Cerebral oxygenation during cardiopulmonary bypass measured by near-infrared spectroscopy: effects of hemodilution, temperature, and flow

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep

We tested whether the brain and kidney respond differently to cardiopulmonary bypass (CPB) and to changes in perfusion conditions during CPB. Therefore, in ovine CPB, we assessed regional cerebral oxygen saturation (rSO2 ) by near-infrared spectroscopy and renal cortical and medullary tissue oxygen tension (PO2 ), and, in some protocols, brain tissue PO2 , by phosphorescence lifetime oximetry. During CPB, rSO2 correlated with mixed venous SO2 (r = 0.78) and brain tissue PO2 (r = 0.49) when arterial PO2 was varied. During the first 30 min of CPB, brain tissue PO2 , rSO2 and renal cortical tissue PO2 did not fall, but renal medullary tissue PO2 did. Nevertheless, compared with stable anaesthesia, during stable CPB, rSO2 (66.8 decreasing to 61.3%) and both renal cortical (90.8 decreasing to 43.5 mm Hg) and medullary (44.3 decreasing to 19.2 mm Hg) tissue PO2 were lower. Both rSO2 and renal PO2 increased when pump flow was increased from 60 to 100 mL kg-1  min-1 at a target arterial pressure of 70 mm Hg. They also both increased when pump flow and arterial pressure were increased simultaneously. Neither was significantly altered by partially pulsatile flow. The vasopressor, metaraminol, dose-dependently decreased rSO2 , but increased renal cortical and medullary PO2 . Increasing blood haemoglobin concentration increased rSO2 , but not renal PO2 . We conclude that both the brain and kidney are susceptible to hypoxia during CPB, which can be alleviated by increasing pump flow, even without increasing arterial pressure. However, increasing blood haemoglobin concentration increases brain, but not kidney oxygenation, whereas vasopressor support with metaraminol increases kidney, but not brain oxygenation.

Kinetics of tissue oxygenation index during fast and slow cardiopulmonary bypass initiation

INTRODUCTION

Despite being a daily clinical application in cardiac operating theaters, an evidence-based approach on how to optimally initiate the heart-lung machine (HLM) to prevent critical phases of cerebral ischemia is still lacking. We therefore designed a study comparing two different initiation times for starting the cardiopulmonary bypass (CPB).

METHODS

We conducted a monocentric, randomized, and prospective study comparing the impact of two initiation times, a rapid initiation of 15 s and a slow initiation of 180 s to reach the full target flow rate of 2.5 L/min/m² times the body surface area, on cerebral tissue oxygenation by near infrared spectroscopy measurements.

RESULTS

The absolute values in tissue oxygenation index (TOI) showed no difference between the groups before and after the CPB with a 10% drop in oxygenation index in both groups due to the hemodilution through the HLM priming. Looking at the kinetics a rapid initiation of CPB produced a higher negative rate of change in TOI with a total of 21% in critical oxygenation readings compared to 6% in the slow initiation group.

CONCLUSION

In order to avoid critical phases of cerebral ischemia during the initiation of CPB for cardiac procedures, we propose an initiation time of at least 90 s to reach the 100% of target flow rate of the HLM.

Low Intraoperative Cerebral Oxygen Saturation Is Associated with Acute Kidney Injury after Off-Pump Coronary Artery Bypass

By monitoring the brain as the index organ of global oxygen supply-demand balance including major organs, regional cerebral oxygen saturation (rScO₂) may indicate adequacy of renal perfusion. The aim of this study was to investigate the relationship between perioperative rScO₂ and acute kidney injury (AKI) after off-pump coronary artery bypass (OPCAB). AKI was diagnosed according to the Kidney Disease: Improving Global Outcomes criteria. Collected rScO₂ variables were baseline, mean, and lowest value during surgery, maximal percentage decrease from baseline, and areas under the threshold below an absolute value of 50% (AUT₅₀) and of 80% of baseline (AUT_80%base). Among 580 patients, AKI developed in 143 (24.7%) patients. Patients with AKI had lower baseline, mean, and lowest rScO₂ and higher AUT₅₀ and AUT_80%base than those without AKI despite routine efforts to restore the rScO₂ values within 20% of the baseline. Among the rScO₂ variables, the area under the receiver operating characteristic curve of mean rScO₂ was the highest (0.636), which was used for the multivariable logistic regression. Multivariable logistic regression revealed mean rScO₂ as an independent predictor of AKI (odds ratio, 0.964; 95% confidence interval, 0.937-0.990; p = 0.008), along with chronic kidney disease and emergency surgery. Low intraoperative mean rScO₂ was independently associated with AKI after OPCAB, which may serve as an early marker of renal injury.

Renal and Cerebral Hypoxia and Inflammation During Cardiopulmonary Bypass

Cardiac surgery-associated acute kidney injury and brain injury remain common despite ongoing efforts to improve both the equipment and procedures deployed during cardiopulmonary bypass (CPB). The pathophysiology of injury of the kidney and brain during CPB is not completely understood. Nevertheless, renal (particularly in the medulla) and cerebral hypoxia and inflammation likely play critical roles. Multiple practical factors, including depth and mode of anesthesia, hemodilution, pump flow, and arterial pressure can influence oxygenation of the brain and kidney during CPB. Critically, these factors may have differential effects on these two vital organs. Systemic inflammatory pathways are activated during CPB through activation of the complement system, coagulation pathways, leukocytes, and the release of inflammatory cytokines. Local inflammation in the brain and kidney may be aggravated by ischemia (and thus hypoxia) and reperfusion (and thus oxidative stress) and activation of resident and infiltrating inflammatory cells. Various strategies, including manipulating perfusion conditions and administration of pharmacotherapies, could potentially be deployed to avoid or attenuate hypoxia and inflammation during CPB. Regarding manipulating perfusion conditions, based on experimental and clinical data, increasing standard pump flow and arterial pressure during CPB appears to offer the best hope to avoid hypoxia and injury, at least in the kidney. Pharmacological approaches, including use of anti-inflammatory agents such as dexmedetomidine and erythropoietin, have shown promise in preclinical models but have not been adequately tested in human trials. However, evidence for beneficial effects of corticosteroids on renal and neurological outcomes is lacking. © 2021 American Physiological Society. Compr Physiol 11:1-36, 2021.

