Episode #94 Keeping Patients Warm and Safe in the Operating Room

April 19, 2022

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Welcome to the next installment of the Anesthesia Patient Safety podcast hosted by Alli Bechtel.  This podcast will be an exciting journey towards improved anesthesia patient safety.

Welcome to another Rapid Response to Questions from our readers episode. This one is from the February 2022 APSF Newsletter. Our featured article today is “Thermal Injury After Use of a Convective Warming System” by Luke Janik and Ryan Lewandowski.

Here are the measures that the authors’ department took following these cases to help keep patients safe and prevent thermal injuries.

  • Always confirm the presence of the air manifold component prior to connecting the hose to the warming blanket.
  • Start with the medium temperature setting (40° Celsius) unless otherwise indicated.
  • Use caution to avoid airflow restriction within the warming blanket.

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© 2022, The Anesthesia Patient Safety Foundation

Hello and welcome back to the Anesthesia Patient Safety Podcast.  My name is Alli Bechtel, and I am your host. Thank you for joining us for another show. Welcome to another Rapid Response to Questions from our readers episode. This one is from the February 2022 APSF Newsletter.

Before we dive into the episode today, we’d like to recognize Edwards Lifesciences, a major corporate supporter of APSF. Edwards Lifesciences has generously provided unrestricted support to further our vision that “no one shall be harmed by anesthesia care”. Thank you, Edwards Lifesciences – we wouldn’t be able to do all that we do without you!”

Our featured article today is “Thermal Injury After Use of a Convective Warming System” by Luke Janik and Ryan Lewandowski. To follow along with us, head over to APSF.org and click on the Newsletter heading. First one down is the Current Issue. Then, scroll down and look in the left-hand column and click on the Rapid Response to questions from readers heading and then click on our featured article. Today, we will be reviewing two cases of thermal injuries related to the use of a convection warming system. In both cases, the “over temperature” audible and visual alarms did not activate, and patients were harmed as a result. Over the course of the show today, we will review the cases, discuss the important points for Smiths Medical, the manufacturer, to consider, discuss challenges related to using the Operator’s Manual, and finally the authors provide tips for using convection warming devices and keeping patients safe.

First up, let’s get into the cases. The authors tell us about two consecutive patients who underwent laparoscopic robotic prostatectomy in the Trendelenburg position with tucked arms in the same operating room with the same anesthesia team. For both cases, a Smiths Medical EQUATOR Level 1 Convective Warming System was used with the Snuggle Warm Small Upper Body Convective Warming Blanket. The upper body warming blanket was placed on the patients’ chest and secured with the built-in adhesive strip. No additional blankets were used on or under the warming blanket. The warming blanket was then tucked into the crease between the operating room table and the mattress with the hose connected to the warming blanket at the connection port near the left shoulder. The hose was then secured with a retaining clip to the pole.

Have you used this device in the operating room to help keep patient’s warm during an operation? Do you know what the “air manifold” component of the warming system looks like and its function? This important component, the “air manifold” was missing from the device. The “air manifold” is the elbow shaped plastic tube that is attached to the end of the warming hose. This piece serves an important function since it has several openings on the end that is connected to the warming blanket to make sure that the warm air is dispersed evenly over the patient. Check out Figure 1 in the article for pictures of the set-up. And check out Figure 2 for photos that demonstrate the components of the hose end, air manifold, and blanket port. In panel C, you can see how easy it would be to inadvertently connect the hose end directly to the blanket port if the air manifold was missing. Back to the cases, the warming device was set to the high setting of 44 degrees Celsius for the duration of the cases. There were no visual or audible alarms from the convective warming system during the cases and the device seemed to be working appropriately. Both patients remained hemodynamically stable throughout the case and were normothermic by nasopharyngeal temperature monitoring. In the PACU, the patients were found to have diffuse erythema on the left upper extremity and chest which was close to the blanket port connection of the warming system. Then, on postoperative day one, the patients had blistering on their shoulders and chest, which you can see in Figure 3 from the article. The burns responded to conservative treatment.

Has this ever happened when you were providing anesthesia care…a patient developed a thermal injury from the convective warming system? The convective warming system is designed to help keep patients safe from hypothermia and maintain normothermia during surgery and anesthesia, but what happens when this device becomes a threat to patient safety? There is so much to discuss…so let’s keep going.

The authors kick off the discussion about the risks related to hypothermia during anesthesia care. These risks include increased surgical site infections, blood loss, and cardiac events. It is critical that we prevent hypothermia in the operating room. The Centers of Medicare and Medicaid Services have included perioperative temperature management as a core anesthesia measure with the requirement for postoperative temperatures greater than 35.5 degrees Celsius following procedures that are longer than 60 minutes. This helps to explain why convective warming systems are used in the operating room – to help keep patients warm to prevent hypothermia during longer surgical procedures. However, thermal injuries from these warming devices are rare especially when the device is used appropriately. Keep in mind that the convective warming system should always be used with a warming blanket and not just the hose placed near the patient’s skin. In addition, the Smiths Medical Equator Level 1 Convective Warming System comes with safety features to help prevent thermal injuries. These safety features include “Over Temperature” alarms, a maintenance indicator, and an occlusion indicator. The authors point out that the thermal injury sustained by their patients was likely due to overheating at the location of where the hose connects to the warming blanket from the resulting burn location. One option is that the “Over Temperature” alarm failed. This alarm should alarm if the temperature is 3 degrees Celsius above the set point. If this occurs, the device should then stop power to the heater and blower. Another possible explanation for the thermal injuries is that the air temperature was higher than the alarm set point temperature of 47 degrees Celsius or perhaps the missing air manifold contributed to the thermal injury (in the one case where it was missing.) Let’s take a closer look at the air manifold that was designed, according to the Operator’s Manual to do the following:

