Dynamic Tilt and Pressure Redistribution

Hello all,

This month, let's focus on dynamic tilt, or tilt-in-space, wheelchairs. We will look at the clinical indicators for their use as well as what the research has found regarding dynamic tilt and pressure redistribution.

Dynamic tilt refers to a change in the orientation of the seat pan relative to the ground, while the seat to back angle remains constant. In a dynamic tilt system, the seat pan can be positioned into various degrees of tilt, depending upon the range offered by the tilt system. This is in contrast to a fixed tilt in a wheelchair, in which the front seat to floor height is greater than the rear seat to floor height, while the seat to back angle remains set at 90° or greater, creating a "dump" or tilt to the seating system, which remains at a constant angle. Dynamic recline, on the other hand, refers to a change in the seat to back angle, while the seat pan remains at a constant orientation relative to the ground.

There are many reasons why dynamic tilt may be prescribed for a client. In their position paper on the application of tilt, recline and elevating legrests, the Rehabilitation and Engineering Society of North America (RESNA) (2009) stated that the use of tilt and recline can have many benefits. These benefits include: postural realignment and function; improved physiological functions, such as orthostatic hypotension, visual orientation, speech, alertness, arousal, respiration, eating, and bowel and bladder management; improved transfers and biomechanics; spasticity; changes in pain, fatigue and sitting tolerance; and pressure relief.

It is important to note that although there are several clinical benefits of the use of dynamic tilt, funding sources, if available, may focus primarily on the benefits related to pressure relief. For example, in Ontario, the Mobility Devices Policy and Administration Manual of the Assistive Devices Program (2012), Section 405.01, specifies that a request for funding of a manual dynamic tilt wheelchair will only be considered when such a device is the minimum "required to achieve one more of the following goals:

1. Increase sitting tolerance where there is risk of tissue trauma due to unrelieved pressure and inability to weight shift independently and/or there is an inability to maintain a functional postural position where abnormal tone is a factor. In both of these situations it must be demonstrated that fixed seating alone is not an adequate solution.
2. Maintain skin integrity where there is past/present history of tissue trauma, inability to weight shift independently and fixed seating alone is not an adequate solution.

The goals will only be achieved where there is an attendant available to regularly alter the angle of tilt in space."

(Section 525 of the Mobility Devices Policy and Administration Manual lists the eligibility criteria for power dynamic positioning devices, which are slightly different than the criteria for manual dynamic tilt.)

Many different models of dynamic tilt wheelchairs are available, with differing degrees of maximum tilt available. Have you ever wondered what happens in terms of pressure distribution in various degrees of tilt? Or how much tilt is required to off-load the ischial tuberosities (ITs) and sacrum? Several studies have been published that address these questions.

A recent Canadian study, published in Spinal Cord, took a sample of 18 subjects recruited through an out-patient spinal cord injury (SCI) clinic and measured the effects on interface pressure through pressure mapping as the participants were put into various degrees of tilt (Giesbrecht, Ethans, and Staley, 2011). The study subjects used the same model of tilt-in-space wheelchair and seat cushion. The seat-to-back angle of the wheelchair fixed to 100° for all participants, to be consistent with procedures of previous related studies. The participants each acted as his/her own control, with a starting measurement position of 0° of tilt. The researchers then took pressure mapping measurements of the ITs and sacrum of the participants in various degrees of tilt (10°, 20°, 30°, 40° and 50°).

What the researchers found was that at least 30° of tilt was required to effect a reduction in pressure of clinical value, which was consistent with previous published research. In 10° of tilt, there appeared to be less than 5% reduction of interface pressure, but with increased loading on the sacrum. In 20° of tilt, there was less than 15% reduction in pressure. Giesbrecht et al. (2011) concluded "Small tilt angles are more suitable for postural control than pressure management." (p. 827.)

The researchers further found that "A minimum tilt of 30° is required to initiate unloading the sacrum and to achieve a clinically important reduction in pressure at the IT. Larger tilt angles resulted in more substantial pressure reduction than previously reported." (Giesbrecht et. al., 2011, p. 827). In this study, increasing the angle of tilt from 20° to 30° resulted in a reduction in interface pressure of ~ 15%; increasing from 30° to 40° resulted in another ~20% reduction; and increasing from 40° to 50° resulted in a further ~ 25% reduction in pressure at the ITs and sacrum.

Another research study looked not only at interface pressure measurements, but also blood flow through Doppler measurement when eleven study participants with SCI were positioned in various degrees of tilt (Sonenblum & Sprigle, 2011). In this study, participants used their own wheelchairs and seating and were measured in various randomized tilt sequences, including upright to 30°, upright to 45°, upright to maximum tilt (whatever maximum tilt was possible on the participant's own wheelchair – 45° or 55°), and upright to 15° to 30°. Upright referred to the minimum degrees possible on the participant's wheelchair, that varied between 0° and 5°.

Sonenblum et al. (2011) found "a tilt of only 15° has a small (8%) but significant increase in superficial blood flow. Pressure did not significantly decrease at 15° of tilt; in some subjects, the pressure actually increased slightly." Tilting from 15° to 30° resulted in decreased pressure, but did not result in further increased blood flow. The authors hypothesized that there are other mechanisms affecting blood flow besides changes in tissue loading. In tilts up to 45°, it was found that there was a large variation in blood flow response of the participants, while interface pressure measurements decreased with greater degrees of tilt. Sonenblum et al. (2011) concluded "Based on the results of this study, tilting for pressure reliefs as far as the system permits is suggested to maximize the potential for significant blood flow increases and pressure relief. The use of interim small tilts is also supported, as they also provide some benefit." (p. 3.)

Many times therapists are surprised at what is required to achieve 30° of tilt for pressure management. If you are unsure of how much tilt is needed to obtain 30° of tilt, the next time you have the opportunity to use a tilt wheelchair that has a built-in inclinometer, I encourage you to tilt the chair and check the inclinometer to see how far back the chair must be tilted in order to achieve 30° of tilt. If you have access to a dynamic tilt wheelchair that does not have an instrument to measure the angle of tilt, you can use a goniometer to measure the degree of tilt of the wheelchair.

In summary, we found that the use of dynamic tilt wheelchairs can have numerous clinical benefits for clients. Often, dynamic tilt wheelchairs are prescribed as a means for pressure redistribution when a client is at risk of skin breakdown due to an inability to weight shift independently. The research demonstrates that small degrees of tilt appear to be beneficial for blood flow and for positioning. Tilt of at least 30° showed some unloading of pressure at the sacrum and a clinically important pressure reduction at the ITs, while greater degrees of tilt demonstrated even greater pressure redistribution away from the pelvis.

References

1. Assistive Devices Program. Ministry of Health and Long-Term Care. (2012). Mobility Devices Policy and Administration Manual. Retrieved from: http://www.health.gov.on.ca
2. Dicianno, B.E., Arva,J.,Lieberman, J.M.,Schmeler, M.R.,Souza, A.,Phillips,K., Lange, M., Cooper, R., Davis, K. & Betz, K.L. (2009). RESNA Position on the Application of Tilt, Recline, and Elevating Legrests for Wheelchairs. Assistive Technology,21(1), 13-22.
3. Giesbrecht, E.M., Ethans, K.D., and Staley, D. (2011). Measuring the effect of incremental angles of wheelchair tilt on interface pressure among individuals with spinal cord injury. Spinal Cord, 49, 827-831.
4. Sonenblum, S.E. & Sprigle, S.H. (2011). The impact of tilting on blood flow and localized tissue loading. Journal of Tissue Viability, 20, 3-13.