Overview of Targeted Temperature Management
Therapeutic hypothermia, or the practice of cooling down a person’s body to slow down biological processes and delay death, has been around for a long time. This idea was even present with the ancient Egyptians and Hippocrates around 450 B.C. Hippocrates recommended covering wounded soldiers in snow to cool them down. Fast forward to the French invasion of Russia in the early 1800s, there was an observation that injured soldiers nearer to campfires died faster than those in cooler places. At this time, doctors also used cold treatment, or cryoanalgesia, for amputations and noted that it helped in reducing pain and slowing bleeding.
Doctors’ interest in using therapeutic hypothermia started in the 1930s when they recorded successful resuscitations on drowning victims who had been without oxygen for a long time. In 1943, Temple Fay wrote a scientific paper on therapeutic hypothermia and noted better outcomes in patients with traumatic brain injury when the body temperature was lowered to between 32.7 and 38.3 degrees Celsius.
In the 1950s and 1960s, medical trials using deep hypothermia were conducted but quickly discontinued due to negative side effects. Then, in the 1990s, doctors used mild hypothermia treatment on three cardiac arrest patients after successful resuscitation. All three patients fully recovered without any remaining brain damage.
Therapeutic hypothermia gained attention after two studies published in the New England Journal of Medicine in 2002 demonstrated significant improvements in survival rates and neurological outcomes. These days, the term “targeted temperature management” (TTM) is often used instead of therapeutic hypothermia. TTM can be used to prevent a fever, maintain normal body temperature, or induce hypothermia.
Anatomy and Physiology of Targeted Temperature Management
Thermoregulation is our body’s way of keeping a steady internal temperature despite changes in the environment. The average human body temperature generally ranges from 36.1 to 37.2 degrees Celsius. This is managed by the hypothalamus, a part of the brain that communicates with receptors in the skin and within itself that monitor temperature to make sure it stays stable.
When your body temperature drops, the hypothalamus sparks reactions to generate and conserve heat. One key way it does this is by causing you to shiver, which is essentially a rapid contraction of muscles that produces warmth. The hypothalamus also sends signals to the sweat glands and blood vessels in the skin to reduce heat loss. It triggers the release of adrenaline and noradrenaline, body chemicals that boost heat production. Additionally, it can stimulate the production of a hormone from the pituitary gland in the brain, that also helps generate heat if the body is experiencing long periods of cold.
Temperature management plays a crucial role, especially during certain medical conditions, like when a person’s brain isn’t getting enough oxygen. Cooling the body down can help slow the body’s metabolism rate by 5% to 7% per 1 Celsius degree decrease in body temperature. This is important because it slows the progression of brain cell death that comes from not having enough oxygen and the build-up of waste products. Certain neurotransmitters, or messaging chemicals in the brain, accumulate and cause brain cell death during such conditions and their release is found to be dependent on temperature.
Reviving the oxygen supply to the brain after it’s been deprived can result in a massive increase in harmful free radicals. These are essentially unstable molecules that can harm cells. This effect, known as reperfusion, can lead to the damage of cell structures like fats, proteins, and DNA. Cooling the body has been shown in lab studies to help reduce this effect by limiting the production of these harmful free radicals.
Reperfusion also sparks inflammation or swelling. While some aspects of inflammation can be protective, if it goes on for too long (up to 5 days), it can worsen brain damage. Cooling the body, however, can suppress the whole swelling process, preventing further harm to the brain due to inflammation.
Why do People Need Targeted Temperature Management
According to the American Heart Association’s 2015 guidelines for caring for patients after a heart attack, some of the key recommendations include:
- Applying a technique called targeted temperature management (TTM), to patients who become unconscious after experiencing a heart attack outside of a hospital. This advice applies particularly to patients whose hearts initially display unusual heart rhythms such as pulseless ventricular tachycardia (a fast, irregular heartbeat) or ventricular fibrillation (a very fast, irregular, and chaotic heart rhythm). The AHA strongly supports this approach.
