Effect of Continuous Cuff Pressure Regulator in General Anaesthesia with Laryngeal Mask Airway

The Journal of International Medical Research 2011; 39: 1900 1907 Effect of Continuous Cuff Pressure Regulator in General Anaesthesia with Laryngeal Mask Airway Y-S JEON, J-W CHOI, H-S JUNG, Y-S KIM, D-W KIM, J-H KIM AND J-A LEE Department of Anaesthesiology and Pain Medicine, Saint Vincent Hospital, The Catholic University of Korea, Suwon, Kyeonggi-Do, Republic of Korea Postoperative pharyngolaryngeal complications (PPLC) occur during anaesthesia due to increased cuff pressure following the insertion of laryngeal mask airways. The use of a pressure regulator to prevent PPLC was evaluated in a prospective, randomized study. Sixty patients scheduled to receive general anaesthesia were randomly assigned to two equal groups of 30, either with or without the regulator. The just seal cuff pressure (JSCP), cuff pressure at 5-min intervals during anaesthesia, incidence of pharyngeal sore throat (PST), dysphagia, dysphonia and other complications were evaluated at 1 and 24 h postoperatively. The combined mean ± SD JSCP of both groups was 20.3 ± 3.2 mmhg. In the group with the regulator, cuff pressure was maintained at a constant level during anaesthesia. This study demonstrated that the regulator is a simple, functional device that can reduce the incidence of PST significantly at 1 h postoperatively, following general anaesthesia. KEY WORDS: PHARYNGOLARYNGEAL COMPLICATION; CUFF PRESSURE; CUFF VOLUME; ANAESTHESIA; REGULATOR Introduction The insertion of a laryngeal mask airway (LMA) to induce inhalation anaesthesia commonly causes a number of postoperative pharyngolaryngeal complications (PPLC). Cuff inflation with air and use of nitrous oxide as an inhalation agent during anaesthesia is one of the main causes of PPLC. Diffusion of nitrous oxide into the cuff increases the cuff volume and pressure and reduces oral mucosal perfusion. Finally, it can cause postoperative sore throat, dysphagia, dysphonia and, in rare cases, nerve injury. 1 To prevent PPLC, the manufacturer recommends that cuff pressure should be checked periodically, with the cuff volume withdrawn intermittently to maintain 44 mmhg or the minimal just seal cuff pressure (JSCP) during general anaesthesia. 2 Nevertheless, clinicians tend to inflate the cuff with maximal volume and do not use a cuff manometer in the clinical situation. Another difficulty is that the volume required to maintain JSCP in even the same patient may vary depending on the size of the LMA used, due to the relative size difference between the hypopharynx and LMA. A cuff volume change of just 1 2 ml, or simply touching the inflation indicator balloon, can make a considerable difference in cuff 1900

pressure. 2 Thus, there is need for a mechanism to maintain constant cuff pressure during anaesthesia. If the JSCP is set up based on the recoil characteristics of a syringe and is maintained during anaesthesia, PPLC may be effectively reduced. The present study aimed to measure JSCP following the insertion of LMA in patients undergoing general anaesthesia. In addition, the use of a simple pressure regulator designed to maintain the minimal JSCP in order to reduce PPLC in patients was evaluated. Patients and methods PATIENTS Patients were recruited from Saint Vincent Hospital, The Catholic University of Korea, Suwon, Republic of Korea, between January and April 2010. Inclusion criteria for the patients undergoing anaesthesia were American Society of Anesthesiologists physical classification status I or II and age between 18 and 80 years old. Patients were excluded if they were undergoing head and neck surgery or had positional change of the trunk, oral cavity problems or chronic obstructive pulmonary disease. Patients were randomly assigned to one of two groups, by opening a sealed envelope: group 1 underwent anaesthesia without a cuff pressure regulator; and group 2 underwent anaesthesia with a cuff pressure regulator following insertion of the LMA. This study was carried out following approval of the Saint Vincent Institutional Review Board, The Catholic University of Korea. Written informed consent for the study was obtained from all patients scheduled to receive general anaesthesia for 1 2 h. PROCEDURE FOR ANAESTHESIA Anaesthesia was induced with 2 mg/kg propofol and muscle relaxation was achieved with 0.6 mg/kg rocuronium intravenously (i.v.). The LMA (LMA Classic, LMA North America Inc., San Diego, CA, USA) sizes used were: size 3 (> 50 kg) or size 4 ( 50 kg) for women; size 4 (> 70 kg) or size 5 ( 70 kg) for men. Cuff pressure was deflated to 45 mmhg before insertion and the cuff was again inflated with 10 ml air before LMA insertion. LMA insertion was performed using the indexfinger insertion technique by an experienced anaesthesiologist. Patients who underwent three or more attempts for LMA insertion were excluded. After LMA insertion, the cuff was inflated with an additional 10 ml of air via a three-way stopcock (labelled i in Fig. 1) using a 20-ml plastic syringe. After achieving adequate cuff inflation, redundant air within the cuff was withdrawn through the syringe. This manipulation was performed three times at 1-min intervals and the mean pressure was recorded as the initial cuff pressure (0 min), termed the JSCP. The cuff volume in this state was termed the just seal cuff volume, namely the preinsertional air volume (10 ml) plus the additional air volume. The adequacy of LMA insertion was evaluated by the Keller method using a fibrescope (score 1, vocal cords not seen; score 2, vocal cords plus anterior epiglottis; score 3, vocal cords plus posterior epiglottis; score 4, only vocal cords seen). 3 Gas leakage was confirmed by the detection of audible noises in the mouth by use of a stethoscope. The end tidal carbon dioxide concentration and tidal volume were confirmed for adequate ventilation. Patients were mechanically ventilated with a tidal volume of 8 ml/kg and a respiratory rate of 10 12 breaths/min. Maximum inspiratory pressure was maintained < 20 cmh 2 O (14.7 mmhg). Anaesthesia was maintained with nitrous oxide (60%) and oxygen (40%), and sevoflurane (1 2 1901

