Effect of extracorporeal membrane oxygenation on cerebral blood flow and cerebral oxygen metabolism in newborn sheep

Cerebral Autoregulation: A Target for Improving Neurological Outcomes in Extracorporeal Life Support

Despite improvements in survival after illnesses requiring extracorporeal life support, cerebral injury continues to hinder successful outcomes. Cerebral autoregulation (CA) is an innate protective mechanism that maintains constant cerebral blood flow in the face of varying systemic blood pressure. However, it is impaired in certain disease states and, potentially, following initiation of extracorporeal circulatory support. In this review, we first discuss patient-related factors pertaining to venovenous and venoarterial extracorporeal membrane oxygenation (ECMO) and their potential role in CA impairment. Next, we examine factors intrinsic to ECMO that may affect CA, such as cannulation, changes in pulsatility, the inflammatory and adaptive immune response, intracranial hemorrhage, and ischemic stroke, in addition to ECMO management factors, such as oxygenation, ventilation, flow rates, and blood pressure management. We highlight potential mechanisms that lead to disruption of CA in both pediatric and adult populations, the challenges of measuring CA in these patients, and potential associations with neurological outcome. Altogether, we discuss individualized CA monitoring as a potential target for improving neurological outcomes in extracorporeal life support.

Moving Towards Therapy in SCA1: Insights from Molecular Mechanisms, Identification of Novel Targets, and Planning for Human Trials

The spinocerebellar ataxias (SCAs) are a group of neurodegenerative disorders inherited in an autosomal dominant fashion. The SCAs result in progressive gait imbalance, incoordination of the limbs, speech changes, and oculomotor dysfunction, among other symptoms. Over the past few decades, significant strides have been made in understanding the pathogenic mechanisms underlying these diseases. Although multiple efforts using a combination of genetics and pharmacology with small molecules have been made towards developing new therapeutics, no FDA approved treatment currently exists. In this review, we focus on SCA1, a common SCA subtype, in which some of the greatest advances have been made in understanding disease biology, and consequently potential therapeutic targets. Understanding of the underlying basic biology and targets of therapy in SCA1 is likely to give insight into treatment strategies in other SCAs. The diversity of the biology in the SCAs, and insight from SCA1 suggests, however, that both shared treatment strategies and specific approaches tailored to treat distinct genetic causes of SCA are likely needed for this group of devastating neurological disorders.

Cerebral Pathophysiology in Extracorporeal Membrane Oxygenation: Pitfalls in Daily Clinical Management

Extracorporeal membrane oxygenation (ECMO) is a life-saving technique that is widely being used in centers throughout the world. However, there is a paucity of literature surrounding the mechanisms affecting cerebral physiology while on ECMO. Studies have shown alterations in cerebral blood flow characteristics and subsequently autoregulation. Furthermore, the mechanical aspects of the ECMO circuit itself may affect cerebral circulation. The nature of these physiological/pathophysiological changes can lead to profound neurological complications. This review aims at describing the changes to normal cerebral autoregulation during ECMO, illustrating the various neuromonitoring tools available to assess markers of cerebral autoregulation, and finally discussing potential neurological complications that are associated with ECMO.

Successful primary use of VVDL+V ECMO with cephalic drain in neonatal respiratory failure

OBJECTIVE

To describe the use of double-lumen venovenous (VVDL) extracorporeal membrane oxygenation (ECMO) with cephalic draining cannula (VVDL+V) as a primary approach for all neonatal respiratory diagnoses and to compare our single-center experience with data as collected in the Extracorporeal Life Support Organization (ELSO) database.

STUDY DESIGN

We retrospectively reviewed all cases of ECMO for neonatal respiratory failure performed in the neonatal intensive-care unit at a large referral children's hospital, the Children's Healthcare of Atlanta at Egleston (CHOA-E). Comparisons were then made to neonatal respiratory ECMO data retrieved from the ELSO database.

