Intensive Care Med (1998) 24:815-820 © Springer-Verlag 1998

J. T. M. Weststrate W.C.J.Hop A. G. J. Aalbers A. W. J. Vreeling H. A. Bruining

Received: 8 August 1997 Accepted: 24 April 1998

J. r. M. Weststrate ( 6 ) • A. G. J. Aalbers A. W. J. Vreeling - H. A. Bruining Department of Surgery, University Hospital Rotterdam, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands Fax: + 31 (10) 4366978 email: [email protected] W.C.J.Hop Department of Epidemiology & Biostatistics, Erasmus University Rotterdam, Dr. Molewaterplein 40, 3015 GE Rotterdam, The Netherlands

The clinical relevance of the Watedow pressure sore risk scale in the ICU

Abstract Objective: To evaluate w h e t h e r the Waterlow pressure sore risk (PSR) scale has prognostic significance for intensive care patients. Design: A prospective study. Setting: T h e surgical intensive care unit (ICU) of the University H o s p i tal R o t t e r d a m . Patients." D a t a were evaluated f r o m 594 patients who had b e e n a d m i t t e d to the I C U during the year 1994. Methods and results: E a c h patient was assessed daily with respect to their Waterlow P S R score and the d e v e l o p m e n t of pressure sores in the sacral region. Actuarial statistical m e t h o d s were used to analyse the predictive value of the risk score. W h e n a patient had a Waterlow P S R score > 25 on admission, the risk o f

Introduction Together, time and pressure [1, 2], in combination with several predisposing intrinsic and extrinsic factors, are responsible for patients developing pressure sores [3]. Generally, pressure sores are related to a negative patient o u t c o m e associated with pain, depression, loss of function and i n d e p e n d e n c e , increased incidence of infection, sepsis and additional surgical interventions, nearly all resulting in a long hospital stay [4]. T h o s e particularly p r o n e to d e v e l o p pressure sores are: (1) patients with spinal cord injuries, (2) geriatric patients, (3) patients w h o have u n d e r g o n e major o r t h o p a e d i c surgery and (4) patients w h o n e e d to be admitted to the intensive care unit ( I C U ) [5]. Pressure sores not only affect patients but also increase the nursing w o r k l o a d by 50 % once a patient has

d e v e l o p i n g a pressure sore was significantly increased c o m p a r e d to patients with a P S R score < 25. A f t e r admission, the daily W a t e r l o w P S R scores o b t a i n e d were significantly associated with the risk o f developing a pressure sore. F o r e a c h additional point this risk i n c r e a s e d by 23 % (95 % c o n f i d e n c e interval 17 to 28 %). Conclusions: T h e W a t e r l o w P S R scale provides the medical and nursing staff at an early stage with reliable i n f o r m a t i o n a b o u t the risk patients have in developing a p r e s s u r e sore. K e y words Pressure sore • I n t e n s i v e care - Clinical research • P r e v e n t i o n • Waterlow - Decubitus

d e v e l o p e d a p r e s s u r e sore [3]. T h e yearly costs o f prevention and t r e a t m e n t of pressure sores in T h e N e t h e r lands is e s t i m a t e d to be DFI 700 000 000 [6]. T h e p r e v e n tion of pressure sores is t h e r e f o r e not only beneficial for the patient but also has a s e c o n d a r y e c o n o m i c b e n e f i t for the h e a l t h system. O n average, 6 - 1 0 % o f all hospitalised p a t i e n t s in T h e N e t h e r l a n d s suffer f r o m pressure sores [6]. In o r d e r to d e t e r m i n e which p a t i e n t has an increased risk o f developing a p r e s s u r e sore, pressure sore risk ( P S R ) scales have b e e n d e v e l o p e d to m e a s u r e the influence o f intrinsic factors o n the d e v e l o p m e n t of pressure sores [7]. Several of those scales have b e e n i m p l e m e n t e d o v e r the last 30 years, o f which the N o r t o n scale is p r o b a b l y the mostwell k n o w n [8]. T h e w o r k i n g o f these P S R scales is based o n the summation of a specific n u m b e r of points for each intrinsic

