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AMBULATORY ANESTHESIOLOGY

Use of ProSeal^TM Laryngeal Mask Airway in 2114 Adult Patients: A Prospective Study

Kai Goldmann, MD, PhD, DEAA^*, Carolin Hechtfischer^*, Amena Malik^*, Andrea Kussin, MD^*, and Christian Freisburger, MD^*

From the *Department of Anaesthesia and Intensive Care Therapy, Philipps University Marburg, Germany; Department of Anaesthesia, Dubai Hospital, Dubai Health Authority, UAE.

Address correspondence and reprint requests to Kai Goldmann, MD, PhD, DEAA, Department Anaesthesia, Dubai Hospital, Dubai Health Authority, PO Box 7272, Dubai, UAE. Address e-mail to kgoldmann{at}dohms.gov.ae.

Abstract

BACKGROUND: There have been numerous studies published on the ProSeal^TM laryngeal mask airway (PLMA). However, few have investigated its utility in a large practice setting. We sought to gather comprehensive data about the characteristics, efficacy, and safety of its use by a representative group of anesthesiologists working at a teaching center.

METHODS: Information was collected on a standardized data collection form. Clinical information obtained included user characteristics, patient characteristics, type and duration of operation, details of airway management and anesthetic technique, details of adverse events, and postoperative status of the patient.

RESULTS: Use of the PLMA was documented in 2114 patients by 81 anesthesiologists (57% trainee, 43% staff grade). The insertion success rate was 99% within a maximum of 3 attempts. Mean airway leak pressure was 28 (11–40) cm H₂O. In 3.2% of cases, the PLMA was abandoned in favor of the endotracheal tube. Ventilation was controlled in 98%. Clinically "relevant" adverse events were recorded in 3.3% of all cases, of which 0.6% were classified as "serious." No long-term adverse sequelae resulted. No signs of aspiration were found in 12 patients with apparent regurgitation of gastric fluid through the drain tube of the PLMA. Five cases of difficult ventilation and 16 cases of difficult endotracheal intubation were successfully managed by the use of the PLMA.

CONCLUSION: This study demonstrates that airway management using the PLMA is safe and effective in a general practice setting. The results support the assumption that a correctly positioned PLMA can protect from pulmonary aspiration of regurgitate gastric fluid. The data also support use of the PLMA for the management of the difficult airway.

The ProSeal^TM laryngeal mask airway (PLMA) (LMA North America, San Diego, CA) was invented with the aim to overcome the main limitations of the Classic^TM laryngeal mask airway (CLMA), the low pressure seal and the lack of protection against aspiration, thereby providing a more secure supraglottic airway for positive pressure ventilation (PPV).1 After its introduction into clinical practice in 2000, several studies showed that the PLMA provides higher airway leak pressures (P_leak) than the CLMA and allows for access to the stomach.2,3 In addition, there is some evidence that a correctly positioned PLMA can protect the patient from pulmonary aspiration of regurgitated gastric fluid.4,5 Most of the scientific data on its usage have been generated in studies in limited numbers of patients. No large scale study on the safety and reliability of the PLMA in the general practice setting has been published. Data gathered by expert users proving the safety and reliability of a device are not automatically applicable to a general population of anesthesiologists. The primary aim of this study was therefore to gather comprehensive data by a large number of trainee and staff anesthesiologists in order to be able to determine the characteristics, efficacy, and safety of its use by a large group of anesthesia providers.

