Process review

This should include infection control (knowledge of local and national guidelines, probe sterilization, cleaning, and tracking), and care of the probe (including procedures for checking integrity before each use). Nasogastric tubes are often in situ, and to ensure interruption of feed is minimized, gastric contents should be aspirated before the study, and postprobe removal protocols should be in place to ensure no displacement has occurred, and feeding is recommenced only and as soon as judged safe.^3,7 The process of consent varies between countries, and although invasive procedures are usually undertaken only after consent is obtained, exceptions are generally allowed in the case of life-threatening emergencies and/or when the patient is unable to give informed consent. In some countries, informing the patient’s documented next of kin before a nonemergency invasive procedure is normal practice. Where research is undertaken, ethical approval must be obtained and consent obtained according to the agreed research protocol and local guidelines. The study should be recorded and reported according to local, national, and international guidelines and recommendations.

Patient review

This should include the indication for TEE and the patient history in terms of the relative and absolute contraindications to TEE (Table 29-1) and to its risk-benefit to the patient. The most significant serious complication from TEE in the outpatient population is esophageal perforation, with the usually quoted rate of 1:10,000 in studies; however, this is variable and may increase with an increasingly aged patient population.⁸ TEE in the intensive care is generally regarded as safe; however, because the critically ill patient is frequently coagulopathic, knowledge of the coagulation status of the patient is vital and, where indicated, possible correction undertaken. When the patient is fully anticoagulated or coagulopathic, probe insertion with laryngoscopic guidance is recommended. This is important if the patient is receiving extracorporeal support; in this circumstance, oropharyngeal bleeding can be life threatening. Critically ill patients undergoing TEE will be intubated and ventilated, and consistent with guidelines in many ICUs, there should be an independent ICU practitioner managing the airway, ventilation, and hemodynamic status of the patient during the study.

The practitioner planning and performing the study must consider the specific question being asked and the effects of vasoactive agents, sedation, and ventilation on patient hemodynamics that might have an impact on findings. For complex studies, the practitioner must also plan any strategy required to mimic/provoke/resolve the echocardiographic findings (i.e., changing ventilator settings, volume challenge, ventricular assist device (VAD) weaning, increased afterload, pacing optimization) and ensure the appropriate skills are present to be able to apply TEE appropriately within this setting.

Image acquisition: The standard views

Guidelines for performance of a comprehensive TEE study have been published, with recommendations for a minimum dataset in a number of circumstances.^3,7 The practitioner will then focus on the specific question that requires answering. In existing guidelines and recommendations, these predominantly relate to the perioperative cardiac surgical setting; however, it is not the mode of echo (TTE vs. TEE) but, rather, the information required that drives the study. Indeed, in undertaking repeated focused studies and/or using TEE as a hemodynamic monitor, only limited views may be required.

The standard order of image acquisition depends upon a number of factors, including the urgency of the study and time frame for acquisition, the type (comprehensive vs. focused), and individual practitioner preference. Ideally, in the critically ill patient, the amount of probe manipulation should be minimized, in particular in the elderly and/or coagulopathic patient. Movement of the probe is described in terms of its position with respect to the patient: withdraw/advance, rotate left/right, anteflex/retroflex, and flex right/left. Additional movement of the ultrasound beam relates to electronic rotation (from 0-180 degrees). As with TTE, as there is anatomic variation between patients, although numbers are given regarding the degree of electronic rotation, these are for guidance only. The standard views are described in Table 29-1, together with the main structures seen (Table 29-2).

Of note, the deep transgastric view is not achievable in all patients. Again, care should be taken to avoid excessive probe manipulation. Imaging of the pulmonary veins can be achieved by standard views (as described in Table 29-1) and additionally at 0 degrees, interrogating the right and left sides of the left atrium (both superiorly and inferiorly) in turn.

Indications for transesophageal echocardiography in the critically ill

The indications for echocardiography in the ICU have been discussed in Chapters 26 and 27, including the choice of TTE versus TEE. Images of diagnostic quality are unobtainable in up to 30% of the general ICU patient population, rising to 85% in those with severe, acute respiratory failure referred for extracorporeal respiratory support (Figure 29-2).⁹ Thus, when image quality precludes obtaining adequate information from the transthoracic route, TEE may be indicated. In addition, there are specific indications for TEE as opposed to TTE (Table 29-3). Guidelines for the appropriateness of undertaking TEE have been published; however, these will inevitably change with the ongoing development of critical care technologies, for example, extracorporeal support.^10,11