Pulsed delivery of inhaled nitric oxide counteracts hypoxaemia during 2.5 hours of inhalation anaesthesia in dorsally recumbent horses.
OBJECTIVE
The study aimed to investigate the effect of varying pulse lengths of inhaled nitric oxide (iNO), and 2.5 hours of continuous pulse-delivered iNO on pulmonary gas exchange in anaesthetized horses.


METHODS
Experimental study.


METHODS
Six Standardbred horses.


METHODS
Horses received acepromazine, detomidine, guaifenesin, thiopentone and isoflurane in oxygen, were positioned in dorsal recumbency and were breathing spontaneously. iNO was on average pulsed during the first 20, 30, 43 or 73% of the inspiration in 15 minute steps. The pulse length that corresponded to the highest (peak) partial pressure of arterial oxygen (PaO(2) ) in the individual horses was determined and delivered for a further 1.5 hours. Data measured or calculated included arterial and mixed venous partial pressures of O(2) and CO(2) , heart rate, respiratory rate, expired minute ventilation, pulmonary and systemic arterial mean pressures, cardiac output and venous admixture. Data (mean ± SD) was analysed using anova with p < 0.05 considered significant.


RESULTS
Although the pulse length of iNO that corresponded to peak PaO(2) varied between horses, administration of all pulse lengths of iNO increased PaO(2) compared to baseline. The shortest pulse lengths that resulted in the peak PaO(2) were 30 and 43% of the inspiration. Administration of iNO increased PaO(2) (12.6 ± 4.1 kPa [95 ± 31 mmHg] at baseline to a range of 23.0 ± 8.4 to 25.3 ± 9.0 kPa [173 to 190 mmHg]) and PaCO(2) (8.5 ± 1.2 kPa [64 ± 9 mmHg] to 9.8 ± 1.5 kPa [73 ± 11 mmHg]) and decreased venous admixture from 32 ± 6% to 25 ± 6%. The increase in PaO(2) and decrease in venous admixture was sustained for the entire 2.5 hours of iNO delivery.


CONCLUSIONS
The improvement in arterial oxygenation during pulsed delivery of iNO was significant and sustained throughout 2.5 hours of anaesthesia.


CONCLUSIONS
Pulsed iNO potentially could be used clinically to counteract hypoxemia in anaesthetized horses.
Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Skara, Sweden. gorel.nyman@slu.se
Görel
G
Nyman
Tamara L
TL
Grubb
Erkki
E
Heinonen
Jan
J
Frendin
Anna
A
Edner
Lais M
LM
Malavasi
Claes
C
Frostell
Marieann
M
Högman
D000777:Anesthetics / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D004334:Drug Administration Schedule; D005260:Female; D006736:Horses; D000860:Hypoxia / Q000188:drug therapy / Q000662:veterinary*; D008297:Male; D009569:Nitric Oxide / Q000008:administration & dosage / Q000494:pharmacology*; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012138:Respiratory Therapy / Q000662:veterinary*
D000777:Anesthetics; D009569:Nitric Oxide