Inadvertent cannulation of the azygos vein during initiation of extracorporeal membrane oxygenation (ECMO) support is a rare complication which has been reported only once in the past in a series of two neonates with right-sided diaphragmatic hernias.1 This report reemphasizes the importance of ancillary testing at the time of ECMO cannulation, particularly in pathologies that result in right atrial or superior vena caval hypertension.
A 3-day-old neonate referred to our tertiary center for persistent pulmonary hypertension received initial support with mechanical ventilation, inhaled nitric oxide, inotropes, and prostaglandins (until a ductal-dependent lesion was ruled out). Prenatal history indicated absence of prenatal care and maternal exposure to cocaine and alcohol. The neonate's delivery necessitated bag-mask ventilation and chest compressions for 2 minutes with APGAR score of 5/4/8 at 1, 5, and 10 minutes, respectively. Transthoracic echocardiogram revealed normal intracardiac anatomy and a right aortic arch without a patent ductus arteriosus despite prostaglandin infusion. Severe right ventricular hypertrophy with dilation of the right atrium and ventricle on initial echocardiography supported the diagnosis of premature arterial duct closure prenatally. Biventricular function was moderately diminished.
Despite aggressive medical management, the patient continued to worsen with progressive hypotension and lactic acidosis. Based on progressive clinical worsening, a decision to support the patient on veno-arterial ECMO by cervical cannulation was made. An arterial cannula (6 French, Medtronic, Fridley, MN) was first placed in the internal carotid artery and advanced 2.5 cm in the aortic arch. Thereafter, a venous cannula (8 French, Medtronic, Fridley, MN) was placed in the internal jugular vein and advanced carefully 7 cm so as to position its tip in the right atrium. However, despite manipulation of the venous cannula, the venous drainage continued to be severely limited. An anteroposterior chest radiograph was initially taken, which showed what appeared the appropriate position of the venous cannula (Figure 1A). A lateral chest radiograph, which is not routinely obtained post-ECMO cannulation at our institution, was taken. It revealed that the cannula was positioned posterior to the cardiac silhouette (Figure 1B), which supported a diagnosis of inadvertent placement of the venous cannula in the azygos vein. A new venous cannula was then reinserted. However, the venous cannula again reentered the azygos vein. Finally, under echocardiographic guidance, a guide wire was advanced via the internal jugular vein into the right ventricle, and then the venous cannula was advanced over the guide wire for appropriate placement within the right atrium (Figure 2). The manipulation in all required 25 minutes during which the patient tolerated the procedure with mean arterial blood pressures no different than the precannulation pressures. Thereafter, the patient continued to have an uneventful ECMO course and was separated after 13 days of ECMO support. The patient remained in the hospital and was discharged at 3 months of age for treatment of pulmonary hypertension, oral aversion, and resolution of social aspects of care and had age-appropriate developmental milestones at 4 months of age.
We describe a rare complication of inadvertent azygos vein cannulation during initiation of ECMO in a neonate with prenatal arterial duct closure and describe a technique to appropriately place the venous cannula in the right atrium in such cases.
Previously, this complication has only been described in a series of two patients in the literature. Both cases were infants with a right-sided diaphragmatic hernia undergoing venous cannulation of the right internal jugular for ECMO support.2 In these patients, the inferior vena cava was compressed externally due to viscera that herniated into the right chest, and the azygos vein decompressed the venous flow from the lower body. As a result of this excess blood flow, the azygos vein became significantly dilated.1 This dilated vein which opens into the superior vena cava represents a larger target for the venous cannula to enter its lumen while the cannula is being placed in the internal jugular vein during ECMO cannulation. In contrast, premature arterial duct closure causes dilatation of the azygos vein secondary to elevation of superior vena cava pressures.2 These elevated superior vena cava pressures could be a result of small foramen ovale and a majority of the cardiac output passing through the high-resistance pulmonary vascular bed in utero.3
The prompt recognition of this complication is that any critically ill patient undergoing ECMO cannulation is crucial as the inability to generate adequate ECMO flow and venous return can be life-threatening. In our patient, a venous return of >50 ml/kg/min could not be generated until the cannula was properly positioned in the right atrium. Our case highlights the importance of a lateral chest radiograph for diagnosing this rare complication and the use of echocardiography for confirming and then guiding appropriate placement of the venous cannula. In the previous case series, this complication was diagnosed by a disparity of the alignment of the ECMO venous cannula and the umbilical venous catheter in the anteroposterior projection in one patient. In the second report, it was recognized by lateral chest radiograph. Previously, Kuenzler et al.4 have demonstrated that using echocardiography to guide appropriate cannula position resulted in a less frequent need for reoperation for cannula malposition. However, in emergent clinical scenarios, resources for echocardiography-guided cannulation may not be immediately available at all institutions at the time of cannulation, especially as extracorporeal cardiopulmonary resuscitation becomes more prevalent. In such situations, instead of waiting for echocardiographic guidance, chest radiography, readily available in most hospitals, can identify this complication in an expeditious manner. This case clearly highlights that lateral projection and the anteroposterior projection should be obtained anytime when venous cannula placement is difficult or when adequate venous drainage cannot be generated. The prompt recognition of inability to generate venous blood flow and a high index of suspicion of cannula malposition in clinical scenarios associated with increased azygos vein blood flow (Budd-Chiari syndrome, extrinsic compression or intraluminal obstruction in the inferior vena cava, interrupted inferior vena cava with azygos continuation, and anomalous pulmonary veins to the azygos vein) or azygos venous dilation by way of elevated superior vena cava pressures (Ebstein's anomaly, right-sided heart failure, restrictive cardiomyopathy, constrictive pericarditis, severe tricuspid regurgitation, and prepulmonary capillary obstruction) is paramount in recognizing this rare complication. In the presence of these physiologic scenarios, further investigation with lateral chest radiography and echocardiography should be sought for appropriate positioning of venous ECMO cannulaes.
The Institutional Review Board reviewed the study and waived the need for informed consent.
The authors thank Chris Wilson, RN, and Joshua Bryant, RN (ECMO specialists) and Donna Roddy, RDCS (Echosonographer).
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