The role of time and pressure on alveolar recruitment

Abstract

Inappropriate mechanical ventilation in patients with acute respiratory distress syndrome can lead to ventilator-induced lung injury (VILI) and increase the morbidity and mortality. Reopening collapsed lung units may significantly reduce VILI, but the mechanisms governing lung recruitment are unclear. We thus investigated the dynamics of lung recruitment at the alveolar level. Rats (n = 6) were anesthetized and mechanically ventilated. The lungs were then lavaged with saline to simulate acute respiratory distress syndrome (ARDS). A left thoracotomy was performed, and an in vivo microscope was placed on the lung surface. The lung was recruited to three recruitment pressures (RP) of 20, 30, or 40 cmH(2)O for 40 s while subpleural alveoli were continuously filmed. Following measurement of microscopic alveolar recruitment, the lungs were excised, and macroscopic gross lung recruitment was digitally filmed. Recruitment was quantified by computer image analysis, and data were interpreted using a mathematical model. The majority of alveolar recruitment (78.3 +/- 7.4 and 84.6 +/- 5.1%) occurred in the first 2 s (T2) following application of RP 30 and 40, respectively. Only 51.9 +/- 5.4% of the microscopic field was recruited by T2 with RP 20. There was limited recruitment from T2 to T40 at all RPs. The majority of gross lung recruitment also occurred by T2 with gradual recruitment to T40. The data were accurately predicted by a mathematical model incorporating the effects of both pressure and time. Alveolar recruitment is determined by the magnitude of recruiting pressure and length of time pressure is applied, a concept supported by our mathematical model. Such a temporal dependence of alveolar recruitment needs to be considered when recruitment maneuvers for clinical application are designed.

Respiratory Care Year in Review 2011: Long-Term Oxygen Therapy, Pulmonary Rehabilitation, Airway Management, Acute Lung Injury, Education, and Management

“…A 40 cm H 2 O recruitment maneuver was applied for 30 s. They found that 50% of the recruited volume was attained within 1.6 s, 95% within 6.8 s, and Ͼ 98% with 10 s of applying the pressure. Further, blood pressure began dropping by 10 s and had decreased significantly at 20 s and 30 s. These observations of recruitment time are in agreement with a recent animal study showing that a majority of recruitment occurs within 2 s. 79 The editorial accompanying the Arnal article makes the case that the sustained pressure recruitment maneuver should be retired in favor of a stepwise increase using pressure ventilation, as it is better tolerated hemodynamically and the patient receives ventilation during the procedure. 80 Although recruitment maneuvers have been shown to improve short-term oxygenation, they have not been associated with improvement in any important outcomes, such as mortality, and should only be considered as part of rescue therapy for severe hypoxemia.…”

Minimization of Ventilator-Induced Lung Injury in ARDS Patients – Part I: Complex Model of Mechanically Ventilated ARDS Lungs

“…12 for consecutive lung lobes from the complex analogue -see trends for Valv1 − Valv4. For the clinicians involved in the management of lung recruitment/de-recruitment during the mechanical ventilation it is interesting to know the moment of airway zone reopening/closure expressed as a function of pressure, volume or even time [15]. Fig.…”

“…Mathematical and physical-mathematical models of alveolar zone, which have been proposed in the literature [15], apply to respiratory mechanisms proper for breathing at volumes lower than the total lung capacity (TLC) [16−19]. The recruitment manoeuvre, especially in patients with ARDS or ALI (acute lung injury), is performed near and even above the TLC level.…”

Visualisation of Time-Variant Respiratory System Elastance in ARDS Models

“…In addition, recruitment is also a function of PEEP and time [8]. Therefore, true minimal E drs can only be determined after a stabilisation period is provided at each PEEP level.…”