RESULTS

At CHOA-E 162 of 189 cases were completed with the VVDL+V approach. Survival in the VVDL+V cohort was 89.1% versus 68.7% from ELSO, P<0.001. For those complications considered, the overall risk of complication favored the CHOA-E VVDL+V group as compared with ELSO (odds ratio (OR) 0.71 (0.52-0.7)) as did the risk of neurologic complications (OR 0.29, (0.15-0.58)), including intracranial hemorrhage (OR 0.39 (0.18-0.97), P=0.011).

CONCLUSION

The VVDL+V approach can be used successfully as the primary approach for ECMO for neonatal respiratory failure of various etiologies and in this single-center cohort this approach was associated with improved survival and lower rates of complication as compared with the ELSO database.

The association of carotid artery cannulation and neurologic injury in pediatric patients supported with venoarterial extracorporeal membrane oxygenation*

OBJECTIVES

To describe the prevalence of neurologic injury in a recent cohort of patients 18 years old or younger cannulated for venoarterial extracorporeal membrane oxygenation. To evaluate the association of carotid artery cannulation with neurologic injury when compared with other cannulation sites. To determine if age impacts the association of carotid artery cannulation with neurologic injury.

DESIGN

Retrospective analysis of data from the Extracorporeal Life Support Organization registry.

SETTING

Neonatal and pediatric medical/surgical and cardiac ICUs of 118 international tertiary care centers worldwide.

PATIENTS

Pediatric patients 18 years old or younger cannulated for venoarterial extracorporeal membrane oxygenation and reported to the Extracorporeal Life Support Organization registry during 2007 and 2008.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Two thousand nine hundred seventy-seven patients underwent venoarterial extracorporeal membrane oxygenation during the study period. Indications for extracorporeal membrane oxygenation included pulmonary (n = 1,390, 47%), cardiac (n = 1,168, 39%), extracorporeal membrane oxygenation during cardiopulmonary resuscitation (n = 418, 14%), and unknown (n = 1). Arterial cannulation sites were aorta (n = 938, 32%), femoral artery (n = 118, 4%), and carotid artery (n = 1,921, 64%). Overall, 611 patients (21%) had evidence of neurologic injury defined as seizures, infarction, and/or hemorrhage. The occurrence of neurologic injury varied significantly by cannulation site: femoral artery (n = 18, 15%), aorta (n = 160, 17%), and carotid artery (n = 433, 23%); p equals 0.001. Neonates represented the largest group of patients cannulated for venoarterial extracorporeal membrane oxygenation (n = 1,807, 61%), the majority of patients cannulated via the carotid artery (n = 1,276, 66%), and had the highest burden of neurologic injury (n = 398, 22%). Age, preextracorporeal membrane oxygenation high-frequency oscillatory ventilation use, preextracorporeal membrane oxygenation arterial pH and serum bicarbonate level, and preextracorporeal membrane oxygenation cardiac arrest were independently associated with neurologic injury in a covariate model. Carotid artery cannulation site was added to this adjusted model and found to independently increase odds of neurologic injury (odds ratio, 1.4 [95% CI, 1.01-1.69]). An interaction term containing age and cannulation site was not associated with neurologic injury (odds ratio, 1.06 [95% CI, 0.84-1.34]).

CONCLUSIONS

Carotid artery cannulation for venoarterial extracorporeal membrane oxygenation in patients 18 years old or younger is associated with statistically significant increased odds of neurologic injury. These increased odds are present across all age groups.

