Abstract
Advances in monitoring and specifically in echocardiography have enabled anesthesiologists to use a gold standard technology across various clinical scenarios encountered in neurosurgical anesthesia. Transesophageal echocardiography in the hands of anesthesiologists enhances patient monitoring and aims to reduce intraoperative adverse cardiac events, such as venous air embolism and intraoperative cardiac dysfunction in high risk patients.
Keywords
Air embolism, Echo, Esophageal echocardiography, Screening
Outline
Introduction 277
Basics of Transesophageal Echocardiography 277
Common Indications for Utilization of Transesophageal Echocardiography in Neuroanesthesia 278
Screening for Venous Air Embolism During Neurosurgical Procedures 278
Absolute Contraindications 279
Relative Contraindications 279
Steps in Preparation for Placement of Transesophageal Echocardiography Probe Under Anesthesia 279
Screening, Risk Stratification, and Preparation of Patients at High Risk for Vascular Air Embolism Prior to Proposed Neurosurgical Procedures 280
Verification of Multiorifice Catheter Placement for High-Risk Neurosurgical Procedures and Ventriculoatrial Shunts 280
Monitoring Intraoperative Cardiac Function in Patients With Cardiomyopathy 281
Complications Associated With Transesophageal Echocardiography 282
Advantages and Disadvantages of Using Transesophageal Echocardiography as an Intraoperative Monitor 282
Summary 283
References 283
Introduction
The ability to visualize the chambers of the heart during neurosurgical procedures provides the anesthesiologist with data regarding cardiac function, valvular abnormalities, and presence or absence of intracardiac shunts; helps to visualize intracardiac extraneous material such as clots and air; and helps facilitate certain bedside hemodynamic and neurosurgical procedures.
Via a detailed literature search, this chapter reviews the utilization of transesophageal echocardiography (TEE) in the management of patients during neuroanesthesia. Upon reading the chapter, the reader will be able to understand the common indications, procedural characteristics, and practical applications of this technique.
Basics of Transesophageal Echocardiography
Unlike surface cardiography, TEE allows real-time visualization of various cardiac chambers. It is facilitated via placement of a TEE probe into the esophagus aimed anteriorly at the cardiac chambers. Due to the proximity to the heart, TEE examination generally provides images with a high degree of spatial resolution. With the probe in place, cardiac walls, valves, interatrial and interventricular septum, pericardial structures, and left and right outflow tract structures can be easily visualized. A traditional complete TEE examination covers such views.
Common Indications for Utilization of Transesophageal Echocardiography in Neuroanesthesia
- 1.
Screening for vascular air embolism during neurosurgical procedures
- 2.
Screening, risk stratification, and preparation of patients at high risk for vascular air embolism prior to proposed neurosurgical procedures
- 3.
Verification of multiorifice catheter placement to assist in air aspiration in high-risk neurosurgical procedures
- 4.
Verification of distal end of a ventriculoatrial (VA) shunt and assessment of VA shunt patency
- 5.
Cardiac monitoring in patients with neurogenic stunned myocardium for neurosurgical and nonneurosurgical procedures
Screening for Venous Air Embolism During Neurosurgical Procedures
Although CO 2 was demonstrated to be a useful agent aiding the detection of venous air embolism (VAE) by Bethune et al. in 1968, it was not until 1980 that detection of intracardiac air by esophageal echocardiography was first described by Duff et al. , who reported detection of entrapped intracardiac air by use of M-mode echocardiography. Since then many investigators have reported utilization of TEE in preoperative screening of patent foramen ovale (PFO) and intraoperative detection of VAE. Pertinent historical landmarks related to VAE and PFO detection are highlighted in Table 15.1 .
| Year | Authors | Screening Method |
|---|---|---|
| 1968 | Bethune et al. | Carbon dioxide used to detect VAE |
| 1972 | Michenfelder et al. | Precordial Doppler to diagnose VAE |
| 1975 | Seward et al. | Contrast ECHO studies (first findings) |
| 1975 | Munson et al. | Swan–Ganz catheters (first use) |
| 1976 | Frazin et al. | First description of esophageal echocardiography |
| 1980 | Duff et al. | Intraoperative surface echocardiography to detect intracardiac air |
| 1980 | Marshall et al. | VAE detection by Swan–Ganz catheter |
| 1981 | Bedford et al. | VAE detection by precordial doppler, ETCO 2 and pulmonary artery catheter |
| 1983 | Furuya et al. | VAE detection by TEE |
| 1984 | Cucchiara et al. | VAE detection by TEE |
| 1985 | Cucchiara et al. | PFO detection by TEE using positive airway pressure |
| 1990 | Black et al. | Pre- and intraoperative ECHO to detect right to left shunt in neurosurgical patients |
| 1991 | Nemec et al. | Comparison of TCD and TEE to detect intracardiac shunts |
| 1994 | Papadopoulos et al. | Compared intraoperative TEE and preoperative TTE to detect PFO in neurosurgical patients |
| 2000 | Stendel et al. 11 | TCD in preoperative setting to screen for PFO |
| 2001 | Kubo et al. | VAE due to PFO detected by use of harmonic contrast ECHO |
VAE has been described in the setting of sitting position craniotomies, where the noncollapsible dural venous sinuses by the virtue of being at higher level than the right atrium are exposed to a negative pressure gradient, facilitating air entrainment into the right atrium, with subsequent passage to right ventricle and pulmonary circulation with sometimes fatal effect. If there is an intracardiac shunt, then it poses an even increased risk for paradoxical air embolism into the cerebral circulation.
