Pulmonary function in the mechanically ventilated patient

Implementing the knowledge and skills obtained from the pulmonary function laboratory is useful in the assessment of pulmonary function in the ventilated patient. In the critically ill patient, special constraints and problems (such as safety and ability to cooperate) are important considerations for the therapist performing the testing. Basic measurements such as MIP, VC, VT, MVV, VE, and respiratory rate are commonly made to assess weanability. For the difficult-to-wean patient, WOB, PTP, P0.1 and O2COB may be of potential value in selected patients. Evidence of their value in routine weaning assessment, however, is lacking. Monitoring has evolved with increased understanding of pulmonary mechanics of the mechanically ventilated patient. Measurements of compliance, resistance, MAP, and autoPEEP provide useful diagnostic and therapeutic information, and guide in the selection of appropriate machine settings to provide effective and safe ventilatory support. Although currently confined to the research setting, P-V curves have contributed to our understanding of the pathophysiology of ALI, and may prove useful in defining an optimal ventilatory strategy in patients with ALI. Finally, waveform monitoring can reveal, graphically and in real time, patient-ventilator interactions such as autoPEEP, lung overdistension, patient effort, or the presence of secretions. Waveform monitoring can bring important issues to the close attention of the practitioners involved in management of the ventilated patient.