What is a multigas monitor, and what should I expect on a preventive maintenance (PM) inspection?
Multigas monitors or detectors are known by various names, including “gas modules.” Most often, they are called by their model name. Regardless of the name by which you know your multigas monitor, the function is the same: supplying information or monitoring a patient's airway gas mixture. These monitors can be found in operating rooms, recovery rooms, outpatient departments, endoscopy areas, obstetrics departments, and emergency departments—essentially anywhere in which medications are used where patient “gas level” needs to be monitored.
When operations or certain procedures are performed, the patient is given oxygen, medical air, nitrous oxide, and some type of anesthetic agent (e.g. sevoflurane, isoflurane, desflurane, halothane). These gases are given to the patient in a certain mixture to ensure that they are sedated throughout the procedure and that they feel no pain.
By way of a sample line, the multigas monitor measures the gases being inspired and expired. The gases are delivered via a mask through a closed-loop system, with the sample line coming off of this loop. In most cases, these systems will have a water trap to collect and eliminate moisture from the line. This also serves as a way to keep moisture from entering the gas monitor. If moisture was allowed to enter the monitor, it could plug the internal lines or contaminate the chambers that measure gases, causing erroneous readings.
Multigas monitors can be stand alone or part of the anesthesia machine. They always will have a wide array of alarm parameters that allow the anesthesia staff to set limits to make them aware of problems. Some of these alarms include: inspired and expired oxygen, high and low oxygen saturation, high and low pulse limits, high and low end-tidal carbon dioxide (CO2), high and low CO2, apnea, and high and low anesthetic gas.
PM involves checking all gas measurements for accuracy. This is accomplished by using a canister of calibration gas and checking to make sure the delivered amount matches the canister. If the measurements do not match, the biomedical technician must calibrate them. (Of course, every manufacturer has different procedures, so the service manual must be consulted.) Calibration must occur before the monitor can be used again. Usually, if the calibration is off, the anesthesia provider will know and immediately notify biomedical engineering.
Each manufacturer has different guidelines regarding the frequency of PM and calibration for multigas monitors. Repairs include replacing inaccurate measurement devices and calibrating them after repair. Also following repair and PM, all alarms must be checked. Electrical safety also must be performed; this is done by measuring the ground resistance and chassis leakages. As technology has improved over the years, in addition to multigas monitors themselves becoming smaller, the measurement devices within the monitors have become smaller.