The most effective means (of cooling a man [woman]) is to give an anesthetic
Sir George Pickering (1958)1
The quality of the workplace environment, including stressors such as excessive noise,2 inadequate lighting,3 excessively cold or warm temperature,4 insufficient ventilation,58 and elevated humidity,5 can have profound effects on worker productivity and health. If inadequately controlled, environmental stress can impede work performance through a number of mechanisms, including increased tiredness and distractibility, and reduced worker well-being, motivation, and capacity to concentrate. Environmental stressors impact workers in an additive fashion, and the effect is cumulative.6
Similarly, an unhealthy work environment has been associated with a number of illness, including skeletomuscular,7,8 psychiatric,9,10 and cardiovascular illnesses.11 It has been estimated that the direct annual costs in the United States of poor indoor environmental quality are as great as $30 billion from disease and $160 billion from reduced worker productivity.12
Proper control of the environment is especially important in an operating room. The operating room is a unique workplace in which the stakes are extremely high and even small deviations in worker attention and productivity caused by occupational stress can have disastrous consequences. A common source of occupational stress in the operating room arises from different preferences concerning the temperature, ventilation (including drafts), and humidity. Typically, surgeons prefer a cool, dry climate to accommodate for the hats, masks, gloves, and gowns they wear and the fact that they work under bright, hot lights.13 Anesthesia personnel, on the other hand, are typically not as physically active or heavily clothed as surgeons and desire a warmer, less breezy climate.
The environmental requirements of the other occupant of the operating room, the patient, often come in conflict with those of the surgical staff. The patient usually is sparsely clothed, often with large areas of bare skin and internal tissues exposed, and frequently is rendered poikilothermic by anesthetic drugs. Patient comfort and safety demand a relatively warm, humid, and quiet environment.
Despite this wide spectrum of requirements, one size must fit all regarding the environment within the operating room. Decisions about the elements of the environment, especially temperature, ventilation, and noise (music) often are arbitrarily made by the first, or the most insistent, member of the surgical team to access the controls. This method is not necessarily, however, the safest or most efficient manner to make these determinations. The goal of this review is to examine some of the elements of the environment in the operating room and appreciate how manipulations can affect each of the occupants.
A computerized literature search was conducted during the period from January 2016 to April 2016 to search for publications in Medline, PubMed, Ovid, and Google Scholar that were published between January 1950 and April 2016. The following terms were searched: operating room or operating suite, combined with climate control, environment control, temperature control, thermal comfort, humidity control, infection control, laminar airflow, hypothermia. The reference lists of each of the articles discovered in these searches were examined for additional references.
GUIDELINES AND STANDARDS
The general goal of environmental control systems within operating rooms has been summarized succinctly in guidelines published by the Centers for Medicare and Medicaid Services (CMS)59: “Temperature, humidity, and airflow in anesthetizing locations must be maintained within acceptable standards to inhibit microbial growth, reduce risk of infection, control odor, and promote patient comfort.” It is interesting to note that the CMS guidelines are focused entirely on patient safety issues and do not address provider’s well-being.
A number of professional societies, licensing agencies, and regulatory organizations have independently published more detailed codes and recommendations that address various aspects of the operating room environment. These include the Centers for Disease Control and Prevention, National Institute of Occupational Safety and Health, National Fire Protection Association, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Joint Commission, Association of Operating Room Nurses, American Institute of Architects, American Society of Anesthesiologists, American College of Surgeons, and the International Organization for Standardization.
A commonly recognized guideline focusing on ventilation requirements for operating rooms has been jointly developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, the American Society for Healthcare Engineering of the American Hospital Association, and the American National Standards Institute.60 Among other requirements found in this document is the necessity to maintain positive pressure within the operating room with respect to adjacent areas, to supply at least 20 air changes/h, of which 4 or more should be fresh air, and to introduce fresh air at the ceiling and exhaust it near the floor. Additional recommendations are made for managing surgical patients with communicable diseases such as tuberculosis.
