Temporal and concentration effects of isoflurane anaesthesia on intestinal tissue oxygenation and perfusion in horses.

This research paper explored how the duration and concentration of isoflurane anaesthesia affects the oxygenation and blood flow in the intestine of horses.

Objective of the Study

• The study aimed to understand the impact of the length and concentration of isoflurane anaesthesia on overall blood flow, and, specifically, microperfusion and oxygenation in the intestine. The team wanted to identify whether these variables influenced central and intestinal oxygenation and perfusion in healthy horses.

Methodology

• Nine Warmblood horses were premedicated with xylazine. The anaesthesia was induced with midazolam and ketamine and then maintained with isoflurane.
• The horses were ventilated to normocapnia and continuously monitored for seven hours under anaesthesia.
• During this time, data on several indicators such as mean arterial blood pressures (MAP), heart rate, central venous pressure, pulmonary artery pressure, expiratory isoflurane concentration (ETIso), and cardiac output were collected. Further, intestinal microperfusion and oxygenation were also measured using laser Doppler flowmetry and white-light spectrophotometry.
• Furthermore, surface probes were placed on the serosal and mucosal site of the jejunum and the pelvic flexion of the colon, via median laparotomy.

Results of the Study

• The results showed that as ETIso increased, the MAP and cardiac index (CI) consistently decreased.
• However, the microperfusion and oxygenation in the intestine remained stable until a decrease in CI and MAP was noted at an ETIso level of 2.0%. After this point, there was a sudden drop.
• When the ETIso was reduced back to the baseline, CI, MAP, microperfusion, and oxygenation also returned to the baseline levels – implying that these effects are reversible.
• Interestingly, the study found that the concentration of isoflurane significantly impacted both central and intestinal oxygenation and perfusion, but the duration of anaesthesia did not have the same effect.
• The findings showed that under an isoflurane-induced state, intestinal perfusion seemed to be preserved until a certain threshold of MAP or blood flow was reached.