Extracorporeal membrane oxygenation: use in meconium aspiration syndrome

Extracorporeal membrane oxygenation (ECMO) has been successful as a rescue therapy for infants with respiratory failure with some diagnoses such as meconium aspiration syndrome (MAS) having a survival rate of more than 94%. New therapies have allowed many infants who would have required ECMO to be kept off ECMO, but at what cost. The survival rate for the neonatal ECMO patient has dropped over the years, whereas the time of ECMO has increased, indicating that the new therapies are keeping the less ill infants off ECMO. The major cause of non-survival in this population remains intraventricular hemorrhage. The primary risk factors related to this are thought to be pre-ECMO events, such as hypoxia and/or ischemia either prenatally or post-delivery. ECMO events that may complicate this are heparinization that is required while on ECMO and concern for the effect of shear stress and blood flow pattern changes created by the ECMO pump with venoarterial ECMO, although these changes are not seen in venovenous ECMO, the more common form of ECMO. Newer low-resistant microporous artificial lungs and miniaturized pumping systems may allow ECMO to be performed using less blood and safer equipment. The smaller low-resistant artificial lungs provide the ability to consider giving extracorporeal life support using only this membrane with flow provided by an arterial-venous shunt, thus eliminating the pumping system all together. Trials are ongoing in adults and, if effective, may direct further research into using this technique in newborns where the umbilical artery and vein could be used as the arterial-venous shunt.

Systemic hyperthermia induces ischemic brain injury in neonatal mice with ligated carotid artery and jugular vein

Postnatal d 7 (p7) or p12 mice had their right carotid artery (CA) and jugular vein (JV) ligated to mimic veno-arterial (VA) access for extracorporeal membrane oxygenation (ECMO). At p9-11 (early) or p19-21 (late) mice were exposed to hyperthermia or normothermia followed by assessment of neuropathological injury score. In separate cohorts of mice, cerebral and peripheral blood flow (CBF, PBF) and cerebral ATP content was measured. Hyperthermia resulted in ischemic brain injury in 57% and 77% of mice subjected to early or late hyperthermia, respectively. Isolated CA+JV ligation induced minimal injury (score 0.47 +/- 0.34) in 2/8 mice from the late normothermia group. No cerebral injury was detected in mice subjected to early normothermia. In 3/19 shams (2/10 early, 1/9 late) hyperthermia induced a subtle (score, 0.6 +/- 0.27) injury in the ipsilateral to the site of surgery cortex. CBF and PBF increased in response to hyperthermia in all mice. The rise in CBF was significantly attenuated in the "ligated" versus intact hemisphere, which was associated with a profound depletion of ATP content. Systemic hyperthermia induces ischemic brain injury in mice with ligated CA+JV. We speculate that hyperthermia/fever can be a potential risk factor for brain injury in infants treated with VA ECMO.

Cerebral Outcome in Adult Patients Treated With Extracorporeal Membrane Oxygenation

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) carries a high risk of brain injury. The aim of this study was to determine the cerebral status in 28 adult survivors on average 5.0 (range, 0.5 to 12) years after ECMO treatment for severe cardiorespiratory failure.

METHODS

All 28 patients were investigated at our institution. A comprehensive assessment protocol included a medical history, physical examination, neuropsychological assessment, electroencephalography, and neuroradiologic assessment.

RESULTS

All patients were ambulant unaided, and 43% were without any clinical findings. Impaired neuropsychological performance was found in 41%, neuroradiologic findings in 52%, and a pathologic electroencephalogram in 41% of the patients. There was a significant correlation between the cognitive outcome and neuroradiologic findings. The incidence of neuroradiologic findings (cerebral infarction, microemboli or hemorrhage) was significantly higher in the venoarterial group compared with the venovenous group (75% versus 17%). There was no correlation between the type of ECMO and neuropsychological impairment. Electroencephalography findings did not correlate with neuropsychological performance, nor with the neuroradiologic findings.

CONCLUSIONS

Late cerebral sequelae were frequently seen in patients treated on venoarterial ECMO. A significant correlation was found between cognitive impairment and neuroradiologic findings.

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.

