Cardiovascular, respiratory and metabolic responses to apnea induced by atlanto-occipital intrathecal lidocaine injection in anesthetized horses.

The research focuses on determining the physiological responses of horses to severe lack of oxygen caused by apnea, induced by injecting lidocaine into the upper spine area. The analysis was performed on horses under anesthesia, with details about their cardiovascular, respiratory, and metabolic responses recorded before and after the injection.

Experimental Details

• The study was prospective and experimental in nature and involved six horses that belonged to a university. Their median body weight came out to be 500 kg, ranging between 220 to 510 kg. The horses were about 13.5 years old, with the youngest being 0.8 years old, and the oldest, 24.
• These horses were first anesthetized using a blend of Xylazine, Midazolam, and Ketamine drugs and allowed to breathe regular air. They were also fitted with facial artery catheters to enable blood sampling and pressure measurement.
• Apnea was then induced in these horses via an injection of lidocaine, a local anesthetic, into the atlanto-occipital area, which is the upper spinal region. The quantity of lidocaine used was 4 mg per kg of the horse’s weight.
• Observations pertaining to cardiopulmonary, hematologic, and biochemical variables were documented at baseline or before the induction of apnea and then every one minute for the following ten minutes post lidocaine injection.

Research Outcome

• The arterial oxygen pressure (PaO) scores were compared from baseline through the ten-minute timeline, showing a consistent drop within the first three minutes and then staying relatively stable for the remaining time.
• Arterial carbon dioxide pressure (PaCO) and Base excess values grew from baseline throughout the 10 minute period. The beating rate of the horses’ hearts increased sharply but stopped after approximately eight minutes.
• Pulse pressures diminished rapidly throughout the experiment. Lactate (acid in the blood) saw an incremental rise toward the end of the experiment. The volume of red blood cells grew significantly after seven minutes of apnea. No other major changes were reported.

Conclusion

• The results of the study reveal that apnea greatly worsened hypoxemia (abnormally low levels of oxygen in the blood) and hypercapnia (excessive carbon dioxide in the bloodstream) immediately. These conditions quickly led to hemodynamic instability (altered blood flow).
• It is concluded that apnea in anesthetized horses suffering from low oxygen levels carries a high likelihood of progressing to cardiovascular collapse, a serious state where the heart can’t pump enough blood to the body.