816

Table I The Waterlow Pressure Sore Risk scale. The weighting factor wt of each element is given. The number of patients with those characteristics on the day of ICU admission are in parenElement

wt

Build/weight for height

*

Element

wt

Element

wt

Special risks

wt

Skin type visual

*

Sex/age (years)

*

Tissue malnutrition

*

0 1

Male (389) Female (205)

1 2

Terminal cachexia (0)

* 8

Average (471) Above average (71)

0 1

Obese (27)

2

risk areas Healthy (521) Tissue paper, dry, clammy, oedematous (59) Discoloured (12)

Below average (25)

3

Broken spot (2)

Continence

*

Mobility

Completely catheterised (550)

0

Occasional incontinence (9) Catheter and incontinent for faeces (31) Incontinent for faeces and urine (4)

theses (NG nasogastric tube, N B M nil by mouth, MS multiple sclerosis, CVA cerebrovascular accident)

24

0-14 (5)

0

Fully mobile (0)

3 * 0

14-49 (148) 50q54 (164) 65-74 (175)

1 2 3

1

Restless or fidgity (0)

1

75-80 (68)

4

Major surgery/trauma

*

2

Apathetic (0)

2

81 + (34)

5

Orthopaedic: spinal or below the waist; operation time > 2 h (364)

5

3

Restricted (0)

3

Appetite

*

Medication

*

Inert/traction (0)

4

Average (91)

0

Cytotoxics. high-dose steroids, anti-inflammatory drugs (114)

4

Chairbound/complete bedrest (594)

5

Poor (27)

1

NG tubes and fluids only (51) NBM/anorexia (425)

2

f a c t o r t h a t is p r e s e n t in t h e p a t i e n t , giving t h e m e a s u r e o f t h e risk a p a t i e n t h a s o f d e v e l o p i n g a p r e s s u r e sore. M o s t P S R scales m a k e use o f a t h r e s h o l d score. W h e n a p a t i e n t r e a c h e s this s c o r e , it p r e d i c t s the d e v e l o p m e n t o f a p r e s s u r e s o r e in t h e n e a r f u t u r e . W a t e r l o w has stress e d t h a t P S R scales a r e n o t d e s i g n e d t o p r e d i c t t h e inevitable development of pressure sores but should mainly serve as a clinical w a r n i n g d e v i c e [9]. T h e p r i m a r y purp o s e o f s u c h a scale is t o p r o v i d e t h e m e d i c a l a n d nursing staff with a s u m m a r y m e a s u r e w h i c h reflects the risk a p a t i e n t has o f d e v e l o p i n g a p r e s s u r e s o r e [10]. This i n f o r m a t i o n m a y b e h e l p f u l in m a k i n g decisions o n w h a t a p p r o p r i a t e p r e v e n t i v e m e a s u r e s n e e d to be taken. A P S R scale w i d e l y u s e d in t h e U n i t e d K i n g d o m is t h e W a t e r l o w P S R scale ( T a b l e 1) [11]. This scale c o n tains a n u m b e r o f intrinsic f a c t o r s , w h i c h m a k e s it suita b l e f o r a v a r i e t y o f clinical s e t t i n g s [12]. I n the Waterl o w P S R scale the risk o f d e v e l o p i n g p r e s s u r e sores varies across a g r a d i e n t o f " n o r i s k " to " v e r y high risk" a n d c a t e g o r i e s i d e n t i f y t h e s e risks. H u n t [13] s u g g e s t e d t h a t

Cardiac failure or peripheral vascular disease (145) Anaemia (54) Neurological deficit

Diabetes, MS, CVA, Motor/sensory paraplegia (72)

5

2 * 4-6

3

f o r the clinical use o f a P S R scale this m i g h t be a m o r e suitable a p p r o a c h to i d e n t i f y at-risk p a t i e n t s t h a n using a single t h r e s h o l d score. O n the basis o f an e a r l i e r s t u d y [14] a n d the s u g g e s t i o n t h a t t h e W a t e r l o w P S R scale is suitable in a v a r i e t y o f clinical settings, w e d e s i g n e d a s t u d y to e v a l u a t e w h e t h e r the W a t e r l o w P S R scale has clinical significance if u s e d in the special g r o u p o f i n t e n s i v e c a r e patients.

