Wednesday, September 19, 2018

“Number of medical students pursuing surgery specialty drops by half”

That was the headline in a September 10 Becker’s ACS Review article. The first sentence of the piece was more specific, “Only 4 percent of medical students surveyed in 2018 said their chosen medical specialty is general surgery, compared with 8 percent in 2016, according to Medscape's Medical Student Life & Education Report 2018.”

This caused some consternation among general surgeons on Twitter. I tweeted, “Interesting. Lifestyle is finally catching up to us. I think it will get worse.”

Thursday, September 6, 2018

How to interpret the literature: A new series of posts

The Salty Statistician will be a recurring feature of this blog wherein we ask statisticians in medicine to break down articles from the surgery literature and assess whether the reported conclusions are supported by the data. Let’s look at this study:

Groh MA et al. Is Surgical Intervention the Optimal Therapy for the Treatment of Aortic Valve Stenosis for Patients With Intermediate Society of Thoracic Surgeons Risk Score? Annals of Thoracic Surgery.

The authors attempted to address the question of whether aortic stenosis patients deemed “intermediate risk” [IR] for surgical aortic valve replacement [AVR] are best treated with open surgery or transcatheter AVR. The authors looked at 1,144 patients who received surgical AVR from 2008-2014 at a single center focusing on the 620 “intermediate risk” patients. At the end of the follow-up period, 72 had died.

Unfortunately, major methodological issues undermine the paper’s conclusions. Fortunately, this provides an excellent teaching opportunity.

First, the authors inappropriately used logistic regression to analyze independent predictors of mortality. Logistic regression treats the outcome as a simple “Yes” or “No” variable, while ignoring the time-at-risk. This study included patients treated over a six-year period (2008-2014) who therefore have substantial differences in the amount of time at risk. Consider the following hypothetical patients.

Patient A treated in 2008 and died in 2014 surviving six years after surgery. The logistic regression model simply counts patient A as “dead.”

Patient B treated in 2014 and alive in 2017 but dies in 2018, after the data were analyzed and the paper published. He survived four years after surgery and in the logistic regression model, counts as “alive” since data were analyzed in 2017.

Patient A lived for six years after surgery, but counts as “worse” in the analysis than Patient B who only lived for four years because of the time at which the data were “frozen” and analyzed. Of course, this is unavoidable in long-term outcomes studies, but one must choose an appropriate statistical method that accounts for time-at-risk.

Cox proportional-hazards models are more appropriate for a long-term survival outcome than logistic regression. When building a Cox model, one specifies both the current status (i.e., alive/dead) as well as an amount of follow-up time. For example, Patient A is “dead” with six years of follow-up; Patient B is “alive” but with only three years of follow-up. This provides a proper assessment of how strongly the independent variables are associated with risk of mortality while accounting for the unequal follow-up time.

Second, the authors state their data supports the conclusion that “SAVR is the optimal therapy for most of the patients” in the IR group in comparison to TAVR. However, their paper lacks any data on outcomes in IR patients who were treated with TAVR. Why the authors believe presenting data from a series of SAVR patients is sufficient to claim that SAVR is the “optimal therapy” absent any comparison data on patients treated with TAVR is unclear. Randomized controlled trials have more appropriately compared SAVR and TAVR in the IR population. Link here and here.

Which patients should receive surgical AVR versus transcatheter AVR is a good question, but to answer it, the paper used an incorrect approach.

Final Rating (1-5 Scalpels): 1 Scalpel - significant methodological issues

This issue of the Salty Statistician was written by Andrew Althouse (@ADAlthousePhD), currently an Assistant Professor of Medicine at the University of Pittsburgh as well as Statistical Editor of Circulation: Cardiovascular Interventions.

We intend this series to focus on work that is perceived to have a high impact on clinical practice, so we welcome reader suggestions. If you have a paper that you would like to see reviewed as part of the Salty Statistician series, please tweet @Skepticscalpel or @ADAlthousePhD or email We cannot promise that all submissions will be reviewed in this space, but we will do our best.

