Cerebral Oxygen Saturation Associates with Changes in Oxygen Transport Parameters during Cardiopulmonary Bypass

(1) Background: Adequate organ perfusion during cardiopulmonary bypass (CPB) requires accurate estimation and adjustment of flow rates which conventional methods may not always achieve. Perioperative monitoring of cerebral oxygen saturation (ScO2) may detect changes in oxygen transport. This study aims to compare estimated and measured perfusion flow rates and assess the capacity of ScO2 to detect subtle changes in oxygen transport during CPB. (2) Methods: This observational study included 50 patients scheduled for elective coronary artery bypass grafting (CABG) surgery, all of whom provided written informed consent. Perfusion flow rates were estimated using the DuBois formula and measured using echocardiography and a flow probe in the arterial line of the CPB system. ScO2 was continuously monitored, alongside intermittent measurements of oxygen delivery and extraction ratios. (3) Results: Significant discrepancies were found between estimated flow rates (5.2 [4.8-5.5] L/min) and those measured at the start of the surgery (4.6 [4.0-5.0] L/min). These discrepancies were flow rate-dependent, being more pronounced at lower perfusion rates and diminishing as rates increased. Furthermore, ScO2 showed a consistent correlation with both oxygen delivery (r = 0.48) and oxygen extraction ratio (r = 0.45). (4) Conclusions: This study highlights discrepancies between estimated and actual perfusion flow rates during CPB and underscores the value of ScO2 monitoring as a continuous, noninvasive tool for maintaining adequate organ perfusion, suggesting a need for improved, patient-tailored perfusion strategies.

Haemodynamic effects of labetalol in isoflurane-anaesthetized dogs that received dexmedetomidine: A randomized clinical trial

OBJECTIVE

To test whether labetalol improved cardiovascular function in anaesthetized dogs injected with dexmedetomidine.

STUDY DESIGN

Prospective, randomized, blinded, clinical trial.

ANIMALS

A group of 20 healthy client-owned dogs undergoing ovariohysterectomy.

METHODS

Each dog received dexmedetomidine (5 μg kg-1) and methadone (0.2 mg kg-1) intramuscularly. General anaesthesia was induced with propofol and maintained with isoflurane in oxygen. All dogs were mechanically ventilated, and epidural anaesthesia with lidocaine was performed. Standard anaesthetic monitoring, invasive blood pressure, oesophageal Doppler and near-infrared tissue perfusion/oxygenation were applied. Peak velocity (PV), mean acceleration and stroke distance (SD) from the oesophageal Doppler were recorded. Arterial elastance (Ea) was calculated. Tissue oxygenation (rStO2) was also recorded. Prior to surgery, animals received either 0.1 mg kg-1 of labetalol intravenously (IV) over 60 seconds or the equivalent volume of saline. Data were recorded for 20 minutes. Age, weight and propofol dose were compared with a Wilcoxon rank-sum test. The effects of time, treatment and their interaction with haemodynamic and perfusion variables were analysed with mixed-effect models and Tukey's post hoc tests.

RESULTS

Significant effects of the interaction between treatment and time were observed whereby heart rate (HR) was higher in dogs given labetalol (p = 0.01), whereas arterial blood pressure and Ea were lower (p < 0.01). Similarly, PV, SD and rStO2 were higher in the labetalol group, and significant effects were detected for the interaction between treatment and time (p < 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

Labetalol at a dose of 0.1 mg kg-1 IV in dogs under general anaesthesia and administered a pre-anaesthetic medication of dexmedetomidine produced mild vasodilation (reduction of Ea), resulting in an increase in HR and left ventricular outflow. Although labetalol could be an effective option to achieve haemodynamic optimization after dexmedetomidine-induced vasoconstriction, future studies are needed to assess long-term effects.

Dynamic thiol/disulphide balance in patients undergoing hypotensive anesthesia in elective septoplasties

OBJECTIVE

We aimed to investigate the effects of hypotensive anaesthesia on oxidative stress with serum thiol/disulphide balance in patients undergoing elective septoplasty procedures under general anaesthesia.

METHODS

Seventy-two patients between the ages of 18-60, with a physical condition I -II, according to the American Society of Anesthesiologists, were included in this prospective observational study. Septoplasty was chosen for standard surgical stress. According to the maintenance of anaesthesia, patients were divided into the groups as Hypotensive Anaesthesia (n = 40) and Normotensive Anaesthesia (n = 32). Serum thiol/disulphide levels were measured by the method developed by Erel & Neşelioğlu.

