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


METHODS
Observational study.


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


METHODS
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).


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.
Department of Anaesthesia, University Hospital Basel, 4031 Basel, Switzerland. lsteiner@uhbs.ch
Luzius A
LA
Steiner
Marcella
M
Balestreri
Andrew J
AJ
Johnston
Marek
M
Czosnyka
Jonathan P
JP
Coles
Doris A
DA
Chatfield
Peter
P
Smielewski
John D
JD
Pickard
David K
DK
Menon
D000293:Adolescent; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D001794:Blood Pressure; D001930:Brain Injuries / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000378:metabolism*; D005260:Female; D015600:Glasgow Coma Scale; D006801:Humans; D006985:Hyperventilation / Q000378:metabolism*; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D013997:Time Factors
D002245:Carbon Dioxide