Surgical Infection in the Age of Minimally-Invasive Surgery

Today marks about 4 years since Prescient Surgical was founded, conveniently marked by the company’s incorporation in the fine state of Delaware. After a full year of exploring various unmet needs in hyperkalemia to Raynaud’s phenomenon as Innovation Fellows in the Stanford Biodesign program, the founding team began to rally around what we called “The SSI Project.” With strong support from the surgical community at Stanford and beyond, and under full sail with the trade winds of public reporting and fines implemented with the Affordable Care Act, it was clear we were chasing down a critical unsolved problem in surgery that required immediate attention.

Naturally, I remain convinced of that fact today, and am thrilled by the progress we’ve made as a company and community towards reducing surgical site infection. Yet from the moment we began this journey, the requisite gauntlet of venture capitalists, health systems, BigCo’s, and physician interaction have buffeted us with a recurring, unseemly paradox that I’d like to address here—mainly, that the evolution of minimally invasive surgical techniques (predominantly laparoscopic surgery) has all but eliminated SSI.

Well…so why do we still see so many infections? Is it because laparoscopic / MIS techniques are in fact a panacea, but have not yet been fully adopted? Probably not, and for the past 5 years at ASCRS we’ve seen laparoscopic adoption in colorectal surgery stagnate at around 30-40%, even as the video game generation enters its prime. Laparoscopic techniques simply aren’t or can’t be used in the majority of some of the most complex surgeries.

In my position I am privileged with access to some of the world’s greatest minds in surgery, and I’m hearing a consistent belief that the next decade of surgical development will be about OR safety, not necessarily OR “MIS-ness.” One prominent single-port laparoscopic surgeon put it this way—“The impact in cholecystectomy was enormous, but when you look at more complex procedures like colectomy, you are taking out a colon, you are extracorporealizing a contaminated specimen. It’s fundamentally invasive, and within that big-picture context, MIS techniques offer real, but comparatively diminished benefits.” He advocates MIS “right-sizing,” that is mitigating patient risk in ways that might include laparoscopy when appropriate as opposed to the uncompromising pursuit of a near-incisionless nirvana. I was surprised to hear this from a surgeon that could perform a single-port colectomy wth one hand tied behind his back! It’s all about striking a balance between the risk and global invasiveness of each surgery with the each surgeon’s ability to perform it effectively and efficiently.

Is it because there are large financial interests that would like you to believe that the increased costs of laparoscopic surgery are justified by unilateral improvements in surgical care? Perhaps. I would never question the net benefit of laparoscopic approaches, but particularly when it comes to SSI, the data are mixed, and high SSI rates persist.

Consider Covidien / Medtronic’s clinical dossier summarizing the benefits of laparoscopic approaches in colorectal surgery (http://www.medtronic.com/content/dam/covidien/library/us/en/clinical-procedural-therapy/colorectal/colorectal-global-value-dossier.pdf):

“Surgical Site Infection: Rates of surgical site infection are consistently lower (often significantly) with laparoscopic colorectal surgery than open colorectal Surgery.”

Covidien data

By “often significantly,” Medtronic means that studies do not always show this benefit with statistical significance, and at times have been associated with higher infection rates in colon surgery. Though the weight of evidence supports the notion that laparoscopic approaches reduce the risk of SSI, there are still infections in laparoscopic surgery (perhaps 4-17% based on the data presented by Medtronic, though the most recent studies, and NSQIP rates at high-volume laparoscopic centers would suggest rates of 7-12%, and prospective studies generally find rates of 15-20%+). We shouldn’t be surprised either. However small, the resulting incisions are still prone to intraoperative contamination and reduced immunological activity. Even with laparoscopic approaches, a comprehensive wound care plan is warranted.

Gloves, Colon Surgery, and…Parachutes

Editor’s Comment: I’d like to welcome back Dr. Goldfarb for another guest post, this time to discuss the importance of glove changes in relation to preventing wound contamination.