Current Application of NIRS and CPB Initiation Times in German Cardiac Surgery Centers: A Survey

Near-infrared spectroscopy (NIRS) has been widely used in cardiac surgery to monitor cerebral oxygen supply. The initiation and perioperative management of cardiopulmonary bypass (CPB) constitute critical events in modifying the normal physiology of adequate blood and oxygen supply to the brain. First, little is known about how frequent NIRS is really used. Second, there are varying practices on how to initiate CPB. We therefore conducted a survey in Germany to get an idea of NIRS usage in cardiac surgery for the duration of initiation of CPB protocols. A web-based e-mail survey using commercial SurveyMonkey^® (SurveyMonkey, San Mateo, CA) software was conducted in August 2017 including all German cardiac surgery centers. About 75% of the perfusion departments do not use NIRS as a standard monitoring device. It is usually reserved for clinical scenarios where cerebral perfusion might be impaired such as aortic arch surgery or carotid artery stenosis. Only one-third of the departments use a standardized duration of initiation of CPB despite a common belief of potential harm with fast initiation. The usual applied time to initiate CPB ranges from 30 to 120 seconds. Our survey revealed that the NIRS technology is only used in specific types of cardiac surgery to this date. In addition, there is a clear need for scientific studies on how to initiate CPB in the best way for the patient.

Comparison of basic regional cerebral oxygen saturation values in patients of different ages: a pilot study

Objective

To explore the basic values of regional cerebral oxygen saturation (rSO₂) among different age groups.

Methods

One hundred twenty patients who were scheduled for elective surgery aged 0 to 80 years (American Society of Anesthesiologists [ASA] physical status I or II) or neonates just after birth via cesarean section were enrolled and divided into the following six groups: infant (0 month and ≤12 months), toddler (>1 and ≤3 years old), preschool (>3 and ≤6 years old), school age (>6 and ≤18 years old), adult (>18 and ≤65 years old), and elderly (>65 and ≤80 years old) groups. There were 20 patients in each group.

Results

The basic values of rSO₂ in infant, toddler, preschool, school age, adults, and elderly groups were 70.41% ± 4.66%, 72.43% ± 3.81%, 70.77% ± 3.27%, 70.62% ± 2.20%, 69.76% ± 6.02%, and 62.69% ± 3.14%, respectively. The basic value in the elderly group was lower compared with other five groups. There was no significant difference among infant, toddler, preschool age, school age, and adult groups.

Conclusions

The basic value of rSO₂ in elderly patients is lower. Age is an important factor that affects the underlying value of rSO₂.

Lawrence K. Optical monitoring of cerebral perfusion and metabolism in adults during cardiac surgery with cardiopulmonary bypass

During cardiac surgery with cardiopulmonary bypass (CPB), adequate maintenance of cerebral blood flow (CBF) is vital in preventing postoperative neurological injury - i.e. stroke, delirium, cognitive impairment. Reductions in CBF large enough to impact cerebral energy metabolism can lead to tissue damage and subsequent brain injury. Current methods for neuromonitoring during surgery are limited. This study presents the clinical translation of a hybrid optical neuromonitor for continuous intraoperative monitoring of cerebral perfusion and metabolism in ten patients undergoing non-emergent cardiac surgery with non-pulsatile CPB. The optical system combines broadband near-infrared spectroscopy (B-NIRS) to measure changes in the oxidation state of cytochrome c oxidase (oxCCO) - a direct marker of cellular energy metabolism - and diffuse correlation spectroscopy (DCS) to provide an index of cerebral blood flow (CBFi). As the heart was arrested and the CPB-pump started, increases in CBFi (88.5 ± 125.7%) and significant decreases in oxCCO (-0.5 ± 0.2 µM) were observed; no changes were noted during transitions off CPB. Fifteen hypoperfusion events, defined as large and sustained reductions in CPB-pump flow rate, were identified across all patients and resulted in significant decreases in perfusion and metabolism when mean arterial pressure dropped to 30 mmHg or below. The maximum reduction in cerebral blood flow preceded the corresponding metabolic reduction by 18.2 ± 15.0 s. Optical neuromonitoring provides a safe and non-invasive approach for assessing intraoperative perfusion and metabolism and has potential in guiding patient management to prevent adverse clinical outcomes.

Impact of CPAP on Forehead Near-infrared Spectroscopy Measurements in Patients With Acute Respiratory Failure: Truth or Illusion

BACKGROUND

Critically ill patients with acute respiratory failure admitted to an intensive care unit are at high risk for cerebral hypoxia. We investigated the impact of continuous positive airway pressure (CPAP) therapy on regional cerebral tissue oxygenation (rSO2).

MATERIALS AND METHODS

In total, 40 extubated surgical intensive care unit patients requiring classic oxygen therapy (COT) for acute respiratory failure were examined. Near-infrared spectroscopy (INVOS 5100C, Covidien) was used for 30 minutes to detect bilateral rSO2 during COT via facemask (6 L/min) and CPAP therapy (40% fraction of inspired oxygen, 8 cm H2O CPAP) using a randomized crossover study design. Patients served as their own control. Continuous hemodynamic routine monitoring and blood gas analysis were performed. The effect of CPAP therapy on rSO2 and influence of assessed covariables were investigated using a mixed linear model.

RESULTS

Median rSO2 increased from 57.9% (95% confidence interval [CI], 54.2-61.5) during COT to 62.8% (95% CI, 59.2-66.5) during CPAP therapy (P<0.0001). The estimated difference from the mixed model between COT and CPAP is -5.0 (95% CI, -6.3 to -3.7). Median arterial partial pressure of carbon dioxide decreased from 47.8±5.1 mm Hg during COT to 43.1±5 mm Hg during CPAP (P<0.001), whereas arterial partial pressure of oxygen remained unchanged (P=0.329). In total, 23% of patients had SO2 levels <50%, with a higher prevalence under COT.

CONCLUSIONS

Our results reveal that CPAP therapy compared with COT may influence rSO2 in patients with acute respiratory failure. However, the cause of the rSO2 increase following CPAP application remains to be elucidated, and the accuracy of cerebral oximetry during CPAP therapy in patients with acute respiratory failure remains questionable.

Comparison of the Effects of Desflurane and Sevoflurane on Cerebral Oxygen Saturation in Patients Undergoing Thyroidectomy: A Randomised Controlled Clinical Study

Objective

The commonly performed sitting position with head extended during thyroidectomy has been shown to cause adverse effects on cerebral regional oxygen saturation (CrSO2). Therefore, the present study aimed to investigate the effects of two well-known anaesthetic agents, desflurane and sevoflurane, on CrSO2 in patients undergoing thyroidectomy in the semi-sitting position by near-infra-red spectroscopy monitoring.