Weight Regulator Pressure transducer Three-way stopcock (ii) Three-way stopcock (i) Laryngeal mask airway FIGURE 1: The cuff pressure regulator used in the present study to control and maintain cuff pressure during anaesthesia. The three-way stopcock (i) was used for cuff inflation with an additional 10 ml of air from a 20-ml plastic syringe after laryngeal mask airway insertion. After achieving adequate cuff inflation, redundant air within the cuff was withdrawn through the syringe. The three-way stopcock (ii) was for installation of a cuff pressure regulator between the cuff pressure monitoring kit and the cuff inflation site so as to be able to evacuate excessive cuff pressure in those patients randomized to anaesthesia with the regulator (group 2). The weight provided the counterforce required to maintain constant cuff pressure vol.%) or desflurane (4 6 vol.%). CUFF PRESSURE EVALUATION Cuff pressure was evaluated at 5-min intervals in both groups using a pressure monitoring kit (TranStar Single Pressure Monitoring Kit; Smiths Medical ASD, Dublin, OH, USA). A simple pressure regulator consisting of a 10-ml glass syringe with weights (between 27 and 38 g) was attached to the syringe plunger. The regulator was installed using a three-way stopcock between the pressure monitoring kit and the cuff inflation site (labelled ii in Fig. 1) to evaluate the change of cuff pressure in group 2; increased regulator volume was only evaluated in group 2. When patients recovered spontaneous respiration and were responsive to verbal commands, the cuff was deflated to 45 mmhg and the withdrawn cuff volume was recorded as the final cuff volume. Increased LMA volume was calculated as the final cuff volume minus the just seal cuff volume. The presence of blood on the LMA was checked after its removal. Both groups received fentanyl 50 µg i.v. 30 min before the end of the operation and i.v. patientcontrolled analgesia was maintained by fentanyl 600 µg and ketorolac 120 mg. Intraoperative gas insufflations, aspiration and laryngospasm were checked. EVALUATION OF PPLC The incidence of pharyngeal sore throat (PST), dysphagia, dysphonia, nausea and 1902

coughing were evaluated at 1 and 24 h postoperatively by nurses blinded to the group allocation. PST was measured as follows: 0, no complaint; 1, throat discomfort; 2, continuous throat pain. STATISTICAL ANALYSES Based on a PPLC incidence of 42% associated with a high cuff pressure, 4 a power of 80% and an α error of 0.05, it was calculated that 30 patients were required in each group to detect a 30% decrease in the incidence of PPLC. Parametric variables are expressed as mean ± SD. All statistical analyses were carried out using SPSS software, version 12.0 (SPSS Inc., Chicago, IL, USA) for Windows. Cuff pressure and cuff volume were analysed using a two-tailed Student s t- test. The χ 2 -test was used to analyse the incidence of PPLC. A P-value < 0.05 was considered to be statistically significant. Results The study included 60 patients who were randomly assigned into group 1 (n = 30) or group 2 (n = 30). Demographic data and patients characteristics are shown in Table 1 and demonstrated no significant differences between the two groups. Intraoperative LMA cuff volume and pressure are shown in Table 2. The combined mean ± SD JSCP of both groups was 20.3 ± 3.2 mmhg (range 16 26 mmhg) and the combined mean ± SD cuff volume of both groups was 14.0 ± 2.9 ml (range 10 18 ml). Gastric insufflations, gas leakage or laryngospasm were not observed in either group. Cuff pressure was maintained at a significantly lower level in group 2 than in group 1 for the duration of anaesthesia (P < 0.05) (Fig. 2). The incidences of PST, dysphonia, and dysphagia at 1 and 24 h postoperatively are shown in Table 3. The incidence of PST at 1 h TABLE 1: Demographic and clinical characteristics of the patients randomized to receive anaesthesia with or without a cuff pressure regulator Without regulator With regulator Characteristics (group 1; n = 30) (group 2; n = 30) Age, years 51.1 ± 14.4 51.0 ± 15.3 Sex, male/female 4/26 6/24 Weight, kg 59.3 ± 9.6 61.2 ± 9.3 Height, cm 157.5 ± 7.2 159.3 ± 8.9 Type of operation Gynaecological 14 11 Orthopaedic 11 13 General surgery 5 6 Duration of anaesthesia, min 87.3 ± 33.2 90.7 ± 19.5 Mallampati classification, 1/2 25/5 26/4 LMA size, 3/4/5 2/26/2 2/24/4 Number of intubations, 1/2 25/5 25/5 Fibrescopic classification, 3/4 a 5/25 5/25 LMA blood stained 2 2 Data presented as mean ± SD or number of patients. a Fibrescopic classifications were evaluated as follows: score 1, cords not seen; score 2, cords plus anterior epiglottis; score 3, cords plus posterior epiglottis; score 4, only vocal cord. No statistically significant between-group differences (P > 0.05); Student s t-test. LMA, laryngeal mask airway. 1903

