Teaching individuals with spinal cord injuries to shift their weight regularly while seated is a common and intuitive recommendation for pressure ulcer prevention as it is hypothesized that this relieves pressure on at risk tissues and allows for recovery of blood flow and oxygenation (Consortium for Spinal Cord Medicine 2000; Coggrane & Rose 2003; Makhsous et al 2007a).  Several techniques have been suggested depending on the physical and cognitive status of the individual and include a lateral, forward lean or vertical push up (Bogie et al 1995; Consortium for Spinal Cord Medicine 2000).  When a manual weight shift cannot be performed the use of a power tilt feature has been recommended (Consortium for Spinal Cord Medicine 2000).

Table: Pressure Relief Practices on Preventing Ulcers Post SCI

Discussion

There are very few studies that have researched which techniques provide adequate pressure relief and how long a weight shift must be performed to unload weight-bearing areas such as the ischia.

Spijkerman et al. (1995) assessed interface pressure while individuals were tilted at 5°, 15° and 25° from horizontal. Results indicated that body tilt had a significant effect on mean pressure p=0.003.  The lowest overall mean pressure (82.91mmHg) was demonstrated at 25° tilt.

Coggrave and Rose (2003), in a retrospective chart review of 46 SCI subjects seen in a seating clinic, assessed the duration of various pressure relief positions required for loaded transcutaneous oxygen tension (t_CPO₂) to recover to unloaded levels.  Results indicated that it took approximately 2 minutes of pressure relief to raise tissue oxygen to unloaded levels for most subjects.  This length of pressure relief was more easily sustained by the subjects leaning forward, side to side or having the wheelchair tipped back at > 65º compared to a pressure relief lift.

Similar to Coggrave and Rose (2003), Makhsous et al (2007a) demonstrated full recovery of tcPO₂ with the dynamic protocol in the off loading configuration but it took > 2 minutes to achieve this result.  Those individuals with paraplegia using a wheelchair pushup were only able to sustain the lift for 49 seconds leading to incomplete recovery of tissue perfusion.

Henderson et al. (1994) pressure mapped 10 SCI subjects and recorded pressures at the ischial tuberosity (IT) and a circumscribed area around the IT.  The authors then pressure mapped the subjects with their wheelchairs tipped back at 35º, 65º and after the subjects were assisted into a forward leaning position >45°.  Results showed that the wheelchairs tipped back at 65º and the subjects in a forward leaning position demonstrated statistically significant pressure reduction at the IT and circumscribed area (p<0.05) with the forward lean showing the greatest reduction (78% reduction at IT, 70% reduction circumscribed area).

Hobson (1992) showed that for individuals with SCI, changes in posture can reduce maximum pressures that occur while seated.  Recline of the backrest to 120º, full body tilt to 20º, forward flexion to 50º and lateral bending to 15º all resulted in decreases in maximum pressures.  Maximum reductions in tangentially induced shear forces (TIS) occurred with forward trunk flexion of 50º and full body tilt of 20º; backrest recline to 120º increased TIS by 25%.

The studies reviewed demonstrate that pressure relief by position change, if sustained for an appropriate length of time, results in pressure reduction and recovery of tcPO₂ to unloaded levels.  The type and duration of pressure relief required to achieve these results varied from individual to individual.  Sustaining a pressure relief lift/pushup for the time required to allow for recovery of tcPO₂ to unloaded levels (1-2 min) would be difficult for most individuals with SCI.

Conclusion

• There is level 3 evidence that 1-2 minutes of pressure relief must be sustained to raise tissue oxygen to unloaded levels.
• There is level 4 evidence to support position changes to reduce pressure at the ischial tuberosities.

• 65° of tilt or forward leaning of >45° both showed significant reduction in pressure.
• The type and duration of pressure relief by position changing must be individualized post SCI using pressure mapping or similar techniques.
• More research is needed to see if decreasing ischial pressures and/or increasing blood flow to tissues using weight shifting techniques will help prevent pressure ulcers post SCI.
• For most individuals with SCI, a pushup/vertical lift of 15-30 seconds is unlikely to be sufficient to allow for complete pressure relief.