Cerebral oxygenation measured by near-infrared spectroscopy: comparison with jugular bulb oximetry

Neurologic monitoring for special cardiopulmonary bypass techniques

Low flow hypothermic cardiopulmonary bypass, deep hypothermic circulatory arrest, and regional low-flow cerebral perfusion are special techniques used to facilitate complex intracardiac and aortic surgery in neonates and infants. Each carries a risk of cerebral hypoxia and neurologic morbidity. Neurologic monitoring in the form of near-infrared spectroscopy for cerebral oxygenation, transcranial Doppler ultrasound, and the bispectral index electroencephalogram can monitor the brain during these techniques to determine the minimum acceptable bypass flow rates or maximum acceptable duration of deep hypothermic circulatory arrest. The use of this monitoring has the potential to improve long-term neurologic and developmental outcome.

Critical care in cardiovascular medicine

The field of cardiac intensive care is rapidly evolving with nearly simultaneous advances in surgical techniques and adjunctive therapies, respiratory care, intensive care technology and monitoring, pharmacologic research and development, and computing and electronics. The focus of care has now shifted toward reducing morbidity and improving "quality of life" while the survival of infants and children with congenital heart defects, including those with univentricular hearts has dramatically improved during the last three decades. Despite these advances, there remains a predictable fall in cardiac output after cardiopulmonary bypass. This article focuses on early identification and aggressive treatment of the low cardiac output syndrome peculiar to these patients. The authors also briefly review the recent advances in the treatment of pulmonary hypertension, mechanical support, and neurologic surveillance after cardiac surgery.

Measurement of tissue oxygenation index during the first three days in premature born infants

No normal values of tissue oxygenation index (TOI) of the brain are known regarding premature born infants. We measured TOI, a measure for the cerebral hemoglobin oxygen saturation, on the head of 15 preterm infants with a median postmenstrual age of 28 weeks (interquartile range (IQR) between 26-29 weeks) with spatially resolved spectroscopy (NIRO 300, Hamamatsu) during the first three days of life. Infants with intra-ventricular hemorrhage or periventricular leucomalacia before the first measurement, as shown by ultrasound, were excluded. The first measurement was done within the first 6 hours of life, the second and third measurement at, respectively, 24 and 48 hours after this first measurement. The mean TOI was calculated if saturation did not change by more than 5% for at least 30 minutes. Other parameters measured were PaO2, PCO2, pH, mean arterial blood pressure, heart rate, hemoglobin, glycemia and peripheral oxygen saturation. There was a significant increase of TOI after 24 (p < 0.05) and 48 (p < 0.001) hours. The median TOI on the first day was 57% (95% CI: 54-65.7), 66.1% on the second day (95%CI: 61.9-82.3%) and 76.1% on the third day (95%CI 67.8-80.1%). No correlation was found between TOI and peripheral oxygen saturation, blood pressure, PaO2, PaCO2 and hemoglobin concentration after multiple regression analysis. TOI increases in the first three days in premature born babies. The increase of TOI is not due to an increase of oxygenation or mean arterial blood pressure. In our opinion, it reflects the increase in cerebral blood flow during the first three days.

Noninvasive monitoring of cerebral oxygenation during vasomotor reactivity tests by a new near-infrared spectroscopy device

BACKGROUND

Spatially resolved spectroscopy is a recently developed technique for noninvasive monitoring of cerebral tissue oxygenation using the photon diffusion theory.

METHODS

We studied this technique with a new, commercial near-infrared spectroscopy (NIRS) device during vasomotor reactivity tests in 28 healthy volunteers (mean age 31.0 years; SD 10.6 years) and compared it with values assessed by the modified Beer-Lambert law and indices from simultaneous transcranial Doppler sonography of both middle cerebral arteries. We measured O(2) reactivity as percentage change of cerebral blood flow velocity (CBFV), as absolute change in the concentrations (measured in micromol/l) of oxygenated (HbO(2)), deoxygenated (Hb) and total hemoglobin (HbT), and as change in the tissue oxygenation index (TOI) during inhalation of 100% oxygen. CO(2) reactivity was calculated as percentage change of CBFV (NCR), as absolute change in the concentrations of HbO(2), Hb, and HbT (micromol/l), and as change in TOI (%) per 1% increase in end-tidal CO(2).

