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Original Papers

Comparative evaluation of the prolonged use of the cuffed oropharyngeal airway and the laryngeal mask airway in spontaneously breathing anaesthetized patients

Voyagis, G. S.; Dimitriou, V. K.; Kyriakis, K. P.

Author Information
European Journal of Anaesthesiology: June 1999 - Volume 16 - Issue 6 - p 371-375

Abstract

Introduction

The cuffed oropharyngeal airway (COPA) is a modified Guedel airway with an inflatable distal cuff and a standard proximal 15-mm connector for direct attachment to the breathing system. The device performs as a non-invasive aid in airway management and is recommended either for anaesthesia with spontaneous ventilation [1] or for supporting the airway of patients emerging from a general anaesthetic [2,3].

The purpose of the present study was to assess objective differences between the COPA and the laryngeal mask airway (LMA) with respect to airway quality and frequency of intra-operative respiratory adverse events in spontaneously breathing anaesthetized patients undergoing procedures of intermediate or prolonged duration.

Materials and methods

The Medical Ethics Committee of our institution approved the study protocol. The study was conducted on 140 consenting adult patients, ASA physical status I-III, undergoing general anaesthesia with spontaneous breathing for elective limb or surface procedures lasting more than 1 h. Patients were randomly assigned to one of two airway management groups (COPA, n = 72; LMA, n = 68). Exclusion criteria are outlined in Table 1[4,5]. Two senior anaesthetists carried out the patients' airway assessment, the induction and maintenance of anaesthesia and the airway control. An assistant managed the recording of the trial according to the protocol.

Table 1
Table 1:
Exclusion criteria

All patients were premedicated with temazepam 20 mg orally 2 h before surgery. The selection of size for both airway devices was carried out using the manufacturers' guidelines [1,6,7]. After insertion of an intravenous (i.v.) cannula and placement of routine intra-operative monitoring devices (electrocardiograph, pulse oximeter, capnograph, non-invasive blood pressure monitor and tidal volume monitor) patients received a standard anaesthetic induction consisting of i.v. fentanyl 1 μg kg−1 and propofol 2 mg kg−1 given over 30 s. Additional boluses of propofol 30-mg could be given at the discretion of the anaesthetist until an adequate level of anaesthesia was obtained. After loss of eye lid reflex, the LMA or the COPA was inserted and the cuff was inflated according to the manufacturers' guidelines [1,6,7]. Adequacy of ventilation was assessed by gently squeezing the reservoir bag and observing chest movement. If it was difficult to ventilate the patient's lungs, airway manipulations (head tilt, chin lift, jaw thrust, external laryngeal pressure) were used as necessary and recorded. Whenever a second or third insertion attempt was required, the anaesthetist was free to try an alternate size. If the anaesthetist could not establish effectively an airway using the initially randomized airway device after three insertion attempts, then the alternative device was used. The number of the insertion attempts required and the final airway control outcome were recorded.

Anaesthesia was maintained with sevoflurane 1-4% and nitrous oxide up to 66% as clinically indicated. Whenever the patient presented coughing, gagging, laryngospasm or body movements, a supplemental 30-mg bolus dose of propofol was given. Supplemental doses of fentanyl 25 μg were administered when required. Ventilation was manually assisted until a regular breathing pattern was established. The airway leak pressures and the respective maximum tidal volumes achieved were measured and recorded when the anaesthetist obtained an acceptable airway immediately after appropriate placement of the device. Leak pressure was determined by closing the expiratory valve of the circuit and noting the airway pressure (measured in the circuit) at which an air leak occurred into the mouth [1]. The inspired tidal volume was not standardized, but gentle manual positive pressure ventilation (PPV) was carried out in order to achieve a peak inspiratory pressure of 15 cmH2O. The inappropriate oropharyngeal air leak was determined as the inability to achieve a seal pressure at 15 cm H2O [8]. The expired tidal volumes were measured using a disposable turbine vane transducer (OhmedaR 5420 volume monitor) which was attached at the Y-piece connection.

Vital signs were recorded before induction, at 1-min intervals until the restoration of spontaneous breathing and every 5 min until the device was removed. The presence of respiratory adverse events (regurgitation, aspiration, laryngospasm, coughing, gagging, oxygen haemoglobin desaturation persisting more than 30 s and hypercarbia persisting more than 3 min) was recorded. The severity of desaturation and hypercarbia was graded as follows; severe desaturation: peripheral oxygen saturation (SpO2) < 90%, moderate desaturation: SpO2 = 90-94%, severe hypercarbia: end-tidal carbon dioxide (ETCO2) > 7 kPa, moderate hypercarbia: ETCO2 = 6.0-7 kPa.

Different frequencies were analysed by the Fisher's exact test, χ2-test Yates corrected and the respective 95% confidence limits for odds ratio (OR) were calculated. Overall stratified analysis of the airway quality was carried out by the Mantel-Haenszel χ2-test Yates corrected and OR and the exact confidence limits were calculated. Differences in continuous variables were assessed by paired t-tests. A P-value < 0.05 was considered to be statistically significant in all cases.

Results

Table 2 shows demographic and surgical details. Randomization was successful in balancing the study groups with respect to age, weight, gender, ASA physical status and type or duration of surgical procedures.

