[Severe head injuries: effects of pre-hospital mechanical ventilation on capnia]

Abstract

Objective: To assess the effect on PaCO2 of mechanical ventilation during prehospital management of severely head-injured patients.

Study design: Retrospective observational study.

Patients: Severely head-injured patients with Glasgow coma score < or = 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 neurosurgical intensive therapy unit they were allocated into one of the following three 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% were included in the recommended capnia group (PaCO2: 34 +/- 2 mmHg), 38% in the hypocapnia group (PaCO2: 23 +/- 3 mmHg) and 43% in the hypercapnia group (PaCO2: 47 +/- 7 mmHg). In all except three, PaO2 was above 95 mmHg. The settings of ventilatory parameters on the ventilators were similar.

Conclusion: In 81% of patients, mechanical ventilation was inadequate as far as PaCO2 levels are concerned. Major hypocapnia and hypercapnia carry a potential risk for cerebral ischaemic. Therefore it is recommended to monitor PETCO2 during prehospital transport in medical ambulances and to determine arterial blood gases at arrival of severely head-injured patients in the admission unit for emergencies.