The laryngeal mask airway (LMA) has been newly introduced to anaesthesia practice as an alternative to the endotracheal tube (ETT) or face mask for airway management. It is capable of providing a rapid and easily achieved patent airway that permits positive pressure ventilation within confined limits. In this study, we aim to evaluate the role of the LMA in cardiopulmonary resuscitation (CPR) in 20 patients as an alternative to tracheal intubation. Study parameters included measurement of oxygen saturation by a pulse oximeter and end-tidal carbon dioxide level (ETCO₂) using the Fenem CO₂ analyser. Five of these 20 cases were resuscitated using endotracheal tubes as a control group. Seven cases were resuscitated using LMA only and eight cases were resuscitated using LMA initially followed by ETT for long term ventilation. In the LMA groups I and III, 12 patients had LMA inserted at the first attempt and three at a second attempt. We concluded that LMA is a good alternative to ETT, although it may not protect against aspiration. We recommend it to be included in CPR chart cards and all medical doctors, nurses and paramedical staff should learn how to use it.

Keywords.- Equipment; Emergency airway; Laryngeal mask; Resuscitation: Basic support

The pre-requisite for adequate resuscitation is the rapid attainment of a clear airway allowing subsequent administration of oxygen. Many devices have been introduced to fulfill this requirement; examples include the oesophageal obturator airway and oesophageal tracheal 'combitube'. All these devices aim to isolate the pulmonary tree from the gastrointestinal tract by intubation of the oesophagus. Still aspiration does occur and experience is needed as damage during insertion can be caused. Devices avoiding penetrating the oesophageal sphincters are less invasive - examples include the Brook airway, the Safar 'S' airway and the Laerdal pocket mask, although none of these offer protection against aspiration. The laryngeal mask airway (LMA) is a new device which avoids penetration of either the glottis or the oesophageal sphincter; it provides rapid and easy airway control[l]. Our study was aimed at assessing the efficacy of LMA as an alternative to the tracheal tube during cardiopulmonary resuscitation.

The study was approved by the Hospital Ethical Committee. All the investigators were trained to use LMA on a manikin and during elective surgery, an instructional video was shown to all.

During the course of the study, all the cardiopulmonary resuscitation (CPR) calls were covered by the investigator and LMA was applied as the principal technique in place of endotracheal intubation. The study resuscitation team was composed of a consultant and registrar from amongst the investigators. Twenty cases of eight males and 12 females were studied. The patients were classified into three groups based on the method of respiratory resuscitation. Seven patients in Group I had only LMA to secure a patent airway. Five patients in Group II had only an endotracheal tube and eight patients in Group III had LMA at the start of resuscitation and then endotracheal intubation was performed to maintain long-term ventilation. Patients already intubated, who required resuscitation, were excluded.

During CPR the patients were connected with the monitoring apparatus which included an electrocardiograph (ECG), a pulse oximeter and a CO₂ analyser using the Fenem Colour indicator. The LMA was inserted according to the standard directions supplied in the manufacturer's manual and checked to ensure that it was sited correctly by gentle inflation of the lung whilst auscultation of the chest was performed. Two attempts at LMA insertion were permitted. If insertion failed, an ETT was inserted and 100% oxygen delivered via the breathing circuit. External chest compression was integrated with the ventilation of the airway according to the Resuscitation Council (UK) guidelines. CPR was continued until the patient was successfully revived or the resuscitation was abandoned on clinical grounds. If the patient required extended ventilation, the LMA was changed for an endotracheal tube. Following successful resuscitation, the LMA was removed when the patient's cough reflex and other vital signs became stable. The arterial blood gases (ABG) were performed by one of the investigators during CPR. The following parameters were noted: (a) arrest time (from onset of arrest to start of CPR); (b) LMA size and any difficulties with insertion; (c) oxygen saturation; (d) end tidal carbon dioxide; (e) ABG results and (f) outcome of CPR.

The patients studied were of both sexes (eight males and 12 females) with a mean age of 54 ± 24 years and a mean weight of 69 ± 17 kg. The cardiac arrests being studied were in the following locations: four in the emergency department, nine on the medical wards, three in the ICU and four on the surgical floor. Eighteen patients had asystole and two patients had severe bradycardia. The aetiology of arrest was variable and 10 patients had multi-organ failure, four of cardiac origin, five of pulmonary origin and one patient of oncology origin. The arrest time (i.e. from onset of arrest to start of CPR) in 18 patients was within a range of 1-5 min and only two patients exceeded 10 min. Among the patients in Groups I and III, three patients had two attempts for insertion of LMA but none of the other cases needed any other intervention (i.e. repositioning or re-inflation of the LMA); only one patient had partial airway obstruction. The insertion attempt did not fail in any patient.

