Systemic Air Embolism During Wedge Resection of the Lung

Systemic air embolism (SAE) is a known complication of lung trauma (1) and has been described as a severe but rare iatrogenic complication during pulmonary procedures, such as biopsy (2) and bronchoscopic laser resections (3), or during pressure ventilation (4). As little as 0.5 to 1 mL of air entering the pulmonary veins can cause coronary embolism and cardiac arrest (5). Air obstructs blood flow and causes an acute intravascular inflammatory response (6,7). Transesophageal echocardiography (TEE) is the most sensitive monitor of air entry into the venous or arterial circulation. TEE has successfully been used to monitor SAE during lung transplantation (8) and lung injury (9). We present a case of systemic air entry into the pulmonary veins during pulmonary wedge resection as detected by TEE. Case Report A 78-yr-old man (height 172 cm, weight 65 kg, ASA physical status III) was admitted to the hospital because of detection of possible metastatic spread of a primary renal cancer during a routine follow-up examination. The patient had not experienced any particular problems after nephrectomy 4 yr earlier. He suffered from dilatative cardiomyopathy with chronic dyspnea corresponding to New York Heart Association III classification. Computerized scan of the thorax and the abdomen showed enlargement of the mediastinal lymph nodes and two suspicious masses in the right upper and lower lung lobes of approximately 2.5 cm in diameter each. Electrocardiography, lung function, and clinical examination showed respiratory distress at minor work, sinus rhythm, and reduced lung function with a forced expired volume in 1 s of 1.83 L. All laboratory results, including tumor markers, were normal. Transthoracic echocardiographic examination confirmed the diagnosis of dilatative cardiomyopathy with a left ventricular ejection fraction of 11% and no patent foramen ovale. The patient was scheduled for mediastinoscopy and explorative right thoracoscopy. Intraoperative TEE was planned to monitor his heart function during the procedure (TEE indication: category II (10)). Routine monitoring during single-lung ventilation consisted of left radial arterial pressure, central venous pressure via double-lumen catheter in the left internal jugular vein, electrocardiography, pulse oximetry, Petco2, and repetitive blood gas analysis. Anesthesia was induced using remifentanil infusion 0.1 μg kg−1min−1 IV and a target controlled IV infusion of propofol programmed to provide a target concentration of 3 mg/mL within 2 min. Intubation with a left-sided double-lumen endotracheal tube (37 Ch) was facilitated using rocuronium 0.6 mg/kg. After intubation, the TEE probe was inserted and an examination was performed confirming the results preoperatively obtained by transthoracic echocardiography. Surgery, in the supine position, commenced with mediastinoscopy and double-lung ventilation (inspiratory volume controlled with a higher than normal ventilation rate of 15/min to reduce tidal volumes and inspiratory peak pressure) to maintain Petco2 between 30–40 mm Hg. Three lymph nodes were removed that showed no pathology. After wound closure, the patient’s position was changed to the left lateral position (head tilted 20 degrees upward and legs down to allow better access for the surgical assistants) for right thoracoscopy. In this position, the correct position of the double-lumen tube was verified by fiberoptic bronchoscopy and single-lung ventilation with 100% oxygen commenced. Throughout the procedure, peripheral oxygen saturation remained above 96% and Pao2 remained above 100 mm Hg. Thoracoscopy revealed numerous areas of scar tissue around the upper lobe and clear identification of the masses was not possible. Therefore, a decision for open thoracotomy removal of the suspicious area was made and a right anterolateral thoracotomy incision was performed in the intercostal space with removal of the fifth rib. The mass in the upper lobe could now easily be identified. The area was dissected to introduce a stapler for wedge resection. During excision of the wedge, microbubbles were suddenly visible on the TEE screen only on the left side of the heart (Fig. 1). The Petco2 and peripheral oxygen saturation did not change nor was there any impairment of heart function. After the stapler was removed (the area was sutured) the microbubbles were no longer visible. The mass in the lower lobe was identified and removed using the auto stapler device. Again, there were microbubbles visible in the left heart during the dissection that disappeared again immediately after autosuturing. The immediate pathological examination revealed metastatic spread but complete removal of both masses. The rest of the surgery was uneventful. The patient’s trachea was extubated and he was brought to the intensive care unit for prolonged postoperative observation.Figure 1: Two-dimensional view of the heart; basal short axis view at aortic valvae level. Left, numerous microbubbles in the left atrium. Right, the schematic view predominantly used to monitor air entry into the heart in our hospital setting.Discussion We present a case of systemic air entry during wedge resection of a solitary pulmonary metastatic mass. Application of the stapler and dissection of lung tissue opens pulmonary veins through which air can enter the systemic circulation. It is interesting to note that the air entry could be detected exactly at the time the stapler was used. Immediately after autosuturing the lung, air entry was stopped without further intervention. Low pulmonary venous pressure and increased airway pressure (positive pressure ventilation) are regarded as factors contributing to SAE. We believe that the surgical position (legs tilted down), which favors ease of access for the surgical assistants, might have created lower pulmonary pressure and created an increased risk of air entry because the pulmonary veins are situated above the heart–similar to conditions presented with the sitting position in neurosurgery. Air entry occurred although the amount of tidal volume entering the right lung was minimal during single-lung ventilation. The fact that there were only microbubbles and no concomitant change in Petco2 is likely attributable to the small area of dissection, the short interval for potential air entry, and the minimal tidal volume entering the right lung. Saada et al. (9) described that in case of lung trauma, a decrease in tidal volume and ventilatory pressure can reduce air emboli. Our case demonstrates that even with no or minimal tidal volume (and consequently no positive pressure ventilation during single-lung ventilation), air embolism is possible. TEE monitoring in this patient was chosen because of the severe dilatative cardiomyopathy and diminished ejection fraction. TEE monitoring during left lateral patient position requires practice, and introduction of the TEE probe with a double-lumen tube in this position has to be done carefully to avoid pharyngeal trauma. The amount of air was minimal and the sensitivity of the TEE made it possible to identify microbubbles. We did not use a Doppler probe for monitoring. In this patient no adverse effect such as impairment of cardiac function or neurological sequelae were detected. We suggest that this case of air embolism during wedge resection should remind anesthesiologists that air embolism, even in lung resection using “modern” techniques (autostapler, single-lung ventilation), can still be the reason for postoperative deterioration of the patient’s condition as it was described 80 years ago (11). To determine the frequency of air embolism during routine lung surgery and to correlate its occurrence with the type and extension of surgery, more studies are needed.

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