METHODS

We conducted a prospective observational study of the practice of PLMA usage at a university hospital between 1 July 2005 and 31 December 2006. The study was reviewed and approved by the local ethics committee. No written patient consent was deemed necessary by the ethics committee as the study was considered a prospective audit of current practice. Anesthesiologists were asked to complete a simple one-page paper questionnaire each time they used the PLMA. The indication for PLMA use, the mode of use, and the choice of anesthetic technique were not influenced by the conduct of the study. Clinical information obtained included user characteristics, patient characteristics, type and duration of operation, details of airway management and anesthetic technique, details of airway management or PLMA use-related critical incidents, and postoperative status of the patient. Patient-related information included: age, height, weight, sex, ASA classification, signs of a potentially difficult airway, mallampati classification, normal or abnormal mouth opening, normal or abnormal status of teeth, normal or short thyromental distance, normal or enlarged tonsils, and normal or high arch palate. Procedure-related information included date, type and duration of operation. Anesthesiologist-related information included: ID number, grade (1st or 2nd yr resident, 3rd–5th yr resident, attending), and experience with CLMA (0–100, 101–500, 501–1000, >1000 uses) as well as PLMA (0–10, 11–50, 51–100, >100 uses). Airway management-related information included: planned or unplanned PLMA use (for unexpected difficult intubation, difficult facemask ventilation, failed regional anesthesia, failed "stand-by" [local anesthesia]), size of mask, preparation of mask (cuff deflated, partially inflated), technique of placement (standard by Brain, alternative), number of placement attempts, change to endotracheal tube (ETT), P_leak,6 intracuff pressure monitoring, and fiberoptic score (optional).7 Anesthetic technique-related information included: type of induction (inhaled, IV), adequacy of anesthetic depth at induction, intraoperative anesthetic technique (total IV, balanced), use of neuromuscular blocking drugs, type of ventilation (spontaneous, volume-controlled, pressure-controlled), use of positive end-expiratory pressure (PEEP), use of gastric tube, and persistent airway leakage. Adverse event-related information included point of time (induction, intraoperative, emergence) and type of adverse event (airway obstruction, bronchospasm, laryngospasm, regurgitation, aspiration, hypoxemia, hypercarbia, and others). The severity of adverse events was graded as minor, relevant or serious. The grading was based on the clinical judgment of the anesthesiologist except for hypoxemia (minor: Spo₂ <95%; relevant; Spo₂ <90%; serious: Spo₂ <85%) and hypercapnia (minor: end-tidal CO₂ >50 mm Hg; relevant: end-tidal CO₂ >60 mm Hg; serious: end-tidal CO₂ >70 mm Hg). Postoperative status-related information included postoperative visit performed or not performed, and complaints of the patient (none, sore throat, hoarseness, nausea and vomiting, others). Apart from information related to patient’s characteristics, surgical procedure, anesthesiologist ID number, and P_leak, all data were provided by ticking boxes to confirm or reject statements. In addition, the anesthesiologist was also encouraged to record comments. All questionnaires were checked for completeness of data upon daily collection. If there were questions on the information provided or any data were missing, the anesthesiologist concerned was contacted immediately and, if necessary, missing data were added according to the anesthesiologist’s information. Patients in whom an airway management-related problem lead to any kind of postoperative complaint or discomfort were followed up until full recovery either by postoperative visit on the ward, or after discharge by telephoning them at home. Data were downloaded onto a database and analyzed using SPSS (SPSS, Chicago, IL) software. After completion of the study, all questionnaires were hand-searched by 3 different individuals to ensure completeness of the database. Unless otherwise stated, data are expressed as mean values ± sd or as median values (range). Statistical analysis was with ² test and t-test, where appropriate. Results were considered statistically significant for a P value <0.05.

RESULTS

A total of 2114 PLMA uses were documented in 1288 female and 826 male patients. The mean (range) age, height, and weight of the patients was 52(18–93) yr, 170(136–198) cm and 74(36–140) kg, respectively. The patients were anesthetized for 90(15–515) min (mean [range]). Five hundred forty-three cases (25.7%) lasted more than 2 h, of which 120 cases (5.7%) lasted more than 3 h. Surgical disciplines for which the PLMA was used were trauma surgery (30%), gynecology (28%), ophthalmology (18%), orthopedics (11%), urology (6%), general surgery (6%), and ear-nose-throat (1%). Use of the PLMA was planned in n = 2054 patients. In n = 29 patients, the PLMA was used when regional anesthesia blocks were incomplete, and in n = 10 patients, when monitored anesthesia care ("stand-by") had failed. In n = 21 patients, successful use of the PLMA was part of unanticipated difficult airway management, in 16 patients to overcome failed conventional endotracheal intubation (ETI), and in 5 patients to overcome difficult mask ventilation leading to oxygen desaturation. In one of these patients, presenting for emergency cesarean delivery, use of the PLMA was considered life-saving in a true cannot-intubate cannot-ventilate situation. However, pulmonary aspiration of gastric fluid had happened during multiple attempts at ETI before the placement of the PLMA. Eighty-one anesthesiologists documented an average 10(1–170) uses. Most patients (57%) were anesthetized by resident anesthesiologists. Most users (58%) indicated an experience with the PLMA of more than 100 uses, 42% of <100 uses, of which 14% indicated <50 uses.