The mean values (± S.D.) of S_P0₂ and ETCO₂ (measured by a Fenem analyser) are given in Tables 1 and 2, respectively for the three groups. S_P0₂ ranged between 50-98 for Group I, 77-89 in group II, and 80.4-91.6 for group III. ETC0₂ ranged between 2.2-4.0% in group I and 3.3-5.3% in group III.

The CPR time (min) for the successful resuscitation groups (11 patients) was 14.9 ± 7.6 min (mean ± S.D.) and for the unsuccessful groups (nine patients) was 30.5 ± 8.8 min (mean ± S.D.), respectively.

In two patients of Group III who had a successful outcome, endotracheal intubation was difficult to achieve, and the LMA was used for ventilation very successfully. No instances of aspiration were detected with the use of LMA.

Group n ETCO₂

Following its recent introduction, the laryngeal mask airway has proved a useful alternative to endotracheal intubation for emergency resuscitation [2], providing rapid attainment of a clear airway and a reliable means of oxygen administration. Although the introduction of an endotracheal tube has been the technique of choice, this requires an advanced skill and may prove difficult and sometimes impossible. In order to avoid the need for this skill, whilst ensuring protection of the lungs from aspiration, alternative emergency devices have themselves become more complicated than the endotracheal tube. Examples of such devices include the oesophageal obturator airway described in 1968 [3,4] and the oesophageal gastric tube airway [5]. More recently, the pharyngo-tracheal lumen airway [6] and the oesophageal tracheal 'Combitube' [7] have been introduced. All avoid the need to visualise the larynx, but may penetrate either the glottic or the oesophageal lumen and, while the intention is generally to intubate the oesophagus, in practice damage may occur to either structure [8]. There is also the added uncertainty for the inexperienced operator in knowing which passage has been intubated [9]. Devices which avoid penetrating sphincters, but aim at providing a clear airway by supporting the back of the tongue are inherently less invasive and their use is easily taught inside and outside the hospital environment [9].

Our study showed that of the LMA insertion attempts in the patients in Groups I and III, three patients had two attempts but none of the other cases needed any further intervention; only one patient had partial airway obstruction after LMA insertion. The mean value of oxygen saturation which was measured by pulse oximeter (Ohmeda) is shown in Table 1. The end-tidal C0₂ level was measured by Fenem colour analyser and is shown in Table 2.

One patient in Group I, a 65-year-old female who was obese (> 90kg) had a respiratory arrest. Endotracheal intubation was difficult to achieve, hence LMA was used for ventilation very successfully. Her initial oxygen saturation dropped to 35% but improved to 99% with the LMA. She made a full recovery.

Regurgitation was not seen in any case in our study. One study [9] that examined the incidence of pulmonary aspiration, comparing the use of the oesophageal obturator and the endotracheal tube, found that aspiration occurred in 4.1% and 0.7%, respectively (P = 0.05). Furthermore, devices which maintain the airway by means of mechanical support of the tongue, e.g. Brook's airway, Safar 'S' airway and the Laerdal pocket mask, remain incapable of preventing aspiration of gastric contents.

John et al. [10] studied airway protection by LMA. Methylene blue was placed in the pharynx of 64 adult patients undergoing surgery under general anaesthesia. With LMA, they found no leak of the dye into the larynx in any patient with fibreoptic inspection of the inside of the mask. Leach et al. [11] used LMA in CPR in district hospitals as an initial method of airway control. Forty patients were included; LMA failed on two occasions and was successful in three cases where ETT was impossible. No aspiration occurred in any patient with LMA, thus it can be regarded as a protection or a guard against aspiration in the emergency situation.

In conclusion, we think that the LMA method is a good alternative to ETT in CPR, but it may not offer absolute protection against aspiration. We recommend that it is listed on the CPR chart card and that all doctors, nurses and paramedics should know how to use it.

Dr Imtiaz Hussain, Department of Surgery and Dr Amir Channa, Department of Anaesthesia, King Khalid University Hospital, Riyadh, Saudi Arabia for revising and editing the manuscript. Maureen Meek for typing the manuscript.