Experimental study on the efficiency and safety of the manual hyperinflation maneuver as a secretion clearance technique* , ** Estudo experimental sobre a eficiência e segurança da manobra de hiperinsuflação manual como técnica de remoção de secreção

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 (P prox ) was higher before instruction than after. However, alveolar pressure (P alv ) never exceeded 42.5 cmH 2 O (median, 16.1; interquartile range [IQR], 11.7-24.5), despite P prox values as high as 96.6 cmH 2 O (median, 36.7; IQR, 22.9-49.4). The tidal volume (V T ) 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 P alv levels despite high P prox . 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 V T .