Utility of near-infrared spectroscopic measurements during deep hypothermic circulatory arrest

Association of Ongoing Cerebral Oxygen Extraction During Deep Hypothermic Circulatory Arrest With Postoperative Brain Injury

Cardiac surgery utilizing circulatory arrest is most commonly performed under deep hypothermia (∼18°C) to suppress tissue oxygen demand and provide neuroprotection during operative circulatory arrest. Studies investigating the effects of deep hypothermic circulatory arrest (DHCA) on neurodevelopmental outcomes of patients with congenital heart disease give conflicting results. Here, we address these issues by quantifying changes in cerebral oxygen saturation, blood flow, and oxygen metabolism in neonates during DHCA and investigating the association of these changes with postoperative brain injury. Neonates with critical congenital heart disease undergoing DHCA were recruited for continuous intraoperative monitoring of cerebral oxygen saturation (ScO₂) and an index of cerebral blood flow (CBF_i) using 2 noninvasive optical techniques, diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS). Pre- and postoperative brain magnetic resonance imaging (MRI) was performed to detect white matter injury (WMI). Fifteen neonates were studied, and 11/15 underwent brain MRI. During DHCA, ScO₂ decreased exponentially in time with a median decay rate of -0.04 min^-1. This decay rate was highly variable between subjects. Subjects who had larger decreases in ScO₂ during DHCA were more likely to have postoperative WMI (P = 0.02). Cerebral oxygen extraction persists during DHCA and varies widely from patient-to-patient. Patients with a higher degree of oxygen extraction during DHCA were more likely to show new WMI in postoperative MRI. These findings suggest cerebral oxygen extraction should be monitored during DHCA to identify patients at risk for hypoxic-ischemic injury, and that current commercial cerebral oximeters may underestimate cerebral oxygen extraction.

The role of diffuse correlation spectroscopy and frequency-domain near-infrared spectroscopy in monitoring cerebral hemodynamics during hypothermic circulatory arrests

OBJECTIVES

Real-time noninvasive monitoring of cerebral blood flow (CBF) during surgery is key to reducing mortality rates associated with adult cardiac surgeries requiring hypothermic circulatory arrest (HCA). We explored a method to monitor cerebral blood flow during different brain protection techniques using diffuse correlation spectroscopy (DCS), a noninvasive optical technique which, combined with frequency-domain near-infrared spectroscopy (FDNIRS), also provides a measure of oxygen metabolism.

METHODS

We used DCS in combination with FDNIRS to simultaneously measure hemoglobin oxygen saturation (SO2), an index of cerebral blood flow (CBFi), and an index of cerebral metabolic rate of oxygen (CMRO2i) in 12 patients undergoing cardiac surgery with HCA.

RESULTS

Our measurements revealed that a negligible amount of blood is delivered to the cerebral cortex during HCA with retrograde cerebral perfusion, indistinguishable from HCA-only cases (median CBFi drops of 93% and 95%, respectively) with consequent similar decreases in SO2 (mean decrease of 0.6 ± 0.1% and 0.9 ± 0.2% per minute, respectively); CBFi and SO2 are mostly maintained with antegrade cerebral perfusion; the relationship of CMRO2i to temperature is given by CMRO2i = 0.052e0.079T.

CONCLUSIONS

FDNIRS-DCS is able to detect changes in CBFi, SO2, and CMRO2i with intervention and can become a valuable tool for optimizing cerebral protection during HCA.

Hemodynamic Assessment and Monitoring of Premature Infants

The management of the hemodynamic status of critically ill preterm infants, particularly around the periviable period, remains a significant challenge in the neonatal intensive care unit for a multitude of reasons. The causes of hemodynamic compromise in this population are heterogeneous and usually superimposed on the complex physiologic processes that occur during transition from fetal to neonatal life. This review outlines the unique nature of low blood flow states in this population and present an overview of the current methods for identification and assessment of hemodynamic compromise.

