Intravenous Air: The Partially Invisible Phenomenon.

BACKGROUND: Air injection is carefully avoided during IV solution administration; however, ambient air is dissolved in all liquids used for intravenous (IV) therapy. A portion of this gas will come out of solution in the form of bubbles as the solution is warmed to body temperature in a fluid warming system and/or within the body. We sought to quantify the proportion of the gas theoretically dissolved in room temperature crystalloid and 4°C blood products that comes out of solution in the IV tubing on warming to 37°C.

METHODS: Equilibrium-dissolved air calculations were performed for sodium chloride (0.9%), packed red blood cells, and fresh frozen plasma at various temperatures according to Henry's Law. Outgassed gas volumes were experimentally measured for room temperature sodium chloride (0.9%) and 4°C blood products (packed red blood cells and fresh frozen plasma) warmed to 37°C during infusion into a body temperature water bath. The measured gas volumes were quantified as a fraction of the theoretical outgassing volumes required to maintain equilibrium saturation.

RESULTS: Measured outgassed volumes in the IV tubing in milliliters of gas per liter of fluid were 1.4 ± 0.3 mL/L (n = 6) for sodium chloride (0.9%), 3.4 ± 0.2 mL/L (n = 6) for packed red blood cells, and 4.8 ± 0.8 mL/L (n = 6) for fresh frozen plasma when these fluids were warmed to body temperature from their respective starting temperatures. Theoretical outgassed gas volumes required to maintain equilibrium saturation for the same fluids and temperatures are 4.7 mL/L for sodium chloride (0.9%), 8.3 mL/L for packed red blood cells, and 10.9 mL/L for fresh frozen plasma. As a fraction of the theoretical outgassing volumes, the measured air volumes represented 30%, 41%, and 44%, respectively, for sodium chloride (0.9%), packed red blood cells, and fresh frozen plasma. Prewarming crystalloid solutions to 37°C before administration significantly reduced the outgassing.

CONCLUSIONS: A significant and potentially clinically relevant amount of the resident dissolved gas in room temperature crystalloid, and 4°C packed red blood cells and plasma solutions comes out of solution on warming to body temperature. A nontrivial fraction of this outgassing is also expected to occur within the body circulation based on the results of this study. This can be substantially prevented by prewarming.