Tracings obtained from ventilator while operating in the volume-controlled mode. Flow, pressure, and volume in time are presented from top to bottom. The dashed circle in the upper panel shows the truncated expiratory flow tracing, indicating intrinsic positive end-expiratory pressure (PEEP). Indeed, when expiration is interrupted (red solid arrow) after the next inspiration, airway pressure rises (middle panel), reflecting total PEEP (applied PEEP and intrinsic PEEP). To measure respiratory resistance, inspiratory hold is applied (red dotted arrow), resulting in rapid decay in airway pressure from peak to P1 and a subsequent slow decay to plateau pressure (P,plat).

Framework for the evaluation of difficult-to-wean patients. For each patient, diagnostics as described in the white box should be performed to assess the reasons(s) for difficult weaning. Endocrine dysfunction is probably relatively rare and therefore is not included in the first line of evaluation. Possible treatment/interventions are mentioned but, of course, need to be individualized. If the first-line evaluation does not improve weaning, proceed to the next level (within the affected column). For instance, if airway resistance is elevated but is not affected by albuterol and optimizing ventilator settings, diagnostic bronchoscopy should be performed to visualize the central airways. Risks and benefits should be weighed in each patient. ACTH, adrenocorticotrophic hormone; BNP, brain natriuretcic peptide; CAM-ICU, confusion assessment method for the intensive care unit; DO₂, oxygen delivery; ECG, electrocardiogram; EIC, end inspiratory cycling; EMG, electromyography; iv, intravenous; P_0.1, airway occlusion pressure at 100 ms; PEEPi, intrinsic positive end-expiratory pressure; Pi, inspiratory pressure; PSV, pressure support ventilation; SBT, spontaneous-breathing trial; SvO₂, mixed venous oxygen saturation.