A tale of two methods: combining near-infrared spectroscopy with MRI for studies of brain oxygenation and metabolism

Combining magnetic resonance imaging (MRI) with near-infrared spectroscopy (NIRS) leads to excellent synergies which can improve the interpretation of either method and can provide novel data with respect to measuring brain oxygenation and metabolism. MRI has good spatial resolution, can detect a range of physiological parameters and is sensitive to changes in deoxyhemoglobin content. NIRS has lower spatial resolution, but can detect, and with specific technologies, quantify, deoxyhemoglobin, oxyhemoglobin, total hemoglobin and cytochrome oxidase. This paper reviews the application of both methods, as a multimodal technology, for assessing changes in brain oxygenation that may occur with changes in functional activation state or metabolic rate. Examples of hypoxia and ischemia are shown. Data support the concept of reduced metabolic rate resulting from hypoxia/ischemia and that metabolic rate in brain is not close to oxygen limitation during normoxia. We show that multimodal MRI and NIRS can provide novel information for studies of brain metabolism.

Selective cerebral perfusion using moderate flow in complex cardiac surgery provides sufficient neuroprotection. Are children young adults?

OBJECTIVE

Selective cerebral perfusion (SCP) is commonly applied during the correction of complex congenital cardiac defects. In this study, we assessed the impact of different flow levels of SCP on potential brain ischaemia.

METHODS

Fifteen piglets (7-10 kg, age 3-4 weeks) received SCP via the right common carotid artery during cardiopulmonary bypass at 25°C for 90 min. Regular brain perfusion (1 ml/g brain weight/min), moderate hypoperfusion (0.5 ml/g/min) and extensive hypoperfusion (0.25 ml/g/min) were evaluated. Clinical parameters and tissue oxygenation index (TOI) were registered online until 3 h of reperfusion. Hematoxylin and eosin (HE) staining and immunohistological analyses for apoptosis inducing factor (AIF) and nitrotyrosine (NO-Tyr) were performed on sections of the hippocampus.

RESULTS

Intracerebral pressure remained stable throughout the study. Haemodynamic parameters, blood gas and lactate measurements were stable until the end of the study. Extensive hypoperfusion led to a moderate reduction of TOI. NO-Tyr immuno-positive cells were 15.7% at regular cerebral perfusion, 23.9% at moderate hypoperfusion (P = n.s.) and 46.1% at extensive hypoperfusion (P < 0.05). AIF immuno-positive nuclei were present in 8.3% of the hippocampus cells after regular perfusion, in 10.8% after moderate hypoperfusion (P = n.s.) and in 17.9% after extensive hypoperfusion (P < 0.05).

CONCLUSIONS

SCP using a moderate SCP flow regime demonstrates comparable results to normal brain perfusion while after extensive hypoperfusion significant morphological brain injury could be found. Thus moderate, but not extensive, hypoperfusion might have the potential to prevent perfusion-related cerebral oedema and an increasing risk of brain injury.

Noninvasive control of adequate cerebral oxygenation during low-flow antegrade selective cerebral perfusion on adults and infants in the aortic arch surgery

Real-time readings of the regional oxygen saturation (rSO(2)) using near-infrared spectroscopy (NIRS) during the aortic arch surgery can provide an early detection of perfusion or oxygenation abnormalities.

BACKGROUND

Aortic arch repair techniques using low-flow antegrade selective cerebral perfusion have been standardized to a certain degree. However, some of the often-stated beneficial effects have never been proven. Especially, the existence of an adequate continuous flow in both cerebral hemispheres during the surgical procedure still remains unclear as the monitoring of an effective perfusion remains a nonstandardized technique.

METHODS

Seventeen patients underwent surgical reconstruction of the aortic arch due to aortic aneurysm surgery (adult group n = 8 patients) or of the hypoplastic aortic arch due to hypoplastic left heart syndrome (HLHS) or aortic coarctation (infant group n = 9 patients) under general anesthesia and mild hypothermia (adult group 28 degrees C; infant group 25 degrees C). Mean weights were 92.75 +/- 14.00 kg and 4.29 +/- 1.32 kg, and mean ages were 58.25 +/- 10.19 years and 55.67 +/- 51.11 days in the adult group and the infant group, respectively. The cerebral O(2) saturation measurement was performed by continuous plotting of the somatic reflectance oximetry of the frontal regional tissue on both cerebral hemispheres (rSO(2), INVOS; Somanetics Corporation, Troy, MI, USA).

