Can patients shower immediately after surgery

Here’s what a recent paper published ahead of print in Annals of Surgery says:

Between May 2013 and March 2014, 222 patients were randomized to the group allowed remove their dressings and shower at 48 hours and 222 to the group permitted to shower only after the original dressing and the sutures were removed in clinic. There were 4 (1.8%) superficial surgical site infections in the early shower group and 6 (2.7%) in the late shower group, an insignificant difference with p = 0.751.

The authors concluded that clean and clean-contaminated wounds can be safely showered 48 hours after surgery, and early postoperative showering may increase patient satisfaction.

I have always been an advocate of early showering after surgery. Wounds properly closed will be bridged by epithelium within 48 hours. Tap water is relatively sterile or we couldnt drink it. Many studies have shown that even irrigating open wounds with tap water instead of sterile saline does not lead to more infections. [Links here and here.]

Much as I would like to believe the Annals study, I can’t because it is probably underpowered to show a difference between the two groups.

Here is a nice definition of statistical power from a website called effectsizeFAQ.com:

“In plain English, statistical power is the likelihood that a study will detect an effect when there is an effect there to be detected. If statistical power is high, the probability of making a Type II error, or concluding there is no effect when, in fact, there is one, goes down.”

To their credit, the authors did try to estimate the sample sizes they would need by doing a power calculation. They knew that the wound infection rate for the cases they intended to enroll was about 1%. The problem is they estimated that showering at 48 hours would result in a wound infection rate of 5%. That seems very high to me for the types of cases included in their investigation—thyroid, lung, inguinal hernia and skin tumors.

If they had hypothesized that early showering would merely triple the rate of wound infections from 1% to 3%, they would have needed at least 1536 patients in each arm of the study. Then if there was no difference, one could conclude that early showering truly does not cause more wound infections.

Even if the known incidence of wound infection was much larger, say 5%, and the rate of infection with showering was presumed to be doubled (10%), to have enough power a study would need 434 patients in each arm.

Many websites provide calculators for determining the appropriate sample sizes to detect with a reasonable degree of certainty whether one intervention is better than another. Anyone thinking about doing a prospective randomized trial should realistically estimate the expected difference and calculate the power.

Whenever you read a negative study, the first question to ask is, “Was the study adequately powered to avoid a type II error?”

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Patients can chew gum immediately before surgery I guess

A study presented at the American Society of Anesthesiologists (ASA) meeting in October of this year found that patients who chew gum in the immediate preoperative period may safely undergo surgery.

The authors, based at the University of Pennsylvania, found that gum chewing increases saliva production and the volume of fluid in the stomach, but stomach acidity was equivalent to that of non-gum chewers. An article about the study said The mean gastric volume, or total amount of liquid in the stomach, was statistically higher in patients who chewed gum before their procedure (13ml) versus those who did not (6ml). A 7 mL difference might be statistically significant, but surely is not clinically important.

The research differed from previous studies because it involved patients who underwent upper gastrointestinal endoscopy, which enabled the investigators to recover all of the fluid in the stomach for testing. Prior studies had been done using nasogastric tubes, and it was impossible to determine whether all gastric fluid was recovered when the tubes were suctioned.

The study involved 34 gum chewers who were allowed to chew any type or any amount of gum compared to 33 patients who did not chew gum.

Another article quoted its lead author.

"We found that although chewing gum before surgery increases the production of saliva and therefore the volume of stomach liquids, it does not affect the level of stomach acidity in a way that would elevate complication risks," explains Dr. Goudra.

He says patients shouldnt be encouraged to chew gum before procedures involving anesthesia, but the habit shouldnt necessitate the cancellation or delay of scheduled cases if other aspiration risk factors arent present.

There has been long-standing debate about the subject of whether using gum and hard candy should be treated the same as ingesting a regular meal.

I wrote about this on my blog back in January 2014 and pointed out that the ASA guidelines do not address the issue.

In an effort to do due diligence, I was able to locate the abstract of this paper on the ASA website. Im glad I did because the abstract came to the opposite conclusion.

When the abstract was submitted, it included fewer patients—24 who chewed gum and 23 who did not.

The average gastric volumes were 9.78 mL for the gum chewers and 24.08 mL for the non-gum chewers (p = 0.027), and pH values were not significantly different (p = 0.094). It looks like regression to the mean occurred as the number of subjects increased.

In the original abstract, the authors concluded the following: Chewing gum in the preoperative fasting period leads to significant increase in the residual gastric volumes, with no difference in pH. We recommend that patients who have inadvertently chewed gum in the fasting period should be treated as full stomach and management modified accordingly. [Emphasis added]

So what is going on here? This would not be the first time that an abstract differed from the final paper. Actually, this sort of thing happens quite frequently. However in this case, the conclusions of the two versions are diametrically opposed to each other.

The study was presented at a meeting. Lets see what happens when it is submitted to a journal for peer review.

The correct way to have done the study would have been to calculate the number of patients needed to be studied (power analysis) beforehand.

Since this was not done, I recommend we go with the conclusion of the larger number of patients studied because it agrees with my bias that chewing gum is not potentially harmful.

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More on activity restrictions after surgery

In early January, I blogged about the dearth of evidence about activity restrictions after surgery.

A number of people commented and most agreed that there is little basis for most of the activity restrictions surgeons currently use.

An anonymous reader told me about a 2008 study from Creighton University that generated some interesting data about intra-abdominal pressures associated with some common activities. Here’s a summary of the paper.

The authors managed to find 10 healthy volunteers all of whom could bench press at least 100 pounds and were willing to have nasogastric manometry catheters placed and Foley catheters inserted into their urinary bladders.

Intra-abdominal pressures were recorded as each subject coughed 10 times as hard as possible, bench pressed varying amounts of weight from 26 to 114 pounds, and vomited after receiving ipecac syrup and drinking about 500 mL of water.

Pressures in the stomach and bladder correlated fairly well. To keep things simple, let’s look at gastric pressures only.

The highest mean and maximum pressures were found during vomiting. Coughing produced similar pressures. Most interestingly, intragastric pressures during weightlifting were significantly lower with a mean of 2 mmHg and a maximum of 52 mmHg, p <0 .001.="" br="">The authors mentioned that another group had found similar intra-abdominal pressures with subjects bench pressing 25 pounds.

Another unexpected finding was that although the differences were not significant, the mean intragastric pressures were inversely proportional to the amount of weight lifted.

Maybe we should tell postoperative patients not lift less than 26 lbs.

The authors were focused on measuring pressures that would disrupt a gastric anastomosis. They calculated that an intragastric pressure of 290 mmHg generated by vomiting was about 1/50 of the 20N [Newton] force that would disrupt a gastric suture line in a porcine model as demonstrated by other investigators.

The effect of repetitive stress such as found in patients with a chronic cough were unknown, but they said “the intra-abdominal pressures generated in our study alone do not appear to be responsible for hernia formation.”

The Creighton study authors concluded, "The common postoperative lifting restriction, although logical, has little evidence to support it." They called for more research in this area.

Unfortunately, their call has not been answered.

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