Frederick A. Burrows

Perioperative effects of alpha-stat versus pH-stat strategies for deep hypothermic cardiopulmonary bypass in infants.

OBJECTIVESnIn a randomized, single-center trial, we compared perioperative outcomes in infants undergoing cardiac operations after use of the alpha-stat versus pH-stat strategy during deep hypothermic cardiopulmonary bypass.nnnMETHODSnAdmission criteria included reparative cardiac surgery, age less than 9 months, birth weight 2.25 kg or more, and absence of associated congenital or acquired extracardiac disorders.nnnRESULTSnAmong the 182 infants in the study, diagnoses included D-transposition of the great arteries (n = 92), tetralogy of Fallot (n = 50), tetralogy of Fallot with pulmonary atresia (n = 6), ventricular septal defect (n = 20), truncus arteriosus (n = 8), complete atrioventricular canal (n = 4), and total anomalous pulmonary venous return (n = 2). Ninety patients were assigned to alpha-stat and 92 to pH-stat strategy. Early death occurred in four infants (2%), all in the alpha-stat group (p = 0.058). Postoperative electroencephalographic seizures occurred in five of 57 patients (9%) assigned to alpha-stat and one of 59 patients (2%) assigned to pH-stat strategy (p = 0.11). Clinical seizures occurred in four infants in the alpha-stat group (4%) and two infants in the pH-stat group (2%) (p = 0.44). First electroencephalographic activity returned sooner among infants randomized to pH-stat strategy (p = 0.03). Within the homogeneous D-transposition subgroup, those assigned to pH-stat tended to have a higher cardiac index despite a lower requirement for inotropic agents; less frequent postoperative acidosis (p = 0.02) and hypotension (p = 0.05); and shorter duration of mechanical ventilation (p = 0.01) and intensive care unit stay (p = 0.01).nnnCONCLUSIONSnUse of the pH-stat strategy in infants undergoing deep hypothermic cardiopulmonary bypass was associated with lower postoperative morbidity, shorter recovery time to first electroencephalographic activity, and, in patients with D-transposition, shorter duration of intubation and intensive care unit stay. These data challenge the notion that alpha-stat management is a superior strategy for organ protection during reparative operations in infants using deep hypothermic cardiopulmonary bypass.

The Efficacy of Tranexamic Acid Versus Placebo in Decreasing Blood loss in Pediatric Patients Undergoing Repeat Cardiac Surgery

The antifibrinolytic drug, tranexamic acid, decreases blood loss in adult patients undergoing cardiac surgery.However, its efficacy has not been extensively studied in children. Using a prospective, randomized, double-blind study design, we examined 41 children undergoing repeat sternotomy for repair of congenital heart defects. After induction of anesthesia and prior to skin incision, patients received either tranexamic acid (100 mg/kg, followed by 10 mg [centered dot] kg-1 [centered dot] h-1) or saline placebo. At the onset of cardiopulmonary bypass, a second bolus of tranexamic acid (100 mg/kg) or placebo was administered. Total blood loss and transfusion requirements during the period from protamine administration until 24 h after admission to the intensive care unit were recorded. Children who were treated with tranexamic acid had 24% less total blood loss (26 +/- 7 vs 34 +/- 17 mL/kg) compared with children who received placebo (univariate analysis P = 0.03 and multivariate analysis P < 0.01). Additionally, the total transfusion requirements, total donor unit exposure, and financial cost of blood components were less in the tranexamic acid group. In conclusion, tranexamic acid can reduce perioperative blood loss in children undergoing repeat cardiac surgery. (Anesth Analg 1997;84:990-6)

Physiologic Dead Space, Venous Admixture, and the Arterial to End-tidal Carbon Dioxide Difference in Infants and Children Undergoing Cardiac Surgery

