Hysteresis and Lung Recruitment in Acute Respiratory Distress Syndrome Patients: A CT Scan Study*

Abstract

Objectives: Hysteresis of the respiratory system pressure-volume curve is related to alveolar surface forces, lung stress relaxation, and tidal reexpansion/collapse. Hysteresis has been suggested as a means of assessing lung recruitment. The objective of this study was to determine the relationship between hysteresis, mechanical characteristics of the respiratory system, and lung recruitment assessed by a CT scan in mechanically ventilated acute respiratory distress syndrome patients. Design: Prospective observational study. Setting: General ICU of a university hospital. Patients: Twenty-five consecutive sedated and paralyzed patients with acute respiratory distress syndrome (age 64 ± 15 yr, body mass index 26 ± 6 kg/m2, Pao 2/Fio 2 147 ± 42, and positive end-expiratory pressure 9.3 ± 1.4 cm H2O) were enrolled. Interventions: A low-flow inflation and deflation pressure-volume curve (5–45 cm H2O) and a sustained inflation recruitment maneuver (45 cm H2O for 30 s) were performed. A lung CT scan was performed during breath-holding pressure at 5 cm H2O and during the recruitment maneuver at 45 cm H2O. Measurements and Main Results: Lung recruitment was computed as the difference in noninflated tissue and in gas volume measured at 5 and at 45 cm H2O. Hysteresis was calculated as the ratio of the area enclosed by the pressure-volume curve and expressed as the hysteresis ratio. Hysteresis was correlated with respiratory system compliance computed at 5 cm H2O and the lung gas volume entering the lung during inflation of the pressure-volume curve (R 2 = 0.749, p < 0.001 and R 2 = 0.851, p < 0.001). The hysteresis ratio was related to both lung tissue and gas recruitment (R 2 = 0.266, p = 0.008, R 2 = 0.357, p = 0.002, respectively). Receiver operating characteristic analysis showed that the optimal cutoff value to predict lung tissue recruitment for the hysteresis ratio was 28% (area under the receiver operating characteristic curve, 0.80; 95% CI, 0.62–0.98), with sensitivity and specificity of 0.75 and 0.77, respectively. Conclusions: Hysteresis of the respiratory system computed by low-flow pressure-volume curve is related to the anatomical lung characteristics and has an acceptable accuracy to predict lung recruitment.

Lung recruitment in neonatal high‐frequency oscillatory ventilation with volume‐guarantee

“…The key to reaching this balanced state is to perform adequate recruitment maneuvers based on lung physiology, 15 increasing airway pressures until reaching critical lung opening pressure and then decreasing them while maintaining the optimal lung volume and before reaching the critical lung closing pressure. In this situation the hysteresis of the respiratory system allows ventilation in the deflation limb of the pressure–volume curve 22 which provides optimal volumes and minimal distending pressure, avoiding both overdistension and atelectasis. This phenomenon has been extensively studied in conventional ventilation and probably provides a similar benefit when ventilating patients in HFOV 13 …”

Management of refractory hypoxemia using recruitment maneuvers and rescue therapies: A comprehensive review

“…However, compliance might be more related to the improvement or deterioration of already ventilated lung units than the actual recruitment of atelectatic lung units ( 58 ). In a human study, a strong correlation was found between the amount of potentially recruitable lung tissue on CT-scan and pressure-volume loop parameters (hysteresis ratio and maximum normalized distance) in patients with early stages of ARDS ( 59 ). However, these strategies for assessing pulmonary recruitability have been performed under static conditions (low-flow method) that require deep sedation or paralysis, which is a potential limitation to the use of this technique ( 59 ).…”

“…However, anatomical recruitment as measured with computed tomography, and oxygenation (termed functional recruitment) have been shown to be poorly correlated with each other ( 58 ). Indeed, incremental PEEP during a recruitment maneuver might affect oxygenation by mechanisms other than non-aerated tissue recruitment, such as changes in cardiac output and blood flow distribution in the lungs ( 58 , 59 ). Improved lung compliance at higher pressures may reflect both improved mechanical properties of already open lung units and recruitment of previously collapsed alveoli ( 39 ).…”

Protective PEEP and Lung Capacity May Be Determined by a Rapid PEEP-step Procedure

“…If the PEEP step method is implemented in a ventilator, it can be programmed to make a PEEP-down procedure from a high initial PEEP level as prolonged expirations step-wise down to lower PEEP levels, which will make the procedure very rapid. However, such a procedure needs to be evaluated as hysteresis phenomenon during fast procedures may cause less adequate results [40][41][42].…”