Methods

The study included 60 patients aged 18-65 years, with an American Society of Anesthesiologists (ASA) physical status classification score I-III, who underwent elective thyroidectomy in the semi-sitting position. The patients were randomly divided into two groups, depending on the anaesthetic agent administered: (1) sevoflurane group (Group S; n=30) and (2) desflurane group (Group D; n=30). After intubation, the patients were placed in a 45-degree semi-sitting position. Vital signs and the CrSO2 levels in both hemispheres were recorded both pre-induction and at the induction minute 1, post-intubation, post-positioning, every 5 minutes intraoperatively and in the case of sudden changes.

Results

No significant difference was found between the groups in terms of age, height, body weight, the ASA score, operative time and left- and right-hemisphere CrSO2 (p>0.05). Moreover, the two groups were statistically similar to each other with regard to peripheral capillary oxygen saturation, heart rate, systolic and diastolic blood pressure, mean artery pressure and end-tidal CO₂ (ETCO₂) levels.

Conclusion

Desflurane and sevoflurane had similar effects in the preservation of CrSO2 in patients undergoing thyroidectomy in the semi-sitting position.

A Case of Persistence of Normal Tissue Oxygenation Monitored by Near-Infrared Spectroscopy (NIRS) Values Despite Prolonged Perioperative Cardiac Arrest

Patient: Male, 65

Final Diagnosis: Aortic dissection

Symptoms: Hemiplegia • hypotension

Medication:—

Clinical Procedure: Emergent surgery

Specialty: Surgery

The Role of Premotor Areas in Dual Tasking in Healthy Controls and Persons With Multiple Sclerosis: An fNIRS Imaging Study

Persons with multiple sclerosis (pwMS) experience declines in physical and cognitive abilities and are challenged by dual-tasks. Dual-tasking causes a drop in performance, or what is known as dual-task cost (DTC). This study examined DTC of walking speed (WS) and cognitive performance (CP) in pwMS and healthy controls (HCs) and the effect of dual-tasking on cortical activation of bilateral premotor cortices (PMC) and bilateral supplementary motor area (SMA). Fourteen pwMS and 14 HCs performed three experimental tasks: (1) single cognitive task while standing (SingCog); (2) single walking task (SingWalk); and (3) dual-task (DualT) that included concurrent performance of the SingCog and SingWalk. Six trials were collected for each condition and included measures of cortical activation, WS and CP. WS of pwMS was significantly lower than HC, but neuropsychological (NP) measures were not significantly different. pwMS and HC groups had similar DTC of WS, while DTC of CP was only significant in the MS group; processing speed and visual memory predicted 55% of this DTC. DualT vs. SingWalk recruited more right-PMC activation only in HCs and was associated with better processing speed. DualT vs. SingCog recruited more right-PMC activation and bilateral-SMA activation in both HC and pwMS. Lower baseline WS and worse processing speed measures in pwMS predicted higher recruitment of right-SMA (rSMA) activation suggesting maladaptive recruitment. Lack of significant difference in NP measures between groups does not rule out the influence of cognitive factors on dual-tasking performance and cortical activations in pwMS, which might have a negative impact on quality of life.

Cerebral Oximetry for Cardiac and Vascular Surgery

The technology of transcranial near-infrared spectroscopy (NIRS) for the measurement of cerebral oxygen balance was introduced 25 years ago. Until very recently, there has been only occasional interest in its use during surgical monitoring. Now, however, substantial technologic advances and numerous clinical studies have, at least partly, succeeded in overcoming long-standing and widespread misunderstanding and skepticism regarding its value. Our goals are to clarify common misconceptions about near-infrared spectroscopy and acquaint the reader with the substantial literature that now supports cerebral oximetric monitoring in cardiac and major vascular surgery.

Maintaining Gait Performance by Cortical Activation during Dual-Task Interference: A Functional Near-Infrared Spectroscopy Study

In daily life, mobility requires walking while performing a cognitive or upper-extremity motor task. Although previous studies have evaluated the effects of dual tasks on gait performance, few studies have evaluated cortical activation and its association with gait disturbance during dual tasks. In this study, we simultaneously assessed gait performance and cerebral oxygenation in the bilateral prefrontal cortices (PFC), premotor cortices (PMC), and supplemental motor areas (SMA), using functional near-infrared spectroscopy, in 17 young adults performing dual tasks. Each participant was evaluated while performing normal-pace walking (NW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT). Our results indicated that the left PFC exhibited the strongest and most sustained activation during WCT, and that NW and WMT were associated with minor increases in oxygenation levels during their initial phases. We observed increased activation in channels in the SMA and PMC during WCT and WMT. Gait data indicated that WCT and WMT both caused reductions in walking speed, but these reductions resulted from differing alterations in gait properties. WCT was associated with significant changes in cadence, stride time, and stride length, whereas WMT was associated with reductions in stride length only. During dual-task activities, increased activation of the PMC and SMA correlated with declines in gait performance, indicating a control mechanism for maintaining gait performance during dual tasks. Thus, the regulatory effects of cortical activation on gait behavior enable a second task to be performed while walking.

Factors affecting intraoperative changes in regional cerebral oxygen saturation in patients undergoing liver transplantation

BACKGROUND

Regional oxygen saturation (rSO(2)) is a sensitive marker of cerebral hypoperfusion during liver transplantation. However, bilirubin absorbs near-infrared light, resulting in falsely low rSO(2) values. We sought to determine whether rSO(2) values vary in response to bilirubin concentrations during liver transplantation and to assess whether rSO(2) changes were associated with factors reflecting cerebral oxygen delivery in patients with hyperbilirubinemia.

METHODS

Measurements of rSO(2) values continuous cardiac output (CO), mean arterial pressure, central venous pressure, body temperature, arterial blood gas analysis, and laboratory parameters were simultaneously performed at 1 hour after the surgical incision (baseline) and at 3 predetermined times during the anhepatic and neohepatic phases in 95 end-stage liver disease patients including 67 males of Child A/B/C/29/29/37 categories respectively. Relationships between changes in parameters were evaluated by correlation and multivariate regression analyses.

RESULTS

The 273 measurements revealed changes in rSO(2) (range, -18% to 40%) to correlate significantly with alterations in hemoglobin (Hb), serum glucose, lactate, prothrombin time, pH, partial arterial CO(2) pressure (PaCO(2)), and CO, but not with serum total bilirubin (TB). Multivariate linear regression analysis revealed that changes in Hb, CO, PaCO(2), and pH were independent of rSO(2) changes during liver transplantation.

CONCLUSIONS

Our findings showed that rSO(2) changes were independently associated with factors reflecting cerebral oxygen delivery, such as Hb, CO, PaCO(2), and pH, whereas rSO(2) values did not correlate with changes in bilirubin concentrations, indicating that rSO(2) changes reveal cerebral oxygen balance regardless of TB levels among patients undergoing liver transplantation.