TABLE 2: Intraoperative laryngeal mask airway cuff volume and pressure in patients randomized to receive anaesthesia with or without a cuff pressure regulator Without regulator With regulator Volume and pressure parameter (group 1; n = 30) (group 2; n = 30) Just seal cuff pressure, mmhg a 20.8 ± 4.6 19.8 ± 1.7 Final cuff pressure, mmhg 54.6 ± 5.4 20.6 ± 0.5 Just seal cuff volume, ml a 13.7 ± 2.2 14.0 ± 2.9 Increased cuff volume, ml 6.1 ± 2.6 5.8 ± 2.9 Increased regulator volume, ml NA 4.2 ± 1.7 Data presented as mean ± SD. P < 0.05 versus group 1; Student s t-test. a Just seal cuff pressure and just seal cuff volume are the initial cuff pressure and volume, respectively (0 min). NA, not applicable. postoperatively was significantly reduced in group 2 compared with group 1 (P < 0.05). In group 1, a low incidence of dysphagia occurred at 24 h postoperatively and a low incidence of dysphonia occurred at 1 h postoperatively; dysphagia and dysphonia did not occur in group 2. Discussion The present study demonstrated that maintenance of the JSCP by the recoil method can ventilate an adequate tidal volume with no gas leakage, gastric insufflations or laryngospasm. Furthermore, the regulator maintained a constant cuff pressure during general anaesthesia and reduced PPLC following insertion of the LMA. The causes of PPLC following the insertion of an LMA are multifactorial and the incidence varies according to the study design. One of the major causes is cuff Cuff pressure (mmhg) 70 65 60 55 Group 1 50 45 40 35 30 25 20 Group 2 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 110 120 Time (min) FIGURE 2: Change in cuff pressure during the period of anaesthesia in patients randomized to receive anaesthesia with or without a cuff pressure regulator (group 1, without regulator; group 2, with regulator; mean ± SD; P < 0.05 group 1 versus group 2) 1904