End-tidal CO2 (PETCO2), arterial CO2 (PaCO2), mixed expired CO2 (PECO2), arterial and mixed venous oxygen contents were measured and the PaCO2 to PETCO2 difference (delta PCO2), physiologic dead space to tidal volume ratios (VD/VT) and venous admixture (Qs/Qt) were calculated in 41 anesthetized infants and children undergoing repair of congenital cardiac lesions. Eighteen children were acyanotic; 9 with normal pulmonary blood flow (PBF) and normal intracardiac anatomy (normal group); and 9 with increased PBF (acyanotic group). Twenty-three children were cyanotic; 14 with right to left intracardiac shunts and decreased PBF (cyanotic (D) group); and 9 with mixing lesions with normal or increased PBF (cyanotic (I) group). Correlations between PaCO2 and PETCO2 in the four groups of children were carried out and the relationship of delta PCO2 to VD/VT and Qs/Qt was determined. PETCO2 correlated closely with the PaCO2 in the normal and acyanotic groups (r2 = 0.97 and 0.91, respectively) and the lines of regression for the relationship between PaCO2 and PETCO2 for both groups did not differ from the line of identity (P less than or equal to 0.05). Mean +/- SD VD/VT for the normal and acyanotic groups were 0.35 +/- 0.17 and 0.39 +/- 0.19, respectively (NS). Corresponding values for the cyanotic (D) group and cyanotic (I) group were 0.38 +/- 0.16 and 0.55 +/- 0.16, respectively (NS), and were significantly greater than those from the normal and acyanotic groups (P less than 0.05). The relationship of delta PCO2 to VD/VT and Qs/Qt demonstrated that VD/VT was the most important determinant of delta PCO2, but in instances where Qs/Qt were large (e.g., cyanotic congenital heart disease) the percentage contribution of Qs/Qt to the delta PCO2 can be considerable.(ABSTRACT TRUNCATED AT 250 WORDS)

The Minimum Alveolar Concentration (MAC) and Hemodynamic Effects of Halothane, Isoflurane, and Sevoflurane in Newborn Swine

To determine the minimum alveolar concentration (MAC) and hemodynamic responses to halothane, isoflurane, and sevoflurane in newborn swine, 36 fasting swine 4-10 days of age were anesthetized with one of the three volatile anesthetics in 100% oxygen. MAC was determined for each swine. Carotid artery and internal jugular catheters were inserted and each swine was allowed to recover for 48 h. After recovery, heart rate (HR), systemic systolic arterial pressure (SAP), and cardiac index (CI) were measured awake and then at 0.5, 1.0, and 1.5 MAC of the designated anesthetic in random sequence. The (mean +/- SD) MAC for halothane was 0.90 +/- 0.12%; the MAC for isoflurane was 1.48 +/- 0.21%; and the MAC for sevoflurane was 2.12 +/- 0.39%. Awake (mean +/- SD) measurements of HR, SAP, and CI did not differ significantly among the three groups. Compared to the awake HR, the mean HR decreased 35% at 1.5 MAC halothane (P less than 0.001), 19% at 1.5 MAC isoflurane (P less than 0.005), and 31% at 1.5 MAC sevoflurane (P less than 0.005). Compared to awake SAP, mean SAP measurements decreased 46% at 1.5 MAC halothane (P less than 0.001), 43% at 1.5 MAC isoflurane (P less than 0.001), and 36% at 1.5 MAC sevoflurane (P less than 0.005). Mean SAP at 1.0 and 1.5 MAC halothane and isoflurane were significantly less than those measured at equipotent concentrations of sevoflurane (P less than 0.005). Compared to awake CI, mean CI measurements decreased 53% at 1.5 MAC halothane (P less than 0.001) and 43% at 1.5 MAC isoflurane (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Propofol or Isoflurane Anesthesia on Cardiac Conduction in Children Undergoing Radiofrequency Catheter Ablation for Tachydysrhythmias

Background To determine suitability for ablation procedures in children, two commonly used anesthetic agents were studied: propofol and isoflurane. Methods Twenty patients presenting for a radiofrequency catheter ablation procedure were included and randomly assigned to two groups. A baseline electrophysiology study was performed during anesthesia with thiopental, alfentanil, nitrous oxide, and pancuronium in all patients. At the completion of the baseline electrophysiology study (EPS), 0.8-1.2% isoflurane was administered to patients in group 1 and 2 mg/kg propofol bolus plus an infusion of 150 micro gram *symbol* kg sup -1 *symbol* min sup -1 was administered to patients in group 2. Nitrous oxide and pancuronium were used throughout the procedure. After 30 min of equilibration, both groups underwent a repeat EPS. The following parameters were measured during the EPS: cycle length, atrial-His interval, His-ventricle interval, corrected sinus node recovery time, AV node effective refractory period, and atrial effective refractory period. Using paired t tests, the electrophysiologic parameters described above measured during propofol or isoflurane anesthesia were compared to those measured during baseline anesthesia. Statistical significance was accepted as P < 0.05. Results There was no statistically significant difference in the results obtained during baseline anesthesia when compared with those measured during propofol or isoflurane anesthesia. Conclusions Neither propofol nor isoflurane anesthesia alter sinoatrial or atrioventricular node function in pediatric patients undergoing radiofrequency catheter ablation, compared to values obtained during baseline anesthesia with alfentanil and midazolam.

