Comparing two strategies of cardiopulmonary bypass cooling on jugular venous oxygen saturation in neonates and infants

Landmark papers in pediatric cardiac anesthesia: documenting the history of the specialty

Pediatric cardiac anesthesia has developed over the past eight decades into a specialty delivering complex clinical care and contributing remarkable scientific progress. The history of this development can be traced through journal articles that mark the strides of the specialty. This article discusses journal articles, chosen by the author, that he considers had a significant impact on the practice of pediatric cardiac anesthesia or are of historical interest.

Prognostic Value of Perioperative Near-Infrared Spectroscopy During Neonatal and Infant Congenital Heart Surgery for Adverse In-Hospital Clinical Events

Background: Perioperative monitoring with multisite near-infrared spectroscopy (NIRS) for congenital cardiac surgery with cardiopulmonary bypass may aid in predicting adverse clinical outcomes. Methods: Forty-one consecutive neonates and infants undergoing bypass were monitored with right + left cerebral and renal NIRS. Near-infrared spectroscopy and lactate were measured at 20 time points, from baseline 1 day preoperatively, during bypass and modified ultrafiltration (MUF; 10 minutes), until 24 hours postoperatively. Adverse events were extracorporeal membrane oxygenation (ECMO)/death, prolonged intensive care unit (ICU) or length of hospital stay. Results: Perioperative mean renal NIRS remained higher than baseline (n = 41) as did cerebral NIRS in all undergoing biventricular repair. During bypass (n = 41), mean right and left cerebral NIRS were equal. During MUF, cerebral and renal NIRS values increased ( P < .001). Cerebral NIRS and lactate inversely correlated during the first six postoperative hours. Extracorporeal membrane oxygenation /death occurred in four patients, correlating with cerebral and renal NIRS below 45% ( P = .030) and 40% ( P = .019) at anytime, respectively, and with mean lactate levels >9.3 mmol/L in the first postoperative 24 hours ( P < .001). Among survivors, renal NIRS below 30% at any time predicted a longer ICU stay. Conclusions: At bypass conclusion, 10 minutes of MUF does not adversely affect cerebral or renal NIRS. Left and right cerebral NIRS are equal, so that biparietal cerebral NIRS monitoring is probably not warranted. Perioperative cerebral and renal NIRS readings, respectively, below 45% and 40% correlate with ECMO/death and renal NIRS below 30% with prolonged ICU stay. Cerebral NIRS and lactate levels showed a strong inverse correlation during the first six postoperative hours.

SjO2/SvO2 correlation during pediatric cardiac surgery with cardiopulmonary bypass

OBJECTIVES

To compare the SjO2 (cerebral oxygenation indicator) and SvO2 (cardiac output indicator) during pediatric cardiac surgery with cardiopulmonary bypass (CPB).

METHODS

Retrospective study. Data of SjO2 and SvO2 measured simultaneously at critical time periods during cardiac surgery with CPB were analyzed by the Spearman correlation test and Bland- Altman plot.

RESULTS

Regression analysis of the pooled data showed poor correlation between SjO2 and SvO2 (r²=0.14, P=0.03) and Bland- Altman plot had a high bias (-7.9), indicating independency of the two variables. SjO2<50% (indicative of cerebral ischemia-hypoxia) were observed in 50% of the measurements after rewarming during hypothermic CPB.

CONCLUSIONS

SvO2 is not a good predictor of SjO2 during pediatric cardiac surgery with CPB, and low SjO2 can be undetected measuring SvO2 only.

Neonatal cerebral oximetry monitoring during ECMO cannulation

OBJECTIVE

Neonates were monitored with a cerebral oximeter before, during, and after cannulation for ECMO to determine the direct effects of ligation of the right internal jugular vein and right carotid artery on cerebral oxygenation.

STUDY DESIGN

After obtaining informed consent, we used the FORE-SIGHT Cerebral Oximeter (CAS Medical Systems, Branford, CT, USA) to monitor neonates undergoing surgical preparation for veno-arterial (VA) or veno-venous (VV) extracorporeal membrane oxygenation (ECMO).

RESULT

A total of 17 subjects were monitored pre-ECMO for at least 48 h after cannulation. Of the 17 subjects, 12 experienced low cerebral tissue oxygen saturation (SctO(2)) <60% during pre-ECMO surgery, with most exhibiting the lowest SctO(2) values between cannulation to the onset of ECMO. Two subjects received cardiopulmonary resuscitation (CPR) during surgery and experienced very low SctO(2) (5 and 36%). Pulse oximetry was found to be unreliable during CPR because of diminished pulsatile flow. SctO(2) increased above 60% after the onset of ECMO for all subjects and remained stable.

