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

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.

Changes in cerebral oxygenation in children undergoing surgical repair of ventricular septal defects

There have been few published studies on changes in cerebral oxygenation during paediatric cardiac surgery as measured by conventional near-infrared spectroscopy. We studied changes in cerebral oxygenation in 16 children undergoing surgical repair of ventricular septal defects. Fifteen of the patients showed similar patterns of changes: brain tissue concentrations of oxyhaemoglobin decreased significantly during cardiopulmonary bypass, whereas there was no significant change in brain tissue concentrations of deoxyhaemoglobin. In the remaining patient, who suffered decreased blood flow to the lower body during surgery, the pattern of changes was different to that of the other subjects. This patient suffered postoperative respiratory and renal failure. This study suggests that conventional near-infrared spectroscopy may be useful for clinical monitoring during ventricular septal defect repair.

Neuroanesthesia. Innovative techniques and monitoring

Advances in neuromonitoring have provided insights into neurologic function during anesthesia. Despite the limitations and necessary caution when using intraoperative monitors to interpret neural function, these technologies have been definite steps in the right direction for assessing neural integrity and level of consciousness during anesthesia. The techniques discussed minimize the adverse sequelae of a variety of neurosurgical and orthopedic procedures, reducing the morbidity rates/risks in the perioperative period. Furthermore, it is likely that such monitoring will become a standard of care, similar to other monitoring standards such as pulse oximetry and capnography. Accurate and reliable monitoring is essential, and on-going large prospective studies comparing the processed EEG or evoked potential with definable end points in both adult and pediatric populations will be necessary. The use of monitoring, such as the BIS, may improve cost efficiency by reducing the total amount of drug used to maintain anesthesia, as well as enhance recovery. A danger in this process, however, is the potential for public opinion, outside regulatory bodies, or medico-legal implications to drive change and enforce standards of care before appropriate data are available.

Near infrared spectroscopy for intraoperative monitoring of the spinal cord

STUDY DESIGN

Animal model study of three healthy commercial pigs was conducted.

OBJECTIVE

To determine whether near infrared spectroscopic monitoring of the spinal cord is feasible, and whether changes in near infrared spectroscopy correlate with changes in blood flow to the cord or operative maneuvers.

SUMMARY OF BACKGROUND DATA

Near infrared spectroscopy is a noninvasive continuous monitoring tool capable of measuring absolute changes in the concentration of three chromophores: oxygenated hemoglobin, deoxygenated hemoglobin, and cytochrome aa3, the terminal enzyme in the electron transfer chain and a measure of cellular energy equilibrium. Near infrared spectroscopy has been used to monitor the brain intraoperatively in multiple circumstances. The authors hypothesized that near infrared spectroscopy could be used to monitor the spinal cord's cellular energy equilibrium during spinal surgery (i.e., that vascular compromise could be identified before irreversible damage occurred).

METHODS

The posterior elements of the spine were exposed, and near infrared spectroscopy optodes (fiberoptic bundles) were sutured to either the lamina or the spinous processes of T9, T10, or both and directed toward the spinal cord. Interventions included manipulation of oxygen saturation and distraction of the T9-T10 disc space.

RESULTS

With reduced oxygen delivery (lower arterial oxygen saturation and blood flow), oxygenated hemoglobin concentration decreased and deoxygenated hemoglobin concentration increased. With distraction, blood volume (oxygenated hemoglobin plus deoxygenated hemoglobin) decreased, and cytochrome aa3 became more oxidized. Changes were apparent within 1 second of the intervention beginning, and recovery to the baseline of near infrared spectroscopy occurred with relief of each intervention.

CONCLUSIONS

This near infrared spectroscopy technique monitors changes in oxygenation of the spinal cord, and therefore appears capable of intraoperative warning about impending vascular compromise of the spinal cord.

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.

Aortic arch branches are no longer a blind zone for transesophageal echocardiography: a new eye for aortic surgeons

OBJECTIVES

Branch arteries of the aortic arch have been a blind zone for transesophageal echocardiography. Information regarding blood flow, which is important in both planned and emergency operations on the aorta, has therefore been limited. We have established a technique for visualizing these arteries in nearly all cases.

METHODS

In 25 consecutive patients requiring either planned or emergency operations on the aorta, the branch arteries were visualized whenever cerebral malperfusion was suspected. Lateral flexion of the probe tip was used when the trachea interfered with visualization of the arteries.

RESULTS

The left subclavian, left and right common carotid, right subclavian, innominate, and left and right vertebral arteries were visualized in 96% (24/25), 92% (23/25), 96% (24/25), 100% (25/25), 84% (21/25), 92% (22/24), and 88% (21/24), respectively. The origin of the innominate artery was visualized in 36% (9/25). In some cases, dissection extended into branch arteries during surgery or during conservative therapy. When the subclavian artery was clamped, retrograde flow was detected in the vertebral artery (steal flow). The cannula for selective cerebral perfusion occasionally was entered into the right common carotid or subclavian artery and obstructed the other branch with a balloon.

