TO PEEP OR NOT TO PEEP

It is well recognised that reducing positive end expiratory pressure ( PEEP) leads to an increase in the tidal volume and minute volume in ve ntilated neonates. The magnitude of this effect is perhaps not commonl y appreciated, however. Effectively, PEEP is four times as potent as p eak inflation pressure (PIP) in bringing about changes in tidal volume . The influence of changes in PEEP and PIP on tidal volume and the rel ative magnitude of each are considered. Twenty one preterm infants wer e studied on 38 separate occasions. All were sedated, paralysed, and v entilated, 19 for hyaline membrane disease. A 1 cm H2O reduction in PE EP was twice as potent as a 2 cm H2O increase in PIP in achieving an i ncrease in tital volume (14 v 7%). Similarly, increasing PEEP by 1 cm H2O was twice as effective as a 2 cm H2O decrease in PIP in reducing t idal volume (13 v 6%). Small (0.5-1 cm H2O) changes in PEEP can often be used to improve ventilation and carbon dioxide elimination. Levels of PEEP of 4-5 cm H2O may, at times, impair gas exchange and contribut e to overdistension.