Patients and methods A prospective study was performed on all patients who were admitted to the surgical intensive care unit (ICU) of the University Hospital Rotterdam in 1994. They were assessed with respect to their PSR score and the development of pressure sores in the sacral region. Patients were excluded from the study if their stay on the ICU was less than 24 h or they had a stage II pressure sore or higher on admission (n = 31) or used a special mattress on admission other than the standard hospital mattress (n = 34). The PSR scale developed by Waterlow was used to measure the risk of pressure sores (Table 1) [11]. This scale uses risk categories in order to de-

817

Table 2 Baseline characteristics of all patients included. D a t a are m e d i a n ( i n t e r q u a r t i l e ranges) or p e r c e n t a g e s

A g e (years) Male/female ( % ) D u r a t i o n of stay on the I C U (days) Waterlow PSR score at baseline Turning the patient (< 5 min)/24 h Nursing the patient on a l t e r n a t e sides/24 h Mobilising the p a t i e n t out of bed/24 h

No pressure sore (n = 547)

Pressure sore (n = 47)

L e v e l of significance

62.7 (48.8-70.9) 67/33 3 (2-5) 17 ( 1 4 2 1 ) 2.5 (1.5-3.5) 0.3 (0.0-0.3) 0.4 (0.0-0.7)

68.9 (54.6-75.9) 49/51 19 (8-33) 20 (16-26) 4.2 (3.7-5.0) 0.6 (0.0-0.7) 0.1 (0.0~).1)

N o t significant p = 0.001 p < 0.001 p = 0.001 p < 0.001 p = 0.003 p < 0.001

termine the risk patients have of developing a pressure sore. It has b e e n suggested that the Waterlow P S R calculation is one of the most appropriate i n s t r u m e n t s to use for intensive care patients [3]. T h e various e l e m e n t s in the sections of the Waterlow PSR score (Table 1) were assessed daily by the nursing night staff for the previous 24 h and registered in the hospital information system. T h e nursing staff was u n a w a r e of the actual score or any previous score. The highest score was r e c o r d e d from each section of the Waterlow P S R scale. S o m e of the elements of the Waterlow P S R sections were redefined to p r e v e n t dual explanation. In the section "'Mobility", all patients scored 5 points. In the section "Tissue Malnutrition", cardiac failure was scored when the patient was t r e a t e d with catecholamines. In the section ~Neurological deficit"~ paraplegia was scored w h e n the p a t i e n t was on muscle relaxants. This item was also scored w h e n p a t i e n t s had leg fractures and were thus immobilised. Lesions of the skin were staged according to the staging of pressure sores d e v e l o p e d by the National Pressure Sore Ulcers Advisory Panel: stage 0 = n o r m a l skin; stage I = nonblanchable e r y t h e m a of skin; stage II: formation of blisters; stage III: superficial ( s u b ) c u t a n e o u s necrosis; stage IV = deep subcutan e o u s necrosis. F r o m stage II onwards, skin lesions were considered to be pressure sores. If the condition of the p a t i e n t allowed, the following precautions to prevent the d e v e l o p m e n t of pressure sores were carried out by the nursing staff: (1) t u r n i n g the patient every 3 h for a short time (< 5 min) o n to one side; (2) nursing the patient for at least 1 h continuously on a l t e r n a t e sides; (3) mobilising the patient out of bed to stand for a few m i n u t e s next to the bed or sit for 15 min in a chair. T h e s e m e a s u r e s were performed according to hospital protocol. Barcodes were used for registration. Each e l e m e n t of the Waterlow PSR scale was linked with a barcode. Each c o m p u t e r that was connected to the hospital i n f o r m a t i o n system had a lightpencil c o n n e c t e d to it which could r e a d the barcodes. O n average, it took the nurse b e t w e e n 30 a n d 60 s to r e c o r d a P S R score for one patient. T h e advantage of this r e g i s t r a t i o n m e t h o d was that all inform a t i o n was stored at a central c o m p u t e r by the nurse who carried out the scoring. In o r d e r to analyse the data gathered, information was transferred to a p e r s o n a l computer. F o r statistical analysis, c o n t i n u o u s outcomes were c o m p a r e d b e t w e e n groups using the M a n n - W h i t n e y test and percentages were c o m p a r e d using the chi-square test. T h e risk of developing pressure sores increases with l e n g t h of stay in the ICU. To adjust for the n u m b e r of days the p a t i e n t s h a d b e e n in the ICU, actuarial m e t h o d s ( K a p l a n - M e i e r curves, logrank tests) were used to evaluate and c o m p a r e the risk of developing pressure sores. To assess the current value of the W a t e r l o w P S R score and the rate of developing a pressure sore, Cox regression, with the daily Waterlow PSR score as t i m e - d e p e n d e n t covariate, was used [15]. T h e limit of significance was c o n s i d e r e d to be p = 0.05 (two-sided).

