Hypocapnia does not alter hepatic blood flow or oxygen consumption in patients with head injury.
OBJECTIVE
To evaluate the effects of hypocapnia on the systemic and hepatic circulations and oxygenation values in patients with head injury.


METHODS
Open-label, prospective study.


METHODS
University hospital, department of anesthesiology and intensive care unit.


METHODS
Eleven mechanically ventilated patients with isolated head trauma and stable hemodynamic status.


METHODS
At the beginning of the study, each patient presented with normocapnic ventilation. Mechanical hyperventilation was then adjusted to obtain stable hypocapnia over an interval of 24 hrs. Cardiac output and other systemic hemodynamic parameters were measured, using a pulmonary artery catheter. Hepatic parameters were measured via a catheter inserted into the hepatic vein. Total hepatic blood flow was determined by the Fick principle using a continuous infusion of indocyanine green. Arterial and hepatic venous blood gases were sampled to determine systemic and hepatic-splanchnic oxygenation. Measurements were done at the end of the four phases: a) 30 mins of normocapnia (N); b) 30 mins of hypocapnia (H0); c) 3 hrs of hypocapnia (H3); and d) 24 hrs of hypocapnia (H24). Intracranial pressure and cerebral perfusion pressure were hourly monitored throughout the study.


RESULTS
There were no significant changes in systemic hemodynamic parameters. The hepatic blood flow index did not differ from normocapnia (N 1.8 +/- 0.4 L/min/m2) to hypocapnia (H0 1.6 +/- 0.3 L/min/m2; H3 1.7 +/- 0.4 L/min/m2; H24 1.7 +/- 0.4 L/min/m2). The ratio of hepatic blood flow index to cardiac index remained stable throughout the study. Hypocapnia did not affect hepatic-splanchnic oxygen delivery and consumption.


CONCLUSIONS
Hypocapnic hyperventilation does not alter hepatic hemodynamic parameters in patients with head injury. This result may be related to the lack of changes in cardiac output or in the hepatic vasoreactivity. Moreover, hypocapnia does not modify hepatic-splanchnic oxygenation. Thus, in case of intracranial hypertension, hypocapnia might be used without undesirable effect on the hepatic-splanchnic perfusion.
Ichai
C
C
Department of Anesthesiology and Intensive Care, University of Nice School of Medicine, Hôpital Saint-Roch, France.
Levraut
J
J
Baruch
I
I
Samat-Long
C
C
Leverve
X
X
Grimaud
D
D
D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D006259:Craniocerebral Trauma / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D005260:Female; D006439:Hemodynamics; D006801:Humans; D016857:Hypocapnia / Q000209:etiology*; D007427:Intracranial Pressure; D008102:Liver Circulation; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D013997:Time Factors