Catalina María Álvarez^*, Sergio Cárdenas^*, Mónica Lucía Soto^**, Héctor Darío Arroyave^***, Iván Darío Arenas^****, Nelson Javier González^****

* MD. Estudiante de posgrado en Anestesiología y Reanimación, Universidad de Antioquia, Medellín, Colombia Email: ivaren2@yahoo.com
** MD. Epidemióloga, Universidad de Antioquia, Medellín, Colombia
*** MD. Anestesiólogo intensivista, profesor titular, Universidad de Antioquia, Medellín, Colombia
**** MD. Anestesiólogo, profesor titular, Universidad de Antioquia, Medellín, Colombia

Recibido: octubre 19/2009 - Aceptado: noviembre 11/2009

Surgical procedures have been dynamised during the last few decades, leading to endotracheal intubation becoming unnecessary in many cases; this has been the reference procedure for airway management in patients under general anaesthesia but implying greater anaesthetic depth and leading to greater risks being associated with its insertion.(1)

New devices have been developed in the search for optimising airway management in short-duration or low-complexity surgical procedures, called supraglotic or extraglotic.(2,3,4) The classic laryngeal mask airway (CLMA) is the extraglotic device which is most used around the world in outpatient surgery; however, in spite of its success, it requires being refitted to make it comfortable in 5% to 10% of cases. (5,6,7,8) it is not recommended patients requiring greater than 20 cm H₂O peak airway pressure. (9,10,11) Other devices have thus been designed, such as the laryngeal mask airway Supreme (LMA-S) offering theoretical advantages such as having greater airway sealing pressure (reported as being up to 37 cm H₂0) (12), easier to insert, aspiring gastric content and reducing the risk of diseases being transmitted by this being a single-use device.

The Latin-American population has average airway anthropometric characteristics differing from north-American and European populations, as observed by Tintinago (13,14) when studying his larynx transplant patients; (15) such differences could alter airway device effectiveness. (16) The ease of inserting extraglotic devices generally leads to a shorter learning curve than that required for suitable laryngoscopy and intubation, less training being needed and their use as airway management devices at many levels being facilitated. (17) No articles have been published in the literature to date evaluating medical trainees inserting LMA-S in the Latin-American population.

This was a randomised, double-blind (patient and analyst), clinical trial which took place in a single centre; its hypothesis was that LMA-S provided equal or better airway sealing pressure than CLMA when inserted into adult patients undergoing outpatient ophthalmology surgery by trainee medical personnel (medical interns and residents studying anaesthesiology) having had previous training in how to insert the devices during studies on dummies.

The personnel who installed the device

Six first- and second-year anaesthesiology interns and six residents received training by the Universidad de Antioquia´s Difficult Airway group in the university´s simulation centred. They were trained in inserting both devices, training being considered to have been suitable when participants managed to successfully inset the device a minimum of 10 times on the dummy.

Two undergraduate medicine students from the Universidad de Antioquia collected data throughout the study from July to September 2008, supervised by the anaesthesiologist.

All patients complying with the inclusion criteria were consecutively included during preanaesthetic evaluation, once the study had been explained to them and they had signed the informed consent form. They were programmed for surgery and assigned a number corresponding to the random distribution at the same time; this was defined by a random number generator (001 to 100 sequence), corresponding to the devices being evaluated. Out of the 100 patients in the random distribution, two did not agree to participate in the study and one had incomplete fasting, meaning that they were excluded from the study. The 97 remaining patients were assigned as follows: 47 in the LMA-S group (intervened group) and 50 in the CLMA group ( control group).

An anaesthesiologist responsible for the patients´ pharmacological management was present throughout the whole procedure; he had experience in airway management and knew about the study and only intervened in airway management when difficulties were presented. Due to the study´s characteristics, it was understood that the person who inserted the device could not be blinded; however, to avoid possible classification bias, the person who collected the information was different to the person carrying out the procedure.

The device´s good working state was tested before induction, as was that of the anaesthesia machine (Datex Ohmeda Excel 210), thereby verifying the absence of leaks. The device´s size was chosen according to a patient´s weight, as recommended by the manufacturer: size 3, 30-49 kg; size 4, 50-69 kg; size 5, 70-99 kg; and size 6, more than 100 kg. All patients were monitored via cardioscope, capnography, non-invasive arterial pressure, pulse oximetry and gas analyser.

All patients were supplied with high flow oxygen (7 L per minute) during the preoxygen period, two minutes before endovenous induction was begun. Conventional induction included: 1-2 mg/kg intravenous (IV) lidocaine, 1-2 ug/kg IV phentanyl, 2 mg/kg IV propofol and 0.1-0.3 mg/kg rocuronium. 4 mg IV dexamethasone was applied at the same time and analgesia during the surgery was achieved with 40 mg/kg dipyrone, 1 mg/kg dychlophenac and 0.05 mg/kg IV morphine.

The posterior parts of the devices were lubricated with hydrosoluble gel. Once a suitable anaesthetic depth had been achieved, determined by clinical means (the absence of corneal reflex, loss of force in extensor muscles and apnoea), the device was inserted and its balloon inflated with a manometer (VBM Medizintechnik GmbH, Ref. 5407000) until mean pressure reached 60 cm H₂O so that the device could then be connected to the anaesthesia machine´s circuit.