Continuous measurement of cerebral oxygenation with near-infrared spectroscopy after spontaneous subarachnoid hemorrhage

Objective. The aim of our prospective study was to investigate the applicability and the diagnostic value of near-infrared spectroscopy (NIRS) in SAH patients using the cerebral oximeter INVOS 5100C. Methods. Measurement of cerebral oximetry was done continuously after spontaneous SAH. Decrease of regional oxygen saturation (rSO₂) was analyzed and interpreted in view of the determined intrinsic and extrinsic factors. Changes of rSO₂ values were matched with the values of ICP, tipO₂, and TCD and the results of additional neuroimaging. Results. Continuous measurement of rSO₂ was performed in nine patients with SAH (7 females and 2 males). Mean measurement time was 8.6 days (range 2–12 days). The clinical course was uneventful in 7 patients without occurrence of CVS. In these patients, NIRS measured constant and stable rSO₂ values without relevant alterations. Special findings are demonstrated in 3 cases. Conclusion. Measurement of rSO₂ with NIRS is a safe, easy to use, noninvasive additional measurement tool for cerebral oxygenation, which is used routinely during vascular and cardiac surgical procedures. NIRS is applicable over a long time period after SAH, especially in alert patients without invasive probes. Our observations were promising, whereby larger studies are needed to answer the open questions.

Near-infrared spectroscopy as a possible device for continuous monitoring of arterial carbon dioxide tension during cardiac surgery

Background: Insufflation of carbon dioxide (CO2) to the operative field has been used to prevent major organ injury attributed to air embolisms in cardiac surgery. However, it may be preferable to avoid hypercapnia induced by CO2 insufflation, owing to its potentially harmful effect. To investigate the effectiveness of near-infrared spectroscopy (NIRS) as a possible method for continuous monitoring of arterial CO2 tension during cardiac surgery, we evaluated the correlation between the change in arterial CO2 tension and the change in regional cerebral oxygen saturation (rScO2) obtained from NIRS in as controlled a condition as possible.

Methods: Thirty patients who underwent surgical correction for atrial or ventricular septal defects were enrolled in this study. Patients who had pulmonary hypertension or other intracardiac anomalies were excluded. Anesthetic and cardiopulmonary bypass (CPB) management were conducted according to our standard institutional practice. Data obtained from arterial blood gas analyses and corresponding regional cerebral oxygen saturation (rScO2) recorded from NIRS before and after the insufflations of CO2 during CPB were used for analysis.

Results: The change in arterial CO2 tension correlated with the change in rScO2 in the left hemisphere (r = 0.681, p <0.001, y = −1.393 + 0.547x) and right hemisphere (r = 0.690, p <0.001, y = −1.999 + 0.486x). To control the effects of other variables, including hematocrit and temperature, these relationship were not reduced (left hemisphere: r=0.678, p<0.001; right hemisphere: r=0.634, p<0.001).

Conclusions: Since the change in regional cerebral oxygen saturation was correlated with the change in arterial CO2 tension during mild hypothermic CPB, NIRS might be a possible non-invasive method for monitoring of arterial CO2 tension without incurring additional cost in this setting.

Does Near-Infrared Spectroscopy Provide an Early Warning of Low Haematocrit following the Initiation of Hypothermic Cardiopulmonary Bypass in Cardiac Surgery?

This study investigated 151 patients undergoing cardiac surgery to determine whether measurement of regional cerebral oxygen saturation (rScO2) using near-infrared spectroscopy (NIRS) can indicate a low haematocrit after initiation of hypothermic cardiopulmonary bypass (CPB). Haematocrit, rScO2, haemoglobin level, arterial partial pressures of carbon dioxide and oxygen, systemic blood pressure, and nasopharyngeal and rectal temperatures were determined 5 min after the initial administration of heparin for CPB and 90 s after completion of the first cardioplegic solution injection. Immediately after initiation of hypothermic CPB, rScO2, haemoglobin and haematocrit values were significantly lower than those before CPB. No significant correlations were found between the change in haematocrit and changes in left, right and mean rScO2; thus, changes in rScO2 before and after initiation of hypothermic CPB did not reflect changes in haematocrit values. This indicates that NIRS cannot provide early warning of a low haematocrit immediately after initiation of hypothermic CPB in cardiac surgery.

Bilateral near infrared spectroscopy in space-occupying middle cerebral artery stroke

BACKGROUND

The crucial importance of monitoring both the infarcted and non-infarcted hemispheres in management of space occupying middle cerebral artery (MCA) infarction is increasingly recognized, but optimal technique is debated. We investigated the potential for bilateral Near Infrared Spectroscopy (NIRS) to non-invasively provide relevant information on intracranial oxygenation.

METHODS

In patients with complete MCA stroke and brain swelling NIRS optodes were placed over both frontal lobes and regional cerebral oxygen saturation (rSO(2)) was measured at 30 s intervals for at least 12 h. The bilateral pattern of changes in rSO(2) was analysed with respect to clinical course and development of brain swelling, and patients compared according to outcome.

RESULTS

A total of 24 patients were analysed, of whom 13 underwent decompressive hemicraniectomy; outcome was good (GOS > or = 3) in 11 cases, and poor (GOS < 3) in 13. Absolute rSO(2) values varied widely and did not correlate with clinical data. The average difference in rSO(2) (rSO(2)-diff) between infarcted and contralateral hemisphere was 10.7% and higher on the infarct side in 22/24 cases. The rSO(2)-diff typically decreased with brain swelling, disappeared in patients who developed herniation, but increased markedly after successful craniectomy and management of brain swelling. The rSO(2)-diff at the end of monitoring was significantly higher in good outcome survivors. The time pattern of rSO(2)-diff can be explained by alterations of perfusion and O(2)-consumption depending on hemispheric swelling.

CONCLUSION

Bilateral NIRS may provide more useful information on cerebral oxygenation than unilateral measurements and its clinical validity to help predict worsening of brain swelling should be investigated further.

