The effect of circuit type, volume delivered and "rapid release" on flow rates during manual hyperinflation

Traditionally, manual hyperinflation has been performed using "rapid release" to promote a fast peak expiratory flow rate (PEFR) but rapid release has not been described. In addition, it has been demonstrated that different resuscitation circuits provide varying degrees of resistance to expiratory flow and it is known that a variety of circuits are used in Australia for manual hyperinflation. The aim of this study was to document current practice, the effect of rapid release, controlling inspiration, different volumes and circuit type on flow rates, and the inspiratory to expiratory flow rate (I:E) ratio during manual hyperinflation. Using a test lung model, 15 physiotherapists performed 11 trials using the Air Viva 2, a Mapleson-C and a Mapleson-F circuit, both with and without rapid release, and delivering two volumes. The order of the trials was randomised. Rapid release produced a faster PEFR irrespective of circuit type or volume delivered. The effect of rapid release, and the absolute PEFR, was less for the Air Viva 2 compared with the Mapleson circuits. Expiratory flow rate was faster for the larger volume. The theoretically optimal I:E ratio to move secretions was achieved delivering the lower target volume with the Mapleson circuits and using rapid release.