TABLE 3: Laryngeal mask airway-related postoperative pharyngolaryngeal complications in patients randomized to receive anaesthesia with or without a cuff pressure regulator Without regulator With regulator Statistical Complication (group 1; n = 30) (group 2; n = 30) significance a PST, 1 h postoperatively Grade 0 9 (30.0) 23 (76.7) Grade 1 12 (40.0) 6 (20.0) P < 0.05 Grade 2 9 (30.0) 1 (3.3) PST, 24 h postoperatively Grade 0 18 (60.0) 24 (80.0) Grade 1 10 (33.3) 6 (20.0) NS Grade 2 2 (6.7) 0 Dysphagia, 1 h postoperatively 0 0 Dysphagia, 24 h postoperatively 2 (6.7) 0 NS Dysphonia, 1 h postoperatively 2 (6.7) 0 Dysphonia, 24 h postoperatively 0 0 NS Data presented as number (%) of patients. a χ 2 test; NS, not statistically significant (P > 0.05). Postoperative sore throat (PST) was graded as follows: 0, no complaint; 1, throat discomfort; 2, continuous throat pain. pressure, which is associated with the anaesthesiologist s skill, the level of insertion difficulty, the number of insertion attempts, the LMA size, 5 the use of dry and cold gas, 6 the duration of anaesthesia, 7 the type of ventilation 8 and the use of analgesics. It is important to use the minimal cuff pressure and cuff volume to reduce PPLC. Hockings et al. 9 reported that a cuff pressure of 40 cmh 2 O showed the least leakage volume compared with 20 or 60 cmh 2 O in paediatric patients with spontaneous breathing. Keller et al. 3 suggested making a change from the recommended volume of 30 ml to 20 ml in size 4 LMA because inflating the cuff to the maximum recommended volume could evoke a suboptimal condition. In contrast, Brimacombe and Keller 10 reported that the efficacy of the seal was not related to pharyngeal mucosal pressure. They also postulated that the soft, semiinflated cuff of the LMA can form an effective seal because it is compliant enough to adapt to a variety of different pharyngeal geometries. The mean ± SD cuff volume of both groups was 14.0 ± 2.9 ml (range 10 18 ml) in the present study. Cuff volume can vary with the frequency of LMA sterilization and the size of the patient s oral cavity and cuff pressure is, therefore, more important than cuff volume. The present study demonstrated that the regulator did not prevent an increase in LMA cuff volume in group 2, but cuff pressure was, nevertheless, constantly maintained during the period of anaesthesia. The compliance of the LMA cuff might be increased by oral temperature. There are conflicting studies regarding LMA cuff-related PPLC. Seet et al. 11 found that limiting the LMA cuff pressure to 44 mmhg could reduce PPLC by 70% compared with routine care, and reduce postoperative PST (2.1% versus 8.7% at 2 h postoperatively; 3.1% versus 13.6% at 24 h postoperatively). Brimacombe et al. 4 reported that a low cuff volume (15 or 20 ml) reduced PST more than a high cuff volume (30 or 40 ml) at 18 24 h postoperatively (20% versus 42%, 1905

respectively). Burgard et al. 12 concluded that a minimal seal reduced PST more than routine care (7.0% versus 15.7%, respectively). The incidence of PST in group 2 in the present study was significantly reduced compared with the incidence in group 1 at 1 h postoperatively, but was higher than in previous studies. 11,12 This may be due to longer anaesthesia times, no use of a heat and moisture exchange device, the use of small amounts of fentanyl (i.e. about 50 µg), or a high proportion of female patients in the study population. 13 One study reported that postoperative discomfort was not related to a variation in LMA cuff pressure. 8 This may have been because, in the four groups in that study, 150 mmhg was the initial cuff pressure. 8 Another study reported that cuff pressures of 30 or 180 mmhg did not significantly reduce the incidence of PST at 8, 24 and 48 h postoperatively. 7 The two groups in that study had a higher incidence of dysphagia than that seen in the present study (40% versus 6.7%, respectively, at day 1 postoperatively; 20% versus 0%, respectively, at day 2 postoperatively). The following instruments and/or processes have been investigated to reduce cuff pressure: use of saline or nitrous oxide and oxygen for cuff inflation; 14,15 use of air as an inhalation gas; 11 use of a specially designed endotracheal tube; 16 18 and use of a detachable device or machine. 19 21 It is, however, expensive to use commercial devices or equipment to maintain the cuff pressure. In the present study, a simple pressure regulator system was devised. It is inexpensive, reliable and easy to use. In practice, an increase in the cuff volume by nitrous oxide diffusion pushes up the regulator piston and, as a result, an opposite force is required in order to maintain a constant cuff pressure. This is achieved by applying a weight to the piston. In addition, to maintain adequate lubrication between the piston and cylinder before installation of the regulator, the inner surface of the regulator should be coated with sterilized water. In conclusion, the present study suggests that the individual JSCP of a patient undergoing anaesthesia by insertion of a LMA must be carefully determined and reduced to a minimum, and the cuff inflation value should be determined using the recoil method. The results indicate that the pressure regulator used in this study is a simple, functional device that reduces early PPLC by maintaining patients cuff pressure at a constant level during the period of anaesthesia. Conflicts of interest The authors had no conflicts of interest to declare in relation to this article. Received for publication 23 March 2011 Accepted subject to revision 5 May 2011 Revised accepted 15 July 2011 Copyright 2011 Field House Publishing LLP References 1 Mizutamari E, Yano T, Ushijima K, et al: A comparison of postoperative PST after use of laryngeal mask airway and tracheal tube. J Anesth 2004; 18: 151 157. 2 The Laryngeal Mask Company Ltd: Instructions For Use LMA Classic, LMA Flexible, LMA Flexible Single Use and LMA Unique. Singapore: The Laryngeal Mask Company Ltd (available at: http://www.lmaco.com/viewifu. php?ifu=16). 3 Keller C, Pühringer F, Brimacombe JR: Influence of cuff volume on oropharyngeal leak pressure and fibreoptic position with laryngeal mask airway. Br J Anaesth 1998; 81: 186 187. 4 Brimacombe J, Holyoake L, Keller C, et al: Pharyngolaryngeal, neck, and jaw discomfort after anaesthesia with the face mask and 1906

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