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The respiratory patterns of 22 premature infants were continuously monitored using an impedance plethysmograph which activated an alarm system for apnea. Apnea of greater than 30 seconds' duration occurred in about 25% of the infants studied in the first 10 days of life. Bradycardia of less than 100 beats per minute occurred within 30 seconds or less of the onset of apnea. The fall in heart rate was more rapid during those apneic episodes most difficult to terminate. All apneic episodes began in expiration during periodic breathing. The response to a standardized method of stimulation to re-initiate breathing was evaluated. In most instances, cutaneous stimulation resulted in resumption of breathing. However, 8% of the episodes required resuscitation with oxygen by bag and mask. Apneic episodes of 45 or more seconds' duration resulted in mottling, cyanosis, hypotonia, and unresponsiveness to stimulation suggesting that early intervention is required to prevent significant hypoxia and central depression from apnea. In six additional infants having apnea, higher environmental temperatures (near the upper limit of the "thermoneutral zone") were associated with an increased incidence of apnea. Continuous monitoring of respiration in small infants is now clinically feasible.
Daily et al. (Tue,) studied this question.