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Abstract
Background: Transesophageal echocardiography (TEE) probe insertion may be associated with many complications. Demographic factors and airway conditions such as high Mallampati scores (MMC) and Cormack-Lehane grades (MCLG) are likely to have an impact on its ease of insertion. The primary aim of this study was to identify the predictive factors for difficult real-time-three-dimensional TEE probe insertion.
Methods: A total of 153 adult patients undergoing cardiac surgery were prospectively evaluated. The upper airway manipulations required for TEE probe placement were jaw thrust, reverse Sellick's maneuver, and laryngoscopy. All the patients who required airway manipulations were grouped under difficult TEE probe placement group. We evaluated the patients' predictive factors such as demographic characteristics and factors related to difficult intubation.
Results: Out of 153 patients, 123 were males and 30 were females. Overall, 27.5% (n = 42) patients had difficulty in probe placement. About 31.7% (n = 39) males had difficulty in TEE probe placement against 13% (n = 4) females (P-value 0.045). Difficulty in TEE probe placement was found in 72.7% (n = 16) of obese patients (body mass index [BMI] > 30), compared to 18.6% (n = 17) in the patients with BMI less than 25 (P-value < 0.001). Probe insertion was significantly more difficult in the presence of MMC III and IV (50%, n = 18) compared to class I (19.2%, n = 10) (P-value 0.001) and MCLG III (73.3%, n = 22) compared to grade I (11.1%, n = 7) (P-value 0.001).
Conclusion: Male gender, obesity, higher grades of MMC and MCLG were found to be the risk factors for difficult TEE probe placement in anesthetized patients.
Keywords: Cardiac surgery, difficult airway, obesity, probe, three-dimensional echocardiography
How to cite this article: Introduction 
Transesophageal echocardiography (TEE) is a monitoring tool extensively used in cardiac surgery. Presently, TEE is being used widely in operation theaters, intensive care units, cardiac catheterization laboratories, and daycare units. Repeated attempts at insertion of the TEE probe by the conventional blind manner may cause various complications such as oropharyngeal injuries, orogastric tract perforation, esophageal perforation, dysphagia, and gastrointestinal bleeding.[1] The incidence of these complications may be more with a real-time-3D TEE (RT-3D-TEE) probe as it is larger than a conventional adult 2D-TEE probe. The American Society of Echocardiography/Society of Cardiovascular Anaesthesiologists consensus guidelines stresses on the need to avoid multiple attempts of TEE probe insertion in anesthetized patients.[2] To prevent complications associated with TEE probe insertion, different techniques have been described such as jaw-thrust maneuver,[3] reverse Sellick's maneuver,[4] rigid laryngoscope assistance[5] or optical-guided insertion,[6] and video-laryngoscope.[7] Ozturk et al.[7] showed that the use of the McGrath MAC video-laryngoscope for TEE probe insertion increases the success rate and reduces pharyngeal injuries compared to the conventional blind insertion technique in cardiac surgery patients. Similarly, Jonathan et al.[6] reported that optically guided TEE probe placement significantly reduced hypopharyngeal injuries and improved patient safety compared to the conventional blind insertion. However, routine use of a video-laryngoscope or optically guided insertion of TEE probe may not be feasible in all the patients because it may not be available in all the places, especially outside operating rooms. Moreover, laryngoscopy causes sympathetic stimulation, which can be detrimental in cardiac surgical patients. A recently published study showed that modified Mallampati class (MMC) is one of the factors determining the success of TEE probe placement in non-sedated patients.[8] To the best of the authors' knowledge, there is scanty literature available related to the prediction of factors that make the TEE probe insertion difficult. Hence, we conducted this study to ascertain the predictive factors associated with difficult TEE probe insertion in anesthetized patients scheduled for cardiac surgery. We hypothesized that there exists no association between difficult airway predictors and TEE probe placement. This prospective observational study was aimed at identifying the predictive factors for difficult insertion of RT-3D-TEE probe in anesthetized adult patients undergoing cardiac surgery and to correlate the predictive factors with the maneuver required to insert the TEE probe.
