The Science Journal of the American Association for Respiratory Care
OBJECTIVE: To determine the effects of exhaled tidal volumes with the addition of PEEP as compared to SET and Delivered volumes. This study was triggered from discrepencies observed during routine calibrations and patient care on fixed-wing transport.
METHOD: A bench test of 3 of our Crossvent CV-4 ventilators in its assigned aircraft using the same circuit, pneumotach, test lung and respirometer for all tests. Tests were conducted with the aircraft on the ground and cabins unpressurized. All measurements were taken after Calibration of circuit compliance and pneumotach as required by manufacturer and company Policy. Volumes measured included Set Tidal Volume, Corrected Tidal Volume, Exhaled Volume by pneumotach and Delivered Tidal Volume by respirometer.
Measurements were taken with 0cm PEEP, +3cm PEEP and +5cm PEEP. Volumes were 300cc, 500cc and 700cc Set. Flows were adjusted to maintain an I:E ratio of 1:4.
Results: In the controlled setting with all other parameters being equal; Rate 12, Fi02 100%, I:E Ratio 1:4, Auto Shift 15sec and Sensitivity -2cm. The following changes occurred with PEEP. For set Tidal Volume of 300c, flow of 20 1/m and with 0cm, +3cm and +5cm PEEP, exhaled tidal volumes increased 1.4% - 3.7% with 0cm PEEP but decreased 6.7% with 3cm and 7.8% with 5cm PEEP. For tidal volumes of 500cc and flow of 30 1/m, exhaled tidal volumes decreased 2.8%, 9.0% and 9.6% respectively. For tidal volumes of 700cc with flows of 40 1/m exhaled tidal volumes decreased 9.7%, 11.4% and 11.5% respectively. CONCLUSION: The data suggests that when adding PEEP it is imperative to check and monitor the exhaled tidal volumes and not corrected delivered volumes. More importantly Set tidal volumes need to be adjusted in order to ensure adequate ventilation has occurred especially if end-tidal C02 is not available.