RESULTS

The native thiol and total thiol values of both groups measured at the 60th min intraoperatively were significantly lower than the preoperative values (both P < .01). Intraoperatively, at the 60th min, there was no significant difference in terms of post-native thiol and post-total thiol levels between hypotensive and normotensive anaesthesia groups (P = .68 and .81, respectively). Age >40 years and female gender were found to have a significant effect on dynamic oxidative stress (P = .002 and .001, respectively).

CONCLUSION

This pilot study has found that hypotensive anaesthesia had no adverse effect on dynamic thiol/disulphide balance in elective surgeries.

Improved haemodynamic stability and cerebral tissue oxygenation after induction of anaesthesia with sufentanil compared to remifentanil: a randomised controlled trial

BACKGROUND

Balanced anaesthesia with propofol and remifentanil, compared to sufentanil, often decreases mean arterial pressure (MAP), heart rate (HR) and cardiac index (CI), raising concerns on tissue-oxygenation. This distinct haemodynamic suppression might be attenuated by atropine. This double blinded RCT, investigates if induction with propofol-sufentanil results in higher CI and tissue-oxygenation than with propofol-remifentanil and if atropine has more pronounced beneficial effects on CI and tissue-oxygenation in a remifentanil-based anaesthesia.

METHODS

In seventy patients scheduled for coronary bypass grafting (CABG), anaesthesia was induced and maintained with propofol target controlled infusion (TCI) with a target effect-site concentration (Cet) of 2.0 μg ml- 1 and either sufentanil (TCI Cet 0.48 ng ml- 1) or remifentanil (TCI Cet 8 ng ml- 1). If HR dropped below 60 bpm, methylatropine (1 mg) was administered intravenously. Relative changes (∆) in MAP, HR, stroke volume (SV), CI and cerebral (SctO2) and peripheral (SptO2) tissue-oxygenation during induction of anaesthesia and after atropine administration were analysed.

RESULTS

The sufentanil group compared to the remifentanil group showed significantly less decrease in MAP (∆ = - 23 ± 13 vs. -36 ± 13 mmHg), HR (∆ = - 5 ± 7 vs. -10 ± 10 bpm), SV (∆ = - 23 ± 18 vs. -35 ± 19 ml) and CI (∆ = - 0.8 (- 1.5 to - 0.5) vs. -1.5 (- 2.0 to - 1.1) l min- 1 m- 2), while SctO2 (∆ = 9 ± 5 vs. 6 ± 4%) showed more increase with no difference in ∆SptO2 (∆ = 8 ± 7 vs. 8 ± 8%). Atropine caused higher ∆HR (13 (9 to 19) vs. 10 ± 6 bpm) and ∆CI (0.4 ± 0.4 vs. 0.2 ± 0.3 l min- 1 m- 2) in sufentanil vs. remifentanil-based anaesthesia, with no difference in ∆MAP, ∆SV and ∆SctO2 and ∆SptO2.

CONCLUSION

Induction of anaesthesia with propofol and sufentanil results in improved haemodynamic stability and higher SctO2 compared to propofol and remifentanil in patients having CABG. Administration of atropine might be useful to counteract or prevent the haemodynamic suppression associated with these opioids.

TRIAL REGISTRATION

Clinicaltrials.gov on June 7, 2013 (trial ID: NCT01871935 ).

Updates on pediatric sepsis

Sepsis, defined as an infection with dysregulated host response leading to life-threatening organ dysfunction, continues to carry a high potential for morbidity and mortality in children. The recognition of sepsis in children in the emergency department (ED) can be challenging, related to the high prevalence of common febrile infections, poor specificity of discriminating features, and the capacity of children to compensate until advanced stages of shock. Sepsis outcomes are strongly dependent on the timeliness of recognition and treatment, which has led to the successful implementation of quality improvement programs, increasing the reliability of sepsis treatment in many US institutions. We review clinical, laboratory, and technical modalities that can be incorporated into ED practice to facilitate the recognition, treatment, and reassessment of children with suspected sepsis. The 2020 updated pediatric sepsis guidelines are reviewed and framed in the context of ED interventions, including guidelines for antibiotic administration, fluid resuscitation, and the use of vasoactive agents. Despite a large body of literature on pediatric sepsis epidemiology in recent years, the evidence base for treatment and management components remains limited, implying an urgent need for large trials in this field. In conclusion, although the burden and impact of pediatric sepsis remains substantial, progress in our understanding of the disease and its management have led to revised guidelines and the available data emphasizes the importance of local quality improvement programs.

Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device

OBJECTIVE

Maintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses.

STUDY DESIGN

Prospective, observational study.

ANIMALS

A group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018.

METHODS

The probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO₂) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites.

RESULTS

The readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO₂, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Thenar Muscle Oxygen Saturation Levels: A Surrogate for Central Venous Oxygen Saturation?

PURPOSE

Shock is associated with increased tissue oxygen extraction. Near-infrared spectroscopy-derived thenar muscle tissue oxygenation (StO₂) levels can provide an estimate of the oxygen supply-demand balance at the tissue level. We hypothesized that thenar StO₂ levels would correlate with central venous oxygen saturation (ScvO₂) levels, the gold standard for global tissue oxygen extraction in the body.

METHODS

We prospectively enrolled 60 pediatric subjects admitted to pediatric intensive care unit or who underwent cardiac catheterization from September 2015 to March 2018. Thenar StO₂ levels were measured using the InSpectra StO₂ probe. Concurrent measurements of ScvO₂ and peripheral tissue oxygenation (StO₂) were achieved through simultaneous testing. For ScvO₂, a central line placed in the superior vena cava was utilized for serum specimen collection, while the InSpectra probe recorded StO₂ measurements from the thenar eminence of the patient's right hand.

RESULTS

Sixty observations of thenar StO₂ and ScvO₂ levels were derived from 60 subjects. Mean thenar StO₂ levels were 74.72 ± 11.18% and displayed significant correlation with paired ScvO₂ measurements ( m = 72.17 ± 9.77%; ρ = 0.317, P = .018). Correlation was much more significant in subjects who were not on mechanical ventilatory support as opposed to those who were on it ( ρ_SORA = 0.496, P_SORA = .003, vs ρ_VENT = 0.161, P_VENT = .433). A thenar StO₂ of 73% had a sensitivity of 80% and a specificity of 77.8% in predicting an ScvO₂ of less than 65%.

CONCLUSION

This is the first study to report correlation of thenar StO₂ and ScvO₂ levels in children. Our study results show a significant correlation between these levels. Thenar StO₂ measurements may have a role in the bedside management of critically ill children in whom ScvO₂ monitoring is not available.

Regional muscle tissue saturation is an indicator of global inadequate circulation during cardiopulmonary bypass: a randomized porcine study using muscle, intestinal and brain tissue metabolomics

Background:

Muscle tissue saturation (StO2) measured with near-infrared spectroscopy has generally been considered a measurement of the tissue microcirculatory condition. However, we hypothesized that StO2 could be more regarded as a fast and reliable measure of global than of regional circulatory adequacy and tested this with muscle, intestinal and brain metabolomics at normal and two levels of low cardiopulmonary bypass blood flow rates in a porcine model.

Methods:

Twelve 80 kg pigs were connected to normothermic cardiopulmonary bypass with a blood flow of 60 mL/kg/min for one hour, reduced randomly to 47.5 mL/kg/min (Group I) or 35 mL/kg/min (Group II) for one hour followed by one hour of 60 mL/kg/min in both groups. Regional StO2 was measured continuously above the musculus gracilis (non-cannulated leg). Metabolomics were obtained by brain tissue oxygen monitoring system (Licox) measurements of the brain and microdialysis perfusate from the muscle, intestinal mucosa and brain. A non-parametric statistical method was used.

Results:

The systemic parameters showed profound systemic ischaemia during low CPB blood flow. StO2 did not change markedly in Group I, but in Group II, StO2 decreased immediately when blood flow was reduced and, furthermore, was not restored despite blood flow being normalized. Changes in the metabolomics from the muscle, colon and brain followed the changes in StO2.

Conclusion:

We found, in this experimental cardiopulmonary bypass model, that StO2 reacted rapidly when the systemic circulation became inadequate and, furthermore, reliably indicate insufficient global tissue perfusion even when the systemic circulation was restored after a period of systemic hypoperfusion.

