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.
Steiner
Luzius A
LA
Department of Anaesthesia, University Hospital Basel, 4031 Basel, Switzerland. lsteiner@uhbs.ch
Balestreri
Marcella
M
Johnston
Andrew J
AJ
Czosnyka
Marek
M
Coles
Jonathan P
JP
Chatfield
Doris A
DA
Smielewski
Peter
P
Pickard
John D
JD
Menon
David K
DK
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