Perioperative transoesophageal echocardiography.
Sound waves are vibrations transmitted through a medium. These waves can cause compression and rarefaction, or positive and negative pressure changes within the medium through which they pass. An ultrasound is a cyclic sound energy in the form of waves with a frequency greater than the upper limit of human hearing. The audible frequency range of humans is 20 to 20 kHz (cycles per second) and frequencies above this range are referred to as ultrasound frequencies. Ultrasound is produced by the piezoelectric crystals that rapidly change their shape producing compression and rarefaction on application of the electric current. Ultrasound frequency used for medical purposes is from 1 to 20 MHz. Transthoracic echocardiography (TTE) uses low-frequency transducers between 2 and 4 MHz (Korula & Hebballi 2010). TTE imaging is obtained by placing a probe containing an ultrasound transducer on the surface of the chest wall. Higher frequency ultrasound waves have better resolution than lower frequencies, but they do not penetrate as far into tissue.
The transoesophageal probe is an endoscope with an ultrasound transducer at its tip. The probe is inserted into the patient's mouth and then passed into the oesophagus. The piezoelectric crystal is the basic element of the transducer which produces ultrasound waves by vibrating in response to a high frequency alternating electrical current. The same crystal is deformed by the returning waves, producing an electrical signal that is detected by the instrument. Ultrasound waves transmitted from the transducer into the patient can be reflected, refracted, scattered and attenuated. Reflected ultrasound waves (echoes) are processed to form the image whereas refraction, scattering and attenuation cause imaging artefacts. The TOE operator should attempt to reduce the risk of imaging artefacts by using different views and different depth settings (Shanewise et al 2003).
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Modes of imaging
was the first imaging mode to be used. Mmode uses a single linear beam of ultrasound. The first reported use of intraoperative echocardiography was in 1972 during mitral commissurotomy (Johnson et al 1972). It is still useful in the assessment of left ventricular (LV) function and for detection of vibrating valvular vegetations.
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Two-dimensional (2D) echocardiography
uses multiple linear beams that are displayed simultaneously to construct a 2D image (Figure 2).
Three-dimensional (3D) echocardiography has recently become available. 3D echocardiography uses an ultrasound probe with an array of transducers collecting volumetric data where each image is defined with respect to its exact position in space. Near real-time 3D reconstruction permits almost simultaneous display of images during the examination (Levine et al 1992). 3D imaging assists in the teaching of echocardiography where a significant amount of spatial understanding is required (Figure 3).
Pulsed-wave doppler (PWD) measures the velocity and direction of the blood flow in specific location, called the sample volume, which can be placed in any area of a 2D image. PWD is used in assessment of LV diastolic dysfunction and pulmonary venous flow pattern (Figure 4).
Continuous-wave doppler (CWD) measures the velocity and direction of blood flow along the line of the ultrasound beam. CWD is used to measure high blood flow velocities in the assessment of valvular stenosis such as aortic stenosis or mitral stenosis.
Colour-flow doppler (CFD) presents a real-time colour display of blood flow superimposed on a 2D image. CFD is used in the detection of valvular regurgitation such as mitral regurgitation by the identification of high-velocity flow through the regurgitant orifice (Otto 2009) (Figure 5).
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The American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists (ASA/SCA) Practice Guidelines for Perioperative TOE are subject to regular revision as warranted by the evolution of medical knowledge, technology, and practice. The guidelines provide basic recommendations that are supported by synthesis and analysis of the current literature, expert opinion, open forum commentary and clinical feasibility data. For further information see www.scahq.org/sca3/TEE%20Practice%20 Guidelines%20Update%20060109.pdf [Accessed July 2011]
Safety and risks
The patient should be asked about the presence of oesophageal disease, history of oesophageal surgery and symptoms of dysphagia and haematemesis. The medical records should be reviewed. Absolute contraindications to TOE include the presence of oesophageal disease (stricture, diverticula, tumour, oesophagitis and varices) and history of oesophageal surgery. The risk-benefit ratio for TOE should be considered and preoperative oesophagoscopy may be useful when the risk of trauma is unclear.
The TOE probe is inserted after the patient is anaesthetised and the tracheal tube is secured. Insertion of the probe at the beginning of the surgical procedure and under controlled conditions is recommended. As the mandible is displaced anteriorly, the well-lubricated probe is gently placed into the posterior pharynx in the midline and inserted gently into the oesophagus. A laryngoscope may be used to displace the mandible anteriorly. As the probe is advanced into the mid-oesophagus (approximately 25-30 cm from the teeth) the heart should come into view (Shanewise et al 2003). The probe may be advanced or withdrawn within the oesophagus, rotated to the patient's left or right, and anteflexed or retroflexed by the large control wheel. In patients with distal oesophageal pathology it may be possible to obtain adequate imaging without advancing the probe into the distal oesophagus or stomach. Poor matching of the probe size to the patient, excessive anteflexion or retroflexion of the probe tip and locking the position of the tip can increase the risk of trauma.
