The cuffed oropharyngeal airway is a modified Guedel-type oral airway with a cuff at its distal end. The objectives of this study were to compare the ability of the cuffed oropharyngeal airway and the laryngeal mask airway to provide positive-pressure ventilation during general anesthesia, and to assess their relative ease of use and ability to reduce total fresh gas flow rates.
In this prospective, randomized study, a cuffed oropharyngeal airway (n = 25) or a laryngeal mask airway (n = 25) device was inserted after induction of anesthesia intravenously using 2 mg/kg propofol. While anesthesia was maintained with sevoflurane and nitrous oxide, the leak pressure, leak fraction (the fractional difference between the inspired and expired tidal volume), minimum fresh gas flow rate, and need for airway manipulations were determined. The anesthesia provider who inserted the device completed an evaluation form at the end of the 15-min study period.
Positive-pressure ventilation was established successfully on the first attempt in 92% of the patients when the cuffed oropharyngeal airway was used and in 88% of the patients when the laryngeal mask airway device was used. However, manipulations of the airway device were necessary more frequently (8 vs. 1 patient; P < 0.05) and the leak pressure was less (22 +/- 6 cm water vs. 26 +/- 5 cm water; P < 0.05) with the cuffed oropharyngeal airway than with the laryngeal mask airway. In addition, the leak fraction (0.19 +/- 0.18 vs. 0.31 +/- 0.22; P < 0.05) and the minimum fresh gas flow rate (1.3 +/- 1.5 vs. 2.4 +/- 2.5; P = 0.12) were less in the laryngeal mask airway group.
Positive-pressure ventilation is possible with the laryngeal mask airway and cuffed oropharyngeal airway devices. Although the cuffed oropharyngeal airway can be inserted easily by inexperienced users with a high first-attempt success rate (> 90%), manipulations of the device may be required to maintain a patent airway. The laryngeal mask airway device allows positive-pressure ventilation at slightly greater peak inspiratory pressures.
THE cuffed oropharyngeal airway (COPA) was introduced recently for clinical use as an alternative to the laryngeal mask airway (LMA) and a face mask- oral airway combination during general anesthesia. The COPA consists of a modified Guedel-type oral airway with a cuff at its distal end, which creates a seal between the patient's upper airway and the anesthesia delivery system. When the cuff is inflated, it displaces the base of the patient's tongue anteriorly and passively elevates the epiglottis away from the posterior pharyngeal wall. The proximal end of the device has a standard 15-mm connector, an integrated bit block (tooth-lip guard), and two posts for attaching the elastic fixation strap. The COPA is available in sizes 8, 9, 10, and 11, which refer to the distance in centimeters between the tooth-lip guard and the distal tip. Although the COPA is inserted easily and the anesthetic requirements for insertion are less than with the LMA device,  additional airway manipulations may be necessary during the intraoperative period.  A recent study that compared the COPA and the LMA found both devices to be safe and effective for use in spontaneously breathing anesthetized patients. 
The LMA has been used successfully to provide positive-pressure ventilation in adults and children. [4,5] A recent survey of LMA use in 11,910 patients revealed that 44% of the patients received positive-pressure ventilation.  When an LMA is used, positive-pressure ventilation may become necessary during periods of hypoventilation or apnea secondary to anesthetic drugs or when the LMA is used emergently during an unexpected difficult intubation. [7–9] Although the COPA device was introduced for use in spontaneously breathing patients, positive-pressure ventilation may be needed unexpectedly for similar reasons. The ability to deliver positive-pressure ventilation with the LMA has been compared with that using the face mask,  but it has not been compared with the COPA device.
We hypothesized that the COPA would be an acceptable able alternative to the LMA when positive-pressure ventilation is necessary. Therefore, we designed a prospective randomized study to compare the COPA and LMA devices with respect to:(1) the ability to provide positive-pressure ventilation, (2) minimum leak pressures, (3) the fraction of inspired to expired tidal volumes, and (4) minimum fresh gas flow rates during general anesthesia.
