CDH: Ventilation strategy

A congenital diaphragmatic hernia (CDH) is an early developmental defect that results in the extrusion of intraabdominal organs (ie. stomach, small intestines, kidney, liver) into the thoracic cavity. This defect can be isolated or associated with multiple congenital abnormalities with cardiac anomalies being the most common. Ninety-percent of CDH are located in the posterolateral diaphragm (Bochdalek’s hernia), 3/4 of which are left sided. Physiologic consequences of CDH include lung hypoplasia, pulmonary hypertension, and pulmonary arteriolar dysregulation/reactivity (Davis, et al). Historically, CDH was considered a surgical emergency. It was approached using aggressive hyperventilatory strategies with the goal of obtaining pulmonary vasodilation through hyperoxia and respiratory alkalosis. This strategy often used high peak inspiratory pressures, ventilatory frequency, and oxygen concentration. This tactic was eventually abandoned after further research stressed the harmful effects of large lung inflations in the postnatal period as well as the prominence of iatrogenic chronic lung disease in CDH survivors (Ingimarsson, et al.)

Due to the concern of aggressive ventilation on both the short-term survival as well as long-term outcomes of CDH, ventilatory strategies that employ small tidal volumes with permissive hypercapnea have gained widespread acceptance. Boloker, et al. suggested preservation of spontaneous ventilation, acceptance of a pre-ductal oxygen saturation of 90-95% with >80% tolerated if the infant appears comfortable, permissive hypercapnia of 60-65 mmHg, and peak inspiratory pressures < 25 cm H₂0. Surgical intervention should be delayed until the ventilator support has been minimized, pre- to post-ductal saturation gradient has decreased, and pulmonary hypertension has minimized as suggested by ECHO. In patients with refractory pulmonary hypertension, some institutions utilize nitric oxide. However, the effectiveness of this intervention in CDH has not been clearly demonstrated (Bloch, et al. 2007). Further salvage techniques involve high frequency oscillatory ventilation (HFOV) and extracorporeal membrane oxygenation (ECMO). While joint studies between Toronto and Boston have shown no survival benefit between the two interventions, many centers now reserve ECMO for rescue therapy for infants who have failed other means of ventilation (Bohn, 2006).