Table 2
Table 2:
Demographic data of patients in both groups

Groups were not different when comparing the first-time successful insertion rates (COPA: 94.5%, LMA: 95.6%; P=0.9). Table 3 shows the distribution of frequencies of the airway quality problems (overall stratified analysis; P<0.0001, OR=4.6, exact confidence limits: 2.1 < OR < 11.3). During the post-induction apnoeic period it was possible to ventilate all patients until spontaneous breathing resumed. The mean (SD) leak pressure was significantly lower with the COPA, than with the LMA; COPA, 18 (4) cm H2O compared with LMA, 22 (3) cm H2O; P<0.0001. However, the groups were not different when comparing the mean (SD) values of the tidal volumes achieved during manual PPV; COPA, 9.5 (4) mL kg−1 compared with LMA, 10.5 (4.5) mL kg−1; P=0.09.

Table 3
Table 3:
Incidence of airway quality problems by patient event

Table 4 shows the distribution of the frequencies of the intra-operative respiratory adverse events. Statistical analysis revealed that the groups were not different when comparing, either the incidence of each adverse event separately, or the overall number of patients with one or more respiratory adverse event. No patient required intensive care management or any additional treatment post-operatively.

Table 4
Table 4:
Incidence of respiratory adverse events by patient event

Discussion

The data presented here were collected [9] before the results of other studies [1,10,11] were published. The present study compared the overall airway and respiratory problems arising during the usage of the COPA and the LMA in spontaneously breathing patients undergoing general anaesthesia of intermediate or prolonged duration. In general, both devices seem to be equivalent, because they were effective in establishing a clinically patent airway and proved to be similar with respect to the incidence of respiratory adverse events. However, this study also revealed some significant differences with respect to the degree of difficulty in achieving an effective air-tight seal in the pharynx during manual PPV. The latter may reflect the variations in the design of the airway devices in which their distal end is fitted in a different anatomical location in the oropharynx or laryngopharynx [12].

The COPA is inserted easily by following a Guedel-type insertion manouevre [13], which is a simple technique and well-known by all anaesthetists. However, the easy insertion is not necessarily associated with a clinically patent airway, since the ventilation through the COPA may fail in up to 50% of patients after the first insertion attempt [1,10]. The results of our study demonstrate that immediately after the first insertion of the COPA there existed clinical signs of inappropriate airway control in 26 of 72 patients (36%) (Table 3). After adjustment of the patient's head and neck and/or the performance of a second or third insertion attempt there remained a leak pressure of lower than 15 cmH2O in 14 of 72 patients (19.5%). In two of the 14 there was a failure to achieve a clinically patent airway and thereafter the use of COPA was abandoned and an LMA was used successfully as an alternative airway device (Table 3). On the other hand, the statistical analysis revealed that the use of LMA is associated with a five-fold decrease in the overall frequency of airway quality problems when compared with the COPA.

The difference seen in leak pressure between the devices is explained by the fact that the LMA cuff is more tightly applied to the glottis, whereas the COPA plugs the tissues in the more extensive and compliant hypopharynx [1]. Manual IPPV through the COPA seems to offer similar tidal volumes when compared with the LMA, although the leak pressure seen with the COPA is lower. The latter could be attributed to the fact that the flexible bars in the bowl of the LMA may impede gas flow and lead to increased resistance to breathing [14], whereas the distal orifice of the lumen of the COPA is entirely open and the resistance to gas flow seems to be relatively lower.

There is a plethora of studies addressing the adequacy of ventilation during PPV with the LMA at ventilation pressures varying from 15 to 30 cmH2O [8,15-20]. Brimacombe has shown that 98% of patients could be ventilated with LMA at tidal volumes of 10 mL kg−1 without an oropharyngeal air leak [20] and Van Damme assessed leak pressures in 4866 patients and showed that a leak pressure of lower than 15 cmH2O occurred in only 3% of patients [8]. On the contrary, there is sparsity of data regarding the efficacy of IPPV with the COPA. The conclusions resulting from a limited series of data [11] demonstrate that the mean tidal volume achieved with the COPA was only 5.5 mL kg−1. The respective value demonstrated in the current study was found to be 9.5 mL kg−1. This disagreement between our findings and that of the previous study [11] should be attributed to the fact that Koga et al. ventilated their patients mechanically.

The data presented here suggest that COPA does not differ from the LMA with respect to the frequencies of intra-operative adverse events that could lead to significant respiratory problems. These frequencies were similar as in previous trials investigating both the LMA [8,21-24] and the COPA [10,24]. In a previous multicentre study, Greenberg et al.[1] demonstrated higher frequencies of respiratory events, either with COPA, or with LMA, when compared with our findings. The incidence of oxygen haemoglobin desaturation (SpO2 < 92%) was 10% with COPA and 7% with LMA [1], whereas the respective frequency of desaturation (SpO2 < 90%) was 3%, either with COPA, or with LMA in the current study. Additionally, the incidence of coughing or gagging was 11% with COPA and 10% with LMA, compared with 6% and 7.5%, respectively, for the current study. The factors producing a lower event rate in the present study may include different thresholds for identifying haemoglobin desaturation, maintenance of anaesthesia by using a volatile agent rather than an intravenous and the anaesthetist's clinical experience with each airway device. Both investigators had been exposed previously, either to LMA with more than 750 uses, or to COPA with more than 50 uses.

The high incidence of moderate hypercarbia, either with COPA, or with LMA seem to be acceptable, because during prolonged spontaneous breathing ETCO2 levels tend to rise depending on the depth of anaesthesia and the plasma levels of other respiratory depressant drugs [12].

We conclude that both devices are equivalent with respect to the overall respiratory problems occuring during spontaneous breathing anaesthesia of intermediate or prolonged duration. However, the LMA is associated with fewer airway quality problems, suggesting that it is more efficacious in securing the airway.

References

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    Keywords:

    GENERAL ANAESTHESIA; AIRWAY DEVICES; AIRWAY MANAGEMENT; COMPLICATIONS

    © 1999 European Society of Anaesthesiology