Effects of ventilation mode and blood flow on arterial oxygenation during pulse-delivered inhaled nitric oxide in anesthetized horses.

The research study aims to determine how mechanical ventilation and perfusion conditions influence the effectiveness of pulse-delivered inhaled nitric oxide in anesthetized horses. The study concluded that the efficacy of pulse-delivered inhaled nitric oxide is primarily influenced by pulmonary perfusion during mechanical ventilation, and its use is most beneficial in horses with adequate perfusion.

Study Design and Procedures

• The study involved 27 healthy adult horses, divided into four groups based on types of breathing and arterial blood pressure conditions.
  Two groups used spontaneous breather (SB) technique, allowing the horses to breathe on their own, while the remaining two groups used mechanical ventilation (MV), where the breathing was artificially controlled.
• Among both the SB and MV groups, one had normal mean arterial blood pressure (MAP) – greater or equal to 70mm Hg (SB-N and MV-N), and the other was subjected to low MAP – less than 70mm Hg (SB-L and MV-L). Here, the MAP for each group was maintained using the drug Dobutamine.
• After one hour of equilibration, data was collected at intervals of 15 and 30 minutes during the administration of pulse-delivered inhaled nitric oxide (PiNO).
• The variables that were monitored included Pao (partial pressure of oxygen in arterial blood), arterial oxygen saturation and content, oxygen delivery, and the ratio of physiologic dead space to tidal volume.
• The collected data were analyzed using various statistical tests, such as Shapiro-Wilk, Mann-Whitney U, and Friedman ANOVA.

Study Results

• The results showed that the three groups (SB-L, SB-N, and MV-N) exhibited a significant increase in Pao, arterial oxygen saturation, arterial oxygen content, and oxygen delivery with the administration of PiNO.
• The MV-L group had significantly diminished oxygenation levels in comparison to the MV-N group and lower than the SB groups during PiNO.
• The ratio of physiological dead space to tidal volume was highest in the MV-L group.

Conclusions and Clinical Relevance

• The findings revealed that pulmonary perfusion greatly influenced the effectiveness of PiNO during mechanical ventilation, but not during spontaneous breathing.
• In the MV-L group, the use of PiNO failed to augment oxygenation due to severe ventilation-perfusion mismatching. However, during SB, PiNO enhanced oxygenation irrespective of the blood flow levels, though hypoventilation and hypercarbia persisted.
• The results highlight that the use of PiNO resulted in the most beneficial outcomes in horses with sufficient perfusion.