Air Venting and In-line Intravenous Fluid Warming for Pediatrics

To the Editor:-

It is important to have suitable fluid warmers for pediatric anesthesia, especially in hypovolemic neonates and infants who require boluses of isotonic crystalloid, packed erythrocytes, or both given over 5-20 min. The purpose of this study was to evaluate the fluid warming and air venting capability of a new device (buddy fluid warmer; Belmont Instrument Corp., Billerica, MA) designed for use in pediatrics. With this device, fluids are heated to 38°C as they pass through a disposable set containing microporous membranes able to vent air. Air is released through the side vents of the set. The small heating unit and disposable set are placed in-line near the patient at the intravenous infusion site and can be used easily with volumetric infusion pumps.

Fluids tested were lactated Ringer's solution, 1 l, at room temperature, and refrigerated, outdated erythrocytes diluted with 100 ml saline, 0.9%. The estimated hematocrit was 50%. Standard or Y-type blood solution sets were attached proximal to the commercial microheater disposable set (priming volume, 4 ml), which was connected to a 12.7 cm T connector (total volume, 0.4 ml). A rapid response thermocouple (Fluke 51 II; Fluke Corp., Everett, WA; accuracy, ±0.05%) was used to measure distal temperature at the point at which the T connector would be attached to the intravenous line. Temperature data were collected at 5-ml intervals for flows of 8 ml/min or greater and at 10-s intervals for slower flows. A volumetric infusion pump was used to regulate flow between 50 and 1,000 ml/h. For gravity-free flow, lactated Ringer's solution was infused from a height of 1.8 m into a cylindrical scored beaker, and measurements were made every 50 ml. Pressure-driven flow was not used, per manufacturer guidelines.

A three-way stopcock with a 0.8 m extension was inserted proximal to the microheater, and a 22-gauge Angiocath (Becton Dickinson, Sandy, UT) was attached to the T connector distally. The Angiocath was submerged in a liquid-filled beaker for crystalloid infusion and attached to a cell salvage waste system for erythrocytes. Without the fluid warmer disposable set, injection of as little as 1 ml of air was readily visible in the liquid-filled beaker with submerged Angiocath. Aliquots of 5, 10, 20, 30, 40, 50, and 60 ml of air were rapidly injected into the stopcock toward the patient infusion site, followed by resumption of fluid flow. Visual inspection for air bubbles distal to the warmer was performed by two observers. Tests were repeated twice for each condition and fluid.

Distal temperatures are summarized in figure 1. Air bubbles were not seen in the T connector or in the liquid-filled beaker for any value of injected air.

Fig. 1

The buddy fluid warmer was effective in delivering warm intravenous fluids at flows of 7 ml/min or greater. At the slowest flows, infusate temperature decreased, likely resulting from significant heat loss distal to the warmer. Venting of air by the fluid warmer is of great advantage to pediatric patients with congenital heart disease. Moreover, use of this warming device might theoretically reduce the risk of accidental infusion of air during crystalloid and blood resuscitation of children with hypovolemic shock. The manufacturer's list price for the buddy fluid warmer is $1,599.00; the disposable set is $14.99.

The authors thank Jeanne Javor, M.T. (A.S.C.P.), S.B.B. (Blood Bank Supervisor, MetroHealth Medical Center, Cleveland, Ohio), for providing outdated erythrocytes and hematocrit estimates; Richard Kramer, C.P.P. (Division of Cardiothoracic Surgery, MetroHealth Medical Center), for useful suggestions; and Denise Kosty Sweeney, R.N., M.S.N. (Administrative Nurse Manager, General Clinical Research Center, MetroHealth Medical Center), for the loan of a stopwatch and beaker.

Ramachandra R. Avula, M.D.

Charles E. Smith, M.D., F.R.C.P.C.*

* MetroHealth Medical Center, Case Western Reserve University, Cleveland, Ohio. [e-mail]