The overall incidence of POST upon discharge from the PACU was 38.4% after the use of one of four types of SADs in patients undergoing elective tympanoplasty. When classified by severity, the incidence of mild POST was 33.3% and the incidence of moderate to severe POST was 5.1%. No patient developed dysphonia or dysphagia. Female sex, certain types of SAD, higher intracuff pressure in the cephalic neutral position, and longer duration of surgery were independent risk factors for developing POST.
Sore throat is a common complaint after surgery. It affects patient satisfaction and can influence activity after discharge. SADs offers an alternative to traditional tracheal intubation, with the potential benefit of reducing the risk of sore throat [5–7]. However, the overall incidence of POST after using an SAD can be as high as 42% [8]. Our 38.4% incidence of POST of any severity at discharge from the PACU is consistent with this previously reported percentage.
Various pre- and intraoperative factors influence the incidence of postoperative pharyngolaryngeal complications. Tracheal intubation, female sex, younger age, pre-existing lung disease, prolonged duration of anesthesia, and presence of a blood-stained tracheal tube on extubation are associated with the greatest risk in adults. Insertion technique, SAD choice, and intracuff pressure may contribute to the incidence of sore throat after anesthesia with an SAD [9]. Careful LMA insertion techniques are of paramount importance for preventing airway trauma and POST [6]. In our study, all SADs were inserted by experienced anesthesiologists using standard insertion techniques, and we found that risk factors for POST in the early postoperative period (at PACU discharge) were female sex, higher intracuff pressure in the cephalic neutral position, longer duration of surgery, and certain types of SAD.
Previous studies have shown that women have a higher risk of POST than men after use of a tracheal tube [10–12]. Likewise, Jaensson et al. reported a higher incidence of POST after LMA use in women than in men (26% vs. 6%) [13]. Our study confirms these findings. By contrast, Grady et al. [14] reported similar incidences of POST after LMA use between men and women. The lower incidence of POST in men may be explained by differences in pharyngeal anatomy between sexes [15]. The design of currently used SADs may be better suited to the anatomical features of the male pharynx rather than the female pharynx.
Overall, the incidence of POST differs minimally between first- and second-generation SADs, with the exception of a lower incidence with the i-gel, which may be attributed to the absence of an inflatable cuff [9, 16, 17]. In the current study, we found that both local brand SADs, the first-generation Tuoren FLMA and the second-generation Tuoren Esophageal Drainage LMA, contributed to POST. Compared to FLMA, both Tuoren devices were significant independent risk factors for POST. The Tuoren Esophageal Drainage LMA was also the strongest independent risk factor for moderate to severe POST, with an OR of 10.75 (95% CI, 4.82–23.99). These results may be at least partially explained by the composition of the SADs. The FLMA and Ambu AuraFlex LMA are both made of polyvinyl chloride (PVC), while the Tuoren SADs are composed of medical-grade silicone. Our findings suggest that silicone may cause more mucosal irritation than PVC. The Tuoren Esophageal Drainage LMA also has a relatively fixed and curved structure with an inflatable airway cuff, and as a second-generation SAD, it has two drain channels that emerge proximally as separate ports and enter a chamber beside the cuff bowl. It has a more strongly tapered leading tip than the other SADs used in our study, which may have caused more mucosal injury.
An increasing body of evidence has confirmed that high SAD intracuff pressures contribute significantly to laryngopharyngeal complications, including POST [8, 9, 16, 18], and adjustment of intracuff pressure reduces the incidence of moderate POST [8, 19, 20]. As SAD intracuff pressure increases, perfusion of the airway mucosa progressively decreases, resulting in postoperative pharyngolaryngeal complications [21]. Use of manometry can reduce pharyngolaryngeal complications by 70%, compared with routine care without manometry [4]. In our study, the mean cuff pressures in the cephalic neutral position were 27.23 cm H2O, 28.75 cm H2O, and 30.33 cm H2O in the no pain, mild sore throat, and moderate to severe sore throat groups, respectively. The differences between these pressures were statistically significant, suggesting that as intracuff pressure increases, the incidence of POST also increases. Multivariate analysis also identified higher intracuff pressure in the cephalic neutral position as a significant risk factor for POST, although it appeared to be a weak predictor (OR, 1.02; 95% CI, 1.00–1.04).
Grady et al. [14] reported that use of a large SAD was associated with a higher incidence of POST in both sexes. In their study, patients were randomized to receive either a large SAD (size 5 in males and size 4 in females) or a small SAD (size 4 in males and size 3 in females). Use of a large SAD was associated with a four-fold increased risk of developing sore throat on the first postoperative day, despite the measured SAD intracuff air pressure being higher in patients with a small LMA. In our study, we found no significant association between POST and SAD size, which is likely because all patients were managed with a small SAD (almost exclusively size 4 in males and size 3 in females). Furthermore, intracuff pressures were relatively low (< 35 cm H2O) and mechanical ventilation was used in our study, in contrast to the higher intracuff pressures (> 60 cm H2O) and use of spontaneous ventilation in the Grady et al study. Grady et al.[14] also reported that males with POST underwent longer procedures than men who did not develop POST. When considering all patients (males and females), the risk of developing POST increased by 33% (OR, 1.33; 95% CI, 1.03–1.71) for each 10-min increase in surgery duration. In the current study, we likewise identified longer surgery duration as a risk factor for POST.
Although pressure neuropraxia from the SAD cuff can result in dysphonia, SAD- related dysphonia is rare [22–24]. Seet et al. [4] reported dysphonia after use of an LMA in 4.1% of patients in their cuff pressure-limited group and 6.8% of patients receiving routine. Similarly, Kan et al. found no instances of dysphonia when LMA intracuff pressure was limited to 25 cm H2O [25], further supporting the suggestion that SAD intracuff pressures influence the occurrence of dysphonia. The low intracuff pressures in the present study may explain the lack of dysphonia.
This study has some weaknesses. First, since data were obtained from a single center, in which local brand (Tuoren) devices were used, the results may not be applicable to other regions. Second, the incidence of POST was assessed only at discharge from the PACU. POST may persist for 2 to 3 days and require additional attention from healthcare providers [26]. However, Seet et al. found that the incidence of POST was low (3.1%) in their pressure-limiting group at 24 hours postoperatively [4]. Third, we did not monitor intracuff pressures intraoperatively. Burgard et al. [15] found that LMA cuff pressures increased significantly during the first 60 minutes of anesthesia because of nitrous oxide diffusion into the cuff. In our study, we avoided nitrous oxide and used only an air/oxygen mixture. Vasanth Karthik et al. observed no change in intracuff pressures 1 hour after SAD insertion when using an air/oxygen mixture [27]. Furthermore, it has been suggested that use of intermittent positive pressure ventilation rather than intracuff pressure may be responsible for postoperative pharyngolaryngeal complications [28]. Further study regarding the association between different ventilation modes and POST is warranted.