The approach taken by anaesthetists to a patient with a potentially full stomach requiring sedation seems to differ widely from that of some emergency physicians. I must qualify this statement by saying that this is not true of many emergency physicians with whom I work clinically. It has been a perspective I’ve largely been exposed to by emergency physicians I’ve had contact with through social media. As such it may be that the real distinction to be made is not between the specialties but between those clinicians who inform their decisions based on opinions expressed in social media and those who don’t. I’m not sure whether this is the case and these are clearly generalisations as it’s unlikely all the emergency physicians using social media share a homogenous view either. Regardless of the reason for this difference of opinion I think its worthwhile stating a few facts on the issue.
For those of you who have access I had a great & detailed discussion with Andy Buck about fasting, airway management & procedural sedation recently on the May Aussie Edition of EMRAP.
The following are facts about fasting and aspiration risk.
FACT 1 – Aspiration Is A Real Risk: aspiration is not theoretical – whilst uncommon, it happens and patients occasionally suffer serious morbidity or mortality from it. It is certainly more common in anaesthetic practice than other potentially lethal events like “Can’t Intubate, Can’t Oxygenate” which we expend considerable effort on adopting strategies to avoid. The seriousness of lung damage produced by aspiration is dependent on the volume & composition of the aspirate with low pH material producing a higher risk of aspiration pneumonia and with aspiration of solid material being much more likely to result in mortality.
How do we know this?: clinical experience & published literature.
Conclusion: It would seem reasonable that we take reasonable precautions to mimimise the risk of aspiration in our patients. In particular avoiding the risk of aspiration of solid material decreases the risk of mortality from aspiration.
FACT 2 – The Risk of Aspiration of Solid Material Is Lower if the Stomach is Empty: having an empty stomach does not eliminate the risk of aspiration of acidic gastric secretions but it does drastically reduce the chance of potentially fatal aspiration of particulate gastric content.
How do we know this?: Common sense. You can’t aspirate something that isn’t there. Whilst the baseline risk of a patient aspirating a burger during sedation if their airway is not protected may be low, it’s infinitely lower if there’s not a burger in the stomach in the first place. Those of you who somehow don’t believe this should have no problem letting your patients snack on nachos right up to the time you administer sedation. Conversely if you adopt sensible strategies to avoid placing solid material into the stomach that might not otherwise be there, immediately prior to sedating a patient sufficiently to potentially impair their airway protective reflexes, you are acknowledging this principle.
Conclusion: In attempting to minimise the risk of aspiration in sedated patients, it would be safer if there was no food in the stomach.
FACT 3 – The Stomach Empties With Time: given enough time all food leaves the stomach. The question is how much time is enough for the stomach to empty? The time required for gastric emptying varies according to the nature of the food (fatty foods empty much slower) and patient factors (pain, nausea, opioids, intra-abdominal “mischief”, pregnancy, sepsis, etc). Many of the factors that delay gastric emptying are present in the patient population presenting for emergency procedures, both in the ED and the operating theatre. As such many of these patients may not ever be able to be considered “fasted” within the time frame that clinical urgency dictates their procedure must be done. This means that looking at studies of ED patients which determine that standard 6 hour fasting doesn’t influence the risk of aspiration doesn’t allow you to conclude that there is no increased risk of aspiration from having a full stomach. Such studies aren’t necessarily comparing full stomach with empty stomach, it is likely they are often comparing full stomach at time zero with full stomach at 6 hours – and as such a difference in the aspiration rate wouldn’t be expected. Thus it’s important that we keep the terminology in relation to “fasted” versus “empty stomach” clear when discussing this issue . The salient point is whether the patient has a full/empty stomach, not whether they are fasted/unfasted. Fasting is only one mechanism by which we can assess whether a patient might have an empty stomach, but it is often of limited use in the ED patient population. This is by no means meant to imply that there is no value in ever fasting ED patients. There are many who may have normal gastric emptying and who may benefit from fasting where this is clinically appropriate. Even patients in whom gastric emptying may be delayed should still be given the opportunity to fast where this does not expose them to unnecessary suffering or clinical risk – as gastric emptying might still occur. Clinical urgency determines the timing of the procedure/sedation, the likelihood of an empty stomach at that time determines the strategies required to minimise the risk of aspiration with sedation. The important point is that saying that fasting doesn’t always decrease aspiration risk is not the same as saying having a full stomach doesn’t always increase aspiration risk.
