Microclimate & Temperature

In considering microclimate — the temperature and moisture content of that small space in which client meets wheelchair — it’s fitting to also discuss the infinitesimal human cells that are part of that client/seating interface.

While our skin and tissues are remarkably resilient in many ways, they’re not invincible, as any seating specialist knows. Our cells survive and thrive best in a specific environment… one that often doesn’t match the microclimates of typical complex rehab clients who spend long periods of time — all year long — in their wheelchairs.

MICROCLIMATE & REACTIONS OF CELLS

Barbara Bowden is Associate Product Manager, Seating & Custom Seating, for Sunrise Medical. Her background is in chemical and biological engineering, with a metabolic engineering concentration: “Basically, chemical reactions of cells,” she explained.

To understand microclimate — and how it can significantly differ from ambient air temperature — think of the last time you sat awhile on a hard seat outside, perhaps at a baseball game on a pleasant afternoon.

“Picture yourself sitting on plastic stadium chairs,” Bowden said, “and your back and bottom get very warm and sweaty because the microclimate between yourself and the seating is different from that of the outside, ambient air. There’s not a lot of breathability on that surface — not a lot of opportunity for air to go in and refresh that microclimate. So even if it is a crisp fall day, with hours of sitting on that surface, you can still be at risk of that temperature affecting your skin.”

As that microclimate gets warmer, our bodies react, Bowden said. “Our bodies like to stay at a comfortable 97° to 98° Fahrenheit. The human body regulates the rise in body temperature by sweating. The body cools itself by pulling heat from our skin to evaporate the sweat. When a wheelchair user starts to sweat heavily, that’s a sign their microclimate temperature is greater than their body temperature.”

And that’s when a client’s risk for skin breakdown and tissue injuries starts climbing. Here are six factors to consider about seating, microclimate and how complex rehab technology (CRT) clients can be affected.

1. ASSESSMENT FOR MICROCLIMATE RISK IS CRITICAL

While evaluating clients for pressure injury risk is a typical part of a seating and mobility assessment, microclimate risk should also be checked — especially since clients at greater risk for pressure injuries could also be at higher risk for prolonged and trapped heat and moisture.

“For the active user who regularly performs weight shifts, you’re going to worry about microclimate less because they’re able to perform the actions they need to protect themselves,” Bowden said. “When [the client] is somebody in a tilt-and-recline wheelchair, or in a power chair with a complex seating system, maybe with custom-molded seating, they’re sitting in more insulation, and that has to be a factor in the [risk assessment] process.”

Clients who are more involved and who use more complex seating systems might also be less able to feel, discern or communicate growing discomfort, and they often use additional positioning components, many of which can create their own microclimates that need to be monitored.

2. MICROCLIMATES OCCUR BEYOND THE SEAT & BACKREST

The cushion and backrest interfaces tend to get the most attention, but microclimates also form in other locations, wherever the client makes contact with a surface. That includes at armrests or under chest harnesses.

“Anytime [the client] touches a surface, you want to circulate air between client and surface at regular intervals,” Bowden said. “If you have someone in a chest strap and it’s a warm day, that’s further thermal insulation. A chest harness or arm trough will hold and trap heat.”

For positioning components such as shoulder supports or chest straps, Bowden added, “Fabric choice can be beneficial to reduce a client’s risk. Fabrics such as ‘spacer’ fabrics enable good air flow. Of late, the CRT industry has introduced products with these fabric options [to] increase the comfort of clients and reduce the risk of skin breakdown.”

Of course, microclimate can be a concern elsewhere, such as at arm troughs, which generally feature foam surfaces. Arm troughs can also feature materials such as leatherette and less breathable options. So any kind of positioning piece can affect microclimate, depending on the types of materials used.

3. TIME MATTERS

Heat and moisture aren’t the only microclimate dangers. How long a client stays in that less-than-optimal environment also matters. “If you sit in a hot car, and it’s 90°F, we can tolerate it for five minutes,” Bowden said. “It’s uncomfortable, but the average person can tolerate it. After a while, it gets to the point where nothing is comfortable, and you just want to get out of the car. It’s the same way for someone in a seating system. For a certain amount of time — and that varies for everyone — the client is fine. After that, their body is cueing their brain to say, ‘I’m not comfortable in my wheelchair anymore, and I need pressure relief.’”