Results A f t e r the exclusion criteria w e r e applied, 594 o f the 686 patients a d m i t t e d w e r e included in the study. T h e g r o u p studied consisted of 389 m e n and 205 w o m e n , with a m e a n age of 58.8 years (range 9 to 96 years). T h e m e a n stay in the I C U was 6.3 days (range 2 to 183 days). O f all the patients, 47 ( 7 . 9 % ) d e v e l o p e d a pressure sore. T h e characteristics of the patients w h o did and did not develop pressure sores are given in Table 2. All characteristics e x c e p t age differed significantly b e t w e e n the groups. T h e n u m b e r of patients with various W a t e r l o w P S R score characteristics present o n admission are given in p a r e n t h e s e s in Table 1. T h e risk of patients d e v e l o p i n g a pressure sore according to the n u m b e r of days they w e r e in the I C U is shown in Fig. 1 ( u p p e r panel). If the I C U stay lasted 30 days, this risk increased to 6 0 % . Patients w e r e g r o u p e d according to baseline W a t e r l o w P S R score: < 15 points (n = 165), 15-19 points (n = 213), 20-24 points (n = 140), ~ 25 points (n = 76). T h e n u m ber of patients developing a pressure sore during their stay on the I C U in these groups were, respectively, 9, 13, 10 and 15. T h e lower panel of Fig. 1 shows that when patients have a score _> 25 on admission, the risk of d e v e l o p i n g a pressure sore during their stay is significantly increased c o m p a r e d with patients with a score < 25. T h e longitudinally o b t a i n e d W a t e r l o w P S R scores are shown in Fig. 2. A t each day of I C U stay, the range, which covers 95 % of the W a t e r l o w P S R scores for those patients w h o did not d e v e l o p a pressure sore at or before that day, is displayed. It can b e seen that patients w h o d e v e l o p e d a pressure sore on a particular day tende d to have higher W a t e r l o w P S R scores c o m p a r e d to those w h o did not d e v e l o p a pressure sore on the same day. Cox regression r e v e a l e d that the rate of d e v e l o p m e n t of pressure sores increases linearly with an increasing W a t e r l o w P S R score. F o r each additional p o i n t of the P S R score this rate increased by 23 % (p < 0.001, 95 % c o n f i d e n c e limits: 17 to 28 %). Relating b o t h the c u r r e n t score and the score o n the previous day to the rate of d e v e l o p m e n t of pressure sores, it a p p e a r e d that the score on the previous day did not significantly im-

818

Fig. 1 Upper panel: cumulative percentage (actuarial) of patients developing a pressure sore according to number of days of ICU stay. N u m b e r s along the curve denote the numbers of patients at risk of developing a pressure sore at the indicated days. Lower panel: cumulative percentage (actuarial) of patients developing pressure sores by time. Patients are grouped according to Waterlow PSR score at admission to the ICU. C u r v e A < 15 points (n = 165), c u r v e B 15-19 points (n = 213), c u r v e C 20-24 points (n = 140), c u r v e D > 2 5 points (n = 76). Difference between curve D and curves A, B and C: all p < 0.001

