This Invited Commentary accompanies the following original article:
McCracken GC, Montgomery J. Postoperative nausea and vomiting after unrestricted clear fluids before day surgery. A retrospective analysis. Eur J Anaesthesiol 2018; 35:337–342.
Pre-operative fasting is intended to reduce the volume and acidity within the stomach in order to reduce the risk, and consequences of regurgitation and aspiration of gastric contents. Since the landmark work of Maltby et al.,1 it has been repeatedly demonstrated that a fluid fast of no more than 2 h achieves gastric conditions at induction of anaesthesia, which are at least as favourable as those resulting from longer fasting intervals and may actually result in lower residual volumes.2 Concurrently, it has been shown that prolonged fluid fasting results in significant distress to adults2 and children,3 through increased feelings of thirst, hunger and anxiety. Furthermore, prolonged fasting may negatively affect insulin resistance4 and severe cases of hypoglycaemia and hypovolaemia have been reported in children.5 Consequently, some guidelines have tried to change the emphasis away from a minimum period of fasting towards encouraging patients not to avoid fluids for longer than necessary.6 In practice, however, patients continue to fast excessively. For example, despite implementation of liberal guidelines and improved information, patients were still found not to have drunk liquids for an average of 7 h, and for as long as 18 h, before induction of anaesthesia.7 This may be because patients take their last drink at home before coming to hospital, usually more than 2 h before surgery, or even stop drinking when going to bed the night before. Furthermore, fasting instructions are invariably biased towards the start of the operating session in the morning, resulting in far longer fasting intervals for subsequent individuals. In practice, healthcare professionals fear causing a delay by individualising fasting periods and frequently err on the side of longer fasting, to the disadvantage of patient comfort and benefit.
In the present issue of the European Journal of Anaesthesiology, McCracken and Montgomery8 have taken a novel approach. They present a challenging report from about 5000 patients with no restrictions on pre-operative intake of clear fluid until transfer to the operating theatre. They observed a 27% reduction in postoperative nausea with this approach when compared with a comparable number of historical control patients not allowed to drink within 2 h of the start of surgery. Importantly, no cases of clinical symptoms from aspiration of fluids into airways were observed in any of these patients. This report challenges an important safety rule in anaesthesia. Some will also say it adds another item to the ever growing list of unjustified dogma in anaesthesia care; a list of so-called safety measures, which turn out to imply only extra work for staff and/or increased discomfort and stress for patients.
In the discussion of evidence-based pre-operative fasting practice, debates have been ongoing for many decades without really being settled. The problem (which is good news for patients!) is that the incidence of clinical aspiration in elective surgical patients is extremely low. It is therefore hard to demonstrate a statistically significant alteration in a prospective, randomised study of any change in clinical practice. In the UK national survey of 2.9 million patients in 2008, aspiration occurred in only 23 patients, mostly with known risk factors, yielding an incidence of less than 1 per 100 000.9 This means that most anaesthesiologists will not encounter this problem during a lifelong career in their own practice or environment. Nevertheless, one preventable case will be regarded as one too many for those who become involved, even if it is rare. However, the ‘preventability’ from applying a prophylactic safety measure to absolutely all patients must be put into context against the associated side effects and extra costs. The reports of McCracken and Montgomery, and also others,10–13 clearly demonstrate a reduced incidence of nausea and increased patient satisfaction with a nonrestricted fluid policy and subsequent better hydration. Even though the numbers needed to treat (NNT) for avoiding nausea by allowing such a liberal policy is only about 75, this may be of clinical importance for millions of day-surgery patients worldwide every year, especially when added to the other known benefits of shorter fasting. Although not addressed in the report of McCracken and Montgomery, these are in terms of cost and convenience: patients’ fear of not obeying rules on pre-operative drinking will disappear, as will the need for detailed instructions on this issue. Also, we are all familiar with the frequent postponement or cancellation of patients who have not strictly adhered to fasting rules and the associated costs in terms of time and effort spent on such discussions, patient distress and subsequent potential delays to the operating programme.
