Vol. 92, Issue 6, 2542-2546, June 2002
Effects of body position on intracranial and cerebral
perfusion pressures in isoflurane-anesthetized horses
Robert J.
Brosnan1,
Eugene P.
Steffey1,
Richard A.
LeCouteur1,
Ayako
Imai1,
Thomas
B.
Farver2, and
Gregg D.
Kortz1
Departments of 1 Surgical and Radiological Sciences
and 2 Reproduction and Population Health, School of
Veterinary Medicine, University of California, Davis, California 95616
Inhalant
anesthetics may interfere with normal cerebrovascular
autoregulation. It was, therefore, hypothesized that
intracranial pressure (ICP) and cerebral perfusion pressure (CPP)
in isoflurane-anesthetized horses would be especially sensitive to body
and head position because of the potential for large hydrostatic
gradients between the brain and heart in this species. Anesthesia was
induced and maintained in six clinically healthy, unmedicated geldings
with 1.57% isoflurane in O2; mechanical ventilation was
used to maintain normocapnia. ICP was measured by using a subarachnoid
strain-gauge transducer. Blood gases and carotid arterial, right
atrial, and airway pressures were also measured. Five body positions
were studied in semirandomized order: dorsal recumbency (DR) with head down (HD), DR with head level (HL), lateral recumbency (LR), sternal recumbency (SR) with HL, and SR with head up (HU). Data were analyzed by using paired t-tests. ICP and CPP values, respectively,
are as follows (means ± SD): 36 ± 4 and 55 ± 18 mmHg
(DR-HD); 34 ± 6 and 51 ± 32 mmHg (DR-HL); 24 ± 5 and
48 ± 4 mmHg (LR); 19 ± 11 and 87 ± 12 mmHg (SR-HL);
and 
14 ± 7 and 71 ± 10 mmHg (SR-HU). Significant
differences were found among all positions, except for SR-HL vs. LR.
Significant increases in CPP were observed only in sternal positions.
In conclusion, ICP in isoflurane-anesthetized horses changes inversely
with the brain-to-heart hydrostatic gradient. DR may also cause
increases in ICP, irrespective of head position.
posture; equine