Complications of TOE (Table 3) are uncommon but may be serious and may not be apparent at the time of procedure (Kallmeyer et al 2001, Brinkman et al 2001). Trauma resulting in pharyngeal or oesophageal perforation is the major risk, but the incidence of perforation after TOE is extremely low. In a multicenter study (Daniel et al 1991) concerning 10,419 TOE examinations, complication rates and mortality rates were 0.18 and 0.0098 per cent respectively. The most common sites for perforation are the cricopharyngeal constriction and the lower oesophageal sphincter. Pharyngeal or oesophageal perforation carries a mortality of 10-25%. Late onset of symptoms (>24 hours) may be more common than early onset (<24 hours) (Shernan 2003). The appearance of dorsal pain, fever, or subcutaneous emphysema after TOE implies the need for investigation for an oesophageal perforation. Airway obstruction is a potentially dangerous complication, which is more common in children. Airway obstruction is easily recognised by increased airway pressure after probe insertion.
Intraoperative TOE examination
The ASA/SCA guidelines define 20 views that comprise a comprehensive TOE examination. The views are named by the location of the probe, the descriptive term of the imaging plane [short axis (SAX) or long axis (LAX)] and the major anatomic structure in the view. Mid-oesophageal views (MO) are obtained with transducer behind the left atrium, transgastric (TG) views are obtained by passing the probe into the stomach and upper oesophageal views are obtained with the probe at the level of the aortic arch (Shanewise et al 1999). The TOE probe is introduced after induction of general anaesthesia and left in place during cardiopulmonary bypass (CPB). When separating from CPB, TOE serves as a monitor of cardiac function. The post-CPB examination assesses the result of the surgical procedure such as prosthetic valve function, the presence of paraprosthetic leak and the adequacy of valve repair or congenital defect repair (Rosenhek & Binder 2002).
A baseline study allows assessment of cardiac function and underlying pathologies. Since diathermy and surgical manipulation of the heart impairs image quality it is advisable to perform the baseline examination prior to the start of surgery (Rosenhek et al 2002). It is important have the echo machine available in the operating theatre at the appropriate time. There are numerous reports of incidental findings such as masses, thrombi, PFO, ASD and membranous subaortic stenosis found during cardiac surgery (Nakao et al 1994, Liu et al 1995, Leslie et al 1998).
Left ventricle (LV) is examined with MO 4chamber view, MO 2-chamber view, MO LAX view, TG mid-SAX view and TG 2-chamber view. Normal inner end-diastolic diameter is less than 5.5cm, and LV wall thickness at end-diastole in TG mid SAX view should be less than 1.2cm. LV function can be assessed quantitatively or qualitatively. Qualitative assessment is performed by estimating the ejection fraction (EF) as normal >55%, moderate 35-55% or severely impaired <35%.
The success of mitral valve repair surgery is highly dependent on intraoperative echocardiographic assessment and description of the morphology, aetiology, mechanism and severity of the valvular lesion. Based on the findings the operative strategy (repair or replacement) and technique (annuloplasty, chordal transfer) may be determined. TOE is used for measurement of the annulus, which helps in sizing of the annuloplasty ring (Maurer et al 1987). Assessment of the adequacy of repair after CPB should exclude significant residual regurgitation or stenosis caused by excessive narrowing of the valve.
Measurement of the aortic valve annulus helps in sizing of aortic valve prosthesis. Pre-CPB assessment of the degree of aortic regurgitation permits planning the optimal strategy for cardioplegia delivery. During separation from CPB intracardiac air can be easily visualised by TOE as echo-dense areas in left atrium, along the atrial septum, adjacent to the pulmonary veins and in the LV apex. After valve replacement, TOE is used to assess aortic valve function and to identify the presence of paraprosthetic leak. Precise localisation of significant paraprosthetic leak by TOE allows surgical correction (Figure 5).
Severe acute endocarditis may be associated with destruction of the valve annulus, abscess formation, fistula formation and valvular perforation, all of which can be detected by TOE (Lerakis et al 2001).
In minimally-invasive cardiac surgery TOE can be used to aid the correct positioning of the coronary sinus catheter, venous cannula and endopulmonary vent catheter.
Cardiac catheterisation laboratory
TOE is crucial during patent foramen ovale closure and atrial septal defect closure to assess the morphology and size of the defect and the presence of multiple shunts. Careful analysis allows appropriate patient selection for transcatheter defect closure (Mazic et al 2001). TOE allows precise guidance, positioning and release of the septal occluder device.
Preoperative TOE is used to identify patent foramen ovale (PFO) prior elective neurosurgery in sitting position. Regardless of position, paradoxical air embolism across a PFO may occur during neurosurgical procedures. Paradoxical air embolism may be associated with events during induction of or emergence from anaesthesia.
