Relationship Between Mixed Venous Oxygen Saturation and Cardiac Index in Patients with Chronic Congestive Heart Failure

The use of mixed venous oxygen saturation ( S v ¯ O 2 ) in patients with chronic congestive heart failure (CHF) has been advocated to analyze the action of therapy on cardiac index (CI). To evaluate the relationship between CI and S v ¯ O 2 , ten CHF patients (mean age 65 years) were studied before and one, two, three, four (T4), six, eight and 24 hours after oral administration of an angiotensin converting enzyme (ACE) inhibitor (perindopril, 4 mg). At T4, a 12 percent increase in CI (p<0.01) was associated with a 16 percent decrease in arteriovenous oxygen difference (p<0.01), a 13 percent increase in mixed venous oxygen pressure ( P v ¯ O2 ) (p<0.01), and a 9 percent increase in S v ¯ O 2 (p<0.05) with no significant change in arterial oxygen pressure. There was no correlation between CI and S v ¯ O 2 (r = 0.22) and between CI and P v ¯ O 2 (r=0.23). Individual analyses were performed and patients were divided into two groups based on CI versus S v ¯ O 2 r value; group 1, n = 6, r>0.65 (0.65-0.90), group 2, n = 4, r<0.65 (0.14-0.20). The lack of correlation in group 2 was due to a drug-dependent increase in oxygen consumption ( V ˙ o 2 ) +18 percent vs –3 percent in group 1 (p<0.05) associated with a lack of increase in P v ¯ O 2 +3 percent vs +14 percent in group 1 (p<0.05) despite a similar increase in oxygen availability +19 percent versus + 16 percent. It was concluded that (1) a correlation between CI and S v ¯ O 2 is not found in every patient with CHF; (2) the lack of correlation in four out of our ten patients was due to an associated and significant increase in CI and V ˙ o 2 in group 2; (3) group 2 patients probably had an important oxygen debt before treatment; (4) S v ¯ O 2 cannot be used instead of CI to determine the hemodynamic consequences of the use of cardiovascular drugs.