Although a safe level of exposure to trace anesthetic gases could not be defined, maximum concentrations to which a worker in the operating room should be exposed were recommended
Trace anesthetic exposure
TRACEANESTHETICEXPOSURE BY DR.SANDEEP
INTRODUCTION• Waste anesthetic gases are small amounts of anesthetic gases that leak from the patient’s anesthetic breathing circuit into the air of operating rooms during delivery of anesthesia.• It is an occupational hazard The purpose of this session is to:Increase awareness about the adverse health effects of waste anesthetic gases Describe how workers are exposed to waste anesthetic gases Recommend work practices to reduce these exposures Identify methods to minimize leakage of anesthetic gases into the work environment
TRACE ANESTHETICS / WASTE GASESDEFINITION: A trace level of anesthetic gas is aconcentration far below than needed for clinicalanesthesia or that can be detected by smell.• Usually expressed in PPM, which is volume by volume (100% of a gas is 10,00,000 ppm ; 1% is 10,000 ppm).
WHO IS EXPOSED TO WASTE ANESTHETIC GASES? The following hospital workers may be exposed towaste anesthetic gases:• Anesthesiologists• Dentists• Nurse anesthetists• Operating-room nurses• Operating-room technicians• Other operating-room personnel• Recovery-room nurses• Other recovery-room personnel• Surgeons
Where are workers most likely to be exposed towaste anesthetic gases? Workers are most likely to be exposed to waste anestheticgases in• Operating facilities with no automatic ventilation or scavenging systems,• Operating facilities where these systems are in poor condition, or• Recovery rooms where gases exhaled by recovering patients are not properly vented or scavenged.
Even when scavenging and venting systems are inplace, workers may be exposed to these gases under thefollowing conditions:• When leaks occur in the anesthetic breathing circuit (which may leak gas if the connectors, tubing, and valves are not maintained and tightly connected)• When anesthetic gases escape during hookup and disconnection of the system• When anesthetic gas seeps over the lip of the patient’s mask or from endotracheal coupling (particularly if the mask is poorly fitted—for example, during pediatric anesthesia)• During dental operations• During induction of anesthesia
• WASTE GASES ARE USUALLY • Nitrous oxide • Halogenated volatile anesthetics • Combination of both
Concentrations in operating rooms vary greatly anddepends on• The fresh gas flow,• The ventilation system,• The length of time that anesthesia has been administered,• The measurement site,• Anesthetic technique,• And other variableshigher with pediatric anesthesia, in dental operations , and in poorlyventilated PACU.
SITES OF LEAK• Mask• Endotracheal tube• Anesthetic gas machine• Ventilator• Pumps• Scavenging devices• All connecting tubing• Other elements- depending on the type of anesthesia delivery system.
• Liver diseases:- Recurrent hepatitis (halothane) enhanced hepatic metabolism of some drugs . Elevated serum autoantibodies that react with specific hepatic proteins, especially females and pediatric anesthesiologists.• Bone marrow abnormalities• Nonspecific polyneuropathy
CONTROL MEASURES• Complete elimination is impossible.• Goal is to reduce concentrations to the lowest level with a reasonable expenditure of effort and money.• To achieve this, attention should be focused on four areas:1. Scavenging,2. Equipment leaks,3. Work techniques, and4. The room ventilation system.
SCAVENGING SYSTEMS• Scavenging is the collection of excess gases from equipment used to administer anesthesia or exhaled by the patient and the removal of these gases to an appropriate place of discharge outside the work environment.• Also referred to as evacuation systems, waste anesthetic gas disposal systems, anesthesia waste exhaust, and excess anesthetic gas-scavenging systems.
SCAVENGING SYSTEMS Consists of five basic parts:• A GAS-COLLECTING ASSEMBLY, which captures gases at the site of emission;• A TRANSFER TUBING, which conveys collected gases to the interface;• THE INTERFACE, which provides positive (and sometimes negative) pressure relief and may provide reservoir capacity• THE GAS-DISPOSAL TUBING, which conducts the gases from the interface to the gas-disposal system; and• THE GAS DISPOSAL SYSTEM, which conveys the gases to a point where they are discharged.
PASSIVE SYSTEMS• Room Ventilation System – non-recirculating and recirculating• Piping Direct to Atmosphere-direct duct or vent, specialized duct system, direct disposal line, or through-the-wall system• Adsorption Device-activated charcoal• Catalytic Decomposition
ROOM VENTILATION SYSTEM• A NONRECIRCULATING SYSTEM takes in exterior air and processes it by filtering and adjusting the humidity and temperature. The processed air is circulated through the room and then all of it is exhausted to atmosphere• A CIRCULATING SYSTEM takes a small amount of air is taken in from the atmosphere, while the remaining air is recirculated
VENTILATION SYSTEM• Install a ventilation system that circulates and replenishes the air in operating rooms (at least 15 air changes per hour, with a minimum of 3 air changes of fresh air per hour).• Install a ventilation system that circulates and replenishes the air in recovery rooms (at least 6 air changes per hour, with a minimum of 2 air changes of fresh air per hour) to prevent exposure to waste anesthetic gases exhaled by patients.
PIPING DIRECT TO ATMOSPHERE• The discharge point on the outside should be selected so that it is away from wind pressures, ignition hazards, windows, and the inlets for the ventilation system. It may be advantageous to attach a short T-piece as a terminal• THE OPEN end should point downward to prevent water and dirt from entering and be fitted with netting to prevent insects, rodents, and foreign matter from entering the pipe.• PROBLEMS include both positive and negative pressure caused by wind currents, obstruction from ice build up, and accumulation of foreign matter at the outlet
ADSORPTION• An adsorption device removes some or all excess anesthetic agents by adsorbing them or converting them to harmless substances Eg: Canisters• The efficiency of adsorption also depends on the flow rate through the canister. Moisture may reduce the efficiency• ADV: Simple and portable, do not require expensive installation or maintenance, halogenated anesthetic vapors are not released to the ozone layer• DIS ADV : No adsorption device for nitrous oxide, expensive, effective for only short periods of time.