“The salient point is whether the patient has a full/empty stomach, not whether they are fasted/unfasted… saying that fasting doesn’t always decrease aspiration risk is not the same as saying having a full stomach doesn’t always increase aspiration risk”
“Clinical urgency determines the timing of the procedure/sedation, the likelihood of an empty stomach at that time determines the strategies required to minimise the risk of aspiration with sedation”
How do we know this? From looking in the stomach of fasted patients. Patients coming for elective gastroscopies following a standard anaesthetic fast of 6 hours for food, 2 hours for water typically have empty stomachs (there may be varying amounts of residual liquid but solid food is very rare). Whilst that establishes that a 6 hour fast seems generally effective it is possible that a shorter fasting time would be equally effective. It’s important to note, however, that a 6 hour fast is not universally effective and that rarely patients who would be expected to have normal gastric emptying, have solid food matter in their stomachs at gastroscopy, despite reporting having fasted for an appropriate duration. Whether this represents a failure of gastric emptying within the 6 hour period or the fact that the patient did not actually fast for 6 hours is unknown. From an ED perspective it is also important to note that this 6 hour fast is from a “light meal” and any margin for error it provides may not be true of large volume fatty meals & alcohol which may be in the stomachs of some of the ED patient population (some fasting guidelines advocate longer fasting periods of 8-10 hours following fatty meals). Given the above, and the fact that a 6 hour fast from food is unlikely to do harm, especially when water is continued up until 2 hours prior to the procedure, I can’t see a particular value in trying to shave the fasting time down further. One final point to note is that patients having gastroscopy who are judged to be at risk of delayed gastric emptying and intubated via RSI despite having been fasted, frequently (though again not universally) have large residual gastric volumes and solid food material in their stomachs, reinforcing the fact that the time taken for the stomach to empty is genuinely impacted upon by the factors listed above.
Conclusion: Fasting for minimum 6 hours for food and 2 hours for water should be routinely undertaken for patients having sedation where clinically feasible in order to promote gastric emptying and achieve an empty stomach. Patients at risk of delayed gastric emptying may continue to have a full stomach despite fasting for the requisite time periods.
Summary:
The above points are facts. Proof of them via large randomised controlled trials is not required. These are things we already know from direct observation & unassailable logic. Any study that fails to validate these facts must be flawed. Aspiration is real and is worse when it involves particulate matter. The risk of aspirating solid material is infinitely higher when there is solid matter in the stomach to aspirate and the likelihood of there being solid matter in the stomach to aspirate diminishes with increased fasting time. Whilst the baseline risk of aspiration may be small, it’s sequelae may be serious. Taking these facts together one can only conclude that, where clinically feasible, in order to minimise risk of (especially particulate) aspiration, all patients should be fasted before receiving any sedation likely to impair their protective airway reflexes. Similarly where patients are judged likely to be at risk of not having an empty stomach either because of delayed gastric emptying or where the clinical urgency of the sedation/procedure precludes fasting, the patient is at increased risk of aspiration.
Only now do we get into an area where clinical evidence is required. In patients who are judged to be at increased risk of aspiration, what is the best strategy to mitigate this risk in patients requiring sedation for short, painful procedures that can be performed in the ED such as reduction of fractures & disclocations? The predominant anaesthetic perspective (and that of many emergency physicians) is that RSI with a cuffed ETT should be used. Another group of emergency physicians advocate sedation with an unprotected airway.
Certainly I don’t think many would dispute that once the cuffed ETT is in place, the risk of the patient aspirating is drastically reduced.The questions to be addressed are what risks of aspiration does the process of intubation & extubation during RSI pose and what other additional risks is the patient exposed to during the process of RSI (eg. anaphylaxis from muscle relaxants – you’d then have to weight this according to risk of serious permanent morbidity/mortality versus that from particulate aspiration). I’m not sure that these risks of RSI are well known or easy to quantify. If these risks are less than those of aspiration during sedation with an unprotected airway, then RSI is the answer. Conversely if they are higher then sedation with an unprotected airway is the safer option. I don’t know the stats on these issues but I’d be keen to hear from those of you that do. There may be other factors like the drugs used for procedural sedation that influence this equation. I will say of the often touted statement that “ketamine doesn’t impair airway protective reflexes” that I’m yet to be shown a legitimate reference for this. Whilst I have seen this statement made in a journal article, when the antecedent references were traced back they lead to an erroneous interpretation by a non-clinical pharmacology journal of what “airway protection” meant, using it to describe findings of unchanged pharyngeal muscle tone in patients receiving ketamine. Anecdotally I’ve noticed that patients induced with ketamine tend to retain a coordinated swallow which seems encouraging to me that they might also retain their airway reflexes better – I wouldn’t be counting on this on that basis though.
This issue of the risks of RSI versus unprotected airway is the only one we should be debating though – not the efficacy of fasting, the significance of having a full stomach or whether the ED has the resources to do RSI’s even if they are required – simply what is the lowest risk approach to sedating patients judged to be at increased risk of aspiration for these procedures. We have to decide what is best practice for our patients, then manage resources appropriately. It is also important to note that for a given subset of procedures, assuming that intubation & extubation are performed appropriately, there should only be one answer to this issue. Those advocating RSI & those advocating sedation with an unprotected airway can’t both be right. This shouldn’t be an anaesthetic versus ED issue, nor a conventional resources versus online learning issue – this is a question of fact not opinion. Now that we’ve defined the question, show me the answer.
“We have to decide what is best practice for our patients, then manage resources appropriately”