Nitrous Oxide: Cardiovascular Effects in Infants and Small Children During Halothane and Isoflurane Anesthesia

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Abstract
MURRAY D, FORBES R, MURPHY K, MAHONEY L. Nitrous oxide: cardiovascular effects in infants and small children during halothane and isoflurane anesthesia. Anesth Analg 1988;67:1059-64. Two-dimensional and pulsed Doppler echocardiography were used to measure cardiovascular function in 31 unmedicated infants and small children. In 15 patients, the cardiovascular effects of equipotent levels of halothane were compared with and without N2O. In 16 patients, the cardiovascular effects of isoflurane with and without N2O were compared. Prior to anesthesia induction, cardiovascular measurements of heart rate (HR), mean blood pressure (MBP), and two-dimensional and pulsed Doppler echocardiography were recorded. The echocardiographic measurements were used to determine cardiac output (CO), stroke volume (SV), ejection fraction (EF), and left ventricular end-diastolic and end-systolic volume (LVEDV and LVESV). Twenty minutes after mask inhalation induction with halothane or isoflurane with N2O and O2 (3:2 liters/min), cardiovascular measurements were repeated with end-expired halothane or isoflurane maintained at 0.9 MAC. A third set of cardiovascular data was collected 10 minutes after the discontinuation of N2O, with inspired isoflurane or halothane levels in O2 (5 liters/min) increased to maintain 1.5 MAC end-expired levels. Ventilation was controlled throughout the study period and the study was completed before intubation and the start of elective surgery. Heart rate and MBP decreased to similar degrees below awake levels in both patient groups during N2O with halothane or isoflurane. When N2O was discontinued and end-expired levels of halothane or isoflurane increased, MBP remained at levels observed during N2O-O2 with halothane or isoflurane. Heart rate increased during isoflurane in O2. Cardiac output decreased significantly and similarly below awake levels during both halothane or isoflurane with and without N2O. Ejection fraction decreased significantly below awake levels during both N2O:O2 and halothane and during halothane in O2 (30 ± 6 and 32 ± 5%) as well as during isoflurane with and without N2O (15 ± 9 and 18 ± 7%). Decreases in EF were significantly greater with halothane. In infants and small children, the cardiovascular effects of combining N2O with halothane or isoflurane were similar to equianesthetic concentrations of halothane and isoflurane in O2, and may be more profound than suggested by clinical studies in adults.