Authors

1. Yancey, Christopher RRNA
2. Merrick, Kelsey RRNA

Abstract

Review question/objective: The overall objective of this review is to examine the effectiveness of high FiO₂ in the prevention of postoperative surgical site infections in adult patients undergoing abdominal surgery.

The specific review question is as follows:

What is the effectiveness of a FiO₂ of.80 in reducing the incidence of postoperative surgical site infections in adults undergoing abdominal surgery compared to a FiO₂ of.40 or less?

Background: Surgical site infections (SSIs) are frequent and serious complications of abdominal surgery. Infection rates following abdominal surgery range from 9% to greater than 20%.1,2 SSIs directly contribute to longer hospital stays, rising healthcare costs and increased morbidity and mortality.1 Data from the United States (US) suggest that SSIs contribute to an increase in length of hospital stay of 9.7 days and an increase in cost of $20,842 (USD) per admission. This translates nationally to one million additional inpatient days and approximately 1.6 billion USD in excess costs.3 A 2004 review of the literature found that SSIs in European countries contributed to excess costs between [Euro sign]1.47 and [Euro sign]19.1 billion.4 The International Nosocomial Infection Control Consortium (INICC) monitored SSIs from 2005 to 2010 in 82 hospitals, across 66 cities in 30 countries and found SSIs occurred in 7,523 patients out of 260,973 surgical procedures; an incidence of 2.9%.5 Therefore, interventions that aim to reduce the incidence of SSIs are of paramount importance for patients and hospitals.2 Despite the fact that an SSI may not be diagnosed for days or weeks after surgery, a wound infection is most likely established in the first several hours after bacterial contamination of the tissue.1 Thus, perioperative interventions that aim to prevent SSIs, such as increased concentrations of supplemental oxygen, can have a direct influence on the occurrence of an SSI.1

Supplemental oxygen is a cost-effective means of preventing an SSI.6 While the cost of treating a postoperative surgical site infection can add thousands of dollars to a single patient's health care costs,3 a quality oxygen concentrator costs between US$600 and US$1,200 per unit.6 As shared medical equipment, oxygen concentrators tend to last for many years and require minimal service, maintenance and cleaning.6 Multiple patients can receive oxygen from a single concentrator with the use of flow dividing equipment and disposable, single use tubing for each patient.6 The number of concentrators needed for one hospital varies based on the number of patients, patient size and the oxygen requirements of each patient.6 Therefore, the implementation of cost-effective prophylactic measures aimed at preventing SSIs is crucial to reducing total health care costs, morbidity and mortality rates and length of hospital stay associated with SSIs and the accompanying costs of treatment.7

The Center for Disease Control and Prevention (CDC) defines an SSI as an infection that occurs after surgery in the part of the body where the surgery took place.8 The infection can take place superficially involving the skin only, or become more serious involving tissues, organs or implanted material. Symptoms of surgical site infection include fever and redness, pain and drainage around the surgical site.3 Hospitals take a number of different steps to prevent SSIs. These steps include washing hands up to the elbow with antiseptic agents, administering antibiotics before, during and after surgery and cleaning the skin at the surgery site with a special antiseptic soap.3 Surgical site infections can still occur, even with strict adherence to the preventive steps listed.

Recently, a number of studies have been conducted to determine non-traditional interventions that can be implemented to prevent SSIs. In particular, researchers have developed increased interest in the topic of hyperoxia, or increased oxygen exposure and its potential benefits as a simple and cost-effective measure in preventing SSIs.2 Anesthesiologists typically administer supplemental oxygen to maintain normal oxygen saturations during the perioperative period.2 Oxygen is required by numerous physiological functions that must take place for adequate wound healing, including the prevention of infection.9 In addition, oxygen tension in tissue is a known risk factor that affects SSI rates.2 A physiological defense mechanism against pathogens is oxidative killing, which facilitates the anti-microbial functions of neutrophils.1 Neutrophils are a type of white blood cell that is essential to the body's immune system. Therefore, increased oxygen tension in tissues contributes to the body's ability to resist infections. By simply increasing arterial oxygen tension levels above normal saturation levels, an anesthesiologist can potentially improve the body's ability to resist infections.1

Abdominal surgical procedures are among the most common surgical procedures performed in the US and can be performed by making small incisions (laparoscopic) or by a larger incision (laparotomy).10 Several examples of abdominal surgical procedures include appendectomy, cholecystectomy, bowel resection, exploratory surgery, tumor resection and cesarean section.

Research has been focused on the use of hyperoxygenation to prevent surgical site infections in patients undergoing abdominal surgery. Due to the large population undergoing abdominal surgery, a systematic review is pertinent to synthesize the current evidence, in order to determine whether hyperoxygenation is effective or not.

Despite the current evidence on the positive effects of hyperoxygenation on preventing SSIs, there are still many unanswered questions for which current research has not provided an answer. While oxygen does help to support the body's innate immune response, reactive oxygen species can also be involved in processes that have contrasting outcomes.2 These processes can produce tissue and cell injury and they may ultimately hinder the body's innate ability to destroy bacteria.2 Researchers currently theorize that the advantageous effects of hyperoxygenation are multi-factorial; it is likely that a combination of healthcare interventions, the microenvironment and individual systemic factors innate to each patient results in the positive effects of hyperoxygenation.2 Therefore, it remains debatable whether hyperoxygenation is advantageous or detrimental to this patient population.2

There are many additional elements of anesthetic management during the surgical (perioperative) period that can affect tissue oxygen tensions and thus bacterial killing and infection rates.2 For example, administration of intravenous fluids has been described as increasing tissue oxygen tensions, but the significance of this intervention is unknown.2 Most studies to date have been limited in their ability to detect the effects of other anesthetic interventions and their effect on SSI rates.2

Several studies have investigated the effect of high supplemental oxygen levels, or an FiO₂ of 0.8 or greater, on SSI rates in patients undergoing abdominal surgery, with conflicting results.1,2,7 The large number of abdominal surgery cases performed each year and the sequelae associated with a postoperative SSI, helps to illustrate the need for additional research on this topic and the completion of a systematic review (SR). If the results of this SR show that hyperoxygenation is effective in reducing SSI rates, both hospitals and patients will reap the benefits of shorter hospital stays and reduced healthcare costs. Therefore, this SR is of supreme importance in today's health care crisis.