TEE remains the most invasive, yet the most sensitive of all available methods to detect air embolism. As little as 0.25 mL/kg of air can be detected by TEE in comparison of 0.5mL/kg as detected by precordial Doppler.
Preparation of Patient for Venous Air Embolism Detection by Transesophageal Echocardiography
The decision to insert a TEE probe for high-risk neurosurgical procedures is left to the attending anesthesiologist. The patient is first screened for any contraindications for placement of TEE probe such as esophageal pathology, gastrointestinal bleeding, or recent gastrointestinal surgery.
Precautions Taken in Performing an Intraoperative Transesophageal Echocardiography
A thorough history and physical examination is important prior to conducting an anesthetic. In patients undergoing intraoperative TEE, history should include prior esophageal surgeries, trauma, or ongoing upper gastrointestinal bleeding. Some of the contraindications to the performance of TEE and complications associated with TEE are as follows :
Absolute Contraindications
- 1.
Previous esophagectomy or esophagogastrectomy
- 2.
Esophageal stricture
- 3.
Tracheoesophageal fistula
- 4.
Postesophageal surgery
- 5.
Esophageal trauma
- 6.
Acute upper gastrointestinal bleeding
Relative Contraindications
- 1.
Esophageal varices
- 2.
Postradiation therapy
- 3.
Previous bariatric surgery
- 4.
Hiatal hernia
If a decision is made to proceed with TEE placement, it is placed after the patient has undergone induction of general anesthesia and prior to pinning of skull and finalizing patient position.
Placement of an adult size TEE is facilitated by oral bite block. The TEE probe is gently advanced to a depth of about 30–35 cm, and baseline images obtained. Table 15.2 highlights the important steps in the performance of TEE for neurosurgical procedures.
|
Steps in Preparation for Placement of Transesophageal Echocardiography Probe Under Anesthesia
With the help of agitated saline, both right and left atrial chambers are examined under the effect of positive airway pressure to detect PFO or interatrial shunt. Presence of PFO is demonstrated by visualization of saline microbubbles crossing across from the right atrium to the left atrium. PFO is reported in approximately 20% of humans.
After the patient has been pinned and prior to fixation of head, the patient’s neck flexion is carefully checked to prevent inadvertent overflexion of the neck, which in turn can cause oropharyngeal injury due to preexisting TEE probe. It is advisable to maintain at least two to three finger breadths between the inner margin of the chin and the suprasternal notch.
Once final positioning is achieved, a second study is performed to confirm optimal placement of the TEE probe and the TEE probe is locked in place and turned off. Operators must remember that if the TEE probe is kept on, overheating of the probe can cause thermal injuries to the esophagus.
The TEE probe is turned on during craniotomy to look for any signs of air entrainment in the right atrium. This is demonstrated by visualization of micro- or macrobubbles in the right atrium ( Fig. 15.1 ). The left ventricle is also visualized for signs of paradoxical air embolism.
If air entrainment is noticed, the neurosurgeon is immediately notified, the surgical procedure is temporarily halted as the surgical field is flooded with saline, and positioning of the patient is changed to a left lateral, reverse Trendelenburg position to prevent air locking of the right ventricle. Careful attention is paid to hemodynamic and oxygenation status, and the patient is switched to 100% O 2 , any nitrous oxide is turned off, and vasopressors or inotropes initiated to maintain systemic perfusion pressures. If hemodynamically significant air embolism is present, then cardiopulmonary resuscitation is initiated with chest compressions.
If severe air entrainment continues, temporary jugular vein compression is initiated.
Grading Severity of Venous Air Embolism: The Tubingen Venous Air Embolism Grading Scale .
This grading system described by Feigl et al. incorporates visibility of air bubbles on TEE, change in end-tidal carbon dioxide, and hemodynamic changes, and is used to stratify the severity of cardiovascular events as a result of VAE, as described in Table 15.3 .
| Grade | Description |
|---|---|
| Grade 0 | No air bubbles visible on TEE, no air embolism |
| Grade I | Air bubbles visible on TEE, no change in ETCO 2 |
| Grade II | Air bubbles visible on TEE, decrease in ETCO 2 ≤ 3 mmHg |
| Grade III | Air bubbles visible on TEE, decrease in ETCO 2 > 3 mmHg |
| Grade IV | Air bubbles visible on TEE, decrease in ETCO 2 > 3 mmHg, decrease in mean arterial pressure ≥20% or increase in heart rate ≥40% (or both) |
| Grade V | VAE causing arrhythmia, with hemodynamic instability necessitating cardiopulmonary resuscitation |
Screening, Risk Stratification, and Preparation of Patients at High Risk for Vascular Air EmbolismPrior to Proposed Neurosurgical Procedures
TEE can be performed in the preoperative period for patients scheduled to undergo high-risk neurosurgical procedures. Stendel et al. studied the sensitivity and specificity of transcranial Doppler (TCD) and transthoracic echocardiography (TTE) using TEE as the gold standard. Echovist-300 was used as the echo contrast medium, and Valsalva maneuver was performed in all patients.
