Targeted Temperature Management - Monitoring and Guidelines

Introduction

Maintaining a normal body temperature is essential for proper bodily functions. During surgery, changes in body temperature can occur with general anesthesia, leading to unintentional hypothermia (lowered body temperature) being more common than hyperthermia (elevated body temperature). The medications and sedatives used during anesthesia make patients less responsive to temperature changes, causing their body temperature to drop when exposed to cooler operating room environments. These temperature fluctuations can have adverse effects on patients' well-being and outcomes.

What Is Targeted Temperature Management (TTM)?

Targeted Temperature Management (TTM), or Therapeutic Hypothermia, is used after a person's heart starts beating again following cardiac arrest. It involves carefully controlling the body's temperature to specific levels to minimize brain damage. Cooling the body aims to protect the brain and improve the chances of recovery after a cardiac arrest.

What Is the Technique of Targeted Temperature Monitoring (TTM)?

The targeted temperature management process involves induction, maintenance, and rewarming. The aim is to quickly reach and maintain a core temperature of 32 to 34 degrees Celsius for 12 to 24 hours, followed by a controlled rate of warming.

Induction Phase:

Different methods are used to cool the body in the ambulance or once the patient arrives at the hospital. Early cooling during ambulance travel does not always result in better outcomes. For example, a patient with cardiac arrest was offered cold treatment either in the ambulance or once they got to the hospital. As a result, the earlier cooling did lower the core temperature, but it had no positive effects on the patient's overall condition after hospital discharge. These results are at odds with earlier animal experiments that suggested earlier cooling would be beneficial, but this makes it more challenging to determine when cooling treatment should begin. There are three main categories of cooling methods:

• Traditional Cooling Techniques: It involves using ice packs and cold saline infusions, which are simple and cost-effective methods. They can be used by paramedics to lower body temperature safely. Maintaining it can be challenging and might only sometimes reach the ideal target temperature.

• Surface Cooling Systems: They use blankets or pads that circulate cold air or fluid to lower body temperature. They are simple and often have automatic features to maintain the desired temperature. The risk of skin burns or irritation is minimal, although, in some instances, the initial cooling phase's temperature may drop too low.

• Intravascular cooling systems: Intravascular catheters are used in core cooling systems to circulate ice-cold saline and reduce body temperature. They are dependable but require an invasive procedure and carry risks of complications. Compared to other methods, they have a higher cooling rate and better temperature control but are more expensive.

Maintenance Phase:

• Accurate temperature measurement is crucial for therapeutic hypothermia to achieve the desired target temperature and control warming.

• Utilizing a pulmonary artery catheter to measure blood temperature is the most accurate technique.

• Commonly used sites like the bladder, rectum, esophagus, and tympanic membrane have time delays, especially during initial cooling, which may lead to overshooting the target temperature.

• Esophageal temperature reflects core temperature best but may interfere with specific procedures.

• Bladder temperature is convenient but less reliable due to low urine production.

• Rectal temperature is simple to detect, and there is a chance of displacement.

• Peripheral sites need to be more accurate and should be avoided.

Rewarming Phase:

The core body temperature slowly increases by 0.2 to 0.5 degrees Celsius per hour until it reaches 36 degrees Celsius. Rewarming should be done gradually to avoid difficulties, as rewarming too quickly can reverse the therapeutic hypothermia's beneficial effects. It is possible to stop using cooling equipment and drugs to stop shivering once the temperature hits 36 degrees Celsius. The rewarming phase typically begins 12 to 24 hours after starting the cooling process and may take up to 8 hours to complete.

How Is Temperature Monitored During Surgery?

Temperature monitoring is essential during anesthesia to detect and manage temperature disturbances. The body's core temperature, the average temperature of vital organs, is typically around 37°C. However, there are natural variations throughout the day. Different body parts, such as the skin, can have lower temperatures than the core. Monitoring core temperature is crucial because it influences the body's thermoregulatory responses and can affect patient outcomes.

Hypothermia or low body temperature is common during surgery and can lead to complications. Anesthesia and the excellent operating room environment contribute to hypothermia. On the other hand, hyperthermia or high body temperature can occur due to various causes and require diagnostic attention.

Thermometers come in a variety of designs and are used to measure temperature. Commonly used thermometers and thermocouples deliver precise readings. Infrared thermometers help measure surface temperature since they can calculate the temperature at a distance.

Zero-heat-flux thermometers use insulators to measure core temperature precisely.

Various sites on the body can be used for temperature monitoring. Core temperature can be measured in the pulmonary artery, esophagus, nasopharynx, or tympanic membrane. These sites provide reliable readings during anesthesia. Temperature estimation can also be done at near-core locations like the mouth and armpit. However, sites like the bladder and rectum are less accurate in reflecting core temperature.

Overall, temperature monitoring is essential during anesthesia to ensure patient safety and prevent complications related to temperature disturbances.

What Are the Guidelines in Temperature Management?

According to ASA standards, anesthesia patients must monitor their temperature when there are anticipated or suspected changes in body temperature. According to the Outcomes Research Consortium guidelines:

• Most patients under general anesthesia for more than thirty minutes should have their body temperature checked.

• It would be ideal to monitor body temperature continuously, but checking every 15 minutes is usually sufficient.

• Patients at risk of hypothermia during spinal or epidural anesthesia should have their core temperatures checked.

• Intraoperative core temperatures should generally be maintained above 36°C unless hypothermia is needed.

According to the NICE proposed Clinical Practice Guidelines for Management of Perioperative Hypothermia in Adults:

• Hypothermia is defined as having a core temperature below 36.0°C.

• Preoperative, intraoperative, and postoperative stages make up the perioperative route.

• Patients should be assessed for hypothermia risk before entering the operating theatre.

• Anesthesia should only be induced when the core temperature is above 36°C.

• Utilizing a warming device, IV fluids, and blood components should be warmed to 37°C.

• The use of forced air warmers is recommended to prevent and treat perioperative hypothermia.

Conclusion

During surgery, monitoring body temperature is often overlooked compared to other vital signs. However, temperature changes can happen frequently during surgery, so monitoring, preventing, and treating them is important as part of the overall anesthesia plan. It's recommended to use a combination of methods to keep the patient warm before, during, and after surgery, such as warming fluids and using devices to warm the skin. The anesthesiologist can decide the specific location and method of temperature monitoring based on the type of surgery and what's most convenient.