RESULTS

During low-flow antegrade perfusion via innominate artery, continuous plots with similar values of O(2) saturation (rSO(2)) in both cerebral hemispheres were observed, whereas a decrease in the rSO(2) values below the desaturation threshold correlated with a displacement or an incorrect positioning of the arterial cannula in the right subclavian artery.

CONCLUSIONS

Continuous monitorization of the cerebral O(2) saturation during aortic arch surgery in adults and infants is a feasible technique to control an adequate cannula positioning and to optimize clinical outcomes avoiding neurological complications related to cerebral malperfusion.

Factors influencing neurologic outcome after neonatal cardiopulmonary bypass: what we can and cannot control

Advances in cardiopulmonary bypass and surgical techniques have led to progress in the early repair of congenital heart defects in children. However, as increasing numbers survive their initial cardiac operation, an awareness is emerging that significant early and late neurologic morbidities continue to complicate otherwise successful operative repairs. Adverse neurologic outcomes after neonatal cardiac surgery are multifactorial and relate to both fixed and modifiable mechanisms. The purpose of this review is to (1) review mechanisms of brain injury after neonatal cardiopulmonary bypass, (2) examine risk factors, and (3) speculate on how investigations may improve our understanding of neurologic injury.

Surrogate markers for neurological outcome in children after deep hypothermic circulatory arrest

Improved survival for infants with congenital heart disease (CHD) has led to increased focus on the most significant morbidities that are neurodevelopmental. Neurologic injury in neurodevelopmental outcome may have many causes in children with complex CHD undergoing cardiopulmonary bypass and deep hypothermic circulatory arrest, including genetic syndromes, abnormal blood flow patterns, prenatal insults, and hemodynamic instability. Although gross neurological injury can be detected in the perinatal and postoperative period, more subtle injury may not be identified until much later. Disabilities in speech and language, motor skills, and attention deficit disorder are present by school age in up to 50% of the complex CHD population. It is imperative that the mechanisms of these injuries be identified to enable the application of neuroprotective interventions. To facilitate clinical investigation, evaluation of surrogate markers for these longer term "real" outcomes continues. Because some abnormalities may not be detected for years, the evaluation of a surrogate marker takes a long time. Thus, identification of surrogate markers is in its infancy. Serologic proteins, seizures, magnetic resonance findings, cerebral oxygenation, and the neurologic examination have all been studied. Continuing innovation in the use of magnetic resonance imaging techniques and the application of physiologic measures including near-infrared spectroscopy currently pose the greatest potential for advances. This article summarizes the state of the art and an admission about how far we have yet to travel as we strive to make the neurodevelopmental outcomes of patients with CHD comparable to their healthy peers.

Measurements of Optical Pathlength Using Phase-Resolved Spectroscopy in Patients Undergoing Cardiopulmonary Bypass

BACKGROUND

Near infrared spectroscopy (NIRS) has been used during cardiac surgery to monitor cerebral oxygenation although the validity of this technique has yet to be established. Although optical pathlength included in the algorithm for calculating NIRS values is supposed to be constant, recent evidence has suggested that optical pathlength could be affected by acute hemodilution in animals. We conducted the present study to investigate whether optical pathlength changes during cardiopulmonary bypass (CPB), and whether these changes affect NIRS values in adult patients.

METHODS

Nine patients undergoing elective cardiac surgery with CPB were enrolled in this study. Optical pathlength and cerebral NIRS values (oxyhemoglobin [DeltaO(2)Hb] and tissue oxygen index) were measured by phase-resolved spectroscopy and NIRO 100, respectively. Optical pathlength, hemoglobin concentration, and NIRS values were measured at the following points: 1) after the induction of anesthesia, 2) 10 min after the start of CPB, 3) 60 min after the start of CPB, and 4) 1 h after CPB. The associations between optical pathlength and other variables were analyzed by Pearson correlation coefficients and multiple regression analysis.

RESULTS

Optical pathlength significantly increased starting at 27.7-30.8 cm at 10 min, and 31.3 cm at 60 min after the start of CPB (P < 0.0001). Hemoglobin concentrations significantly decreased (from 11.2 to 7.1 g/dL at 10 min and 7.7 g/dL at 60 min P < 0.0001). There was a significant correlation (r = 0.55, P < 0.001) between percentage changes in pathlength and hemoglobin concentration. Multiple regression analysis showed that optical pathlength was a significant determinant of DeltaO2Hb.