The effect of extracorporeal life support on the brain: a focus on ECMO

Extracorporeal membrane oxygenation (ECMO) therapy has significantly improved outcome in the newborn, pediatric, and adult patient in respiratory and cardiac failure. Despite this therapy providing a life-saving technology, the morbidity in patients treated with ECMO therapy is primarily related to neurologic alterations and not pulmonary findings. For ECMO, this is not unexpected since most patients are being placed on ECMO support because of severe hypoxemia, with ECMO being considered a rescue therapy for respiratory failure in most instances. As use of ECMO becomes common place for infants and children in respiratory failure, our investigations into the outcome of these children must focus not only on survival versus nonsurvival, but on the causes of morbidity in this population. A further understanding of factors associated with morbidity may allow us to alter techniques used in extracorporeal life support (ECLS), hopefully to improve our long-term outcome in this population, while allowing us to expand use of these technologies to other populations such as the premature infant. This article will focus on the effect of ECMO on the brain, with the following chapter by Dr. Richard Jonas outlining the effect of cardiopulmonary bypass on the brain.

Cerebral blood flow and oxygenation during venoarterial and venovenous extracorporeal membrane oxygenation in the newborn lamb

BACKGROUND

Concern exists that extracorporeal membrane oxygenation (ECMO) may decrease cerebral blood flow (CBF), impair cerebral autoregulation, and thereby increase the risk of neurologic injury.

OBJECTIVE

This study was undertaken in newborn lambs to compare the effects of initiation of venoarterial and venovenous ECMO on CBF and cerebral oxygen delivery as measured by laser-Doppler flowmetry. This study also evaluates the effects of carotid artery and jugular vein ligation on CBF.

DESIGN

CBF, arterial blood pressure, sagittal sinus pressure, heart rate, cardiac output, arterial blood gases, and hemoglobin saturation were measured. After anesthesia, instrumentation, and a 1-2 hr stabilization period, values were recorded during a 30-min control period, and the carotid artery or jugular vein was cannulated. The animals were then studied during venoarterial or venovenous ECMO for 1 hr.

MAIN RESULTS

Carotid ligation resulted in a transient decrease in right cortex CBF that resolved within 60 secs. Next, during a 60-min period of venoarterial ECMO (flow rate of 100 mL.min(-1).kg(-1), n = 11), cerebral resistance to flow increased, CBF decreased 25%, and cerebral oxygen delivery decreased by 30%. Native cardiac output and Paco(2) remained constant. Pulsatility in the lingual artery, representing the pulsatility of arterial flow to the brain, decreased throughout venoarterial ECMO. In contrast, in those lambs receiving ECMO in the venovenous mode (n = 7), resistance to flow, CBF, cerebral oxygen delivery, and pulsatility did not change.

CONCLUSIONS

There was no sustained decrease in CBF after ligation of either the carotid artery or jugular vein. Venoarterial but not venovenous ECMO induced decreases of CBF that could not be attributed to changes in blood gases or blood pressure but that may relate to diminished pulsatility in cerebral resistance vessels or to differences in levels of circulating vasoactive compounds.

Longitudinal follow-up of a cohort of newborn infants treated with inhaled nitric oxide for persistent pulmonary hypertension

OBJECTIVE

To describe the outcome of a group of term newborn infants treated with inhaled nitric oxide for severe persistent pulmonary hypertension.

STUDY DESIGN

We performed a prospective longitudinal medical and neurodevelopmental follow-up of 51 infants treated as neonates for persistent pulmonary hypertension of the newborn with inhaled nitric oxide. The original number of treated infants was 87, of whom 25 died in the neonatal period; of 62 infants who survived, 51 were seen at 1 year of age and 33 completed a 2-year evaluation. Statistical analysis used population medians, means, and standard deviations for parameters assessed. Paired t tests and chi-square analysis were used to compare outcomes measured at 1 year with assessment at 2 years for the 32 infants seen at both 1- and 2-year visits.

