Effects of pulsed inhaled nitric oxide delivery on the distribution of pulmonary perfusion in spontaneously breathing and mechanically ventilated anesthetized ponies

Abstract

OBJECTIVE To measure changes in pulmonary perfusion during pulsed inhaled nitric oxide (PiNO) delivery in anesthetized, spontaneously breathing and mechanically ventilated ponies positioned in dorsal recumbency. ANIMALS 6 adult ponies. PROCEDURES Ponies were anesthetized, positioned in dorsal recumbency in a CT gantry, and allowed to breathe spontaneously. Pulmonary artery, right atrial, and facial artery catheters were placed. Analysis time points were baseline, after 30 minutes of PiNO, and 30 minutes after discontinuation of PiNO. At each time point, iodinated contrast medium was injected, and CT angiography was used to measure pulmonary perfusion. Thermodilution was used to measure cardiac output, and arterial and mixed venous blood samples were collected simultaneously and analyzed. Analyses were repeated while ponies were mechanically ventilated. RESULTS During PiNO delivery, perfusion to aerated lung regions increased, perfusion to atelectatic lung regions decreased, arterial partial pressure of oxygen increased, and venous admixture and the alveolar-arterial difference in partial pressure of oxygen decreased. Changes in regional perfusion during PiNO delivery were more pronounced when ponies were spontaneously breathing than when they were mechanically ventilated. CLINICAL RELEVANCE In anesthetized, dorsally recumbent ponies, PiNO delivery resulted in redistribution of pulmonary perfusion from dependent, atelectatic lung regions to nondependent aerated lung regions, leading to improvements in oxygenation. PiNO may offer a treatment option for impaired oxygenation induced by recumbency.

Cardiac output affects the response to pulsed inhaled nitric oxide in mechanically ventilated anesthetized ponies determined by CT angiography of the lung

“…In those experiments, PaCO 2 was lower in the MV group but no differences in PVR were observed regardless of ventilation mode, suggesting that PaCO 2 had little influence on the overall results. 14 In this study, hypotension and poor  Qt affected the expected response to PiNO based on previous work where indices of oxygenation improve. [14][15][16][17][18][19] However, this poor response to PiNO agrees with a previous study in anesthetized horses.…”

“…14 In this study, hypotension and poor  Qt affected the expected response to PiNO based on previous work where indices of oxygenation improve. [14][15][16][17][18][19] However, this poor response to PiNO agrees with a previous study in anesthetized horses. 20 In anesthetized humans with nitroprusside-induced hypotension, gas exchange is adversely affected:  Qs/  Qt Statistical comparisons were performed for T1 and T2.…”

“…The administration of pulsed inhaled nitric oxide (PiNO) to anesthetized horses, improves perfusion to ventilated lungs and reduces perfusion to atelectatic lung (reduced intrapulmonary shunting), and  V/  Q matching is enhanced. [12][13][14] This movement of blood has been quantified using gamma scintigraphy in horses, 12 and using CT angiography (CTA) in ponies. 13 The beneficial effect of PiNO on oxygenation indices in anesthetized horses has been described in numerous studies.…”

“…13 The beneficial effect of PiNO on oxygenation indices in anesthetized horses has been described in numerous studies. [14][15][16][17][18][19] However, if PiNO is administered to mechanically ventilated horses exhibiting concurrent hypotension, PiNO is ineffective. 20 This is in contrast to hypotensive, spontaneously breathing horses, presumably because of differing respiratory mechanics between the 2 modes of ventilation.…”