Warmed Hospital Blankets:
How Warm Should
They Be?

Warmed cotton blankets have been used at least fifty years to provide comfort to patients in hospitals, but how warm should they be? Much attention is focused on the temperature of the blankets, and what temperature is considered ‘safe’. But, equally important is the measure of the heat capacity of the blankets, and how much heat (or energy) flows to the patient.

‘In physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature. On the macroscopic scale, temperature is the unique physical property that determines the direction of heat flow between two objects placed in thermal contact. When two systems are at the same temperature, no heat transfer occurs between them.’ But, the temperature level does not in itself account for the amount of heat transfer that takes place. ‘Heat capacity is the measure of the heat energy required to increase the temperature of an object by a certain temperature interval. Heat capacity is an extensive property because its value is proportional to the amount of material in the object: for example, a bathtub of water has a greater heat capacity than a cup of water.’

So, the temperature difference between two objects is the ‘driving force’ for the heat transfer to occur, but the amount of heat transferred depends on the heat capacity of both objects, particularly the heat capacity of the higher-temperature object. The heat transfer will occur from the higher-temperature object to the lower-temperature object until thermal equilibrium occurs.

A typical cotton hospital blanket has a very low total heat capacity because the cotton and air of which it is comprised have very low densities and low specific heat capacities, and it’s not very large (low mass). Cotton and air also are substances with low thermal conductivity. Even if the blanket is warmed to 200F, the amount of heat energy in the blanket is very small. The (variable) temperature of the blanket should be as reasonably high as possible because the (fixed) heat capacity is so low. And, the heat transfer process will begin immediately when the blanket is removed from the warmer, but the interaction will be between the blanket and the ambient air. The warmed blanket will cool before it reaches the patient, and this is another reason the blanket should be as warm as possible in the warmer. A blanket heated to only 110F will likely be at 98F or lower when it reaches the patient, so no heat transfer could occur. And if it cools in the ambient air to a temperature lower than 98F, the direction of heat transfer would be from the patient to the blanket!

A common mistake made in evaluating the ‘safety’ of various temperatures is in comparing objects or materials with disparate heat capacities. Water is a common substance, and is sometimes used as a temperature ‘reference’. But, water has an unusually high heat capacity; it is very dense with a high specific heat value. It requires a large amount of heat energy to change temperature, and so it absorbs or loses a relatively large quantity of heat for each degree of change. This is unlike cotton, and a warmed blanket can barely make it to the patient without losing much of its heat. Water and cotton are very dissimilar regarding heat capacity, and should not be confused with one another.

Of course, the purpose of a warmed blanket is to trigger a positive psychological reaction in the patient, and it has to be warm enough to do this. The warmed blanket contains too little heat for any significant heat transfer to the skin to occur, and certainly not enough to influence core body temperature. The very comfortable feeling of warmth is transitory, but important to the patient and the caregiver. ‘Postoperative thermal discomfort per se is not life-threatening; nonetheless, numerous patients recall feeling cold as the worst aspect of surgery. Efforts to prevent and treat such unpleasant sensations deserve the same attention we currently give pain management.’

When ENTHERMICS Medical Systems entered the medical blanket/fluid warming market about fifteen years ago, we knew that blankets had been warmed to 150-160F for many, many years. Yet, this temperature was not warm enough to ensure the patient really received a blanket that was ‘warm enough’. We believed that the maximum temperature chosen for the blankets was simply the recommended maximum temperature for irrigation pour bottles since most machines warmed both blankets and irrigation fluids. But, because our machines have completely separate chambers for blankets and fluids with independent heating systems for each, we could offer the better, higher, and perfectly safe maximum temperature of 200F for blankets. And, now we have thousands of warmers installed throughout the world operating safely and effectively at this temperature, and providing clinically significant comfort to patients.

For further discussion, contact Mark at marks@enthermics.com

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Oasis of Comfort

Barbara Laderoute, OR manager at Centre University De Sante - McGill in Montreal recently wrote that they have several Enthermics warmers and are very pleased with them. Barbara says “The Enthermics blanket and fluid warmers are very beneficial to our patients. The warmed blankets give our patients a feeling of warm comfort prior to and after surgery. This adds an oasis of comfort in an otherwise uncomfortable situation.