RESULTS

At 1-year follow-up median growth percentiles were 20%, 72.5%, and 50% for weight, length, and occipitofrontal circumference, respectively. Thirteen of 51 infants (25.5%) were < 5th percentile in weight. Nine of 51 infants (17.6%) had feeding problems (need for gastrostomy feeding or gastroesophageal reflux), and 14 (27.5%) had a clinical diagnosis of reactive airways disease. Infant development as measured by the Bayley Scales of Infant Development was 104 +/- 16 for the mental development index and 97 +/- 20 for the psychomotor index. Six of 51 infants (11.8%) were found to have severe neurologic handicaps, defined as a Bayley score on either the mental development or psychomotor index of < 68, abnormal findings on neurologic examination, or both. Fewer children (6.1% vs 15.7%) required supplemental oxygen at 2 years compared with 1 year, and performance on the psychomotor index of the Bayley Scales improved significantly.

CONCLUSIONS

One- and 2-year follow-up of a cohort of infants with persistent pulmonary hypertension of the newborn who were treated with inhaled nitric oxide had an 11.8% (1 year) and 12.1% (2-year) rate of severe neurodevelopmental disability. There are ongoing medical problems in these infants including reactive airways disease and slow growth that merit continued close longitudinal follow-up.

Impairment of cerebral autoregulation during venovenous extracorporeal membrane oxygenation in the newborn lamb

OBJECTIVE

To study the effects of venovenous extracorporeal membrane oxygenation (ECMO) on cerebral autoregulation in the newborn lamb.

DESIGN

Animal studies, using newborn lambs, with comparison of two randomized treatment groups.

SUBJECTS

Newborn lambs of mixed breed, 1 to 7 days of age, were randomized into two study groups: control animals, with jugular vein ligation but no ECMO (n = 6), and ECMO animals placed on venovenous ECMO (n = 6).

SETTING

Laboratory animal facilities of the Department of Anesthesiology and Critical Care Medicine at The Johns Hopkins Medical Institutions, Baltimore, MD.

INTERVENTIONS

Animals were anesthetized with pentobarbital, intubated, and ventilated, and monitoring catheters were inserted. Control animals had their right jugular vein ligated, and a cerebral autoregulation curve was performed after 1 hr of stabilization. ECMO animals were placed on venovenous ECMO and after 1 hr of stabilization, they had a cerebral autoregulation curve performed. Cerebral autoregulation was examined by increasing intracranial pressure, thereby decreasing cerebral perfusion pressure. Intracranial pressure was increased by infusion of artificial cerebrospinal fluid into the lateral ventricle of the brain.

MEASUREMENTS AND MAIN RESULTS

Four ranges of cerebral perfusion pressure were evaluated: a) baseline (1 hr after initiation of bypass in venovenous ECMO or completion of surgery in controls); b) cerebral perfusion pressure of 55 to 40 mm Hg; c) cerebral perfusion pressure of 39 to 25 mm Hg; and d) cerebral perfusion pressure of < 25 mm Hg. Cerebral blood flow (radiolabeled microspheres), cerebral oxygen consumption, fractional oxygen extraction, and oxygen transport values were calculated at each study period. In ECMO animals, cerebral blood flow (cerebral hemispheres) decreased from a baseline measurement of 46 +/- 9 (SD) mL/100 g/ min to 29 +/- 12 mL/100 g/min at a cerebral perfusion pressure of < 25 mm Hg. In the control group, cerebral blood flow was unchanged from baseline at any range of cerebral perfusion pressure. Cerebral oxygen consumption was unchanged from baseline as cerebral perfusion pressure decreased in either group. When cerebral oxygen consumption was compared between the two groups, it was lower in the ECMO group at baseline and at a cerebral perfusion pressure of < 25 mm Hg. At a cerebral perfusion pressure of < 25 mm Hg, cerebral blood flow, cerebral oxygen delivery, and metabolic rate were lower in the ECMO group than in the control group, and fractional oxygen extraction and cerebral vascular resistance were higher, indicating that autoregulation was impaired. There was no difference between blood flow in the right and left cerebral hemispheres when autoregulation was impaired in the ECMO animals.