ACTIVE SYSTEMS• Piped Vacuum Systems• Active Duct System
PREVENTIVE MEASURES1. Checking equipment before use-check for irregularities or breaks and circuit for negative pressure and positive pressure relief as part of the daily machine checklist.2. Turn on the local/ room ventilation system.3. Using scavenging equipment-make sure the scavenging equipment is properly connected & connect the gas outlet to the hospital’s central scavenging system4. Start the gas flow after the laryngeal mask or endotracheal tube is installed
PREVENTIVE MEASURES5. Proper use of airway devices-Make sure that uncuffed endotracheal tubes create a completely sealed airway6. Using low fresh gas flows-Use the lowest anesthetic gas flow rates possible for the proper functioning of the anesthesia delivery system and for patient safety7. Avoiding insufflation techniques AND HIGH FLOW Rates-rates to prevent leaks: high flow rates generate more waste anesthetic gases than low flow rates.8. Preventing liquid agent spills-Fill vaporizers before or after the anesthetic procedure [1 mL of a volatile liquid anesthetic = 200 mL of vapour = 2ppm (closed room measuring 20 by 20 by 9 ft)]
PREVENTIVE MEASURES9. Proper mask fit10. Washout of a Anesthetic gases at the end of the case-Eliminate residual gases through the scavenging system as much as possible before disconnecting a patient from a breathing system11. Preventing Anesthetic Gas Flow Directly into the Room-Turn the gas off before turning off the breathing system.12. Alteratons in work practices
PREVENTIVE MEASURES13. Using intravenous and regional anesthesia14. Keeping scavenging hoses off the floor15. Leak control
MONITORING Develop a monitoring program supervised by aknowledgeable person in every operating facility. Such aprogram should include• Quantitatively evaluating the effectiveness of a waste-gas control system and• Repeatedly measuring concentrations of anesthetic gas in the breathing zones of the most heavily exposed workers while they perform their usual procedures.• Keep good records of all collected air sample results for at least 30 years.
MONITORING• Keep medical records of a worker’s exposure for 30 years after his or her employment has ended• Obtain baseline liver and kidney data for operating- room personnel and monitor their liver and kidney functions periodically.• Record medical histories for workers and their families, including occupational histories and outcomes of all pregnancies of female workers and wives of male workers (if possible
MONITORNG TRACE GASES• Air monitoring• EQUIPMENT:- • Infrared analyzers • Proton transfer reaction mass spectrometry • Dosimeters • Ionizing leak detectors • Oxygen analyzer • Carbon dioxide analyzer
SAMPLING METHODS• Instantaneous sampling• Sampling at the air conditioning exhaust• Time weighted average sampling• Continuous sampling• Personnel sampling
AGENTS TO BE MONITERED• Nitrous oxide• Volatile agents
SITES TO BE MONITORED• Monitoring should be scheduled so that the work of each anesthesia provider and of each operating room is checked while using a mask, supraglottic device, and tracheal tube.• Monitoring should be performed during spontaneous, manually assisted, and manually controlled and automatic ventilation.• The results of the monitoring should be analyzed and discussed with all parties concerned
OTHER ASPECTS• Personal Monitoring• Area (room) sampling• Monitoring frequency
MONITORING FREQUENCY The following schedule has been suggested :• An annual comprehensive survey in which exposure levels are measured, leaks detected and corrected, and TWA exposure levels are calculated or measured.• Quarterly follow-up with a less-detailed survey; if there appears to be a problem, a comprehensive survey should be performed to determine causes and assess corrective actions.• A repeat comprehensive survey in the event of major changes to the ventilation system, anesthesia equipment, or scavenging systems.• TWA monitoring of each member of the staff for a short period, such as a week, repeated on a 6-month basis also has been suggested
MEDICOLEGAL ASPECTS OCCUPATIONAL SAFETY AND HEALTH ACT(OSHA) Agencies The national institute of OSHAsafety and health (NIOSH)• NIOSH under the department of Health and human services• OSHA under the department of Labour
• NIOSH- conducting and funding research and education and for preparing criteria documents to be used to develop standards.• OSHA - enacting job safety and health standards, establishing reporting and recordkeeping procedures, inspecting workplaces, and enforcing the requirements of the act by using citations and fines.
ARBITRARY SAFETY LIMITS• For Nitrous Oxide alone-exposure limit of 25 ppm• For halogenated agents used alone, the limit was 2 ppm .• When halogenated agents are used in combination with Nitrous Oxide, the recommended limits were 25 ppm nitrous oxide and 0.5 ppm of the halogenated agent• For dental facilities, a level of 50 ppm Nitrous Oxide was recommended.• During mask induction, the level of Sevoflurane should be less than 2 ppm.
• The 1970 act gives each employee the right to request an OSHA inspection if an employee believes that he or she is in imminent danger from a hazard or if OSHA standards are being violated.• The American Society of Anesthesiologists (ASA) legal counsel has advised that it is within the right of an employer to refuse to permit an OSHA representative to enter the facility unless that individual has either a search warrant or a court order compelling the inspection.• All states have workers compensation laws so that individuals suffering from occupational diseases can collect benefits, irrespective of whether or not the employers negligence caused the disease