Severe head injuries: effects of prehospital mechanical ventilation on capnia.

Objective: To assess the effect on PaCO2 of mechanical ventilation during p rehospital management of severely head-injured patients. Study design: Retrospective observational study, Patients: Severely head-injured patients with Gasgow coma score less than o r equal to 8. All patients were sedated, with the trachea intubated and the lungs mechanically ventilated. Methods: According to the capnia measured at the admission in the neurosurg ical intensive therapy unit they were allocated into one of the following t hree groups : hypocapnia group (PaCO2 < 30 mmHg), recommended capnia group (PaCO2 = 30-38 mmHg) and hypercapnia group (PaCO2 > 38 mmHg). Results: Out of the 42 patients with similarly severe head injuries, 19% we re included in the recommended capnia group (PaCO2 : 34 +/- 2 mmHg), 38% in the hypocapnia group (PaCO2 : 23 +/- 3 mmHg) and 43% in the hypercapnia gr oup (PaCO2 : 47 +/- 7 mmHg). In all except three, PaO2 was above 95 mmHg. T he settings of ventilatory parameters on the ventilators were similar. Conclusion: In 81% of patients, mechanical ventilation was inadequate as fa r as PaCO2 levels are concerned. Major hypocapnia and hypercapnia carry a p otential risk for cerebral ischaemic. Therefore it is recommended to monito r PETCO2 during prehospital transport in medical ambulances and to determin e arterial blood gases at arrival of severely head-injured patients in the admission unit for emergencies. (C) 1999 Elsevier, Paris.