CONCLUSION

Neonates are vulnerable to SctO(2) during the pre-ECMO surgical period.

Perioperative neuroprotective strategies

Long-term neurodevelopmental impairment is common in newborns and infants undergoing corrective or palliative congenital heart surgery. The etiologies of neurodevelopmental morbidity in these children are multifactorial and include prenatal, preoperative, intraoperative, and postoperative factors. Perioperative neurologic monitoring is thought to be integral to prevention or rescue from adverse neurologic events. Recent advances in perfusion techniques for congenital heart surgery now ensure adequate cerebral O(2) delivery during all phases of cardiopulmonary bypass. Periventricular leukomalacia and other serious neurologic injury can be minimized by an optimized perfusion strategy of continuous high-flow, high hematocrit cardiopulmonary bypass, minimal use of deep hypothermic circulatory arrest, antegrade cerebral perfusion during aortic arch reconstruction, pH-stat blood gas strategy, and cerebral monitoring with NIRS and trans-cranial Doppler. Because there is evidence that brain injury can also occur in the prenatal, preoperative, and postoperative periods, improved strategies to prevent injury in these arenas are much needed. Extensive further clinical investigation is warranted to identify neuroprotective management strategies for the operating room and intensive care unit to preserve neurologic function and optimize long-term neurodevelopmental outcomes in children with congenital heart disease.

Neurologic monitoring on cardiopulmonary bypass: what are we obligated to do?

Improving survival from congenital cardiac repairs using cardiopulmonary bypass has appropriately shifted focus to neurologic outcomes. Hypoxic-ischemic mechanisms are the major cause of neurologic injury in neonatal cardiac surgery, and modifications of techniques of cardiopulmonary bypass can affect organ oxygen delivery and the propensity to injury both during and after surgery. Through successive refinements in the techniques of cardiopulmonary bypass, the risk factors for hypoxic-ischemic injury have been reduced, but not eliminated. The application of specific monitoring to enhance detection of hypoxic conditions associated with neurologic injury would both allow intervention on individual patients and drive refinements in strategies to further reduce risk. Specific neurologic monitoring techniques that can be used during cardiopulmonary bypass include near-infrared spectroscopy, transcranial Doppler ultrasonography, and electroencephalographic techniques. Of these, only near-infrared spectroscopy provides a continuous quantitative signal of the physiologic variable most related to injury and most amenable to intervention. This review will advocate wide adoption of near-infrared spectroscopy monitoring throughout the perioperative period, to enhance detection of hypoxic conditions and to drive patient-specific interventions.

Systemic venous oxygen saturation after the Norwood procedure and childhood neurodevelopmental outcome

OBJECTIVE

Neonates with hypoplastic left heart syndrome have impaired systemic oxygen delivery and also have a high risk of hypoxic ischemic brain injury with resultant neurodevelopmental impairment. We hypothesized that decreased postoperative oxygen delivery, as measured on the basis of systemic venous oxyhemoglobin saturation, would be related to persistent neurodevelopmental abnormality assessed in childhood.

METHODS

Early perioperative hemodynamic data, prospectively acquired from neonates undergoing staged palliation of hypoplastic left heart syndrome by using deep hypothermic circulatory arrest with uniform perioperative management, were tested for relationship to later neurodevelopmental outcome assessed at age 4 years.

RESULTS

Complete hemodynamic and neurodevelopmental data were available in 13 patients aged 7 +/- 8 days at the time of the Norwood procedure and aged 4.5 +/- 0.7 years at follow-up assessment. The subjects scored significantly below the population mean for motor, visual-motor integration, and composite neurodevelopmental outcomes. The 5 (38%) patients with abnormal outcomes had significantly lower postoperative systemic venous oxygen saturation values than those with normal outcomes (46% +/- 8% vs 56% +/- 6%, P = .024). Standard hemodynamic parameters did not differentiate patient outcomes. The risk of abnormal outcome increased with increasing time at a systemic venous oxygen saturation of less than 40% (P < .001). A multivariate model of deep hypothermic circulatory arrest time, systemic venous oxygen saturation, blood pressure, and carbon dioxide tension accounted for 79% of the observed variance (P < .001).

CONCLUSIONS

Decreased systemic oxygen delivery in the neonatal postoperative period is associated with hypoxic-ischemic brain injury and childhood neurodevelopmental abnormality. Measures of systemic oxygen delivery should be used to guide perioperative strategies to reduce the risk of hypoxic-ischemic brain injury.

