Postoperative sore throat occurs with reported incidences of 21% and 74% and is an undesirable consequence of endotracheal intubation.1,2 Although minor, sore throat can adversely affect patient satisfaction and postoperative function.3
Although the mechanism of postoperative sore throat is incompletely understood, 1 cause is irritation and inflammation related to the presence of the endotracheal tube (ETT) within the trachea.4 This effect of the ETT is mediated by factors including the ETT size, intracuff pressure, and duration of intubation.5,6 Specifically, the area of cuff–trachea contact has been associated with postoperative sore throat and hoarseness. Currently, ETTs with high-volume and low-pressure cuffs are suggested to reduce ischemic complications as a result of high ETT cuff pressure, but the greater area of cuff–tracheal contact may cause postoperative sore throat.7,8
Because aspiration of upper airway secretions along the longitudinal folds of the ETT cuff is a major cause of intubation-related pneumonia,9 an ETT with a distally tapered cuff has been developed (Figure 1). Compared with a conventional ETT with a cylindrical-shaped cuff, an ETT with a tapered-shaped cuff may decrease postoperative sore throat and hoarseness because the cuff diameter and cuff–tracheal contact area are smaller.10 To test this hypothesis, we compared the incidence and severity of postoperative sore throat and the incidence of hoarseness after endotracheal intubation using ETTs with a cylindrical-shaped cuff or a tapered-shaped cuff.
This study was approved by our institutional ethics committee (No. 20141107/16-2014-132/121), and it was registered before patient enrollment in the Clinical Research Information Service (KCT0001329, date of registration: December 26, 2014). Written informed consent was obtained from all patients.
The study enrolled adult patients scheduled for elective surgery performed in the supine position requiring tracheal intubation. Patients were excluded if they had a known or predicted difficult airway; had diseases or anatomic abnormalities in the neck, larynx, or pharynx; were at risk of aspiration; or were scheduled for laparoscopic surgery. Patients with Cormack and Lehane grade 3 or 4 during direct laryngoscopy11 or who required postoperative mechanical ventilation were also excluded.
Patients were randomized into 2 groups: endotracheal intubation using a conventional ETT with cylindrical-shaped cuff (Mallinckrodt Hi-Lo; Covidien, Athlone, Ireland; Group C) or an ETT with a taper-shaped cuff (TaperGuard; Covidien; Group T) using a computer-generated randomization program with a block size of 4 and an allocation ratio of 1:1. The randomization sequence was concealed in sequentially numbered, opaque, sealed envelopes and determined by an investigator with no clinical involvement in the study. As a result of the nature of the study, only patients were blinded to the group assignments. The characteristics of the ETT cuffs used in this study are shown in Figure 1 and Supplemental Digital Content, Appendix 1, http://links.lww.com/AA/B675.
No preanesthetic medication was given to the patients. Standard monitoring consisted of electrocardiography, noninvasive arterial pressure, pulse oximetry, and gas analyzer. Propofol at 1.5 mg/kg and 1.5−2.0 μg/kg fentanyl were administered for induction, and 0.6 mg/kg rocuronium was given to establish neuromuscular blockade. Direct laryngoscopy was performed with a curved blade (in men; a Macintosh blade #4, in women; a Macintosh blade #3). Endotracheal intubation was performed by 2 experienced board-certified anesthesiologists performed using unlubricated ETTs with an internal diameter of 7.5 mm for men and 7.0 mm for women. An ETT stylet was not used. Tracheal intubation was confirmed by capnography, and intracuff pressure was maintained at 25 cm H2O using a handheld aneroid manometer (VBM Medizintechnik, Sulz am Neckar, Germany) with monitoring and adjustment every 30 minutes. Anesthesia was maintained with 2–4 vol.% sevoflurane in an oxygen–medical air mixture. If required, fentanyl and rocuronium were administered intermittently. Volume-controlled ventilation with a tidal volume of 8 mL/kg predicted body weight and an adequate respiratory rate to maintain normocapnia was used in all patients.
