VOL: 103, ISSUE: 9, PAGE NO: 44
RN, Dip, is staff nurse and tissue viability link nurse, Cardiothoracic Critical Care, Papworth Hospital
Gannon, R. (2007) Wound cleansing: sterile water or saline? Nursing Times; 103: 9, 44-46.
Robert Gannon discusses whether sterile 0.9% saline or sterile water should be used as the main cleansing solution in hospital settings. He also explores the importance of warming cleansing solutions before use. The physiological and practical benefits of each solution will be analysed.
Despite significant advances in wound care technology in recent years, very little attention has focused on the use of cleansing solutions. There are only two trials identified in a Cochrane review (Fernandez et al, 2002) that have specifically investigated the benefits of sterile water versus normal saline when used as wound-cleansing solutions - added to which, a literature review on the subject has failed to find any new relevant research.
Water as a cleansing solution
Water has been used as a cleansing solution for centuries without ill effect (Flanagan, 1997). Water is a hypotonic solution, which means it can cause cellular oedema and rupture under the influence of osmotic pressure (Cunliffe and Fawcett, 2002). Water can be an inappropriate choice for regular wound irrigation as it may be detrimental to cells (Towler, 2001). If wounds are exposed to water for too long they can absorb the liquid through osmosis, which increases the production of exudates, leading to more frequent dressing changes (Flanagan, 1997).
In practice this would necessitate further use of wound care products, nurses’ valuable time and additional discomfort for the patient both physically and psychologically. Cells can also burst, as demonstrated by adding water to a suspension of red blood cells causing them to lyse (Lawrence, 1997). Water irrigation of raw tissue can cause pain and useful dissolved substances in wound intracellular fluid may be lost (Lawrence, 1997). The loss of valuable dissolved wound substances could lead to delayed wound healing, extended treatment and possibly a delayed discharge. In practice, water irrigation could cause patients to experience greater pain and additional analgesia may then be required.
Despite possible theoretical disadvantages, water has to be considered when a product licence states that 0.9% saline cannot be used, for example when using Acticoat silver dressings. Sterile water can be used as long as a task is performed efficiently and without exposing or immersing the wound unnecessarily. In practice, patients can cleanse wounds with water as a part of a normal hygiene routine, as long as wounds are not soaked for long periods (Flanagan, 1997).
Saline as a cleansing solution
Sterile 0.9% saline is an isotonic solution. It neither donates fluid nor draws it away from the wound bed (Blunt, 2001). Isotonic solutions do not impede normal healing, damage tissue, cause allergy or alter the normal bacterial flora of the skin that would allow the growth of more virulent organisms (Griffiths et al, 2001). This is an important consideration for all patients and particularly for immune-compromised patients.
Classic animal studies concluded that normal saline has little or no effect on blood flow in capillaries and is not detrimental to underlying granulation tissue (Brennan and Leaper, 1985). Normal saline does not affect collagen or DNA synthesis (Brennan et al, 1986). It is important to acknowledge, however, that there are concerns in transferring experimental animal data to human practice. The reliability and validity of animal data must always be questioned as the experiment may not replicate what the patient experiences or how the wound may react in humans.
Saline is more expensive than sterile water (British Medical Association/Royal Pharmaceutical Society of Great Britain, 2006) so water has the potential to be more cost effective if it were chosen as the solution of choice.
If water or saline is used it should be at body temperature as it can take 40 minutes for a wound to return to normal temperature and three hours for leukocyte activity to recover after a dressing change (Fletcher, 1997). Experiments on humans demonstrated that wound temperature drops significantly at dressing changes, mitosis is inhibited and it takes 40 minutes for a freshly cleansed wound to return to normal temperature and three hours for cell mitotic division to restart (Lock, 1979). Wound healing occurs at normal core body temperature and a body surface temperature above 33ºC; below this temperature or when it is above 42ºC, wound healing is delayed (McGuinness et al, 2004).
Experimental studies on 137 dressing episodes in human wounds found that wounds cleansed with ambient-temperature solution (mean 29ºC) led to a 2º drop in wound temperature, resulting in a mean temperature of 32.6ºC in all wounds studied - below the target of 33ºC (McGuinness et al, 2004).
In practice nurses should warm a solution to between 37ºC and 42ºC and cleanse in an efficient manor so as to minimise a fall in temperature. A dressing changed daily for one week has the potential to be without mitotic capability for up to 21 hours a week unless due care is taken to minimise this. Maintaining optimum wound temperature helps increase blood flow to the wound bed, enhance the rate of gain of wound tensile strength and increase oxygen tension, which aids wound repair (MacFie et al, 2005). It also helps prevent uncontrolled bacteria proliferation, thereby reducing the risk of infection (Lock, 1979).