Methods This prospective study was conducted after obtaining permission from the institute ethics committee and informed consent from the patients from November 2018 to October 2019. A total of 153 adult patients undergoing cardiac surgery were serially evaluated for the difficulty in the placement of the RT-3D-TEE probe. Study subjects included adult patients, aged between 18 and 70 years, scheduled for cardiac surgery. Exclusion criteria were known absolute and relative contraindications to the TEE probe placement as described by the ASE guidelines.[2] The patients with restricted mouth opening and/or neck extension (<30°) were excluded from the study. Reverse Sellick's maneuver was described as a step for the insertion of the TEE probe, which involves manipulation of the neck. As there is a potential risk of atherosclerotic plaque embolization during the neck manipulation in the patients with carotid artery disease, they were excluded from the study. After routine anesthesia induction and muscle relaxation, the trachea was intubated with 8.5 and 7 mm endotracheal tubes in men and women, respectively. Standard monitoring was established and a well-lubricated RT-3D-TEE probe (X7-2t, Philips Ultrasound, Bothell, WA, USA) was inserted by a senior anesthesiologist experienced in placing more than 100 TEE probes. The distal 10 cm of the probe was generously lubricated with water-soluble jelly on all sides. In all the patients where laryngoscopy was not required for probe insertion, the bite block was placed first following which the probe was inserted. For the patients requiring laryngoscopy, a bite block was slid over the probe after inserting the probe. Initially, we tried to pass the TEE probe in the sniffing position given for endotracheal intubation after elevating the head by 10 cm from the operation table using folded sheets and bringing the ear canal to the level of the anterior shoulder. The shaft of the TEE probe was held with the right hand and the handle in the left hand. The shaft of the probe was gently anteflexed to make it curved like an endotracheal tube. We tried the upper airway manipulations if we failed to insert the TEE probe into the esophagus in this position. Failure to insert the TEE probe into the esophagus was defined as a firm resistance encountered on advancement of the probe in the pharynx on the application of a gentle but steady force, which prevented placement of the probe into the esophagus. The placement of the probe in the esophagus was defined as the insertion of the probe beyond 15 cm from incisor teeth and free to-and-fro movement of the probe. The upper airway manipulations required in succession during the TEE probe placement were jaw thrust, reverse Sellick's maneuver, and direct laryngoscopy. Video-laryngoscopy-guided insertion was performed on the failure of the above-mentioned maneuvers. Each maneuver was attempted twice without applying undue force before trying the next maneuver. According to the study protocols, we categorized the patients who required jaw thrust, reverse Sellick's maneuver, and laryngoscopy into difficult TEE probe placement category, grading the difficulty as grade 1 (requiring jaw thrust), grade 2 (requiring reverse Sellick's maneuver), and grade 3 (requiring laryngoscopy), respectively. Predictive factors related to difficult endotracheal intubation were evaluated for difficult TEE probe placement, which included age, sex, BMI, MMC, and modified Cormack-Lehane grade (MCLG). All the patients underwent video-laryngoscopy after the TEE probe removal to inspect for any obvious oropharyngeal injuries or persistent bleeding (IEC Date of approval: 30-Oct-2020).
Qualitative data were expressed in percentages; the Chi-square test was used to determine whether there was a significant difference between the expected frequencies and the observed frequencies among the groups. The SPSS software was used for statistical analysis (Statistical Package for the Social Sciences). With reference to the previous research article,[7] the success rate of TEE probe insertion at the first attempt using the conventional method was 43.9%, i.e., the difficulty in probe insertion in the first attempt was 56.1%. Based on this study, the minimum sample size was calculated.
