POSTOPERATIVE APNEA IN FORMER PRETERM INFANTS AFTER INGUINAL HERNIORRHAPHY - A COMBINED ANALYSIS

Background: Controversy exists as to the risk for postoperative apnea in former preterm infants, The conclusions of published studies are li mited by the small number of patients. Methods: The original data from eight prospective studies were subject to a combined analysis. Only p atients having inguinal herniorrhaphy under general anesthesia were in cluded; patients receiving caffeine, regional anesthesia, or undergoin g other surgical procedures were excluded. A uniform definition far ap nea was used for all patients, Eleven risk factors were examined: gest ational age, postconceptual age, birth weight, history of respiratory distress syndrome, bronchopulmonary dysplasia, neonatal apnea, necroti zing enterocolitis, ongoing apnea, anemia, and use of opioids or nonde polarizing muscle relaxants. Results: Two hundred fifty-five of 384 pa tients from eight studies at four institutions fulfilled study criteri a. There was significant variation in apnea rates and the location of apnea (recovery room and postrecovery room) between institutions (P < 0.001). There was considerable variation in the duration and type of m onitoring, definitions of apnea, and availability of historical inform ation. The incidence of detected apnea was greater when continuous rec ording devices were used compared to standard impedance pneumography w ith alarms or nursing observations. Despite these limitations, it was determined that: (1) apnea was strongly and inversely related to both gestational age (P = 0.0005) and postconceptual age (P < 0.0001); (2) an associated risk factor was continuing apnea at home; (3) small-for- gestational-age infants seemed to be somewhat protected from apnea com pared to appropriate- and large-for-gestational-age infants; (4) anemi a was a significant risk factor, particularly for patients, 43 weeks' postconceptual age; (5) a relationship to apnea with history of necrot izing enterocolitis, neonatal apnea, respiratory distress syndrome, br onchopulmonary dysplasia, or operative use of opioids and/or muscle re laxants could not be demonstrated. Conclusions: The analysis suggests that, if it is assumed that the statistical models used are equally va lid over the full range of ages considered and that the average rate o f apnea reported across the studies analyzed is accurate and represent ative of actual rates in all institutions, the probability of apnea in nonanemic infants free of recovery-room apnea is not less than 5%, wi th 95% statistical confidence until postconceptual age was 48 weeks wi th gestational age 35 weeks. This risk is not less than 1%, with 95% s tatistical confidence, for that same subset of infants, until postconc eptual age was 56 weeks with gestational age 32 weeks or postconceptua l age was 54 weeks and gestational age 35 weeks. Older infants with ap nea in the recovery room or anemia also should be admitted and monitor ed. The data do not allow prediction with confidence up to what age th is precaution should continue to be taken for infants with anemia. The data were insufficient to allow recommendations regarding how long in fants should be observed recovery. There is additional uncertainty in the results due to the dramatically different rates of detected apnea in different institutions, which appear to be related to the use of di fferent monitoring devices. Given the limitations of this combined ana lysis, each physician and institution must decide what is an acceptabl e risk for postoperative apnea.