The Application of Near-infrared Oximetry to Cerebral Monitoring During Aneurysm Embolization: A Comparison With Intraprocedural Angiography

Near-infrared spectroscopy (NIRS) has been used to monitor regional cerebral oxygen saturation (rSO2) in patients at risk of cerebral desaturation during surgical and neurointerventional procedures. However, the quantitative capabilities of the method have been questioned, as has its validation compared with jugular bulb oximetry. Here, we compare NIRS data acquired during coil embolization procedures with incidence of vasospasm as detected from angiography. Thirty-two subarachnoid hemorrhage patients underwent embolization. Bilateral SomaSensor strips (Invos 4100, Somanetics) were affixed to the forehead at constant anatomic positions, avoiding frontal sinuses and scalp hair. Mean arterial pressure, SaO2, end-tidal pCO2, temperature and Hb were held within a narrow range during the procedure. Ipsilateral angiography was performed every 10 to 15 minutes. An independent neuroradiologist classified any vasospasm in the parent vessel as mild (25% baseline), moderate (50%), severe (75%), or total (100%). Of all, 15/32 (46.9%) patients developed spasm; in 2 it was severe or total. There was no significant association between World Federation of Neurological Surgeons grade and baseline rSO2 signal (either ipsilateral or contralateral to the side of the aneurysm) (P=0.598). There was no significant association between side of aneurysm and baseline rSO2 signal (P=0.243). However, episodes of angiographic spasm were strongly associated with reduction in trend ipsilateral NIRS signal (P<0.001); furthermore, the degree of spasm (especially more than 75% vessel diameter reduction) was associated with a greater reduction in same-side NIRS signal (P<0.001) (2-level random effects regression model, Stata 8.2, Stata Corp, TX). NIRS may have a useful role to play in the detection of cerebral desaturation secondary to vasospasm during neuroendovascular procedures.

A retrospective study of changes in cerebral oxygenation using a cerebral oximeter in older patients undergoing prolonged major abdominal surgery

BACKGROUND AND OBJECTIVE

The objective was to carry out a retrospective study of changes in regional cerebral oxygen saturation (rSO2) using the Somanetics Invos Cerebral Oximeter (SICO) in older patients undergoing prolonged major abdominal surgery. Since evidence is accumulating that detection and correction of falls in rSO2 may be associated with a reduced incidence of postoperative cognitive dysfunction, the study assessed the incidence and possible predisposing factors for significant falls in rSO2 and strategies for correction.

METHODS

Data from 46 consecutive patients aged 55 yr or above undergoing major abdominal surgery were collected and studied. A SICO electrode was placed over the right forehead prior to commencement of anaesthesia and values of rSO2 were recorded automatically on a floppy disk at 20 s intervals throughout the procedure and until transfer of the patient to the postanaesthesia care unit. Anaesthesia and physiological data were routinely collected by the author on an anaesthetic record computer and transferred to an Excel spreadsheet for analysis.

RESULTS

Average duration of the surgery exceeded 7 h. Average blood loss was 1363 mL (interquartile range 500-2000). In 11 of the 46 patients the rSO2 drop exceeded 20%, and in six, there was a significant temporal association of rSO2 drop with ongoing major haemorrhage. In 23 of the 46 patients, a maximum drop in rSO2 occurred, which was about 15% or more. Fall in rSO2 in the 46 patients significantly correlated with blood loss (P < 0.05) and percentage fall in haemoglobin (Hb) (P = 0.01) but not with lowest Hb. Despite maintenance of conventional haemodynamic parameters such as systolic blood pressure (BP) in most patients, the fall in rSO2 seemed only reversible by blood transfusion. In five of the six patients who experienced the greatest decline in rSO2 during haemorrhage, there was no correlation between fall in rSO2 and systolic BP.

CONCLUSIONS

This retrospective study confirms that a significant reduction in rSO2 is a common accompaniment to prolonged major abdominal surgery in elderly patients, especially if associated with blood loss, and is correctable by blood transfusion. In most cases, these changes would have gone unnoticed with conventional monitoring.

Assessment of Cerebral Oxygen Balance During Deep Hypothermic Circulatory Arrest by Continuous Jugular Bulb Venous Saturation and Near-Infrared Spectroscopy

OBJECTIVE

The purpose of this study was to compare jugular venous bulb saturation (SjvO(2)) and regional cerebral oximetry (rSO(2)) by near-infrared spectroscopy (NIRS) during procedures with deep hypothermic circulatory arrest (DHCA).

DESIGN

Prospective observational study.

SETTING

Academic hospital.

PARTICIPANTS

Patients undergoing aortic reconstructive surgery with DHCA from July 2001 to January 2005.

INTERVENTION

The authors examined cerebral oxygenation by continuous NIRS monitoring and by blood gas analysis of intermittently sampled jugular bulb blood (SjvO(2)). Data were obtained during various stages of the procedure in 29 patients. NIRS measurements were compared with SjvO(2).

MEASUREMENTS AND MAIN RESULTS

NIRS and SjvO(2) trends were similar. Overall, cerebral venous oxygen saturation obtained from NIRS was lower compared with SjvO(2) (p < 0.05), especially during periods of low temperature. The mean correlation between NIRS and SjvO(2) was 0.363, and the individual correlations varied from -0.11 to 0.91. The low mean correlation was because of a high degree of variability in the NIRS data between patients.

CONCLUSION

It was concluded that NIRS does not closely correlate with SjvO(2) in this patient population. Cerebral oximetry measured by NIRS could not replace jugular bulb saturation as an intraoperative marker of adequate metabolic suppression.

Cerebral oxygenation in neonatal and pediatric patients during veno-arterial extracorporeal life support

OBJECTIVE

To observe the effects of right carotid artery ligation and variations in extracorporeal life support (ECLS) flow on regional cerebral oxygenation index (rSO2i) measured using near infrared spectroscopy.

DESIGN

Prospective observational study.

SETTING

Tertiary children's hospital.

PATIENTS

Eleven neonatal and pediatric patients requiring veno-arterial ECLS support between June 2000 and March 2003.

INTERVENTIONS

Near infrared spectroscopy probe placement on left and right frontal regions of patients undergoing ECLS, before vessel cannulation or within 24 hrs of initiation of ECLS.

MEASUREMENTS AND MAIN RESULTS

Regional cerebral oxygenation was measured every minute for 72 hrs or until the patient was decannulated. The effect of cannulation on rSO2i from each hemisphere of the brain and the relationship between ECLS flow and rSO2i during ECLS support and "trialing off" periods were determined. Ligation of the right carotid artery resulted in a 12-25% decrease in rSO2i from baseline in the right frontal region for a duration ranging from 17 to 45 mins before returning toward baseline. No substantial change in the left frontal region rSO2i was detected during cannulation. Following this depression in rSO2i on the right, there was a transient increase above baseline in rSO2i observed in both hemispheres on initiating ECLS. No correlation between ECLS flow and rSO2i was found over the 72-hr period. Periods of "trialing off" ECLS were not related to any change in rSO2i in either hemisphere.