When I was training in General Surgery, from 1967-1972, the every other night on call rotation was not the most rigorous part of the ordeal of training. The harder part was the daily routine working under strict surgeons who themselves were not even allowed to get married during their training. The Chief of Surgery was a meticulous surgeon who demanded total silence during surgery and total focus on the part of all participants. Other than opening and closing the abdomen, he performed all of the surgery on his private patients. The residents were responsible for the clinic and/or non-private patients. But the “eyes and spies” of the Chief of Surgery were everywhere, and if a resident skipped steps during an operation, it was expected that an OR nurse would report that misdemeanor to the Chief.  And you might be told to “Go home,” if you omitted any of these critical steps, if you omitted any steps.

One of the steps that became tattooed on my mind was the frequent glove changes during surgery, a critical step in preventing bacterial contamination of the surgical wound.  The glove changes during open bowel surgery would occur automatically every one to two hours. We changed gloves even if they had not become shriveled at the fingertips or covered with blood or stool, or otherwise have any obvious holes. The nurse or often the senior surgeon would simply say, “Let’s change gloves.” Then, after the bowel surgery, we washed out the wound, usually with a bulb syringe of saline. Before closing, we ALWAYS changed gloves. If you began to close a wound after an intestinal operation and did not change gloves, you wouldn’t just “Go home,” but rather might “Burn in hell!” as a result of this transgression. Verbal abuse aside, you were very sternly reminded that you might be responsible for seeding a wound infection in the patient. And if you caused a deep wound infection, you guaranteed a long course of healing, with prolonged hospital stay and eventual incisional hernia.

There have been so many myths perpetrated throughout surgical history. Are frequent glove changes during colon surgery one of those myths? As a “type A” compulsive surgeon, I did not want to tempt fate and so I changed my gloves often and ALWAYS before closing a wound. An article, “Bacterial Migration Through Punctured Surgical Gloves Under Real Surgical Conditions,” Huber N et al., BMC Infectious Diseases, 2010;10:192, stressed that “unnoticed perforations of surgical gloves are not uncommon and that their frequency increases with duration of wear. Suggested preventative measures to lower the risk of glove perforation include a change of gloves at least every 90 minutes, the use of double gloving, or the strengthening of common glove puncture sites.”

So maybe it was not a myth regarding the undetected glove punctures and contamination of wounds. But, beyond unnoticed perforations, I was also concerned with the direct contamination of the wound by gloves that had created a bowel anastomosis, just a little earlier in the operation.  How can a surgeon use the same gloves that touched stool to close a wound? In either case, touching a wound with a hole in the glove finger or touching a wound with stool from a bowel anastomosis could both cause wound infection.  Modern measures to decrease wound infection for colon surgery, ranging from type of bowel preparation to type of wound preparation may all help decrease the high rate of wound infection. But perhaps simply not touching a wound with a hole in the glove or not touching a wound with stool on the glove are also significant, and too often ignored. You do not need a randomized double blind study to test the validity of a parachute.

In the News: Closing the Stable Door After the Horse has Bolted

Thanks to Google Alerts, I recently came across an article published by the folks at MedPage Today reporting on an algorithm developed by Dr. Cromwell at The University of Iowa  Hospital and Clinics touted to cut surgical site infections (SSI) by 58%. Results of that magnitude certainly pique my interest, so I did some internet sleuthing to learn more, and eventually came across a more thorough review on the WSJ CIO Blog and an unpublished manuscript describing their approach.

Although predictive analytics for surgical site infection isn’t in itself novel (NSQIP developed a patient risk assessment tool, for example), the novelty of Cromwell’s approach seems to be rooted in the strength of their data analytics and committment to incorporate detailed intraoperative factors into the assessment.

From the WSJ post:

“During surgery, as the surgeon closes up the patient’s abdomen, the circulating nurse logs onto a Web portal for the software and enters real-time data such as patient blood loss during the operation, the wound classification and whether it was contaminated, said Dr. Cromwell.”

