Preoperative fasting: we need a new consensus.

It is widely acknowledged among health care professionals that patients are being excessively fasted before surgery (Jester and Williams, 1999; Chapman, 1996; Green et al, 1996), yet hospital tradition and custom continues to dictate the fasting regime (Seymour, 2000). Patients are typically fasted from midnight if scheduled for morning surgery, and from 6 a.m. for afternoon surgery. This is standard practice in many health care settings (Methery, 1996). In the past, anaesthetists recommended that patients should be fasted for up to eight hours before surgery (Shevde and Trivedi, 1991). A blanket 'nil by mouth' from midnight on the day of surgery is not only accepted policy in the UK, but is also a worldwide reality (Pandit and Pandit, 1997).

If the length of fast is inadequate, a patient may potentially aspirate the contents of their stomach into their lungs, which could lead to aspiration pneumonitis, a life-threatening event occurring in 1-6 per 10,000 anaesthetics (Olsson et al, 1986). According to Mendelson (1946), the risk factors associated with aspiration pneumonitis are increased when the patient has gastric volume above 25ml and a gastric pH lower than 2.5. The ideal fasting time, then, aims to avoid these conditions. However, simply prolonging the fasting time does not necessarily produce the desired effect. Other studies (Hung, 1992; Green et al, 1996) indicate that an extended fast does not produce an optimum gastric environment but instead may precipitate other problems, such as dehydration, electrolyte imbalance, malnutrition and general malaise.

Work by Shevde and Trivedi (1991) found that two hours after ingestion of a fluid (water, orange juice or black coffee) all volunteers had a gastric volume less than 25ml and a pH less than 2.5. The authors concluded that in healthy adults it was safe to induce general anaesthesia two hours from the ingestion of moderate amounts of clear fluids. This was despite the fact that all patients had a pH below 2.5, a point that Mendelson (1946) considers a risk factor. Shevde and Trivedi justify this by comparing it to the results of another study by Coombs et al (1979) which suggested that patients who were fasted for 11-13 hours continued to have a pH less than 2.5, indicating that a prolonged fast may actually contribute to a lower pH. According to Mendelson, a low pH increases the patient's potential to aspirate, causing lung damage.

A study by Agarwal et al (1989) on the effects of oral fluids before surgery showed that there was no statistical difference in the pH of gastric contents between a group fasted overnight (group 1), a group who ingested 150ml of water two hours prior to surgery (group 2), and a group who ingested water two hours before surgery and received intramuscular morphine (group 3). Even more importantly, the study showed that there was a decrease in gastric volume of patients in groups 2 and 3. this indicates that patients who endure long periods of fasting may increase their gastric volume, a predisposing factor for aspiration pneumonitis (Mendelson, 1946). These findings are supported by Maltby et al (1986) and Sutherland et al (1987) who observed that 150ml of water administered two to three hours before surgery was effective in lowering residual gastric volume and raising pH in most patients. Therefore, it could be argued that patients are as much at risk from aspiration due to an excessive fast as they would be if the fast were inadequate.

Smith et al (1997) suggest that allowing patients to drink up to two hours preoperatively may make postoperative vomiting less likely. This contrasts with traditional views that suggest a long fast is necessary to prevent postoperative nausea and vomiting (Methery, 1996). Palazzo and Strunin (1984) found that a substantial number of patients felt sick after fasting for up to 8.5 hours. This implies that instead of minimising postoperative vomiting, an extended fast can lead to an increase in postoperative emesis.

Patients who undure excessive periods of fasting may find that they are unable to resume their normal eating habits following surgery due to postoperative nausea/vomiting and so become malnourished and dehydrated.

Even before surgery, a fasting patient can become dehydrated quickly since an average adult requires 2,500ml of fluid daily simply to reduce the volume lost through urination (1,500ml), the skin (600ml) and the lungs (400ml) (Lee et al, 1996). The dehydrated individual may be subject to electrolyte imbalances, tachycardia, hypotension, oliguria, decreased levels of consciousness and confusion (Goode at al, 1985).

Hung (1992) argues that there are real dangers associated with prolonged fasting as it can cause discomfort, irritability, dehydration and malnutrition, and at worst, contribute to postanaesthetic mortality and morbidity. Psychologically, the excessively fasted patient may become non-complaint and resentful (Green et al, 1996).

Jester and Williams (1999) have explored the opinions of nurses, anaesthetists and patients regarding fasting. Results showed that patients were being fasted according to tradition and custom rather than research. But, through education and with the anaesthetist prescribing the last time a patient could eat and drink, fasting times were reduced. Chapman's study (1996) suggests that some health care professionals lack the appropriate knowledge and that, despite universal agreement between nurses and anaesthetists, patients routinely fast for longer than the recommended times for fluids (Phillips et al, 1993; Smith et al, 1997). Half of anaesthetists were aware of recent literature, but none of the nurses. Chapman also found that fasting times were planned to accommodate a wide range of theatre list times, to compensate for any changes. Nurses and anaesthetists felt it was safer to follow tradition in case the theatre list order changed; both overestimated the frequency of theatre list changes.

For elective patients, Maltby et al (1986) and Sutherland et al (1987) advocate a fasting time for clear fluids of two to three hours. Shevde and Trivedi (1991) suggest a fasting time for clear fluids of two hours in day-case patients, while both Phillips et al (1993) and Maltby et al (1986) support a fasting time for clear fluids of two hours. The American Society of Anesthesiologists (ASA) recommends a fast from solids for at least six hours and a fluid fast of between two and four hours (ASA, 1999).

Strunin (1993) suggeke that 'nil by mouth' after midnight should be abandoned and clear fluids should be offered to patients up to three hours before anaesthesia. Nygren et al (2001) recommend giving a carbohydrate drink 90 minutes before elective surgery. Their studies show complete gastric emptying of the 50g carbohydrate drink within 90 minutes of intake. Taking oral carbohydrates also reduced postoperative insulin resistance as well as improving a patient's pre- and postoperative well-being.

Practice appears to be based on custom and tradition and to accommodate the unpredictability of the operating list rather than what is best for the patient. This contradicts the UKCC's Code of Professional Conduct (1992) which directs nurses to 'act always in such a manner to promote and safeguard the well-being of patients'. The citadels of age-old belief and ideals with regards to the fasting regime need to change. All health care professionals should be up to date with the latest research on fasting regimes. We suggest the introduction of a national protocol that identifies 'at risk' patients such as those with hiatus hernia, the obese and trauma patients. Clear guidelines would bring all health professionals up to speed on the important subject of patient fasting.

© Watson K and Rinomhota S (2002); Nursing Times; 98; 15; 36-37.