Correspondence |
Near-fatal pulmonary air embolus from iatrogenic injection of air during contrast administration
Sir,Venous air embolism is an increasingly common form of non-thrombotic embolism, reflecting the variety of invasive surgical and medical procedures, the broad use of indwelling central venous catheters,2 and the use of high levels of positive end expiratory pressure during ventilation. We report a case of symptomatic VAE in which immediate displacement of the air trap by turning the body into the left lateral position was life-saving.
A 42-year-old female presented to the emergency room with a 4-day history of anorexia, nausea, vomiting and abdominal pain. She was taken to radiology for a computed tomography (CT) scan with IV contrast of chest, abdomen and pelvis. Shortly after the scan, the patient sat up, became diaphoretic, complained of severe chest pain and then syncopized on the CT table. No pulses were palpable. The patient was immediately manoeuvred into the left lateral decubitus position, and 100% oxygen was administered. She regained consciousness almost immediately. Vitals taken at that time were blood pressure 88/36, heart rate 96, and respiratory rate 19. The 12-lead EKG demonstrated no evidence of acute myocardial ischaemia or right ventricular strain. The CT scan is shown in Figure 1. The patient was admitted to intensive care unit and remained haemodynamically stable until discharge.
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Admission of air into the venous system requires a source of gas, a communication between the venous system and this source, and a pressure gradient favouring passage of air into the circulation.1 Several factors influence the clinical significance of VAE. Durant et al. (1947) reported that the most important factors in determining mortality after experimental VAE in dogs were: (i) amount of air entering vein; (ii) speed of entry; and (iii) position of the body at the time of embolization.3
In humans, the fatal dose is uncertain but is estimated as 200–300 cc.4 A much lower volume can prove fatal if a right-to-left shunt allows air to bypass the lungs and enter the systemic circulation, or in critically ill patients with compromised haemodynamics.1 Air infusion rates of 1.8 ml/kg/min are fatal in dogs.5 In animal models, the cross-sectional area of the right ventricular outflow tract at its most superior point, is much more closely related to the fatal dosage than is the weight of the animal.3 In our case, a known volume of air (150 cc) was injected rapidly into the venous system, resulting in symptomatic haemodynamic collapse. The patient responded immediately to placement in the left lateral position and administration of 100% oxygen.
The true occurrence of VAE is uncertain, as the entity may be obscured by resultant cardiovascular, pulmonary or neurological manifestations that are felt to be primary in nature. If autopsy examination is delayed, air in the venous system may be resorbed, contributing to the difficulty in diagnosis.
The symptoms of VAE are variable and non-specific. These include alteration of sensorium, chest pain, dyspnoea and dizziness. Physical examination may reveal tachycardia, tachypnoea, and signs of elevated right heart pressure. A ’mill wheel‘ murmur produced by movement of air bubbles in the right ventricle is the only specific sign, but it is rare, transient and a late finding.
Precordial low-frequency Doppler ultrasound is the most sensitive method for detection of venous air. Other useful indicators of VAE include helical CT, echocardiography, transoesophageal echocardiography, and aspiration of air on an indwelling central venous catheter.
Prevention and early detection are the best approaches to VAE. Because of the non-specific signs and symptoms, a high index of suspicion in the appropriate clinical setting is important, since prompt recognition and institution of treatment, including immediate placement in the left lateral decubitus position, can be life-saving. Other measures designed to restore blood flow include removal of air through a central venous catheter or direct needle aspiration and external cardiac massage. Measures designed to increase absorption of air include the use of 100% O2 and early institution of hyperbaric oxygen.
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Department of Medicine Mercy Catholic Medical Center Drexel University College of Medicine Philadelphia USA e-mail: tasbirul{at}msn.com
References
1. Orebaugh SL. Venous air embolism: Clinical and experimental considerations. Critical Care Med 1992; 20:1169–77.[Web of Science][Medline]
2. Kashuk JL, Penn I. Air embolism after central venous catheterization. Surg Gynec Obst 1984; 159:249.
3. Durant TM, Long J, Oppenheimer MJ. Pulmonary (venous) air embolism. Am Heart J 1947; 33:269–81.
4. Toung TJK, Rossberg MI, Hutchins GM. Volume of air in a lethal venous air embolism. Anesthesiology 2001; 94:360–1.[CrossRef][Web of Science][Medline]
5. Adornato DC, Gildenberg PL, Ferrario CM. Pathophysiology of intravenous air embolism in dogs. Anesthesiology 1978; 49:120–217.[CrossRef][Web of Science][Medline]
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