Overcoming common patient warming misconceptions in the Ambulatory Surgery Center (ASC) environment

As most know, one hallmark characteristic of the Ambulatory Surgery Center (ASC) environment is high reliability, meaning there is an expectation of consistently good postoperative outcomes, especially when compared to alternative treatment settings. ASCs, and other high reliability systems have several common features including:

• Restricted, well-defined and repeatable processes
• Efficiency
• Quality assurance
• An intense focus on data and outcomes

Because of the highly refined processes in the ASC environment, most surgical procedures can be completed in substantially less time than required in a hospital. The trade-off for this time efficiency is the need to modify some therapeutic processes, like patient warming, so their effects can be synchronized to match the reduced surgical duration.

Patient warming is a good example of a well-known therapy that is generally optimized for longer hospital procedures but should be adjusted to achieve best results in shorter procedures.

Regardless of the surgical facility and procedure length, every degree matters for surgical patients because just a small drop in core body temperature can result in inadvertent hypothermia. It should be the goal of every perioperative team to keep their surgical patient in the normothermic temperature zone, between 36.0 and 37.5°C. Below are two frequent misconceptions about effective normothermia management in ASCs that will help clinicians better manage that normothermic zone.

Misconception: “It’s a short procedure; my patient doesn’t need warming.”
Patients undergoing short procedures – less than one hour – become hypothermic very quickly due to the immediate and forceful effect of redistribution, a process which cannot be quickly reversed by intraoperative warming,2,3, however, short-procedure patients can benefit substantially from prewarming. Patients undergoing shorter procedures who are properly prewarmed and receive intraoperative warming can remain normothermic throughout the perioperative journey and should not require rewarming in the recovery room.

Intraoperative warming is always needed, even in shorter surgical procedures, but it can’t always produce normothermia in procedures less than 60 minutes. Active prewarming (warming patients before anesthesia induction) is an effective way to help prevent intraoperative hypothermia before it begins, regardless of surgery length, because it helps deter anesthesia’s impact on core body temperature regulation.

While loss of insulation and a cooler than normal ambient temperature in the OR are minor contributors to the development of intraoperative hypothermia, the major initial cause is anesthesia-induced thermoregulatory impairment, leading to heat redistribution within the body.1 Redistribution is caused by the movement and mixing of cooler blood in the peripheral thermal compartment with warmer blood in the core. The temperature decrease that follows cannot be quickly reversed by any type of external warming. This drop can be dramatic following general or neuraxial anesthesia too, causing temperatures to decrease at rates of almost 2°C/h immediately following anesthetic induction.2,3

Under normal conditions, the body maintains its core temperature in the normothermic temperature zone regardless of the ambient conditions. Peripheral tissues (mostly in the arms and legs), on the other hand, are considerably cooler than those in the core, even at normal room temperature. When those peripheral tissues are purposefully warmed before anesthesia, a considerable amount of heat may be stored in them before anesthesia-induced thermoregulatory impairment produces redistribution.4,5 In patients who have been adequately prewarmed, core temperatures can be more effectively maintained within the normothermic zone using standard intraoperative warming methods.6

Misconception: “Prewarming isn’t necessary because my patient’s temperature doesn’t change preoperatively.”
A major difficulty with prewarming relates to the lack of a method to measure its success. In awake patients, prewarming does not alter their core temperature because their thermoregulatory system is not impacted by anesthesia. This means preoperative core temperature is not an indicator of adequate prewarming. This confusion causes some clinicians to forgo prewarming because it doesn’t seem to have an immediate effect. On the contrary, prewarming should be utilized as a way to help maintain the normothermic zone during surgery.

At present, the best practice is a relatively short, but aggressive, period of warming for 10 to 20 minutes using either a forced air warming blanket or gown system.7 This practice minimizes thermal discomfort and maximizes heat transfer.

It is worth noting that treating postoperative hypothermia in the PACU is substantially more expensive than helping to prevent it in the preoperative area.8 To avoid postoperative hypothermia, it’s important to practice proactive normothermia management by consistently monitoring core body temperature and actively warming patients, starting in the perioperative area and continuing throughout the entire surgical journey.

About the author
Al Van Duren is the global director of scientific affairs and education in 3M’s Infection Prevention Division. He has a master’s degree in physiology from the University of Minnesota and holds 26 patents for warming, pulmonary and thermometry devices.

References
1. Sessler DI. Temperature monitoring and perioperative thermoregulation. Anesthesiology. 2008;109(2):318-338.
2. Matsukawa T, Sessler DI, Sessler AM, et al. Heat flow and distribution during induction of general anesthesia. Anesthesiology. 1995;82(3):662-673.
3. Matsukawa T, Sessler DI, Christensen R, Ozaki M, Schroeder M. Heat flow and distribution during epidural anesthesia. Anesthesiology. 1995;83(5):961-967.
4. Moayeri A, Hynson J, Sessler DI, McGuire J. Pre-induction skin-surface warming prevents redistribution hypothermia. Anesthesiology. 1991;75 Suppl(3A):A1004.
5. Hynson JM, Sessler DI, Moayeri A, McGuire J. Heat storage capacity of the peripheral thermal compartment. Anesthesiology. Vol 751991:A195.
6. Menzel M, Grote R, Leuchtmann D, Lautenschläger C, Röseler C, Bräuer A. [Implementation of a thermal management concept to prevent perioperative hypothermia: Results of a 6‑month period in clinical practice]. Der Anaesthesist. 2016.
7. Horn EP, Bein B, Böhm R, Steinfath M, Sahili N, Höcker J. The effect of short time periods of pre-operative warming in the prevention of peri-operative hypothermia. Anaesthesia. 2012;67(6):612-617.
8. de Brito Poveda V, Clark AM, Galvão CM. A systematic review on the effectiveness of prewarming to prevent perioperative hypothermia. J Clin Nurs. 2013;22(7-8):906-918.

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