Recommended average room temperatures during routine surgery range from 20°C to 23°C.14 Recognized exceptions to these temperature limits include certain types of surgical procedures, including cardiac, pediatric, and burn surgery, in which ambient temperatures are as low as 17°C and as high as 27°C, respectively, have been advocated.14 Interpretive guidelines from the CMS recommend that each operating room should have separate temperature controls.59
The requirements for relative humidity levels in surgical sites have changed in recent years to reflect a decreased concern about the risk of fire and explosion from flammable anesthetic gases and heightened awareness of conditions that might increase the risk of surgical-site infections. Many pathogenic bacteria that thrive at elevated relative humidities do not survive when humidity is lowered to more arid levels. Accordingly, the earlier requirements to maintain relative humidity greater than 35% to minimize static electricity discharges has been replaced with the current acceptance of relative humidity from 20% to 60%.59
Air cleanliness and airborne particulate control is maintained through various forms of air filtration. Standards for particulate limits in clean rooms such as operating rooms have been established by the International Organization for Standardization (ISO 14644-1:2015).61
OPERATING ROOM VENTILATION SYSTEMS
Heating, ventilation, and air-conditioning systems in operating rooms must simultaneously serve several, potentially conflicting functions: (1) provide comfort and safety for the patient, (2) limit the circulation of various chemical and biological pollutants, and (3) provide a comfortable environment for the surgical team. The ventilation systems in operating rooms are designed to achieve these goals by allowing for independent control of temperature, humidity, ventilation, and scavenging of waste anesthetic gases and other pollutants.
Important factors that determine the efficacy of ventilation systems include the pattern of airflow, the air exchange rate, and whether recirculation of air back into the operating room is permitted. Air exchange is a measure of the volumetric airflow through the room divided by the volume of the space, expressed as the number of air exchanges per hour. A common recommendation for ventilation in operating rooms is 20 air changes per hour. Greater air exchange levels might provide better dilution of particulate matter in the air, but would also introduce undesired turbulence and drafts, excessively low humidity, increased levels of noise, and cause thermal discomfort to the inhabitants.
The patterns of airflow commonly used in modern operating rooms include conventional or laminar diffuser systems. Each system has its strengths and shortcomings.15 Although laminar systems offer some theoretical benefits for limiting surgical-site infections, the optimal pattern of airflow is easily disturbed by fixtures; overhead lights;16 personnel; and other sources of drafts, such as forced air warmers,17 opening and closing of doors, and personnel traffic.18 Extensive clinical trials have failed to convincingly prove consistent advantages for laminar flow systems.19,20 One meta-analysis even concluded that laminar airflow might heighten the risk of development of surgical-site infections.21 The Centers for Disease Control and Prevention classifies the utilization of laminar airflow as an unresolved issue requiring additional study and no longer recommends its use for orthopedic implant surgery or other procedures that have a high risk for contamination.22
Achieving the correct balance of humidity, temperature, and fresh airflow in operating rooms can be technically and logistically difficult. High-velocity airflows help to dilute any airborne particles; however, high-volume airflows also increase turbulence and redistribution of microbes within the surgical field and contributing to patient hypothermia. In addition, the requirement for frequent air exchanges can introduce a large moisture burden that can be difficult to adequately dehumidify.
The control of air pollutants such as micro-organisms, dust, and electrocautery smoke is controlled through air-filtering systems. For special care areas of hospitals, such as operating rooms and intensive care units, the recommended system consists of 2 filter beds in series, with the efficiency of the first filter bed being 30% and that of the second being 90%, which together is capable of removing airborne particles of 0.3 μm or greater with an efficiency of 99.7%.23,24
Scavenging systems to vent and evacuate waste anesthetic gases from the operating room are the fourth important component of operating room ventilation systems. Waste anesthetic gas scavenging systems are designed to be independent of the ventilation and vacuum systems and to exhaust directly to the outside.