CONCLUSION

The results indicate that optical pathlength can change during CPB and its changes may affect DeltaO2Hb.

Regional cerebral saturation monitoring with near-infrared spectroscopy during selective antegrade cerebral perfusion: Diagnostic performance and relationship to postoperative stroke

OBJECTIVE

To investigate whether regional cerebral tissue oxygen saturation monitoring during hypothermic selective antegrade cerebral perfusion in surgery involving the aortic arch can predict neurologic sequelae and to evaluate the diagnostic performance of near-infrared spectroscopy monitoring in this setting.

METHODS

Data from 46 consecutive patients were analyzed. Selective antegrade cerebral perfusion was established by perfusion of the right subclavian artery (with or without left carotid artery perfusion) or by separate concomitant perfusion of the innominate and the left carotid arteries. The bilateral regional cerebral tissue oxygen saturation index was monitored by using near-infrared spectroscopy equipment (INVOS 4100). Stroke was the primary clinical end point, along with the indices of diagnostic performance.

RESULTS

Six patients died in the hospital, and 6 patients (13%) experienced a perioperative stroke. In patients with stroke, regional cerebral tissue oxygen saturation values were significantly lower during selective antegrade cerebral perfusion, and regional cerebral tissue oxygen saturation tended to be lower in the affected hemisphere. In receiver operating characteristic curve analysis, the area under the curve for relative regional cerebral tissue oxygen saturation values ranged from 0.72 to 0.87. During selective antegrade cerebral perfusion, regional cerebral tissue oxygen saturation between 76% and 86% of baseline had a sensitivity up to 83% and a specificity up to 94% in identifying individuals with stroke. The associated odds ratio for stroke was 5.6 (95% confidence interval, 0.5-144) to 21 (95% confidence interval, 1.8-566).

CONCLUSIONS

Monitoring of regional cerebral tissue oxygen saturation by using near-infrared spectroscopy during selective antegrade cerebral perfusion allows detection of clinically important cerebral desaturation. It can help predict perioperative neurologic sequelae. Its performance as a diagnostic instrument is satisfying and supports its use as a noninvasive trend monitor of cerebral saturation.

Brain, spine, and muscle cytochrome Cu-A redox patterns of change during hypothermic circulatory arrest in swine

Past near infrared spectroscopy (NIRS) studies have reported different changes in cytochrome C oxidase (Cyt) redox status during similar interventions that cause tissue ischaemia. We investigated whether there were distinctive differences when NIRS signals were obtained simultaneously from different tissues during total circulatory arrest. Forty-two healthy 10 kg commercial swine (Sus scrofa) on cardiopulmonary bypass, each underwent 2 to 8 sequential periods of hypothermic circulatory arrest for 7.5 min. Prior to each arrest, key physiologic variables were adjusted to 1 of 81 combinations of high, normal, or low levels of core temperature, hematocrit, pH, and serum glucose. Each combination was repeated at least twice. Simultaneous NIRS monitoring yielded 202 brain, 191 spine, and 199 muscle Cyt data sets, which were then classified into 13 distinctive patterns of change. The data sets always differed between tissues in the same arrest trial and subject. Typically, brain Cyt rapidly became more reduced at the start of arrest and changed little thereafter, muscle Cyt behaved comparably to brain Cyt but continued to become reduced throughout the arrest, and spine Cyt either did not change status or gradually became more reduced over the course of arrest. The spine pattern's mean rate of change was 12 times slower than those of the brain or muscle. The Cyt patterns of change were classified into 13 groups which were significantly related to core temperature in the brain and spine, and hematocrit in muscle. The respiratory response in mitochondria during systemic circulatory arrest differs between brain, spine and muscle tissues in the same subject.

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.

Low postoperative hematocrit increases cerebrovascular damage after hypothermic circulatory arrest

OBJECTIVE

The objective of this study was to evaluate the systemic and cerebral effects of different postoperative hematocrit management following cardiopulmonary bypass and deep hypothermic circulatory arrest.

DESIGN

Animal case study.

SETTING

Laboratory.

