While in a state of quiet sleep, 15 full-term male, 15 full-term female, and 15 premature male infants were presented a single auditory stimulus. Heart rate was continuously monitored and scored for mean and standard deviation in the 10-sec prestimulus period, as well as for peak and trough magnitude of the response and the latencies to these points. The infants tended to show a diphasic response, acceleration followed by rebound deceleration below baseline. Prestimulus mean and variability were inversely related, and significantly predictive of the amount of acceleration. Premature infants showed a high resting heart rate, and a milder response to the stimulus. Also evident were larger accelerations and longer latencies to trough for full-term females.

Premature infants are capable of mounting physiologic and metabolic responses to pain. Systemic and local anesthesia reduce stress responses to major and minor surgical procedures. We evaluated the effects of local anesthesia (5 mg/kg lidocaine) preceded by either 1 mg/kg secobarbital (S) intravenously or by 2 micrograms/kg fentanyl (F) intravenously on the stress response to Broviac catheter placement. Twenty-nine premature infants ages 5 to 30 days, weighing between 650 and 1350 gm, were randomly assigned to either S or F groups. Age, birthweight, sex, race, and severity of illness were similar among S and F groups. Heart rate and blood pressure remained unchanged throughout the procedure. Oxygen saturation (O2sat) declined significantly in both groups during skin preparation and wound closure, but not during incision, dissection, or tunneling. In spite of fractional inspired oxygen adjustments made in 13 of 14 S- and 3 of 15 F-treated patients, decline in O2sat was more common and more pronounced (p less than 0.01) in S-treated babies. Hyperglycemic responses occurred in all S- and in none of the F-treated patients (p less than 0.001). Norepinephrine plasma concentrations did not change during Broviac catheter placement in either F or S group. Epinephrine concentrations were more elevated in S- than in F-treated patients, although these differences were not statistically significant. Low-dose fentanyl analgesia effectively complements local lidocaine anesthesia during Broviac catheter placement. Sedatives neither abolish metabolic responses to surgical stress nor prevent profound and persistent oxygen desaturation.