Long-term neurodevelopmental outcomes in school-aged children after neonatal arterial switch operation

OBJECTIVE

Neurodevelopmental status of children between 8 and 14 years of age after neonatal arterial switch operation for transposition of the great arteries has not previously been systematically evaluated.

METHODS

Within a longitudinal study, 60 unselected children operated on as neonates with combined deep hypothermic circulatory arrest and low-flow cardiopulmonary bypass were reevaluated at the age of 7.9 to 14.3 years (mean +/- SD 10.5 +/- 1.6 years). Clinical neurologic status and standardized tests to assess gross motor function, intelligence, acquired abilities, language, and speech were carried out, and the results were related to preoperative, perioperative, and postoperative status, to management, and to neurodevelopmental status at a mean age of 5.4 years.

RESULTS

Neurologic and speech impairments were evidently more frequent (27% and 40%, respectively) than in the general population. Intelligence and socioeconomic status were not different (P =.29 and P =.11), whereas motor function, acquired abilities, and language were reduced (P < or =.04 for each). Overall rate of developmental impairment in one or more domains was 55%, compared with 26% at age 5.4 years. Multivariable analysis showed that severe preoperative acidosis and hypoxia predicted reduced motor function (mean deficit 52.7 points, P <.001), whereas longer bypass duration predicted both neurologic (odds ratio per 10 minutes of bypass duration 1.8, P =.04) and speech (odds ratio per 10 minutes of bypass duration 1.9, P =.02) dysfunction, and perioperative and postoperative cardiocirculatory insufficiency predicted neurologic (odds ratio 6.5, P =.04) and motor (mean deficit 6.8 points, P =.03) dysfunction.

CONCLUSIONS

The neonatal arterial switch operation with combined circulatory arrest and low-flow bypass is associated increasingly with age, with reduced neurodevelopmental outcome but not with cognitive dysfunction. In our experience, the risk of long-term neurodevelopmental impairment after neonatal corrective cardiac surgery is related to deleterious effects of the global perioperative management and to special adverse effects of prolonged bypass duration. Severe preoperative acidosis and hypoxia and postoperative hemodynamic instability must be considered as important additional risk factors.

Cardiopulmonary bypass in infants and children

Cardiopulmonary bypass (CPB) systems have evolved from futuristic visions of surgical pioneers to a safe and efficient tool in the therapy of treatment of cardiac disorders. There are many significant differences in the physiology between neonates and adult patients. There are currently very few congenital cardiac malformations that cannot be addressed effectively with surgical therapy. Yet, the necessity of CPB in the repair of these patients can still result in significant morbidity. A clearer understanding of the effects of CPB, hypothermia, and circulatory arrest is evolving and there is a considerable amount of research in these areas. It seems likely that modification of current CPB systems, minimization of exposure, and surgical techniques to avoid or limit the adverse effects may reduce mortality and morbidity in the future. The problems faced in these complex patients and procedures require that infant and neonatal cardiac surgery be performed in specialized centers with a multidisciplinary approach and specialized personnel. Future improvements in technology will likely result in improved long term outcome for children with congenital cardiac disease. Copyright 2000 by W.B. Saunders Company

Hypothermic cardiopulmonary bypass alters oxygen/glucose uptake in the pediatric brain

OBJECTIVES

Neurologic morbidity related to cardiac surgery has been recognized as a major morbidity. A variety of causes related to cardiopulmonary bypass, including microemboli, nonpulsatile flow, hemodilution, and inflammatory mediation, have been proposed. Because oxygen and glucose are the predominant metabolic substrates for the brain, we sought to examine the uptake of these substrates by the pediatric brain during hypothermic cardiopulmonary bypass.

METHODS

Eleven children (median age 5 months, range 1 day-17 years) undergoing a variety of cardiac surgical procedures with the use of hypothermic cardiopulmonary bypass were studied. Cerebral arteriovenous differences for oxygen, glucose, and lactate were obtained before, during, and after bypass. On the basis of the predictable stoichiometric relationship for the oxidation of glucose, the relationship of substrate uptake was expressed as the oxygen/glucose index.Oxygen/glucose index (%) = (arteriovenous oxygen difference [micromol/mL]/arteriovenous glucose difference [micromol/mL] x 6) x 100

RESULTS

All children survived with no obvious neurologic sequelae. During cooling on cardiopulmonary bypass, the oxygen/glucose indexes fell significantly from prebypass values (53% +/- 19% at 28 degrees C and 54% +/- 25% at 24 degrees C vs 117% +/- 70%; P <.05, analysis of variance). This decline resulted from decreased oxygen uptake with stable glucose uptake (P <.05). Although oxygen and glucose uptake both increased with rewarming, the net effect was only a slight increase in oxygen/glucose index (62% +/- 16%). Postbypass oxygen/glucose index exceeded prebypass values (149% +/- 83%).

