Today's anesthesia machines are increasingly complex, offering such advanced features as:

• automated safety checks that check for leaks and test calibration;
• electronic flow meters that dial in your desired fresh gas flow rate; and
• additional ventilation modes that sense when a spontaneously ventilating patient has stopped breathing.

These features are designed to make life easier for your anesthesia providers, but what do they really do? Here's a primer to keep you in the know.

1 Flow meters
These gas-mixing modules control gas flow and the proportion of oxygen to nitrous oxide. Mechanical flow meters require that you manually calculate the flow rates necessary to achieve the optimum 30% oxygen. The electronic flow meters that are commonplace on newer machines, however, automatically proportion gases for you. It's important to note, though, that some machines also include a mechanical flow meter as a contingency, in the event the electronic flow meter fails. If the flow meter works properly, you should be able to adjust the flow of gases through the machine's full range without damaging flow tubes. To test the machine's hypoxic mixture alarm, try to create a hypoxic O2 and N2O mixture. The alarm system should activate and prevent gas mixtures containing less than 21% to 25% oxygen from being delivered to the patient. Modern machines should automatically add oxygen to the fresh gas flow, even if the anesthetist tries to deliver 100% nitrous oxide. ?

A flow meter's minimum oxygen flow setting is critical, as the lowest setting should let you use less volatile anesthetics, says Sem Lampotang, PhD, professor of anesthesiology at the University of Florida College of Medicine in Gainesville. The minimum setting should also be a measure of how economical a machine can be for your center, he says. "The flow you set with the gas-mixing module is what's going to flow through the vaporizer. The more flow you put through that vaporizer, the more of that expensive liquid anesthetic you're going to evaporate," he says, adding that some newer machines provide guidance on when to back off on total fresh gas flow to save anesthetic consumption.

2 Ventilators
Mechanical ventilators serve a basic purpose: to keep the patient breathing as close to normal as possible while under anesthesia. But how they perform this function has become increasingly complex.

Today's ventilators are sophisticated, with some machines offering up to 7 ventilation modes designed to accommodate the breathing rates of a wide range of patients. In the outpatient setting, however, "you generally need a basic machine that ventilates the patient with the standard pressure-control or volume-control modes," says William Landess, CRNA, MS, JD, director of anesthesia at Palmetto Health Richland Campus in Columbia, S.C. In the volume-control mode, a set volume breath is delivered at a selected rate, while the pressure-control mode adjusts to changes in patient position and delivers volume accordingly.

"Since outpatients generally have good lung function, and are not expected to be supported for long periods of time, outpatient facilities may find a 'simpler' ventilator with these modes will suffice quite nicely," adds David Paulus, MD, professor of anesthesiology at the University of Florida College of Medicine in Gainesville.

3 Vaporizers
Charged with accurately delivering the set concentration of inhalation anesthetic vapor to the patient at a range of gas flows, vaporizers are an essential component of any anesthesia machine.

Most new machines' vaporizers are "highly calibrated and very reliable," says Mr. Landess.

In terms of accurate delivery of anesthetics, a machine's vaporizer shouldn't require hands-on evaluation. Manufacturers' specifications should include the accuracy of a machine's vaporizer, says Dr. Lampotang. Review the specifications to make sure the vaporizer is capable of accuracy at flow rates of 1 L/min up to 10 L/min, he says.

4 Breathing circuits
The breathing circuit connects the patient to the anesthesia machine, delivering oxygen and anesthetic gases to patients while eliminating the CO2 they exhale.

When evaluating a machine's breathing circuits, a simple visual inspection should be done to check for kinks or tears in the circuit's tubing, says Harry Lattas, RRT, anesthesia technical coordinator at Royal Victoria Hospital in Montreal, Quebec.

"You can have a brand new breathing circuit, still in the package, but if someone has squashed the tubing, you may have tears that can cause cracks, which can cause leaks around the distal part of the circuit and contaminate the air," says Mr. Lattas.

Breathing circuits also feature either swivel or more rigid "elbow-type" connectors, and manufacturers should provide whichever you request, he says. Naturally, swiveling circuits are more flexible, and can be more easily placed around the patient's neck or head. These are especially beneficial for centers frequently using laryngeal mask airways for airway management, adds Mr. Lattas.

5 Scavenging systems
These systems, which are either active or passive, are responsible for capturing and exhausting waste, minimizing your patients' and OR staff's exposure to harmful anesthetic gases. Active systems use suction to remove gases, while passive systems allow gas to exit the room through corrugated tubing to the ventilation exhaust grill of the OR. Active scavenging systems are the standard for today's OR, and you should ensure that an active system "is not shared in any way with the suction used to protect the patient airway, or for any other reason," says Mr. Landess. Have a biomedical engineer evaluate how the system is hooked up, perform a visual inspection and test air quality to verify the integrity of the scavenging system and its ability to protect patients and staff from leaked volatile agents, he says.

6 Safety checkouts
A checkout process to ensure anesthesia machines are properly functioning is done at the start of every day. Many newer machines walk you through the checkout process on a digital screen, prompting you to push buttons to control gas flow and advising you of difficulties, says Mr. Landess. If a machine has a circuit leak and won't maintain positive pressure, the screen will direct the user to the likely problem area, or areas, that you should check. Test the checkout process on new machines to ensure that the machine alerts you to trouble and, moreover, steers you toward a solution. "The better the machine can lead you through the maze of possible problems," says Mr. Landess, "the less chance you have of experiencing real problems during a case."

Should you standardize?
With today's advances, standardizing the anesthesia machines at your center may help flatten out what can be a steep learning curve.

"It's like a pilot going into the cockpit of any plane and seeing the same layout in each one. That familiarity improves safety," says John Dombrowski, MD, director of the Pain Management Center in Washington, D.C. "With standardized machines, you don't have to search for components on a machine you're not accustomed to using. When you need to find the flush valve, you'll know exactly where it is on every machine in every room. That's crucial in a life-saving situation."