The Science Journal of the American Association for Respiratory Care
Introduction: Use of pressure-volume curves (PVC) to determine lower and upper inflection points for PEEP and plateau pressure adjustments are recognized to be key factors in preventing cyclic re-expansion and over distension lung injury. PVC determination using the super syringe technique correlates closely with low flow inflation methods (1,2). The super syringe method is time consuming, labor intensive, subject to technique variability, and requires that the patient be removed from the ventilator. The ideal method for this measurement should be easily performed using automated precision without removing the patient from the ventilator. We describe a PVC measurement method that partially meets these criteria using the Drager E2 ventilator.
Method: During ventilation in any mode on the E2, preset APRV mode parameters to mimic the current ventilation settings by adjusting cycle times and pressures. Switch the ventilator to the APRV mode and adjust the FiO2 to 100%. Following the switch to APRV, preset SIMV mode parameters to Vt = 990 ml, Insp. Time = 10 seconds, Rate = 0.5 per minute, Insp. Flow = 6L/min, PEEP = 0, Flow Trigger = 0, and Slope = 0. Sedate the patient until spontaneous respiratory efforts cease. Switch the mode to SIMV. After 10 seconds of apnea, press the manual inspiration button to deliver a slow inflation at the parameters set above. Allow the patient to passively exhale and immediately switch the mode back to APRV to resume ventilation. The PVC can then be viewed on the ventilator display if the freeze screen function is activated during the maneuver or printed from the Drager Evita View graphics extension application (see figure).
Conclusion: Our experience in using this technique in critically ill patients has proven to be safe when performed by properly trained personnel. It requires numerous manipulations of the ventilator and requires several practice runs on a test lung to achieve competency. Development of a fully automated algorithm is within the technological capabilities of current micro processor controlled ventilators. PVC determination using the Drager E2 ventilator appears to be a reasonable alternative method until an automated measurement maneuver becomes available.
1)Mankikian B, Lemaire F, Benito S, et al. A new device for measurement of pulmonary pressurevolume curves in patients on mechanical ventilation. Crit Care Med 1983;11:897-901.
2) Lu Q, Viera S , Richecoeur J, et al. A simple automated method for measuring pressure-volume curves during mechanical ventilation. Am J Crit Care Med 1999;159:275-282.
(See Original for Figure)