The effects of pulse‐delivered inhaled nitric oxide on arterial oxygenation, ventilation‐perfusion distribution and plasma endothelin‐1 concentration in laterally recumbent isoflurane‐anaesthetized horses

Effects of pulse-delivered inhaled nitric oxide administration on pulmonary perfusion and arterial oxygenation in dorsally recumbent isoflurane-anesthetized horses

“…Although continuous delivery of iNO over the entire inspiratory phase of ventilation did not improve arterial oxygenation in a previous study 23 of halothane-anesthetized horses, PiNO administration during the early phase of inspiration did counteract hypoxemia and Qs/Qt formation in dorsally recumbent 13,15 and laterally recumbent 11,12 isoflurane-anesthetized horses. It appears that pulsing iNO in the first 30% to 45% of the inspiratory phase, as was done in the present study, is the most effective method to improve oxygenation in anesthetized horses.…”

“…It appears that pulsing iNO in the first 30% to 45% of the inspiratory phase, as was done in the present study, is the most effective method to improve oxygenation in anesthetized horses. 12,13,23 However, the pulse dose can be too small to be effective, and PiNO administration in only 20% of the inspiratory phase can result in minimal or no improvement. 12 Administration of PiNO at 45% of the inspiratory phase in a horse with a small tidal volume, as for 1 horse in this study, can result in less improvement than when a full dose is delivered.…”

“…12,13,23 However, the pulse dose can be too small to be effective, and PiNO administration in only 20% of the inspiratory phase can result in minimal or no improvement. 12 Administration of PiNO at 45% of the inspiratory phase in a horse with a small tidal volume, as for 1 horse in this study, can result in less improvement than when a full dose is delivered. This could be caused by the fact that a small volume of iNO reaches the conducting airways but delivery to the alveoli (ie, area of gas exchange) is minimal.…”

“…11 Inhaled NO preferentially reaches only areas of adequate alveolar ventilation, and the subsequent vasodilation redistributes perfusion to these ventilated alveoli, thereby improving V A /Q matching and PaO 2 . Nitric oxide pulsed into the early phase of inhalation has been used to improve PaO 2 and V A /Q matching while decreasing Qs/Qt in recumbent isoflurane-anesthetized horses, [12][13][14][15] but the intrapulmonary location of redistribution of perfusion induced by PiNO administration is not known. Redistribution could occur at individual alveoli scattered throughout the lungs or by mass movement of blood flow away from discrete dependent atelectatic areas.…”

Effects of pulsed inhaled nitric oxide on arterial oxygenation during mechanical ventilation in anaesthetised horses undergoing elective arthroscopy or emergency colic surgery

“…Using this technique, hypoxaemia is treated by redirecting blood flow, or pulmonary perfusion, to the ventilated regions of the lung rather than by changing ventilation of the lung . However, PiNO does not affect ventilation and hypercarbia developed in all or most horses in previous studies . These findings were also confirmed in a clinical study where spontaneously breathing horses undergoing colic surgery treated with PiNO remained hypercarbic despite improved arterial oxygenation .…”