After we obtained institutional review board approval, we enrolled 50 consenting adult patients who were classified as American Society of Anesthesiologists physical status I-III and scheduled for minor orthopedic, urologic, or general surgical procedures. Patients were assigned randomly to receive either the COPA or the LMA device for airway management based on a computer-generated randomization table. Patients were excluded from the study if they were pregnant, had a history of difficult intubation, were at risk for pulmonary aspiration (i.e., gastroesophageal reflux, ingestion of solid food < 8 h before the procedure, morbid obesity, or delayed gastric emptying), or had clinically significant chronic lung disease. In the operating room, the standard monitors were attached to the patient and the anesthetic machine (Ohmeda Modulus II; Liberty Corner, NJ), and delivery circuits were checked carefully for the presence of any leaks.
Anesthesia was induced intravenously with 2 mg midazolam, 1 [micro sign]g/kg fentanyl, and 2 mg/kg propofol (based on lean body weight), and the COPA or LMA was inserted 30 s after loss of the eyelid reflex. The anesthesia providers inserting the airway device were given verbal instructions regarding the recommended insertion technique before anesthesia was induced. The size of the COPA was determined by placing the distal tip of the upright COPA at the angle of the mandible. The transition line between the colored proximal end and the clear airway was at the level of the teeth, with the proximal end of the COPA extending 1 cm beyond the lips, when the proper size was selected. A size 3 LMA was selected for women who weighed less than 65 kg, and a size 4 LMA was used for all other patients. The airway devices were coated with a water-soluble lubricant and inserted with the patient's head in the standard intubating position using the manufacturer's recommended technique (COPA: Mallinckrodt Medical, Athlone, Ireland; LMA North America, San Diego, CA). The time needed to insert the airway device successfully and the number of insertion attempts (defined as withdrawing and reinserting the device) were recorded. Before the cuff was inflated with sufficient air to create an effective seal, the COPA was secured using the enclosed elastic fixation strap, and the LMA was taped to the upper lip in the usual manner. Mean arterial blood pressure, systolic and diastolic blood pressures, and heart rate values were measured before induction and 1- to 2-min intervals after induction during the 15-min study period.
Anesthesia was maintained with sevoflurane, 1% inspired, and nitrous oxide, 67%, in oxygen during the 15-min postinsertion study period before skin incision. Manual positive-pressure ventilation was used to assess the patency of the airway. The presence of airway obstruction or an inadequate seal with a large gas leak was managed by increasing the volume of air in the cuff, manipulating the patient's airway (i.e., chin lift or jaw thrust, turning the head) or repositioning the airway device. The need to reposition the airway device and the number of manipulations necessary to obtain a patent airway were recorded. The threshold inspiratory pressure at which an audible air leak occurred (i.e., the leak pressure) was determined by closing the expiratory relief ("pop-off") valve and delivering a sustained breath with increasing airway pressure applied.
Subsequently, patients' breathing was aided mechanically using an Ohmeda 7900 series anesthesia ventilator with a tidal volume of 10 ml/kg, a respiratory rate of 10 breaths/min, and an inspiratory:expiratory ratio of 1:2. The total fresh gas flow of nitrous oxide and oxygen (in a fixed 2:1 ratio) was adjusted to determine the lowest (minimum) total gas flow rate at which the ascending bellows of the ventilator remained completely filled. The inspiratory tidal volume, expiratory tidal volume (measured using an in-line spirometer), peak inspiratory pressure, and mean airway pressure were recorded every 3 min during the 15-min study period. The degree of leak was calculated as the difference between the inspired and expired tidal volumes and expressed as a fraction of the inspiratory volume (the so-called leak fraction).  The anesthesia providers who inserted the COPA or LMA device completed forms that detailed their previous experience with the LMA and COPA devices and that evaluated their ability to choose an appropriate airway size, the ease of insertion of the device, their ability to maintain an adequate seal during positive-pressure ventilation, and their overall impression of the airway management technique.
