Warming patients preoperatively with the Bair hugger prevent hypothermia

Does warming patients preoperatively with the Bair hugger prevent hypothermia in patients undergoing general anesthesia?

Literature Review

According to Scheer, a major complication involved with accessing the radial artery is hand ischemia, with permanent hand ischemic damage being reported at 0.09%.2 This study was performed on patients who received arterial cannulation from a straight blood draw or indwelling catheter. The study involved patients in the United States of all races and backgrounds. Scheer goes on to mention that the cannulation of the radial artery is the most common site that anesthesia providers use in the acute setting, specifically the operating room.2 The incidence of radial artery occlusion is high with indwelling catheters, due to thrombi formation at the catheter tip site.2 This is a very common side-effect that occurs from a long-standing indwelling catheter (>5 hours).

Many times, patients who have an indwelling radial artery catheter for longer than 5 hours have heparin infusing through the catheter at a slow rate, to allow the catheter to remain patent and prevent thrombosis of the radial artery, without causing a systemic effect on the patient. With the formation of a thrombi being relatively high and the incidence of damage being extremely low, Allen’s test may only be an unnecessary step in the process of cannulating the radial artery, according to the Scheer. In a separate study by Martin and associates, 1000 patients were scheduled to undergo cardiac catheterization through the radial artery and they had the following Allen’s test results; 49% had a normal modified Allen’s test with a return of blood flow within 5 seconds, 24% had borderline return of blood flow at 5-9 seconds, and 27% showed abnormal return of blood flow at greater than 10 seconds.

Of these 1000 participants in the study, angiographic imaging showed 76% of patients to have complete or partial obstruction of the radial artery due to thrombosis formation with an indwelling radial artery catheter, and of those 1000 patients, none showed any clinical evidence of hand ischemia or damage. Martin concluded the study with an interesting statement as follows, “an abnormal modified Allen’s test does not necessarily imply that hand ischemia will result if the radial artery is harvested for coronary artery bypass graft or cardiac catheterization.”

From this information, Martin makes it clear that regardless of the outcome of Allen’s test, it should not alter the decision or process that goes into cannulating the radial artery. In the third study by Meharwal and associates, they reported no acute ischemic hand symptoms that related to inadequate blood flow in a large series of 4,172 harvests for coronary artery bypass graft in open heart surgery.

After 4 weeks postoperative, 5.2% of patients exhibited hand weakness according to the study, but no hand ischemia or necrosis. This study followed patients for their entire stay in the hospital and found that no hand symptoms relating to the harvest of the radial artery were present. This meant that regardless of the outcome of Allen’s test, the collateral blood flow was adequate in providing these patients with sufficient flow to the distal hand. This research has been shown to be the largest of its kind for the study of hand ischemia following the harvest of the radial artery. This study did not give the percentage of negative or positive Allen’s tests, but if we go according to previous research and literature, about half of Allen’s tests performed in the hospital are normal with adequate collateral blood flow. This means that the other half of Allen’s test performed will show to have some sort of abnormal collateral flow.

With this in mind, half of the patients in this study might’ve had a positive Allen’s test, but did not exhibit any signs of hand ischemic damage. Experts have reported harvesting the radial artery during coronary bypass graft surgery despite an abnormal Allen test, according to the study done by Abu-Omar and associates. They concluded that Allen’s test had a 50% normal/abnormal rate, and of the 129 patients who received Allen’s test and had their radial artery harvested, they did not show any ischemic sequelae following the surgery.

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