CONCLUSIONS

This study demonstrated no relationship between ECLS flow and rSO2i changes during the 72-hr observation period. A brief period of cerebral oxygen desaturation of the right frontal region at the time of right carotid ligation was seen in all three study patients examined during cannulation, followed by an increased rSO2i with initiation of ECLS flow. Near infrared spectroscopy measurement may offer an important adjunct for neurologic monitoring of ECLS patients.

Effect of closed minimized cardiopulmonary bypass on cerebral tissue oxygenation and microembolization

OBJECTIVE

Coronary artery bypass grafting with cardiopulmonary bypass carries a risk for neurologic complications because of cerebral hypoperfusion and microembolization. The basic goals of a novel closed minimized extracorporeal circulation are to prevent excessive hemodilution and to avoid blood-air interface. The aim of this prospective randomized study was to determine the effect of using the minimized extracorporeal circulation system compared with open conventional extracorporeal circulation on cerebral tissue oxygenation and microembolization.

METHODS

Forty patients undergoing coronary artery bypass grafting (20 in each group) were continuously monitored for changes in cerebral oxygenated hemoglobin and tissue oxygenation index by using near-infrared spectroscopy. Total microembolic count and gaseous embolic count in both median cerebral arteries were monitored with multifrequency transcranial Doppler instrumentation.

RESULTS

In the conventional extracorporeal circulation group there was a highly significant reduction in both cerebral oxygenated hemoglobin and tissue oxygenation index from the start to the end of cardiopulmonary bypass (P < .01). The rate of decrease in cerebral oxygenated hemoglobin after aortic cannulation was faster in the conventional extracorporeal circulation group (F test = 9.03, P < .001). No significant changes with respect to cerebral oxygenated hemoglobin or tissue oxygenation index occurred in the minimized extracorporeal circulation group, except at the beginning of rewarming (P < .01). Total embolic count, as well as gaseous embolic count, in the left and right median cerebral arteries was significantly lower in the minimized extracorporeal circulation group (all P < .05). Postoperative bleeding was greater (P < .05) and the transfusion rate was higher (P < .05) in the conventional extracorporeal circulation group.

CONCLUSIONS

Use of closed minimized cardiopulmonary bypass compared with conventional open cardiopulmonary bypass preserves cerebral tissue oxygenation and reduces cerebral microembolization.

Temperature, hematocrit, pH, and glucose 4-way ANOVA of cytochrome C oxidase redox status during systemic cold circulatory arrest in swine

Various investigators using near infrared spectroscopy (NIRS) have reported differing patterns of cytochrome C oxidase (cytochrome a,a3) redox status in similar brain oxygenation studies. We investigated whether distinctive differences could be due to combinations of variations in temperature, hematocrit, pH, and glucose.

METHODS

Thirty-six healthy 10 kg commercial juvenile swine on cardiopulmonary bypass underwent 2-8 sequential periods of circulatory arrest. Prior to each arrest, key physiological variables were adjusted to match a random selection of one of 81 combinations of high, normal, or low levels of hypothermia, hematocrit, pH, and serum glucose. In the course of the study, the combinations were repeated twice to yield 162 NIRS data sets.

RESULTS

The mean rate of change in net oxidized minus reduced cytochrome a,a3 redox status in the brain following 7.5 min of ischemia was 0.49 +/- 0.26 micromol L(-1) min(-1), and, the corresponding mean magnitude of change was -1.23 +/- 0.57 micromol L(-1). The rate of change was influenced by temperature but not by hematocrit, pH, or glucose, either singly or in combination.

CONCLUSION

The respiratory response in mitochondria during systemic circulatory arrest is significantly influenced by temperature.

Comparison of changes in jugular venous bulb oxygen saturation and cerebral oxygen saturation during variations of haemoglobin concentration under propofol and sevoflurane anaesthesia

BACKGROUND

A severe reduction in haemoglobin concentration can lead to a decrease in jugular venous bulb oxygen saturation (Sj(O(2))). However, recent evidences suggests that cerebral oxygen saturation (Sc(O(2))) measured by near infrared spectroscopy decreased during even mild haemodilution. We therefore tested the hypothesis that the changes in Sc(O(2)) may not be parallel to those in Sj(O(2)) during haemodilution. In addition, as cerebral oxygen balance during the operation can vary depending on the anaesthetics used, the changes in Sj(O(2)) and Sc(O(2)) during haemodilution were compared between patients under propofol and isoflurane/nitrous oxide anaesthesia.

METHODS

Forty-two patients with pre-donated autologous blood were randomly assigned to receive propofol (Group P) or sevoflurane/nitrous oxide (Group S) anaesthesia. A fibreoptic catheter was placed in the jugular bulb to measure Sj(O(2)). A cerebral oximeter, INVOS 4100S was used to monitor Sc(O(2)). Arterial and jugular bulb blood samples were drawn simultaneously at: (i) 10 min after the start of operation, (ii) after 400 ml of blood loss, (iii) after 800 ml of blood loss, (iv) just before the transfusion of pre-donated autologous blood, and (v) after 400 ml transfusion.

RESULTS

Mean (sd) control values of Sj(O(2)) in Group P were significantly lower than those in Group S (55 (8)% vs 71 (10)%, respectively; P<0.05), whereas there was no significant difference in control values of Sc(O(2)) between the two groups. During the operation, haemoglobin (Hb) concentrations significantly deceased in the both groups compared with control values (from 9.8 to 7.6 g dl(-1) in Group P and from 9.9 to 8.0 g dl(-1) in Group S). During a reduction in Hb concentration, Sj(O(2)) values remained unchanged in both groups, whereas Sc(O(2)) values significantly decreased in both groups (from 57 to 51% in Group P and from 59 to 52% in Group S).

CONCLUSION

The results indicated that, although the changes in Sj(O(2)) and Sc(O(2)) during a reduction in haemoglobin concentration were similar under propofol and sevoflurane/nitrous oxide anaesthesia, the changes in Sc(O(2)) were not parallel to those in Sj(O(2)). The discrepancy of the results in Sj(O(2)) and Sc(O(2)) may make the interpretation of their values difficult during haemodilution.

Cerebral near-infrared spectroscopy in adult heart surgery: systematic review of its clinical efficacy

PURPOSE

This systematic review is aimed at answering the following questions: 1) Is near-infrared spectroscopy (NIRS) clinically effective in detecting cerebral desaturation during heart surgery? 2) Are these results based on studies with solid methodology?

SOURCES

MEDLINE, internet, and hand searches up to February 2004 for English and French papers on NIRS.

