The unique contribution of manual chest compression–vibrations to airﬂow during physiotherapy in sedated, fully ventilated children* Rachael K. Gregson, PhD; Harriet Shannon, PhD; Janet Stocks, PhD; Tim J. Cole, PhD; Mark J. Peters, MD; Eleanor Main, PhD E ndotracheal intubation with mechanical ventilation is an essential component of inten- sive care; however, it is also associated with compromised airway clearance. The endotracheal tube can ir- ritate the wall of the trachea causing mi- crotrauma, resulting in mucus hyperse- cretion. Mucociliary transport stops at the tip of the endotracheal tube, where mucus is likely to pool (1), and the ability to cough is also weakened by muscle re- laxants and sedation used during ventila- tory support. The result is an increased risk of airway occlusion and atelectasis. One of the aims of chest physiotherapy is to remove excess mucus and optimize ventilation in patients who are mechani- cally ventilated. Mucus movement in the airways is thought to occur through two primary mechanisms: expulsive airﬂow and two-phase gas–liquid interactions. Expulsive ﬂow such as that generated by coughing or sneezing requires glottic closure and Valsalva maneuvers, which are not possible in mechanically venti- lated patients, because the glottis is held open by the endotracheal tube. The sec- ond mechanism, two-phase gas–liquid in- teraction, is thus the more likely expla- nation for mucus movement during physiotherapeutic interventions. It refers to the way in which airﬂow (gas) in the lungs disrupts the mucus layer (liquid), creating instability and turbulence on the surface of the mucus (2). Studies in ani- mal and lung models have demonstrated that for mucus movement to occur in a cephalad direction through this mecha- nism, an overall expiratory ﬂow bias of at least 10% must exist (2– 4). In other words, expiratory air ﬂow must exceed inspiratory air ﬂow, PEF:PIF ratio 1.1. Chest physiotherapy for mechanically ventilated patients often involves a com- bination of airway clearance techniques, including manual lung inﬂations inter- spersed with chest compressions with vi- brations (5–7). During these chest com- pression–vibrations, the physiotherapist aims to increase expiratory air ﬂow by rapidly compressing the patient’s chest at the beginning of expiration with contin- *See also p. 238. From the Portex Anaesthesia, Intensive Therapy & Respiratory Medicine Unit (RKG, HS, JS, MJP, EM), UCL Institute of Child Health and Physiotherapy Department, Great Ormond Street Hospital for Children NHS Trust, London, UK; and the Department of Paediatric Epidemi- ology & Biostatistics (TJC), UCL Institute of Child Health, London, UK. Supported by Sparks (Sport aiding medical research for kids), London, UK; the Physiotherapy Research Foundation, The Chartered Society of Physiotherapy, London, UK; and Great Ormond Street Hospital Trustees, London, UK. The authors have not disclosed any potential con- ﬂicts of interest. For information regarding this article, E-mail: r.gregson@qub.ac.uk Copyright © 2012 by the Society of Critical Care Medicine and the World Federation of Pediatric Inten- sive and Critical Care Societies DOI: 10.1097/PCC.0b013e3182230f5a Objective: This study aimed to quantify the speciﬁc effects of manual lung inﬂations with chest compression–vibrations, com- monly used to assist airway clearance in ventilated patients. The hypothesis was that force applied during the compressions made a signiﬁcant additional contribution to increases in peak expira- tory ﬂow and expiratory to inspiratory ﬂow ratio over and above that resulting from accompanying increases in inﬂation volume. Design: Prospective observational study. Setting: Cardiac and general pediatric intensive care. Patients: Sedated, fully ventilated children. Interventions: Customized force-sensing mats and a commercial respiratory monitor recorded force and respiration during physiotherapy. Measurements: Percentage changes in peak expiratory ﬂow, peak expiratory to inspiratory ﬂow ratios, inﬂation volume, and peak inﬂation pressure between baseline and manual inﬂations with and without compression–vibrations were calculated. Anal- ysis of covariance determined the relative contribution of changes in pressure, volume, and force to inﬂuence changes in peak expiratory ﬂow and peak expiratory to inspiratory ﬂow ratio. Measurements and Main Results: Data from 105 children were analyzed (median age, 1.3 yrs; range, 1 wk to 15.9 yrs). Force during compressions ranged from 15 to 179 N (median, 46 N). Peak expi- ratory ﬂow increased on average by 76% during compressions com- pared with baseline ventilation. Increases in peak expiratory ﬂow were signiﬁcantly related to increases in inﬂation volume, peak inﬂation pressure, and force with peak expiratory ﬂow increasing by, on average, 4% for every 10% increase in inﬂation volume (p < .001), 5% for every 10% increase in peak inﬂation pressure (p  .005), and 3% for each 10 N of applied force (p < .001). By contrast, increase in peak expiratory to inspiratory ﬂow ratio was only related to applied force with a 4% increase for each 10 N of force (p < .001). Conclusion: These results provide evidence of the unique con- tribution of compression forces in increasing peak expiratory ﬂow and peak expiratory to inspiratory ﬂow ratio bias over and above that related to accompanying changes from manual hyperinﬂa- tions. Force generated during compression–vibrations was the single signiﬁcant factor in multivariable analysis to explain the increases in expiratory ﬂow bias. Such increases in the expiratory bias provide theoretically optimal physiological conditions for cephalad mucus movement in fully ventilated children. (Pediatr Crit Care Med 2012; 13:e97– e102) KEY WORDS: physiotherapy (techniques); vibration; respiratory therapy; intensive care; child; airway clearance e97 Pediatr Crit Care Med 2012 Vol. 13, No. 2