The usefulness of a 10% air-10% blood-80% saline mixture for contrast echocardiography: Doppler measurement of pulmonary artery systolic pressure.

Objectives: We assessed an air-blood-saline mixture for Doppler measurement of pulmonary artery systolic pressure (PASP) and the mechanism of enhancement of the Doppler signal by this mixture.

Background: Underestimation of PASP by Doppler echocardiography occurs with inadequate continuous wave (CW) signals of tricuspid regurgitation (TR).

Methods: We assessed in vitro the diameter and concentration of microbubbles of agitated air-saline mixture, air-blood-saline mixture and 10% air-10% plasma-80% saline mixture immediately, 5, 10 and 20 s after agitation. In 20 patients, PASP was estimated by Swan-Ganz catheter and CW Doppler of TR: 1) without contrast injection; 2) with intravenous injection of 10% air-90% saline; and 3) 10% blood-10% air-80% saline mixture.

Results: Compared to air-saline, addition of blood or plasma to the air-saline solution significantly increased the concentration of microbubbles (p < 0.001). The air-blood-saline (26.7 +/- 7.2 microm) and air-plasma-saline mixture (25.3 +/- 7.4 microm) had smaller microbubbles than air-saline mixture (31.6 +/- 8.2 microm) (p < 0.001). The correlation between Doppler- and catheter-measured PASP at baseline (r = 0.64) improved with agitated air-saline (r = 0.86). With the air-blood-saline mixture, the correlation further improved (r = 0.92) and the best limits of agreement were obtained.

Conclusions: The combination of the patient's own blood is a method of making a sterile solution of numerous small microbubbles for injection into the right-sided cardiac chambers. Clinically, the air-blood-saline mixture is easily prepared at bedside and is superior to the air-saline mixture in assessing PASP in patients with inadequate CW Doppler signals.