Blood from the right atrium may provide closer estimates of mixed venous saturation than blood from the superior vena cava. A pilot study.

Background: As a rule, central venous catheters (CVC) should not be positioned in the right atrium (RA) to avoid the risk of perforation and cardiac tamponade. However, in ICUs where ECG monitoring can detect any initial damage of the atrial wall, CVCs may probably be safely positioned in the RA. We investigated whether mixed venous saturation (SvO2) was better estimated by measuring central venous saturation (ScvO2) in the RA or in the superior vena cava (SVC) in patients undergoing cardiac surgery.

Methods: A CVC and a pulmonary artery catheter (PAC) were positioned before surgical coronary revascularization in sixty patients. Under transesophageal echocardiographic guidance, CVC tips were randomly positioned inside the RA (group A) or the SVC (group C). In each patient, eight pairs of blood samples were collected from CVC and PAC distal ports and saturation measured. Cardiac arrhythmias that occurred in the first 48 postoperative hours and CVC tip position on chest X-rays were also registered.

Results: ScvO2 and SvO2 correlated better in group A (r=0.95) than in group C (r=0.84). The 95% interval of confidence of the gap between ScvO2 and SvO2 was narrower in group A (-6.9/+ 3.2 vs. -11.6/+5.5; p<.01). The incidence of arrhythmias was equal in the two groups (16.7%). On chest X-rays, CVC tips were 5.4 (SD=3.6) cm below the tracheal carina in group A and 5.3 (SD=3.9) cm in group C.

Conclusion: In monitored patients, positioning CVC tips in the RA rather than in the SVC may allow closer estimates of SvO2 and may be safe. Yet, safety should be confirmed by further studies with larger samples of patients.