H. pylori, Peptic Ulcer Disease, Bayes' Theorem, and treatment thresholds

I was slightly surprised today to read the authors' discussion in the Clinical Crossroads in JAMA (December 7th issue; original case November 1st issue - when the reader responses are published, there may be even more to say about this topic).  I was more thoroughly surprised when I cross-referenced UpToDate and the references that both used to defend the suspect practice.  Apparently Bayes' Theorem does not apply to H. pylori (HP), and neither does the concept of treatment thresholds.  Time to apply some uncommon sense.

At issue is whether a patient with peptic ulcer disease (PUD) should receive empiric treatment for HP, or whether "confirmatory" testing is indicated.  Early estimates suggested that 95% of patients with PUD will have HP (I recall that figure from the 13th edition of Harrison's Principles of Internal Medicine, now in it's 18th edition), but three epidemiological studies in the 1990s challenged this estimate as too high, with new estimates of 73% (study n=2394), 61% (study n=144), and 36% (studied n=95).  The binomial confidence intervals (CIs) for those numbers are 71-75%, 53-69%, and 26-45%.  The first study, with an estimate of 73% and n=2394 is actually a summary statistic derived from a combination of six other studies.  So, which estimate do we choose?  We could do a meta-analysis and combine all of these studies, but we already know what the result will be becasue the first study will trounce the others when weights are assigned.  So I'm going to just conclude that while the prevalence of HP in PUD might not be 95%, it is likely close to 73%.

This is important because you have to decide what threshold of probability you will use to trigger treatment of HP.  If that threshold is 75%, well then you might as well just treat everybody with PUD because the prior probability is so close to your treatment threshold.  One of four of the patients you treat will have been treated "unnecessarily", on average.  If that threshold is too low, then you need to raise it with testing.  But, testing is not without its own set of pitfalls, and the gains in reducing  false positives may be much less than you think.

When Care is NOT Worth it Even if the End is Life

Oh dear.  I'm a fan of Dr. Peter Bach.  We trained under some of the same mentors.  But....

In this article When Care Is Worth It, Even if End Is Death, he makes so many logical errors in thinking that I just can't let it pass tightlipped.

He describes the case of a middle aged man whom he cared for some 20 years ago who presented to the ER in extremis (about to die) from what turned out to be mesenteric ischemia (some of the bowel is dying for lack of blood flow.)  His supervisor mused that the man was hours from death.  After surgical treatment and a two week ICU stay, the patient walked out of the hospital alive, and Dr. Bach uses the case to attempt to illustrate the point that treating patients near death is not a waste of time, effort, and money.  Allow me to summarize the many errors in his logic.

Protection via Violation: A Sheriff Joe Arpaio approach to the Airway

Left: Posterior arytenoid web developed after a 40 minute intubation
Right: After endoscopic laser therapy

The subject of overdoses segues me to another topic of interest to the skeptical observer in the emergency department (ED) and intensive care unit (ICU).  Patients with alcohol intoxication, drug overdose, and various other maladies that cause decreased level of consciousness (LOC) are often intubated (a breathing tube inserted through the vocal cords and into the trachea [airway]) so as to "protect the airway".  Under normal conditions, there are powerful reflexes in the oropharynx, larynx, and trachea that cause you to gag and cough to keep everything but air out of the airway to prevent the development of an obstruction or pneumonia.  Because of this, powerful sedatives and often paralytic medications have to be given to a person to enable the insertion of the tube - otherwise it will be violently rejected by these reflexes.  Various conditions, chief among them drug and medication effects but including even normal sleep, can cause a depression of the intensity of these reflexes, which often arouses concern that patients with decreased LOC will aspirate (get liquid or solid material in the form of saliva, mucous, food, etc. into the airway).  By intubating such patients with a tube that effectively seals off the airway (by means of a balloon that is inflated at the end of the tube), it is thought that the airway is thusly "protected".

Why the Rumack-Matthew nomogram is a dangerous distraction

When a known or suspected overdose (OD) comes to the emergency department (ED), levels of several commonly ingested agents such as aspirin and tylenol are checked.  If the history or laboratory results suggest acetaminophen (APAP) overdose, the "standard of care" (if there is one - see:  Heard APAP OD review in NEJM, 2008) is to investigate the time of the ingestion and refer to the Rumack-Matthew nomogram (RMN) to determine whether toxicity is likely and to initiate a course of n-acetylcysteine (NAC) if the level is above the line on the nomogram.

Now there are several problems with the RMN that I will not fully delve into here. Suffice it to say that the RMN came from a review of a (striking!) 30 cases in a 1975 paper in Pediatrics.  The nomogram was extrapolated from this case review.  And while I'm no pediatrician, I suspect that pediatric poisionings are quite different from adult ones.  In any case, when the timing of ingestion is accurate the RMN has been a useful guide for ED physicians to determine who could be safely sent home and who would need to be admitted for treatment for APAP poisioning.