RESULTS

One hundred percent oxygen inhalation lead to a decrease in CBFV (mean +/- SD: left -8.0 +/- 7.0%, p = 0.000; right -9.6 +/- 7.6%, p = 0.000), an increase in HbO(2) (0.99 +/- 1.07 micromol/l), Hbdiff (2.23 +/- 1.72 micromol/l), and TOI (3.1 +/- 1.5%), and a decrease in Hb (-1.22 +/- 0.74 micromol/l), significant from baseline values (p = 0.0000). CO(2) reactivity was: NCR left 25.4 +/- 14.7%; NCR right 25.9 +/- 13.4%; HbO(2) 1.99 +/- 0.97 micromol/l; Hb -1.24 +/- 0.81 micromol/l; HbT 0.81 +/- 1.0 micromol/l, and TOI 3.7 +/- 2.2%. O(2) reactivity in TCD did not correlate with NIRS reactivities (Pearson p > 0.05), but NCR did correlate with changes in HbO(2), Hb, and TOI (Pearson p < 0.01). TOI was closely related to indices derived from the Beer-Lambert law (Pearson p < 0.03), but not with mean arterial blood pressure or skin blood flow during vasomotor reactivity tests.

CONCLUSION

Spatially resolved spectroscopy provides an encouraging, noninvasive new tool to study cerebral tissue oxygenation during vasomotor reactivity tests consistent with physiological changes.

Novel cerebral physiologic monitoring to guide low-flow cerebral perfusion during neonatal aortic arch reconstruction

OBJECTIVE

This study was undertaken to describe the combined measurement of cerebral blood flow velocity and cerebral oxygen saturation as a guide to bypass flow rate for regional low-flow perfusion during neonatal aortic arch reconstruction.

METHODS

Data were prospectively collected from 34 patients undergoing neonatal aortic arch reconstruction with regional low-flow perfusion. Cerebral oxygen saturation and blood flow velocity were measured by near-infrared spectroscopy and transcranial Doppler ultrasonography, respectively, throughout cardiopulmonary bypass. After cooling to 17 degrees C to 22 degrees C, baseline values of cerebral oxygen saturation and blood flow velocity were recorded during full-flow bypass. Regional low-flow perfusion was instituted for aortic arch reconstruction, and bypass flow rate was adjusted to maintain cerebral oxygen saturations and blood flow velocities within 10% of baseline recorded during cold full-flow bypass. Cerebral oxygen saturations and blood flow velocities were recorded again after repair during full-flow hypothermic bypass. Bypass flow during regional low-flow perfusion was recorded, as were arterial pressure and blood gas data. One-way repeated measures analysis of variance was used to determine differences in values during regional low-flow perfusion relative to baseline and after perfusion.

RESULTS

A mean bypass flow of 63 mL/(kg x min) was required to maintain cerebral oxygen saturations and blood flow velocities within 10% of baseline. Mean arterial pressure had a poor correlation with the required bypass flow rate (r(2) = 0.006 by linear regression analysis). Fourteen of 34 patients had a cerebral oxygen saturation of 95% during regional low-flow perfusion, placing them at risk for cerebral hyperperfusion if the cerebral oxygen saturation had been used alone to guide bypass flow. Pressure was detected in the umbilical or femoral artery catheter (mean 12 mm Hg) in all patients during regional low-flow perfusion.

CONCLUSIONS

Cerebral blood flow velocity, as determined by transcranial Doppler ultrasonography, adds valuable information to cerebral oxygen saturation data in guiding bypass flow during regional low-flow perfusion. Its most important use may be prevention of cerebral hyperperfusion during periods with high near-infrared spectroscopic saturation values.

Cerebral tissue oxygenation index in very premature infants

AIM

To describe normal values of the cerebral tissue oxygenation index (TOI) in premature infants.

METHODS

TOI was measured by spatially resolved spectroscopy in preterm infants on the first 3 days of life. Infants with an abnormal cranial ultrasound were excluded. Other simultaneously measured variables were PaO(2), PaCO(2), pH, mean arterial blood pressure, heart rate, haemoglobin, glycaemia, and peripheral oxygen saturation.

RESULTS

Fifteen patients with a median postmenstrual age of 28 weeks were measured. There was a significant increase in median TOI over the first 3 days of life: 57% on day 1, 66.1% on day 2, and 76.1% on day 3. Multiple regression analysis showed no correlation between TOI and postmenstrual age, peripheral oxygen saturation, mean arterial blood pressure, PaO(2), PaCO(2), and haemoglobin concentration.

CONCLUSION

Cerebral TOI increases significantly in the first 3 days of life in premature babies. This increase probably reflects the increase in cerebral blood flow at this time.