Results A total of 153 patients were analyzed, out of which 123 were males and 30 were females. About 27.5% (n = 42) patients had difficulty in probe placement. We were able to pass probe with neck in sniffing position in 72.5% (n = 111) patients. Altogether, in 72.5% (n = 111) of the patients, there was no difficulty in placing the probe as we were able to pass the probe with simple neck extension alone. About 21.6% (n = 33) grade 1 patients required jaw thrust in addition to neck extension, 4.6% (n = 7) grade 2 patients required reverse Sellick's maneuver, and 1.3% (n = 2) grade 3 patients required video-laryngoscope-guided insertion of probe. About 31.7% (n = 39) males had difficulty in TEE probe placement compared to 13% (n = 4) females (P-value 0.045) [Figure 1]. The patients were divided into four categories based on the BMI. The patients categorized as underweight (BMI <18), normal weight (BMI 18–25), overweight (BMI 25–30) and obese (BMI >30) were 7.8% (n = 12), 51.6% (n = 79), 26% (n = 40), and 14.3% (n = 22) in proportion, respectively. We did not evaluate our results by further subdividing the obesity into obesity, severe obesity, and morbid obesity as the patients with severe obesity and morbid obesity were very few. Difficulty in TEE probe placement was the highest in 72.7% (n = 16) of obese patients (BMI >30), compared to 18.6% (n = 17) in the patients with BMI less than 25 (P-value < 0.001) [Table 1]. The distribution of the MMC class among the patients was as follows: MMC class I in 34% (n = 52), MMC class II in 42.5% (n = 65), MMC class III in 21% (n = 32), and MMC class IV in 2.6% (n = 4), suggesting that MMC class II was the commonest to prevail among the patients. We found probe insertion significantly difficult in the presence of MMC classes III and IV (50%, n = 18) compared to class I (19.2%, n = 10) (P-value – 0.001) [Table 2]. Prevalence of MCLG among the patients in a descending order was MCLG I in 41% (n = 63), MCLG IIa in 25% (n = 38), MCLG III in 20% (n = 30), and MCG IIb in 14% (n = 22). Probe placement was significantly difficult in the higher Cormack-Lehane grade (73.3%, n = 22 in MCLG III vs 11.1%, n = 7 in MCLG I) (P-value 0.001) [Table 3]. We did not observe any association of age with difficulty in TEE probe placement. There was no obvious oropharyngeal injury or persistent bleeding in any of the patients after the probe removal.
Figure 1: Influence of gender on difficulty in the insertion of TEE probe
Table 1: Influence of body mass index (BMI) on difficulty in insertion of TEE probe
Table 2: Influence of modified Mallampati class (MMC) on difficulty in insertion of TEE probe
Table 3: Influence of modified Cormack-Lehane grading (MCLG) on difficulty in insertion of TEE probe Discussion With the advent of 3D echocardiography in cardiac surgery, RT-3D-TEE probe placement has become a routine during cardiac surgery. The tip of the X7–2t RT-3D-TEE probe measures 16.6 mm in width, which is larger than the outer diameter of a 9.0 mm endotracheal tube and also is larger than the conventional adult 2D-TEE probe (S7-2 Omni TEE) which measures 14.9 mm in width.[9] Direct trauma to the gastrointestinal tract may be associated with the size of the probe tip relative to the esophagus.[10] Hence, more incidence of complications related to the probe insertion may be expected with RT-3D-TEE insertion. Although, there is no objective evidence to define parameters predicting difficult TEE probe placement, some of the experts opine that there may be a concurrence of the factors influencing the difficult endotracheal tube placement and difficult TEE probe placement. Hence, we evaluated if there exists an association between difficult airway predictors and TEE probe placement. Our study sample consisted predominantly of the male subjects than the female subjects (80% vs 20%) because of a higher incidence of coronary artery disease among men requiring coronary artery bypass grafting. Male gender and obesity are found to be the risk factors for difficulty in probe placement, which may be attributed to the anatomical modulation of the upper airway in the presence of these factors through which the probe courses its way to the esophagus. Lingual fat, which is a consistent feature of central obesity, is deposited more in men than women and exponentially increases with weight gain.[11] Increased tongue adiposity is influenced by gender and is associated with abnormal upper airway patency and body configuration parameters. Prior studies have shown that obesity may lead to upper airway soft tissue enlargement by fat infiltration of the tongue, soft palate, and lateral pharyngeal walls.[12]
