Endotracheal intubation with cuffed tubes is a standard technique for securing airway during general anesthesia. The cuff of endotracheal tube (ETT) creates seal between the tracheal wall and the tube, thereby preventing air leakage and reducing the likelihood of aspiration during mechanical ventilation. However, the continuous pressure exerted by inflated cuff on tracheal mucosa leads to some degree of mucosal ischemia and postoperative sore throat (POST) and cough. Although nowadays we are using high-volume low-pressure cuffs unlike previous ones with low-volume high-pressure cuffs of red rubber tubes, inflation of the cuff stimulates the stretch receptors in the tracheal mucosa that leads to uncontrollable cough during extubation and in the postoperative period. If the lateral pressure exerted by an inflated cuff on tracheal mucosa exceeds capillary perfusion pressure (≥30 cm H2O), it may lead to loss of mucosal cilia, ulceration, hemorrhage, and tracheal stenosis. Moreover, anesthetic gases including nitrous oxide and air are known to diffuse into an already inflated cuff of ETT, thereby increasing the cuff pressure intraoperatively and leading to postoperative laryngotracheal morbidity. As a result, the patients may complain of sore throat, hoarseness, and dysphagia in the postoperative period.
Coughing during emergence as well as in the postanesthesia care unit is not only distressing to the patient but it can also lead to potentially dangerous complications such as hypertension, cardiac arrhythmias, myocardial ischemia, and raised intracranial pressure, which may be detrimental for patients with cardiac or intracranial pathologies, respectively. The recommended techniques of preventing cough response at the time of extubating are intravenous (i.v.) administration of preservative free local anesthetics or opioids, extubating in a deep plane of anesthesia, i.v. injection of dexamethasone, etc. However, each technique has its own limitations.
Routinely, air is used for inflating the cuff of ETT and nitrous oxide can diffuse into the air interface of the cuff, resulting in an increase in pressure inside the cuff. Various media such as anesthetic gases, saline, xylocaine, alkalinized xylocaine, and ketamine have been used to inflate the cuff to prevent POST, cough, dysphagia, dysphonia, etc. We have not found any study using propofol for inflating the cuff. Hence, we hypothesized that filling the ETT cuff with propofol could minimize this diffusion besides providing the cushioning effect. The primary objective of this study was to compare post extubation cough response and postoperative laryngotracheal morbidity in terms of sore throat, hoarseness of voice, and dysphagia following inflation of cuff with air, 1% propofol, 4% xylocaine, and 0.9% saline. The secondary objective was to compare the intraoperative hemodynamic parameters.
This was a prospective, randomized, double-blind comparative study conducted at Mahatma Gandhi Hospital, a tertiary care centre over a period of 6 months (July 2021–January 2022). After getting clearance from the Institute Ethics Committee, IRB number: ECR/125/Inst/RJ/2023/RR-19 and the study was prospectively registered with clinical trial registry – India (CTRI/2021/06/03423). Written informed consent was obtained from each patient prior to enrolment in the study and use of the patient data for research and educational purposes. The procedures followed the guidelines laid down in the Declaration of Helsinki. The patients were randomly divided into four groups of thirty each using computer-generated randomization tables. Group A: 4–6 mL of air, Group S: 4–6 mL of 0.9% saline, Group L: 4–6 mL of 2% lignocaine, and Group P: 4–6 mL of 1% propofol were used to inflate the cuff. The anesthesia consultant carried out laryngoscopy and intubation, as well as inflated the cuff as per the group. The postoperative ward nurse evaluated cough, sore throat, and dysphagia. Both the patient and the nurse were blinded to the study.
