Effect of body position on the arterial partial pressures of oxygen and carbon dioxide in spontaneously breathing, conscious dogs in an intensive care unit.
OBJECTIVE
To evaluate the effect of body position on the arterial partial pressures of oxygen and carbon dioxide (PaO(2), PaCO(2)), and the efficiency of pulmonary oxygen uptake as estimated by alveolar-arterial oxygen difference (A-a difference).


METHODS
Prospective, randomized, crossover study.


METHODS
University teaching hospital, intensive care unit.


METHODS
Twenty-one spontaneously breathing, conscious, canine patients with arterial catheters placed as part of their management strategy.


METHODS
Patients were placed randomly into lateral or sternal recumbency. PaO(2) and PaCO(2) were measured after 15 minutes in this position. Patients were then repositioned into the opposite position and after 15 minutes the parameters were remeasured.


RESULTS
Results presented as median (interquartile range). PaO(2) was significantly higher (P=0.001) when patients were positioned in sternal, 91.2 mm Hg (86.0-96.1 mm Hg), compared with lateral recumbency, 86.4 mm Hg (73.9-90.9 mm Hg). The median change was 5.4 mm Hg (1.1-17.9 mm Hg). All 7 dogs with a PaO(2)<80 mm Hg in lateral recumbency had improved arterial oxygenation in sternal recumbency, median increase 17.4 mm Hg with a range of 3.8-29.7 mm Hg. PaCO(2) levels when patients were in sternal recumbency, 30.5 mm Hg (27.3-32.7 mm Hg) were not significantly different from those in lateral recumbency, 32.2 mm Hg (28.3-36.0 mm Hg) (P=0.07). The median change was -1.9 mm Hg (-3.6-0.77 mm Hg). A-a differences were significantly lower (P=0.005) when patients were positioned in sternal recumbency, 21.7 mm Hg (17.3-27.7 mm Hg), compared with lateral recumbency, 24.6 mm Hg (20.4-36.3 mm Hg). The median change was -3.1 mm Hg (-14.6-0.9 mm Hg).


CONCLUSIONS
PaO(2) was significantly higher when animals were positioned in sternal recumbency compared with lateral recumbency, predominantly due to improved pulmonary oxygen uptake (decreased A-a difference) rather than increased alveolar ventilation (decreased PaCO(2)). Patients with hypoxemia (defined as PaO(2)<80 mm Hg) in lateral recumbency may benefit from being placed in sternal recumbency. Sternal recumbency is recommended to improve oxygenation in hypoxemic patients.
McMillan
Matthew W
MW
Department of Clinical Studies, Royal Veterinary College, Hertfordshire, UK. mwm32@cam.ac.uk
Whitaker
Katie E
KE
Hughes
Dez
D
Brodbelt
David C
DC
Boag
Amanda K
AK
D000818:Animals; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood*; D018592:Cross-Over Studies; D004283:Dog Diseases / Q000097:blood*; D004285:Dogs; D000860:Hypoxia / Q000097:blood / Q000662:veterinary*; D007362:Intensive Care Units; D010100:Oxygen / Q000097:blood*; D011187:Posture; D011659:Pulmonary Gas Exchange; D012119:Respiration; D012582:Schools, Veterinary
D002245:Carbon Dioxide; D010100:Oxygen