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. 2008 Nov;43(11):1085-1091.
doi: 10.1002/ppul.20905.

Measurement of maximal inspiratory pressure in ventilated children

Gopinathannair Harikumar  1   2 , John Moxham  1   3 , Anne Greenough  1   2 , Gerrard F Rafferty  1   2   3
Affiliations

Measurement of maximal inspiratory pressure in ventilated children

Gopinathannair Harikumar et al. Pediatr Pulmonol. 2008 Nov.

Abstract

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX(OCC)) to that when a unidirectional valve (PIMAX(UNI)), which allowed expiration, but not inspiration was used. Twenty-two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX(UNI) was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX(UNI) (45.5 (15.2) cmH(2)O) was significantly greater than mean (SD) PIMAX(OCC) (30.9 (9.0) cmH(2)O) (P < 0.0001). The mean (SD) expired volume during PIMAX(UNI), was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15 sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 sec or eight breaths (99% CI of mean).

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Figures

Fig 1
Fig 1
A diagram of the 3 way slide valve and its position in the ventilator circuit. Arrows show direction of airflow with the valve positioned at standby, for PIMAXOCC and PIMAXUNI
Fig 2
Fig 2
Bland and Altman plot of the agreement between PIMAXOCC and PIMAXUNI with the mean of PIMAXOCC and PIMAXUNI plotted on the horizontal axis and the difference between PIMAXOCC and PIMAXUNI plotted on the vertical axis. Dashed lines represent the mean difference and 2SD
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