Dynamic cerebral autoregulatory response to blood pressure rise measured by near-infrared spectroscopy and intracranial pressure

OBJECTIVES

Noninvasive near-infrared spectroscopy (NIRS) continuously monitors changes in cerebral hemoglobin saturation (Hb(Diff) ) and content (Hb(Total)). It may allow visualization of the dynamic cerebral autoregulatory response to rapid blood pressure increases without relevant contamination of the NIRS signal from extracerebral hemoglobin.

DESIGN

Prospective cohort study.

SETTINGS

Multidisciplinary pediatric intensive care unit.

PATIENTS

Six consecutive children in coma due to severe encephalopathy (head trauma, five patients; mumps encephalitis, one patient) requiring artificial ventilation, invasive arterial blood, and intracranial pressure monitoring.

INTERVENTIONS

Frontotemporal recording of Hb(Diff) and Hb(Total) while rapidly elevating blood pressure by bolus injection of phenylephrine.

MEASUREMENTS AND RESULTS

During an increase of blood pressure of 13 +/- 1 mm Hg with a "rise time" of 16 +/- 1 secs (mean of a total of 31 injections +/- sem), a significant linear correlation was found between Hb(Diff) and intracranial pressure signals (mean coefficient, 0.46 +/- 0.04) but not between Hb(Total) and intracranial pressure. Three response patterns were observed. First, Hb(Diff) and intracranial pressure reduction, corresponding with vasoconstriction and normal dynamic autoregulation (n = 3); second, Hb(Diff) and intracranial pressure increase, corresponding with persistent vasodilation and abolished autoregulation (n = 11); and third, transient Hb(Diff) and intracranial pressure increase followed by a decrease at peak blood pressure elevation, called impaired autoregulation (n = 15). In one patient with fatal brain swelling, phenylephrine testing showed no effect on NIRS signals (n = 2). Furthermore, there were significant correlations between 31 pooled interindividual pairs of Hb(Diff) changes with intracranial pressure changes (values at baseline averaged over 60 secs subtracted from values at peak blood pressure elevation averaged over 5 secs), with a correlation coefficient of .82 (p <.001).

CONCLUSIONS

NIRS represents a new and promising technique for bedside determination of dynamic cerebral autoregulation during acutely induced blood pressure rise. The significant correlations found between NIRS signals and intracranial pressure excluded relevant extracerebral contamination of the NIRS signals. In our patients with severe encephalopathy, dynamic autoregulation was in most instances not fully preserved.

Cerebral oxygen saturation assessed by near-infrared spectroscopy during coronary artery bypass grafting and early postoperative cognitive function

BACKGROUND

Cerebral oxygen saturation (ScO2) can be assessed by near-infrared spectroscopy. We investigated the correlation between early postoperative cognitive performance and intraoperative ScO2 in a prospective observational setting.

METHODS

Forty-seven patients undergoing elective coronary artery bypass grafting with cardiopulmonary bypass underwent preoperative and postoperative neuropsychological evaluation. Patients were classified according to the presence or absence of postoperative cognitive dysfunction. Cognitive dysfunction was defined as an individual test score decrease of more than one standard deviation in two or more of the five tests. During operation ScO2 was continuously measured using an INVOS 4100 device. Cerebral oxygen saturation values were analyzed with reference to two cutoff points, which should reflect low cerebral oxygenation: an ScO2 less than 40% and a drop of more than 25% from individual baseline values. The duration and extent of ScO2 values below these two cutoff points was compared between the patients with and without cognitive dysfunction.

RESULTS

Sixteen patients (34%) showed postoperative cognitive dysfunction. Cerebral oxygen saturation values less than 40% occurred in 17 patients for a mean (+/- standard error of the mean) of 17.2 +/- 6.5 minutes, whereas a decrease of more than 25% from baseline values occurred in 37 patients for 52.7 +/- 7.8 minutes. The duration and extent below the two cutoff ScO2 values was similar in patients with and without cognitive dysfunction.

CONCLUSIONS

Intraoperative regional ScO2 as assessed by near-infrared spectroscopy with the INVOS 4100 device is not predictive for postoperative cognitive performance in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass.

Effect of deep hypothermia on cerebral hemodynamics during selective cerebral perfusion with systemic circulatory arrest

OBJECTIVE

We studied the effect of deep hypothermia on cerebral hemodynamics during selective cerebral perfusion with systemic circulatory arrest.