SUBJECTS

Four-week-old Yorkshire piglets.

INTERVENTIONS

Twelve piglets were subjected to cardiopulmonary bypass (hematocrit = 25%) and 100 mins of deep hypothermic circulatory arrest (15 degrees C). After weaning cardiopulmonary bypass, they were randomized to either group L or H, in which the postoperative hematocrit was maintained approximately 20% vs. approximately 30%, respectively, and survived for 6 hrs.

MEASUREMENTS AND MAIN RESULTS

Changes in body weight, bioimpedance, and colloid oncotic pressure were assessed. Near-infrared spectroscopy and immunohistochemical assays for cerebral transforming growth factor-beta(1) and caspase-3 were performed. Postoperative weight gain (kg) and decreases in bioimpedance (ohms) were significantly less in group H (1.5 +/- 0.2 [H] vs. 2.4 +/- 0.6 [L], p = .01; 39.3 +/- 15.5 [H] vs. 89.1 +/- 29.6 [L], p = .01). Mean colloid oncotic pressure (mm Hg) was significantly higher in group H (10.8 +/- 1.6 [H] vs. 8.2 +/- 0.8 [L], p = .01) at 6 hrs postoperatively. Oxyhemoglobin, oxidized cytochrome aa(3) (muM x differential path-length factor), and tissue oxygenation index (%) were significantly better in group H (65.7 +/- 31.8 [H] vs. -104.7 +/- 55.2 [L], p = .0001; 0.52 +/- 4.1 [H] vs. -12.8 +/- 6.1 [L], p = .0001, and 55.7 +/- 4.6% [H] vs. 45.3 +/- 6.4% [L], p = .004, respectively). Cerebral transforming growth factor-beta(1) and caspase-3 scores were significantly better in group H (3.0 +/- 0.6 [H] vs. 1.9 +/- 0.9 [L], p = .04 and 1.8 +/- 0.5 [H] vs. 3.2 +/- 0.8 [L], p = .02, respectively). Mean arterial pressure (mm Hg) was consistently higher with group H (94.7 +/- 13.0 [H] vs. 78.3 +/- 11.5 [L], p = .003) despite comparable central venous pressure ( approximately 11 mm Hg).

CONCLUSIONS

Lower postoperative hematocrit was associated with increased fluid retention, lower perfusion pressure, and worse cerebrovascular injury following deep hypothermic circulatory arrest. Postoperative hematocrit management may have profound systemic and cerebral effects after deep hypothermic circulatory arrest and merits further investigation.

Near-infrared spectroscopy: a tool to monitor cerebral hemodynamic and metabolic changes after cardiac arrest in rats

INTRODUCTION

Cardiac arrest (CA) is associated with poor neurological outcome and is associated with a poor understanding of the cerebral hemodynamic and metabolic changes. The objective of this study was to determine the applicability of near-infrared spectroscopy (NIRS), to observe the changes in cerebral total hemoglobin (T-Hb) reflecting cerebral blood volume, oxygenation state of Hb, oxidized cytochrome oxidase (Cyto-C), and brain water content following CA.

METHODS

Fourteen rats were subjected to normothermic (37.5 degrees C) or hypothermic (34 degrees C) CA induced by 8 min of asphyxiation. Animals were resuscitated with ventilation, cardiopulmonary resuscitation (CPR), and epinephrine (adrenaline). Hypothermia was induced before CA. NIRS was applied to the animal head to measure T-Hb with a wavelength of 808 nm (n = 10) and oxygenated/deoxygenated Hb, Cyto-C, and brain water content with wavelengths of 620-1120 nm (n = 4).

RESULTS

There were no technical difficulties in applying NIRS to the animal, and the signals were strong and consistent. Normothermic CA caused post-resuscitation hyperemia followed by hypoperfusion determined by the level of T-Hb. Hypothermic CA blunted post-resuscitation hyperemia and resulted in more prominent post-resuscitation hypoperfusion. Both, normothermic and hypothermic CA resulted in a sharp decrease in oxygenated Hb and Cyto-C, and the level of oxygenated Hb was higher in hypothermic CA after resuscitation. There was a rapid increase in brain water signals following CA. Hypothermic CA attenuated increased water signals in normothermic CA following resuscitation.

