Wednesday, January 22, 2014

Preoperative fasting and evidence-based medicine

The other day Mike Blackburn, a South African anesthesiologist I follow on Twitter, posted this: "Colleague just fb’d about a surgeon who said, 'I know we should wait 6 h but she ate at 12 and looks like a fast digester.'"

This was followed by a tweet from someone who calls him- or herself @LessIsMoreMed who said, "funnier still is the lack of evidence re: pre-op fasting" and included links to two references on the subject.

This reminded me of an incident that occurred about three years ago. I was working as a surgical hospitalist and had admitted a patient with acute cholecystitis in the middle of the night. I put her on the add-on OR schedule for that day.

By and by the patient was called for and when I got to the operating room holding area, the anesthesiologist met me with a frown on his face and told me the case would have to be postponed for a minimum of 6 hours.

I asked why. He told me that when he interviewed the patient, he noticed that the patient had a piece of hard candy in her mouth. He informed me that, in terms of gastric secretion, the act of sucking on a piece of hard candy was equivalent to having a eaten a full meal of solid food.

Being a very reasonable guy, I went ballistic and demanded to see evidence that sucking on a piece of hard candy was problematic in any way for a patient receiving anesthesia. No such evidence was produced. I appealed to the chairman of the anesthesia department to no avail.

Later as my blood pressure was returning to normal and I was killing time waiting for the 6 hours to elapse, I tried unsuccessfully to find some literature on the subject. I just rechecked—still nothing.

I did find some papers about chewing gum.

In 1994, a paper found that randomizing patients to sugarless gum vs. no gum and varying the timing of cessation of chewing had no effect on either gastric volume or pH. The authors concluded, "The data suggest that induction of anesthesia is safe and surgery does not need to be delayed if a patient arrives in the OR chewing sugarless gum."

Another randomized study showed that nonsmokers who chewed sugar-free gum preoperatively had significantly more fluid in their stomachs than a control group, p = 0.03. However, this looks like a statistically significant difference that is not clinically important because the volumes were a mean of 30 mL for the gum chewers vs. 19 mL for the controls. Also, the pH of the fluid was 2.2 for both groups. Compared to smokers who did not chew nicotine gum, smokers who did had similar volumes (about 30 mL) and pH's (1.7 vs. 1.5 respectively). Despite this flimsy evidence, the authors suggested that the increase in gastric fluid volume in the nonsmokers should mandate that patients not chew gum on the morning of surgery. They also discounted the fact that the nonsmoking gum chewers had gastric fluid volumes identical to those of smokers who did or did not chew nicotine gum.

A paper from Yale in 2006 looked at children randomized to no gum, sugar-free gum or sugared gum. The non-chewers had significantly lower gastric fluid volumes than either chewing group ( p = 0.0001), and lower pH's (all groups below 2.25, p= 0.007). The median fluid volumes for a 40 kg (88 lb) child would have been 14 mL for non-chewers vs. 35 mL for the sugared group. They concluded that the clinical significance of the findings was "unclear," and that no specific recommendations could be made about whether to delay a case.

A long-overdue revision of the American Society of Anesthesiologists' 1999 Preoperative Fasting Guidelines appeared in 2011. The words "chewing gum" and "hard candy" do not appear anywhere.

Yet if you google "hard candy and anesthesia" you will find that nearly every hospital's preoperative instructions say not to chew gum or use hard candy or in fact eat or drink anything after midnight before a procedure. In addition to the total lack of evidence than gum or candy causes any problems, they all disregard the new guidelines which state that patients can have clear liquids up until 2 hours before surgery and solid food in the form of a "light meal" until 6 hours before surgery.

Not only are most hospitals' preop fasting policies wrong, it turns out that giving patients oral carbohydrates up to 2 hours before surgery does not increase gastric fluid volume or pH and may be beneficial in preventing energy deficits in the postoperative period.

I've heard that it takes something like 10 to 20 years to change just about anything we do in medicine.

Let's hope this one doesn't take so long.


Chris Porter MD said...

I had the same conversation (and found the same recs) when an inpatient chole patient was served coffee just before surgery. Because the patient took his coffee with cream, we waited six non-evidence-based hours.

Skeptical Scalpel said...

Yes, those 5-10 mL of cream can cause a lot of problems, can't they?

Clark Venable said...

I think part of the problem is that aspiration is a rare event and to show that changing fasting guidelines is safe would require a huge study to get sufficient power. The other problem is that if we proceed and the patient aspirates, plaintifs' council would easily be able to claim we breached the accepted standard of care--and I doubt a jury would be swayed by the lack of evidence for waiting after hard candy.

Skeptical Scalpel said...

Clark, thanks for commenting and being a long-time follower. The problem is that the standard of care needs to change. Otherwise, progress will never be made. The standard of care could be set by the American Society of Anesthesiologists if they had a pair.

artiger said...

Scalpel, that may be true about our Anesthesia colleagues, but I don't see a lot of the other specialty societies making bold moves either. And let's not even get started on the surgical boards and societies being slow to change. Oops, looks like I just did.

Anonymous said...

(Anesthesiologist here - in practice since 1980).

The problem is the fact that any good studies to support loosening the NPO guidelines are few and far between. Should you have a problem, despite the "innocent until..." "rule," the burden is upon YOU to prove that you didn't violate the standard of care. And you know as well as I do that there's going to be an expert who says that you did - and he'll have the "science" to support him.

A colleague of mine had a patient with a hiatal hernia aspirate on induction. She went on to die of that complication. There are several studies indicating that applying cricoid pressure is of no use (and may be of harm - it's frequently more difficult to intubate with CP). Nevertheless he was held to the "standard" and went on to settle the resultant lawsuit.

Yeah, the science might be there for some, but the standard lags. Until the standard changes, I'll be sufficiently paranoid. Thankyouverymuch.

BTW, love the blog. You're a curmudgeon that I'd be proud to consider a colleague.

Anonymous said...

I agree that the "standards" for pre-op fasting and routines are minimal, and even the 6-hour criterium for full meals has no science behind it.

But surely, a piece of hard candy an hour pre-op? Or black coffee 4 hours before? There are no standards for either, just use of common sense. In fact, in most practices I have encountered as a locums, almost all anesthesiologists would proceed in these scenarios.

There are still anesthesiologists who routinely give Reglan/Pepcid to all elective patients, despite zero evidence for benefit and in fact recommendation against it by their own professional association.

It is not just anesthesiology; it is all specialties. The older guys say that whatever the standards are, in their experience....blah, blah, blah. Even the younger practitioners, presumably versed in EBM, do things just because. For a supposedly science-based discipline, day-to-day medical practice is remarkably non-scientific.

Skeptical Scalpel said...

First anon, thanks for the comment and the kind words about the blog. I agree that the "standard of care" (by the way, as defined by lawyers) is the real problem. It has nothing to do with EBM.

Second anon, thanks. I've found that when common sense bumps into the standard of care, common sense loses. And it is the same in all specialties.

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