METHODS

Ten anesthesized pigs were placed on cardiopulmonary bypass and cooled to a rectal temperature of 22 degrees C (n = 5) or 15 degrees C (n = 5). During selective cerebral perfusion, the descending aorta was clamped and perfusion of the lower body was discontinued. As the pump flow was changed, we monitored the perfusion pressure, local cerebral blood flow, and local cerebral oxygenation using laser Doppler flowmetry and near-infrared spectroscopy. We also measured the free flow of the left internal thoracic artery during selective cerebral perfusion.

RESULTS

Perfusion pressure and local cerebral blood flow decreased as the pump flow decreased. Oxygenated and deoxygenated hemoglobin in cerebral tissue remained unchanged at a perfusion flow of 10 ml/kg/min, whereas oxygenated hemoglobin decreased and deoxygenated hemoglobin increased progressively and reciprocally as the pump flow decreased. The pump flow for maintaining perfusion pressure above 35 mmHg with stabilized local cerebral oxygenation was significantly higher at 15 degrees C than at 22 degrees C. The internal thoracic artery free flow was higher at 15 degrees C than at 22 degrees C.

CONCLUSIONS

Selective hypothermic cerebral perfusion with systemic circulatory arrest produces an extracranial shunt through the internal thoracic artery, especially under deep hypothermia. Our data suggests that selective cerebral perfusion during deep hypothermia is best managed by perfusion pressure control rather than by flow control.

The effects of low-pressure carbon dioxide pneumoperitoneum on cerebral oxygenation and cerebral blood volume in children

We examined the effects of low-pressure carbon dioxide pneumoperitoneum on regional cerebral oxygen saturation (ScO(2)) and cerebral blood volume (CBV) in children. Fifteen children, ASA I--III, scheduled for laparoscopic fundoplication, were investigated in the head-up position (10) and ventilated to a baseline end-tidal CO(2) (PETCO(2)) between 25 and 33 mm Hg. Ventilatory settings remained unchanged during the operation. ScO(2) and CBV were assessed with near-infrared spectroscopy and recorded together with end-tidal and arterial carbon dioxide (PaCO(2)) at 5 time points: before insufflation, 30, 60, and 90 min after the start of CO(2) insufflation, and 10 min after desufflation. The intraabdominal pressure was kept between 5 and 8 mm Hg. During insufflation, PETCO(2) increased from 30.0 plus minus 2.8 to 38.3 plus minus 5.1 mm Hg (P < 0.001) and PaCO(2) increased from 32.0 plus minus 4.7 to 40.4 plus minus 5.9 mm Hg (P < 0.001). ScO(2) increased by 15.7% plus minus 8.8% (from 61 plus minus 9 to 70 plus minus 9 arbitrary units ) (P < 0.001). CBV increased by 4.6% plus minus 8.8% (from 123 plus minus 66 to 128 plus minus 66 arbitrary units [P = 0.048]). After desufflation, PETCO(2) and PaCO(2) decreased, but did not return to preinsufflation values. ScO(2) and CBV also decreased after desufflation. In conclusion, hyperventilation and the head-up position before CO(2) insufflation are not sufficient to prevent the CO(2)-mediated cerebral hemodynamic effects of low-pressure pneumoperitoneum (5--8 mm Hg) in children.

IMPLICATIONS

Peritoneal CO(2) absorption during laparoscopic surgery causes hypercapnia and CO(2)-mediated cerebral hemodynamic effects. Hyperventilation and the head-up position before CO(2) insufflation is not sufficient to counteract these effects of low-pressure pneumoperitoneum (5--8 mm Hg) in children.

Cerebral oxygenation monitoring for total arch replacement using selective cerebral perfusion

BACKGROUND

This study was undertaken to verify the safety of our total arch replacement assisted by selective cerebral perfusion with respect to cerebral oxygenation.

METHODS

Subjects to be evaluated were selected between February 1999 and March 2000 and comprised 13 patients who underwent total arch replacement (TAR) (TAR group) and 18 patients who had undergone coronary artery bypass grafting or valve replacement (control group). They were monitored throughout the operation by two-channel near-infrared spectroscopy. Changes in intracranial oxyhemoglobin and the tissue oxygenation index were compared between the two groups. Additionally, jugular venous oxygen saturation was simultaneously measured in 10 patients from each group. Maximum changes in these variables from baseline in the TAR group were compared with those in the control group. Bilateral oxygenation differences between two hemispheres were also evaluated.

RESULTS

There was no incidence of postoperative cerebral infarction, and no significant difference was observed in the maximum decrease in these variables between the two groups. Bilateral oxygenation differences between the two hemispheres in the TAR group were similar to those in the control group, except for the tissue oxygenation index in the rewarming phase.