CONCLUSION

NIRS can be applied to monitor cerebral blood volume, oxygenation state of Hb, Cyto-C, and water content following CA in rats.

Extracorporeal membrane oxygenation for cardiac disease: no longer a mistaken diagnosis

Extracorporeal membrane oxygenation (ECMO) has become a valuable adjunct in caring for infants and children with heart disease. Since the initial reports of ECMO support for cardiac failure in children, the number of centers providing cardiac support and the number of cases of cardiac ECMO have steadily increased. The International Registry for Extracorporeal Life Support Organization has reported survival statistics for cardiac cases in neonates, children, and adults ranging from 33% to 43%. These numbers are similar to the survival from recent reports by Morris (39%) and Chaturvedi (49%). Survival is influenced by ability to be weaned from bypass in the operating room and by residual structural disease and multi-organ system failure but not by cardiac arrest and single ventricle physiology. To improve results in the future, we need to focus on better predicting the need for support and avoiding multi-organ system failure before initiating ECMO. Rapid deployment of ECMO may further improve results for patients who deteriorate suddenly in the intensive care unit.

Combination of alpha-stat strategy and hemodilution exacerbates neurologic injury in a survival piglet model with deep hypothermic circulatory arrest

BACKGROUND

The optimal pH strategy and hematocrit during cardiopulmonary bypass with deep hypothermic circulatory arrest (DHCA) remain controversial. We studied the interaction of pH strategy and hematocrit and their combined impact on cerebral oxygenation and neurological outcome in a survival piglet model including monitoring by near-infrared spectroscopy (NIRS).

METHODS

Thirty-six piglets (9.2+/-1.1 kg) underwent DHCA under varying conditions with continuous monitoring by NIRS (pH-stat or alpha-stat strategy, hematocrit 20% or 30%, DHCA time 60, 80, or 100 minutes). Neurological recovery was evaluated daily. The brain was fixed in situ on postoperative day 4 and a histological score (HS) for neurological injury was assessed.

RESULTS

Oxygenated hemoglobin (HbO2) and total hemoglobin signals detected by NIRS were significantly lower with alpha-stat strategy during cooling (p < 0.001), suggesting insufficient cerebral blood supply and oxygenation. HbO2 declined to a plateau (nadir) during DHCA. Time to nadir was significantly shorter in lower hematocrit groups (p < 0.01). Significantly delayed neurologic recovery was seen with alpha-stat strategy compared with pH-stat (p < 0.05). The alpha-stat group had a worse histological score compared with those assigned to pH-stat (p < 0.001). Neurologic impairment was estimated to be over 10 times more likely for animals randomized to alpha-stat compared with pH-stat strategy (odds ratio = 10.7, 95% confidence interval = 3.8 to 25.2).

CONCLUSIONS

Combination of alpha-stat strategy and lower hematocrit exacerbates neurological injury after DHCA. The mechanism of injury is inadequate cerebral oxygenation during cooling and a longer plateau period of minimal O2 extraction during DHCA.

Systemic steroid pretreatment improves cerebral protection after circulatory arrest

BACKGROUND

This study evaluates whether systemic steroid pretreatment enhances neuroprotection during deep hypothermic circulatory arrest (DHCA) compared with steroid in cardiopulmonary bypass (CPB) prime.

METHODS

Four-week-old piglets randomly placed into two groups (n = 5 per group) were given methylprednisolone (30 mg/kg) into the pump prime (group PP), or pretreated intravenously 4 hours before CPB (group PT). All animals underwent 100 minutes of DHCA (15 degrees C), were weaned off CPB, and were sacrificed 6 hours later. Postoperative changes in body weight, bioimpedance, and colloid oncotic pressure (COP) were measured. Cerebral trypan blue content, immunohistochemical evaluation of transforming growth factor-beta1 (TGF-beta1) expression, and caspase-3 activity were performed.