A Comparison of Dexmedetomidine-Midazolam with Propofol for Maintenance of Anesthesia in Children Undergoing Magnetic Resonance Imaging

BACKGROUND:Dexmedetomidine is an &agr;2 agonist that is currently being investigated for its suitability to provide anesthesia for children. We compared the pharmacodynamic responses to dexmedetomidine-midazolam and propofol in children anesthetized with sevoflurane undergoing magnetic resonance imaging (MRI). METHODS:Forty ASA 1 or 2 children, 1–10 yr of age, were randomized to receive either dexmedetomidine-midazolam or propofol for maintenance of anesthesia for MRI after a sevoflurane induction. Dexmedetomidine was administered as an initial loading dose (1 &mgr;g/kg) followed by a continuous infusion (0.5 &mgr;g · kg−1 · h−1). Midazolam (0.1 mg/kg) was administered IV when the infusion commenced. Propofol was administered as a continuous infusion (250–300 &mgr;g · kg−1 · min−1). Recovery times and hemodynamic responses were recorded by one nurse who was blinded to the treatments. RESULTS:We found that the times to fully recover and to discharge from the ambulatory unit after dexmedetomidine administration were significantly greater (by 15 min) than those after propofol. Analysis of variance demonstrated that heart rate was slower and systolic blood pressure was greater with dexmedetomidine than propofol. Respiratory indices for the two treatments were similar. During recovery, hemodynamic responses were similar. Cardiorespiratory indices during anesthesia and recovery remained within normal limits for the children’s ages. No adverse events were recorded. CONCLUSION:Dexmedetomidine-midazolam provides adequate anesthesia for MRI although recovery is prolonged when compared with propofol. Heart rate was slower and systolic blood pressure was greater with dexmedetomidine when compared with propofol. Respiratory indices were similar for the two treatments.

Cerebral Hemodynamics in Neonates and Infants Undergoing Cardiopulmonary Bypass and Profound Hypothermic Circulatory Arrest: Assessment by Transcranial Doppler Sonography

Profound hypothermic circulatory arrest (PHCA) is followed by a transient period of increased intracranial pressure and a longer period of neurophysiologic dysfunction. To investigate the effect of cardiopulmonary bypass (CPB) with PHCA on cerebral hemodynamics, we used transcranial Doppler sonography to measure cerebral blood flow velocity in 10 neonates and infants before and after PHCA. Cerebral blood flow velocity was compared before and after PHCA during normothermic cardiopulmonary bypass at the same mean arterial pressure, central venous pressure, hematocrit, and arterial carbon dioxide tension. Cerebral blood flow velocity decreased exponentially with decreasing nasopharyngeal temperature before PHCA (P < 0.05) and remained decreased after PHCA during normothermic CPB, compared with values for normothermic CPB before PHCA (P < 0.005). During normothermic CPB after PHCA, the modified cerebral vascular resistance (mm Hg-cm-s−1) was increased above values for normothermic CPB before PHCA (P < 0.05). The results of this study suggest that the observed increase in intracranial pressure during PHCA is not caused by increased cerebral perfusion, but rather that cerebral perfusion is reduced in response to a decreased demand for cerebral metabolic oxygen.

Cerebral pressure-flow velocity relationship during hypothermic cardiopulmonary bypass in neonates and infants.

To examine the effect of temperature on the relationship between cerebral perfusion pressure (CPP) and cerebral blood flow velocity (CBFV) and the effect of low-flow cardiopulmonary bypass (CPB) on cerebral perfusion, we studied 25 neonates and infants ranging from 3 to 210 days of age at three nasopharyngeal temperature (NPT) ranges during cardiopulmonary bypass. Pressure-flow velocity relationships were studied during normothermic (NPT = 36-37 degrees C), moderate hypothermic (NPT = 23-25 degrees C), and profound hypothermic (NPT = 14-20 degrees C) CPB. A transcranial Doppler monitor was used to obtain CBFV, which was measured in the M1 segment of the middle cerebral artery. The CBFV was used as an index of cerebral perfusion. Anterior fontanel pressure (AFP) was subtracted from mean arterial pressure (MAP) to calculate CPP in mm Hg. Nasopharyngeal temperature, PaCO2, and hematocrit were controlled during the study period. Arterial blood gases were analyzed at 37 degrees C, uncorrected for body temperature (alpha-stat acid-base management). The CBFV measurements were made over a range of CPP from 6 to 90 mm Hg. Using nonlinear regression analysis, we showed that cerebral pressure-flow velocity autoregulation was present during normothermic CPB (r2 = 0.68). Autoregulation became pressure-passive, using linear regression analysis, during moderate hypothermic CPB (r2 = 0.33) and profound hypothermic CPB (r2 = 0.69). Cerebral blood-flow velocity was not detectable at a mean (+/- SD) CPP of 9 (+/- 2) mm Hg induced by the low-flow CBP state but became apparent when CPP was increased to 13 (+/- 1) mm Hg (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The limits of detectable cerebral perfusion by transcranial doppler sonography in neonates undergoing deep hypothermic low-flow cardiopulmonary bypass☆☆☆★★★