Residual neuromuscular block was reversed with pyridostigmine and glycopyrrolate. When patients were fully recovered and able to obey commands, the trachea was extubated after gentle suctioning of oropharyngeal secretions. If requested, patients received an intravenous patient-controlled analgesia device at the end of the surgery.
The Cormack and Lehane grade, number of intubation attempts, and time to achieve intubation were recorded during tracheal intubation. The duration of tracheal intubation and fentanyl administration were also recorded.
Postoperative sore throat and hoarseness were evaluated at 1, 6, and 24 hours after surgery by observers blinded to the group assignments. A 0- to 100-mm visual analog scale was used to evaluate the severity of sore throat (0, no pain; 100, worst pain imaginable). Hoarseness was defined as a voice quality change as perceived by the patient compared with the preoperative state. If patients felt a voice quality change, the presence of hoarseness was recorded as “yes.” The overall postoperative sore throat or hoarseness cases included patients who reported any degree of sore throat or hoarseness over the 24-hour evaluation period (at 1, 6, and 24 hours after surgery). Patient-controlled analgesia drug consumption and medications given for postoperative analgesia within 24 hours after surgery were recorded.
The primary outcome of this study was the overall cumulative incidence of postoperative sore throat in the 24-hour evaluation period in the 2 groups. Secondary outcomes included the incidence and severity of sore throat at 1, 6, and 24 hours after surgery, the overall cumulative incidence of postoperative hoarseness, and the incidence of hoarseness at 1, 6, and 24 hours after surgery.
SPSS version 20 for Windows (IBM, Armonk, NY) was used for the statistical analyses. The normality of data was tested using Shapiro–Wilk test. Data are expressed as numbers (%) or means (standard deviation). Data analyses were conducted on a modified intention-to-treat basis. The modified intention-to-treat population included patients who had at least 1 assessment of postoperative sore throat and hoarseness. Differences in the time to achieve tracheal intubation and duration of intubation were compared between the 2 groups using the Mann-Whitney U test. Difference in the overall cumulative incidence of postoperative sore throat between the 2 groups, the primary outcome, was tested using the χ2 test. In the secondary analyses, differences in the overall cumulative incidence of postoperative hoarseness between the groups were compared using the χ2 test. In addition, differences in the incidence of sore throat and hoarseness at 1, 6, and 24 hours after surgery between the groups were tested using the χ2 test. Relative risks with intervals estimates were determined for between-group differences in the incidences of postoperative sore throat and hoarseness. The confidence intervals for the incidence of postoperative sore throat and hoarseness at individual times were adjusted for multiple comparisons by Bonferroni correction. Based on our clinical concern, between-group differences of the sore throat severity at each time point were compared using the Mann-Whitney U test. The Bonferroni correction was used to adjust for the multiple comparisons of outcomes (individual incidence and severity of postoperative sore throat and the incidence of hoarseness at each time point) by multiplying the unadjusted P value by the number of comparisons (ie, 3), and Bonferroni-adjusted P value was denoted by “corrected P.” P< .05 and the corrected P < .05 were considered statistically significant.
Based on a reported incidence of postoperative sore throat with a cylindrical-shaped cuff tube of 40%,12 and assuming a clinically significant reduction in postoperative sore throat of 20%, 91 patients per group were required with α = .05 and β = .20. To compensate for possible dropouts, 100 patients were enrolled per group.
The study recruited 215 patients between January and November 2015. Of these, 15 patients were excluded because they were not eligible. Two hundred patients were then randomized into the 2 groups. Two patients in each group were then excluded because of Cormack and Lehane grade 4 on direct laryngoscopy, and 3 patients in Group C and 2 patients in Group T were excluded as a result of the requirement for postoperative mechanical ventilation. The remaining 191 patients were then included in the modified intention-to-treat population (Figure 2).
Patient characteristics, postoperative analgesia method, fentanyl consumption, and type of surgery are shown in Table 1. No patient received dexamethasone during the perioperative period. The Cormack and Lehane grade, number of intubation attempts, time to achieve endotracheal intubation, and duration of intubation were similar in the 2 groups (Table 2).
