To the Editor:
Air embolism can complicate peripheral IV fluid therapy (1) or central venous catheter monitoring, including problems with IV infusion pumps (2), improper flushing of IV sets (3), incorrect injection of drugs into the infusion system (3), and accidental disconnection of the hub or removal of central venous catheters (4). Air embolism can cause blockage of small vessels in the pulmonary vasculature with compromise of gas exchange, cessation of ventricular pumping caused by blockage by air and arrhythmia (5), and paradoxical air embolism to the systemic circulation through a probe-patent foramen ovale (6). We describe a complication with an IV blood pump infusion set, with potential for air embolism.
Y-type IV infusion blood pump sets are commonly used during anesthesia administration (Fig. 1). Typically, one arm of the Y is attached to a bag of crystalloid fluid. Often, the other infusion arm dangles unused, and its roller valve B is closed. Fluid flow rate should be controlled with the lower roller valve C (manufacturer’s recommendation).
We recently provided anesthesia for a patient, using a 14-gauge peripheral vein catheter connected to a Y-type Blood Pump Set™ (McGaw Inc., Irvine, California; 10 drops/mL, approximately 40-mL capacity pump chamber). However, roller valve A was controlling and limiting the IV fluid rate, roller valve C was open, and infusion arm B was not connected to a fluid bag. Unintentionally, roller valve B was left partly open, and room air entered and completely filled the drip and pump chambers. The air/fluid interface was descending in the tubing below the pump chamber, before we recognized and corrected the air entrainment.
When roller valves A and C are both wide open, positive fluid pressure (relative to ambient atmospheric pressure) exists throughout the tubing system. Then, if roller valve B is partly open, fluid will simply leak retrograde through it and drip onto the floor. When roller valve A is wide open and fluid flow rate is correctly controlled by partial closure of roller valve C, positive fluid pressure exists above roller valve C. Again, if roller valve B is left partly open, fluid will leak backward through it. However, if the IV fluid bag empties, then air could entrain through infusion arm B into the IV tubing system (see following).
When roller valve C is open and the IV fluid rate is incorrectly controlled by roller valve A, negative pressure, relative to atmosphere, exists in the tubing below roller valve A, which counters the weight of the hydrostatic column of fluid below (and hence limits its flow). Then, if roller valve B is accidentally left open (or partly open), room air will be suctioned into the IV tubing system and fill the drip and pump chambers and the IV tubing down to the level (if and) where fluid pressure in the tubing becomes positive. Furthermore, air could be pumped into the patient by squeezing the now air-filled pump chamber. Entrainment of air through infusion arm B will be enhanced by the use of larger IV catheters (which allow higher fluid flow rates) and by progressive closure of roller valve A.
Furthermore, consider a patient with a central venous catheter and negative central venous pressure (e.g., sitting, relatively hypovolemic patient). Then, in the preceding condition (open roller valve C and control of IV fluid rate with roller valve A), if roller valve B is inadvertently open, room air will be entrained into the IV tubing and infuse into the patient, without activation of the pump chamber.
Other situations with the potential for venous air embolism include venting of air from infusion systems by an open needle in an injection port (7) and an open needle to vent a rigid glass bottle container (e.g., albumin).
In conclusion, always control fluid flow rate in Y-type tubing infusion sets with the lower roller valve C to help prevent entrainment of air. If infusion arm B is not connected to a fluid bag, ensure that its roller valve is fully closed. Maintain an unobstructed view of the pump and drip chambers, look for air bubbles in the tubing, and be aware of the different compliance of the pump chamber when filled with air compared with fluid.
Peter H. Breen MD, FRCPC
Aaron Hong MD
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