Pulse oxygen saturation measured in standing and squatting positions may be useful in evaluating tetralogy of Fallot

Left-ventricular end-diastolic volume index (LVEDVI) and Nakata index, which in most cases are evaluated by echocardiography and cardiac catheterization, are 2 important predictors for the prognosis of surgical correction of tetralogy of Fallot (TOF). Nonetheless, performing these procedures on TOF patients is not always feasible. We therefore investigated whether the difference in transcutaneous pulse oxygen saturation between the standing position and squatting position (DeltaSPO2) reflected the LVEDVI and Nakata index, allowing DeltaSPO2 to be used as a supplement to echocardiography and cardiac catheter evaluation.

Nineteen TOF patients (11 boys, 8 girls; median age 6 years) were randomly selected for this study. In each patient, we used a pulse oximeter placed on the left index finger to measure transcutaneous pulse oxygen saturation, first with the patient in a standing position and then with the patient in a squatting position. We then performed correlational analyses of DeltaSPO2 and the LVEDVI or Nakata index.

The mean SPO2 was 79%+/-4% in standing patients and 84%+/-4% in squatting patients, and the mean DeltaSPO2 was 5%+/-3%. The LVEDVI was 41+/-5 mL/m2, and the Nakata index was 188+/-37 mm2/m2. DeltaSPO2 correlated with both LVEDVI (gamma=0.854, P< .05) and the Nakata index (gamma=0.641, P< .05).

For patients with TOF, the DeltaSPO2 between SPO2 measured in a standing and squatting position has a positive correlation with the LVEDVI and Nakata index. Thus these measurements may be used as supplemental factors in evaluating LV function and performing a preoperative assessment of the pulmonary artery.