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Duration of Preoperative Fast Correlates with Arterial Blood Pressure Response to Halothane in Infants

Friesen, Robert H., MD; Wurl, Jonathan L., MD; Friesen, Richard M.

doi: 10.1097/00000539-200212000-00018
PEDIATRIC ANESTHESIA: Research Report
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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.

Department of Anesthesiology, The Children’s Hospital and the University of Colorado School of Medicine, Denver, Colorado

August 21, 2002.

Address correspondence and reprint requests to R. H. Friesen, MD, Department of Anesthesiology, The Children’s Hospital, 1056 E. 19th Ave., Denver, CO 80218. Address e-mail to Friesen.Robert@tchden.org.

Although preoperative fasting guidelines have been developed to optimize patient care (Table 1) (1), it is difficult for the anesthesiologist to actually control fasting duration in the nonhospitalized preoperative infant and child. Significant hypotension is common during halothane anesthesia in infants (2,3) and is age related (4). We hypothesized that the duration of the preoperative fast affects the decrease in blood pressure observed in infants and children during halothane anesthesia.

Table 1

Table 1

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Methods

This study was approved by the IRB of The Children’s Hospital. Two-hundred-fifty unpremedicated patients, aged from 0 to 12 yr and scheduled for elective surgical procedures, were studied. All were of ASA physical status I–III and were without known cardiac disease, pulmonary disease, or diseases affecting intravascular fluid volume or balance (e.g., gastrointestinal obstructive or inflammatory diseases). Patients were divided into 5 age groups: term neonates (older than 37 wk gestational age and <1 mo postnatal age) (n = 50), 1–6 mo (n = 50), 6–24 mo (n = 50), 2–6 yr (n = 50), and 6–12 yr (n = 50). Preoperative fasting time was not controlled but was recorded by the investigators at the time of anesthetic induction.

Anesthesia was induced with increasing concentrations of halothane in oxygen and air (fraction of inspired oxygen, 0.50) via mask and a semiclosed circle absorber system. The inspired halothane concentration did not exceed 2 minimum alveolar anesthetic concentration (MAC) by more than 0.5 vol%. Soon after consciousness was lost, a peripheral IV catheter was inserted, and vecuronium 0.1 mg/kg was administered. During normocapnic (end-tidal Pco2, 35–40 mm Hg) manual ventilation by mask, end-tidal halothane was maintained at twice the age-specific MAC (5,6) for 10 min to allow myocardial uptake of halothane (at least 4 times the myocardial time constant for halothane) (7). Peak inspiratory pressure during manual ventilation was maintained within a range of 14–18 cm H2O. The patients remained supine and were not exposed to noxious stimuli, such as tracheal intubation or surgical incision, during the study period. Body temperature was maintained by the use of warming blankets and/or radiant heating lamps. IV infusion of 10 mL/kg of lactated Ringer’s solution with 5% dextrose solution was completed by the end of the 10-min period of maintenance at 2 MAC halothane.

Inspired and end-tidal carbon dioxide and halothane concentrations were monitored with an infrared respiratory gas monitor (RGM 5250; Ohmeda, Louisville, CO). Respiratory gases were sampled from the inlet of low-dead-space Rendell-Baker Soucek masks (Sims Portex, Kent, UK). Heart rate (HR) and systolic (SAP) and mean (MAP) arterial blood pressure were monitored noninvasively by using an automated blood pressure device (Dinamap 1846SX; Critikon, Tampa, FL) (8) and were recorded at 1-min intervals. After 10 min of maintenance at 2 MAC halothane, the study was terminated and the patient managed as appropriate for the surgical procedure.

Patients were grouped by duration of preoperative fast (0–4 h, 4–8 h, 8–12 h, and >12 h). Within each age group, the HR, SAP, and MAP data (baseline values, 2 MAC values, and absolute changes from baseline to 2 MAC values) were compared among fasting groups by using one-way analysis of variance, followed post hoc by Fisher’s protected least significant difference test for multiple means comparisons. Logistic regression analysis was used to correlate the duration of fasting with the change in SAP, MAP, and HR within each age group. P < 0.05 was considered to be statistically significant.

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Results

Demographic data are displayed in Table 2. Twenty-one patients aged 0–1 mo, 6 patients aged 1–6 mo, 4 patients aged 6–24 mo, and 1 patient aged 6–12 yr were given maintenance fluids IV up to the time of induction and were, therefore, described as having zero fasting time.

