Review question/objective

The objective of this systematic review is to synthesize the best available evidence comparing forced air warming devices to other active warming devices to determine whether or not there is an increased risk of surgical site contamination by microbial emissions during the perioperative period.

Specifically the review question is: Do forced air warming devices compared to other active warming devices have an increased risk of surgical site contamination during the perioperative period?

Background

Perioperative hypothermia is a common issue that is experienced by patients during the operative period. On average, a patient's core body temperature drops over the course of the intraoperative period between 1[degrees]C and 3[degrees]C.1 Multiple factors contribute to patient heat loss in the operating room, (OR) including room temperature, degree of cutaneous exposure, the planned procedure, the opening of large body cavities and cold intravenous fluids. The largest amount of heat loss occurs within the first hour of anesthesia with a 1 to 1.5[degrees]C drop in core temperature.2 Anesthesia-specific factors that contribute to the internal redistribution of body heat are proportional to the core to periphery internal heat gradient. The gradient is affected by elements such as the OR temperature, the patient's body composition of adipose tissue, the use of volatile agents, intravenous induction agents and neuraxiial anesthesia.2 The use of anesthesia itself attenuates the patient's thermoregulation capabilities, allowing the opening of arterio-venous shunts and impairing the vasoconstriction threshold of blood vessels.2 In neuraxial anesthesia, heat redistribution results from peripheral versus central inhibition; however, the lower extremity mass is adequate enough to contribute to core hypothermia.2 Overall, the major mechanisms of heat loss during the perioperative period is through the skin surface via radiation and convection, and to a much lesser degree through evaporation and conduction.

Hypothermia is defined as body temperature less than 36[degrees]C and is associated with many complications that can compromise the patient. The consequences of perioperative hypothermia are significant and include shivering, myocardial events, coagulopathies, wound infections, delayed healing, and the deferment of patient discharge from the post anesthesia care unit (PACU).2 In addition, important enzymatic processes operate in a specific temperature range and any slight increase or decrease of body temperature can lead to inadvertent change in the pharmacokinetics and pharmacodynamics of drugs and anesthetic agents used during the induction and intraoperative period.2

Normothermia during surgery is an important factor in minimizing the risk of surgical site infections.3 The vasoconstriction that accompanies hypothermia causes a decrease in the partial pressure of oxygen at the tissue level. An oxygen deficit decreases the body's ability to utilize oxidative processes such as bactericidal activity of neutrophils. Surgical site infections remain the most common hospital associated infection despite infection control efforts such as the Surgical Cite Improvement Project (SCIP).4,5 Other measures, such as controlling the OR environment itself, are taken to decrease the risk of infection perioperatively. Laminar airflow is utilized for proper ventilation of the OR. As opposed to turbulent airflow over the surgical site, laminar airflow decreases the amount of microbial particulates in the operating field, thus decreasing surgical site contamination.

The negative sequelae that perioperative hypothermia can cause reinforce the importance of maintaining the patient's temperature in the OR. It is a standard of anesthesia care to monitor patient temperature and to maintain patient normothermia unless specifically indicated otherwise.6 There are several options of warming strategies to prevent hypothermia within the intraoperative setting. The use of cotton and reflective blankets constitutes passive warming technique. Active warming has shown to be superior to passive warming at maintaining core body temperature during the critical hours of heat redistribution.7 Active warming technologies include forced air warming (FAW), blankets or mattresses that utilize water circulation or electric elements, radiating heat lamps, and warm infusions. Overall FAW has shown to be effective in maintaining core body temperatures when used during the preoperative and intraoperative period.8 This technology pulls in environmental air through a microbial filter. The air is heated and exits through a detachable hose.

During the most critical period of heat loss, a sterile operating field is prepared and the surgical site is exposed. There is concern that initiating the use of forced air warming before the patient is surgically prepped and draped can contribute to surgical site contamination. Forced air warming may disrupt laminar airflow causing an increase of microbial particulates at the site of surgical incision. The benefits of maintaining patient normothermia have been well established and FAW has been widely accepted as an effective technology.9 While it is difficult to quantify the cause of surgical site infections due to multiple variables, it is important to establish whether the use of FAW to prevent hypothermia is a contributing factor by contaminating the surgical site.

A systematic review concerning active warming and the effective management and prevention of patient hypothermia during the perioperative period has been conducted and published in the Joanna Briggs Institute International Journal of Evidence Based Healthcare.9 This review identifies that active warming is more effective than passive warming in preventing patient hypothermia but does not discuss the risk of surgical site contamination associated with active warming. There are multiple conflicting studies in the current literature that compare the microbial emissions of FAW to other active warming devices.10,11 Some authors find that FAW contributes to a significantly greater amount of microbial contamination while others find that there is no difference between the compared devices.10,11

The purpose of this systematic review is to identify the best available literature that compares the microbial emissions of other active warming devices to FAW and determine if concerns of contamination merit the discontinuation of FAW for preventing hypothermia.

Inclusion criteria

Types of participants

This review will consider studies that include subjects (patients, volunteers, mannequins) of all ages that were warmed perioperatively in any type of surgery or simulated surgical environment.

Types of intervention(s)

This review will consider studies that compare only forced air warming devices to other active warming technologies such as a radiant warming blanket.

Types of outcomes

This review will consider studies that include the following outcome measures: particle counts or neutrally buoyant bubble counts, measured by: a laser particle count device or time-lapse photography.

Types of studies

This review will consider experimental designs including randomized controlled trials, non-randomized controlled trials, quasi-experimental, and prospective and retrospective cohort studies for inclusion to identify the best available evidence comparing forced air warming to other active warming devices on perioperative contamination risks.

Search strategy

The search strategy aims to find both published and unpublished studies. A three-step search strategy will be utilized in this review. An initial limited search of MEDLINE and CINAHL will be undertaken followed by an analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. A second search using all identified keywords and index terms will then be undertaken across all included databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies. Studies published in the English language will be considered for inclusion in this review. Studies published between January 1987 and February 2015 will be considered for inclusion. January 1987 is the earliest date for search because the technology was not utilized clinically prior to this date.12

The databases to be searched include:

MEDLINE

CINAHL

EMBASE

Nursing at Ovid Joanna Briggs Institute

Cochrane Central Register of Clinical Trials

Clinical Key

Web of Science

The search for unpublished studies will include:

Google Scholar

Index to Theses

New York Academy of Medicine Grey Literature Report

MEDNAR

ProQuest database for theses and dissertations

Initial keywords to be used will be:

Forced air warming AND operating room AND contamination OR infection

Assessment of methodological quality

Papers selected for retrieval will be assessed by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) (Appendix I). Any disagreements that arise between the reviewers will be resolved through discussion, or with a third reviewer.

Data extraction

Quantitative data will be extracted from papers included in the review by two independent reviewers using the standardized data extraction tool from JBI-MAStARI (Appendix II). The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. If raw data from an included study is not reported the authors of the primary studies will be contacted to see their assistance in providing clarification or missing data.

Data synthesis

Quantitative data will, where possible, be pooled in statistical meta-analysis using JBI-MAStARI. All results will be subject to double data entry. Effect sizes expressed as odds ratio (for categorical data) and weighted mean differences (for continuous data) and their 95% confidence intervals will be calculated for analysis. Heterogeneity will be assessed statistically using the standard Chi-square and also explored using subgroup analyses based on the different study designs included in this review. Where statistical pooling is not possible the findings will be presented in narrative form including tables and figures to aid in data presentation where appropriate.

Conflicts of interest

The authors have no conflict of interest to declare.

References