The size 4 and 5 were used for male and female patients, whereas the size 3 was used for female patients only. Placement was successful in n = 1693 patients at the first attempt (80.1%), in n = 332 patients at the second attempt (15.7%), in n = 67 patients at the third attempt (3.2%), and in n = 22 patients (1%) at the fourth attempt using the standard digital technique by Brain in 95.3% of all patients. In n = 5 patients (0.2%) placement was not possible within 4 attempts. In n = 59 patients (2.8%), the initially selected size was changed after the first failed attempt, leading to a successful placement. In n = 67 patients (3.2%), the PLMA was changed to an ETT. Table 1 shows the reasons for changing. In n = 52 patients, the exchange was performed preoperatively, whereas in n = 15 patients, the exchange was required intraoperatively. PLMA use failure was influenced by the level of PLMA as well as CLMA use experience. Failure was highest if the experience was <100 CLMA uses (5.5%) or <10 PLMA uses (5.4%); failure was lowest if the experience was more than 1000 CLMA uses (2%), or more than 100 PLMA uses (2.9%), (P < 0.001). The mean P_leak determined by one of the methods described by Keller et al.6 was 28(12–40) cm H₂O (n = 2008). The mean P_leak documented for the size 3 (25 ± 6 cm H₂O) was significantly lower than the mean P_leak documented for the size 4 (29 ± 7 cm H₂O) and 5 (28 ± 7 cm H₂O), (P < 0.001).

Anesthesia was induced IV in n = 2109 patients (99.8%). Anesthesia maintenance was by total IV anesthesia (propofol) in n = 1608 patients (76.1%) and by sevoflurane or desflurane in n = 489 patients (23.1%). Neuromuscular blocking drugs were used in 111 patients (5.3%). In n = 162 patients (7.7%), the depth of anesthesia at induction was judged insufficient by the anesthesiologist, leading to problems with placement of the PLMA. A gastric tube was placed through the drain tube (DT) of the PLMA in n = 781 patients (36.9%). Pressure-controlled ventilation was used in n = 1858 patients (87.9%), volume-controlled ventilation in n = 219 patients (10.4%), and spontaneous ventilation in n = 37 patients (1.7%). Controlled ventilation was combined with PEEP in n = 1182 patients (55.9%). An intraoperative leakage was documented in n = 148 patients (7.1%) but only requiring exchange to an ETT in n = 11 patients (0.5%). Cuff pressure was monitored constantly in n = 1774 patients (84%) and maintained at or below 60 cm H₂O. Mask position was assessed by fiberoptic inspection in n = 308 patients (14.6%) (Table 2). Parts or the entire vocal cords were visible in 91.2% of all patients.

Airway management or PLMA use-associated adverse events were documented in n = 250 patients (11.8%). Table 3 shows the type of critical incidents and the severity. The incidence of problems during induction of anesthesia (5.2%) and the maintenance phase (4.6%) was significantly higher than during emergence from anesthesia (1.8%) (P < 0.001). The incidence of adverse events was significantly higher when a balanced anesthetic technique was used (19%) compared to a total IV technique (9.3%) (P < 0.001) even after elimination of trauma-related adverse events, obviously not related to the anesthetic technique (17% vs 6.5%). First and second year residents had a higher incidence of adverse events (15.2%) than third-fifth year residents (10.1%) and attending anesthesiologists (9.5%) (P < 0.001). Adverse events were judged as "relevant" in 2.7% and as "serious" in 0.6% of all cases.

