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A-565
2004
FDO2 Accuracy When Supplying Nasal Cannulae from Common Gas Outlets
Samsun Lampotang, Ph.D., David A. Paulus, M.D., Nikolaus Gravenstein, M.D.
Anesthesiology, University of Florida, Gainesville, Florida.
Introduction: In a June 2003 Sentinel Event Alert, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) recommended: "As a general policy, use air or FiO2 at ≤30% for open delivery (consistent with patient needs)" to prevent surgical fires. When contacted, ECRI, the source of the JCAHO recommendation, confirmed that it meant the fraction of O2 delivered, FDO2, to a nasal cannula, not the fraction of O2 inspired, FiO2, which can be diluted by ambient air and is generally not monitored in open delivery systems. Thus the common practice of providing 100% O2 to nasal cannulae from auxiliary ball-in-tube O2 flowmeters infringes on the recent JCAHO recommendation.

An anesthesia machine equipped with an air rotameter can be used to provide a delivered fraction of oxygen, FDO2 = 30% in air to a nasal cannula via the common gas outlet (CGO) or auxiliary CGO (ACGO) depending upon the anesthesia machine model. The flow resistance of a nasal cannula imposes a higher back pressure on the air and O2 rotameters than the regular gas flow path as evidenced by the dip in the air and O2 bobbins when a nasal cannula is connected to a CGO or ACGO. This dip does not occur when connecting the fresh gas flow (FGF) hose to the CGO in a Modulus I or II, confirming that the flow resistance of the FGF hose and breathing circuit is lower than that of a nasal cannula. When contacted, Datex-Ohmeda indicated that it has no recommendations against supplying nasal cannulae from the CGO or ACGO. We conducted preliminary experiments to determine whether the increased back pressure imposed upon the O2 and air rotameters by the added flow resistance of a nasal cannula impacts on set FDO2 in three anesthesia machines (Modulus I, Modulus II, Aestiva, Datex-Ohmeda, Madison, WI).

Methods: The FGF hose was disconnected from the CGO (Modulus I and II) or the ACGO was selected as the gas outlet (Aestiva). O2 and air rotameters were set at a 1:7 ratio to deliver an FDO2 of 30%, specifically 3.5 L/min air and 0.5 L/min O2. FDO2 was measured at the CGO/ACGO with a gas analyzer (Capnomac Ultima, Datex, Helsinki, Finland). The O2 rotameter was adjusted, if necessary, to obtain an FDO2 of 30% at the CGO/ACGO. Next, an adult nasal cannula (#1104, Hudson RCI, Temecula, CA) was connected to the CGO/ACGO using a 5 mm endotracheal tube connector. The prongs of the nasal cannula and the distal tip of the sampling tube from the gas analyzer were inserted into a 3 L breathing bag (Portex Inc., Keene, NH). After the FDO2 stabilized, it was recorded. This was repeated three times.

Results: With all three anesthesia machines, the O2 and air bobbins dipped when the nasal cannula was connected to the CGO/ACGO but FDO2 delivered at the nasal prongs was 30%, similar to FDO2 at the CGO/ACGO without a nasal cannula attached.

Conclusions: Back pressure imposed on the O2 and air rotameters by the increased flow resistance of a nasal cannula connected to the CGO/ACGO does not affect FDO2 accuracy at FGFs of 4 L/min on the machines studied. For anesthesia machines equipped with an air rotameter, the CGO/ACGO provide a means for complying with the JCAHO recommendation.

References:

Joint Commission on Accreditation of Healthcare Organizations Sentinel Event Alert. Preventing surgical fires. Issue 29, June 24, 2003 http://www.jcaho.org/about+us/news+letters/sentinel+event+alert/sea_29.htm

Anesthesiology 2004; 101: A565