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Intensive Care Med. 2004 Dec;30(12):2180-7. Epub 2004 Oct 12.

Sustained moderate reductions in arterial CO2 after brain trauma time-course of cerebral blood flow velocity and intracranial pressure.

Author information

1
Department of Anaesthesia, University Hospital Basel, 4031 Basel, Switzerland. lsteiner@uhbs.ch

Abstract

OBJECTIVE:

In healthy volunteers cerebral blood flow starts to recover towards baseline within a few minutes of continued hyperventilation due to normalisation of perivascular pH. We investigated the time-course of changes in middle cerebral artery mean flow velocity (FVm) and intracranial pressure (ICP) in head-injured patients during sustained moderate reductions in arterial partial pressure of CO(2) (PaCO(2)).

DESIGN:

Observational study.

PATIENTS:

Twenty-seven sedated, mechanically ventilated patients with severe head injury.

INTERVENTIONS:

Measurements were made during and after routine determination of CO(2)-reactivity: an acute 20% increase in respiratory minute volume was followed by a 10-min stabilisation period and 50 min of continued moderate hyperventilation at a constant PaCO(2) (>3.5 kPa).

MEASUREMENTS AND RESULTS:

FVm was monitored with transcranial Doppler, ICP was monitored with intraparenchymal probes. During the 50-min period with stable PaCO(2) FVm increased in 36% of patients. All other patients showed a decline in FVm over the same time period. Overall FVm recovery was -0.03+/-0.14%.min(-1). The time-course of ICP changes was significantly different from that of FVm, with ICP reaching its lowest value earlier than FVm (23+/-12 vs 37+/-20 min; P = 0.001) and returning more rapidly towards baseline than FVm (0.23+/-0.23 vs -0.03+/-0.14%.min(-1); P< 0.0001).

CONCLUSIONS:

Head-injured patients may adapt differently to hyperventilation than healthy volunteers. Potentially harmful reductions in cerebral blood flow may persist beyond the duration of useful ICP reduction.

PMID:
15480563
DOI:
10.1007/s00134-004-2463-6
[Indexed for MEDLINE]

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