Effects of ventilation and isoflurane end-tidal concentration on intracranial and cerebral perfusion pressures in horses.

The research conducted an examination on the impact of isoflurane concentration and different types of ventilation on intracranial pressure and cerebral perfusion pressure in horses under anesthesia.

Study Design and Methods

• The study was conducted on six healthy, adult horses of various breeds. These horses were not pre-medicated prior to the experiment.
• Anesthesia was induced and maintained with isoflurane in oxygen.
• For measurement of intracranial pressure (ICP), a subarachnoid strain gauge transducer was used. Furthermore, blood gas tensions and carotid artery pressures were recorded.
• Four different isoflurane doses were used throughout the experiment, which corresponded to 1.0, 1.2, 1.4, and 1.6 times the minimum alveolar concentration (MAC).
• Data were collected from the horses under two ventilation conditions – spontaneous and controlled – at each dosage level.

Study Findings

• It was observed that an increase in the end-tidal concentration of isoflurane led to significant, dose-dependent decreases in both mean arterial pressure (MAP) and cerebral perfusion pressure (CPP). However, no notable change was observed in intracranial pressure (ICP).
• Spontaneous ventilation under a state of hypercapnia resulted in a significant increase in both MAP and ICR when compared to controlled ventilation under normocapnia; there was no observed change in CPP for this case.

Conclusions from the Study

• The study concluded that hypercapnia potentially increases the cerebral blood flow (CBF) by maintaining CPP amidst assumed cerebral vasodilation in healthy anesthetized horses.
• However, the influence of isoflurane dose on cerebral blood flow remains uncertain as it appears to depend on the contrasting effects of a reduction in CPP and cerebral vasodilation.