CONCLUSIONS

Hypothermic cardiopulmonary bypass alters the relationship between oxygen and glucose uptake in the pediatric brain. The relationship of these findings to bypass-related neurologic morbidity remains to be explored.

Jugular bulb oximetry during cardiac surgery

Imbalance between cerebral oxygen supply and demand is thought to play an important role in the development of cerebral injury during cardiac surgery. This article presents an overview of cerebral oxygenation monitored by jugular bulb oximetry during cardiac surgery with cardiopulmonary bypass. The general principles of jugular bulb oximetry including physiology, intermittent and continuous monitoring, technical considerations, limitations and potential complications are discussed. Different applications of jugular bulb oximetry during bypass surgery and the possible therapeutic approaches to impaired cerebral oxygenation are described.

Neurological evaluation and intelligence testing in the child with operated congenital heart disease

BACKGROUND

The immediate and intermediate-term neurodevelopmental outcome in infants undergoing open heart procedures using deep hypothermic cardiopulmonary bypass was assessed prospectively.

METHODS

One hundred consecutive infants (age 2 to 174 days) were operated on using either deep hypothermic bypass only (group A, n = 28), or with associated circulatory arrest (group B, n = 72). Early neurological outcome was recorded. Survivors underwent mental development evaluation after 31 to 55 months. Fifty other children of similar demographic profile but without heart disease were also tested as controls.

RESULTS

In group A, there were two neurological deaths. In group B, 5 patients had clinical seizures, 1 had monoparesis and 1 had hyperkinetic syndrome with decreased attention span. Mean mental performance quotient was 90.0+/-8.2 in group A, and 89.1+/-6.8 in group B, (group A vs. B, p = 0.60). Mean mental performance quotient in the control group was 101.4+/-8.4, which was significantly higher than the patient population (p << 0.001). No correlation was found between duration of circulatory arrest and postoperative mental performance quotient.

CONCLUSIONS

There was significant retardation of mental development in infants operated with deep hypothermic cardiopulmonary bypass. However, use of total circulatory arrest and its duration did not affect clinical outcome up to preschool age.

Cerebral hypothermia for prevention of brain injury following perinatal asphyxia

The possibility that hypothermia has a therapeutic role during or after resuscitation from severe perinatal asphyxia has been a longstanding focus of research. Early studies using short periods of cooling had limited and contradictory results. We now know that resuscitation can be followed by a "latent" phase, characterized by transient recovery of cerebral energy metabolism, before secondary deterioration occurs with seizures, cytotoxic edema, and cerebral energy failure 6 to 15 hours after birth. Recent experimental studies have shown that moderate cerebral hypothermia initiated as soon as possible in the latent phase, before the onset of secondary injury, and continued for 48 hours or more is associated with potent, long-lasting neuroprotection. These encouraging results must be balanced against the well-known adverse systemic effects of hypothermia. Randomized clinical trials are in progress to test the safety and efficacy of cerebral hypothermia.

Surgical techniques. Aortic arch and deep hypothermic circulatory arrest: real-life suspended animation

Surgical reconstruction of the aortic arch is a complex procedure requiring careful preoperative analysis of the pathology and forethought toward surgical approach. Development of surgical techniques has brought dramatic improvement survival and reduction of neurological events associated with these procedures, yet significant morbidity is still encountered. New approaches to the patient with these pathologies include antegrade and retrograde perfusions to the brain. Continued research into physiology of hypothermic circulatory arrest offers the promise of pharmacological protection of the brain during aortic reconstruction and potentially development of therapeutic modalities to treat and limit ischemic brain damage.

Delayed impairment of cerebral oxygenation after deep hypothermic circulatory arrest in children

BACKGROUND

Clinical studies of deep hypothermic circulatory arrest (DHCA) have focused only on the immediate postoperative period. However, experimental findings suggest impairment of cerebral oxygenation at 2 to 8 hours after reperfusion.

METHODS

In 10 children who had DHCA for heart operations, transcerebral differences of hemoglobin oxygen saturation and plasma hypoxanthine, xanthine, and lactoferrin concentrations were measured in concurrently obtained cerebral venous, arterial, and mixed venous samples up to 10 hours postoperatively.