A power analysis was performed to determine the number of patients needed to detect a 50% difference in the leak fraction between the two airway devices based on the previously published variability of the leak fraction when an LMA device (n = 24) is used.  A mean leak fraction of 0.25 with a standard deviation of 0.15, an alpha error of 0.05, and a power of 80% were used in the calculation. Demographic data and parametric variables were analyzed using an unpaired, two-tailed Student t test. Nonparametric variables and variables that were not normally distributed were evaluated using chi-square analysis. Significance was defined as a P value < 0.05, and data are reported as the mean +/- SD unless otherwise noted.
The patient demographic characteristics were similar in both airway device groups (Table 1). None of the patients had abnormal results on the airway examination, and only one patient in each group had a Mallampati score more than 2. A size 3 LMA was used in 28% and a size 4 was used in 72% of the patients in the LMA group. All four sizes of the COPA devices (size 8, 8%; size 9, 40%; size 10, 32%; size 11, 20%) were used during the study. There were no differences in mean arterial pressure, systolic and diastolic blood pressures, or heart rate values at baseline (preinduction), 1 min after induction, or 1 min after insertion of the airway device. The anesthetic requirements for induction and successful insertion of the devices were similar for both groups, and there was no difference in the end-tidal sevoflurane concentration during the 15-min postinsertion period (Table 2).
In all patients, positive-pressure ventilation was provided using the selected airway device. The airway device was inserted successfully (defined as the ability to use the airway for positive-pressure ventilation) on the first attempt in 92% of the patients in the COPA group and in 88% of the patients in the LMA group (Table 2). No patient required more than two insertion attempts to obtain a satisfactory airway. The cuff volume was greater in the COPA group than in the LMA group (33 +/- 5 ml vs. 21 +/- 6 ml; P < 0.05), and the insertion time was significantly shorter with the COPA device (12 +/- 5 s vs. 27 +/- 13 s; P < 0.05). After the COPA was positioned initially, manipulations to the patient's upper airway or the device itself were necessary more frequently than with the LMA during the 15-min study period (8 vs. 1 patient; P < 0.05). These eight patients in the COPA group required a median of three manipulations (range, one to five manipulations) during the study.
Although the inspired (delivered) tidal volume was similar in both groups (Table 3), the expired tidal volume was significantly less in the COPA group (507 +/- 174 ml vs. 638 +/- 177 ml). As a result, the median calculated leak fraction was greater in the COPA group (0.28 vs. 0.16). In addition, more patients in the COPA group had a leak greater than 25% compared with the LMA group (60% vs. 28%). There were no differences in the peak or mean airway pressures, respiratory rates, or end-tidal carbon dioxide measurements. However, the pressure at which an oropharyngeal leak could be detected (leak pressure) was significantly less in the COPA group (22 +/- 6 cm water vs. 26 +/- 5 cm water; P < 0.05). The fresh gas flows rates could be reduced in both groups, but a mean minimum fresh gas flow rate less than 1.5 l/min was possible only with the LMA device.
All the anesthesia providers had previous experience inserting the LMA device (range, 5 to > 100 uses); however, only 20% had used a COPA device before (range, one to five uses). The median level of anesthesia experience was 3 yr in both groups (ranges: COPA, 1–24 yr; LMA, 1–25 yr). The responses to the questionnaire revealed that the ability to choose an appropriately sized device and to obtain a satisfactory airway seal was more difficult with the COPA compared with the LMA (Figure 1). Although the anesthesia providers had significantly less experience with the COPA, they thought that it was clearly easier to insert (91% scored insertion of the COPA as "easy" compared with only 72% who gave this rating in the LMA group;Figure 1).
This study shows that it is possible to provide positive-pressure ventilation in anesthetized adults using the LMA or COPA airway devices. Although all of the anesthesia providers in this study had some experience with the LMA device (median, 50 previous uses), only 20% had used the COPA device before. Despite the lack of experience with the COPA device, 91% of anesthesia providers rated it as easy to insert (compared with only 72% with the LMA device).
