Changes in arterial-mixed venous oxygen content difference (CaO2 - CvO2) and the effect on shunt calculations in critically ill patients.
Many commonly used indices of pulmonary oxygen transfer assume that CaO2 - CvO2 is constant. We studied changes in CaO2 - CvO2 in critically ill patients to determine the effect on calculated shunt of assuming a fixed CaO2 - CvO2. Two hundred pairs of arterial and mixed venous blood gas measurements were obtained retrospectively from 43 patients, each providing four or five pairs from a period of 48 h. CaO2 - CvO2 range from 13 to 74 ml l-1. The mean within-patient sd was 6.8 ml l-1 and the overall between-patient sd was 10.9 ml l-1. Our results show that assuming a fixed CaO2 - CvO2 leads to errors in quantifying pulmonary oxygen transfer.
Intensive Care Unit, Withington Hospital, Manchester.
M
M
Nirmalan
T
T
Willard
A
A
Khan
P
P
Nightingale
D003422:Critical Care; D016638:Critical Illness; D006801:Humans; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D011651:Pulmonary Artery; D011659:Pulmonary Gas Exchange; D012016:Reference Values; D015203:Reproducibility of Results; D012189:Retrospective Studies
D010100:Oxygen