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Fig. 2 Graph of the Waterlow PSR score versus the number of days after e n t r y into study. Solid lines (n = 47) r e p r e s e n t data for patients w h o d e v e l o p e d a pressure sore. T h e right e n d of each solid line indicates the score o n the day the score was recorded. The left a n d indicates the score on the preceding day. T h e vertical dotted lines r e p r e s e n t the 5-95 percentile r a n g e of the W a t e r l o w PSR score for t h o s e p a t i e n t s w h o were still at risk of d e v e l o p i n g a pressure sore at each day, apart from those w h o h a d already developed a pressure sore on t h a t day

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prove the predictive value of the current score. F u r t h e r analyses s h o w e d that as long as the Waterlow P S R score continuously r e m a i n e d b e l o w 15 in the I C U (total: 166 patient days), n o n e of the patients d e v e l o p e d a pressure s o r e . Figure 3 shows the actuarial risk of d e v e l o p i n g a pressure sore a c c o r d i n g to w h e t h e r or not patients had a Waterlow P S R score which exceeded a specific threshold. Curve I d e m o n s t r a t e the risk for patients if the Waterlow P S R score r e m a i n e d b e l o w 20. C u r v e I I shows the risk for those w h o h a d a score exceeding 20 but not 25 and curve I I I the risk for patients with a score exceeding 25. T h e risk increases greatly with increasing cut-off level. W h e n patients e x c e e d e d a score of 25, the risk of d e v e l o p i n g a pressure sore within a p e r i o d of 10 days equaled 50 %.

Discussion The most i m p o r t a n t result o f o u r study is that it produced a pressure sore risk assessment m o d e l which can be used as a reliable warning for intensive care patients in daily practice. W h e n the W a t e r l o w P S R scale was developed, four risk categories were suggested: n o risk (< 10 points), at risk (_> 10-_< 14), high risk (___ 15-_ 20) [11]. These risk categories

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Fig.3 T h e risk (actuarial) of developing a pressure sore. Curve I Patients showing a W a t e r l o w P S R score below 20 points continuously from admission. Curve I1 A f t e r a first score of at least 20 points but less t h a n 25 points. T h e time axis represents the number of days that p a t i e n t s continuously stayed within this range. Curve I I I A f t e r t h e first score of at least 25 points. T h e n u m b e r of patients at day 0 for curves I, II and III are 378, 206 and 116, respectively

were never quantified through research, only globally. When we quantified the risk categories in our study, we found that as long as patients had a score below 15 they developed no pressure sores during their stay on the ICU. This finding is in contrast to the suggested risk of that category. On the other hand, when patients developed a score >_ 25, the risk of developing a pressure sore during their ICU stay was extremely high. This finding has p r o m p t e d us to place patients who have a Waterlow P S R score >_ 25 points for more than 2-3 days on a special bed or mattress that reduces the pressure on the skin. Without considering the length of stay in the ICU, we found a pressure sore incidence of 7.9 %. Other studies have shown incidences varying between 13 and 56 % [4, 16-18]. On average, between 6 and 10 % of the patients admitted to Dutch hospitals develop a pressure sore [6]. The m o d e r a t e risk for the total group of ICU patients in our study is mainly due to the fact that most patients had only a short stay on the ICU. At 30 days, the risk of developing a pressure sore in our study increased to about 60 % (Fig. 1, top panel). As a result of this study, greater attention to pressure sore prevention is given to patients with a longer ICU stay. Our results indicated that the PSR score for the last 24 h is the best indicator for the development of a pressure sore in the next 24 h. As the physical condition of ICU patients can change dramatically in a very short period, this also influences the risk of developing a pressure sore [18]. This study shows that it is important to assess this risk every day, that nursing and medical staff