CONCLUSIONS

The branch arteries of the aortic arch, including the vertebral artery, are no longer a blind zone for transesophageal echocardiography. The information obtained with our new transesophageal echocardiography technique is helpful for diagnosis, monitoring, and decision making during aortic surgery and in critical care medicine. Visualizing these vessels is worth the effort.

Comparison of two commercially available near-infrared spectroscopy instruments for cerebral oximetry. Technical note

Two near-infrared spectroscopy (NIRS) devices were compared with regard to their responses to changes in cerebral hemoglobin oxygenation induced by hypoxia and hypercapnia in five healthy volunteers. Sensors belonging to each NIRS device were placed on opposite sides of the volunteer's forehead. The INVOS-3100A device, approved by the United States Food and Drug Administration, records the percentage of oxyhemoglobin (HbO2) saturation and the investigational NIRO500 device records absolute changes in HbO2, deoxyhemoglobin, and total hemoglobin in micromolar concentrations referenced to an arbitrary baseline. The volunteers breathed separate mixtures of 7% CO2 in O2 and 10% O2 for 5 minutes in random order. Arterial blood pressure, end-tidal CO2 (ETCO2), arterial O2 saturation, and electrocardiographic data were continuously monitored. Hypercapnia increased (p < 0.01) ETCO2 from 42+/-2 to 56+/-3 mm Hg (mean +/- standard deviation), resulting in a 7.3+/-0.2% increase (p < 0.005) in cerebral HbO2 saturation detected by the INVOS3100A device and an 11.6+/-3 microM increase (p < 0.0008) in HbO2 detected by the NIRO500. Hypoxia decreased (p < 0.01) arterial HbO2 saturation from 98+/-1 to 87+/-3%, causing a 5.1+/-1.2% decrease (p < 0.01) in the percentage of HbO2 saturation detected by the INVOS3100A device and a 9.7+/-6.3 microM decrease in HbO2 detected by the NIRO500. The responses of the NIRO500 and the INVOS3100A instruments to changes in cerebral oxygenation resulting from hypercapnia and hypoxia were generally similar; however, responses tended to be greater when recorded by the NIRO500 device, perhaps because, unlike the INVOS3100A device, the NIRO500 does not correct for skin and bone contamination.

Monitoring regional cerebral oxygen saturation using near-infrared spectroscopy during pulsatile hypothermic cardiopulmonary bypass in a neonatal piglet model

Impairment of cerebral oxygenation in neonates and infants after hypothermic nonpulsatile cardiopulmonary bypass (CPB) support is well documented. The objectives of this study were: 1) using a neonatal piglet model to continuously monitor the regional cerebral oxygen saturation (rSO2) by near-infrared spectroscopy during pulsatile hypothermic CPB; and 2) to quantify the pulsatile flow in terms of energy equivalent pressure (EEP). After initiation of CPB, all piglets (n = 5) were subjected to 15 minutes of core cooling, reducing the rectal temperature to 25 degrees C, followed by 60 minutes of hypothermic CPB, then 10 minutes of cold reperfusion, and 30 minutes of rewarming. During CPB, mean arterial pressures (MAPs) and pump flow rates were maintained at 40-45 mm Hg and 150 ml/kg/min, respectively. During normothermic CPB, the rSO2 was significantly increased, compared with the pre-CPB level (56.8 +/- 5.2% vs. 41.8 +/- 5.5%, p < 0.01). At the end of cooling, the rSO2 level was 76.8 +/- 8.6% (p < 0.001 vs. pre-CPB). After 60 minutes of hypothermic CPB and 30 minutes of rewarming, the rSO2 level was decreased to 38.6 +/- 4.2%, which was not significantly different compared with the pre-CPB level. The average increase in pressure (from MAP to EEP) was 5 +/- 1%, and the average increase in extracorporeal circuit pressure (from ECCP to EEP) was 13 +/- 2%. This extra pressure may help to provide better regional cerebral oxygen saturation. During pulsatile CPB, there was no rSO2 deficiency in this high flow model. Near-infrared spectroscopy responded well to changes in rSO2 during different stages of these experiments and might be a helpful tool for intraoperative monitoring.

Early detection of neurologic injury and issues of rehabilitation after pediatric cardiac extracorporeal membrane oxygenation

Neurological impairment results in a significant population of children after extracorporeal membrane oxygenation (ECMO) for treatment of otherwise intractable circulatory failure. Pre-ECMO hypoxia/ischemia, reperfusion injury, and impaired cerebral perfusion during low output situations possibly aggravated by harmful effects of a pulsatile perfusion are discussed in terms of possible etiological reasons. To develop preventive strategies or to enable curative measure, early detection of neuronal injury seems mandatory. Electroencephalographic surveillance and/or monitoring of evoked potentials and monitoring of cerebral oxygenation by means of near infrared spectroscopy or jugular venous bulb oxygen saturation, as well as measurements of serum neuron specific enolase, S-100 protein, and brain type creatine kinase can be employed clinically. To improve functional outcome following neuronal injury, early rehabilitation seems essential to minimize the resulting effects on physical, cognitive, and emotional development.