CONCLUSIONS

These findings indicate that cerebral autoregulation was altered in animals on venovenous ECMO, with cerebral blood flow decreasing at a cerebral perfusion pressure of < 25 mm Hg, compared with control animals which showed no changes at the same cerebral perfusion pressure. This disruption of cerebral autoregulation decreased cerebral oxygen metabolism despite an increased oxygen extraction in ECMO animals.

Cerebral blood flow and carbon dioxide reactivity in neonates during venoarterial extracorporeal life support

OBJECTIVES

a) To determine if cerebral blood flow is symmetric after internal carotid artery and ipsilateral internal jugular vein ligation in infants during venoarterial extracorporeal life support. b) To determine the cerebral CO2 reactivity (delta cerebral blood flow/delta torr CO2) of neonates during venoarterial extracorporeal life support and its correlation to neurodevelopmental outcome.

DESIGN

Prospective, clinical study.

SETTING

University hospital pediatric intensive care unit.

PATIENTS

Fourteen neonates with respiratory failure who were receiving venoarterial extracorporeal life support.

INTERVENTIONS

PaCO2 was altered by adjusting the CO2 gas flow through the membrane oxygenator. Cerebral blood flow was measured over both parietal-temporal regions at three PaCO2 values using xenon-133 clearance methodology. Cerebral blood flow measurements were made early (< or = 12 hrs of extracorporeal life support, n = 10) or late (> or = 48 hrs of extracorporeal life support, n = 10). In six of 14 infants, both early and late cerebral blood flow rates were measured. PaO2, mean arterial pressure, pump flow rate, and temperature were stable during each study period. Neurodevelopmental outcome was assessed in the neonatal follow-up clinic.

MEASUREMENTS AND MAIN RESULTS

Right and left hemispheric cerebral blood flow rates were significantly correlated with each other during early and late extracorporeal life support (p = .0001; r2 = .91). Overall, hemispheric cerebral blood flow was statistically symmetric. There was no association of CO2 reactivity (delta cerebral blood flow/delta torr PCO2, range 0.04 to 1.36 mL/min/100 g/torr) with short-term neurodevelopmental outcome. Infants with normal neurodevelopmental outcome had variable CO2 reactivity (range 0.04 to 0.67 mL/min/100 g/torr). Normal short-term neurodevelopmental outcome was observed in two infants with cerebral blood flow of < 10 mL/min/100 g.

CONCLUSIONS

Hemispheric cerebral blood flow was symmetric in infants during early and late venoarterial extracorporeal life support. Some subgroups showed a trend toward decreased right hemispheric cerebral blood flow, but the small number of patients limited interpretation of this finding. CO2 reactivity and cerebral blood flow were highly variable in this population, and were not predictive of short-term neurodevelopmental outcome. Stressed neonates with extremely low cerebral blood flow rates may have relatively normal short-term neurodevelopmental outcome after venoarterial extracorporeal life support.

Jugular ligation does not increase intracranial pressure but does increase bihemispheric cerebral blood flow and metabolism

OBJECTIVES

To answer the following questions: a) Does jugular venous ligation (simulating venovenous extracorporeal life support) alter proximal jugular venous pressure, intracranial pressure, hemispheric cerebral blood flow, or cerebral metabolism? b) Does release of ligation reverse these effects? and c) What are the comparative effects of venous ligation alone vs. venous ligation in combination with arterial ligation?

DESIGN

Prospective, randomized, laboratory investigation.

SETTING

Multidisciplinary laboratory setting.

SUBJECTS

Sixteen swine, weighing 8.1 to 12.1 kg, 3 to 4 wks of age.

INTERVENTIONS

Sixteen swine were randomly assigned to two groups, utilizing a random sequence of vessel ligation. Nine swine underwent occlusion of the right internal and external jugular veins alone (venovenous ligation) followed by release of the occlusion and then occlusion of the right common carotid artery and the right internal and external jugular veins together (venoarterial ligation). The remaining seven swine underwent venoarterial ligation, followed by release of the occlusion and then venovenous ligation. In the experimental group in which venovenous ligation was performed first, the 5, and 30-min release periods after ligation were taken to represent the effects of draining the right jugular vein during venovenous extracorporeal life support.

