Esophageal stethoscope insertion into the esophagus increased tracheal cuff pressure under general anesthesia. Cuff pressure change over 5 cmH2O induced by esophageal stethoscope insertion was observed more in female patients than in male patients.
Several previous studies presented that the TEE probe raised tracheal cuff pressure by 6.3 to 8.5 cmH2O from the baseline value, while using a single lumen tube for general anesthesia in adult patients [13, 14]. In our study, the mean change in cuff pressure was 3.0 ± 3.4 cmH2O in 112 patients who received general anesthesia with a single lumen tube. This discrepancy may be due to the diameter difference between the TEE probe and esophageal stethoscope. However, the esophageal stethoscope is widely used for body temperature monitoring in these days. Therefore, clinicians should be aware of the possibility of cuff pressure change when an esophageal stethoscope is used for body temperature monitoring. Moreover, this knowledge could be helpful in the case of Levin tube insertion for bowel surgeries because 18 Fr. of esophageal stethoscopes and Levin tubes is mostly used in the clinical setting for adult patients. In our study, we used 18 Fr. of esophageal stethoscopes in all patients.
Optimal cuff pressure has been suggested to be between 20 and 30 cmH2O [9–12]. Routine monitoring of cuff pressure has been emphasized because improper high cuff pressure can cause tracheal injuries [15–17]. To date, however, it seems that cuff pressure monitoring has not been routinely performed in clinical situations, and there is no strong guidance for monitoring cuff pressure [18, 19]. This may be because tracheal injury by high cuff pressure has rarely occurred or has been reported limitedly. In real practice, many clinicians seem to indirectly check cuff pressure by palpating the pilot balloon. Anesthesiologists who performed tracheal intubation and inflation of cuff in this trial were allowed to check the cuff in a routine manner. All of them checked the level of cuff pressure by manual palpation of the pilot balloon. However, this method can cause high cuff pressure because clinicians seem to have a tendency to believe in themselves even though this method cannot estimate exactly cuff pressure [20, 21]. Additionally, it can induce overinflation [10, 15]. In our study, the high initial cuff pressure consisted of these concerns. The initial cuff pressure in our study was different for each clinician. This supports the knowledge from previous studies . Therefore, we believe that there should be a strong guideline for cuff pressure management.
Some previous studies revealed that cuff pressure can be affected by patient position  or body temperature [23, 24]. We investigated the effect of esophageal stethoscope insertion only on cuff pressure while performing the trial with the patient’s neck in a neutral position. Additionally, we checked the cuff pressure during a short period of tracheal intubation and the initial period of surgical preparation. For that time period, the body temperature of the patient should rarely change. Additionally, we did not use nitrous oxide in the trial. We evaluated the correlation between an increase in cuff pressure and patient characteristics. One of the previous studies did not evaluate the patient risk factors for significant cuff pressure change induced by the insertion of medical instruments . One previous study showed that patient sex, height, weight and anteroposterior/transverse tracheal diameter were not associated with cuff pressure increase. However, the study was performed with a total of 44 patients with unpaired sex ratios (32 males and 10 females), and a single lumen tube was used for only 22 patients (19 males and 3 females) . One previous study investigated whether the cuff pressure increase by a TEE probe varied across 4 age groups in pediatric patients . However, the authors in the study presented no relationship between cuff pressure increase and age. We found that sex was related to cuff pressure change over 5 cmH2O when we investigated the relationship between potential risk factors and significant cuff pressure change induced by esophageal stethoscope insertion, which may be because the cuff pressure of the smaller tube within the smaller trachea could easily increase by air-inflation. However, this should confirm with additional studies with a large sample size.
There were several limitations in the study. First, we did not evaluate the effect of the esophageal stethoscope on the cuff pressure for the whole operation time. Patient body temperature might change during the ongoing operation, and patient position would be different for various types of surgeries. These factors combined with the esophageal stethoscope would not be easy to evaluate. Additionally, we believe that the esophageal stethoscope should increase the cuff pressure, in addition to these factors. Therefore, we decided to evaluate the effect of esophageal stethoscope insertion alone on cuff pressure, excluding other factors.
In conclusion, esophageal stethoscope insertion for body temperature monitoring during general anesthesia could cause an increase of cuff pressure, especially in female patients. Therefore, anesthesiologists should pay special attention to the effect of esophageal stethoscope insertion on cuff pressure and manage cuff pressure more meticulously.