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From the Department of Anesthesiology, Erasmus University Medical Center, Rotterdam, The Netherlands.
Address correspondence and reprint requests to Eilish Galvin, MB, FCARCSI, Department of Anesthesiology, Erasmus University Medical Center Rotterdam, P.O. Box 2040, 3015 GD Rotterdam, The Netherlands. Address e-mail to eilishgalvin{at}hotmail.com.
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Abstract |
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METHODS: Forty patients received either an LMA-Classic or a CobraPLA. Insertion, ventilation and removal characteristics were noted, as well as any throat morbidity.
RESULTS: Devices were similar for insertion characteristics, adverse events, and throat morbidity. Before pneumoperitoneum, peak airway pressures were 20.3 ± 4.9 cm H2O in the LMA-Classic group versus 25.5 ± 7.9 cm H2O in the CobraPLA group, P = 0.01. This difference was maintained during pneumoperitoneum; LMA-Classic (22.8 ± 6.1 cm H2O) and CobraPLA (28.1 ± 8.5 cm H2O), P = 0.04. Macroscopic blood occurred only on the CobraPLA, seen on 40% of the devices after removal, P = 0.001.
CONCLUSION: During gynecological laparoscopy, the CobraPLA provides similar insertion characteristics, but higher airway sealing pressures than the LMA-Classic. The usefulness of this finding requires further investigation.
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Introduction |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Both the LMA-Classic and CobraPLA consist of a tube with a distal cuff, inflated when positioned in the patient’s hypopharynx, to achieve a seal, thus allowing ventilation of the lungs. However, the CobraPLA has a larger internal tube diameter and a larger more proximally situated circumferential cuff. The CobraPLA has been evaluated and found to be an adequate alternative to the LMA-Classic in terms of insertion and recovery characteristics (1,2). Higher sealing pressures have been reported with the CobraPLA when compared with the LMA-Classic during controlled ventilation (1).
In this current randomized, controlled, single-blind study, the primary aim was to evaluate the use of the CobraPLA as an alternative to the LMA-Classic in patients undergoing laparoscopic gynecological surgery. In particular, we compared the devices for insertion and removal characteristics and ability to ventilate at higher airway pressures.
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METHODS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Patients received either an LMA-Classic or CobraPLA. IV access was established and patients had routine monitors attached. After administration of 100% oxygen, anesthesia was induced using sufentanil and propofol. All devices were inserted by one of the two anesthesiologists.
Insertion time was measured from the moment the device was placed in the patient’s mouth to time of connection of the breathing circuit. Additional manipulations performed to achieve an adequate airway were recorded. A failed insertion could be followed by two further attempts. Using a cuff inflator pressure gauge (Portex, Kent, England), air was injected until the cuff pressure measured 60 cm H2O. Successful placement was confirmed by the presence of bilateral chest wall movement and occurrence of a square wave trace on the capnograph during manual ventilation. Anesthesia was maintained with propofol at 10–15 mg · kg–1 · h–1 with a fresh gas flow rate of 3 L/min with 33% oxygen in air. Volume-controlled ventilation was used; tidal volume of 8 mL/kg and respiratory rate of 10 bpm with rate adjustment to ensure an end-tidal carbon dioxide of 4–6 KPa. The inspiratory to expiratory ratio was set at 1:2.
The peak pressure at which a leak occurred for each airway device was then assessed before and during pneumoperitoneum. To measure the pressure at which a leak was audible, pressure-controlled ventilation was used, commencing at a pressure of 10 cm H2O and increasing in intervals of 5 cm H2O to a maximum of 40 cm H2O. A pressure difference of at least 15 cm H2O was maintained between peak airway pressures and positive end-expiratory pressure, throughout the testing period by adjustment of positive end-expiratory pressure. Once an audible leak occurred, peak airway pressure was recorded and testing stopped. Before induction of a pneumoperitoneum, a muscle relaxant, mivacurium, was given at a dose of 0.01 mg/kg to facilitate the surgical technique. Maximal allowed head-down Trendelenberg position was approximately 15° and maximal intraabdominal pressure was 15 mm Hg. The testing process was repeated during pneumoperitoneum until a leak was heard and peak pressures were recorded. Adverse events were also recorded.
Airway devices were removed when patients were breathing spontaneously and able to respond to simple commands. The presence or absence of macroscopic blood on each device, as well as throat pain or difficulty swallowing was noted.
Power Analysis
To estimate the group size, a pilot study was conducted measuring the leak pressures for the LMA-Classic in patients during laparoscopic gynecological surgery in 30 patients. The standard deviation of the leak pressure in this group was 4.5 cm H2O. For our power calculation, we assumed equal standard deviation for leak pressure in the CobraPLA group. We wanted to be able to show a difference of 4 cm H2O in leak pressure between the two. With an 
= 0.05, two tailed and a power of 80%, we needed 20 patients per group, hence a total of 40 patients were included in this study.
Statistical Analysis
Data are expressed as mean ± sd or as categorical distributions. Between-group comparisons for numerical data were analyzed with an unpaired t-test. Between-group comparisons for distributions were analyzed using a Fisher’s exact test for data with two categories and a 
2 test for data with more than two categories.
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RESULTS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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The LMA-Classic insertion time was 10.3 ± 3.5 s, successful on first attempt in 19 of 20 patients. The CobraPLA insertion time was 11.6 ± 5.9 s, successful on first attempt in 17 of 20 patients. There were no adverse events. Adequate ventilation was achieved in both groups with just one patient in the LMA-Classic group experiencing a brief oxygen desaturation to <94%.
