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Therapeutic hypothermia is applied to reduce hypoxia-induced organ injury. In the past decades, the use of hypothermia has increased in critically ill patients who are mechanically ventilated (MV). Data on the effect of hypothermia on gas exchange and lung mechanics in these patients are limited. In this retrospective study, we describe the effect of induced hypothermia and rewarming on respiratory parameters in patients after a cardiac arrest.
Patients with a Glasgow Coma Scale <8 after resuscitation for a cardiac arrest in whom hypothermia was applied (32 to 34°C), were enrolled. Patients with PaO2/FiO2 ratio <200 or MV with positive end-expiratory pressure (PEEP) >15 cmH2O were excluded. Ventilator settings and arterial blood gasses were retrieved from the electronic patient database during hypothermia and at every °C grade increase during rewarming. Statistics include z paired t test.
From a cohort of 98 patients, 35 patients were excluded, leaving 62 patients for analysis. During hypothermia, arterial pCO2 decreased, while end tidal (et) CO2 was low at unchanged minute volume ventilation (Figure (Figure1).1). Hypothermia increased the P/F ratio from 255 ± 55 to 283 ± 12 at unchanged PEEP (P < 0.05), while fluid balances were positive in all patients (2.5 ± 1.6 l). After rewarming, arterial pCO2 was unchanged while etCO2 increased. The P/F ratio after rewarming was unchanged compared with the start of hypothermia, while lower PEEP levels were applied (7.0 ± 0.4 cmH2O vs 6.1 ± 0.3 cmH2O, P < 0.05).
Induced hypothermia improved ventilation and oxygenation in critically ill patients. Hypothermia may be considered in patients with acute lung injury, in whom low minute ventilation results in severe hypercapnia.