A 7-month-old female (59.4 cm, 5.6 kg) with Down syndrome was admitted for repair of an atrial septal defect and a ventricular septal defect. In the operating room, a peripheral arterial line was placed at the left radial artery after induction of general anesthesia. Her initial vital signs were stable: systolic blood pressure 90 mm Hg and heart rate 100 beats/min. An 8 mm diameter, 3- to 7-MHz omniplane transesophageal echocardiography (TEE) probe (S7-3t, Philips iE33 system, Philips Healthcare, Andover, MA) was inserted after intubation. When the aorta was cannulated for cardiopulmonary bypass (CPB), the arterial blood pressure waveform suddenly disappeared, and blood was not aspirated through the aortic cannula. The surgeon immediately removed the aortic cannula suspecting acute aortic dissection and the arterial blood pressure waveform reappeared. The surgeon then purse-string sutured the decannulated site. Echocardiographic evaluation followed, but there was no significant anatomical lesion except for a small amount of hematoma at the aortic wall. Aortic cannulation was again performed distal to the previous cannulation site.
Repair of an atrial septal defect and a ventricular septal defect proceeded without event. The total aorta cross-clamping time was 60 minutes. Before weaning from CPB, the surgeon reinforced the initial aortic cannulation site with a purse-string suture. When the patient was weaned from CPB, her systolic blood pressure was low (40–50 mmHg). TEE confirmed that there was no ventricular failure or valvular lesion resulting in systemic hypotension. However, a modified midesophageal (ME) ascending aorta long-axis view demonstrated a stenotic lesion at the purse-string site (Fig. 1; Supplemental Digital Content 1, Video 1, http://links.lww.com/AA/B18). The blood flow peak velocity at the site of the stenotic lesion was 4.17 m/s (mean pressure gradient 49 mm Hg) which was consistent with severe supravalvular aortic stenosis (Fig. 2A). The diameter of the ascending aorta proximal to the stenotic site was 6 mm and 3.5 mm at the site of stenosis.
Suspecting iatrogenic ascending aortic stenosis secondary to the reinforcement suture, the anesthesiologist recommended that the surgeon release the additional reinforcement suture. After the additional suture was released, the patient’s systolic blood pressure increased from 62 to 80 mm Hg. TEE revealed the stenotic area increased to 6 mm in diameter with a peak blood flow velocity of 2.62 m/s and mean pressure gradient of 13 mm Hg (Fig. 2B; Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/B19). Because hemodynamics were stable with good left ventricular function, further interventions were considered unnecessary. Total CPB time was 130 minutes. The patient was transferred to the intensive care unit, and her postoperative course was uneventful.
Cannulation for CPB is difficult, especially in small children, because of their small vessel size and the narrow safety margin of the cannula position.1 Accordingly, complications associated with cannulation are not rare. Possible complications related to cannulation include air embolism, aortic dissection, vena cava tear, and stenosis of the superior vena cava (SVC)2 or the aorta.3
There has been 1 pediatric case reported of ascending aorta stenosis after decannulation detected by TEE.3 Additional surgical management to correct the stenosis was not performed because the patient’s vital signs were stable. In our case, however, severe stenosis of the ascending aorta affected the patient’s vital signs, and immediate management was required.
Cannulation in pediatric cardiac surgery should be performed with caution because of anatomic variations and small vessel size.1 Suture ties after decannulation can cause significant stenosis combined with hemodynamic instability in pediatric patients.
TEE can confirm the correct position of the cannula and detect complications after decannulation. Table 1 summarizes TEE views associated with cannulas for CPB in pediatric patients. Generally, the aortic cannula can be assessed in the ME ascending aorta long-axis view. In adults and older children, there is an invisible segment within the distal part of the ascending aorta (“blind spot”) because of the interposition of the right bronchus and trachea.4,5 In neonates and infants, however, the entire ascending aorta and proximal aortic arch are usually identified in the ME ascending aortic long-axis view, and the shaft of the aortic cannula in the distal ascending aorta can be visualized without difficulty. Also the flow direction and position of the cannula tip can be confirmed, especially in the case of a distally located aortic cannula during aortic root surgery, such as transposition of great arteries. Aortic blood velocity can be measured in this view.