must have access to this information and that the day staff compares the score in the morning with the scores for previous days in relation to the patient's present condition. Following this, they can adjust the type and frequency of preventive measures when possible. D u e to respiratory and haem odynam i c instability, patients on the ICU often do not tolerate being nursed on alternate sides, or even being turned. In these cases, the only other way to reduce pressure on the affected areas is to use a special mattress. Most categories in the Waterlow PSR scale have a confirmed influence on the development of pressure sores. The combination of these categories and the weighting of the various category items were based on a study of the relevant literature and a discussion with other health care professionals. This process was confirmed in a clinical study in which 650 patients from different types of wards participated [11]. The scale has been designed as an instrument to warn care providers about the PSR level in patients and not to predict whether or not the patient will inevitably develop a pressure sore [9]. T he use of this evaluation m e t h o d is therefore different from other PSR scales that calculate the sensitivity and specificity of a threshold score above which a patient will develop a pressure sore. N o quantitative risk evaluations of the Waterlow PSR score regarding the devel opm ent of pressure sores are available, and so far only global evaluations have been made: two in a geriatric patient population [19, 20] and one in a community setting [21]. Both studies found that the Waterlow PSR scale was highly sensitive but the specificity was very low (10-14 %), indicating that it overpredicts those at risk of developing a pressure sore [22]. By using actuarial statistical methods, as in our study, the results not only indicate a new score range in the various risk categories but also provides insight about the course of the risk in due time. This is a valuable contribution because care providers can then determine at what risk level more expensive precautions have to be taken [12, 17]. In our study, patients who developed a pressure sore had a longer ICU stay compared with patients who did not develop a pressure sore. This was also found by Jiricka et al. [4]. Patients who developed a pressure sore in our study also had a significantly higher Waterlow PSR score on admission. Again, other investigators also found this, although they used the PSR scale developed by Braden [23, 24]. This suggests that the longer a patient stays on an ICU, with an increased P S R score on admission, the higher the risk he or she has of developing a pressure sore despite whether or not the PSR score is decreasing. This supports the view that if a patient has a stay on the ICU greater attention should be given to pressure sore prevention. Patients who developed a pressure sore in our study received significantly more frequent short turning epi-

820

s o d e s (< 5 m i n ) , a n d w e r e n u r s e d s i g n i f i c a n t l y m o r e o n alternate sides. These precautions did not prevent the development of pressure sores. Because nurses were b l i n d e d t o t h e t o t a l P S R s c o r e o f e a c h p a t i e n t , t h e y rel i e d o n t h e c l i n i c a l a s s e s s m e n t o f t h e p a t i e n t ' s s k i n as an indicator whether or not to initiate preventive prec a u t i o n s , as w a s a l s o f o u n d in a n e a r l i e r s t u d y [14]. T h i s study shows that initiating pressure sore preventive measures on the basis of the patient's skin assessment does not prevent the development of pressure sores but often only confines the area of damage. The following limitations and drawbacks need to be c o n s i d e r e d . A p o s s i b l e r e a s o n w h y n o t all p a t i e n t s w i t h a n i n c r e a s e d r i s k d e v e l o p e d a p r e s s u r e s o r e is t h a t t h e nursing staff increased the number of preventive measures at a very early stage. The influence of such interv e n t i o n s in c o m b i n a t i o n w i t h t h e u s e o f a P S R scale is o f t e n o v e r l o o k e d in o t h e r s t u d i e s t h a t e v a l u a t e d t h e effectiveness of these scales. Further, different kinds and

timing of interventions influence the time span between measuring an increased risk of developing a pressure s o r e a n d t h e a p p e a r a n c e o f t h e p r e s s u r e s o r e . It is t h e r e f o r e d i f f i c u l t t o g e n e r a l i z e t h e r e s u l t s o f this s t u d y to o t h e r p a t i e n t s e t t i n g s d u e t o p r o b a b l e d i f f e r e n t levels o f n u r s e a l e r t n e s s in t a k i n g m e a s u r e s a g a i n s t p r e s s u r e sores. T h e r e s u l t s o f t h i s s t u d y s e r v e n o w as a m o d e l for t h e m a n a g e m e n t o f p r e s s u r e s o r e p r e v e n t i o n at o u r I C U . The method of evaluation can be used for quantitative risk evaluations of any PSR model. This study demonstrates that evaluating PSR models by means of actuarial s t a t i s t i c a l m e t h o d s s u p p l i e s t h e u s e r w i t h m u c h v a l u a b l e i n f o r m a t i o n o n t h e d e v e l o p m e n t o f p r e s s u r e sores.

Acknowledgement This study was made possible by Toshiba Benelux systems which donated some of the necessary hardware for analysis of the data.

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