OBJECTIVEnNeurologic morbidity including seizures, abnormal neurologic function, and delayed psychomotor development continue to be significant problems for some patients undergoing operations for congenital heart disease, particularly for those subjected to deep hypothermic circulatory arrest. The technique of low-flow cardiopulmonary bypass has been advocated to decrease the incidence of neurologic sequelae. Our study examined the limits of detectable blood flow in the middle cerebral artery during low-flow cardiopulmonary bypass in 28 neonates undergoing the arterial switch procedure.nnnMETHODSnCerebral blood flow velocity was measured noninvasively in the M1 segment of the middle cerebral artery with a 2 MHz range-gated pulsed-wave transcranial Doppler sonographic probe that was placed over the left temporal window. As part of the initiation of a planned period of deep hypothermic circulatory arrest, the cardiopulmonary bypass flow rate was decreased in stages to five low-flow rates (50, 40, 30, 20, and 10 ml/kg per minute). After a period of stabilization, cerebral blood flow velocities were recorded at each of the five low-flow rates and reported as a percentage of baseline.nnnRESULTSnAll 28 neonates had detectable perfusion in the middle cerebral artery at flow rates of 30 ml/kg per minute or higher. At flows of 20 and 10 ml/kg per minute, one and eight, respectively, of the 28 neonates had no detectable perfusion in the middle cerebral artery.nnnCONCLUSIONSnOur data show that cerebral perfusion can be detected by transcranial Doppler sonography in the middle cerebral artery in some neonates at bypass pump flows as low as 10 ml/kg per minute. However, when transcranial Doppler sonography was used in our patient population, a minimum bypass flow rate of 30 ml/kg per minute was needed to detect cerebral perfusion in all neonates.

Anterior Fontanel Pressure and Visual Evoked Potentials in Neonates and Infants Undergoing Profound Hypothermic Circulatory Arrest

To determine the effects of cardiopulmonary bypass with profound hypothermic circulatory arrest (PHCA) on anterior fontanel pressure (AFP) and visual evoked potentials (VEPs), 21 neonates and infants undergoing cardiopulmonary bypass (CPB) with PHCA for surgical correction of congenital heart defects were studied. Mean (+/- SD) minimum nasopharyngeal, esophageal, and rectal temperatures of 16.4 +/- 2.2, 11.2 +/- 2.7, and 17.7 +/- 1.9 degrees C, respectively, were achieved for a mean duration of PHCA of 51.6 +/- 18.7 min. AFP increased significantly above pre-CPB values for the first 21.7 +/- 8.1 min of rewarming. The duration of this increase in AFP was related logarithmically and directly to the product of the nasopharyngeal temperature (NPT) at the end of PHCA and the duration of PHCA (r2 = 0.82, P less than 0.0001). Nineteen of these patients had simultaneous monitoring of VEPs. The latency of both the N70 and P100 components of the VEPs increased as temperature decreased. The cerebral perfusion pressure was linearly and inversely related to the AFP (r2 = 0.72, P less than 0.01). The VEPs disappeared as a nasopharyngeal temperature (NPT) of 18.9 +/- 2.8 degrees C and reappeared after 21.9 +/- 8.8 min post-PHCA at an NPT of 32.8 +/- 1.4 degrees C. There was no significant difference between duration of increased AFP (20.9 +/- 8.1 min) and the duration of absence of VEPs during the post-PHCA period. The duration of increased AFP correlated linearly and directly with the duration of absence of VEPs (r2 = 0.84, P less than 0.005). These data demonstrate that transient neurophysiologic dysfunction occurs after PHCA. This dysfunction is related to the duration of elevation of the AFP and cannot be explained solely by a temperature effect.