Anesth Analg 2003;96:1537-1538
© 2003 International Anesthesia Research Society
LETTERS TO THE EDITOR
Fasting, Halothane, and Hypotension
Joel B. Gunter, MD
Department of Anesthesia, Children’s Hospital Medical Center, Cincinnati, OH
To the Editor:
I find it impossible to concur with the conclusion of Friesen et al. (1) that duration of fasting correlates with the hemodynamic response to halothane. Indeed, in a study involving 250 children divided into 20 subgroups based on age and duration of fast, only one subgroup, containing only four subjects, demonstrated a change in systolic blood pressure (and, by extension, in mean arterial pressure) different from any age-equivalent subgroup. Given 30 subgroup pairings for comparison (6 subgroup pairings within each of 5 age groups), it would be surprising if there were not at least one significant result. As there were no other significant differences in hemodynamic responses to halothane induction related to duration of fast among the other 29 pairings, it appears that, in fact, halothane induction is tolerated equally well (or poorly) regardless of duration of fasting.
Even in the subgroup demonstrating a difference, there was no difference in the absolute blood pressure versus the comparator group; the difference in blood pressure change was attributable to a higher baseline blood pressure in the 8- to12-h fast subgroup versus the 0- to 4-h fast subgroup. Examination of Figures 1 and 2 in the article reveals no obvious trends in the magnitude of the blood pressure response to halothane induction other than the trend seen for 1- to 6-mo-old infants; in fact, for the 6–24 mo and 2–6 y groups, the greatest decreases in blood pressure were seen in the subgroups with the shortest fast (although the 2–6 y, 0–4 h subgroup contained only one subject).
The proliferation of subgroups within a study can make analysis and interpretation of results problematic. Analysis of this data using a multiple linear regression model with blood pressure response as the dependent variable and age and duration of fast (as continuous variables) as the independent variables would reveal whether or not there was indeed any relationship between either age or duration of fast and hemodynamic response to halothane induction. Incorporation of an interaction term between age and duration of fast would allow examination of the question of whether or not the effect of duration of fast on hemodynamic response varied with age.
The authors are to be commended on addressing, in a systematic fashion, an issue of importance to all who anesthetize children with halothane. However, their results should be interpreted as a reassurance that increasing duration of fasting does not negatively impact the hemodynamic response to halothane induction, or, perhaps, as a caution that significant decreases in blood pressure after halothane induction are likely regardless of the brevity of fasting.
Reference
- Friesen RH, Wurl JL, Friesen RM. Duration of preoperative fast correlates with arterial blood pressure response to halothane in infants. Anesth Analg 2002; 95: 1572–6.[Abstract/Free Full Text]
Response
Robert H. Friesen, MD
Department of Anesthesiology, Children’s Hospital, Denver, Colorado
In Response:
We believe that prolonged preoperative fasting may be a significant clinical problem in infants and sought to look at the issue from a perspective that has not been previously reported. The weaknesses of our study were acknowledged and discussed in our paper. Of course, it would have been preferable to have equal numbers of subjects in each fasting category, but to increase the number of infants subjected to prolonged fasts by randomization would not have been ethical. Our statistical methods were valid and support our conclusion. Our statistical design was not as elaborate as Dr. Gunter supposes. Each age group was analyzed separately, so there were only four subgroups within each age group. Our method of comparing the absolute changes from baseline, rather than the means of the lowest blood pressures, is clearly preferable when comparing groups that may have different baseline values and did, indeed, demonstrate a difference among the fasting groups within the 1–6 month age group.
One of Dr. Gunter’s observations raises an interesting question. Although the baseline blood pressures were statistically similar among the fasting groups of the 1- to 6-mo-old infants, the mean baseline blood pressure in the 8–12 h fasting group was higher. Does this indicate that an additional problem—preoperative stress—is associated with prolonged preoperative fasting in infants? As adherence to published preoperative fasting guidelines improves, we hope that prolonged fasts will become truly rare events in infants and children.
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