Microcirculation measured by vascular occlusion test during desflurane-remifentanil anesthesia is superior to that in propofol-remifentanil anesthesia in patients undergoing thoracic surgery: subgroup analysis of a prospective randomized study

General anesthesia can affect microcirculatory properties. However, differential effects on the microcirculation according to the anesthetic technique used during thoracoscopic surgery have not been well documented. We conducted a randomized clinical trial in which the effects of desflurane and propofol, both with remifentanil, on systemic arterial oxygenation during one-lung ventilation were compared in patients undergoing thoracoscopic surgery. As a subgroup analysis, we compared the effects of two commonly used anesthetic techniques, desflurane-remifentanil (n = 52) and propofol-remifentanil (n = 48), on tissue oxygen saturation using a vascular occlusion test in patients undergoing thoracoscopic surgery. Tissue oxygen saturation was higher in the desflurane than the propofol group (mean ± standard deviation, 83 ± 6 vs. 80 ± 9, 84 ± 6 vs. 76 ± 10, and 87 ± 7 vs. 77 ± 10 % at 30 and 60 min of one-lung ventilation and at two-lung ventilation; adjusted p = 0.026, <0.001, and <0.001, respectively). The recovery slope during the vascular occlusion test, reflecting microvascular reperfusion adequacy, was higher in the desflurane than the propofol group during surgery (mean difference, 0.5 %/s; 95 % CI 0.0-0.9 %/s; p = 0.037). Desflurane-remifentanil anesthesia is associated with better microcirculation than propofol-remifentanil anesthesia in patients undergoing thoracoscopic surgery.

Effect of Prewarming during Induction of Anesthesia on Microvascular Reactivity in Patients Undergoing Off-Pump Coronary Artery Bypass Surgery: A Randomized Clinical Trial

Background

General anesthesia may induce inadvertent hypothermia and this may be related to perioperative cardiovascular complications. Microvascular reactivity, measured by the recovery slope during a vascular occlusion test, is decreased during surgery and is also related to postoperative clinical outcomes. We hypothesized that microvascular changes during surgery may be related to intraoperative hypothermia. To evaluate this, we conducted a randomized study in patients undergoing off-pump coronary artery bypass surgery, in which the effect of prewarming on microvascular reactivity was evaluated.

Methods

Patients scheduled for off-pump coronary artery bypass surgery were screened. Enrolled patients were randomized to the prewarming group to receive forced-air warming during induction of anesthesia or to the control group. Measurement of core and skin temperatures and vascular occlusion test were conducted before anesthesia induction, 1, 2, and 3 h after induction, and at the end of surgery.

Results

In total, 40 patients were enrolled and finished the study (n = 20 in the prewarming group and n = 20 in the control group). During the first 3 h of anesthesia, core temperature was higher in the prewarming group than the control group (p < 0.001). The number of patients developing hypothermia was lower in the prewarming group than the control group (4/20 vs. 13/20, p = 0.004). However, tissue oxygen saturation and changes in recovery slope following a vascular occlusion test at 3 h after anesthesia induction did not differ between the groups. There was no difference in clinical outcome, including perioperative transfusion, wound infection, or hospital stay, between the groups.

Conclusions

Prewarming during induction of anesthesia decreased intraoperative hypothermia, but did not reduce the deterioration in microvascular reactivity in patients undergoing off-pump coronary artery bypass surgery.

Trial Registration

ClinicalTrials.gov NCT02186210

A systematic review of human and veterinary applications of noninvasive tissue oxygen monitoring

OBJECTIVE

To describe the methodology for and utilization of tissue oxygen monitoring by near infrared spectroscopy, and to review the current literature on the use of this monitoring modality in human and veterinary settings.

DATA SOURCES

Scientific reviews and original research found using the PubMed and CAB Abstract search engines with the following keywords: "tissue oxygen monitoring," "near-infrared tissue spectroscopy," and "tissue oxygen saturation (StO2 )."

HUMAN DATA SYNTHESIS

Tissue oxygen monitors have been evaluated in a wide variety of human clinical applications including trauma and triage, surgery, sepsis, and septic shock, and early goal-directed therapy. StO2 more rapidly identifies occult shock in human patients compared to traditional methods, which can lead to earlier intervention in these patients.

VETERINARY DATA SYNTHESIS

Veterinary studies involving tissue oxygen monitoring are limited, but the technology may have utility for identification of hemorrhagic shock earlier than changes in base excess, blood lactate concentration, or other traditional perfusion parameters.

CONCLUSION

Tissue oxygen monitoring is most commonly performed utilizing a noninvasive, portable monitor, which provides real-time, continuous, repeatable StO2 measurements. A decline in StO2 is an early indicator of shock in both human and veterinary patients. Low StO2 values in human patients are associated with increased morbidity, mortality, and length of hospitalization, as well as the development of multiple organ system dysfunction and surgical site infections.

