Is there a risk of bottoming out when using a Vicair cushion incorrectly?

Vicair cushion

1 Introduction

Vicair cushions provide optimal skin protection when used correctly. But we must also keep in mind that sometimes a cushion is inadvertently placed incorrectly in a wheelchair. The cushion can end up backwards or rotated in the wrong direction in the wheelchair. It is also conceivable that a cushion could end up upside down in the cover, for example after cleaning, and therefore end up unseen upside down in a wheelchair. Incorrect placement can also be due to the fact that a wheelchair is often measured with two fingers (4cm) of space between the user’s calves and the front of the cushion. Thus, the cushion may be placed so far forward that it touches the user’s calves. For wheelchairs with an open back support, the cushion may also be placed too far to the back of the wheelchair.

Therefore the aim of this research was to find out what the risks are for the user when a cushion is used incorrectly. It is important to research whether there is bottoming out and how well the risk zones are protected against high-pressure forces. Bottoming out is defined as the state of support surface deformation beyond critical immersion whereby effective pressure redistribution is lost (EPUAP/ NPIAP guideline).


  1. Method

To answer the research question 6 different cushions are tested with the ISO indenter and skinny indenter. The following cushions were tested for this study: Vicair Adjuster O2 10cm, Vicair Vector O2 10cm, Vicair Active O2 9cm, Vicair 4 8cm, Jay J3 and ROHO Quadtro Select High Profile. These cushions were 40x45cm or the size closest to that. The Vicair cushions and Jay J3 are tested out of the box, the ROHO is adjusted to the corresponding testing weight. After loading 65kg with the ISO indenter, for 5 minutes, pressure distribution and immersion was measured in the positions:



  • Correct;
  • Rotated 90 degrees clockwise;
  • Backwards;
  • 4cm forward;
  • 4cm backwards;
  • Cushion upside down in cover;
  • Cushion & cover upside down is only tested for Vicair Active O2 and Vicair 4.



The immersion was also measured in all positions with the skinny indenter with a load of 130 kg to simulate a worst case scenario.

The pressures were measured (Xsensor pressure sensor mat) at five locations. These places correspond to the position of the tuberosities ischii left (LIT) and right (RIT), the trochanter major of the femur left (LGT) and right (RGT) and the coccyx bone.




3.1 Results

For the overview of all the results see table 1 and 2, this section discusses the most striking and important results.

3.1.1 Immersion at 65kg (ISO indenter)

The immersion generally decreases somewhat in improperly placed cushions compared to the correct position. This can be explained by the fact that the indenter does not enter the cushion at the correct position. The exception to this, is the test in which the cushion was placed 4cm too far back. With the Vicair Adjuster O2 and Vector O2, there was 1 to 2 mm more immersion but no bottoming out with at least 41mm of space below the lowest point of the indenter (table 1).

3.1.2 Immersion at 130kg (skinny indenter)

To simulate the worst case scenario the skinny indenter is loaded with 130kg, at this high load the limit of 25mm (stated by the Vicair Manual) below the lowest point of the indenter is exceeded in all Vicair cushions, except the Vector. To assure safe use of the cushion the Vicair manual states that the lowest bony prominence should be supported by at least 2,5cm/1” of SmartCells. This prevents the risk that the bony prominence touches the wheelchair seat.

Although the Adjuster and Vector have less than 25mm left (table 2) the pressure does not increase significantly, indicating that the definition of the EPUAP/NPIAP for bottoming out is not yet fulfilled. The Vicair 4 has the lowest immersion space left, 11mm (table 2), this is about the height of 1 SmartCell, increasing the risk of bottoming out. But according to the user manual of the Vicair 4, bottoming out is: “touching the bottom of the cushion with a bony prominence”, this is not the case yet, since there is still a SmartCell below the bony prominence.

3.2 Dispersion index and coefficient of variation

The dispersion index and coefficient of variation give an impression of the pressure distribution on the cushion. The dispersion index looks at the ratio between the high-risk zones that have been chosen and the pressure on the rest of the surface. The coefficient of variation looks at the distribution of pressure across the entire surface.

In almost all measurements, these values worsened when the cushion was not positioned correctly. When this was not the case, for example, when the cushion was placed too far back, this was offset by a decrease in contact area and an increase in average pressure. So it is important to assess all values in the whole context.

  1. Conclusion

With loads appropriate to the size of the cushion, there is no chance of bottoming out with improper placement of the cushion. With extreme loads, it is more important that the cushion is placed correctly in the wheelchair.

Forward and backward placement has a strikingly large influence on immersion and pressure distribution. It is therefore important that users and therapists are aware that the cushion is placed correctly in the wheelchair. With a correctly fitted wheelchair and an appropriate cushion, there is the possibility that the user will place the cushion too far forward in the wheelchair, thus resulting in inferior pressure distribution and immersion, but without creating any risk for the user.

If the cushion ends up upside down in the cover, this has a major impact on the performance of the cushion. The contact area decreases and the average pressure increases. It is therefore important that the risk of this is properly addressed with communication in the manual, quick installation guide and on the cushion itself. However, the risk of bottoming out is really small, and with that the risk of any damage to the user as a result of the misuse of the cushion.

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