MEASUREMENTS AND MAIN RESULTS

Data were obtained at baseline, 5, and 30 mins after each ligation/release period. Intracranial pressure, right and left internal jugular pressures/flow rates, and cerebral sinus lactate concentrations were measured. Cerebral blood flow was determined using 133Xe clearance methodology, and the cerebral metabolic rate was calculated. There were no significant differences between the ipsilateral internal jugular pressure or extracorporeal life support at 5 or 30 mins after venovenous or venoarterial ligation compared with baseline values or compared with the release of the ligation at 5 or 30 mins. There was a significant increase in right-side (44.7 +/- 2.0 vs. 38.8 +/- 2.4 mL/kg/min; p < .05) and left-side (42.9 +/- 2.3 vs. 38.7 +/- 1.9 mL/kg/min; p < .05) cerebral blood flow 5 mins after venovenous ligation when compared with baseline values. Similarly, after venoarterial ligation, there was a significant increase in right-side (44.6 +/- 2.2 vs. 38.8 +/- 2.4 mL/kg/min; p < .05) and left-side (43.9 +/- 1.5 vs. 38.7 +/- 1.9 mL/kg/min; p < .05) and cerebral blood flow. Cerebral oxygen consumption was significantly increased after venovenous (2.7 +/- 0.2 to 3.2 +/- 0.2 mL/kg/min; p < .05) and venoarterial (2.7 +/- 0.2 to 3.1 +/- 0.2 mL/kg/min; p < .05) ligation at 5 mins after ligation. This increase persisted at the 30-min period and after release of ligation.

CONCLUSIONS

Ligation of the right jugular veins alone (venovenous ligation) or jugular veins and right carotid artery (venoarterial ligation) does not increase jugular venous pressures or intracranial pressure. However, this procedure does increase cerebral blood flow and cerebral oxygen consumption. These findings demonstrate that there is adequate decompression of the venous system by the cerebrovascular system and retrograde decompression during extracorporeal life support appears unwarranted.

Cerebral hemodynamics and distribution of left ventricular output during inhalation of nitric oxide

OBJECTIVES

Inhaled nitric oxide is being utilized as a selective pulmonary vasodilator in the treatment of persistent pulmonary hypertension of the newborn. However, the effects of inhaled nitric oxide on cerebral hemodynamics and distribution of left ventricular output in newborn subjects have not been studied. This study was designed to measure quantitatively the effect of inhaled nitric oxide on the distribution of left ventricular output and on cerebral hemodynamics in a perinatal animal model.

DESIGN

Prospective, controlled, experimental study.

SETTING

Research laboratory.

SUBJECTS

Eight fetal sheep.

INTERVENTIONS

Each animal was exposed to three separate study periods: a) mechanical ventilation with low FIO2 (maintaining fetal levels of PaO2); b) inhalation of nitric oxide (20 parts per million) during mechanical ventilation and low FIO2; and c) mechanical ventilation with an FIO2 of 1.0.