The incidence of postoperative sore throat and hoarseness is presented in Table 3. The overall cumulative incidence of postoperative sore throat was lower in Group T than in Group C (32% vs 54%, respectively; relative risk = 0.60, 95% confidence interval: 0.43–0.85; P = .003). Forty-three patients in Group C reported sore throat at 1 hour, and 5 of 43 did not have sore throat at 6 hours. Eight patients in that group newly reported sore throat at 6 hours after surgery. No patients in Group C reported a new sore throat at 24 hours. In Group T, no patients reported a new sore throat at 6 or 24 hours after surgery. The incidence of postoperative sore throat was lower in Group T compared with Group C at 6 hours (corrected P= .006), but not at 1 and 24 hours after surgery. The severity of sore throat was lower in Group T compared with Group C at 6 hours after surgery (corrected P= .003; Figure 3).
Postoperative hoarseness also occurred less frequently in Group T compared with Group C (19% vs 37%, respectively; P= .006). In the assessment of hoarseness, 33 in Group C and 16 patients in Group T reported hoarseness at 1 hour, but 7 in Group C and 8 patients in Group T reported no hoarseness at 6 hours. Instead, 2 patients in each group newly reported hoarseness at 6 hours after surgery. Group T had a lower incidence of hoarseness at 1 and 6 hours after surgery than in Group C (corrected P< .05), but the incidence of hoarseness at 24 hours after surgery was not different between the 2 groups.
We found that the use of an ETT with a tapered-shaped cuff reduced the overall incidence of postoperative sore throat in the 24-hour evaluation period after surgery compared with use of ETT with a cylindrical-shaped cuff. The group with tapered-shaped cuff tubes had a lower incidence and lesser severity of sore throat at 6 hours. The overall incidence of postoperative hoarseness was also lower in the group with tapered-shaped cuff tubes compared with that with cylindrical-shaped cuff tubes. The group with tapered-shaped cuff tubes also had a lower incidence of hoarseness at 1 and 6 hours after surgery than the group with cylindrical-shaped cuff tubes.
We found that 54% of patients intubated with cylindrical-shaped cuff tubes had postoperative sore throat, which is consistent with that of previous studies.13–15 Higgins et al13 reported that 45% of patients experienced a postoperative sore throat after endotracheal intubation after 24 hours postoperatively. Furthermore, a 2007 study found that 56% of patients intubated with a tracheal tube with a cylindrical-shaped cuff had a postoperative sore throat during the first 24 hours postoperatively.14 In a 2012 study of magnesium lozenges,15 57% of patients reported a sore throat at 2 hours after surgery.
In the present study, the overall incidences of postoperative sore throat and hoarseness were reduced with the use of tapered-shaped cuffs compared with cylindrical-shaped cuffs. This finding may be related to the cuff–trachea contact area. Loeser and colleagues evaluated the effect of ETTs with different cuff designs on postoperative sore throat and found that high-volume cuffs also resulted in a higher incidence of sore throat as a result of the greater area of cuff–trachea contact.7 They explained that high-volume and low-pressure cuffs caused a greater area of tracheal mucosal injury, but that injury was more superficial than that from high-pressure cuffs. Consequently, they recommended that the cuff folds within the trachea and the cuff–tracheal contact area should be minimized.7,8,16 Tapered-shaped ETT cuffs were originally introduced to reduce fluid leakage across the cuff. Inflation of such tapered cuffs creates a sealing zone in which the outer cuff diameter corresponds to the internal tracheal diameter (Figure 1).10 The sealing zone and the lower part of the cuff do not fold within the trachea, thus limiting the cuff–tracheal contact area to the sealing zone and the upper part of the cuff. As shown in Supplemental Digital Content, Appendix 1, http://links.lww.com/AA/B675, the diameters of tapered cuffs are also smaller than those of cylindrical cuffs. Thus, the use of ETTs with tapered-shaped cuffs results in a smaller cuff–trachea contact area, potentially affecting postoperative sore throat and hoarseness.