The inclusion criteria were age 18–60 years, either gender, American Society of Anesthesiologists (ASA) physical status Classes I and II, Mallampati class I and II, scheduled for surgeries of duration 90–120 min, performed under general anesthesia, and in supine position. Those not consenting to study and having laryngotracheal disease/surgery, chronic cough, asthma, cognitive disorders, ear nose throat diseases, ASA Classes III and IV, body mass index >30 kg.m−2, anticipated difficult airway, raised intracranial or intraocular pressures, requiring nasogastric tube insertion, and prone position were not included in the study. Similarly, those requiring multiple attempts at intubation were also excluded. There was no drop out in this study. The i.v. line was secured in peripheral vein and injection ringer lactate was started. Patients were continuously monitored for arterial oxygen saturation, electrocardiogram, noninvasive blood pressure, and end-tidal carbon dioxide concentration using the multiparameter monitor. Patients were preoxygenated for 3 min with 100% oxygen. Induction sequence included i.v. administration of fentanyl 2 ug.kg−1, midazolam 1 mg, and propofol 2 mg.kg−1. Injection vecuronium bromide 0.1 mg.kg−1 i.v. was administered to ease endotracheal intubation. ETT of appropriate size was inserted, preferably 7 mm–7.5 mm internal diameter for female patients and 8 mm–8.5 mm internal diameter for male patients. We used high-volume low-pressure cuffed ETT of standard sizes of similar make (Portex® Blue line™) and the pilot balloon was connected to pressure transducer throughout the procedure to detect any inadvertent leak. The ETTs were prechecked for any leaks. Each ETT was checked in a liquid media for leakage before and after procedure. Anesthesia was maintained with nitrous: oxygen 60:40% and isoflurane dial concentration around 1% to maintain bispectral index (BIS) around 40–60. Vecuronium bromide 0.06 mg.kg−1 was administered as i.v. bolus to maintain train of four (TOF) count of 1 or less.
After intubation, the cuff was inflated with air or liquid media as per the groups mentioned above. In Group A, pressure was adjusted at ≈ 20 mmHg using an aneroid manometer: Mallinckrodt® hand-held pressure manometer. Similarly, the cuff pressure measurement for liquid media was done with a pressure transducer via PHILIPS® Intellivue MX550 monitor. It was connected to the pilot balloon of ETT. After inflating the cuff, an audible leak was checked around the tube with positive pressure administered at ≈ 20 mmHg. Intracuff pressure was continuously monitored and was maintained constant throughout the surgery.
At the end of the surgery, the residual neuromuscular blockade was reversed with i.v. neostigmine 0.05 mg.kg−1 and glycopyrrolate 0.01 mg.kg−1 when TOF count was 3 or greater. Oral suctioning was done gently, under vision by experienced anesthetist to avoid trauma. At the time of extubation, hemodynamic monitoring was done at 1, 2, 5, and 10 min immediately postextubation and patients were assessed for incidence and severity of cough at the time of emergence. Airway morbidity measurement was done by the parameters of cough, sore throat, dysphagia, and hoarseness of voice. The cough was recorded at 15 min, 30 min, and 60 min after extubation. The sore throat was recorded at 2, 6, and 24 h after extubation. It was graded as 0 = no sore throat, 1 = mild (scratch throat), 2 = moderate (similar to that noted with cold), and 3 = severe (more severe than cold). Dysphagia was noted at 24 h after extubating and graded as 0 = no dysphagia, 1 = mild (pain on swallowing solids), 2 = moderate (pain on swallowing liquids), and 3 = severe (pain on swallowing saliva). Hoarseness of voice was noted at 24 h after extubating and graded as Grade 0 = (none) no hoarseness of voice, Grade 1 = (mild) noted by the patient, Grade 2 = (moderate) obvious to observer, and Grade 3 = (severe), patient not able to speak.
Sample size was calculated assuming an error of 0.05, power of 80%, and confidence interval of 95%. Thus, a total of 120 patients were obtained. We assessed 120 patients with 30 in each of the four groups to minimize error and increase the accuracy of results.
All the parameters were recorded in the study Proforma and analyzed using Microsoft Excel 2007 analysis tool. Quantitative data were recorded, mean ± standard deviation calculated. Further, Student's t-test was applied and P value was calculated. Analysis of variance test was applied for intergroup comparison. Qualitative data were recorded as number of patients and analyzed using Chi-square test.
P < 0.05 was considered statistically significant and P < 0.01 as statistically highly significant.
One hundred and twenty patients aged 18–65 years (median age 43 years) were studied. The demographic characteristics were comparable in all four groups [Table 1]. The incidence of cough after extubation was greatest in Group A and least in Group P. This difference attained statistical significance till 15 min after extubation [Table 2]. The occurrence of sore throat without and with swallowing at 2 h postoperatively was highest in Group A, followed by Group S and Group L, and least in Group P. Similar trend was observed until 24 h postoperatively [Table 3]. Dysphagia or hoarseness of voice was not witnessed in any of the study groups. In order to maintain constant cuff pressure, the cuff had to be deflated more times in the air group as compared to liquid media groups and minimum in propofol group. There was no incidence of leak around the cuff, rupture or blood staining of the cuff.
Basal hemodynamic parameters were comparable in all the four groups [Figures 1-3].
