Halothane anesthesia in infancy: identification and correlation of preoperative risk factors with intraoperative arterial hypotension and postoperative recovery

The halothane era in pediatric anesthesia: The convergence of a cardiac depressant anesthetic with the immature myocardium of infancy

Introduced in the late 1950s, halothane became the anesthetic of choice for inhalational induction of children for over 40 years. Halothane enjoyed a generally favorable safety record during its time, but its cardiac contractility depressant effect-well tolerated by most age groups-was profoundly heightened in neonates and infants, leading to increased incidences of hypotension and cardiac arrest. The neonatal myocardium is immature and is characterized by poor ventricular compliance, poor contractility due to fewer contractile elements, immature sympathetic innervation with decreased norepinephrine stores, and immature mechanisms for storage and exchange of calcium in the sarcoplasmic reticulum. In vitro studies of myocardial contractility of mammalian fetal and adult myocardium demonstrated that the fetal heart was twice as sensitive to halothane as the adult. Clinical studies demonstrated that most neonates and infants less than 6 months of age experienced hypotension during halothane induction of anesthesia and significantly (p < .01) greater decreases in blood pressure than older children at equipotent concentrations of halothane. Intraoperative cardiac arrest during the halothane era occurred over twice as frequently in neonates aged less than 1 month than in infants aged 1-12 months and nearly 10 times more frequently than children 1-5 years of age. Halothane was associated with 66% of intraoperative drug-related cardiac arrests in children. The halothane era began to close in the late 1990s with the introduction of sevoflurane, which had a more favorable hemodynamic profile. Shortly thereafter, halothane was completely displaced from pediatric anesthesia practice in North America.

The influence of duration of fluid abstinence on hypotension during propofol induction

BACKGROUND

Prolonged preoperative fasting might be expected to exacerbate hypotension during the induction of general anesthesia. We aimed to establish whether the duration of preoperative abstinence from fluids independently contributed to arterial blood pressure changes and dosage requirements during propofol induction.

METHODS

We prospectively recruited 130 ASA I or II nonhypertensive patients, ages 18 to 65 years scheduled for surgery under general anesthesia. Standard physiological and electroencephalographic bispectral index (BIS) monitoring was applied to each patient. Intravenous propofol infusion was commenced at 40 mg · kg(-1) · h(-1) and reduced to 8 mg · kg(-1) · h(-1) when the BIS decreased to 50. Frequent cardiovascular data were collected for 15 minutes. The primary endpoint was maximal percentage decrease from baseline mean arterial blood pressure (max%ΔMAP). The secondary endpoint was the propofol dose at which BIS decreased to 50 (PDBIS50). Univariate linear regression and then multivariate linear regression was used to analyze the associations between potential predictors, including fasting time, and these 2 endpoints.

RESULTS

Mean fluid abstinence time was 694 minutes (range: 115 to 1263 minutes). Unstandardized regression coefficients (95% confidence intervals [CIs]) for fluid abstinence (minutes) versus max%ΔMAP (%) and PDBIS50 (mg) were, respectively, 0.003% (-0.002% to + 0.009%) and 0.021 mg (-0.017 mg to + 0.059 mg). On adjusting for other, significant predictors in a multivariate model and applying type II sum of squares tests, the corresponding values were -0.0001% (-0.004% to + 0.004%, P = 0.94) and -0.006 mg (-0.039 mg to + 0.026 mg, P = 0.70). The effect of a 1-hour increase in fluid abstinence on max%ΔMAP was therefore -0.01% (-0.26% to + 0.24%) and on PDBIS50, -0.38 mg (-2.34 mg to + 1.58 mg).

CONCLUSION

When propofol is infused rapidly for induction of anesthesia in healthy adults younger than 65 years, the duration of preoperative fluid abstinence does not appear to affect MAP or propofol dose requirements.

