Anaesthesia for ex–preterm infants

Abstract

An increasing number of preterm neonates survive, some of them with very short gestational age. Artificial ventilation is needed for about one forth of the heterogeneous preterm neonate group, oxygen therapy and continuous positive airway pressure for at least half of them. This treatment often results in lung disease (bronchopulmonary dysplasia BPD) with persistent need for oxygen therapy and sometimes prolonged ventilatory support. Secondary to this cardiac decompensation is common. Also without foregoing artificial ventilation and other intensive therapy a considerable number of preterm infants have complications related to their immaturity such as respiratory insufficiency and disturbanceof respiratory regulation, intracranial haemmorage, retrolental fibroplasia and feeding difficulties.The dominating indication for surgery is repair of inguinal hernia, reported to be present in 1555% of prematures (1) and ophthalologicaltreatnt. Careful perioperative anaesthetic and recovery care is of course neccesary for extensive surgery or other major treatment but also for minor surgical procedures. The anaesthetist will face several problems with the expreterm infant. This presentation is focused on the immatum control of breathing. For the ex-preterm having been through period of a neonatal intensive care therapy respiratory insufiiency and cardiac decompensarion and its consequences for anaesthesia must always be evaluated. These subjects are shortly depicted. For the low weight infant practical details such as airway control, temperature instability, drug and fluid administration also deserve special attention but are not dealt with in this presentation. Moreover the relatives very often need support having been through a long period of fear and uncertainty at the time when the child needs operation and anaesthesia. CONTROL OF BREATHINGApnea and periodic breathing is common in preterm neonates. The subject has recently been covered in two succinct reviews (2,3) with an extensive litterature survey to be consulted when specific references are not given in this text.The incidence of disturbance of respiratory control is inversly related to gestational and postconceptional age as is its consequences; hypoxia and bradycardia, eventually resulting in circulatory collapse. The interactive mechanisms behind the controlof breathing are not fully adapted to extrauterine life in the preterm infant, Prolonged ventilatory support and oxygen therapy appears to delay the maturing of this vital function. Hypoxia has an inhibitory effect on ventilation in the neonate and for a longer period in the expreterm baby. This may emanate from a protective fetal reflex inhibiting breathing movements during periods of reduced placental oxygen supply in order to spare unnecessary oxygen consumtion. Hypoxia in combination with little increase in ventilation in response to hypercarbia, especially with acidosis and/or hypothermia may result in prolonged apnoea. Anemia, commonly found in prematures, also contributes to an increased incidence of r...