This study is designed to evaluate the various physiologic maneuvers (Valsalva, humming, breath-hold) for the potential prevention of air embolism during central venous catheter placement. Central venous pressure measurements were prospectively obtained in 40 patients undergoing central venous catheter placement. The average central venous pressure at baseline was 3.275 mm Hg (range = -4 to 16, SD = 5.99). The average central venous pressure during breath hold was 6.1 mm Hg (range = -6 to 24, SD = 7.99). The average central venous pressure during humming was 5.1 mm Hg (range = -4 to 20, SD = 6.4) The average central venous pressure during the Valsalva maneuver was 18.43 (range = -3 to 48, SD = 14.73). Forty percent of patients (16 of 40) had negative central venous pressures at rest, 25% (10 of 40) had negative pressures during breath hold, 20% (8 of 40) had negative pressures during humming, and 2.5% (1 of 40) had negative pressures during Valsalva maneuver. The average increases in central venous pressure during breath hold, humming, and Valsalva were 2.85, 1.82, and 15.2 mm Hg, respectively. The difference between pressures during Valsalva and other maneuvers was statistically significant (P <.05). The conclusion is that the Valsalva maneuver is superior to breath-hold and humming for increasing central venous pressure during central venous catheter placement and, therefore, it is more likely to prevent air embolism in cooperative patients.