CONCLUSIONS

From the standpoint of cerebral oxygenation, our technique of total arch replacement was nearly as safe as an ordinary cardiac operation.

Spatially resolved spectroscopy (NIRO-300) does not agree with jugular bulb oxygen saturation in patients undergoing warm bypass surgery

PURPOSE

Near infrared spectroscopy (NIRS) is a promising non-invasive method for continuous monitoring of cerebral oxygenation during cardiac surgery with cardiopulmonary bypass (CPB). This study was designed to study the agreement between tissue oxygen index (TOI) measured by spatially resolved spectroscopy (NIRO-300) and jugular bulb oxygen saturation (SjO2) in patients undergoing warm coronary bypass surgery.

METHODS

Seventeen patients undergoing warm coronary artery bypass surgery were studied. NIRS was continuously monitored and was averaged before CPB, five, 20, 40, 60 min on CPB, five minutes before end of CPB and ten minutes after CPB to coincide with SjO2 measurements. Bypass temperature was maintained at 34-37 degrees C.

RESULTS

Bland and Altman analysis showed a bias (TOI-SjO2) of -6.7%, and wide limits of agreement (from 16% to -28%) between the two methods. In addition, mean TOI was lower than mean SjO2 during and after CPB. We observed a statistically significant correlation between arterial carbon dioxide and SjO2 measurements (r2=0.33; P=0.0003), but the former did not correlate with TOI values (r2=0.001; P=0.7).

CONCLUSION

Our results demonstrate a lack of agreement between SjO2 and TOI for monitoring cerebral oxygenation during cardiac surgery. We conclude that the two methods are not interchangeable.

Cerebral oximetry for the detection of cerebral ischemia during temporary carotid artery occlusion

The near-infrared spectroscopy cerebral oximeter was assessed as a monitoring device for detecting and/or predicting cerebral ischemia during carotid endarterectomy (CEA) and the balloon occlusion test in 24 patients, 12 males and 12 females aged 28 to 77 years (mean 59.9 years). Tolerance testing of complete internal carotid artery (ICA) occlusion by balloon inflation for 20 minutes was performed in nine patients (cerebral aneurysm 6, neck tumor 3) and CEA was performed in 15 patients. The probe of the cerebral oximeter was placed on the forehead of the affected side and regional cerebral oxygen saturation (rSO2) was monitored continuously during all procedures. Stump pressure was measured just after ICA occlusion. Collateral circulation detected by digital subtraction angiography was classified into three groups: good, moderate, or poor. Stump pressure was 41-90 mmHg (mean 61.3 mmHg) in the good collateral circulation group, 40-43 mmHg (41.5 mmHg) in the moderate group, and 14-30 mmHg (23.8 mmHg) in the poor group. Change in rSO2 after ICA occlusion was +3.5(-)-4.2% (mean -1.6%) in the good collateral circulation group, -1.2(-)-6.6% (-3.2%) in the moderate group, and -2.4(-)-10.2% (-6.6%) in the poor group. Changes in rSO2 were significantly different between the good and poor collateral circulation groups (p < 0.01). A greater than 5% fall in rSO2 was observed in 0 of 15 patients in the good collateral circulation group, one of five in the moderate group, and three of four in the poor group. The cerebral oximeter is a useful, real-time, non-invasive method to measure brain oxygenation during CEA, skull base surgery, or other procedures which need to evaluate brain ischemia. A fall of greater than 10% from the rSO2 baseline value is dangerous, but less than 5% is safe.

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

BACKGROUND

Near-infrared spectroscopy (NIRS) is used to monitor cerebral oxygenation during cardiac surgery. However, interpretation of the signals is controversial. The aim of the study was to determine which NIRS variable best correlated with brain damage as assessed by animal behavior and neurohistologic score and to compare the accuracy of NIRS and magnetic resonance spectroscopy (MRS) in predicting brain injury.

METHODS

Forty 5-week-old piglets underwent 60 minutes of deep hypothermic circulatory arrest (DHCA) at 15 degrees C. Changes in brain adenosine triphosphate (ATP), phosphocreatine (PCr), and intracellular pH (pHi) were determined by MRS and correlated to changes in oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and oxidized cytochrome a,a3 (CytOx) NIRS signals. Brains were fixed on day 4 and examined using a neurohistologic score.