We should also challenge whether there is any risk at all from a free clear fluid policy in the day-surgery setting. Maybe this is not a discussion of the very rare problem of aspiration set against a lot of benefit, but an even simpler case of no proven problems ever in this setting, which will make the conclusions easier to draw.
In order to pursue this issue, prospective, randomised controlled studies of sufficient statistical power are almost impossible to conduct; multimillion numbers of patients would need to be recruited and it would then be hard to control for other important confounders. Thus, we still have to rely on case reports and studies of indirect evidence of risk: what type and amount of gastric content will be a potential problem? How and during what circumstances will such gastric conditions occur? What are the prerequisites for this content to potentially be regurgitated into the pharynx? What are the risk factors for any pharyngeal content to get into the airways? What amount and type of airway aspiration will induce problems? What will the nature of these problems be? How favourable will the outcome be with current treatments?
Numerous good studies have been done throughout the years on these issues and we already know a lot, which also challenges the general rules of fasting,6,14 not just for clear fluids. For elective patients, we can try to control preoperative aspects which ensure a low amount of potentially risky gastric content at the start of anaesthesia. We know that water is fully cleared from the stomach within 30 min; other fluids usually within 1 to 2 h, more rapidly if the caloric content is low.15 The evidence of slower clearance of milk16,17 is, at best, controversial; and studies show that fluids do not have to be clear, or even to be fluids, in order to have rapid gastric emptying.15 Mixtures of solids and fluids, such as with a light meal, may be cleared much faster than the 6 h fasting prescribed for food, whereas a big fatty dinner may take more than 8 h to empty completely.18
Where does this discussion leaves us in relation to the new data from McCracken and Montgomery? Although many of the issues above may be relevant to revising our dogmatic fasting rules in upcoming reviews of the literature, we should at this point restrict our discussion to the conditions and data in the present paper. This is a study on elective day-surgery patients. The strength of the study is the inclusion of all patients over several years, including the obese, patients with symptoms of reflux, the elderly and others with potential risk factors for regurgitation. The reliable, routine collection of quality outcome data from more than 10 000 patients and the ability to detect any readmissions in a well controlled geographical area are further strengths. Some problems may still exist with this report: we do not know if all risk factors for nausea, such as nonsmoking status, postoperative opioid use, specific type of surgery, previous postoperative nausea and vomiting (PONV) or travel sickness and use of antiemetic drugs were well controlled and similar before and after the change in fluid policy. Furthermore, we do not know the number ‘treated per protocol’; that is, how many patients in the liberal group actually drank fluid in the 2-h preoperative period or if some in the fasting group had something to drink in spite of being told otherwise.
Nevertheless, the study confirms what we know from case reports and other studies; the risks from a liberal fluid policy are virtually nil and there is no reason to postpone or cancel an otherwise low-risk patient simply because of fluids consumed within the 2-h period. This is also consistent with some guidelines, such as from Scandinavia,19 of allowing tablets to be taken with sips of water (typically up to half a glass) up to 1 h before the start of surgery. As the time from start of transfer to the operating room to the start of surgery is usually close to 30 min, the policy of McCracken and Montgomery is only a small step onwards from the rule already practised for tablets in water. It is, however, delightfully simple to instigate and allows patients to continue drinking without having to anticipate exactly when their operation will start.
Whether the data from McCracken and Montgomery are enough to recommend a worldwide change in fasting policy may still be disputed. A good rule is to ask for more than one high-quality study from more than one institution in order to justify changing a well established routine. However, the data have sufficient strength to urge us to gain more experience with a liberal policy in the low-risk day-surgical patient for the benefits of reduced nausea, simpler logistics and improved comfort in our patients, still with a little caution for rare, potential problems.
Acknowledgements relating to this article
Assistance with the commentary: none.
Financial support and sponsorship: none.
Conflicts of interest: IS and PK contributed to the European Society of Anaesthesiology pre-operative fasting guidelines.
Comment from the editor: this Invited Commentary was checked by the editors but was not sent for external peer review. PK is an Associate Editor of the European Journal of Anaesthesiology.
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