Effects of positive end-expiratory pressure titration on intestinal oxygenation and perfusion in isoflurane anaesthetised horses.

The plain-language overview: The research team conducted an experiment on anesthetized horses to explore the effects of incremented airway pressure adjustments on both central and intestinal blood flow as well as oxygenation. They found that escalating airway pressures, though improving oxygen levels in the blood, unexpectedly reduced the efficiency of blood delivery and lowered the oxygen supply in the gastrointestinal area.

Methodology

• The study involved a live experimental set-up with 10 horses that were put under anaesthetics.
• The horses were subjected to intermittent positive pressure ventilation shortly after induction.
• After a span of 90 minutes, the end-expiratory pressure (PEEP) was slowly increased in increments of 5 cmH2O every 10 minutes till it reached a PEEP of 30 cmH2O.
• The PEEP was then gradually reduced to zero, while keeping the airway pressure difference constant at 20 cmH2O.
• Several measurements were taken during the experiment including mean arterial blood pressure (MAP), heart rate, central venous pressure, pulmonary artery pressure, expiratory isoflurane concentration, and cardiac output.
• Arterial blood gases were also checked to assess arterial partial oxygen pressure (PaO2) and calculate arterial oxygen saturation (SaO2).
• Intestinal microperfusion and oxygenation were measured using laser Doppler flowmetry and white-light spectrophotometry, based on a probe located on different parts of the stomach, jejunum, and pelvic flexion of the colon.

Findings

• The recruitment of the lungs led to a substantial increase in PaO2 from a baseline of 201 ± 58 mmHg to a maximum of 495 ± 75 mmHg.
• Both the Cardiac Index (CI) and Mean Arterial Pressure (MAP) showed a continuous decline with the increasing airway pressures.
• Upon the decline of CI and MAP to 37 ± 9 ml/kg/min and 52 ± 8 mmHg respectively (at PEEP of 25 cmH2O), there was a sharp drop in intestinal perfusion, which was subsequently followed by a delayed decrease in oxygenation.

Conclusion

• The study observed a linear relationship between airway pressures and both CI and MAP, but not between central and gastrointestinal perfusion.
• While the escalating airway pressures boosted the arterial blood oxygenation, the consequent reduction of CI resulted in decreased oxygen delivery, leading to a decline in gastrointestinal oxygenation.