Visualization of SVC and inferior vena cava (IVC) cannulas can be difficult due to collapsed right atrium and posterior shadowing of the cannula during CPB. A color Doppler image may be helpful to identify the venous cannula tip. TEE should be used to direct cannulation of the SVC in cases of atrial septal defect. Patients with persistent left SVC sometimes need additional venous cannula for drainage from the left SVC. The left SVC can be seen by tracing the coronary sinus. For cannulation of the IVC, TEE should be used because the safety margin from the right atrium to the confluence of the hepatic veins to the IVC is narrow.
In healthy children, the average peak velocity in the ascending aorta is approximately 1.3 m/s regardless of age.6 Although this may vary in patients with specific anomalies, such as hypoplastic left heart syndrome or interrupted aortic arch,1 any turbulent flow by color Doppler examination should be considered abnormal.7
In our case, aortic blood flow velocity was underestimated because the Doppler beam and aortic blood flow were not completely parallel. However, the mean pressure gradient was >40 mm Hg despite the misalignment; therefore, there was no doubt that severe stenosis occurred in the ascending aorta.
In conclusion, we experienced cannulation-related ascending aorta stenosis, and TEE played a critical role in early detection of cannula-related complications. An understanding of TEE imaging during cannulation is helpful for early detection and prevention of cannula-related complications.
Clinician’s Key Teaching Points
By Nikolaos J. Skubas MD, andMartin J. London MD
- Vascular cannulation for cardiopulmonary bypass in pediatric patients may be challenging because of the small size of the arch vessels.
- Air embolism, vessel dissection or wall tear, occlusion of vessels, iatrogenic stenosis, and cannula malposition are possible complications of vascular cannulation that may be detected with transesophageal echocardiography (TEE).
- In this case of an infant with Down syndrome presenting with atrial and ventricular septal defects, cannulation of the ascending aorta was accompanied by systolic arterial hypotension. TEE imaging excluded aortic dissection but detected a hematoma of the aortic wall. The cannula was removed, the cannulation site reinforced with purse-string sutures, and the aortic cannula was reinserted distally. Arterial systolic hypotension (40–50 mm Hg) occurred immediately after cardiopulmonary bypass. The absence of ventricular failure or valvular pathology findings by TEE prompted the exploration of the initial arterial cannulation site. A narrowed lumen (3.5 mm; normal 6 mm), turbulent flow and increased velocity by color Doppler (4.17 m/s; normal 1.3 m/s), and a mean pressure gradient (49 mm Hg) suggested iatrogenic supravalvular aortic stenosis, which resolved after release of the reinforcement sutures (systolic arterial blood pressure 80 mm Hg).
- In contrast to adults and older children, in which the anatomic orientation of the left bronchus results in a “blind spot,” the entire ascending aorta and proximal arch can be imaged in neonates and infants (using the midesophageal ascending aorta short-axis view). Therefore, despite being rare, any arterial cannula-associated iatrogenic injuries should be easily detected with TEE and promptly managed.
Name: Ji-Hyun Lee, MD.
Contribution: This author prepared the manuscript.
Attestation: Ji-Hyun Lee is the archival author.
Name: Karam Nam, MD.
Contribution: This author prepared the manuscript.
Attestation: Karam Nam approved the final manuscript.
Name: Yong-Hee Park, MD.
Contribution: This author helped prepare the video files.
Attestation: Yong-Hee Park approved the final manuscript.
Name: Jin-Tae Kim, PhD.
Contribution: This author prepared the manuscript.
Attestation: Jin-Tae Kim approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
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