14.4.3 Transesophageal echocardiography (TEE)

The TEE procedure

With miniaturised probes, it is possible to perform TEE on children of small sizes. A 6 mm paediatric probe is perfectly suitable for children weighing 5 to 20 kg. A neonatal probe (4 mm) is used with neonates (< 5 kg). In children, the risk of oesophageal lesions is lower than that of vascular compression and respiratory obstruction of the trachea, a primary bronchus or the tracheal tube – sometimes babies cannot be ventilated once the probe is introduced. It is essential to monitor pressure in the airways while positioning the probe in very young children [1]. Moreover, there is an inevitable risk of accidental extubation due to equipment clutter and handling. The incidence of TEE complications varies between 1% and 3% in young children. The main complications are respiratory obstruction, tracheal tube displacement, accidental extubation, haemodynamic instability, and oesophageal lesions. The latter result in mucosal lesions and transient dysphagia [14]. A specific indication is therefore required to justify the use of TEE in neonates.

The probe should be carefully lubricated and encased in a sterile protective cover if the child's size allows this. It is inserted once the child has been put to sleep and intubated. Two techniques are in use:
 

The examination must be performed before CPB for two reasons: 1) to capitalise on the high incidence of new findings it allows (5-8% of cases), and adjust the surgical strategy accordingly, and 2) to gain a means of comparison for judging surgical reconstruction at the end of the procedure [2].

With two imaging levels in the oesophagus and one in the stomach, a virtually complete anatomical view of the heart is possible if the numerous viewing angles of the multiplane probe are used [9,12].
 

Posterior structures (e.g. LA, pulmonary veins) are always easier to analyse than anterior structures (RVOT, LV apex), which are further from the transducer in the oesophagus. Given the interposition of the tracheobronchial tree, it is not possible to examine the distal part of the ascending aorta, the proximal part of the aortic arch, and the left branch of the PA by TEE. The isthmus (coarctation) and ductus arteriosus areas are generally visible. The descending aorta is not always easy to examine in young children.

Indications

There are five circumstances in which TEE is useful to anaesthetists [2,5,6].
 

TEE is recommended for the following situations in paediatric cardiac surgery [7,8].
 

When three-dimensional paediatric probes are available on the market, it will be possible to observe complex pathologies in three dimensions and in motion. However, dynamic viewing is currently limited to two-dimensional images and the operating field only provides a static view of structures while the heart is stopped and flaccid.

Impact

The clinical impact of TEE varies depending on the pathology. It is particularly useful in cases of obstructed right or left outflow tract, valve repair or atrioventricular discordance [10]. In cases of coronary reimplantation after a switch operation for TGA, TEE is necessary for assessing ventricular segmental wall function and diagnosis of myocardial ischaemia (Table 14.11). In contrast, the contribution of TEE after a simple ASD procedure is not significant. However, perioperative TEE enables the immediate evaluation of surgical corrections and repairs; in 8-14% of the cases, the post-CPB examination prompts an immediate return to bypass because of residual lesions [4]. This allows a complete reconstruction in a single procedure and prevents a secondary reoperation, and is highly cost-effective. The drawback of TEE is a high rate of discoveries without clinical significance or surgical impact (6-25% of cases) [11]; this is due to its high sensitivity and its high-quality images. Indeed, 27% of post-repair defects are considered either acceptable, irreparable, or do not justify the risk of a second CPB [16]. Although it is tempting to require operators to realise echo-perfect corrections, not all residual pathological findings are worth a second run on bypass. Excessive focus on TEE images may cause clinicians to overlook genuine benefits for patients. As the saying goes: "Treat the patient, not the image".

The second strong point of TEE is monitoring. TEE is useful under all circumstances for assessing and correcting patients’ blood volume, individual ventricular function and myocardial ischaemia. This is particularly true of congenital patients since their haemodynamics are very specific: with their peculiar anatomy, pressure measurements do not genuinely reflect ventricular filling or systolic function. As such, TEE is the determining factor for catecholamine administration in 25% of the cases [4,10]. This is crucial, because long-term prognosis is improved if ventricular function is adequate in the perioperative phase [15]. Moreover, the occurrence of untreated wall motion abnormalities is linked to a mortality of 33% if it affects the RV, and of 25% if it affects the LV [17].

Routine use of TEE for all congenital heart patients is no longer questioned given the high incidence of fortuitous findings with a surgical impact before CPB (5-8% of cases) and the high rate of immediate secondary corrections after CPB (8-14%). These figures indicate that it is an economically profitable tool in congenital heart surgery, given the number of subsequent operations avoided by immediate correction of diagnoses or procedures [3]. The problem remains that anaesthetists must be qualified to perform these perioperative cardiological duties. This requires appropriate training, as demonstrated by the following impact study: in instances where qualified echocardiographers monitor the TEE post-CPB, the rate of return to bypass for correction of residual lesions is 9.6%, but it is 0% when untrained observers watch the TEE. The percentage of undetected residual problems is 21% in the former case, and 74% in the latter [13]. Therefore, the impact of TEE is highly dependent on the degree of excellence of the echocardiographer.

 

 

 

 

© BETTEX D, BOEGLI Y, CHASSOT PG, June 2008, last update February 2020
 

 
References