The mask size, cuff volume, fixation technique, degree of muscle relaxation, and position of the head and neck all influence the effectiveness of the seal established between the LMA and the upper airway.  These factors were standardized in both airway groups in an attempt to compare the ability to provide positive-pressure ventilation with the two devices. The cuff of the LMA creates a low-pressure seal around the glottis, and studies suggest that air leakage can occur during ventilation with peak inspiratory pressures in the range of 15–33 cm water. [9,11] In this study, an oropharyngeal leak occurred at a mean (+/- SD) peak airway pressure of 26 +/- 5 cm water (range, 16–38 cm water) with the LMA device. Two patients in the LMA group had leaks with an inspiratory pressure less than 20 cm water. Both patients were large men who weighed more than 80 kg and were taller than 180 cm. A recent article suggests that a size 5 LMA would be more effective in creating an airway seal in large men.  Unfortunately, the size 5 LMA was not available at our institution when this study was conducted, and therefore size 4 LMA devices were used for all the men. The leak pressure could have been greater in these two patients if the larger LMA device had been used.
Although it was possible to provide aided ventilation for all the patients with the COPA device, the adequacy of the seal and patency of the airway were less satisfactory with that device than with the LMA (Figure 1). The airway device or the patient's head position had to be manipulated to improve the airway seal in 32% of the patients who had the COPA compared with only 4% of those with the LMA. Even with these manipulations, the leak pressure and expired tidal volume were less (and the leak fraction was greater) with the COPA compared with the LMA device. The lower mean leak pressure suggests that the COPA would be less suitable for providing positive-pressure ventilation in obese patients and in those with decreased lung or chest wall compliance.
In this era of cost containment, low-flow anesthesia is becoming increasingly popular. The primary advantages of low-flow anesthesia include reduced waste of nitrous oxide and the volatile agent, reduced environmental and operating room pollution, and minimization of heat and fluid losses through the expired gases. Although the safety of flow rates less than 2 1/min with sevoflurane was initially questioned because of its degradation to compound A (a known nephrotoxin in rats),  recent study suggests that the renal effects of low-flow (1 l/min) sevoflurane were not different from those of isoflurane.  The use of low-flow and minimal-flow (0.5 l/min) anesthesia are possible with the LMA device,  but this technique has not been evaluated with the COPA. In this study, the mean (+/- SD) minimum gas flow rate was less with the LMA compared with the COPA (1.3 +/- 1.5 l/min vs. 2.4 +/- 2.5 l/min). However, this difference was not significant because of interpatient variability (LMA, 0.45–7.5 l/min; COPA, 0.55–9 l/min). Although it was possible to markedly reduce gas flow rates in most patients in both groups, some patients required high fresh gas flows to compensate for the presence of a leak even after the device was repositioned. The practitioner's limited experience with the COPA may have exacerbated the problem in this group because of inappropriate size selection.
One criticism of this study could be that patients did not receive any muscle relaxants while the positive-pressure ventilation was evaluated. However, to minimize the effect of chest wall compliance on the testing procedure, a standardized induction-maintenance technique was used and the evaluation was completed before the surgical procedure began. Residual muscle tone in the posterior pharynx also may have interfered with the ability to obtain an optimal seal with both airway devices. Because chest wall compliance is less in patients who are not paralyzed, greater peak inspiratory pressures must be used to ensure adequate ventilation. It would be interesting to perform a follow-up study with these airway devices in paralyzed patients.
In conclusion, positive-pressure ventilation is possible with the LMA and the COPA devices. Although the COPA device can be inserted more easily by inexperienced users, it is more difficult to obtain an adequate airway seal for positive-pressure ventilation, and additional manipulations may be necessary after insertion. The LMA provides a better airway seal, thereby allowing for ventilation with greater peak inspiratory pressures; however, the ease of insertion of the COPA device may make it an attractive alternative to the LMA for use by inexperienced medical personnel in emergency situations.