EFFECT OF THE ENVIRONMENT ON PERSONNEL IN THE OPERATING ROOM
Effect on the Surgical Patient
Body heat can be rapidly lost in a surgical patient who is exposed to the relatively cold, dry environment of the operating room and in whom thermal homeostasis has been compromised by anesthetic agents. As many as 70% of patients undergoing an anesthetic develop some degree of hypothermia,25 and a low ambient operating room temperature is one of the leading causes.26
The adverse effects of even mild degrees of hypothermia on surgical outcomes include the increased risks of surgical-site infection, cardiac complications, bleeding, and prolonged stay in the postanesthesia care unit. A reduction of core body temperature of as little as 1.9°C has been associated with a 3-fold increase in the incidence of surgical wound infection after colorectal surgery.27
A second commonly reported complication associated with intraoperative hypothermia is the adverse cardiovascular outcomes. In one study, a 3-fold increase in adverse myocardial events, such as arrhythmia and ischemic changes, was seen in patients who experienced decreases in core temperature of as little as 1.4°C.28
Effect on Surgical Staff
The effect of the thermal environment on the health and productivity of the surgical team has not been studied extensively; however, generalizations can be drawn from research conducted in other analogous workplaces.4,29,30 Workers exposed to extremes of temperature will suffer a significant decrement in work performance and will need to exert additional effort to perform familiar tasks.4 Heat exposures have their most pronounced effect on attentional, perceptual, and mathematical processing tasks.29 Cold exposure exerts its most negative effects on reasoning, learning, and memory tasks. A number of factors influence the severity of these effects, including the duration of exposure to the temperature change, and the nature of the task undertaken.29 One study established a “sweet spot” for productivity in normal office work at approximately 22°C with a 2% decrease in performance per degree centigrade deviations from that norm.62 Many of the complex cognitive-demanding attentional and vigilance chores performed by an anesthesiologist fall into the categories described earlier and are especially impacted by thermal stress.31
Because of their additional clothing and positioning under high-intensity lights, surgeons and scrub nurses tend to be most affected by greater ambient temperatures. A study of the effect of thermal stress upon simulated laparoscopic surgical techniques found that a brief exposure (30 minutes) of surgical residents to ambient temperatures of 26°C did not directly impact their performance of surgical tasks but did induce an increased perception of distraction and physical demand.32 Elevated operating room temperatures also can cause excessive sweating that can contribute to the contamination of the surgical field.33 In a previous study, it was reported that surgeons were most comfortable at 19°C, with 50% relative humidity and 25 ft/min airflow, whereas anesthesiologists preferred 21.5°C.34
CONSIDERATIONS FOR BALANCING PATIENT AND STAFF REQUIREMENTS
A number of approaches have been used in an attempt to maintain patient normothermia while minimizing staff discomfort.25 Because an inverse relationship exists between room temperature and heat loss, a potentially simple method to minimize heat loss is to raise the ambient temperature of the operating room. To be consistently effective, however, the ambient temperature must be elevated to >27°C, which is warmer than is permitted by most regulatory agencies and would be intolerable to the surgical staff.35 Furthermore, recent studies have failed to demonstrate an association between ambient operating room and core body temperature among critically ill trauma patients, when other active warming strategies were used aggressively.36 This approach may only be practical in a situation in which active skin warming is not possible such as in extensive burn surgery.
A second approach that has been advocated is to elevate the operating room temperature during anesthetic induction and surgical skin preparation and subsequently lowering it before surgical incision and repeating the process during anesthetic emergence. This method has limited effectiveness among adult patients because the time interval for warming the room is relatively brief and requires wide swings in temperature to have a significant clinical effect.37
One strategy that has proven helpful toward maintaining normothermia is by warming patients before incision.38,39 This increases the heat content of the peripheral compartment thus minimizing the amount of heat lost through redistribution from the core during anesthetic induction. This approach has proven to be particularly effective among patients who receive both general and neuraxial anesthesia and are especially vulnerable to hypothermia.40
An alternative approach to excessively elevating the ambient temperature is to take steps to minimize the body heat that is lost to the environment. Passive insulators such as plastic sheeting or reflective composites can reduce body heat loss to the environment by as much as 30%, provided that they cover most of the skin surface.41 Heated blankets are less effective because of the low heat capacity of cotton or synthetic fiber. Warming IV fluids can also be helpful when fluid volumes of greater than 1.0 L/h are being administered. The temperatures of the fluid should not exceed 37°C.