That discomfort can cause decreased sitting tolerance and require the client to move from a wheelchair to a less mobile and functional location, such as bed. Other clients might lack the sensation to know that their microclimates have put them at risk. Wheelchairs with tilt and recline functions allow clients to more easily relieve pressure to refresh their microclimates.

“If you look at our pelvises, they’re pretty bony,” Bowden said. “Throughout evolution, humans have generally been standing, so we could have a bonier pelvis. But when we sit [wheelchair users] down, their ischial tuberosities are putting a great deal of pressure on internal tissues of their cells. That causes deformation, it restricts bloodflow, and that’s a recipe for cells to start dying.”

4. DISTRESSED CELLS SEND OUT SIGNALS

As someone who has closely studied how cells ideally live, communicate and die, Bowden said, “They take their signals essentially from chemical responses. Those responses tells them if everything is okay in their world or not.

“When pressure is introduced to the surface of the skin, cells receive signals that tell them that their environment has changed,” she added. “Cells live in a very specific environment, and they are heavily influenced by blood flow, oxygen, moisture and deformation. Cellular death may be triggered if any of these variables are substantially altered.”

In simple terms, if the cell determines that its current environment is insufficient, the cell will begin to die. This action is the start of a pressure injury.

“Heat and moisture may accelerate cellular breakdown,” Bowden said. “They don’t like to be deformed, they don’t like to be hot. So when there’s heat, not only are cells not in the optimal environment they’re used to, but the sweating affects the elasticity of the cells.”

Fortunately, relatively small changes can make a big difference in cell survival. For example, Bowden noted that cooling a microclimate’s temperature by just 1° Celsius can slow skin breakdown.

“When you have heat, that can accelerate the cell-death cycle,” she said. “All the other cells are getting those chemical signals faster, and they’re dying faster as well. So if you can lower the heat in that microclimate, you’re saving those cells from accelerating their breakdown.”

5. PRESSURE RELIEF TACTICS CAN HELP

Fortunately, a regimen that should already be part of every wheelchair user’s routine can have a great impact on managing microclimate.

“The number one way to prevent microclimate from adversely affecting a patient is to do weight shifts and pressure reliefs,” Bowden said. “It’s the best way to mitigate that temperature and allow the ambient air to rush onto that surface and refresh it — to take out that hot, humid, stale air that’s been sitting between the patient and the surface, and bring in fresher, less humid air that’s more equal to the environment.”

Choosing seating that manages a client’s microclimate (see sidebar) can also help; so can self-care best practices such as cleaning up food spills or incontinence accidents as quickly as possible so the client’s skin isn’t exposed to those fluids for lengthy times.

“The faster a client is removed from a wet surface, the more beneficial,” Bowden said. “Problems just compound when you introduce moisture into the microclimate.”

6. MANAGING MICROCLIMATE IS A BALANCING ACT

Perhaps the biggest challenge to managing microclimate is the balancing act between keeping the wheelchair user safe and keeping that user mobile, functional and active. Sure, microclimates could be easier to manage if clients remained in climate-controlled, indoor settings at all times and never exerted themselves. But how functional or meaningful would that kind of existence be?

“It needs to be a balancing act,” Bowden said, while suggesting that clinicians also factor in other risk factors as part of managing microclimate. “What is their skin like during the day, and how does it present itself? Is it at high risk, moderate or low risk? You have to think about that to evaluate how sweating will impact them. Someone at low risk who has high skin integrity is going to be at low risk with sweating and moisture. With someone who has had multiple pressure injuries and is very bony, you’re going to worry about moisture a lot more, and you’re going to ask, ‘Do we need to take action?’

“If it gets to the point that the user is heavily sweating, and pressure reliefs are not working, that’s when you need to worry about their microclimate and say, ‘Shall we evaluate whether we should get them off the seating system and get their temperature down again?’ One of the clinician’s roles is to say, ‘How can I position someone in a way that they are safe and comfortable and will not further endanger themselves in the chair, while balancing the fact that this might be someone who has trouble regulating their temperature?’ These clients can swing from hot to cold very quickly. So the clinician’s struggle is to answer what that balance is, what kind of positioning they can [achieve], and when they should favor microclimate more. We do need to start factoring microclimate into the decisions that clinicians make for their patients.”