Table 2

Table 2

Table 2

Table 2

Hemodynamic values and changes are displayed for each age group in Table 2 and Figures 1 and 2. Baseline blood pressure values were within normal limits for age (9) and did not differ significantly among the fasting groups within each age group. In the 1- to 6-mo age group, the changes (decreases) in SAP and MAP from baseline to 2 MAC were significantly (P < 0.05) greater in infants who had fasted 8–12 h than in infants who had fasted 0–4 h. Among neonates, no statistically significant differences were noted, but fasting duration exceeded 8 h in only three patients. Differences in the changes of SAP and MAP among fasting groups were not significantly different within the older age groups. The changes in HR from baseline to 2 MAC were not significantly different among the fasting groups in any age group. Logistic regression analysis of the decreases in SAP from baseline to 2 MAC (mm Hg) by fasting group was significant in the 1- to 6-mo age group (SAP, P = 0.027; MAP, P = 0.075), but not in the other groups.

Figure 1

Figure 1

Figure 2

Figure 2

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Discussion

Depression of blood pressure by halothane in pediatric patients is dose dependent (10) and age dependent (4). The results of this study demonstrate that the duration of the preoperative fast is an additional risk factor for the development of hypotension during halothane anesthesia in infants. When preoperative fasting exceeded 8 hours in infants one to six months old, the decreases in SAP and MAP were significantly greater than in similar patients who had fasted for less than 4 hours. The decreases in SAP correlated significantly with the duration of fasting in infants one to six months old.

Fasting guidelines for children were developed to minimize the volume of gastric contents (liquid and solid) at the time of anesthetic induction (1). As such, many practitioners regard the guidelines as minimum fasting duration. Viewing the guidelines as recommendations for optimal fasting duration, on the other hand, would tend to eliminate prolonged fasts. Adherence to the guidelines with this goal has been shown to achieve benefits of clinical importance in infants and children; these benefits range from maintenance of patient comfort to avoidance of hypoglycemia and dehydration (11–17).

Ingestion of clear liquids up to two hours before surgery was shown to significantly diminish irritability and improve the perioperative experience of children without altering the volume or acidity of gastric contents at the time of anesthetic induction (11). Similarly, ingestion of apple juice three hours before anesthetic induction reduced thirst and hunger in children when compared with subjects who fasted after midnight (12).

Some children who have undergone a prolonged preoperative fast have been found to be hypoglycemic at the time of anesthetic induction. This association has been documented in several reports over many years (13–17). Ingestion of apple juice two to three hours before surgery probably prevents hypoglycemia in most infants and children, although its effect on perioperative glucose homeostasis is less predictable (17).

Avoiding prolonged preoperative fasting has been assumed to prevent hypovolemia and hypotension during anesthetic induction (3,17,18). Diaz (3) believed that the incidence of hypotension was more frequent in infants who fasted for longer than eight hours before surgery, but the differences in his retrospective study were not statistically significant. Coté(18) speculated that, by offering clear glucose-containing solutions two to three hours before surgery, “the incidence of severe hypotension during mask induction, due to relative hypovolemia in fasting infants and small children, may be reduced.” The results of our study support this statement, although measurement of intravascular volume will need to be performed before hypovolemia can be proven to exist.

An important weakness of this study is that adequate power was not achieved in most age groups to significantly reduce the probability of a Type II statistical error; i.e., fasting duration may have affected blood pressure in more groups, but sample size was inadequate to prove this. Retrospective power analysis demonstrated that adequate power was achieved in only the one- to six-month age group. The fact that the duration of the preoperative fast was not controlled in this study contributed to this problem and led to uneven distribution and great variability in the number of subjects in each fasting group. Thus, the number of infants fasting for longer than eight hours, for example, was relatively small. However, we believe that prospectively assigning patients to different fasting groups and requiring a fast of more than eight hours by protocol would have been unethical. Despite this variable distribution among the fasting groups, we still observed significant differences in the one- to six-month age group.

Most anesthesiologists follow preoperative fasting guidelines that are similar to those published by the American Society of Anesthesiologists (Table 1) (19) and share them with surgeons and patients. Actual adherence to guidelines, however, can be quite variable because of variance in instructions from surgeons’ offices, compliance of patients and their families, and disruptions of surgical schedules. Furthermore, fasting guidelines are frequently viewed as recommendations for minimum fasting times without regard to the maximum duration of fasts. These problems can result in a wide range of actual fasting durations when infants and children present for anesthetic care.

Previous investigations cited above have demonstrated that prolonged fasting times are associated with irritability, thirst, and hypoglycemia and that feeding clear fluids two to four hours before surgery can prevent these problems. The results of our study demonstrate that fasting for longer than eight hours is also associated with a significantly larger decrease in blood pressure during halothane anesthesia in infants. We recommend that prolonged fasting be avoided in infants by adhering to published fasting guidelines.

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References

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© 2002 International Anesthesia Research Society