All patients undergoing elective neurosurgery in the sitting position should be screened for PFO and considered for percutaneous closure. This strategy will permit safer surgery to be performed in the most appropriate position (Webb et al 2009).
TOE can be effectively used during balloon aortic valvuloplasty and mitral valvuloplasty, which are alternatives to cardiac surgery in certain cases of aortic stenosis or mitral stenosis (Abascal et al 1997).
Transcatheter aortic valve implantation (TAVI) and transcatheter mitral valve repair using a mitral closure device are emerging procedures. Both require comprehensive intraoperative TOE examinations to guide the procedures.
TOE is a semi-invasive procedure, carrying significant risk of cross-infection. TOE equipment is expensive and delicate, and probe care should be meticulous (Table 4). The TOE equipment consists of a transducer probe and a motor housing with articulation Q knobs followed by a cable ending at the connector. The probe is covered by a hard, black, smooth plastic with depth markings (Figure 6). The cost of a new TOE probe ranges from 25,000 [pounds sterling] to 50,000 [pounds sterling]. TOE probes are often used in demanding clinical environments and are exposed to many different hazards that can result in damage.
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Many studies have shown that improperly functioning probes can negatively affect the results of the TOE examination (Weigang et al 2003, Powis & Moore 2004, Moore et al 2005). The operator should normally be the first to observe any changes in the ultrasound image and should regularly look for obvious structural damage. All staff (clinicians, operating department practitioners, theatre nurses, ICU nurses) involved in using and disinfecting TOE probes need to be properly trained on how to test, inspect and handle TOE probes. Dropping or bending the probe can cause serious damage to the very fragile piezoelectric crystals. A disposable scanhead protection cover should be used whenever carrying the probe or the probe should be carried in the special suitcase. Not using a bite guard can also result in what is referred to as 'tooth drag'; pulling the insertion tube over a tooth that may have a sharp edge can result in a cut or tear in the insertion tube. These cuts, holes or tears create a potential entry point for fluids. Proper use of the bite guard means placing and securing it in the patient's mouth prior to insertion of the TOE probe.
TOE probes should be stored in a dedicated cabinet and hung up straight (Figure 7). TOE probes should be inspected daily (Table 5) and never used without proper cleaning and decontamination (Table 6). The proper disinfectant is one that is listed as approved for use in the documentation provided by the manufacturer of the particular probe. This information is normally found in the TOE probe operator's manual. The instructions on the disinfectant should be followed, and they include information such as how long the solution can be used once activated, how many minutes the transducer should be soaked, how to test the solution to ensure it is still effective and how to properly dispose of the solution. Sporicidal, mycobactericidal, bactericidal, virucidal and fungicidal wipes which incorporate chlorine dioxide are convenient and easy to use (Figure 8). The wipes kill all organisms within 30 seconds on pre-cleaned surfaces from which organic matter has been removed (Hernandez et al 2008).
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Accreditation and certification process in transoesophageal echocardiography
The first examination to test all areas of echocardiography (ASeXAM) was conducted in 1996.
In the same year, an American Society of Anesthesiologists/Society of Cardiovascular Anesthesiologists (ASA/SCA) Task Force published practice guidelines on indications for intraoperative TOE. The first pilot examination was in 1997, and the first formal examination in perioperative TOE was in 1998. Towards the end of 1998, the SCA and ASE combined their two examination processes and founded the National Board of Echocardiography (NBE). The NBE was established to develop and administer examinations in the field of clinical echocardiography, and has been conducting these annually ever since.
The British transoesophageal echocardiography accreditation process represents a joint venture between the British Society of Echocardiography (BSE) and the Association of Cardiothoracic Anaesthetists (ACTA). The process is primarily offered as a service to the members of both these specialist societies. Full details and registration forms are on the website www.bsecho.org.
TOE has become an integral part of perioperative care for cardiac surgery and cardiac catheterisation laboratory procedures. TOE is an invaluable diagnostic tool, which is relatively safe and noninvasive. TOE probes are often damaged requiring high cost replacement or repair. Careful probe handling will bring about significant financial savings. Staff knowledge is crucial to the infection control bottom line, and annual competency should be documented.
No competing interests declared
Provenance and Peer review: Commissioned by the editor; Peer reviewed; Accepted for publication June 2011.