RESULTS

Reductions in CytOx and HbO2 values were correlated closely with decreases in ATP, PCr, and pHi. The changes in CytOx and PCr showed the strongest correlation (r = 0.623). Maximal CytOx reduction during DHCA of more than -25 microM * differential pathlength factor (DPF) predicted brain damage with a sensitivity of 100% and a specificity of 75%. The histologic score was also correlated with a decrease in ATP (r = -0.52 for CytOx; r = -0.32 for ATP); HbO2, PCr, and pHi showed no correlations.

CONCLUSIONS

Reduction in CytOx correlates with decreased brain energy state and predicts histologic brain injury after DHCA with a high sensitivity. These data suggest that the level of CytOx could be a very important predictor of brain damage during DHCA.

New technologies in pediatric neurology. Near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a relatively new technology that offers the enormous advantage of making measurements in vivo of changes in cerebral hemodynamics and oxygenation. Because NIRS is noninvasive and portable, it can provide real-time measurements of these changes at the bedside. Thus NIRS is ideally suited to the study of many physiological and pathological processes affecting the brain, particularly in the infant or young child in the intensive care unit or operating room. This review outlines the basic principles, advantages, and limitations of the current state of NIRS technology. An emphasis is placed on the animal and clinical studies that are relevant to the field of child neurology, with an eye to the future evolution and potential applications of this promising technique.

A multiwavelength frequency-domain near-infrared cerebral oximeter

This study tests a multiwavelength frequency-domain near-infrared oximeter (fdNIRS) in an in vitro model of the human brain. The model is a solid plastic structure containing a vascular network perfused with blood in which haemoglobin oxygen saturation (SO2) was measured by co-oximetry, providing a standard for comparison. Plastic shells of varying thickness (0.5-2 cm), with a vascular network of their own and encircling the brain model, were also added to simulate extracranial tissues of the infant, child and adult. The fdNIRS oximeter utilizes frequency-domain technology to monitor phaseshifts at 754 nm, 785 nm and 816 nm relative to a 780 nm reference to derive SO2 through photon transport and Beer-Lambert equations. We found a linear relationship between fdNIRS SO2 and co-oximetry SO2 with excellent correlation (r2 > or = 0.95) that fitted the line of identity in all experiments (n = 7). The bias of fdNIRS oximetry was -2% and the precision was 6%. Blood temperature and fdNIRS source-detector distance did not affect fdNIRS oximetry. Low haemoglobin concentration (6 g dl(-1)) altered the fdNIRS versus co-oximetry line slope and intercept, producing a 15% error at the extremes of SO2. The infant- and child-like shells overlying the brain model did not alter fdNIRS oximetry, whereas the adult-like shell yielded an error as high as 32%. In conclusion, fdNIRS accurately measures SO2 in an in vitro brain model, although low haemoglobin concentration and extracranial tissue of adult thickness influence accuracy.

Cerebral oxygenation during paediatric cardiac surgery: identification of vulnerable periods using near infrared spectroscopy

OBJECTIVE

Neurologic sequelae remain a well recognised complication of paediatric cardiac surgery. Monitoring of cerebral oxygenation may be a useful technique for identifying vulnerable periods for the development of neurologic injury. We sought to measure regional cerebral oxygenation in children undergoing cardiac surgery using near infrared spectroscopy to ascertain such vulnerable periods.

METHODS

Observational study of 18 children (median age 1.3 years) undergoing cardiac surgery (17 with cardiopulmonary bypass, 8 with circulatory arrest). Regional cerebral oxygenation was monitored using the INVOS 3100 cerebral oximeter and related to haemodynamic parameters at each stage of the procedure.

RESULTS

Prior to the onset of bypass, 10 patients had a decrease in regional cerebral oxygenation of > or = 15% points, reaching an absolute haemoglobin saturation less than 35% in 5 cases. The most common cause was handling and dissection around the heart prior to and during caval cannulation. With institution of bypass, regional cerebral oxygenation increased by a mean 18% points to a mean maximum of 75%. During circulatory arrest regional cerebral oxygenation decreased with rate of decay influenced by temperature at onset of arrest (0.25%/min at < 20 degrees C; 2%/min at > 20 degrees C). Reperfusion caused an immediate increase in regional cerebral oxygenation followed by a decrease during rewarming. Discontinuation of bypass caused a precipitous decrease in regional cerebral oxygenation in 5 patients, reaching less than 50% in 3 patients.

CONCLUSIONS

These observations suggest that the pre- and early post-bypass periods are vulnerable times for provision of adequate cerebral oxygenation. Near infrared spectroscopy is a promising tool for monitoring O2 supply/demand relationships especially during circulatory arrest.

