Effect of Intensive vs Moderate Alveolar Recruitment Strategies Added to Lung-Protective Ventilation on Postoperative Pulmonary Complications: A Randomized Clinical Trial.

Importance: Perioperative lung-protective ventilation has been recommended to reduce pulmonary complications after cardiac surgery. The protective role of a small tidal volume (VT) has been established, whereas the added protection afforded by alveolar recruiting strategies remains controversial. Objective: To determine whether an intensive alveolar recruitment strategy could reduce postoperative pulmonary complications, when added to a protective ventilation with small VT. Design, Setting, and Participants: Randomized clinical trial of patients with hypoxemia after cardiac surgery at a single ICU in Brazil (December 2011-2014). Interventions: Intensive recruitment strategy (n=157) or moderate recruitment strategy (n=163) plus protective ventilation with small VT. Main Outcomes and Measures: Severity of postoperative pulmonary complications computed until hospital discharge, analyzed with a common odds ratio (OR) to detect ordinal shift in distribution of pulmonary complication severity score (0-to-5 scale, 0, no complications; 5, death). Prespecified secondary outcomes were length of stay in the ICU and hospital, incidence of barotrauma, and hospital mortality. Results: All 320 patients (median age, 62 years; IQR, 56-69 years; 125 women [39%]) completed the trial. The intensive recruitment strategy group had a mean 1.8 (95% CI, 1.7 to 2.0) and a median 1.7 (IQR, 1.0-2.0) pulmonary complications score vs 2.1 (95% CI, 2.0-2.3) and 2.0 (IQR, 1.5-3.0) for the moderate strategy group. Overall, the distribution of primary outcome scores shifted consistently in favor of the intensive strategy, with a common OR for lower scores of 1.86 (95% CI, 1.22 to 2.83; P = .003). The mean hospital stay for the moderate group was 12.4 days vs 10.9 days in the intensive group (absolute difference, -1.5 days; 95% CI, -3.1 to -0.3; P = .04). The mean ICU stay for the moderate group was 4.8 days vs 3.8 days for the intensive group (absolute difference, -1.0 days; 95% CI, -1.6 to -0.2; P = .01). Hospital mortality (2.5% in the intensive group vs 4.9% in the moderate group; absolute difference, -2.4%, 95% CI, -7.1% to 2.2%) and barotrauma incidence (0% in the intensive group vs 0.6% in the moderate group; absolute difference, -0.6%; 95% CI, -1.8% to 0.6%; P = .51) did not differ significantly between groups. Conclusions and Relevance: Among patients with hypoxemia after cardiac surgery, the use of an intensive vs a moderate alveolar recruitment strategy resulted in less severe pulmonary complications while in the hospital. Trial Registration: clinicaltrials.gov Identifier: NCT01502332.

Airway Clearance Techniques for Mechanically Ventilated Patients: Insights for Optimization.

Secretion management in mechanically ventilated patients is a paramount task for clinicians. A better understanding of the mechanisms of flow bias and airway dynamic compression during airway clearance therapy may enable a more effective approach for this population. Ventilator hyperinflation, expiratory rib cage compression, a PEEP-ZEEP maneuver, and mechanical insufflation-exsufflation are examples of techniques that can be optimized according to such mechanisms. In addition, novel technologies, such as electric impedance tomography, may help improve airway clearance therapy by monitoring the consequences of regional secretion displacement on lung aeration and regional lung mechanics.

Real-time detection of pneumothorax using electrical impedance tomography.

OBJECTIVES: Pneumothorax is a frequent complication during mechanical ventilation. Electrical impedance tomography (EIT) is a noninvasive tool that allows real-time imaging of regional ventilation. The purpose of this study was to 1) identify characteristic changes in the EIT signals associated with pneumothoraces; 2) develop and fine-tune an algorithm for their automatic detection; and 3) prospectively evaluate this algorithm for its sensitivity and specificity in detecting pneumothoraces in real time. DESIGN: Prospective controlled laboratory animal investigation. SETTING: Experimental Pulmonology Laboratory of the University of São Paulo. SUBJECTS: Thirty-nine anesthetized mechanically ventilated supine pigs (31.0 +/- 3.2 kg, mean +/- SD). INTERVENTIONS: In a first group of 18 animals monitored by EIT, we either injected progressive amounts of air (from 20 to 500 mL) through chest tubes or applied large positive end-expiratory pressure (PEEP) increments to simulate extreme lung overdistension. This first data set was used to calibrate an EIT-based pneumothorax detection algorithm. Subsequently, we evaluated the real-time performance of the detection algorithm in 21 additional animals (with normal or preinjured lungs), submitted to multiple ventilatory interventions or traumatic punctures of the lung. MEASUREMENTS AND MAIN RESULTS: Primary EIT relative images were acquired online (50 images/sec) and processed according to a few imaging-analysis routines running automatically and in parallel. Pneumothoraces as small as 20 mL could be detected with a sensitivity of 100% and specificity 95% and could be easily distinguished from parenchymal overdistension induced by PEEP or recruiting maneuvers. Their location was correctly identified in all cases, with a total delay of only three respiratory cycles. CONCLUSIONS: We created an EIT-based algorithm capable of detecting early signs of pneumothoraces in high-risk situations, which also identifies its location. It requires that the pneumothorax occurs or enlarges at least minimally during the monitoring period. Such detection was operator-free and in quasi real-time, opening opportunities for improving patient safety during mechanical ventilation.

Ventilation patterns influence airway secretion movement.