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Brinkman WT, Shanewise JS, Clements SD et al 2001 Transesophageal echocardiography: not an innocuous procedure Annals of Thoracic Surgeiy 72 1725-1726
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www.echocardiographer.org/TEE.html www.bsecho.org www.echoboards.org
Thys D, Abel MD, Brooker RF, Cahalan MK et al 2010 Practice guidelines for perioperative transesophageal echocardiography. An updated report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on transesophageal echocardiography. Available from: www.scahq.org/sca3/TEE%20Practice%20Guidelines %20Update%20060109.pdf [Accessed July 2011] Anesthesiology 112 (1) 1
Correspondence address: Stephen Webb, Department of Anaesthesia and Intensive Care, Papworth Hospital NHS Foundation Trust, Papworth Everard, Cambridge, CB23 3RE. Email: Stephen.firstname.lastname@example.org
About the authors
Barbora Parizkova MUDr
Consultant in Anaesthesia Papworth Hospital NHS Foundation Trust, Cambridge
Stephen T Webb MB, BCh, BAO, FRCA, EDIC, FFICM
Consultant in Anaesthesia and Intensive Care Medicine, Papworth Hospital NHS Foundation Trust, Cambridge
Table 1 Summary of American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists (ASA/SCA) Practice Guidelines 2010 - Indications Indications Cardiac and thoracic aortic procedures Cardiac and thoracic aortic surgery * For adult patients without contraindications, TOE should be used in all open heart and thoracic aortic surgical procedures and should be considered in coronary artery bypass graft (CABG) procedures: * to confirm and refine the preoperative diagnosis * to detect new or unsuspected pathology * to adjust the anaesthetic and surgical plan accordingly * to assess the results of the surgical intervention. * In small children, the use of TOE should be considered on a case-by-case basis because of risks unique to these patients. Transcatheter intracardiac procedures * TOE may be used. Non-cardiac surgery * TOE may be used when the nature of the planned surgery or the patient's known or suspected cardiovascular pathology might result in severe hemodynamic, pulmonary, or neurologic compromise. * If equipment and expertise are available, TOE should be used when unexplained lifethreatening circulatory instability persists despite corrective therapy. Critical care * TOE should be used when diagnostic information that is expected to alter management cannot be obtained by transthoracic echocardiography or other modalities in a timely manner. Table 2 Summary of American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists (ASA/SCA) Practice Guidelines 2010 - Contraindications Contraindications TOE may be used for patients with oral, oesophageal, or gastric disease, if the expected benefit outweighs the potential risk, provided that the appropriate precautions are applied. These precautions may include: * considering other imaging modalities (eg epicardial echocardiography) * obtaining a gastroenterology consultation * using a smaller probe * limiting the examination to the midoesophageal views * avoiding unnecessary probe manipulation * using the most experienced operator. Table 3 Complications of transoesophageal echocardiography (Shanewise 2003) * Dental and oral trauma * Laryngeal dysfunction * Tracheal tube displacement * Bronchial compression in children * Aortic compression in children * Pharyngeal/oesophageal mucosal injury * Pharyngeal/oesophageal perforation Table 4 Proper care of the TOE probe * Follow the manufacturer's recommended disinfection procedures * Use of bite guards in patients with teeth * Regular testing of the probe function * Meticulous visual inspection * Very careful handling, transportation and storage Table 5 Daily probe inspection * Floppiness or stiffness of the probe tip * Discoloration of the probe shaft * Cuts in the probe shaft * Cracks in the transducer * Bent pins in the probe connector * Bite marks, holes or tears of the bending section Table 6 Example of TOE probe decontamination protocol The approved product in our hospital is the Tristel Wipes System which incorporates a: * Pre-clean wipe * Sporicidal wipe * Rinse wipe * Audit/traceability trail Do NOT use if the wipe sachet or foam bottle has been damaged. Step 1 * Put on gloves. * Take a Pre-Clean Sachet, tear and remove wipe, alternatively use a detergent wipe. * Unfold the wipe and lay out on the palm of your hand. Clean scope until soil and organic matter have been visibly removed from the scope or probe. * Discard the wipe and gloves into clinical waste. Step 2 * Put on clean pair of gloves. * Take a Sporicidal Wipe Sachet, tear and remove wipe. * Unfold the wipe and lay out on the palm of your hand. * Take lid off TRISTEL Activator Foam Bottle and pump 2 measures of foam onto wipe. * Scrunch the wipe until it is covered with foam, wait 15 seconds. * Wipe the surface of the probe - all areas of the probe must come into contact with the wipe at least once, wait 30 seconds. * Discard the wipe into clinical waste. Step 3 * Take a Rinse Wipe Sachet, tear and remove wipe. * Thoroughly wipe the surface of the probe, which has been decontaminated. * Wash your hands. The probe is now ready to be used on the patient. Trail book should be completed and signed by the individual responsible for carrying out the decontamination process. Staff who are using the TRISTEL decontamination process must receive training and be assessed in proficiency.
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|Title Annotation:||CLINICAL FEATURE|
|Author:||Parizkova, Barbora; Webb, Stephen T.|
|Publication:||Journal of Perioperative Practice|
|Date:||Sep 1, 2011|
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