Cerebral and tissue oximetry

The use of near-infrared spectroscopy (NIRS) has been increasingly adopted in cardiac surgery to measure regional cerebral oxygen saturation. This method takes advantage of the fact that light in the near-infrared spectrum penetrates tissue, including bone and muscle. Sensors are placed at fixed distances from a light emitter, and algorithms subtract superficial light absorption from deep absorption to provide an index of tissue oxygenation. Although the popularity of NIRS monitoring is growing, definitive data that prove outcome benefits with its use remain sparse. Therefore, widespread, routine use of NIRS as a standard-of-care monitor cannot be recommended at present. Recent investigations have focused on the use of NIRS in subgroups that may benefit from NIRS monitoring, such as pediatric patients. Furthermore, a novel application of processed NIRS information for monitoring cerebral autoregulation and tissue oxygenation (e.g., kidneys and the gut) is promising.

Low tissue oxygen saturation at emergency center triage is predictive of intensive care unit admission

PURPOSE

Timely recognition of critical patients by emergency center triage is an ongoing challenge. Peripheral tissue oxygen saturation (StO2) measurement has been used to monitor shock patients' responses to resuscitation. Interest has developed in evaluating StO2 as a triage tool, but limited studies have addressed critically ill patients.

MATERIAL AND METHODS

This is a single-center, retrospective study of 158 emergent cancer patients with hypotension and/or modified systemic inflammatory response syndrome who underwent StO2 spot measurement at triage.

RESULTS

Of the 57 patients with StO2 less than 70%, 17 went to the intensive care unit (ICU), whereas only 14 of the 101 patients with StO2 of 70% to 89% (P = .01) went to the ICU. There was no significant difference in non-ICU hospital admission or mortality between the 2 groups. The odds ratio of ICU admission for patients with StO2 less than 70% relative to those with StO2 of 70% to 89% was 2.64 (95% confidence interval, 1.18-5.87) and 2.87 (95% confidence interval, 1.23-6.66) when adjusted for mean arterial pressure, pulse, and temperature.

CONCLUSIONS

In this patient population, an StO2 less than 70% significantly increased the risk of ICU admission. Tissue oxygen saturation at triage identifies critical patients who may not be recognized by vital signs alone. Tissue oxygen saturation measurement could help providers make earlier decisions regarding hospital resource allocation.

Bedside assessment of tissue oxygen saturation monitoring in critically ill adults: an integrative review of the literature

Objective. Tissue oxygen saturation (StO2) monitoring is a noninvasive technology with the purpose of alerting the clinician of peripheral hypoperfusion and the onset of tissue hypoxia. This integrative review examines the rigor and quality of studies focusing on StO2 monitoring in adult critically ill patients. Background. Clinicians must rapidly assess adverse changes in tissue perfusion while minimizing potential complications associated with invasive monitoring. The noninvasive measurement of tissue oxygen saturation is based on near-infrared spectroscopy (NIRS), an optical method of illuminating chemical compounds which absorb, reflect, and scatter light directed at that compound. Methods. An integrative review was conducted to develop a context of greater understanding about complex topics. An Integrative review draws on multiple experimental and nonexperimental research methodologies. Results. Fourteen studies were graded at the C category. None reported the use of probability sampling or demonstrated a cause-and-effect relationship between StO2 values and patient outcomes. Conclusions. Future research should be based on rigorous methods of sampling and design in order to enhance the internal and external validity of the findings.

Validation of sepsis screening tool using StO2 in emergency department patients

BACKGROUND

Sepsis is a deleterious systemic response to an infection with a high incidence of morbidity and mortality, affecting more than a million patients a year in the US. The purpose of this study was to develop a screening tool for the early identification of sepsis in emergency department patients using readily available information at triage.

MATERIALS AND METHODS

This prospective, observational study took place at an academic tertiary referral hospital. Over a period of 10 wk, all patients who were seen at triage were screened for study enrollment. Inclusion criteria were adult (age≥18 y) nontrauma patients and exclusion criteria were prisoners and pregnant women. Using a Spot Check StO2 device to measure StO2 value, heart rate, respiratory rate, and temperature, these values were used to generate a cumulative screening score indicating whether a patient may have sepsis.