Various strategies have been suggested to reduce postoperative sore throat and hoarseness resulting from endotracheal intubation. Intraoperative monitoring and adjustment of intracuff pressure can reduce postoperative sore throat after endotracheal intubation.6 Use of a smaller sized ETT has also been proposed.5 When nitrous oxide is used in anesthesia, inflation of the ETT cuff with saline17 or nitrous oxide18 reduced the incidence of sore throat. Various pharmacologic strategies such as IV dexamethasone,14 topical benzydamine hydrochloride,12 ketamine gargle,2 and oral magnesium lozenges15 have also been tested. However, the adverse effects of some pharmacologic interventions limit their use. In our study, the use of an ETT with a tapered-shaped cuff is an effective method to reduce postoperative sore throat and hoarseness compared with the use of an ETT with a cylindrical-shaped cuff.
We did not include patients undergoing laparoscopic surgery or cases in which surgery was performed with the patient in a nonsupine position because the intracuff pressure changes with the patient’s position and the use of laparoscopy.19 Two 2015 studies found that the tapered-shaped cuff induced a smaller change in intracuff pressure during laparoscopic surgery and may preserve tracheal mucosal perfusion better than the cylindrical-shaped cuff.20,21 Another recent study observed that the intracuff pressure is higher in the tapered-shaped cuff versus the cylindrical-shaped cuff after a change from supine to lateral position.22 In these studies, airway complications including postoperative sore throat and hoarseness were unchanged. However, the authors noted that these studies were not powered to detect a difference in postoperative airway complications. Overall, existing literature suggests that close monitoring of the intracuff pressure and gentle ETT management can affect sore throat incidence. Further study about the effect of cuff shape on postoperative sore throat and hoarseness in patients undergoing laparoscopic surgery or requiring positional changes is needed.
This study had several limitations. First, the investigators that performed endotracheal intubation were not blinded to the group assignment and followed a detailed standardized protocol. However, the investigators who recorded the incidence and severity of postoperative sore throat and hoarseness were blinded to group allocation. Second, we did not evaluate tracheal mucosal injury by direct visualization, instead evaluating postoperative sore throat and hoarseness using the patients’ subjective assessment of voice quality change and visual analog scale. This subjectivity may have introduced variability and bias. However, to minimize these effects, the investigators provided a detailed explanation about the evaluation protocol for postoperative sore throat and hoarseness to patients during the preoperative visit and assessed them according to a standardized protocol. Third, patients with a known or predicted difficult airway were excluded from the study. Our results cannot thus be generalized to patients with difficult airways. Fourth, coughing or bucking events that might have caused injury and irritation during emergence and extubation were not evaluated. Although it is possible that 1 group had more such events, the same extubation protocol was applied in all patients. Finally, patients were only followed up for 24 hours. Although the incidence and severity of sore throat and the incidence of hoarseness tend to decrease over the 24-hour evaluation period after surgery, further study evaluating postoperative sore throat and hoarseness during the long-term period is needed.
In conclusion, the use of an ETT with a tapered-shaped cuff reduced the overall incidence of postoperative sore throat in the 24-hour evaluation period after surgery compared with the use of ETT with a cylindrical-shaped cuff. At each observation time point, the incidence and severity of postoperative sore throat were significantly lower at 6 hours after surgery. The overall incidence of postoperative hoarseness was also lower in the group with tapered-shaped cuff tubes compared with that with cylindrical-shaped cuff tubes, and postoperative hoarseness occurred less frequently at 1 and 6 hours after surgery with the use of a tapered-shaped cuff.
The authors thank Sohee Oh, PhD, Department of Biostatistics in Seoul Metropolitan Government, Seoul National University Boramae Medical Center, for statistical advice.
Name: Jee-Eun Chang, MD.
Contribution: This author helped design the study, conduct the study, and analyze the data.
Name: Hyerim Kim, MD.
Contribution: This author helped design the study and analyze the data.
Name: Sung-Hee Han, MD, PhD.
Contribution: This author helped design the study, conduct the study, and analyze the data.
Name: Jung-Man Lee, MD, PhD.
Contribution: This author helped conduct the study, analyze the data, and write the manuscript.
Name: Sanghwan Ji, MD.
Contribution: This author helped conduct the study and analyze the data.
Name: Jin-Young Hwang, MD, PhD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
This manuscript was handled by: Avery Tung, MD, FCCM.
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