Cardiorespiratory effects of changes in end expiratory pressure in ventilated newborns

Abstract

Background:Positive pressure ventilation in premature infants can improve oxygenation, but may also diminish cerebral blood flow and cardiac output. Low brain and upper body flow (superior vena cava flow, SVC) increases the risk of intraventricular haemorrhage, with previous research showing that higher mean airway pressure is associated with low SVC flow. It is not known whether this is a direct effect of positive pressure ventilation or a reflection of severity of lung disease. The aim of this study was to determine whether positive end expiratory pressure (PEEP) in ventilated newborns could be increased without causing clinically relevant cardiorespiratory changes.

Methods:Ventilated newborns were studied before and 10 minutes after increasing PEEP from 5 to 8 cmH2O, then again when returned to baseline. Simultaneous echocardiographic and respiratory function measurements were collected during the intervention.

Results:Fifty infants were studied. Overall, increased PEEP was associated with a non-significant difference in mean SVC flow of -5 ml/kg/min (95%CI -12 to 3) but a significant reduction in right ventricular output of 17 ml/kg/min (95%CI 5 to 28). There was a non-significant increase in lung compliance of (median difference 0.02 ml/cmH2O/kg; p 0.093) and a significant decrease in lung resistance of 18 cmH2O/L/s (95%CI 10 to 26). There was a positive association between % change in lung compliance and % change in SVC flow when corrected for paCO2 changes (regression coefficient 0.4 % (95%CI 0.2 to 0.6)).

Conclusion:A short-term increase in PEEP does not result in a significant change in systemic blood flow, although 36% of infants had clinically important changes in flow (+/-25%).The intervention can improve dynamic lung function, especially airway resistance. Improvements in compliance tend to be associated with improvements in blood flow.