MEASUREMENTS AND MAIN RESULTS

Left ventricular output and cerebral blood flow were measured with radiolabeled microspheres. Cerebral oxygen delivery and consumption variables were calculated using measurements of arterial and cerebral venous (sagittal sinus) oxygen content. Total left ventricular output did not differ among the three treatment groups: 235 +/- 16 mL/min/kg with hypoxic ventilation; 283 +/- 13 mL/min/kg with nitric oxide inhalation; and 242 +/- 17 mL/min/kg with an FIO2 of 1.0. Lung blood flow increased 2.7-fold with inhaled nitric oxide and 1.6-fold during mechanical ventilation with an FIO2 of 1.0. With a left ventricle microsphere injection, increased lung blood flow is indicative of increased systemic-to-pulmonary shunt across the ductus arteriosus. Whole brain blood flow did not differ between the three groups: 49.6 +/- 6.7 mL/min/100 g with hypoxic ventilation; 46.4 +/- 7.4 mL/min/100 g with nitric oxide inhalation; and 36.4 +/- 3.8 mL/min/100 g with an FIO2 of 1.0. Cerebral oxygen delivery increased during inhalation of an FIO2 of 1.0 when compared with nitric oxide inhalation (p < .007); fractional extraction of oxygen decreased (p < .004 compared with hypoxic ventilation, p < .0005 compared with nitric oxide inhalation). Cerebral oxygen consumption did not differ between the three groups (1.11 +/- 0.12 microns/min/100 g with hypoxic ventilation, 0.95 +/- 0.12 microns/min/100 g with nitric oxide inhalation, and 0.96 +/- 0.08 microns/min/100 g with an FIO2 of 1.0).

CONCLUSION

Acute pulmonary vasodilation caused by inhalation of nitric oxide does not change left ventricular output, cerebral blood flow, or cerebral oxygen consumption, despite an increased systemic-to-pulmonary shunt across the ductus arteriosus.

Median nerve somatosensory evoked potentials in children receiving ECMO

Somatosensory evoked potentials (SEPs) were recorded from 11 patients receiving venoarterial extracorporeal membrane oxygenation (ECMO). Cortical responses recorded from the right and left hemispheres were compared to those from 2 other groups of children who were not receiving ECMO. One group consisted of 99 brain-injured patients, while the other consisted of a group of 17 neurologically normal controls. SEP responses from each hemisphere were categorized into 3 grades based on the N20 component--normal latency, abnormal (latency increased > 3 S.D.), or absent. For ECMO patients, 15% of tests disclosed a disagreement between the right and left hemispheres, while 27% of tests from the control group revealed a disagreement between the right and left hemispheres. SEPs were normal over the right hemisphere in 9 patients. Central conduction times obtained from the right and left hemispheres were similar in ECMO patients and were not different from those recorded from a group of patients suffering hypoxic-ischemic injuries and a group of normal controls who did not receive ECMO. The results of this pilot study suggest that SEPs may be employed to evaluate ECMO patients as they are in other brain-injured patients.

Effect of extracorporeal life support on cerebral blood flow, metabolism and electrophysiology in normothermic cats

OBJECTIVE

Recently, extracorporeal life support (ECLS) by venoarterial bypass perfusion has been recommended for the treatment of refractory respiratory and/or cardiac failure but the safety of this application for the brain is not yet established. Therefore, the effects of normothermic ECLS on cerebral blood flow, metabolism and electrophysiology were studied in cats with total arrest of cardiopulmonary circulation.

DESIGN

An extracorporeal circulation (ECC) system, consisting of a roller pump, a membrane oxygenator and a heat exchanger, was connected to the circulation of cat by cannulae inserted via the jugular vein and femoral vessels. After 2 h ECLS brains were frozen in situ and investigated for changes in regional metabolism.

MEASUREMENTS AND RESULTS

During 2 h ECC hematocrit declined from 37 +/- 7% to 21 +/- 10% (means +/- SD, p < 0.05), cerebral blood flow decreased to 73 +/- 14% of control (p < 0.05) and cerebral oxygen delivery to 46 +/- 13% of control (p < 0.05) although arterial blood pressure and bypass flow rate did not change. Plasma lactate increased from 0.8 +/- 0.3 to 9.2 +/- 4.2 mumol/ml (p < 0.05), and brain tissue lactate from 2.3 +/- 0.9 to 10.6 +/- 2.7 mumol/g (p < 0.05). Hematocrit correlated positively with cerebral oxygen delivery (r = 0.86, p < 0.001).

CONCLUSIONS

These data demonstrate that ECLS is associated with reduced cerebral oxygen delivery and may cause brain hypoxia despite normal blood pressure. This complication may contribute to the high incidence of neurological disturbances after prolonged ECLS.