This is a follow-up of last week’s Briefs on ketamine. How long do you really need to keep a patient NPO prior to moderae/procedural sedation in the ED? Let’s look at this issue form a few different angles and explore the evidence since there is such a significant degree of practice variation.
Certainly the main goal of fasting is to prevent vomiting with pulmonary aspiration. During OR procedures the risk of aspiration is quite low – 1/7,000 with a mortality of nearly 1/100,000. The risk of aspiration is increased in patients who cannot fast (emergencies) and in conditions with potential for delayed GI transit hypertrophic pyloric stenosis, duodenal hematoma, traumatic/surgical abdomen, history of severe gastroesophageal reflux. Looking at the aforementioned numbers it is clear that aspiration doesn’t always lead to adverse outcomes. Furthermore it is interesting to note that pre-procedure antacids or motility drugs don’t make a difference on aspiration risk either.
Length of NPO status
If I haven’t driven it home already, this is an area of significant practice variation. In a study of more than 2,000 children sedated in an ED Roback et al. noted that there was no increased risk of adverse events – desaturation, vomiting, apnea, laryngospasm – in children who met ASA fasting guidelines vs those who didn’t. Their study saw 150 children who fasted less than 2 hours, and 400 that fasted between 2-4 hours. NO patients had aspiration. The drugs used included ketamine, ketamine + midazolam, and midazolam+ fentanyl. Babl et al noted that although, 71% of their patients receiving nitrous oxide sedation did not meet guidelines there were no adverse events.
It is also helpful to look at this in terms of the type of procedure (elective vs emergent for instance). So let’s start with elective procedures – which admittedly some procedures in the ED would qualify as.
The American Society of Anesthesiologists (ASA) recommends the following
- Two hours after clear liquids
- Four hours after breast feeding
- Six hours after ingesting solid foods, formula, or milk other than human milk
The majority of the evidence here is looking at clears. A systematic review of children undergoing elective procedures showed that fasting 2 hours for clears showed no difference in intraoperative gastric volume or pH and provided greater patient comfort vs 6 hours of NPO for clears. when compared to six hours of complete fasting. There isn’t much compelling evidence otherwise.
There definitely seems to be no consensus here. The recommendations from Anesthesiology and the American College of Emergency Physicians aren’t exactly on the same page. If the procedure must be done right away to reduce the risk of mortality then proceed. It is important to note that intubation does not prevent aspiration, and airway manipulation can make you vomit. Otherwise it may be wise to follow the elective recommendations/suggestions:
- The patient is less than 6 months of age
- Predicted difficult airway – don’t sedate the patient as deeply
- ASA Class 3 and above (at which point you shouldn’t be doing sedation for an Urgent Procedure without conulting Anesthesiology anyway)
- Increased risk of aspiration as assessed clinically (altered mental status, bowel obstruction etc,.)
In the UK, it is recommended that fasting recommedations don’t need to be followed if:
- Nitrous alone is used
- The patient can verbalize despite the drugs administered
How do I practice?
If the procedure is urgent, I will sedate if the child has fasted between 2-4 hours. Most often this is with ketamine, and airway protective reflexes are still present. I also will not sedate if the procedure is estimated to be longer than 30-40 minutes (especially if I’m the only Attending around). For any patient that is ASA class III I’ll consult Anesthesiology to be on the safe side. I recommend that you familiarize yourself with the literature and arrive at your own conclusions.
FYI: American Society of Anesthesiologists (ASA) Classification
- Class I – A normally healthy patient
- Class II – A patient with mild systemic disease (eg, mild asthma, controlled diabetes mellitus)
- Class III – A patient with severe systemic disease (eg, moderate-to-severe asthma, poorly controlled diabetes mellitus, pneumonia)
- Class IV – A patient with severe systemic disease that is a constant threat to life (eg, severe bronchopulmonary dysplasia, advanced cardiac disease)
- Class V – A moribund patient who is not expected to survive without the operation (eg, septic shock, severe trauma etc,.)