Pressure distribution Imagine resting an elbow on a table; this represents one small area being loaded with pressure. Now imagine an entire forearm and hand on the table; the pressure is now distributed over a larger area, reducing the load on the elbow. By distributing pressure over as large an area as possible, pressure can be reduced. This is often accomplished by using materials that increase immersion into the seating surface or increasing contact with body surfaces through contoured cushions or molded seating surfaces. Many experts recommend achieving peak pressures at or below 80 mmHg (measured by pressure mapping; Chisholm & Yip, 2018). One of the drawbacks to increasing pressure distribution is that transfers may be more difficult due to the level of immersion and contact. Also, some materials used to reduce pressure, such as viscous fluids and air, are less stable and so do not provide as much postural control (Chisholm & Yip, 2018). Careful assessment is required to achieve an appropriate balance of pressure distribution and postural stability for an individual client. This assessment is greatly dependent on pressure injury risk, as not every client requires significant pressure distribution. Pressure relief Even with significant pressure distribution, pressure relief is required for clients who are at high risk of pressure injury development. Pressure relief techniques provide complete off- Vision and posture The brain is hardwired to find upright and midline positions. The head seeks to right itself when the body leans to the side. The sense of being upright and midline results from many factors, including sensors in the semicircular canals, but is strongly dependent on vision. What is seen and how it is seen directly affect posture, particularly in seeking an upright position of the trunk and head (Plummer, 2014). Visual perception Vision is more than just acuity; it is also perception. Many clients experience field cuts or visual neglect, having lost the awareness of part of their vision as a result of an insult such as a stroke. Midline shifts can skew the client’s sense of midline position. Other clients may have cortical visual impairment (CVI) resulting from a neurological problem, and still others may have low vision or blindness. Vision and head position Acuity, perception, field cuts, and neglect can affect mobility but do not generally affect posture. A client with very low or no vision may flex his or her head forward much of the time because visual feedback to drive head righting is not present. In these situations, head support is not usually successful. Such a client will lift his or her head when he or she wants or needs to. The main drawback to this position is that this forward flexed position often leads to trunk flexion as well. In some cases, a client may lift his or her head if engaged or if attending to auditory or other sensory input. Clients with cerebral palsy and traumatic brain injuries may demonstrate vertical midline shifts. The brain is able to detect upright and midline through various inputs, including vision. For example, in one screening test for midline shift, a pencil is moved horizontally in front of the client’s face from left to right and then from right to left. The client is instructed to say when the pencil is just in front of his or her nose (at midline). Clients with a horizontal midline shift will “stop” the pencil in front of one eye, rather than in front of the nose. The pencil is then moved vertically in front of the client’s face from top to bottom and bottom to top. The client is again instructed to say when the pencil is just in front of the eyes. Clients with a vertical midline shift will “stop” the pencil in front of the forehead or nose instead of the eyes. Their sense of midline has shifted such that the head is held in a mild to moderate flexed position in order to optimize vision (Figure 14). However, the pointer test is a relative test (Padula, Capo-Aponte, Padula, Singman, & Jenness 2017). Observing posture and weight shift is the best way to
loading to specific areas for specific lengths of time. Strategies include tilt and/or recline; alternating air cushions; cushions that completely unweight key areas (such as the ITs); and weight shifts (such as forward lean, wheelchair push-ups, lateral lean, and wheelies). The Consortium of Spinal Cord Medicine of the Paralyzed Veterans of America recommends tilting every 15 to 30 minutes for at least 1 minute to allow compressed tissues to recover (Paralyzed Veterans of America, 2014). A tilt of more than 30° is required to provide true pressure relief. Optimal pressure relief is achieved by 25° to 35° of tilt in combination with 120° of recline and is often used to justify a combination tilt-and-recline system on a power wheelchair for a client at high risk of pressure injury development. Clinical impact Seating interventions can help reduce the risk of pressure injury development by pressure distribution; pressure relief; and the reduction of causative factors, such as heat, moisture, and shear. Seating materials, as well as upholstery, can retain heat or promote airflow. Seating surfaces that retain heat can also increase moisture (sweating) and can increase pressure injury risk. Some upholstery types actually wick moisture away from the client, helping to keep skin dry and prevent maceration. Proper positioning can also reduce high-pressure areas and thus reduce the risk of pressure injuries. note a visual midline shift. This problem can be corrected with specialized lenses and vision therapy that correct this shift and results in an upright head position (Padula et al., 2017). Figure 14: Vertical Midline Shift
Note . From “Post Trauma Vision Syndrome & Visual Midline Shift Syndrome,” by W. V. Padula and S. Argyris, 1996, NeuroRehabilitation, 6, pp. 165-17 1. Retrieved from https:// padulainstitute.com/education/articles/post-trauma-vision-syndrome. Reprinted with permission of William V. Padula. Cortical visual impairment CVI results when information from the eyes is not processed correctly by the brain. CVI is common in clients with cerebral palsy. These clients can see, but functional vision may be quite impaired, may fluctuate throughout the day, and can improve over time as a child grows older. This client may sit with the head slightly forward and tilted to the side to better see the environment. Sustained visual gaze may be difficult, so the client may repeatedly glance at what he or she wants to see. In this case, it is important to provide head support in an upright position for when the client brings his or her head to this position, but it is also important to allow the client to assume needed head positions to optimize vision.
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