Most problems were related to minor trauma, usually evident by blood on the PLMA on removal, followed by laryngospasm and other types of upper airway obstruction. Apart from the above-mentioned case of aspiration before placement of the PLMA, there were no cases of aspiration. In 12 patients, regurgitated gastric fluid was vented through the DT away from the larynx. Regurgitation occurred in 5 patients after induction, in 5 patients during maintenance, and in 2 patients during emergence from anesthesia. None of the patients had clinical signs of pulmonary aspiration, and no signs of aspiration were found by subsequent fiberoptic inspection of the tracheo-bronchial tree of 9 of these patients. In 3 patients, a fiberoptic examination of the tracheo-bronchial tree was not performed. Postoperative visits in n = 1049 patients (49.6%), including all patients in whom a critical incident had been witnessed, showed no long-term adverse sequelae in any patient. Postoperative complaints consisted of sore throat in n = 48 patients (4.6%), hoarseness in n = 3 patients (0.3%), and a pressure trauma to the tongue causing temporary neuropraxia in n = 9 patients (0.9%).

DISCUSSION

This study provides comprehensive data on routine PLMA use in more than 2000 adult patients by a large group of anesthesiologists under nonstandardized conditions, thereby giving an insight into how well this device works in routine clinical practice. The participating users represent a typical population of anesthesiologists at a teaching institution, consisting of a large number of trainees and users of a broad variation of CLMA/PLMA use experience. The spectrum of surgical specialties and the type of operations for which the PLMA was used are similar to those previously reported for CLMA use.8

Probably the most notable data confirmed by this study are a mean P_leak in the range of previously reported values in controlled studies2,3,9 and an overall placement success rate of 99%.2,3,9 A mean P_leak of 28 cm H₂O demonstrates that the airway seal provided by the PLMA is well within the range required for PPV in most adult patients. The results suggest that the size 3 PLMA provides a less effective seal than the sizes 4 and 5 PLMA. Although the low first placement success rate of 80% contrasts with a higher success rate for expert users,10,11 the high overall success rate proves that the PLMA can be placed successfully with a clinically acceptable number of placement attempts applying the recommended digital insertion technique.

Although this study demonstrates that the PLMA is a reliable and safe tool for airway management, it also shows that it does not always work 100% of the time during routine practice. This clearly contrasts with the results reported in more limited studies.10,11 Considering that the majority of patients was anesthetized by trainees, a 3.2% overall failure rate and a 0.7% intraoperative failure rate appear, in our opinion, quite acceptable. Analyzing the reasons for changing the PLMA to an ETT, it appears that the depth of anesthesia is an important aspect of PLMA failure. This is supported by a frequent incidence of reasons that are clearly related to an insufficient depth of anesthesia, for instance hiccup, sudden airway obstruction or airway leakage after initially obtaining a sufficient airway. The documented 8% incidence of an insufficient depth of anesthesia at induction also supports this assumption. The same seems to be true for PLMA use-related critical incidents, as anesthesia depth-related critical incidents also make up a large proportion of these. Both aspects underline the importance of an adequate level of anesthesia in the successful use of the PLMA.

An overall incidence of 11.8% adverse events in our study seems to be relatively high compared to a reported incidence of <1% in a 1996 large scale survey of CLMA use.8 However, it is important to notice that different definitions of "adverse events" were used, and to differentiate the severity as well as the clinical relevance of reported events. In our study, the users were instructed to report any airway-related incident, independent of the degree and the actual relevance for the clinical management. For instance "regurgitation" was considered an adverse event although in no case did any complication result. A thorough analysis of the severity of reported incidents showed that the majority of critical incidents (8.5%) was of a "minor" nature, for instance, blood staining of the PLMA on removal, as well as a minor degree of hypoxemia (Spo₂ <95%) or hypercarbia (end-tidal CO₂ >50 mm Hg). Only 2.7% and 0.6% of all incidents were classified as "relevant" or "serious." Our study shows that the incidence of PLMA use-associated adverse events posing a relevant clinical problem to the anesthesiologist is low. One particular type of adverse event deserves to be highlighted as it has not been reported and seems to be PLMA-specific. Within the first 6 mo of the survey, we noted pressure trauma to the tip of the tongue causing temporary neuropraxia in 9 patients. In 8 patients, normal sensory function of the tongue returned within the first postoperative days, however, in 1 patient it took 4 wk to fully recover. As it was noticed on multiple occasions at removal of the PLMA that the tip of the tongue had been wedged between the lower incisors and the bite-block of the mask, the anesthesia staff were informed to pay meticulous attention to this aspect. As a consequence, no such complication was observed during the following months of the survey.