The person responsible for collecting the data timed each device´s insertion from the point where this passed a patient´s incisor teeth until it connected to the circuit´s tubes. Sealing quality was classified as: 1: no leaks; 2: leak <200 ml; 3: leak >200 ml which corrects itself with flow increased to 2 litres; 4: leak >200 ml which does not correct itself. If the anaesthesiologist determined that the device was not functioning correctly, he repositioned it, and if it failed again then it was replaced. If the patient was from the LMA-S group, then the device was initially replaced by CLMA and if from this group then by orotracheal tube.

Once correct functioning had been confirmed, then sealing pressure was measured by closing the valve (APL) and fresh gas flow increased to 10 litres. the pressure generated in the circuit was observed until leaks were presented and sealing pressure was marked once the barometer nee dle became stabilised. The valve was released if pressure reached 40 cm H₂O.

Anaesthetic maintenance was done with 2%-3.5% sevoflurane with 1 L per minute 100% O₂ fresh gas flow. Respirators were programmed with 8 ml/kg tidal volume, 10 per minute respiratory frequency, without positive end-expiratory pressure (PEEP) and 1:2 inspiration:expiration ratio.

The assistant recorded ventilation variables and, once surgical intervention was over, recorded the presence or absence of macroscopically visible blood in the device, as: 1: abundant; 2: pints; 3: scarce, or 4: absent. This was an indicator of trauma in the airway or oropharynx in our study. Events related to the airway were also recorded, such as bronchospasm, laryngospasm or cough both during surgery and immediate postoperative period.

A blinded observer questioned the patients one hour and 24 hours after finishing the procedure about the presence of any discomfort in the airway and upper digestive route.

Simple size was calculated on published research involving extraglotic devices (9,18,19). Such literature reported that average LMA-S sealing pressure could reach 37 cm H₂O and 20 cm H₂O for average CLMA sealing pressure (10 and 15 cm H₂O standard deviations, respectively). According to the number of outpatient procedures carried out in the Universidad de Antioquia´s IPS, it was considered feasible to complete the sample size of 84 patients corresponding to 90% power for detecting a 10 cm H₂O average minimum difference and 0.05 a error (with 10% adjustment for patients where the device had to be changed).

The Medical Research Institute was responsible for the study´s internal control. The investigation was approved by the ethics committee from the Universidad de Antioquia´s Faculty of Medicine´s University IPS. Informed consent was signed by all the patients who were included in the study.

Statistical analysis

Assigning interventions corresponding to CLMA and LMA-S devices was defined by a random number generator (001 to 100 sequence). The assignation was kept safe in a file in the data coordinating centre and remained unknown by the team of investigators until the data was analysed.

Collected data was recorded on a form and then stored in a database created in EPI Info 6.0. Effectiveness was analysed from when treatment began. Continuous variables were compared as average differences in insertion time and sealing pressure with their respective standard deviations, 95% exact confidence intervals and analysed by Kruskal-Wallis test (α 0.05%).

Categorical variables were compared as percentages of failed attempts, fall of the bellows, capnography level above initial one and the presence of bleeding and dysphagia, having 95% exact confidence intervals; the statistical test used was the Chi-squared test. Final results were adjusted for independent variables different to intervention were heterogeneously distributed amongst the groups.

All patients were undergoing ophthalmology surgery, 44 for extraction of a cataract by facoemulsification, 44 for extracapsular cataract extraction and the remaining 9 patients were undergoing other surgery including trabeculectomy, reduction of hernia of the iris and anterior chamber implant. Females represented 56% of the patients and their frequency was greater in the group in which LMA-S was used. Detected preoperative morbidity was similar in both groups (table 1).

Flowchart

Heavy smoking was an important part of patients´ background was present in 22.6% of the patients; 80% of them had some morbidity (78/97) and 57.69% (45/78) presented an associated diagnosis. The most frequent diagnoses were arterial hypertension (51/78), diabetes mellitus (14/78), hypothyroidism (6/78), osteoarticular diseases (4/78) and EPOC (3/78).(figure 1)

The LMA-S device´s sealing pressure measurement was greater immediately after insertion and after its extraction, such differences being statistically significant (table 2) . Even though mean balloon pressure was higher before withdrawing the CLMA device, this was not statistically significant.

There were no differences in intraoperative complications between both groups; laryngospasm and cough were the only two complications presented in 8.42% of the patients and these were resolved without any adverse effects. No bleeding of any importance was presented in either of the groups and no relationship between postoperative bleeding and adverse effects found were observed. Dysphagia and cough were the postoperative adverse effects related to the use of the devices, being present in 11% (10/88) of the patients.

BMI, weight, height and thyroid-chin distance results were lower in females than males (p<0.05); however, these parameters were similarly distributed in both groups.

As surgical techniques have evolved, so have procedures been developed which do not require endotracheal intubation due to their characteristics regarding duration and low demand for anaesthetic depth. (1) New devices known as extraglotics have been developed which allow respiratory assistance for patients having minor airway invasion. (2,3,4) The one currently having greater theoretical-practical recognition is CLMA; however, in spite of the great benefits associated with it, it does have limitations for managing patients who might require greater than 20 cm H₂O airway pressure, (9, 10,11) as is the case for those suffering from EPOC, asthma and/or obesity.

The same average CLMA sealing pressures were found in our study as those found in other studies. (9, 10,11) It can be confirmed that average LMA-S airway sealing pressure was greater compared to CLMA. Average LMA-S sealing pressure found in our study population was similar to that found by S. Eschertzhuber; (20) however, it did not reach the 37 cm H₂O reported by A. Zundert. (12) This could be partly explained by the study population which mainly consisted of older adults, such population group frequently having no teeth.

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Conflicto de intereses: ninguno declarado.