PRINCIPAL FINDINGS

Forty-eight papers were retrieved, with a total of 5,931 cardiac surgery patients monitored by NIRS. More than 83% of patients underwent coronary artery bypass graft surgery. The majority of studies were prospective for the monitored group. Clinically, NIRS monitoring appears to detect brain desaturation episodes encountered during surgery. However, the majority of studies retrieved suffered from major methodological limitations and a low level of evidence. NIRS validity vs jugular bulb oximetry is questioned together with its predictive value in identifying those who will suffer postoperatively from neurological deficits. The sole randomized controlled trial appears to have recorded negative results in this respect.

CONCLUSION

The clinical application of NIRS in heart surgery as a brain-monitoring device seems interesting. However, NIRS has to be investigated more rigorously to prove its clinical utility in cardiac surgery.

Open Heart Surgery for Small Children Without Homologous Blood Transfusion by Using Remote Pump Head System

BACKGROUND

To avoid excessive hemodilution, the transfusion of a large amount of homologous blood may be required in open heart surgery for small children, which in turn, can cause a significant immunologic response.

METHODS

Cardiopulmonary bypass systems with remote pump heads were used for patients weighing 5 kg or less that were undergoing ventricular septal defect repair. The procedures took place from January 1997 to August 2002. The surgery was started with bloodless prime in 122 out of 158 (77.2%) consecutive patients. Exclusion criteria were a predicted hematocrit after the initiation of bypass of less than 15%, respiratory failure or heart failure (or both), and pulmonary vascular obstructive disease.

RESULTS

The mean age and body weight were 3.8 +/- 1.8 months and 4.3 +/- 0.5 kg, respectively. The priming volume was 181.0 +/- 32.5 (minimum: 130) mL. The hematocrit after cardiopulmonary bypass was initiated was 16.7% +/- 2.3%. Six patients required subsequent blood transfusion owing to postoperative complications that resulted in compromised hematopoiesis. In the rest, the hematocrit before discharge was 30.6% +/- 3.0%. Renal and liver function tests were maintained within the normal range. Patients were extubated at 5.6 +/- 2.8 hours after operation with proper oxygenation. Neurodevelopment was apparently normal. The Japanese psychomotor developmental scale assessment was given to patients without chromosomal abnormality between the ages of 1 and 3 years; the resulting score was 102.2 +/- 15.4 (mean = 100 for normal population).

CONCLUSIONS

Open heart surgery was achieved without blood transfusion in the selected group of small children. The use of remote pump heads reduced the overall need for blood transfusions and possibly inflammatory reactions.

Effects of pH management during deep hypothermic bypass on cerebral oxygenation: alpha-stat versus pH-stat

OBJECTIVE

There is a remarkable lack of scientific evidence to support the option to use alpha-stat or pH-stat management, as to which is more beneficial to brain protection during deep hypothermic CPB. This study examined cortical blood flow (CBF), cerebral oxygenation, and brain oxygen consumption in relation to deep hypothermic CPB with alpha-stat or pH-stat management.

METHODS

Twenty-two pigs were cooled with alpha-stat or pH-stat during CPB to 15 degrees C esophageal temperature. CBF and cerebral oxygenation were measured continuously with a laser flowmeter and near-infrared spectroscopy, respectively. Brain oxygen consumption was measured with standard laboratory techniques.

RESULTS

During CPB cooling, CBF was significantly decreased, about 52.2%+/-6.3% (P<0.01 vs 92.6%+/-6.5% of pH-stat) at 15 degrees C in alpha-stat, whereas there were no significant changes in CBF in pH-stat. While cooling down, brain oxygen extraction (OER) progressively decreased, about 9.5%+/-0.9% and 10.9%+/-1.5% at 15 degrees C in alpha-stat and pH-stat, respectively. At 31 degrees C the decreased value in pH-stat was lower than in alpha-stat (29.9%+/-2.7% vs 22.5%+/-1.9%; P<0.05). The ratio of CBF/OER were 2.0+/-0.3 in alpha-stat and pH-stat, respectively; it was kept in constant level in alpha-stat, and significantly increased by 19 degrees C to 15 degrees C in pH-stat (4.9+/-0.9 vs 2.3+/-0.4; P<0.01). In mild hypothermia, cerebral oxyhemoglobin and oxygen saturation in alpha-stat were greater than that in pH-stat (102.5%+/-1.4% vs 99.1%+/-0.7%; P<0.05). In deep hypothermia, brain oxygen saturation in pH-stat was greater than that in alpha-stat (99.2%+/-1.0% vs 93.8%+/-1.0%; P<0.01), and deoxyhemoglobin in pH-stat decreased more greatly than that in alpha-stat (28.7%+/-6.8% vs 54.1%+/-4.7%; P<0.05).

CONCLUSIONS

In mild hypothermic CPB, brain tissue oxygen saturation was greater in alpha-stat than in pH-stat. However, cerebral oxygenation and brain tissue oxygen saturation were better in pH-stat than in alpha-stat during profound hypothermia. PH-stat strategy provided much more oxygen to brain tissue before deep hypothermic circulatory arrest.

The effect of bloodless pump prime on cerebral oxygenation in paediatric patients

BACKGROUND

In paediatric patients, crystalloid prime for cardiopulmonary bypass (CPB) causes further haemodilution in comparison with blood-containing prime. Thus it may affect the cerebral oxygen supply/demand balance. The purpose of the study was to compare the effect of bloodless pump prime with that of blood-containing prime on cerebral oxygenation in children.

METHODS

Thirty-six paediatric patients scheduled for elective repair of atrial or ventricular septal defect were enrolled. In Group C (n = 18), the CPB circuit was primed only with crystalloid. In Group B (n = 18), red blood cells were added to achieve a haematocrit (Hct) of 20% during CPB. The regional cerebral oxygen saturation (rSO(2)) value measured by near-infrared spectroscopy was compared between the two groups.

RESULTS

In both groups, rSO(2) decreased below baseline at the start of CPB and during rewarming (P < 0.001, for both groups during each period). At the start of CPB, haemodilution was greater in Group C than in Group B (Hct 16.1 +/- 0.7% vs. 20.7 +/- 0.5%; P < 0.01), and there was a greater reduction in rSO(2) in Group C (49.0 +/- 5.4% vs. 59.2 +/- 7.0%; P < 0.01). During rewarming, rSO(2) was significantly lower in Group C than in Group B (57.8 +/- 5.3% vs. 62.8 +/- 6.2%; P < 0.01).

CONCLUSIONS

In paediatric patients, the haemodilution associated with crystalloid priming causes a greater reduction in rSO(2) than with blood-containing prime at the starting period of CPB and the rewarming period.