- The same TTM technique is advised for patients who become unconscious after a heart attack that occurs inside a hospital. This recommendation also applies to patients with other types of abnormal heart rhythms. Again, the AHA strongly supports this method.
Additionally, the 2015 international agreement called the International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations (made by the International Committee on Resuscitation or ILCOR) suggests:
- Using therapeutic hypothermia (TH), a procedure of cooling the body to a lower than usual temperature, for unconscious patients after a heart attack that occurs outside of a hospital. This applies regardless of whether the patient’s heart initially showed unusual or usual rhythms.
- Applying therapeutic hypothermia also for unconscious patients who had a heart attack inside the hospital, as long as there was an abnormal heart rhythm displayed initially.
When a Person Should Avoid Targeted Temperature Management
If you have certain health issues, using therapeutic hypothermia (cooling the body on purpose) can cause more problems. But even in these cases, doctors can still use a method called targeted temperature management to keep your body temperature normal. If you’ve had a certain type of stroke that causes bleeding in the brain, if your Glasgow Coma Scale (GCS) score is more than 8 (which measures how conscious or awake you are), if you’re bleeding uncontrollably, have unsteady heartbeats that can’t be controlled, or if your heart stopped because of trauma, therapeutic hypothermia should be absolutely avoided.
In other situations, therapeutic hypothermia should be used with caution. These situations include: having a low platelet count (platelets help blood to clot), having a bleeding disorder, if the heart took a really long time (more than 60 minutes) to restart after a cardiac arrest, or if the patient’s blood pressure stays low even after getting fluids and medication (vasopressors) to increase it.
Preparing for Targeted Temperature Management
Before starting a treatment called Targeted Temperature Management (TTM), doctors need to ensure the patient’s overall condition is stable. This means the heart should be functioning properly, and the patient should have a good airway, which is the path air takes to get to your lungs. They should also have the right levels of oxygen and air going in and out of their body (ventilation). It’s also important for doctors to know the patient’s health status before starting this treatment, and have a proper monitoring system in place to check the heart’s activities.
Before they start TTM, doctors need to get a series of tests done. These include blood tests to check the levels of certain substances in the blood, including gases (ABG), heart-related substances (cardiac enzymes), mineral salts (electrolytes), different cells in the blood (CBC), a heart failure marker (BNP), as well as clotting ability (INR, PT/PTT), a muscle enzyme (CPK), a heart-related protein (troponin), and a fatigue-related substance (lactate). These tests help doctors to have a clear idea about the patient’s current health status.
The patient will be hooked up to a continuous EKG monitor to keep a constant eye on the function of the heart. They will have a tube inserted into their windpipe (endotracheal intubation) which is then connected to a machine to help them breathe (mechanical ventilation).
A small device (pulse oximeter) will be placed on a finger or earlobe to check the level of oxygen in the blood. Non-invasive blood pressure monitoring will be used, which means the blood pressure is taken from outside of the body. If an accurate blood pressure reading is needed, an arterial catheter may be inserted in an artery. A central venous catheter, which is a tube placed in a large vein in the neck, chest, or groin, will also be used.
Doctors will also set up two large needles (peripheral IVs) into a vein, continuously measure the body temperature with a probe (inserted into food pipe, rectum, or bladder), and insert a catheter into the bladder for urine collection (Foley catheter). There will be special equipment used for changing the body temperature (cooling equipment), and a warming system will be kept ready just in case the body temperature goes down too much. The type of cooling equipment used will depend on the hospital’s protocol.
How is Targeted Temperature Management performed
When managing a patient’s temperature we try to follow three main stages: getting the body cool quickly, keeping it at the cooler temperature for a while, and gradually warming it back up again. We’re aiming to rapidly lower the body’s core temperature to between 32 and 34 degrees Celsius (89.6-93.2 degrees Fahrenheit), hold it there for 12 to 24 hours, and then carefully rewarm at a rate of 0.2 to 0.5 degrees Celsius per hour (0.36-0.9 degrees Fahrenheit).
