Using S3I Methods to Evaluate Immersion and Envelopment of Turning and Positioning Products on a Support Surface

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Adding layers alters support surface performance.1‐2 In the absence of standards, clinicians must balance potential benefits of caregiver safety and the ease of care from using Turn and Position devices (TPDs) against the risk of decreased protective benefits from support surface for each patient. Testing was conducted to evaluate the impact of TPD on a standard hospital support surface.


  1. Immersion: Mannequin was immersed into support surface & TPD, using linear transducers to measure support of a supine patient.3‐4
  2. Envelopment: Hemispheric indenter with embedded sensors was immersed to measure pressure distribution around area of load.3‐4
  3. Horizontal Stiffness: F. E. indenter was pulled by Chatillon cable orthogonally to measure shear and bulk modulus forces on supine patient.3‐4


  • When Surface 1 was added to the control surface, immersion decreased. When Surface 2 was added to control, immersion improved.(Data not shown.) 4
  • Area of envelopment increases with each Ring. (See Fig 1) The difference between Ring 5 and Ring 7 represents a greater than 25% increase in patient envelopment.
  • Figure 2 compares the force needed to displace the indenter, and thus shows resistance to the sliding and shear forces placed on a patient.
  • Surface 2 provides both the greatest resistance to sliding (horizontal stiffness) when in Tucked position, and also the least resistance when in Untucked position.
  • Contrary to usual findings, Surface 2 enhances the support surface performance.4 Surface 2 when Tucked provides greatest resistance to patient sliding in bed, but when Untucked it releases resistance, allowing for better patient repositioning.


  • With embedded handles and low friction when untucked, Surface 2 provides safe patient handling opportunities without compromising patient safety.
  • Immersion and envelopment are tied together in providing comfort and protection for patients. Better immersion and envelopment provide patients lying on a hospital bed more pressure relief. Greater horizontal stiffness indicates less sliding and shear forces on patient.
  • Although each method was designed to evaluate only a certain aspect, the S3I methods were designed to work together to evaluate a support surface as a whole. Addressing these three factors together will help to prevent pressure injuries.


  1. Williamson R; Lachenbruch C; VanGilder C. The effects of multiple layers of linens on Surface Interface Pressure: Results of a Laboratory Study. OWM. 2013;59(6):38‐47.
  2. Fader M, Bain D, Cottenden A. Effects of absorbent incontinence pads on pressure management mattresses. J Adv Nurs 2004;48(6):569‐74.
  3. RESNA SS‐1:2014 & 2019 Requirements and Test Methods for Full Body Support Surfaces.
  4. Tanner L, Cheney A, Call E. Results of Laboratory Testing for Immersion, Envelopment and Horizontal Stiffness on TPDs to manage pressure injury. ASWC Feb 2020 (submitted).
  5. Hoogendoorn I, et al. The effect of pressure and shear on tissue viability of human skin in relation to the development of PU: a systematic review. J Tiss Via 2017; 26:157‐171.

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