The effect of two different intra-operative end-tidal carbon dioxide tensions on apnoeic duration in the recovery period in horses.

The research investigates the impact of two different intraoperative end-tidal carbon dioxide tensions (Pe’CO2) on the duration of apnoeic (lack of breathing) period in horses after surgery. The study found that higher carbon dioxide tension leads to a more rapid return to spontaneous ventilation (RSV), even though it lowers oxygen tension during and at the end of anesthesia.

Study Design and Methodology

• This research is based on a prospective, randomized clinical study involving 18 healthy, client-owned adult horses. These horses, varying in body mass and age, were admitted for elective surgery and were randomly allocated to one of two groups.
• A standardized anesthetic protocol was used. The controlled mechanical ventilation (CMV) was adjusted to maintain the horses’ end-tidal carbon dioxide (Pe’CO2) tensions at either 40 ± 5 mmHg (5.3 ± 0.7 kPa) (group 40) or 60 ± 5 mmHg (8.0 ± 0.7 kPa) (group 60).
• Arterial blood gas analysis was performed at different stages, from the start of anesthesia (T0), during anesthesia (T1), right before disconnection from the breathing system (T2), and at the resumption of the first spontaneous breath (T3).
• The duration between disconnection from the breathing system and the return of spontaneous ventilation (RSV) was recorded and analyzed via two-sample t-test or Mann-Whitney U-test, and the significance was assigned where p < 0.05.

Results

• The study found significant differences in the time it took for spontaneous breathing (RSV) to resume between the two groups. Horses in group 60 resumed spontaneous breathing far earlier than those in group 40, with 52 (14-151) seconds for group 60 compared to 210 (103-542) seconds for group 40 (p < 0.001).
• Variables such as arterial oxygen tension (PaO2), pH level, base excess, and plasma bicarbonate concentration did not show significant differences between the groups at return of spontaneous ventilation (RSV).
• However, the research observed a significantly lower arterial oxygen tension (PaO2) in group 60 during anesthesia (T1) and at the end of anesthesia (T2).

Conclusions

• The research recommends maintaining the intra-operative end-tidal carbon dioxide at 60 ± 5 mmHg (8.0 ± 0.7 kPa) in mechanically ventilated horses for a faster return to spontaneous ventilation.
• Despite this advantage, it also suggests a potential trade-off as higher carbon dioxide tension was associated with lower arterial oxygen tension during and after anesthesia.