Experimental study on the efficiency and safety of the manual hyperinflation maneuver as a secretion clearance technique

Abstract

Objective: To evaluate, in a lung model simulating a mechanically ventilated patient, the efficiency and safety of the manual hyperinflation (MH) maneuver as a means of removing pulmonary secretions.

Methods: Eight respiratory therapists (RTs) were asked to use a self-inflating manual resuscitator on a lung model to perform MH as if to remove secretions, under two conditions: as routinely applied during their clinical practice; and after receiving verbal instructions based on expert recommendations. In both conditions, three clinical scenarios were simulated: normal lung function, restrictive lung disease, and obstructive lung disease.

Results: Before instruction, it was common for an RT to compress the resuscitator bag two times, in rapid succession. Proximal pressure (Pprox) was higher before instruction than after. However, alveolar pressure (Palv) never exceeded 42.5 cmH₂O (median, 16.1; interquartile range [IQR], 11.7-24.5), despite Pprox values as high as 96.6 cmH₂O (median, 36.7; IQR, 22.9-49.4). The tidal volume (VT) generated was relatively low (median, 640 mL; IQR, 505-735), and peak inspiratory flow (PIF) often exceeded peak expiratory flow (PEF), the median values being 1.37 L/s (IQR, 0.99-1.90) and 1.01 L/s (IQR, 0.55-1.28), respectively. A PIF/PEF ratio < 0.9 (which theoretically favors mucus migration toward the central airways) was achieved in only 16.7% of the maneuvers.

Conclusions: Under the conditions tested, MH produced safe Palv levels despite high Pprox. However, the MH maneuver was often performed in a way that did not favor secretion removal (PIF exceeding PEF), even after instruction. The unfavorable PIF/ PEF ratio was attributable to overly rapid inflations and low VT.

Figures

Figure 1. Experimental setup.

Figure 2. Differences in proximal pressures achieved by two different respiratory therapists (A and B) before and after explicit verbal instruction (routine clinical practice vs. expert recommendations-dashed lines and solid lines, respectively).

Figure 3. Median values of proximal and alveolar pressures (interquartile ranges as error bars) obtained in the pre-instruction (routine clinical practice) and post-instruction (in accordance with expert recommendations) phases of the study. The major effect of instruction was the generation of lower proximal pressures. The dashed line indicates 30 cmH2O. *p

Figure 4. Median values for peak inspiratory and expiratory flows (interquartile ranges as error bars) obtained in the pre-instruction (routine clinical practice) and post-instruction (in accordance with expert recommendations) phases of the study. The major effect of instruction was the generation of lower peak inspiratory flow. The dashed line indicates 1 L/sec. *p