RESULTS

A total of 500 patients were screened. The incidence of sepsis in the present study population was 8.4%. The screening tool yielded a sensitivity of 85.7%, a specificity of 78.4%, a positive predictive value of 26.7%, and a negative predictive value of 98.4%.

CONCLUSIONS

Heart rate, respiratory rate, and temperature have good diagnostic potential for the early identification of sepsis among emergency department triage personnel. Additionally, early evidence suggests StO2 may play a complementary and synergistic role in the early identification of sepsis by triage personnel.

Near-infrared spectroscopy in the assessment of suspected sepsis in the emergency department

BACKGROUND AND AIMS

The conventional approach to sepsis resuscitation involves early interventions targeting global oxygenation and macro-haemodynamic variables such as central venous and systemic arterial pressures. There is increasing recognition of the importance of microcirculatory changes in shock states, including sepsis, and the relationship of these to outcome. Near-infrared spectroscopy (NIRS) is a recently developed non-invasive technology that measures tissue oxygen saturations (StO2), which may be an indirect measure of the adequacy of the microcirculation. StO2 measurements, therefore, have the potential to identify patients who are at risk of progressing to organ dysfunction and could be used to guide resuscitation. This article reviews the current state of knowledge of NIRS in the setting of sepsis, examining its application, validity and prognostic value.

METHODS

A search of the relevant literature was performed using Medline, Embase and Cochrane databases, and a qualitative analysis was undertaken.

RESULTS

A limited number of observational studies, mostly conducted among patients with severe sepsis, have shown that NIRS may correlate with severity of illness but demonstrate a variable relationship between StO2 and outcome.

CONCLUSIONS

Outstanding questions still remain as to whether NIRS can help to risk-stratify patients with suspected sepsis in the emergency department and the utility of StO2 as a resuscitation target.

Tissue oxygen saturation for the risk stratification of septic patients

PURPOSE

Peripheral tissue oxygen saturation (Sto2) has shown promise as an early indicator of tissue hypoperfusion and as a risk stratification tool in various forms of shock. The purpose of this study was to determine if Sto2 would predict admission to an intensive (ICU) or progressive care unit in patients with early signs of sepsis.

METHODS

In this prospective observational study, a rapid response team measured Sto2 levels in patients screening positive for sepsis. Using a logistic regression model, the value of Sto2 as a predictor for ICU admission within 72 hours of the initial assessment was determined.

RESULTS

The 31 (47%) of 66 patients who required ICU admission within 72 hours of evaluation had a significantly lower Sto2 value (median, 78% vs 81%; P = .05). All patients with Sto2 less than 70% required ICU admission. A 1-point increase in Sto2 was associated with a 7% decrease in the odds of requiring ICU admission, and the area under the curve for Sto2 was 0.64 (0.51-0.77, P = .01).

CONCLUSIONS

Low Sto2 levels in patients screening positive for sepsis are associated with an increased risk of ICU admission, but their reliability as a predictor is rather low. An Sto2 below 70% might be an interesting cutoff value for further study.

Near infrared spectroscopy: clinical and research uses

BACKGROUND

Pulse oximetry is routinely used to measure hemoglobin saturation and is currently the gold standard to assess oxygenation in patients. Due to attenuation of infrared light by skin, bone, and other organs, pulse oximetry cannot assess end-organ tissue oxygenation (StO(2)). Near infrared spectroscopy (NIS) penetrates a broad range of tissues and utilizes reflection rather than direct transmission between an emitter and receiver pair. NIS is able to measure StO(2) and assess end-organ perfusion in a variety of applications.

STUDY DESIGN AND METHODS

A retrospective review of recent animal and human StO(2) studies was undertaken. StO(2) measurements and outcomes were assessed.

RESULTS

StO(2) measurements identified visceral organ ischemia in animal hemorrhage models. These measurements were also able to guide optimization of resuscitation and end-organ oxygenation. Human studies demonstrated StO(2) changes preceded those seen in traditionally measured parameters such as blood pressure, heart rate, base deficit, serum lactate, and mental status. Additionally, StO(2) thresholds identified trauma patients who required massive transfusions, developed multiple organ dysfunction syndrome, or experienced lower extremity compartment syndrome. StO(2) measurements also demonstrated a benefit in selecting resuscitation fluids, assessing end-organ oxygenation during blood transfusion, and quantifying the oxygen-carrying deficit secondary to the blood storage lesion.