The Process of Cooling Down:
We call the cooling down phase “Induction of hypothermia”. This is when we aim to quickly get the body’s core temperature down to the target range. We can achieve this with several different methods that could start in the ambulance or once the patient reaches the hospital. Although it was once believed that starting the cooling as soon as possible would lead to better results, some studies have shown this might not always be the case. Some studies have found no improvements in patient outcomes even when the core temperature was lowered sooner. This has led some scientists to question the optimal start time for cooling.
Cooling techniques can be categorized into three main groups: conventional methods, surface cooling systems, and internal (intravascular) cooling systems:
Conventional Methods:
These techniques include using cold saline (salt water) infusions and ice packs. They’re the simplest and most cost-effective methods. Plus, they can kickstart the cooling process even before the patient arrives at the hospital, and they can be used in addition to more advanced methods for speeding up the cooling. The downside is they need a lot of manual labor, can sometimes cool the patient too much, and don’t do a great job of keeping them at the targeted temperature.
Surface Cooling Systems:
These systems use blankets or pads that are cooled by circulating cold air or fluid around the patient’s body. They require less manual labor, have automatic temperature control, and are generally easier to use. However, they pose a small risk of causing skin burns and irritation, and sometimes they can lower the body temperature too much.
Internal Cooling Systems:
This method mainly uses catheters (thin tubes) placed in a major vein that circulate cold saline. They’re regarded as the most reliable for all three stages of temperature management. Though, they do have some disadvantages. They require a minor invasive procedure to place the catheter, there’s a risk of blood clotting or infection at the catheter site, and they’re relatively expensive.
When it comes to monitoring body temperature throughout this whole process, it’s important to have accurate real-time measurements. We typically get these measurements from a catheter placed in the pulmonary artery (a major blood vessel leading from the heart to the lungs). Other methods, such as bladder, rectum, esophagus, and tympanic membrane (the eardrum) measurements, can be a bit slower to respond when the body’s temperature is changing rapidly, which could cause us to cool the body too much during the induction phase. The esophagus provides one of the fastest and most accurate measurements, with a delay of around 5 minutes. But it does have the drawback of possibly getting in the way of some other procedures. Other methods have longer delays, but they can be more straightforward to implement.
Possible Complications of Targeted Temperature Management
When patients undergo targeted temperature management, there may be changes in the body that can lead to problems during treatment. The people taking care of these patients need to know about these issues and how to handle them. By taking preventative action, spotting issues early, and addressing them swiftly, we can help improve the patient’s survival chances.
Most of the issues linked to targeted temperature management can have an impact on the heart and blood vessels. This is mainly because about 80% of these patients have heart conditions. As the body’s temperature drops, the blood vessels close to the skin become narrower. There may also be a rise in the production of certain hormones, which can put a strain on an already weak heart by increasing its need for oxygen. This fall in temperature can also reduce blood supply to the heart and decrease the amount of blood pumped by the heart by around a quarter. Changes may also include higher blood pressure, increased resistance in the blood vessels, and slower heart rate. Severe issues with heart rhythm don’t usually happen, but if the body temperature falls too low, the risk of this increases.
Targeted temperature management can also have a significant impact on the kidneys. The decrease in temperature can lead to increased urine production. This happens due to a range of factors, including the narrowing of blood vessels, release of certain hormones, and lower levels of another hormone that is usually responsible for controlling water balance in our bodies. If this issue isn’t addressed, it may lead to problems like low blood volume, irregularities in the levels of dissolved substances in the blood, and increased concentration of red blood cells.
The process of lowering body temperature can also cause a decrease in the levels of several dissolved substances in the blood, including magnesium, potassium, and phosphate. It’s essential to regularly check and, if required, correct these levels. A lack of these substances in the blood can cause problems like narrowing of blood vessels, rapid heartbeat, and weakening of the respiratory muscles, making it difficult to breathe.
