Effects of body position on intracranial and cerebral perfusion pressures in isoflurane-anesthetized horses

Abstract

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 O(2); 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.

Different Compartments of Intracranial Pressure and Its Relationship to Cerebral Blood Flow

“…24 Body position shows only an influence on global ICP levels. 25 ICP changes may be related to changes in abdominal pressure or organ displacement producing possible cranial displacement of the diaphragm, increased thoracic pressure, and external compression of the vena cava. 24 But neither head nor body position have any influence on focal ICP levels or intracranial ICP gradients.…”

Neurologic Abnormalities and Cerebrospinal Fluid Changes in Horses Administered Fumonisin B1Intravenously

“…Intracranial pressure in horses is clearly sensitive to changes in body and head position because of the potential for large hydrostatic gradients between the brain and heart in this species. 53 When horses ingesting fumonisin lower their heads to eat, we think they are more prone to developing cerebral edema from hydrostatically driven increased blood flow because of fumonisin blockade of normal vascular regulatory mechanisms.…”

Central Nervous System Trauma

“…55 More invasive diagnostic and monitoring modalities are available (Table 24.3). Methods to measure and monitor intracranial and cerebral perfusion pressures have been described for use in foals 56 and adult horses [57][58][59][60][61] ; however, these techniques have thus far not been scientifically evaluated in clinical cases. In human medicine, development of advanced bedside neuromonitoring devices has been an important focus in neurocritical care.…”