Cerebral oxygenation during cardiopulmonary bypass

Cerebral fractional oxygen extraction (FOE) was monitored in 30 children, using near infrared spectroscopy during cardiopulmonary bypass, to investigate the effect of hypothermia and circulatory arrest. One group of children (n = 15) underwent profound hypothermia with total circulatory arrest (n = 8) or continuous flow (n = 7). Another group (n = 15), of whom only one had circulatory arrest, underwent mild (n = 6) or moderate (n = 9) hypothermia. The mean FOE (SD) before bypass was 0.35 (0.12) and this correlated negatively with the preoperative arterial oxygen content (r = -0.58). Between the stage of cooling on bypass and cold bypass there was a reduction in FOE in all groups. Between cold bypass and rewarming there was an increase in FOE only in the groups with continuous flow. In the circulatory arrest group, the FOE remained low during rewarming and was significantly lower than that of the continuous flow group. No patients died and none had neurological abnormalities postoperatively. Apparent changes in oxidised cytochrome oxidase concentration were also monitored using near infrared spectroscopy. There was a fall in cytochrome aa3 on starting cardiopulmonary bypass, but there were no significant differences in the changes in cytochrome aa3 between any stage in any of the patient groups. Using this non-invasive technique, cooling was shown to reduce cerebral FOE. During rewarming on bypass there was an increase in cerebral FOE only in patients who had had continuous flow bypass. In contrast, the cerebral FOE in those with circulatory arrest remained constant after arrest and during the duration of the study. This may have implications for the timing of hypoxic brain injury.

[Blood flow velocity in the ophthalmic artery measured by Doppler ultrasonography during cardiopulmonary bypass--usefulness for cerebral perfusion monitor]

Brain blood flow is supplied from the internal carotid artery, and the ophthalmic artery is the first branch of the internal carotid artery. We studied how blood flow velocity in the ophthalmic artery (OAV) changes during cardiopulmonary bypass (CPB) and investigated whether it can be used to monitor brain blood flow during CPB. In 13 open heart surgeries in adults, OAV and blood flow velocity in the common carotid artery (CAV) were measured with Doppler ultrasonography, and blood flow volume in the brachiocephalic artery (BA flow) was measured simultaneously with an electromagnetic flow meter. Maximal blood flow velocity in the ophthalmic artery (OAVmax) and the common carotid artery (CAVmax) were 0.27 +/- 0.13 m/sec and 0.64 +/- 0.40 m/sec, BA flow was 486 +/- 226 ml/min before CPB. When CPB pump flow was varied (2.4, 2.2, 2.0, 2.2, 2.4 l/min/m2), the parameters during and after CPB changed as follows (as percentage of pre-CPB levels): OAVmax, 58.1%, 50.9%, 37.6%, 49.4%, 64.7%, 108.4%; CAVmax, 67.0%, 58.0%, 48.2%, 113.6%, 105.5%, 134.3%; and BAflow, 87.3%, 39.8%, 53.9%, 50.5%, 95.0%, 159.8%. Our results indicate that OAVmax more accurately reflects changes in pump flow than does CAVmax and BA flow. Because vessel resistance in the ophthalmic artery was small during CPB, OAVmax was thought to be determined mainly by CPB pump flow. OAVmax was useful for monitoring brain blood flow during CPB.

Cerebral effects in superior vena caval cannula obstruction: the role of brain monitoring

A pediatric cardiac case of transient obstruction of the superior vena cava by the venous cannula before cardiopulmonary bypass is presented. With venous obstruction and increase in central venous pressure, reduced cerebral blood flow velocities and absence of diastolic Doppler flow were detected. This was followed by regional cerebral venous oxygen desaturation and global electroencephalographic slowing. Reposition of the venous cannula led to the recovery of these physiologic indicators and a noncomplicated clinical outcome.

Near-infrared spectroscopic method for assessing the tissue oxygenation state of living lung

To quantify changes in tissue oxygenation of pathologic lungs, we applied a novel method using near-infrared spectroscopy (NIRs). In in vitro experiments, we assayed the effect of photon scattering on the absorption spectra of an in vitro system simulating structures of lung, which consists of test tube containing air in hematocrit tubes and red blood cell suspension with various predetermined hemoglobin concentrations. It was determined that photon scattering of the tissue containing air did not affect the absorption in the NIR region. In in vivo experiments, we tested the applicability of the NIRs technique in rat lungs under the following conditions: (1) hypoxic loading; (2) administration of an inhibitor (NaCN) of the mitochondrial respiratory chain; (3) hemorrhagic shock. We found that: (1) Changes in hemoglobin oxygenation state in the lung measured by NIRs depended on inspired oxygen concentrations; (2) NaCN-induced reduction of cytochrome oxidase a,a3 in the lung was observed; and (3) Total hemoglobin levels in the lung decreased after bleeding. Changes in the hemoglobin oxygenation state and cytochrome oxidase redox state in the lung were determined using the least-square-curve fitting for NIR absorption spectra. Our NIRs technique was capable of assessing the hemoglobin oxygenation and cytochrome oxidase redox state in the lung.