Thursday, August 23, 2018

A perforated colon case report raises a few issues

When a medical paper is featured on the Daily Mail website, you know it’s going to be something odd.

An autistic young man with prior hospitalizations for chronic constipation and megacolon was admitted to a hospital in London, UK with a markedly distended abdomen. A CT scan showed a dilated rectum and colon with a diameter as large as 18 cm (7 inches).

He was treated conservatively for two days with laxatives. Enemas were ordered, but the patient declined. He then developed peritonitis, kidney dysfunction, mental status changes, and metabolic acidosis.

Friday, August 17, 2018

Patient worries after accessing his chest x-ray report online

I received an email a few days ago. It has been edited for length and clarity.

I would like some advice please. I am a 46-year-old male with an off and on cough for 4-5 months. I have never smoked. After my primary care physician examined me, he ordered a chest x ray. A few days later I got a call from the doctor who said my x ray was normal. I was happy to hear that, but I am enrolled with My Chart which allows you to review your results online. Well, I read it and to me it doesn't sound what you would call totally normal, but I have no medical training so I could be wrong. I copied and pasted the report from the radiologist below. What concerns me is the "elevation" he refers to and using the word "fairly" clear lungs. Should I ask for another test or see another doctor for an opinion? If I was your family member would you suggest looking into this more?


FINDINGS: The frontal view demonstrates fairly clear lungs with slightly increased elevation of the left hemidiaphragm compared with the prior study. This may be at least partially caused by air in the adjacent bowel. No pleural effusion or pneumothorax is noted. The cardiomediastinal silhouette is unremarkable. The lateral view demonstrates fairly stable appearance of the lung bases compared with the previous study.

Monday, August 6, 2018

More proof medical error is not the third leading cause of death

Over the last 20 years, estimates of the number of deaths caused by medical error have risen from 44,000-98,000 in 1999 [1] all the way up to 440,000 [2] and 251,000 [3]. Despite my efforts [4, 5] and those of others [6, 7] to debunk these guesses, they continue to permeate the lay press. If you Google “third leading cause of death,” you will find countless headlines naming medical error.

The papers claiming medical errors cause so many deaths assume that all complications result from errors and all complications are preventable. They extrapolate their final numbers from small studies not designed to or capable of estimating deaths due to medical error nationwide.

The most recent figures available from the National Hospital Discharge Survey [8] state that the number of hospital deaths dropped from 776,000 in the year 2000 to 715,000 in 2010. It is simply not plausible that 251,000 (35%) or 440,000 (61%) inpatient deaths are due to medical error.

A recent study [9] from Norway found that of 1000 consecutive in-hospital deaths reviewed, only 42 (4.2%) were judged to be probably (greater than a 50% chance) to definitely avoidable.

Friday, July 13, 2018

Everything you ever wanted to know about operating room head coverings

In case you might want to challenge your hospital’s policy on the subject, I have gathered all of the recent research I could find on surgical head wear.

In response to a 2013 question from a reader, I blogged about the complete lack of evidence that OR staff hair caused wound infections or any other problem. After a similar question from another reader three years later, I pointed out nothing had changed.

Finally a 2017 paper in the journal Neurosurgery appeared online comparing the incidence of wound infections in clean cases for the 13 months before and the 13 months after the institution of a ban on the wearing of the traditional surgeons’ ca`p. Over 15,000 patients were included in the study which found no statistically significant difference in the rate of wound infections.

Monday, July 9, 2018

Are neckties dangerous to your health?

Wearing a necktie significantly decreases cerebral blood flow says a new study in the journal Neuroradiology. This finding caused a minor flurry of activity on Twitter, and as usual, the press sensationalized and misinterpreted the study’s results.

Here’s a headline from the Deccan Chronicle: “Wearing ties hamper [sic] productivity in office; here’s why.” The sub- heading is “Study suggests men who wear T-shirts in the office may produce better work.” T-shirts were not mentioned in the paper. The name of the journal that published it was incorrect in the article too.

Forbes didn’t do much better. It’s lede is “Neckties are stupid. Could they also make you stupid?” The paper said nothing of the kind.