Cerebral cortical oxygenation changes during OPCAB surgery

BACKGROUND

We investigated the changes occurring in cerebral cortical oxygenation during off-pump coronary artery bypass (OPCAB) surgery using near infrared spectroscopy (NIRS).

METHODS

Measurement of cerebral cortical oxygenation changes included concentration of deoxygenated hemoglobin [HHb], oxygenated hemoglobin [O(2)Hb], changes in the redox status of the cytochrome c oxidase [Cyt-Ox], cerebral saturation as expressed by the tissue oxygenation index (TOI), and cerebral blood volume (CBV) as expressed by tissue hemoglobin index (THI). Measurements were performed in 23 consecutive patients during grafting of: left anterior descending (LAD setup 1; n = 23), posterior descending (PDA setup 2; n = 17), and Circumflex (Cx setup 3; n = 19) coronary arteries. Measurements were performed before any surgical manipulation (baseline), following positioning of the pressure stabilizer during construction of the distal anastomosis and 2 minutes after the completion of each distal anastomosis with the heart returned to its natural position.

RESULTS

There were no in-hospital deaths, neurologic deficits, or myocardial infarcts. Compared to baseline, during LAD grafting there was a marked reduction in [O(2)Hb] [-1.08 (-1.77 to -0.39), mean difference (95% CI) (p < 0.0008)], without a significant change in [HHb]. There was also a 4% reduction in cerebral saturation and a 3% fall in CBV (both p < 0.05). Setup 2 (PDA) was associated with a marked decrease of [O(2)Hb] [-1.92 (-2.95 to -0.88) mean difference (95% CI) (p < 0.0025)], which was accompanied by an increase in [HHb] [1.89 (1.00 to 2.77) mean difference (95% CI) (p < 0.0025)], and a 4% reduction in cerebral saturation (p < 0.0008). Grafting of the Cx was associated with a marked increase in [HHb] [2.85 (1.46 to 4.2) mean difference (95% CI) (p < 0.0025)], with no changes in [O(2)Hb], a 6% reduction in cerebral saturation, and a 12% increase in CBV (both p < 0.05). In all 3 settings, however, the changes were not associated with a modification in the redox state of [Cyt-Ox]. On returning to baseline condition, the changes in [O(2)Hb] and TOI observed in setup 1 persisted, and a significant reduction was observed in the redox state of the [Cyt-Ox] when compared with baseline [-0.08 (-0.14 to -0.02) mean difference (95% CI) (p < 0.002)]. For setups 2 and 3 there was recovery of the cerebral cortical oxygenation.

CONCLUSIONS

Grafting of the LAD on the beating heart is responsible for changes in cerebral cortical oxygenation which persist early after returning the heart to its natural position. Grafting of the Cx and PDA result in transient reversible changes. Trendelenburg positioning and right lateral tilting of the operating table during grafting of lateral and posterior walls might have a protective role in preventing cerebral cortical ischemia. Further studies are needed to assess the clinical importance of these observations.

Influence of Patient Variables and Sensor Location on Regional Cerebral Oxygen Saturation Measured by INVOS 4100 Near-Infrared Spectrophotometers

Cerebral oximeter based on near-infrared spectroscopy has been used as a continuous, noninvasive monitoring of regional cerebral oxygen saturation (rSO2). Although the absolute rSO2 values have a wide range of variability, the factors affecting a variability of rSO2 values have not been extensively investigated. The authors investigated the influence of patient variables and sensor location on rSO2 measured by the cerebral oximeter INVOS 4100 in 111 patients anesthetized with sevoflurane, fentanyl, and nitrous oxide in oxygen. The sensors for rSO2 measurements were applied on the right forehead (R), 1 cm lateral to R (R1), on the left forehead (L), 1 cm lateral to L (L1), and on the center of the forehead (C). The relationship between the rSO2 values and patient variables were also analyzed. Values of rSO2 at R1 and L1 were significantly lower than those at R and L, respectively. Values of rSO2 at C were significantly higher compared with those at other sites. There were no significant correlations between the rSO2 values and values of weight, height, and head size. Values of rSO2 were similar between males and females. A significant negative correlation between the rSO2 values and age and a positive correlation between the rSO2 values and hemoglobin concentration were observed. These data indicate that patient age, hemoglobin concentration at the measurement, and sensor location can affect rSO2 values.

Regional tissue oxygenation during hemorrhage: can near infrared spectroscopy be used to monitor blood loss?

We investigated whether near infrared spectroscopy could be used to monitor regional tissue oxygenation during uncompensated hemorrhage in man. A Somanetics INVOS 4100 oximeter was used to measure regional hemoglobin oxygen saturation in the cerebral cortex (CsO2, left frontal area) and from the left calf muscle (PsO2) in 40 volunteers donating 470 mL of the whole blood. A Critikon 2001 Cerebral Redox Instrument was used to monitor total (tHb), oxygenated (O2Hb), and deoxygenated (HHb) hemoglobin in the right calf muscle. The oxygenation index, [HbD] = [O2Hb] - [HHb] was derived. CsO2 decreased by a mean (95% CI) of 2 (1-3.3%) (P < 0.001), PsO2 decreased by a mean (95% CI) of 3.2 (1.7-4.6%) (P < 0.001), and HbD decreased by a median (95% CI) of 6.4 (2.65-10.16) delta microM/cm (P < 0.001) during blood collection. There was an inverse correlation between blood loss and CsO2 (R = -0.59, P < 0.001), PsO2 (R = -0.61, P < 0.001), and HbD (R = -0.5, P < 0.001). Regional tissue oxygenation decreases in proportion to uncompensated blood loss. Near infrared spectroscopy may potentially be developed into a transfusion trigger.

Metabolic changes after cardiac surgery

The metabolic changes that occur after cardiac surgery result from a complex interaction between the effects of surgery and extracorporeal circulation per se, the inflammatory response to surgical trauma and extracorporeal circulation, perioperative use of hypothermia, the cardiovascular and neuroendocrine responses characteristic to cardiac surgery, and the drugs and blood products used to support circulation during and after operation. These changes include among others increased oxygen consumption and energy expenditure and increased secretion of insulin, growth hormone, adrenocorticotrophic hormone, cortisol, epinephrine and norepinephrine. Other changes include decreased total-Trijodthyronine levels, hyperglycemia, hyperlactatemia, increased glutamate, aspartate and free fatty acid concentrations, hypokalemia, an increased production of inflammatory cytokines and increased consumption of complement and adhesion molecules. There is evidence that better control of metabolic abnormalities improves the patients' outcome.