Changes in the intracuff pressure of the laryngeal masks airway caused by repeated use.

PURPOSE To observe the changes in permeability and elasticity in the cuff of the laryngeal mask airway (LMA) caused by repeated use. METHODS In vitro use was simulated on six # 4 LMAs on 140 occasions. Ambient air was insufflated into the cuff until a value of 200 mmHg intracuff pressure (ICP) was reached, and this was maintained for 50 min. After each simulation, the LMA was sterilized at 121 degrees C for 20 min. After every 20 simulations insufflation of 40 ml air was carried out to determine the maximum value of ICP (initial ICP), and after three hours, spontaneous deflation (final ICP) was measured. The values of initial and final ICPs throughout the eight tests were attributed to the elastance and the permeability of the cuff respectively. At the end of the study the thickness of the wall of the cuffs was measured using an optical microscope. RESULTS The initial ICP with the new LMA (first test) was of 191 +/- 4.4 mmHg. This value increased from the fifth test onwards until the end of the study. The value of the final ICP in the first test was 111 +/- 3 mmHg and decreased with successive sterilizations. Between 80 and 100 simulations, initial ICP increased from 186.5 +/- 2.9 to 191.7 +/- 2.3 (P = 0.006). The thickness of the wall (694 +/- 17 microns) was inversely related with the elasticity and the permeability of the cuff. CONCLUSIONS The "safe" life-span of the cuff of the LMAs, measured by the initial modifications of the physical properties of the silicone during simulations, was estimated to be 80-100 uses and was related to the thickness of its wall.