In addition, the warmed fluids are extremely helpful in preventing Perioperative Hypothermia in our surgical patients. The pre-warming of the IV and irrigation fluids eliminates the potential negative side effects of unintended Perioperative Hypothermia in our operating environment."

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Unauthorized Entry

One of the easiest ways to deter unauthorized entry or theft of the contents in your fluid warmer is to keep the door locked at all times. But what can you do to safeguard those substances if your keys are lost or end up in the wrong hands? That’s a question that should be carefully considered.

Each time a key is issued to a new user, it puts the facility, and the people who use that facility, at increased risk. Standard locking systems allow anyone with a key to easily make a copy. With an unauthorized duplicate key or just a lost key, a thief has complete access to the contents inside.

A programmable lock is an ideal solution for facilities with multiple users and access points and basic access control management requirements. It eliminates the need for keys and you control who has access.

The Enthermics Combination Lock Kit is designed to safely secure your medical fluids. The easy to use electronic lock is equipped with a five (5) digit keyless control, an electro-mechanical mechanism to secure the fluid warmer door, and a standard mechanical key lock override if a power failure should occur. The lock can store any three-digit combination password code. Numerical codes are easily changed via the lock keypad. Combination lock kits are available on all new Enthermics Medical Systems fluid warmers and can be added to existing units with a filled upgrade kit.

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Don’t Laugh Off Humor

Have you ever heard of “laughing off” a bad situation? Much more than a time-honored cliché, laughter is an effective and easy way to ward-off stress.

Aside from adopting a lighthearted view of things, laughter has many positive effects on the body, including:

• Physical release – Much like stretching or brief exercise, laughter provides an internal physical release that leaves a refreshed feeling.
  
• Distraction – Instead dwelling on stress-causing situations, laughter can provide a momentary mental vacation from the situation. Borrowing from a Coca-Cola campaign, it can be the “pause that refreshes.”
  
• Hormone release – Laughter increases the levels of health-enhancing hormones like endorphins and neurotransmitters, while building the body’s immune system. At the same time, stress hormones such as cortisol, adrenaline, dopamine, and growth hormones are suppressed by laugher.
  
• Social benefits – Laugh and the world laughs with you. It’s an excellent social connector, and contagious as well. Make someone else laugh and you’ll find yourself feeling better in return.

When you’re stressed, it may be harder to find humor in your life, but with a little effort, it can come out of its hiding place.

• TV and Movies – When’s the last time you gave yourself the escape of a good movie or TV show? Getting lost in an absurd world can be a wonderful getaway.
• Toys – Why should kids have all the fun? Keeping a little stash of Silly Putty or a yo-yo in your desk is perfect for keeping things from getting too serious.
• Go to extremes – Humor is often based in taking one aspect of a situation and blowing it way out of proportion. Imagine you’re stuck in traffic. You could imagine being stuck there for hours, days, or even weeks. You would develop a new circle of friends with everyone in the cars around you. This could grow into a tight-knit group of friends that vow to get together at that same place every year and have a traffic jam for old time’s sake.

There are many places in our lives where stress rears its ugly head. In the end, you may find that you’re only as stressed as you decide you’re going to be. 

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Top 10 Foods You Aren’t Eating, But Should

Cabbage: Loaded with nutrients like sulforaphane, a chemical said to boost cancer-fighting enzymes.
Swiss chard: A leafy green vegetable packed with carotenoids that protect aging eyes.
Cinnamon: May help control blood sugar and cholesterol.
Pomegranate juice: Appears to lower blood pressure and loaded with antioxidants.
Dried plums: Okay, so they are really prunes, but they are packed with antioxidants.
Pumpkin seeds: The most nutritious part of the pumpkin and packed with magnesium; high levels of the mineral are associated with lower risk for early death.
Sardines: Dr. Bowden calls them “health food in a can.’’ They are high in omega-3’s, contain virtually no mercury and are loaded with calcium. They also contain iron, magnesium, phosphorus, potassium, zinc, copper and manganese as well as a full complement of B vitamins.
Turmeric: The “superstar of spices,’’ it may have anti-inflammatory and anti-cancer properties.
Frozen blueberries: Even though freezing can degrade some of the nutrients in fruits and vegetables, frozen blueberries are available year-round and don’t spoil; associated with better memory in animal studies.
Canned pumpkin: A low-calorie vegetable that is high in fiber and immune-stimulating vitamin A; fills you up on very few calories.

Source: July 6, 2008 NY Times Blog

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