Evaluation of brain oxygenation during selective cerebral perfusion by near-infrared spectroscopy

BACKGROUND

Although selective cerebral perfusion (SCP) has been used for cerebral protection in aortic arch operations, the appropriate perfusion conditions of SCP are unclear.

METHODS

We used near-infrared spectroscopy, which evaluates brain ischemia noninvasively and continuously, to determine whether perfusion with SCP (core temperature, 20 degrees C; flow rate, 10 mL.kg-1.min-1) was acceptable in terms of oxyhemoglobin and deoxyhemoglobin in patients having SCP for aortic arch operations (SCP group, n = 6) versus patients having cardiopulmonary bypass (CPB) for coronary artery bypass grafting (CPB group, n = 6).

RESULTS

There were no significant differences in age (65 +/- 10 versus 63 +/- 12 years), CPB time (199 +/- 67 versus 199 +/- 52 minutes), changes in hematocrit (-12.9% +/- 3.7% versus -12.5% +/- 6.0%), lowest blood pressure (43 +/- 7 versus 45 +/- 10 mm Hg), or highest central venous pressure (8 +/- 2 versus 9 +/- 4 mm Hg) between the SCP and CPB groups. In the SCP group, the maximum decrease in oxyhemoglobin level and the maximum increase in deoxyhemoglobin level were -5.0 to -11.4 mumol/L and -0.1 to 3.9 mumol/L, respectively; in the CPB group, the respective changes were -3.2 to -14.2 mumol/L and -0.4 to 3.6 mumol/L. Changes of oxyhemoglobin and deoxyhemoglobin levels in the SCP group were almost within the range of those in the CPB group. There were no brain complications in either group.

CONCLUSIONS

As described here, SCP is acceptable and safe for brain protection in aortic arch procedures.

Cerebral hemoglobin and optical pathlength influence near-infrared spectroscopy measurement of cerebral oxygen saturation

Near-infrared spectroscopy (NIRS) is a noninvasive optical technique to monitor cerebral oxygen saturation at the bedside. Despite its applicability, NIRS has had limited clinical use because of concerns about accuracy, noted by intersubject variability in slope and intercept of the line between NIRS- and weighted-average arterial-cerebrovenous saturation (SMO2). This study evaluated transcranial optical pathlength and cerebral hemoglobin concentration as sources for this intersubject variability. Experiments were performed in an in vitro brain model and in piglets. Optical pathlength and cerebral hemoglobin concentration were measured by time-resolved spectroscopy (TRS). NIRS and TRS were recorded in the model, as perfusate blood saturation was varied (0%-100%) at several hemoglobin concentrations, and in piglets, as SMO2 was varied (15%-90%) before and after hemodilution. In the model, hemoglobin concentration significantly altered the NIRS versus blood saturation line slope and intercept, as well as optical pathlength. In piglets (before hemodilution), there was significant intersubject variability in NIRS versus SMO2 line slope (0.73-1.4) and intercept (-24 to 36) and in transcranial optical pathlength (13.4-16 cm) and cerebral hemoglobin concentration (0.58-1.1 g/dL). By adjusting the NIRS algorithm with optical pathlength or cerebral hemoglobin measurements, intersubject variability in slope (0.9-1.2) and intercept (-9 to 18) decreased significantly. Hemodilution significantly changed NIRS versus SMO2 line slope and intercept, as well as transcranial optical pathlength and cerebral hemoglobin concentration (before versus after hemodilution: slope 0.9 vs 0.78, intercept 13 vs 19, pathlength 13.9 vs 15.6 cm, cerebral hemoglobin 0.98 vs 0.73 g/dL). By adjusting the NIRS algorithm with the cerebral hemoglobin measurements, slope and intercept remained unchanged by hemodilution. These data indicate that intersubject variability in NIRS originates, in part, from biologic variations in transcranial optical pathlength and cerebral hemoglobin concentration. Instruments to account for these factors may improve NIRS cerebral oxygen saturation measurements.