Duration of preoperative fast correlates with arterial blood pressure response to halothane in infants

In this study, we sought to determine whether the duration of preoperative fasting affects the decrease in blood pressure observed in infants and children during halothane anesthesia. Two-hundred-fifty pediatric patients were divided into 5 age groups: term neonates (n = 50), 1-6 mo (n = 50), 6-24 mo (n = 50), 2-6 yr (n = 50), and 6-12 yr (n = 50). After anesthetic induction with halothane, end-tidal halothane was maintained at 2 minimum alveolar anesthetic concentration (MAC) for 10 min to allow myocardial uptake. Patients were grouped by duration of preoperative fast (0-4 h, 4-8 h, 8-12 h, and >12 h). Changes in heart rate and systolic (SAP) and mean (MAP) arterial blood pressure from preinduction to 2 MAC were compared among fasting groups within each age group. In the 1- to 6-mo age group, the changes in SAP and MAP were significantly greater in infants fasting 8-12 h than in those fasting 0-4 h (SAP, -51 mm Hg versus -31 mm Hg, respectively; MAP, -48 mm Hg versus -32 mm Hg; P < 0.05). No statistically significant differences were noted in the older age groups. The results of this study demonstrate that prolonged preoperative fasting is associated with a greater decrease in blood pressure in infants. This exacerbation of the already significant hemodynamic depression observed in infants during halothane anesthesia underscores the importance of adherence to published fasting guidelines.

IMPLICATIONS

We studied changes in blood pressure during halothane anesthesia in infants and children and found that blood pressure decreased to a greater extent in infants who fasted for longer than 8 h before surgery. This exacerbation of the already significant hemodynamic depression observed in infants during halothane anesthesia underscores the importance of adherence to published fasting guidelines.

Haemodynamic depression by halothane is age-related in paediatric patients

The hypothesis that young infants are more sensitive to the haemodynamic depressant effects of halothane compared with older children was tested. One hundred and sixty unpremedicated, ASA physical status I or II paediatric patients without cardiac or pulmonary disease were divided into five age groups: term neonates, 1-6 months, 6-24 months, 2-6 years and 6-12 years. Anaesthetic induction was achieved with halothane in oxygen and air via mask. Vecuronium 0.1 mg.kg-1 was administered intravenously. During normocapnic manual ventilation by mask, endtidal halothane concentration was maintained at either 2xage-specific MAC (Method I) or 1.7% (Method II) in 20 patients in each age group for 10 min. In both Method I and Method II, systolic and mean blood pressure of term neonates and infants aged 1-6 months decreased significantly (P < 0.01) compared with other age groups. The results of this study demonstrate that neonates and young infants are more susceptible to haemodynamic depression during halothane anaesthesia than are older children, confirming clinical experience.

Inguinal herniorrhaphy in young infants: perianesthetic complications and associated preanesthetic risk factors

STUDY OBJECTIVES

(1) To prospectively observe and tabulate all perianesthetic complications in young infants undergoing herniorrhaphy with general anesthesia and (2) to identify all major postnatal complications and determine which, if any, might be significant risk factors for perianesthetic complications.

DESIGN

Prospective case control study.

SETTING

Columbus, Ohio, Children's Hospital, a teaching and tertiary referral center.

PATIENTS

One hundred two consecutive infants 60 weeks postconceptual age (PCA) or younger undergoing herniorrhaphy with general anesthesia.

INTERVENTIONS

None

MEASUREMENTS AND MAIN RESULTS

All perianesthetic complications occurring during anesthesia, in the postanesthesia care unit (PACU), during the remaining hospital stay, and within 30 days of anesthesia were recorded, and a detailed postnatal history was compiled. Fifty-five percent of 60 preterm infants [37 weeks gestational age (GA) or younger] and 50% of 42 term infants (older than 37 weeks GA) experienced at least one perianesthetic complication. Following discharge from the PACU, in-house complications were confined to the preterm group. Significant risk factors included a history of apnea, bradycardia, and ventilatory support for at least 24 hours after birth, mainly for respiratory distress syndrome.

CONCLUSIONS

In a teaching hospital, prospectively observed perianesthetic complications can occur in more than 50% of infants 60 weeks PCA or younger undergoing herniorrhaphy with inhalation anesthesia. Infants younger than 49 weeks PCA with a significant preanesthetic risk factor should be monitored overnight for apnea and bradycardia.