Cardiorespiratory effects of changes in end expiratory pressure in ventilated newborns.

Background: Positive pressure ventilation in premature infants can improve oxygenation but may diminish cerebral blood flow and cardiac output. Low superior vena cava (SVC) flow increases risk of intraventricular haemorrhage, and higher mean airway pressure is associated with low SVC flow. Whether this is a direct effect of positive pressure ventilation or a reflection of severity of lung disease is not known. This study aimed to determine if positive end expiratory pressure (PEEP) in ventilated newborns could be increased without clinically relevant cardiorespiratory changes.

Method: Ventilated newborns were studied before and 10 min after increasing PEEP (5 cm H(2)O to 8 cmH(2)O) and again when PEEP returned to baseline. Echocardiographic and respiratory function measurements were collected during the intervention.

Results: In 50 infants, increased PEEP was associated with a non-significant difference in mean SVC flow of -5 ml/kg/min (95% CI -12 to 3 ml/kg/min) but a significant reduction in right ventricular output of 17 ml/kg/min (95% CI 5 to 28 ml/kg/min). The increase in lung compliance was non-significant (median difference 0.02 ml/cmH(2)O/kg) and the decrease in lung resistance (18 cmH(2)O/l/s; 95% CI 10 to 26 cm H(2)O/l/s) was significant. Changes (%) in lung compliance and SVC flow, when corrected for Paco(2), were positively associated (regression coefficient 0.4%; 95% CI 0.2% to 0.6%).

Conclusion: A short-term increase in PEEP does not lead to significant changes in systemic blood flow, although 36% of infants in the present study 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.