Effect of Laryngeal Mask Cuff Pressure in Geriatric Patients

This study received permission from Dokuz Eylül University Medical Faculty Non-Interventional Ethics Committee and informed consent was obtained from the patients. Ninety patients above the age of 65 with American Society of Anesthesiologists (ASA) physiological classification group I-III, undergoing elective surgery and with indications for laryngeal mask placement participated in this prospective, randomized and double blind study.

Patients taken to the operating room were given standard monitoring (ECG, pulse oxymetry, non-invasive blood pressure) and BIS monitoring [BIS-Vista ™ (Aspect Medical Systems, USA)] before anesthesia induction.

After patients were preoxygenated with 6 L/min oxygen through a face mask for 3 minutes anesthesia induction was provided by 0.02 mg/kg midazolam, 1-2 µg/kg fentanyl and 1-2 mg/kg propofol. During respiration Airway was not used, unless there was ventilation difficulty with the face mask. Before insertion the laryngeal mask used in daily routine (Laryngeal Mask Unique® (LMU)) was lubricated with a water-based gel and the cuff was completely deflated. After induction when bispectral index (BIS) values were between 40 and 60 and sufficient chin relaxation was obtained for patients weighing less than 50 kg no. 3 LMU, for those between 50-90 kg no. 4 and for patients above 90 kg no. 5 LMU was inserted by an anesthetist with more than five years experience. The placement method was according to the manufacturer's instructions. All patients were respirated by a breathing circuit with heat and moisture filter.

After the laryngeal mask was inserted the cases were manually respirated so peak inspiratory pressure was less than 20 cmH2O and the cuff of both groups was inflated with a 20 ml injector until the leak sound ceased. To evaluate ventilation the capnogram showed square wave forms and the patients' chest movements were observed, in unsuccessful situations the procedure was repeated. During attempts depending on the patients' reactions and with the requirement of keeping BIS values between 40 and 60, an additional dose of 0.5 mg/kg propofol was administered.

After Laryngeal Mask was determined and when anesthetic depth was sufficient (BIS 40-60) the inner pressure of the LMU cuff was measured and recorded by a manometer (cuff pressure manometer, Rusch, Germany). Later groups were divided in two using a random number table. In the group with cuff pressure limitation (Group Pressure Limiting (PL), n=45) cuff inner pressure was held below 60 cmH2O (44 mmHg), while the routine group (Group Routine Care, n=45) pressure was only recorded.

Anesthesia was maintained by 50% O2:50% air mix with 1.5-2.5% sevoflurane, with sevoflurane concentration and additional fentanyl doses arranged to keep BIS between 40 and 60. All patients were respirated with positive pressure ventilation tidal volume 7-8 ml/kg, inspiring: expiring rate 1:2, respiration frequency on the capnograph end tidal carbon dioxide held between 30-35 mmHg. Oropharyngeal leak pressure measurement was recorded as the pressure value when a leak sound was heard from the mouth after the expiring valve was closed and fresh gas flow was reduced to 3 L/min. Immediately after the laryngeal mask was inserted, every 5 minutes in the first half hour and every 15 minutes after that, tidal volume, mean airway pressure, end tidal carbon dioxide levels and peripheral oxygen saturation values were recorded. If the operation lasted more than one hour a second manometric measurement was taken and stable values were maintained.

After the operation, the LMU's were removed when the patients were awake and could open their mouths on an oral command and unless necessary, aspiration was not applied.After anesthesia the patients were monitored in the recovery unit and analgesia was provided by 5-10 mg intravenous dolantin titration. A researcher blind to the groups recorded throat pain, voice loss and difficulty swallowing in the 1st and 24th hour, classifying as Likert scale ranges from 1 (none) to 4 (severe). Cases developing rare complications of recurrent laryngeal nerve, hypoglossal nerve and lingual nerve paralysis were recorded. The cases were brought to the ward when Aldrete scoring criteria were appropriate. Cases discharged early from the ward had 24th hour evaluation by telephone communication.