  • “Distributes the warmed air to delivery channels in a pattern designed to promote heat transfer to the patient”

In addition, the air manifold has perforations located on the patient side to help evenly disperse the warmed air through the warming blanket. Thus, if the air manifold is missing the warmed air may be delivered to a focused area over the patient leading to an increased risk of a thermal injury. Following these cases, the devices were returned to the manufacturer, Smiths Medical, for further investigation.

The next step that the authors took was to start a conversation with Smiths Medical about the device failure and subsequent threat to patient safety. Let’s take a look at each of these questions.

First, what is the importance of the air manifold? If this device is so important to the safe operation of the device, why is it able to be removed and why is the device able to be used without the air manifold correctly in place? If you look closely at Figure 2, you can see that there is no warning label to alert the user that the air manifold must be attached prior to use. Should there be a warning label on the end of the hose to alert the user that it is dangerous to connect the hose directly to the warming blanket without the air manifold in place? Other option that the authors suggest is the use of a “forcing function” that would prevent the hose from being directly connected to the blanket port. This is similar to how a diesel fuel pump cannot be inserted into a regular fuel tank. Was this something that the manufacturers considered?

The next couple of questions are related to the Operator’s Manual for the EQUATOR Level 1 Convective Warmer. If you read this manual, you will see a list of warnings to help prevent patient injury when using the device. Some of these warnings do not seem to apply to patients in the operating room or under general anesthesia. So, let’s take a closer look.

The manual reads: “To prevent thermal injury, do not use the highest temperature setting when treating patients who have decreased sensation, are non-sensate, or have poor perfusion.”

So, does this mean that the highest temperature should not be used for patient’s under general anesthesia who are non-sensate? However, patients under general anesthesia often require active warming to prevent hypothermia.

Another warning from the manual is this. “Always start therapy on the lowest non-ambient temperature setting to prevent thermal injury. Increase the temperature setting, if required, using core body temperature and cutaneous response of skin in contact with the convective warming blanket as indicators.”

Is this how you use the convection warmer in the operating room? Many times, the convection warmer must be started at the highest setting because patients under general anesthesia are at risk for heat loss from radiation, conduction, convection, and evaporation. Should we not be doing this or are there times when it is safe and appropriate to start the  convection warmer at the highest setting such as for burn patients or trauma patients? If the device is started at the lowest setting, how much time must elapse before increasing the temperature setting?

Another warning from the manual advises the user to “…Observe cutaneous response at regular intervals to prevent thermal injury. If erythema or instability in vital signs is evident, decrease the temperature setting or discontinue use of the convective warming therapy.”

The authors experience with these thermal injuries helps to demonstrate that it may be difficult or impossible for anesthesia professionals to detect clinical signs in the operating room when the warming device is being used and patients remain hemodynamically stable. It is often difficult to observe the patient’s skin under the warming device and under the surgical drapes. It may be even more difficult with dimmed lighting in the operating room to see any new skin changes, such as erythema. Hemodynamic instability in the operating room during surgery and anesthesia may be due to a number of reasons that are unrelated to the warming device. The authors remind us that hypotensive patients in shock may require active warming to prevent hypothermia and coagulopathy.

Another warning from the manual states that ““To prevent thermal injury, do not allow any of the patient’s body parts to rest on the active hose inlet.”

It makes sense, but given the design of the Snuggle Warm blanket it is difficult to prevent the patient’s shoulder from coming into contact with the active hose inlet. Is there a different design that could be created to make sure that connection port is further away from the patient, such as an elephant trunk type extension? In addition, when the patient’s arms are tucked during the procedure, how should the upper body warming blanket be used to keep patients warm and safe?

We are almost out of time for today, but before we wrap up, we are going to review the measures that the authors’ department took following these cases to help keep patients safe.

  • Always confirm the presence of the air manifold component prior to connecting the hose to the warming blanket.
  • Start with the medium temperature setting (40° Celsius) unless otherwise indicated.
  • Use caution to avoid airflow restriction within the warming blanket.

The authors conclude by inviting Smiths Medical to respond to these questions and continue to the discussion on the safe use of convective warming systems.

If you have any questions or comments from today’s show, please email us at [email protected]. Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. We hope that you will visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.  If you have not done so already, we hope that you will rate us and leave a review on iTunes or wherever you get your podcasts and feel free to share this podcast with your friends and colleagues and anyone that you know who is interested in anesthesia patient safety. Plus, you can let us know that you are listening by tagging us @APSForg using the hashtag #APSFpodcast.

Until next time, stay vigilant so that no one shall be harmed by anesthesia care.

© 2022, The Anesthesia Patient Safety Foundation