RESULTS

Compared with preoperative levels (57% +/- 7%), cerebral venous oxygen saturation was not significantly reduced until 2 hours (44% +/- 6%) and 6 hours (42% +/- 5%) after DHCA (p < 0.05). A statistically significant transcerebral (ie, cerebral vein versus artery) concentration difference of hypoxanthine was observed at 30 minutes (3.6 +/- 0.9 micromol/L), 1 hour (3.4 +/- 1.1 micromol/L), and 2 hours (3.1 +/- 0.8 micromol/L) after DHCA but not preoperatively (0.4 +/- 0.2 micromol/L). A transcerebral concentration difference of lactoferrin occurred 30 minutes after DHCA (196 +/- 70 microg/mL) but not preoperatively (16 +/- 20 microg/mL).

CONCLUSIONS

Cerebral venous oxygen saturation of hemoglobin decreased as late as 2 to 6 hours after DHCA, in association with impaired cerebral energy status. Neutrophil activation in the cerebral circulation occurred 30 minutes after reperfusion.

The pursuit of effective neuroprotection during infant cardiac surgery

Advances in infant cardiac surgery have resulted in a dramatic decline in mortality rates; however, neurological morbidity remains an important concern. The effectiveness of a number of interventional strategies to prevent or minimize brain injury during open heart surgery are currently being investigated. This article provides an overview of two approaches: (1) interventions to enhance intraoperative cerebral oxygenation so as to prevent hypoxic-ischemic insults, and (2) the application of cerebral rescue therapies to attenuate the cascade of brain injury. Infant cardiac surgery provides a controlled environment in which to apply these neuroprotective approaches, so as to optimize the quality of life of these vulnerable children.

Selective head cooling in newborn infants after perinatal asphyxia: a safety study

AIMS

To determine the practicality and safety of head cooling with mild or minimal systemic hypothermia in term neonates with moderate to severe hypoxic-ischemic encephalopathy.

METHODS

Study group infants >/=37 weeks' gestation, who had an umbilical artery pH </=7. 09 or Apgars </=6 at 5 minutes, plus evidence of encephalopathy. Infants with major congenital abnormalities were excluded. TRAIL DESIGN: Infants were randomized to either no cooling (controls; rectal temperature = 37.0 +/- 0.2 degreesC, n = 10) or sequentially, either minimal systemic cooling (rectal temperature = 36.3 +/- 0.2 degreesC, n = 6) or mild systemic cooling (rectal temperature = 35.7 +/- 0.2 degreesC, n = 6). Head cooling was accomplished by circulating water at 10 degreesC through a coil of tubing wrapped around the head for up to 72 hours. All infants were warmed by servo-controlled overhead heaters to maintain the allocated rectal temperature. The rectal, fontanelle, and nasopharyngeal temperatures were continuously monitored.

RESULTS

From January 1996 to October 1997, 22 term infants were randomized from 2 to 5 hours after birth. All infants showed a metabolic acidosis at delivery, with similar umbilical artery pH in the control group (mean +/- standard deviation, 6.79 +/- 0.25), minimal cooling group (6.98 +/- 0.21), and mild cooling group (6.93 +/- 0.11), and depressed Apgar scores at 5 minutes in the control group (4.5 +/- 2), minimal cooling group, (4.7 +/- 2) and mild cooling group (6.0 +/- 1). In the mild-cooled infants, the nasopharyngeal temperature was 34.5 degreesC during cooling, 1.2 degreesC lower than the rectal temperature. This gradient narrowed to 0.5 degreesC after cooling was stopped. No adverse effects because of cooling were observed. No infants developed cardiac arrhythmias, hypotension, or bradycardia during cooling. Thrombocytopenia occurred in 2 out of 10 controls, 2 out of 6 minimal cooling infants, and 1 out of 6 mild cooling infants. Hypoglycemia (glucose <2.6 mM) was seen on at least one occasion in 2 out of 10 controls, 4 out of 6 minimal cooling infants, and 1 out of 6 mild cooling infants. Acute renal failure occurred in all infants. The metabolic acidosis present in all infants at the time of enrollment into the study progressively resolved despite cooling, even in the mild hypothermia group.

CONCLUSIONS

Mild selective head cooling combined with mild systemic hypothermia in term newborn infants after perinatal asphyxia is a safe and convenient method of quickly reducing cerebral temperature with an increased gradient between the surface of the scalp and core temperature. The safety of mild hypothermia with selective head cooling is in contrast with the historical evidence of adverse effects with greater depths of whole-body hypothermia. This safety study and the strong experimental evidence for improved cerebral outcome justify a multicenter trial of selective head cooling for neonatal encephalopathy in term infants.

[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.