The theory is that if caregivers are armed with this information before patients leave the operating room, doctors can create a plan to reduce the subsequent risk of infection by “altering medication or using different techniques in treating the wound.” The reader is left to wonder what those medications or techniques might be, especially when the physiology of wound healing dictates that infection prevention strategies are severely impaired after the incision is closed due to fibrosis and encapsulation of infectious material (Surgical Infections, March 2013).

Regardless, I think Cromwell is on to something here, because the events of operation itself represent the best opportunity to reduce risk. But assessing these predictive variables at closure is a bit like closing the stable door after the horse has bolted. A better approach would be to make sure the stable door is closed to begin with.

As an illustrative example, consider the Cromwell’s results: factors associated with increased risk of infection include certain patient zip codes, ostomy creation, higher wound class (i.e. wound contamination), higher ASA score, higher total # of procedures (per patient), surgical apgar score, and open procedural approach. We highlighted the importance of wound contamination in an earlier post, and would further maintain that of these factors, wound class (i.e. wound contamination) is the only one under direct control of the surgeon. So why aren’t we doing more to prevent wound contamination? We could start by directing powerful analytical tools like those developed by Cromwell towards the operative field.

Is Surgical Site Infection a Unifactorial Problem?

A quick look at the search term “surgical site infection” on Google Trends reveals that has trended positively relative to the Health category  over the past decade. And no doubt a large proportion of the search results have used the term “multifactorial” to describe the problem (see below; blue line = “surgical site infection;” black line = Health category).

Google Trends time ssi

But is SSI really a multifactorial problem? In an era of unfettered access to data, we risk measuring the impact of too many variables–jeopardizing the core assumption of independence central to the statistical techniques employed to analyze the data.  As a result of this “data fatigue,” over-fitting and information gain are real concerns. Furthermore, this data rich environment can make us lazy–after all, why bother collecting your own data if others have already curated a ton of it for your consumption?

What if this focus on collecting more data distracted us from collecting the right data? When we started exploring surgical site infection as Fellows in the Stanford Biodesign Program, we were immediately drawn to the link between wound contamination and SSI. Nothing new here–we recognized that this was well-established in the literature over the years, quantitatively by bacterial concentration risk thresholds of 10^4 CFU/g  (Krizek, 1975), and qualitatively through use of the NRC Wound Classification. But nonetheless, we we struck by the flood of results over the years demonstrating a strong, consistent link between the perceived (“subjective”) degree of wound contamination and the observed SSI rate.

wound class

Alas, the NRC Wound Classification is a bit too subjective and categorical for detailed risk model development, so we dug deeper. A few researchers (Fa-Si-Oen, 2005, Horiuchi, 2010, and Waldron, 1983) went as far as to measure the presence (and sometimes degree) of bacterial contamination present at the wound edge at the time of closure. The result of these studies are pooled and summarized below.

contamination graph

The implications are sobering:

  • 50% of abdominal wounds are contaminated during surgery
  • 20-33% of contaminated wounds result in infection
  • Remarkably, when there was no bacterial contamination present, there is correspondingly no risk of subsequent infection. Perhaps SSI is indeed a unifactorial problem!

Around the same time, the results of the CHIR-Net study were published, representing one of the most comprehensive studies evaluating the effect of wound protection devices on SSI rates. Might bacteriology results be predictive of these SSI results? Fortunately, a study by Mohan et al in 2012 evaluated the rate of bacterial contamination in a similar patient population on the exposed and protected surfaces of the wound protection device. As illustrated below, Mohan’s contamination rates, in view of the contamination studies mentioned above, effectively predicted the results of the CHIR-Net study.

alexis back calculated

To be entirely fair, post-hoc analyses like this can be subject to bias, but the results are highly suggestive, and certainly worthy of follow-up consideration and research. To that end, Prescient Surgical is currently sponsoring one of the most comprehensive studies of wound bacteriology to date, and we look forward to learning how the results expand our scientific knowledge in this arena. I look forward to updating this community with the results this summer.