Cardiopulmonary effects associated with head-down position in halothane-anesthetized ponies with or without capnoperitoneum.

The research article confronts the cardiopulmonary effects of changing the position of anesthetized horses to head-down or maintaining a horizontal position, with or without introducing capnoperitoneum. The study found that the position of the horse and the presence of capnoperitoneum influence blood gas levels, blood pressure, and ventilation-perfusion ratios.

Objective of The Study

• The main objective of the study was to analyze the cardiopulmonary effects of a head-down position, both with and without capnoperitoneum, in horses that have been anesthetized with halothane.

Study Methodology

• This was a prospective randomized study involving 5 ponies (four mares and one stallion). The mean body weight of the ponies was 302 ± 38.4 kg.
• The ponies were anesthetized using xylazine, guiafenesin, and ketamine. Halothane and oxygen were used for maintenance of anesthesia. The lungs of the ponies were ventilated to maintain a 40 ± 2 mm Hg (5.3 ± 0.3 kPa) end-tidal carbon dioxide tension.
• Baseline cardiopulmonary measurements were made. Ponies were then kept in a horizontal position for 30 minutes. Following this, they were tilted to a head-down position of 30° from the horizontal for 60 minutes. Lastly, they were returned to a horizontal position for final measurements.
• Capnoperitoneum was introduced at a pressure of 12 mm Hg (1.6 kPa) after the initial cardiopulmonary measurements and maintained till 5 minutes before the final measurements. Ponies that didn’t receive capnoperitoneum were part of the control group (CON).

Study Results

• In both treatments, switching to a head-down position led to significant decreases in oxygen partial pressure (PaO.) and significant increases in carbon dioxide partial pressure (PaCO.), right atrial blood pressure, the gradient between arterial and end-tidal CO, and calculated V/Q and Q/Q ratios.
• In the control group (CON), a decrease in cardiac index when in the head-down position was observed. For the treatment group (INS), where capnoperitoneum was introduced, decreases in arterial plasma pH and increases in mean systemic arterial and airway pressures were observed in the head-down position.
• The study also found that ponies in the capnoperitoneum treatment (INS) developed ventilation-perfusion mismatch early on in the experiment, while also having a substantially longer recovery time than the control group.

Conclusions from The Study

• The study concluded that the cardiac index and systemic blood pressure seem to be preserved in the capnoperitoneum treatment (INS) while the ponies are in the head-down position. However, the head-down position and capnoperitoneum also led to an early onset of ventilation-perfusion mismatch.
• Apart from this, it was learned that healthy ponies can tolerate capnoperitoneum with an intra-abdominal pressure of 12 mm Hg (1.6 kPa) when tilted head-down 30° to the horizontal position.