The mean volume of air inserted in the cuffs to achieve a cuff pressure of 60 cm H2O was 16.6 ± 6.8 mL for the LMA-Classic group and 34.5 ± 9.2 mL for the CobraPLA group. There were more additional device movements required in the CobraPLA group when compared with the LMA-Classic group. Airway ventilation pressures required to hear a leak were 20.3 ± 4.9 cm H2O in the LMA-Classic group and 25.5 ± 7.9 cm H2O in the CobraPLA group before pneumoperitoneum. These differences were statistically significant, P = 0.01 (Fig. 1). During pneumoperitoneum, peak airway pressure at which a leak was audible around the LMA-Classic was 22.8 ± 6.1 cm H2O and for the CobraPLA was 28.1 ± 8.5 cm H2O. This was also statistically significant, P = 0.04 (Fig. 1). On removal of the device, no macroscopic blood was seen in any patient in the LMA-Classic group. Blood was seen in eight patients in the CobraPLA group, which was statistically significant, P = 0.001. No patient had sore throat and/or dysphagia before discharge.
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DISCUSSION |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Earlier studies have shown that the LMA-Classic may be successfully used to ventilate patients’ lungs during laparoscopic surgical procedures (3,4). Our findings confirm the results of a published study (1), which demonstrated a higher airway sealing pressure using a CobraPLA compared to a LMA-Classic during positive-pressure ventilation, in the absence of pneumoperitoneum. Our study is the first to confirm that there is also a statistically significant difference in sealing pressures between the CobraPLA and LMA-Classic, during positive-pressure ventilation in the presence of a pneumoperitoneum.
More additional airway and device maneuvers were required in the CobraPLA versus the LMA-Classic group. We also noted an absence of a definitive resistance when placing CobraPLA devices, unlike the easily felt resistance observed when placing LMA-Classic devices. Interestingly, the amount of air inserted in the cuff of both devices to achieve a cuff pressure of 60 cm H2O was far less than the values recommended by the manufacturers, highlighting the importance of cuff pressure measurement when using supra-laryngeal devices, as excessive cuff pressure may have potentially damaging the effects on local structures (5,6).
There are several publications reporting successful and safe use of LMA-Classic devices in patients undergoing laparoscopic surgery (3,4,7). In our series of selected patients, there was no evidence of gastric regurgitation or pulmonary aspiration, with airway pressures in some cases briefly as high as 40 cm H2O. As stated in an editorial (8), estimating the risk for pulmonary aspiration can be extremely difficult and requires consideration of patient, operative and anesthetic factors. The use of supra-laryngeal devices in patients undergoing laparoscopic surgery requires careful attention to patient selection and adherence to strict guidelines for maximum intraabdominal pressures and degree of head down (Trendelenberg) positioning.
It is important to note that while this and earlier studies demonstrate that higher airway sealing pressures may be achieved using the CobraPLA when compared with the LMA-Classic, the manufacturers of both devices recommend peak airway pressures to be maintained <20 cm H2O for routine use (9,10). The use of higher airway pressures in conjunction with supra-laryngeal airway devices may result in greater flow of gases into the gastrointestinal tract with resultant gastric distention and a possibly increased risk of regurgitation and aspiration. Because of the more proximal positioning of the CobraPLA cuff in the patient’s hypopharynx and its circumferential design which contributes to its ability to achieve a higher sealing pressure, should regurgitation of gastric contents occur, the chances that any regurgitated gastric secretions might flow toward the trachea may, in theory, be greater than with the more proximally, situated, noncircumferential cuff of the LMA-Classic.
Other supra-laryngeal devices such as the Proseal LMA, have been studied and successfully used during laparoscopic surgery (11,12). An advantage of this device is the presence of a conduit extending from the distal end of the cuff to the exterior, which is designed to drain gastric contents. In this study we chose to compare the newer CobraPLA with the LMA-Classic, as the latter device is widely available and has been successfully used during laparoscopic surgery. However, a future study comparing the Proseal-LMA with the CobraPLA might offer further useful information.
We noted a more frequent occurrence of macroscopic blood on the CobraPLA (40%) when compared with the LMA-Classic (0%) after device removal. We postulate that this may have been a consequence of the relatively stiff nature of the device tip. However, none of the patients in this study group reported throat morbidity, in contrast to earlier studies which reported an incidence of throat pain of 10%–50% after CobraPLA use (1,2,13).
In conclusion, it would appear from this study that both the LMA-Classic and CobraPLA provide an adequate airway for positive pressure ventilation in selected patients with and without pneumoperitoneum. Higher airway pressures were tolerated using the CobraPLA, the usefulness of which requires further investigation. CobraPLA use was associated with a higher incidence of macroscopic blood on the device after removal.
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Footnotes |
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Supported by the Department of Anesthesiology, Erasmus University Medical Center Rotterdam, Rotterdam, The Netherlands.
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REFERENCES |
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This article has been cited by other articles:
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  D. Alfery Is the Cobra Perilaryngeal Airway (CobraPLATM) Appropriate for Use in Patients Undergoing Gynecological Laparoscopy? Anesth. Analg., August 1, 2007; 105(2): 546 - 546. [Full Text] [PDF]
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E. M. Galvin Is the Cobra Perilaryngeal Airway (CobraPLATM) Appropriate for Use in Patients Undergoing Gynecological Laparoscopy? Anesth. Analg., August 1, 2007; 105(2): 546 - 547. [Full Text] [PDF]
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