Abstract
Background: Even though laryngeal mask airways (LMAs) are the most commonly used airway in paediatric anaesthesia, little is known about the assessment of respiratory mechanics in this setting.
Methods: We measured respiratory resistance (R) and reactance (X) with forced oscillations at 16 Hz superimposed on spontaneous breathing following induction of anaesthesia. Children between 1.3 and 5.6 years of age (n=20) with healthy respiratory status were studied. R and X were corrected for the impedance of the LMA and other equipment parts.
Results: R exhibited large flow related fluctuations (Fig. 1) amounting on average to 169% and 180% in expiration and inspiration, while the changes in X were milder. Minimum R was attained at end expiration (10.2±3.6 hPa.s/L), much lower than the mean values for whole breaths (18.1±5.1 hPa.s/L). Fast flow transitions at end inspiration resulted in high R values (16.4±5.9 hPa.s/L). All R indices were significantly (r=-0.49 … -0.75) related to height.
Conclusions: LMA introduces marked flow-related nonlinearities in R, making the conventional assessment of the lower respiratory tract difficult. However, within-breath tracking identifies the flow-independent values of R and can be instructive for the proper placement of LMA.
Grant Support: HSRF (105403), NHMRC (APP1050427), ANZCA (AEG13/003) and Princess Margaret Hospital Foundation (9622).
- Copyright ©ERS 2015