BACKGROUND: Retention of airway secretions is a common and serious problem in ventilated patients. Treating or avoiding secretion retention with mucus thinning, patient-positioning, airway suctioning, or chest or airway vibration or percussion may provide short-term benefit. METHODS: In a series of laboratory experiments with a test-lung system we examined the role of ventilator settings and lung-impedance on secretion retention and expulsion. Known quantities of a synthetic dye-stained mucus simulant with clinically relevant properties were injected into a transparent tube the diameter of an adult trachea and exposed to various mechanical-ventilation conditions. Mucus-simulant movement was measured with a photodensitometric technique and examined with image-analysis software. We tested 2 mucus-simulant viscosities and various peak flows, inspiratory/expiratory flow ratios, intrinsic positive end-expiratory pressures, ventilation waveforms, and impedance values. RESULTS: Ventilator settings that produced flow bias had a major effect on mucus movement. Expiratory flow bias associated with intrinsic positive end-expiratory pressure generated by elevated minute ventilation moved mucus toward the airway opening, whereas intrinsic positive end-expiratory pressure generated by increased airway resistance moved the mucus toward the lungs. Inter-lung transfer of mucus simulant occurred rapidly across the "carinal divider" between interconnected test lungs set to radically different compliances; the mucus moved out of the low-compliance lung and into the high-compliance lung. CONCLUSIONS: The movement of mucus simulant was influenced by the ventilation pattern and lung impedance. Flow bias obtained with ventilator settings may clear or embed mucus during mechanical ventilation.

Airway Clearance With an Optimized Mechanical Insufflation-Exsufflation Maneuver.

BACKGROUND: Standard mechanical insufflation-exsufflation (MI-E) therapy is applied with fast insufflation-exsufflation pressures to achieve high peak expiratory flows (PEF) and assist airway clearance. No attention is given to the resultant high peak inspiratory flows (PIF), although it may impair secretion removal. It has been proposed that an expiratory flow bias (ie, PEF higher than PIF) might be the key determinant for mucus clearance instead of the PEF alone. We examined the effects of 2 MI-E maneuvers, standard versus optimized, with fast and slow insufflation, respectively, along with different MI-E pressure settings on secretion displacement in 3 lung-impedance scenarios that simulated a patient on mechanical ventilation. METHODS: The MI-E device was connected to a lung model that simulated a patient on mechanical ventilation. Known quantities of mucus simulant were injected into the system and exposed to various MI-E ventilation conditions. Mucus movement was examined with image-analysis software. RESULTS: The optimized MI-E maneuver resulted in a much lower PIF (37.5 L/min [interquartile range, 24.9-47.9 L/min] vs 101.8 L/min [interquartile range, 89.1-115.7 L/min], P < .001). Consequently, the expiratory flow bias, expressed by PEF:PIF and the PEF-PIF difference, was much higher in the optimized maneuver. The higher expiratory flow bias in the optimized maneuver displaced the mucus outward, with a difference of 2.6 cm compared with the standard maneuver. Multivariate analysis revealed that the type of maneuver (optimized vs standard), PEF-PIF difference and MI-E pressure gradient were significantly correlated with mucus displacement (r2 = 0.817, P < .001), whereas the PEF was not. PEF:PIF and the PEF-PIF difference were lower in the obstructive lung scenario when compared with the restrictive and normal lung scenarios. CONCLUSIONS: The optimized MI-E maneuver, applied with slow insufflation, resulted in a higher expiratory flow bias, which made the therapy more effective at moving mucus outward, compared with the standard MI-E maneuver, typically applied with fast insufflation.

Effects of manual hyperinflation, clinical practice versus expert recommendation, on displacement of mucus simulant: A laboratory study.

INTRODUCTION: Manual hyperinflation (MH), a maneuver applied in mechanically ventilated patients to facilitate secretion removal, has large variation in its performance. Effectiveness of MH is usually evaluated by its capacity to generate an expiratory flow bias. The aim of this study was to compare the effects of MH-and its resulting flow bias-applied according to clinical practice versus according to expert recommendation on mucus movement in a lung model simulating a mechanically ventilated patient. METHODS: Twelve physiotherapists were asked to apply MH, using a self-inflating manual resuscitator, to a test lung as if to remove secretions under two conditions: according to their usual clinical practice (pre-instruction phase) and after verbal instruction to perform MH according to expert recommendation was given (post-instruction phase). Mucus simulant movement was measured with a photodensitometric technique. Peak inspiratory flow (PIF), peak inspiratory pressure (PIP), inspiratory time (TINSP), tidal volume (VT) and peak expiratory flow (PEF) were measured continuously. RESULTS: It was found that MH performed post-instruction delivered a smaller VT (643.1 ± 57.8 ml) at a lower PIP (15.0 ± 1.5 cmH2O), lower PIF (38.0 ± 9.6 L/min), longer TINSP (1.84 ±0.54 s) and lower PEF (65.4 ± 6.7L/min) compared to MH pre-instruction. In the pre-instruction phase, MH resulted in a mean PIF/PEF ratio of 1.73 ± 0.38 and mean PEF-PIF difference of -54.6 ± 28.3 L/min, both out of the range for secretion removal. In the post-instruction phase both indexes were in the adequate range. Consequently, the mucus simulant was moved outward when MH was applied according to expert recommendation and towards the test lung when it was applied according to clinical practice. CONCLUSIONS: Performance of MH during clinical practice with PIF higher than PEF was ineffective to clear secretion in a lung model simulating a mechanically ventilated patient. In order to remove secretion, MH should result in an adequate expiratory flow bias.