Neonate: duration of post-anesthesia monitoring

The development of postoperative apnea is a major concern with surgery in neonates.Infants at highest risk are those born prematurely, those with multiple congenital anomalies, those with a history of apnea and bradycardia, and those with chronic lung disease.It is thought that the etiology is multifactorial. Decreased ventilatory control and hypo-responsiveness to hypoxia and hypercarbia may be potentiated by anesthetic agents. Hypothermia, anemia, and respiratory muscle fatigue may also play a role. Other risk factors includepost-conceptual age less than 46-60 weeks at time of surgery.Anemia (hematocrit < 30%) has been determined to be independent of post-conceptual age for risk in the development of postoperative apnea.In general, the younger the patient’s gestational and post-conceptual ages, the greater the risk for postoperative apnea. Infants at high risk for development of postoperative apnea may benefit from a regional anesthetic as opposed to a general anesthetic. If supplemental sedation is used, the advantage is lost.

Cote combined data from eight prospective studies (255 patients) to develop an algorithm based on gestational age, post-conceptual age, apnea at home, size at gestational age, and anemia (Cote CJ et. al. Anesthesiology 82: 809, 1995). Cotes data showed that the incidence of apnea following inguinal hernia repair did not fall below 5% until gestational age reached 35 weeks and post-conceptual age reached 48 weeks, and that the incidence of apnea following inguinal hernia repair did not fall below 1% until gestational age reached 32 weeks and post-conceptual age reached 56 weeks (or post-gestational 35 weeks with post-conceptual 54 weeks). Any infant that exhibits apnea, has a history of apnea, or is anemic, should not undergo outpatient surgery

Background

Controversy exists as to the risk for postoperative apnea in former preterm infants. The conclusions of published studies are limited by the small number of patients. METHODS: The original data from eight prospective studies were subject to a combined analysis. Only patients having inguinal herniorrhaphy under general anesthesia were included; patients receiving caffeine, regional anesthesia, or undergoing other surgical procedures were excluded. A uniform definition for apnea was used for all patients. Eleven risk factors were examined: gestational age, postconceptual age, birth weight, history of respiratory distress syndrome, bronchopulmonary dysplasia, neonatal apnea, necrotizing enterocolitis, ongoing apnea, anemia, and use of opioids or nondepolarizing muscle relaxants. RESULTS: Two hundred fifty-five of 384 patients from eight studies at four institutions fulfilled study criteria. There was significant variation in apnea rates and the location of apnea (recovery room and postrecovery room) between institutions (P less than 0.001). There was considerable variation in the duration and type of monitoring, definitions of apnea, and availability of historical information. The incidence of detected apnea was greater when continuous recording devices were used compared to standard impedance pneumography with 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 less than 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 compared to appropriate- and large-for-gestational-age infants; (4) anemia was a significant risk factor, particularly for patients greater than 43 weeks’ postconceptual age; (5) a relationship to apnea with history of necrotizing enterocolitis, neonatal apnea, respiratory distress syndrome, bronchopulmonary dysplasia, or operative use of opioids and/or muscle relaxants could not be demonstrated. CONCLUSIONS: The analysis suggests that, if it is assumed that the statistical models used are equally valid over the full range of ages considered and that the average rate of apnea reported across the studies analyzed is accurate and representative of actual rates in all institutions, the probability of apnea in nonanemic infants free of recovery-room apnea is not less than 5%, with 95% statistical confidence until postconceptual age was 48 weeks with gestational age 35 weeks. This risk is not less than 1%, with 95% statistical confidence, for that same subset of infants, until postconceptual age was 56 weeks with gestational age 32 weeks or postconceptual age was 54 weeks and gestational age 35 weeks. Older infants with apnea in the recovery room or anemia also should be admitted and monitored. The data do not allow prediction with confidence up to what age this precaution should continue to be taken for infants with anemia. The data were insufficient to allow recommendations regarding how long infants should be observed in 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 different monitoring devices. Given the limitations of this combined analysis, each physician and institution must decide what is an acceptable risk for postoperative apnea” .

Findings from Cote et al Meta-Analysis (255 patients in 8 studies)

• Risk of apnea is related tobothgestational ageandactual age
• Anemiais a risk factor
• Apnea at homeis a risk factor
• SGAisprotective

An important question regarding postoperative apnea in infants is who should be admitted and monitored (and for how long) after outpatient surgery.The most conservative approach is to admit (for monitored 24 hour observation) all infants younger than 60 weeks post-conceptual age.Different hospitals have different age post-conceptual age guidelines for admission. The incidence of significant apnea and bradycardia is highest in the first 4 to 6 hours after surgery but has been reported up to 12 hours after surgery.A widely accepted guideline is to monitor all infants younger than 50 weeks post-conceptual age for at least 12 hours after surgery.In addition, outpatient or elective/non-urgent surgery may be delayed in infants younger than 50 weeks post-conceptual age if possible.High dose caffeine (10 mg/kg) and theophylline (because neonates metabolize the drug to caffeine) have been used as respiratory stimulantsto prevent and/or treat postoperative apneic episodes. Blood transfusion in anemic infants is not clearly beneficial in preventing post-operative apnea. Instead, it is recommended that anemic children get iron supplementation and the surgery be postponed (if possible) until the anemia resolves.