More than one-third of Americans aged 20 years or older are classified as obese, defined as having a body mass index greater than 30 kg/m2, according to the Centers for Disease Control and Prevention. Moreover, many orthopaedic patients, especially arthroplasty patients, fall into this category.
Obesity is a known risk factor for postoperative infections after numerous orthopaedic procedures. Surgical times are often longer for patients who are obese, and hematoma/seroma formation leading to prolonged drainage is more common. Many of these patients are also at an increased risk of allogenic blood transfusion, an independent risk factor for periprosthetic joint infections, and poor wound healing.
The pathogenesis for postoperative infections in obese patients is multifactorial. Because the diet of obese patients is often devoid of essential nutrients, perioperative nutritional supplements, although counterintuitive on the surface, may be helpful in some cases. These patients should be advised not to try to lose weight during the healing process as this may lead to a catabolic state.
The subcutaneous layer in patients who are obese is often poorly vascularized and, as a result, they require a significantly greater fraction of inspired oxygen to reach an arterial oxygen tension of 150 mm Hg. Perioperative step-down monitoring, especially in patients with sleep apnea, is often necessary. Meticulous treatment of soft tissues and expedited surgeries by experienced surgeons should be considered whenever possible.
Although some authors have questioned the use of deep drains for the routine primary joint replacement, I actually supplement deep drains in obese patients with superficial channeled drains. The deep drains are always pulled within 24 hours; the channeled drain is often kept one day longer and “stripped” to encourage removal of excess fluid. Data collection is underway, but I find that this practice, along with multiple-layer closure, keeps wounds very dry in this difficult patient population.
One of the most important aspects of infection control in patients who are obese relates to antibiotic dosing. Although antibiotic pharmacokinetics in this patient population is less predictable, dosages should generally be proportional to the patient’s weight. For example, patients who weigh less than 80 kg should be given 1 g of cefazolin; patients who weigh 80 kg or more should be given 2 g. The recommended dose of clindamycin is between 600 mg and 900 mg.
The recommended dose of vancomycin in patients with normal renal function is 10 mg/kg to 15 mg/kg. Orthopaedic surgeons should pay particular attention to this slowly infused medication with respect to timing of administration relative to incision time and consider consulting with an infectious disease colleague to confirm dosages for patients who are morbidly obese.
The decision to perform surgery on patients who are obese should not be taken lightly. No surgeon wants to deny patients the opportunity to lead a pain-free life and most obese patients who undergo joint replacement surgery do very well. Although I always try to discuss bariatric surgery and nutritional counseling with patients who are obese, the reality is that most of them do not choose this option before surgery. For now, orthopaedic surgeons can only do their best to minimize the risk of surgical complications, such as infection, in this patient population.
Infection prevention—always be in the know!
Calin S. Moucha, MD, is an assistant professor of orthopaedics and associate chief of joint replacement surgery in the Peter and Leni May department of orthopaedic surgery at Mt. Sinai Hospital in New York City.