The Science Journal of the American Association for Respiratory Care
Introduction: Adjusting PEEP above the lower inflection point and limiting plateau pressure below the upper inflection point of the PVC is considered to be a key element in preventing reexpansion and over distension lung injury during ARDS and ALI. Incremental volume inflation and static pressure measurements using a super syringe is time consuming, labor intensive, and subject to technique variability. PVC determination using the super syringe technique has been shown to correlate closely when compared to the low flow inflation method 1,2. We describe a simple method to record a low inspiratory flow PVC for inflection point determination using the Novametrix VenTrak Respiratory Mechanics Workstation.
Method: The NVT with attached printer, a Pediatric/Adult flow sensor, an oxygen gas source connected to a Washington T adapter (WT) are the supplies needed. Following connection of the NVT to the sedated patient and a brief period of ventilation with 100% oxygen, the patient is disconnected from the ventilator and attached to a WT with an oxygen flow set at 3 liters per minute. After 10 seconds of apnea, the open end of the WT is occluded for 30 seconds and a slow inflation to a volume of 1.5 liters is achieved. The patient is allowed to passively exhale and is reattached to the ventilator. The monitoring session is terminated and saved. The review recordings function is used to view the P-V curve in the combination waveform screen format and printed using the print screen command. The hard copy of the P-V curve can then be viewed and analyzed visually for lower and upper inflection point determination.
Lower inflection point is easily identified at 12 cm H2O in this patient.
Conclusion: This simplified method brings PVC measurement to the bedside utilizing a relatively inexpensive, commercially available device. Our experience in using this technique in critically ill patients has proven it to be safe and easily performed within a two minute time span. It requires little training or practice to master and facilitates the interpretation of the results. We believe this method provides another accurate alternative for performing this important clinical measurement.
1) Mankikian B, Lemaire F, Benito S, et al. A new device for measurement of pulmonary pressure-volume 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)