Circulating warm water or electrical blankets deliver the heat by conduction and provide some protection against intraoperative hypothermia. When placed under the patient, they are less effective and, if not carefully monitored, can be the source of pressure ulcers and burns.42 Newer adaptations of this basic technology, such as warming garments, may provide a more effective and safer solution.43,44
Among the most effective and commonly used devices for maintaining core temperature intraoperatively are forced air warmers. These devices are frequently combined with other interventions, such as warming of intravenous fluids, to achieve maximal effect.45 Considerable debate, however, has been generated by reports that forced air warming devices might increase the risk of surgical-site infections by interfering with clean airflow over the surgical site or, if inadequately filtered, by circulating contaminated air into the surgical field.17,46–49
Other less practical or marginally effective methods to minimize patient hypothermia during surgery include the use of radiant heat devices, placement of warmed fluid bottles in selected locations around the body, irrigation of surgical sites with fluids warmed as high as 38°C,50 and use of humidified or heated anesthetic gases.
Limiting airborne contamination is another key ingredient in maintaining optimal air quality and minimizing the risk of surgical-site infection. The largest source of airborne contamination of surgical wounds arises from pathogens from skin flora of both patients and staff. The ventilation system in the operating room plays a major role in how and to where these airborne contaminants are distributed through dilution, directional airflow, room pressurization, and filtration.63 Excessive foot traffic increases air turbulence and dispersal of airborne particles. In an early study, investigators reported that bacterial counts were increased 34-fold in an operating room containing 5 people as compared with its previously empty state.51 A more recent study has corroborated this direct correlation between the number of people in an operating room and air quality.52 Door openings and closings, which occur in some procedures as frequently as 0.84 times/min, also contribute disproportionally to air turbulence and the risk of unclean air reaching surgical fields.53 Around 27% of these door openings and closings are completely unnecessary, and many of the others could be avoided by improved perioperative planning.54 On the basis of this evidence, increasing emphasis is being placed on limiting unnecessary staff movement.55
Each of these interventions must be accomplished while preserving patient safety and thermal comfort of the operating room staff.56 At any given ambient temperature, the different members of the surgical team will experience differing degrees of thermal comfort. For example, in one study that asked various members of surgical teams to assess their level of thermal comfort, only surgeons consistently reported a comfortable thermal environment.13 Anesthesia personnel and nurses perceived the environment, on average, as too cold. A portion of this discrepancy can be attributed to the different levels among the team members of physical activity, clothing, and positioning relative to the fresh airflow. The differences in attire is especially important in this regard because gowns worn by surgeons and their assistants must be waterproof, relatively impermeable to bacteria and viruses, and have adequate tensile strength to avoid tearing. Each of these design details adds an additional thermal burden on the wearer. Recent research has focused on improving surgeon thermal comfort by utilization of better design and materials for surgical garments and innovative technologies such as a cooling vest using phase change materials capable of absorbing excess body heat.57
The quality of the environment, including temperature, humidity, air circulation, and air purity, affects the well-being, health, and safety of all who work or are being cared for in the operating room. The range of acceptable limits of each of these parameters is specified in guidelines and codes set by various agencies. Components of the internal climate of the operating room are accessible to manipulation by members of the surgical team. Decisions about these adjustments should include considerations of established codes as well as the comfort and well-being of each of the inhabitants.
Name: Jonathan D. Katz, MD.
Contribution: This author wrote the manuscript.
This manuscript was handled by: Richard C. Prielipp, MD, MBA, FCCM.
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