8), p=.017)), followed by a significant increase in response to arterial declamping (5.5 kPa, IQR 0-7.3), p=.017)). Arterial clamping resulted in a statistically significant increase in tcpCO₂ (0.9 kPa, IQR 0.3-5.4), p=.008)) and a significant decrease following declamping (-0.7 kPa, IQR -2.6; -0.2), p=.011)).

CONCLUSION

Transcutaneous monitoring of oxygen and carbon dioxide is a feasible method for detection of extreme changes in tissue perfusion during arterial clamping and declamping, and its use for improving patient outcomes should be explored. Clinical Trials identifier: NCT04040478. Registered on July 31, 2019.

Fluid-responsiveness, blood volume and perfusion in preoperative haemodynamic optimisation of hip fracture patients; a prospective observational study

BACKGROUND

Preoperative resuscitation strategies in patients with hip fracture (HF) are lacking. We aimed to investigate fluid-responsiveness, peripheral perfusion index (PPI) and blood volume (BV)-status in patients with HF undergoing resuscitation in the preoperative phase.

METHODS

In a prospective observational study, we evaluated preoperative fluid-responsiveness, indices of perfusion and BV before and after lumbar epidural analgesia in 50 patients with HF shortly after admittance.

RESULTS

Initially, 18 (36%) patients were fluid-responsive (≥10% increased SV in response to 250 ml fluid bolus) and 13 (26%) presented hypovolaemia (deviation of measured BV from estimated BV ≤ 0.9). According to fluid-responsiveness, no difference in absolute values of cardiac index (CI) (2.7 L [2.1-3.3] vs. 2.8 L [2.3-3.4], p = .5) was seen, but cardiac output (CO) rose significantly in the hypovolaemic patients: 9% [5-18] vs. 1% [-3-7], p = .004. After epidural analgesia, 26 (52%) patients were again fluid-responsive and 15 (30%) were hypovolaemic. CI was now significantly lower in fluid-responsive patients (2.2 L [1.7-2.7] vs. 2.9 L [2.3-3.5], p = .001). Prior to epidural analgesia, no significant trend towards hypovolaemic patients having lower indices of perfusion was seen. After epidural analgesia, more patients with hypovolaemia presented with PPI≤1.5 (8 (53%) vs. 3 (9%), p = .001) and absolute values of PPI were also significantly lower if IBV was low (1.4 [0.9-3.2] vs. 3.2 [2.4-4.8], p = .01). PPI correlated with hypovolaemia after epidural analgesia (rho 0.4 [0.1-0.7], p = .007).

CONCLUSIONS

Preoperative fluid-responsivity in HF patients might be attributable to elements of hypovolaemia and sympathetic compensatory ability conjointly, confounding the use of SV-guided resuscitation. PPI could be associated with BV, which may support clinicians during perioperative haemodynamic optimisation.

Blood pressure and flow in pediatric anesthesia: An educational review

During recent years, a lot of interest has been focused on blood pressure in the context of pediatric anesthesia, trying to define what is normal in relation to age and what numeric values that should be regarded as hypotension, needing active intervention. However, blood pressure is mainly measured as a proxy for flow, that is, cardiac output. Thus, just focusing on specific blood pressure numbers may not necessarily be very useful or appropriate. The aim of this educational review is to put the issue of intraoperative blood pressure in the context of pediatric anesthesia in further perspective.

Perfusion index: Physical principles, physiological meanings and clinical implications in anaesthesia and critical care

Photoplethysmography (PPG) has been extensively used for pulse oximetry monitoring in anaesthesia, perioperative and intensive care. However, some components of PPG signal have been employed for other purposes, such as non-invasive haemodynamic monitoring. Perfusion index (PI) is derived from PPG signal and represents the ratio of pulsatile on non-pulsatile light absorbance or reflectance of the PPG signal. PI determinants are complex and interlinked, involving and reflecting the interaction between peripheral and central haemodynamic characteristics, such as vascular tone and stroke volume. Recently, several studies have shed light on the interesting performances of this variable, especially assessing regional or neuraxial block success, and haemodynamic monitoring in anaesthesia, perioperative and intensive care. Nevertheless, no review has yet been published concerning the interest of PI in these fields. In this narrative review will be exposed first the physiological and pathophysiological determinants of PI, and then the mean to measure this value as well as its potential limitations. In the second part, the existing data concerning usefulness of PI in different clinical settings such as operating theatres, intensive care units and emergency departments will be presented and discussed. Finally, the perspectives concerning the use of PI and mentioned aspects that should be explored regarding this tool will be underlined.

Plethysmographic Peripheral Perfusion Index: Could It Be a New Vital Sign?

The plethysmographic peripheral perfusion index (PPI) is a very useful parameter with various emerging utilities in medical practice. The PPI represents the ratio between pulsatile and non-pulsatile portions in peripheral circulation and is mainly affected by two main determinants: cardiac output and balance between sympathetic and parasympathetic nervous systems. The PPI decreases in cases of sympathetic predominance and/or low cardiac output states; therefore, it is a useful predictor of patient outcomes in critical care units. The PPI could be a surrogate for cardiac output in tests for fluid responsiveness, as an objective measure of pain especially in un-cooperative patients, and as a predictor of successful weaning from mechanical ventilation. The PPI is simple to measure, easy to interpret, and has continuously displayed variables, making it a convenient parameter for detecting the adequacy of blood flow and sympathetic-parasympathetic balance.