Intracranial elastance in isoflurane-anesthetized horses.

This research seeks to understand whether higher intracranial pressure (ICP) during spontaneous ventilation in anaesthetised horses corresponds with increased intracranial elastance (i.e., ICP changes in relation to changes in intracranial volume). The study found that in isoflurane-anesthetized horses, small shifts in intracranial volume can provoke significant ICP changes and exacerbate existing intracranial hypertension. However, the removal of small CSF volumes might lead to rapid compensatory replacement, indicating a possible equilibrium maintenance of heightened intracranial volumes during the anesthesia process.

Research Method

• The study involved six adult horses. All horses were anaesthetised and maintained under anesthesia for five hours using isoflurane, administered at a constant dose (1.2 times the minimum alveolar concentration).
• ICP measurements were taken directly via a strain gauge transducer inserted in the subarachnoid space. Arterial blood pressure measurements were taken from a carotid artery.
• Physiological responses were recorded after 15 minutes of normocapnic controlled ventilation and then after 10 minutes of spontaneous ventilation.
• Aliquots (3 mL) of cerebrospinal fluid (CSF) were taken from each horse during SV until the ICP returned to CV values. The resultant pressure-volume curves were then used to determine intracranial elastance.

Research Findings

• ICP measurements after the removal of the first CSF aliquot ranged from 0.2 to 3.7 mm Hg/mL.
• The largest curves concerning pressure-volume were observed after removing the initial CSF aliquot.
• There was a noted second-order relationship between spontaneous ventilation ICP and initial intracranial elastance.

Conclusions

• The research concluded that small changes in intracranial volume could lead to significant changes in ICP in isoflurane-anesthetized horses.
• Increased intracranial elastance could also further worsen existing intracranial hypertension.
• Removal of small volumes of CSF may prompt rapid compensatory replacement from other intracranial compartments, suggesting a potential to maintain steady-state increase in intracranial volume during the administration of isoflurane anesthesia.