A meta-analysis of the incidence of problems associated with the use of either an IV or a balanced anesthetic technique and the CLMA did not reveal any technique to be superior.12 Our results are in clear contrast to these findings. We found that an IV anesthetic technique was associated with a significantly lower incidence of adverse events. The potential reason for this is the familiarity of our users with an IV-based anesthetic when using a PLMA.

Probably, the most important finding of this study is related to the potential of a correctly positioned PLMA to protect the airway from regurgitated gastric fluid. In all patients in which regurgitation was noted, the PLMA performed reliably in preventing aspiration. In all cases, the fluid was vented through the DT away from the larynx and, consequently, none of the patients had any clinical signs of pulmonary aspiration. Our finding supports the assumption that a PLMA can protect against pulmonary aspiration of regurgitated gastric fluid if positioned correctly with the orifice of its DT aligned with the upper esophagus sphincter. The incidence of about 0.5% regurgitation might appear relatively high considering that the incidence of obvious regurgitation with the CLMA in routine clinical use can be expected to be <0.1%.13 However, some controlled studies revealed that the incidence of silent pharyngeal regurgitation under general anesthesia with the CLMA can be as high as 5%.13 A possible explanation of a much lower incidence of clinically apparent regurgitation might be that even the CLMA provides some protection against pulmonary aspiration of regurgitated gastric fluid due to an attenuation of liquid flow by the distal cuff forming a plug above the upper esophageal sphincter. With the PLMA, the cuff now offers an escape route to regurgitated gastric fluid. This might explain a relatively frequent incidence of clinically apparent regurgitation in our study.

Originally, the CLMA was mainly used as a replacement for the facemask with spontaneous ventilation. Over the years, this practice has changed and the CLMA has increasingly been used with a controlled mode of ventilation,8 although it remained controversial.14 Our data show that, at our institution, introduction of the PLMA has lead to further expansion of this practice, so that ventilation is almost always controlled when the PLMA is used; in addition, PPV is combined with PEEP in the majority of patients. Our data do not show that this is associated with a high rate of clinically relevant adverse events. The practice of pressure-controlled ventilation without the use of muscle relaxants therefore seems to be safe and effective. Finally, successful use of the PLMA in 16 cases of failed ETI and 5 cases of difficult mask ventilation, including one life-threatening cannot-intubate cannot-ventilate situation, strongly support the assumption that the PLMA might have a similar role to the CLMA in the management of the difficult airway. A high rate of vocal cord visibility, as confirmed by our study, and the absence of a grille might be considered an advantage over the CLMA in such a situation when ETI is warranted. A better seal with the airway and the ability to drain the stomach might be considered an advantage over the CLMA if a patient at risk of aspiration requires use of a supraglottic airway device in such a situation.

Although the results of this prospective observational study offer a comprehensive insight into PLMA use, important limitations need to be mentioned. Probably the most important is that it was conducted at one center, and therefore, represents institutional practice rather than PLMA practice in general. Although the number of uses is the largest number reported, the dataset is still limited compared to large scale studies of CLMA use.8 It can not therefore provide an explanation for all aspects of use found in this survey. Also, data were not collected by an independent observer and only cross-checked for completeness and not accuracy. This could be a potential source of inaccuracy. The fact that other techniques of airway management, such as CLMA or ETT use, were not surveyed at the same time might also be considered a limitation, as direct comparison of these techniques with each other is not possible.

In summary, this survey demonstrates that airway management using the PLMA and a controlled mode of ventilation without muscle relaxants is both effective and safe in the hands of a large academic practice consisting of staff grade and trainee anesthesiologists. The results support the assumption that a correctly positioned PLMA can protect patients from pulmonary aspiration of regurgitated gastric fluid during PPV. The results also support the use of the PLMA in the management of the difficult airway. The data underline the role of inadequate anesthesia if PLMA use is associated with problems or fails.

Footnotes

Accepted for publication August 5, 2008.

Supported by Institutional Resources.

REFERENCES

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Goldmann, K. Articles by Freisburger, C. Search for Related Content PubMed PubMed Citation Articles by Goldmann, K. Articles by Freisburger, C.