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Durant et al. demonstrated that dogs that were subjected in experiments to air emboli were more tolerant of air infusion, as indicated by measurement of hemodynamic variables, while lying on their left sides.2 Durant et al. observed that this position placed the right ventricular outflow tract in a position inferior to the right ventricular cavity, allowing the air bolus to migrate superiorly and removing the obstruction to blood flow. In addition, Trendelenburg's position prevents the gas embolism from occluding the outflow tract by placing the right ventricular cavity in a more superior position.3 These simple positional maneuvers should be performed in patients with a suspected venous gas embolism; they have been recommended by others who have written on the subject.3,4,5
Terrence D. Coulter, M.D.
Herbert P. Wiedemann, M.D.
Cleveland Clinic Foundation
Cleveland, OH 44195
References
David M. Eckmann, Ph.D., M.D.
University of Pennsylvania
Philadelphia, PA 19104
Annette B. Branger, M.S.
Northwestern University
Evanston, IL 60208
Daniel P. Cavanagh, Ph.D.
Bucknell University
Lewisburg, PA 17837
References
We have treated four patients with serious complications of gas embolism. Two cases occurred after the removal of a central venous catheter, and two occurred because of a delay in seeking care after the accidental removal of a central venous catheter.
Fibrin tracts consistently form around catheters, sometimes within 24 hours, creating a potential for portal venous air entry after the removal of a catheter3 — even several minutes after the removal of the catheter.4 Therefore, central venous catheters should be removed while the patient is either supine or in Trendelenburg's position, and the insertion site must immediately be covered with a sterile gauze, with firm manual pressure maintained until hemostasis is achieved. The insertion site must then be covered with an air-occlusive dressing. The dressing should remain in place for 24 to 72 hours.1 It is also important to remember that urgent care is required to prevent gas embolism after the accidental removal of a central venous catheter.
Carlos Chamorro, M.D.
Miguel A. Romera, M.D.
Cándido Pardo, M.D.
Clínica Puerta de Hierro
Madrid 28035, Spain
References
To the Editor: Chamorro and colleagues point out the need for vigilance during the removal of a central venous catheter. We included this potential mechanism in Table 1 of our article: "entry of air through disconnected intravascular catheter, inadvertent infusion of air through intravascular catheter." This is an important mechanism of gas embolism and deserves to be emphasized.
Eckmann and colleagues correctly suggest that an intraarterial gas bubble in vivo is more sausage-shaped than spherical — a point that helps explain why a bubble induces damage through complex interactions with the blood vessel's endothelium and the surrounding tissues. Our Figure 2 was designed to summarize the complex pathophysiology in a simple diagram.
Coulter and Wiedemann believe the left lateral decubitus position with the head tilted downward is the preferred position for the treatment of venous gas embolism, citing a study that was performed more than 50 years ago.1 The results of that study suggested that dogs that received massive infusions of air were more likely to survive if they were in the left lateral decubitus position. More recent studies2,3 indicate that hemodynamic responses are not improved by the use of alternative positions instead of a flat, supine position. These studies did demonstrate that intracardiac air relocates to more nondependent regions. If a transvenous catheter is present in the right side of the heart, placing the patient in the left lateral decubitus position before attempting to withdraw the air may have merits, as we mentioned in Table 2.
For most patients with venous gas emboli, placing them in the supine position affords physicians a better opportunity to administer supportive therapy, including ventilatory support and oxygen, to establish access for catecholamine delivery, and to perform cardiopulmonary resuscitation. Thus, since there are no demonstrated hemodynamic improvements associated with the use of the left lateral decubitus or head-down position, we believe that the supine position is the best choice.
Finally, the legend for Figure 2 should have read, "Sodium and water enter the neurons, and cytotoxic edema develops," not "Sodium and water enter the vessel . . . ," as printed.
Claus Martin Muth, M.D.
Universitätskliniker des Saarlandes
66424 Hamburg/Saar, Germany
Erik S. Shank, M.D.
Massachusetts General Hospital
Boston, MA 02114
References
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