RESULTS

Percentage weight gain (group PP 25.0% +/- 10.4% versus group PT 12.5% +/- 4.0%; p = 0.036), and percentage decrease in bioimpedance (PP 37.2% +/- 14.5% versus PT 15.6% +/- 7.9%; p = 0.019) were significantly lower, whereas postoperative COP was significantly higher in group PT versus group PP (PT 15.3 +/- 1.8 mm Hg versus PP 11.6 +/- 0.8 mm Hg; p = 0.003). Cerebral trypan blue (ng/g dry tissue) was significantly lower in group PT (PT 5.6 x 10(-3) +/- 1.1 x 10(-3) versus PP 9.1 x 10(-3) +/- 5.7 x 10(-4); p = 0.001). Increased TGF-beta1 expression and decreased caspase-3 activity were shown in group PT.

CONCLUSIONS

Systemic steroid pretreatment significantly reduced total body edema and cerebral vascular leak and was associated with better immunohistochemical indices of neuroprotection after DHCA.

Prediction of safe duration of hypothermic circulatory arrest by near-infrared spectroscopy

OBJECTIVE

Hypothermic circulatory arrest is widely used for adults with aortic arch disease as well as for children with congenital heart disease. At present, no method exists for monitoring safe duration of circulatory arrest. Near-infrared spectroscopy is a new technique for noninvasive monitoring of cerebral oxygenation and energy state. In the current study, the relationship between near-infrared spectroscopy data and neurologic outcome was evaluated in a survival piglet model with hypothermic circulatory arrest.

METHODS

Thirty-six piglets (9.36 +/- 0.16 kg) underwent circulatory arrest under varying conditions with continuous monitoring by near-infrared spectroscopy (temperature 15 degrees C or 25 degrees C, hematocrit value 20% or 30%, circulatory arrest time 60, 80, or 100 minutes). Each setting included 3 animals. Neurologic recovery was evaluated daily by neurologic deficit score and overall performance category. Brain was fixed in situ on postoperative day 4 and examined by histologic score.

RESULTS

Oxygenated hemoglobin signal declined to a plateau (nadir) during circulatory arrest. Time to nadir was significantly shorter with lower hematocrit value (P <.001) and higher temperature (P <.01). Duration from reaching nadir until reperfusion ("oxygenated hemoglobin signal nadir time") was significantly related to histologic score (r (s) = 0.826), neurologic deficit score (r (s) = 0.717 on postoperative day 1; 0.716 on postoperative day 4), and overall performance category (r (s) = 0.642 on postoperative day 1; 0.702 on postoperative day 4) (P <.001). All animals in which oxygenated hemoglobin signal nadir time was less than 25 minutes were free of behavioral or histologic evidence of brain injury.

CONCLUSION

Oxygenated hemoglobin signal nadir time determined by near-infrared spectroscopy monitoring is a useful predictor of safe duration of circulatory arrest. Safe duration of hypothermic circulatory arrest is strongly influenced by perfusate hematocrit value and temperature during circulatory arrest.

Near infrared spectrophotometry reflects cerebral metabolism during hypothermic circulatory arrest in adults

Near-infrared spectrophotometry (NIRS) is assumed to reflect cerebral oxygenation during hypothermic circulatory arrest (HCA). However, the rationale for the use of NIRS as a marker of cerebral metabolism remains to be elucidated. We examined whether cerebral oxygenation measured by NIRS correlated with cerebral metabolic function assessed by cerebral oxygen extraction ratio (OER) during HCA in adults. NIRS was continuously monitored in 14 patients undergoing thoracic aortic surgery using HCA (17.9 +/- 2.9 degrees C esophageal temperature at HCA onset). Jugular venous oxygen saturation and OER were also monitored. OER was significantly reduced from 37.3 +/- 7.2% at the onset of cardiopulmonary bypass to 13.6 +/- 6.2% at the onset of HCA (p < 0.0001). A linear decrease in oxygenated-hemoglobin (oxy-Hb) and increase in deoxygenated-hemoglobin (deoxy-Hb) were found during HCA, which returned to baseline levels after rewarming. The rate of decrease in oxy-Hb and increase in deoxy-Hb were -0.63 +/- 0.45 and 0.51 +/- 0.30 (10(-5) OD/cm per sec), respectively, both of which significantly correlated with OER at the onset of HCA (R2=0.739 and 0.633; p < 0.0001 and p = 0.0007, respectively). NIRS may serve as a reliable diagnostic modality for monitoring cerebral metabolism during aortic surgery using HCA.