The tongue is the single major structure in the mouth affecting the ease of access to the laryngeal inlet[12] and the esophagus. Modified Mallampati classification indirectly associates the tongue size to the oropharyngeal size that predicts difficulty in direct laryngoscopy.[13] Khongkaew et al.[8] reported that in awake patients with narrow oral cavity (MMC III and IV), a longer time is needed for successful TEE probe placement than those who have a broader oral cavity (MMC I and II). We also observed that the patients with MMC III and IV had significantly difficult probe placement compared to MMC I and II (50% vs 19.2%, P value 0.001). Posterior displacement of the tongue is one of the etiologies for higher Cormack-Lehane grade,[14] which also is associated with difficult TEE probe placement. Thus, we noted that a large tongue, which affects the MCLG, is a major anatomical factor contributing to the difficult TEE probe placement in the patients with higher MCLG [Figure 2]. The jaw thrust, which lifts the mandible anteriorly and caudally, usually opens the mouth and shifts the tongue anteriorly to permit smooth probe placement.[2] The inferior constrictor muscle forms the anatomic beginning of the esophagus, which is just posterior to the cricoid cartilage.[4] The Sellick's maneuver eases the difficult endotracheal intubation by moving the laryngeal apparatus posteriorly and bringing the glottic opening in focus of the operator. In contrast, the cricoid cartilage is manually lifted anteriorly during the reverse Sellick's maneuver which facilitates the placement of the TEE probe by opening the collapsed upper esophageal inlet, which allows easy passage of the probe into the esophagus.[4] However, this maneuver may be avoided in the patients with carotid plaques, which may potentially get dislodged with external pressure leading to cerebral thromboembolism. Placement of the TEE probe under direct laryngoscopy remains a handy option to the anesthesiologists when all other airway manipulations fail to guide the probe to the esophagus. Direct laryngoscopy not only reduces the trauma due to the blind attempts of the probe insertion, but also provides better access to the esophageal inlet as the endotracheal tube can be displaced anteriorly with the help of the laryngoscope blade. However, direct laryngoscopy may be associated with significant hemodynamic disturbances such as tachycardia, hypertension, ventricular arrhythmias, and development of myocardial ischemia due to sympathetic stimulation.[15] The magnitude of cardiovascular response is directly related to the force and duration of laryngoscopy,[15] and hence, it may not be the first choice for guiding insertion of a TEE probe. Blind repeated manipulations of the probe in the pharynx in difficult situations may cause hemodynamic disturbances, bleeding, injury to adjacent structures, including perforation of Zenker's diverticulum.[16] Hence, in the patients with anticipated difficulty in TEE probe placement due to the coexistence of multiple risk factors such as male gender, obesity, higher MMC, and MCLG, due consideration may be given for probe placement directly under laryngoscopic vision.
Figure 2: A representative image depicting the influence of tongue size on modified Cormack-Lehane grade (MCLG). In image b, the large tongue (in comparison to image a) is obscuring the view of the glottis, thereby increasing MCLG during direct laryngoscopy. Thus, a large, posteriorly protruding tongue increases MCLG and is likely to hinder the smooth passage of the TEE probe into the esophagus. Abbreviations: G: glottic opening; black line: depicts oropharyngeal axis during laryngoscopyWe do acknowledge limitations to our study. Although our study was adequately powered, larger studies are necessary to validate the risk factors, which we identified for difficult RT-3D-TEE probe placement. The risk factors evaluation applies to the current generation of RT-3D-TEE probes, which may vary with the miniaturization of the probes in the future with advancing technology. We did not analyze our results for the subcategory of severe obesity and morbid obesity, as these patients were limited in number. The difference between male and female subjects was significant. The oropharyngeal injury caused by TEE probe insertion, which was observed with the video-laryngoscope may also be attributed to the laryngoscopy during endotracheal intubation.
In summary, all the factors which make the upper airway narrower like male gender, higher BMI >30), higher MMC, and MCLG may pose difficulty in the passage of the TEE probe. Reverse Sellick's maneuver and jaw thrust may facilitate the advancement of the probe. In the patients with anticipated difficulty in TEE probe placement due to coexistence of multiple risk factors such as male gender, obesity, higher MMC, and MCLG, due consideration may be given for probe placement directly under the laryngoscopic vision.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References 
Correspondence Address:
Shrinivas Gadhinglajkar
Department of Cardiac Anesthesia, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum - 695 011, Kerala
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/aca.aca_287_20
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