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LETTER TO THE EDITOR

Concerns About the Use of Forced-Air Warming to Facilitate Intravenous Cannulation: Don’t "Hose" the Patient

Department of Anesthesiology; Long Beach Veterans Affairs Medical Center; University of California at Irvine; Orange, CA; david.wong{at}med.va.gov

In Response:

Dr. Dillon (1) and Dr. Wax (2) raise important issues about my Letter to the Editor and I thank them for sharing their concerns (3). The main rationale for the local warming technique is to counteract the effect of acute vasoconstriction caused by a cool environment. I agree that sedated patients might not be able to respond to overheating which is the reason that this technique has only been used in adult patients before induction of anesthesia. Furthermore, monitoring the heated site is also necessary and the heat source should be removed if excessive redness is observed.

The relative risk of burn is probably temperature dependent and time dependent. Lenhardt et al. (4), used an actively heated mitt warmed to 52°C for 15 min in 50 neurosurgical patients to vasodilate hand veins without any skin irritation or patient report of discomfort. They reported an average skin temperature after active warming of 40.6 ± 2.3°C (mean ± sd). The Food and Drug Administration (FDA) has issued a warning that the use of forced-air warming units without blankets for treating systemic hypothermia can result in burns (5), and the FDA has also given guidelines to manufacturers of transcutaneous gas monitors to avoid burn: the set temperature should not exceed 44°C for more than 4 h; after 4 h, a different site must be used (6).

Reducing the temperature of the forced-air warming unit to <44°C should reduce the risk of burn, while retaining some vasodilatory effect. Another modification of the described technique could be to use an actual forced-air warmer rather than the clear plastic bag, particularly if the warming device is going to be used during surgery.

We agree with Dr. Wax that it is important to weigh the relative risk versus benefit of any procedure in each patient and that the true margin for safety of using forced-air warming for venodilation is unknown. If anesthesia providers choose to enhance venodilation using forced-air warming, they should limit the duration of warming with air at 44°C to 5 min, use a lower temperature if possible, and ideally use the warming blanket for which the hose was intended.

REFERENCES

1. Dillon F. Concerns about the use of forced air warming to facilitate IV cannulation: don’t "hose" the patient. Anesth Analg 2007;104:739–40.[Free Full Text]
2. Wax D. Difficult IV Access: Second Thoughts. Anesth Analg 2007;104:739.[Free Full Text]
3. Wong DH. Difficult IV access: a warm thought. Anesth Analg 2006;103:786.[Free Full Text]
4. Lenhardt R, Seybold T, Kimberger O, et al. Local warming and insertion of peripheral venous cannulas: single blinded prospective randomized control trial and single blinded randomized crossover trial. BMJ 2002;325:409–12.[Abstract/Free Full Text]
5. Anesthesia Patient Safety Foundation Newsletter 2002;17:42.
6. FDA. Center for Devices and Radiological Health "Class II Special Controls Guidance Document: Cutaneous Carbon Dioxide (PcCO2) and Oxygen (PcO2) Monitors; Guidance for Industry and FDA, December 13, 2002, document 1335. Available at http://www.fda/gov/cdrh/1335.html

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