CONCLUSION

StO(2) measurements have been used to guide resuscitation efforts in trauma patients. This technology and its applications continue to evolve and represent a novel change in patient care.

Monitoring tissue oxygenation by near infrared spectroscopy (NIRS): background and current applications

Conventional cardiovascular monitoring may not detect tissue hypoxia, and conventional cardiovascular support aiming at global hemodynamics may not restore tissue oxygenation. NIRS offers non-invasive online monitoring of tissue oxygenation in a wide range of clinical scenarios. NIRS monitoring is commonly used to measure cerebral oxygenation (rSO(2)), e.g. during cardiac surgery. In this review, we will show that tissue hypoxia occurs frequently in the perioperative setting, particularly in cardiac surgery. Therefore, measuring and obtaining adequate tissue oxygenation may prevent (postoperative) complications and may thus be cost-effective. NIRS monitoring may also be used to detect tissue hypoxia in (prehospital) emergency settings, where it has prognostic significance and enables monitoring of therapeutic interventions, particularly in patients with trauma. However, optimal therapeutic agents and strategies for augmenting tissue oxygenation have yet to be determined.

The impact of induction of general anesthesia and a vascular occlusion test on tissue oxygen saturation derived parameters in high-risk surgical patients

OBJECTIVES

Tissue oxygen saturation (StO(2)) assessed using Near Infrared Spectroscopy and its derived parameters during a vascular occlusion test (VOT) can detect microvascular changes in septic shock patients. General anesthesia (GA) impacts microcirculation. Our aim was to study the effects of general anesthesia on StO(2) and StO(2) derived parameters obtained during VOT in patients referred for cardiac surgery.

METHODS

We studied 15 patients referred for cardiac surgery before and after induction of GA. Before GA induction, we also studied 15 healthy volunteers (non patients) in order to compare baseline physiological data between patients and healthy subjects. Hemodynamic and microcirculatory (StO(2), ischemic slope, reperfusion slope, and hyperemic response) data were recorded at each step. We used the Inspectra StO(2) system (Hutchinson Inc, MN, USA) with a sensor placed on the thenar eminence. StO(2) values were obtained at baseline and during a VOT. A sphyngomanometer was placed on the forearm above the StO(2) probe and the cuff was then rapidly inflated 30 mmHg above systolic pressure and was maintained inflated until the StO(2) value reached 40%. It was then rapidly deflated.

RESULTS

Healthy volunteers had significantly higher reperfusion slope than patients (348 [251-393] vs. 261 [185-279] %/min; P < 0.05). GA induction induced no significant change in StO(2) value compared to baseline (79 [75-85] vs. 80 [76-86]%; P = 0.57). We observed a significant decrease in ischemic slope (from -12 [-16--8] to -8 [-10--6] %/min; P = 0.004) and in reperfusion slope (from 261 [185-279] %/min to 164 [151-222] %/min; P = 0.008) suggesting a decrease in local metabolic rate and a negative impact on reperfusion reserve induced by anesthesia.

CONCLUSION

StO(2) derived parameters during a VOT are impacted by GA induction. These parameters may have potential for microcirculation assessment in patients undergoing surgery.

Tissue Oxygen Saturation Predicts the Need for Early Blood Transfusion in Trauma Patients

Near-infrared spectroscopy (NIRS) has been used to measure regional tissue oxygen saturation (StO2) in skeletal muscle as an indicator of perfusion in trauma patients. In an effort to prospectively examine the usefulness of StO2 in identifying trauma patients in hemorrhagic shock, we evaluated the need for blood transfusion within 24 hours of injury as a marker of significant hemorrhage. A 6-month prospective, observational study was conducted at a university-affiliated, urban Level I trauma center using a convenience sample of 26 trauma patients thought to be at high risk for hemorrhagic shock. Baseline demographic data, vital signs, laboratory values, and amounts of fluid and blood products administered were collected. NIRS-derived StO2 values were measured for 1 hour after arrival to the trauma bay and the minimum value noted. A minimum StO2 less than 70 per cent correlated with the need for blood transfusion with a sensitivity of 88 per cent and a specificity of 78 per cent. The positive predictive value was 64 per cent and the negative predictive value was 93 per cent. The need for blood transfusion within 24 hours of arrival was not predicted by hypotension, tachycardia, arterial lactate, base deficit, or hemoglobin. StO2 may represent an important screening tool for identifying trauma patients who require blood transfusion or other limited medical resources.