Different cuff filling methods have been suggested such as saline, lignocaine, sodium bicarbonate, ketamine, alkalinized lignocaine, and hydrocortisone. We hypothesized that the use of liquid media such as propofol may reduce the incidence of cough, sore throat, and dysphagia in the postoperative period as well as may lead to stable hemodynamic parameters in the intraoperative period. Hence, we used cuff inflation with air as the control group and compared various liquid media in terms of prevention of laryngotracheal morbidity.
The capillary perfusion pressures of tracheal mucosa range from 22 to 32 mmHg. The tracheal mucosal blood flow may be compromised when lateral wall pressures exceed 30 cm H2O (30 cm H2O = 22.06 mmHg). In our study, we constantly maintained the cuff pressure in normal range of 20 mmHg resulting in no hoarseness of voice or dysphagia postoperatively in any of the study groups. We observed that the incidence of cough was significantly lower in propofol group as compared to lignocaine and saline and was maximum in the air group. This finding may be attributed to propofol being viscous media, does not diffuse through the semipermeable membrane of polyvinyl chloride cuff, and also provides a cushion effect on tracheal mucosa. Fagan et al. observed that inflating the cuff with 4% lignocaine reduced the incidence of post-extubation coughing compared to air or saline. They also observed that there was a progressive rise in cuff pressures in the air group, thereby suggesting that nitrous oxide diffuses into air but not in liquid media. Another group of researchers was also of the opinion that with the use of air as cuff inflation medium, coughing is a common occurrence during emergence from general anesthesia and the overall incidence is 40%–96%. This is in accordance with our study. We searched the literature but could not obtain studies regarding propofol, thus making our study unique.
A few case reports have demonstrated inadvertent cuff rupture after 4 h intraoperatively due to N2O diffusion in the endotracheal cuff inflated with gaseous media chiefly room air. This phenomenon does not occur when inflating endotracheal cuff with liquid media as gas gets dissolved in it without exerting any significant pressure on the endotracheal cuff. In another case reported by Kim et al., 55 patients were enrolled and scheduled for lumbar spine surgery. Neutral angle, which was the angle on the mandibular angle between the neck midline and mandibular inferior border, was measured. They reported that the position change from supine to prone without head movement can cause a change in ETT cuff pressure. We have searched the literature and found a case report on ETT cuff rupture during nasal intubation and was thought to be due to spur and/or in facial trauma patients. Our study included cases requiring oral intubation and those requiring nasal intubation were excluded from the study.
Despite so much advancement in anesthesia techniques, sore throat is one of the most common complications in the postoperative period and is distressing to the patient. The overall incidence was around 20%–74%. It can activate the mechanical and chemical receptors of the respiratory tract and trigger Bötzinger ventral respiratory group in the medulla, leading to coughing. This is also very evident in our study that the majority of patients who coughed postextubation had complained of sore throat in the immediate postextubation period. In another study, comparing cuff inflation with air versus plain lignocaine and alkalinized lignocaine, it was observed that cuff pressure gradually increased in the air group. They concluded that this increase contributed to POST as well as mucosal injuries. Similarly, we also observed that the incidence of POST and cough was more in air group as compared to other groups. Furthermore, when comparing among the liquid media groups, it was minimum in the propofol group than the xylocaine and saline group. This may be due to different cushioning effect of various liquid media with maximum effect of propofol since it is a suspension media. Regarding evaluation time, several publications have described that POST is worse in the early postoperative period up to 6 h and then decreases over time. Hence, we measured it at 2, 6, and 24 h after extubation.
Besides cuff pressure and inflating medium, other factors which affect POST and cough are age, gender, duration of surgery, patient position, laparoscopic surgeries, depth of anesthesia, etc. Hence, we excluded such surgeries and patient position to minimize confounding factors. We maintained adequate depth of anesthesia as per BIS monitoring. Other variables were statistically comparable.
Since the size and quality of cuff may be a confounding variable, we used high-volume low-pressure cuffed tubes of standard sizes of similar make (Portex® Blue Line™).
The hemodynamic parameters and oxygen saturation were comparable in all the four groups. This may be because we maintained constant cuff pressure and adequate depth of anesthesia as monitored with BIS as well as adequate muscle relaxation under the continuous monitoring by peripheral nerve stimulator. This is in accordance with observations made by other researchers.
The limitation of the study was the failure to assess the tracheal mucosal capillary perfusion pressures and the rate of diffusion of nitrous oxide inside the cuff of ETT.
The present research concluded that inflation of ETT cuff with liquid media reduces the incidence of POST as compared to air. Of the liquid media, emulsion agent such as 1% propofol is better than 4% lignocaine and 0.9% saline.
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Conflicts of interest
There are no conflicts of interest.
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