As the body’s temperature is increased back to normal, the levels of these substances can change again. This change can cause the levels of potassium in the blood, specifically, to increase, leading to problems with the heart’s rhythm. Increasing the body temperature slowly and steadily helps the kidneys to remove the excess potassium safely and can potentially prevent this issue.
Lowering body temperature can also affect the immune system, often leading to a lower risk of brain injury. But, this can also increase the chances of infection as it can slow down the body’s response to injury and infection. It’s been found that the risk of lung infection and blood infection can increase with this treatment. Therefore, it’s crucial to regularly keep a check on potential infections and carry out preventative measures like maintaining blood sugar levels, regularly inspecting the places of tube insertion, etc.
Lastly, dropping body temperature can influence the body’s metabolism. It slows down the breakdown of oxygen, which may contribute to changes in the blood pH levels. Changes can also occur in the body’s response to different medications. Especially in cases where patients are on multiple drugs, some might react differently to changes in body temperature. Also, the body may become less responsive to insulin, leading to changes in blood sugar levels.
What Else Should I Know About Targeted Temperature Management ?
In this study, we examined some medical procedures that help to cool down the body after a cardiac arrest has occurred outside of a hospital setting. Cardiac arrest is when the heart suddenly stops beating, and it is a very serious situation that needs immediate medical attention. Cooling the body, or “therapeutic hypothermia,” is one way to help people who remain unconscious after their heart has started beating again.
One study done in Australia between September 1996 and June 1999, took 77 patients who had a cardiac arrest outside the hospital and were still unconscious even after their heart was beating again. Patients with a heart attack that was not caused by a heart disease, people with a very low blood pressure caused by heart problems, males under 18 and females under 50 were not included in the study. The patients were split into two groups. One group’s body was cooled to a temperature of 33°C, and the other group’s body was maintained at 37°C, which is the normal human body temperature.
External cooling devices, like ice packs, were used to lower the body temperature of the first group in the ambulance on the way to the hospital. Once they arrived, the cooling continued. The target temperature of 33°C was maintained for 12 hours after they arrived at the hospital.
At the end of the study, it was observed that 49% of the patients in the cooled group had a good recovery and could be sent home or to a rehab facility, compared to 26% in the group that was kept at the normal body temperature. Accordingly, cooling the body after cardiac arrest outside of the hospital can lead to better recovery. Cooling the body was also found to be safe, with no significant changes observed in the blood pressure, heart rate and levels of potassium and glucose.
An European study involved 275 patients from nine different centers in five countries who had a cardiac arrest outside the hospital. This study also divided the patients into two groups – one group was cooled to a temperature between 32°C and 34°C, and the other group was kept at the normal body temperature. The cooling was started as soon as they reached the hospital and maintained for 24 hours. After the cooling, they were allowed to slowly return to the normal body temperature.
In this study, the main measuring point was how well the patients were doing neurologically, meaning how well their brains were functioning six months after the heart attack. 55% of the patients in the cooled group had a good neurological recovery, as compared to 39% in the normal temperature group. The death rate was also lower in the cooled group.
But, it was also observed that the cooled group had more complications like infections which might be due to keeping the body cool for a longer duration. As such, while cooling the body can improve survival and brain function, it can also increase the risk of complications.
A large-scale study involving 950 patients in 36 intensive care units in Europe and Australia also showed similar results. This study tried to find the best body temperature to cool to between 33°C and 36°C. This study also included patients who had an irregular heartbeat that was not responding to treatment, which the previous studies did not. Surface coolants were used in 76% of patients, and devices placed inside the body were used in 24% of patients to start the cooling process.
This study found no significant difference in survival rates and neurological function between the patients cooled to 33°C and those cooled to 36°C. Therefore, cooling the body after a cardiac arrest outside of the hospital can be beneficial and can improve both survival rates and neurological functioning.