Pulsed inhaled nitric oxide improves arterial oxygenation in colic horses undergoing abdominal surgery

Objective To evaluate the effect of pulsed inhaled nitric oxide (INO) on arterial oxygenation in horses during abdominal surgery. Study design Prospective, randomized, clinical trial. Animals Thirty horses that underwent abdominal surgery at the University Animal Hospital in Uppsala, Sweden. Methods Anaesthesia was induced according to a standard protocol - romifidine, butorphanol, diazepam and ketamine and maintained with isoflurane in oxygen. Fifteen horses were administered pulsed INO and 15 served as controls. After baseline data collection, pulsed INO delivery commenced. Arterial and venous blood were collected and analysed. Cardiorespiratory parameters were measured, and oxygen content and F-shunt were calculated. Results Arterial oxygen tension (PaO2) and arterial oxygen saturation (SaO(2)) increased from 10.9 +/- 5.7 kPa (82 +/- 43 mmHg) and 93 +/- 6% to 17.3 +/- 6.9 kPa (134 +/- 52 mmHg) (p < 0.0001) and 98 +/- 2% (p < 0.0001), respectively, in horses administered pulsed INO. In the control group, PaO2 and SaO(2) decreased from 13.9 +/- 9.1 kPa (104 +/- 68 mmHg) and 93 +/- 7% to 12.1 +/- 8.6 kPa (91 +/- 65 mmHg) (p = 0.0413) and 91 +/- 8% (p = 0.0256), respectively. At the end of anaesthesia, the oxygen content was significantly higher in horses administered pulsed INO compared to controls (p = 0.0126). The calculated F-shunt decreased from 39 +/- 10% to 27 +/- 6% (p < 0.0001) in horses administered pulsed INO, and remained unchanged in controls, 40 +/- 12% to 44 +/- 12%. Blood lactate concentration decreased (-17 +/- 21%) in horses administered pulsed INO (p = 0.0119), whereas no difference was measured in controls (2 +/- 31%). Conclusions and clinical relevance The present study showed that it is possible to effectively reduce the F-shunt and improve arterial oxygenation in horses during abdominal surgery by continuous delivery of pulsed INO.