Pulse densitometer indocyanine green dilution curves: a simple applicable and accurate method for determination of cardiac shunts.

OBJECTIVE: Adequate hemodynamic evaluation is crucial in the management of patients with congenital heart disease. Although non-invasive diagnostic tools have reduced the need for invasive procedures, cardiac catheterization is still mandatory for absolute quantification of pressures, flows and vascular resistances in selected patients. We therefore investigated the feasibility of a new technique, non-invasive pulse densitometry (PD) in patients with intracardiac shunts and compared its results with the established standards: cuvette densitometry (CD) and oximetry (OX). DESIGN: Measurement method comparison study. OUTCOME MEASURE: In 12 patients with intracardiac shunt, dye dilution curves, using both pulse and cuvette densitometry, were recorded and oximetry was performed. Left-to-right shunt expressed as percentage of pulmonary blood flow Qp, was calculated from dye dilution and oximetry. In 4 patients with atrial septal defect, dye dilution curves were also recorded after closure of the defect with a device. RESULTS: The mean difference +/- SD between the shunt derived from PD and CD was 2.8 +/- 10.0% of Qp, 95% confidence interval -2.5 to 8.2. (Shunt-PD vs. Shunt-CD was 32.3 +/- 23.9% vs. 29.5 +/- 23.9% of Qp resp., n = 16). The mean difference +/- SD between the shunt derived from PD and OX was 0.8 +/- 9.8% of Qp, 95% confidence interval -5.4 to 7.0 (Shunt-PD vs. Shunt-OX was 41.5 +/- 20.3% vs. 40.7 +/- 19.7% of Qp resp., n = 12). CONCLUSION: Transcutaneous recording of dye dilution curves with a pulse dye densitometer allows easy and accurate quantification of intracardiac left-to-right shunt flows over a wide range in both children and adults with congenital heart diseases.

Misconceptions in reporting oxygen saturation.

BACKGROUND: We describe some misconceptions that have become common practice in reporting blood gas and cooximetry results. In 1980, oxygen saturation was incorrectly redefined in a report of a new instrument for analysis of hemoglobin (Hb) derivatives. Oxygen saturation (sO2) was redefined as the ratio of oxyhemoglobin (O2Hb) to total Hb instead of the ratio of O2Hb to active Hb (O2Hb + desoxyhemoglobin). In addition, the new terms "functional saturation" and "fractional saturation" were introduced. Since the new parameter was implemented in a widely used cooximeter, its use is now widespread and has caused misunderstandings. METHODS: In this report, we review the development of the definitions and measurements of sO2 and related quantities and contend that the misconceptions should be resolved by standardizing instrument read-outs and clinical reports, so that sO2, defined as the ratio of O2Hb to active Hb, should replace FO2Hb and be reported along with the total Hb concentration and the common dyshemoglobin fractions (%CO-Hb and % methemoglobin [metHb]). RESULTS: The redefinition of sO2 as the %O2Hb or FO2Hb did not address the confusion that might result from interchanging these two often-similar but different terms. The term fractional saturation is an inappropriate terminology and lacks clear physiological meaning. We see frequent cases of confusion: (a) the difference between the sO2 in pulse oximetry and the FO2Hb in cooximetry is called the "pulse oximeter gap;" (b) sO2 results are described as "method dependent;" and (c) reference ranges for these terms are substituted. CONCLUSIONS: Although either parameter could be used by clinicians who fully understand the relatively simple difference between these parameters, we find clear evidence that there is widespread confusion of these terms, even among experts in the field. Standardization of the reporting format would help, and instrument manufacturers could contribute by standardizing the reporting format for cooximetry results.