The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

MEASUREMENT OF TOTAL FLOW AND FIO2 IN BI-LEVEL NON INVASIVE MECHANICAL VENTILATION

Rodrigo S. Adasme1, Alejandra Martinez1, Camilo Navarro1, Hernan Polanco1, Juan E. Romero1



Background: Current Non Invasive mechanical ventilation equipments using an internal turbine to produce positive pressure. The use of this equipment in Intensive care need oxygen administration in higher or lower concentrations(FiO2)according to the patient's needs, thus it has to be injected into the circuit at a chosen place. There is no agreement on where it should be located to provide a higher FiO2 with the least total flow administered to the patient.

Objective: To determine the most effective position in oxygen injection at a bi-level according to FiO2 and total oxygen flow.

Materials and method: We used a Respirotronics ST 30 NIMV. Parameters were: ST, RR 12 rpm, IPAP 12, EPAP 6cmH2O, with a conventional circuit and end branch connected to a ?6 mm exhalatory port and a test lung. Into this circuit oxygen was injected from the wall outlet with a compensated flowmeter in three positions was before the exhalatory portal and the third was located after this portal.
Pressure was measured near the test lung by a DHD Healthcare manometer. FiO2 was determined between the pressure line and the exhalatory portal by a Hudson RCI 5801 oxygen analyzer. A Ferraris Haloscales Wright respimeter measured the flow 10 cm below the oxygen connection. Three measurements were done according to the injection site with oxygen. Flows of O,5,10 and 15 l/min were tested.

Results: see in table 1 (Means and SD). The system without oxygen injection shows no differences. The highest FiO2 at a 5 l/min flow was achieved by injecting oxygen near the patient(post portal). The same was observed for regarding the lesser flow. Higher oxygen concentrations can be reached at 10 l/min by injecting it near the patient or the equipment but the final lowest flow is reached by injecting oxygen near the equipment(then near patient). The highest FiO2 at 15 l/m is reached by delivering oxygen near the equipment and subsequently post the exhalatory portal. The lowest flow is reached by injecting oxygen near the equipment.

Conclusion: Oxygen flows under 5 l/min have a better ventilatory performance when delivered near the patient, unlike injection flows above 5 l/min near the equipment that reach a higher FiO2 with a lesser flow. As this was a wench study with just one equipment, we need further clinical studies on this topic.