Of 92 patients studied PFO was detected in 24 (26%) patients using TEE. TTE correctly identified only 10 (10.8%) patients, whereas TCD correctly identified 22 patients, missing 2. Thus, it was concluded that using TEE as reference standard, TCD was a highly sensitive (92%, with a high negative predictive value of 97%) tool to detect PFO. TTE achieved very low sensitivity (42%) and fairly high negative predictive value (83%) as compared to TEE. In this study if a PFO was demonstrated by TEE, surgical positioning was altered or extreme caution was used to prevent or stop air entrainment.
In a systematic review of PFO among patients undergoing neurosurgical procedures conducted by Fathi et al. the authors recommend for routine screening of patients who are scheduled for sitting position neurosurgical procedures with TEE.
Verification of Multiorifice Catheter Placement for High-Risk Neurosurgical Procedures and Ventriculoatrial Shunts
Multiorifice catheters such as the Albin–Bunegin catheters are sometimes placed in patients at high risk for VAE during certain neurosurgical procedures. Traditional teaching is to place these catheters with continuous electrocardiographic (ECG) tracing and optimizing the position of catheter tip after P wave deflection is noted. With the advent of TEE and its placement immediately postanesthesia induction allows the anesthesiologists to use the TEE images to guide placement of catheter tip. In this technique midesophageal bicaval view is used to visualize air aspiration catheter tip at the superior vena cava–right atrial junction.
TEE has been used in the evaluation of placement and verification of patency of a VA shunt. Machinis et al. describe four patients who underwent placement of VA shunt under fluoroscopy and TEE guidance while under general anesthesia. First introduced by Calliauw et al., patency of the VA shunt was determined by demonstration of echogenic material around the tip of the atrial end of the catheter, which was enhanced during inspiration and on performance of Valsalva maneuver. In a case series of 16 patients with a suspected VA shunt obstruction, the authors were able to perform the procedure under 5 min, with no complications.
Monitoring Intraoperative Cardiac Function in Patients With Cardiomyopathy
Echocardiography has been increasingly used for patients who present with or are at risk for intraoperative cardiac dysfunction. The use of TEE has increased over the past decade. Patients with intracranial hemorrhage and subarachnoid hemorrhage (SAH) have been noted to present with acute, transient left ventricular dysfunction and pulmonary edema, mediated by increased circulating catecholamine levels. Systolic dysfunction has been identified in a variety of neurologic injury paradigms, including stroke, brain death, and traumatic brain injury. Many of these patients will present to the operating room for intervention early during their injury, and hemodynamic instability may ensue once these patients have received anesthetic drugs. Therefore, a growing role of TEE has included intraoperative monitoring for hemodynamic status, as well as to optimize interventions, such as vasopressor and fluid therapy.
Several mechanisms including catecholamine excess, neuroendocrine dysfunction, and possibly inflammation have been implicated in the pathogenesis of systolic dysfunction following neurologic injury. Cardiac failure after SAH has been associated with higher mortality rate, longer hospital length of stay, and higher health care costs. SAH-induced cardiac dysfunction has been described as having both a Takotsubo (apical predominant) and an “inverted” Takotsubo (basal predominant) pattern on echocardiography ; while neurogenic causes of systolic dysfunction are thought to share pathophysiologic features similar to those of nonneurologic stress cardiomyopathies, there may be subtle nonclinical features that differentiate the two entities.
In addition to incident cardiac dysfunction from neurologic injures, the use of intraoperative TEE in patients with prevalent cardiac dysfunction who undergo neurosurgical procedures has been described. Griffin et al. describe a case report of patient with hypertrophic obstructive cardiomyopathy for endoscopic transsphenoidal resection of pituitary tumor, with intraoperative management aimed to preserve preload, prevent increases in contractility, and avoid reduction in afterload. In this report, data obtained from TEE was used to determine optimal positioning tolerated by the patient, as well as guide fluid management and need for vasopressors. One of the important events in the chronology of changes that occur during an episode of acute myocardial infarction (MI) is the occurrence of new regional wall motion abnormalities (RWMAs). While ECG is the most commonly used practical diagnostic test of choice, RWMAs can be diagnosed on a TEE well before ECG changes become apparent. RWMAs that appear during an acute episode of MI can be differentiated from those underlying neurogenic myocardial dysfunction, as the latter often appear not conforming to a particular coronary artery distribution.
Assessing Systolic Function
Two main measurements used to derive systolic function are end systolic and end diastolic volumes. Systolic function is estimated from fractional area change, which is proportional to the measured end systolic and diastolic areas, and is expressed by the following formulae :
F A C = E D A − E S A E D A × 100 , normal FAC ∼ 36 − 64 %
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