Lack of temperature-recording equipment may be an issue as estimating the solution temperature is not ideal. A tool called ‘Derma Temp’ from Exergen Corporation can measure wound-bed temperature (McGuiness et al, 2004) but comes at a cost. Alternatively, practice settings could invest in ‘warmer cabinets’ that keep cleansing solutions at an optimal temperature until ready to use. This may be a more practical solution to maintaining correct wound-bed temperatures as the cleansing solution is warmed to an optimal temperature before use and this helps to maintain the temperature of the wound bed during dressing changes.
This is an approach to decision-making in which the clinician uses all available evidence in consultation with the patient to decide on the option that suits the patient best (Muir Gray, 1997). Most relevant evidence comes from two studies: Angeras et al (1992) and Griffiths et al (2001). Subject to a Cochrane database systematic review (Fernandez et al, 2002) along with four others that were not applicable to this article, the studies focused on comparing normal saline with tap water. As no bacteria isolated in the water was cultured from treated wounds, the findings may be credible and transferable to practice where sterile water is being considered.
Angeras et al (1992) studied 705 patients in a randomised study of saline versus water in treating acute traumatic wounds. Half were aged 18-35 and 77% were male. The findings need to be considered with caution as the younger sample population will not be affected by the many co-morbidities that delay wound healing in an older population. Not all the wounds sampled in the study would be encountered by every nurse, hence the need for further caution when transferring findings to the practice setting. Bias was reduced as doctors cleaning the wounds did not know which solution they were using.
The sample size may not guarantee a national population subset as all wounds originate from one hospital centre, but is much larger than any from any other relevant studies. The infection rate, judged by wound appearance and delayed healing in the water group was 5.4% and the solution was warmed to 37ºC. For those cleansed with ambient-temperature saline, the infection rate was 10.3%. Angeras et al (1992) concluded that water should replace saline as the cleansing solution of choice, despite acknowledging that the wound-temperature variable may have influenced the result.
Variables are not desirable as they lead to bias and it can be difficult to establish whether the difference between two treatments is due to the treatment or chance (Polit et al, 2001). The temperature variable constitutes a major methodological flaw that may have led to an increased incidence of sepsis in the saline group (Selim et al, 2001). A Cochrane database systematic analysis on the two studies also supports the argument that the temperature variable may have lead to higher infection rates in the saline group (Fernandez et al, 2002). The Cochrane review found that although the reporting of the trial was good, overall quality was poor and there was a lack of replication of most comparisons. The review found that the data analysis regarding wound infection was complicated by a lack of consistency in the criteria used to assess wound infection (Fernandez et al, 2002). Wound-infection criteria are different in many hospital centres and so the findings of this trial are viewed with caution.
Griffiths et al (2001), the same experts who assisted the Cochrane database review, carried out a double-blind randomised control trial of tap water versus sterile saline in 49 subjects. Male and female participation was almost equal and the mean age was greater than 75. The wounds studied were a mix of chronic and acute surgical wounds. The small sample size may affect validity and reliability and, in practice, applying the finding from such a small group could be unsafe as a much larger trial would be required to detect whether or not the intervention had a positive effect on treatment outcomes. Yet the sample population is similar to many nurses’ practice populations and, thus, enhances transferability to practice.
The results found that 6.1% of the group given saline became infected against 0% of those given water. Infection was judged by the presence of purulent discharge after six weeks; this is a different set of assessment criteria to Angeras et al’s study group. A total of 61.5% of those given saline healed after six weeks compared with 34.7% of those given water. The six-week reporting period is more robust as more stages of wound healing are encountered than in the two-week period set out by the Angeras et al (1992) trial.
Griffiths et al’s study is more likely to be valid as it was a double-blind randomised trial but this is offset by the small sample size (Cunliffe and Fawcett, 2002) and statistical significance was not achieved. The Cochrane database systematic review (Fernandez et al, 2002) criticised the trial in a similar fashion to that of Angeras et al, concluding that there is insufficient evidence to support or refute the routine use of water for wound cleansing in practice and that further extensive trials are required.
Sterile 0.9% saline should remain the cleansing fluid of choice in the hospital setting. This is based on a more convincing physiological argument that favours the use of saline and the lack of convincing evidence to support the routine use of water. The research does not exclude the use of water and the author feels that it can be used to cleanse wounds where normal saline is contraindicated.
It is recommended that further education is required for staff so as to highlight the rationale for choosing either saline or water in practice. Nurses should warm their cleansing solution to 37ºC to help minimise loss of wound temperature at dressing change and change dressings efficiently.
Further large-scale trials of sterile water versus saline using sound research principles are required. National and international guidelines on what constitutes an infected wound would facilitate sound and reliable research in this controversial area of wound care.
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