The effect of induced hypothermia on respiratory parameters in mechanically ventilated patients

Mild hypothermia is increasingly applied in the intensive care unit. Knowledge on the effects of hypothermia on respiratory parameters during mechanical ventilation is limited. In this retrospective study, we describe the effect of hypothermia on gas exchange in patients cooled for 24 h after a cardiac arrest.

Respiratory parameters were derived from electronic patient files from 65 patients at the start and end of the hypothermic phase and at every centigrade increase in body temperature until normo-temperature, including tidal volume, positive end expiratory pressure (PEEP), plateau pressure, respiratory rate, exhaled CO(2) concentrations (etCO(2)) and FIO(2). Static compliance was calculated as V(T)/P(plateau)-PEEP. Dead space ventilation was calculated as (PaCO(2)-etCO(2))/PaCO(2).

During hypothermia, PaCO(2) decreased, at unchanged PaCO(2)-etCO(2) gap and minute ventilation. During rewarming, PaCO(2) did not change, while etCO(2) increased at unchanged minute ventilation. Dead space ventilation did not change during hypothermia, but lowered during rewarming. During hypothermia, PaO(2)/FIO(2) ratio increased at unchanged PEEP levels. Respiratory static compliance did not change during hypothermia, nor during rewarming.

Hypothermia possibly improves oxygenation and ventilation in mechanically ventilated patients. Results may accord with the hypothesis that reducing metabolism with applied hypothermia may be beneficial in patients with acute lung injury, in whom low minute ventilation results in severe hypercapnia.