Ventilator technology has come a long way since medieval anatomist Andreas Vesalius made small animals breathe artificially by inserting a hollow reed down their pharynx and blowing into the open end of the tube. And—were he alive today—the inventor of the first mechanical ventilator, George Poe, Jr, would no doubt marvel at the strides in design and engineering that followed the unveiling of his original clinical marvel in 1908.
But despite the improvements, the one constant for ventilators is that they remain now as then life-critical equipment, which is why making sure they stay up and running is essential.
“It’s critical to respond to a call concerning a ventilator,” says Tim McKenna, a biomed and ventilator specialist in the clinical technology and biomedical engineering department at the Lucille Packard Children’s Hospital and Stanford Hospital and Clinics, Palo Alto, Calif. He adds that the starting point is to try to get as much information from the respiratory therapist or nurse who was the operator of that machine when the trouble occurred.
“In emergency situations where the ventilator is on a patient, I’ll drop what I’m doing to respond to the call,” McKenna says, so crucial is it that the device be swiftly restored to proper functioning.
Among the most typical ventilator service issues encountered are problems with user-interface components, such as knobs and keyboards, notes Ken Humphrey, a supervisor in the technical services department at equipment rental and third-party service organization Universal Hospital Services of Englewood, Colo.
Also vulnerable to failure: sensors. “Today’s ventilators are built with multiple sensors for self-diagnosis of problems,” Humphrey says. “For example, sensors compare inspiratory flow rates against expiratory flow rates. The data from each sensor is continually compared by the machine, and an alarm will go off if the system detects a variance from what it understands to be the norm for a particular setting. It’s the same thing with pressure readings. Multiple pressure readings will be collected from various points in the breathing circuit, and a failure error indication will be triggered if those pressures don’t correspond or fall within established parameters.”
Another malady seen from time to time in ventilators is an oxygen cell that drops below voltage specifications. Often, this problem can be remedied on the spot rather than having to cart the ventilator back to the shop for servicing. This is true of other types of ventilator troubles. On the chance that he can affect a field repair, McKenna tries to anticipate which tools and parts to bring with him so as to avoid a time-wasting trip back to his bench for needed items. At minimum, “I usually grab a ratchet set with multiple bits, a wrench, and possibly an all-in-one tool, like a Leatherman,” he says. “However, there isn’t a good way of opening the ventilator and doing anything to it while the patient is connected. Whatever you might attempt to do would have to be conducted ‘live’—and, except for the very most minor work, it’s too big a risk for the patient’s safety to do that. The machine has to be turned off and the patient removed and placed on another, properly working ventilator before you do anything consequential to the one that’s down. Otherwise, you’re asking for trouble.”
If it happens that the ventilator must be disconnected from the patient and turned off, then the device might just as well be taken back to the shop for bench work, McKenna suggests.
Shop repairs are usually a straightforward process. Occasionally, though, they can test the limits of patience and budgets. McKenna’s most frustrating ventilator repair experience was born of a graphic control board failure. “The clinician who called in the problem indicated the screen had a strange rippled pattern, so we brought it into the shop to test it and, after 3 days, found nothing,” McKenna remembers.
Not long after that, the same ventilator was back in the shop. This time, its screen blacked out completely. “We decided that the prudent move would be to replace the graphics controller board, a $2,800 item,” McKenna says. The ventilator was again returned to operational status, and again the graphics controller board failed. So did the graphics controller boards of other vents of the same make and model. “We suspected this might be a heat-related issue after noticing that the graphics controller board in this type of ventilator was encased within the display and without ventilation,” McKenna continues. “We contacted the manufacturer and recruited their help in coming up with a solution for this. The manufacturer initially did not recognize there was a problem but subsequently issued a technical service bulletin explaining how to fix the problem and prevent recurrence.” However, the recommended fix proved to be less than 100% effective. “We still had a few incidents here and there. The ultimate remedy was a manufacturer redesign of the display which included a different board with venting in the bottom of the display.”
Humphrey, too, has had his share of frustrations with ventilators, recalling an experience centered around a ventilator that kept developing a new ailment almost immediately after the previous one had been addressed. “I took a call on a ventilator that had shut down and would not turn back on,” he says. “When I inspected it, sure enough, it would not operate on either AC or DC power. Diagnostics I performed pinpointed the problem as a bad power supply board. I ordered a new board. When it arrived, I installed it and tested it. It powered up, but would not run on battery power. Charging voltage was present, but the battery was not holding it. I figured that what happened was the battery was damaged when the power supply board failed, resulting in complete drainage of the battery’s charge and destruction of its cells. The failure of that power supply board initially went unnoticed because the battery power kicked in and took over until it was spent.
“I next procured a new battery, charged it overnight, and installed it. Then, when I conducted a performance test on the vent, it failed a portion of that, indicating it had a bad sensor board, possibly damaged by a power spike when the power board went out. This meant more parts ordering, more waiting for parts delivery, more installation, more testing. So, altogether, this one unit was offline for about 10 days, when, typically, we can get a vent with routine problems back in operation within about 3 hours. Also, we had to purchase a total of $6,000 in new parts, which was very unusual.”
The most exasperating ventilator repair challenge for Kelly Wright, BS, CBET, RRT, interim coordinator in the clinical engineering department at Christus St Michael Healthcare, Texarkana, Tex, stemmed from inaccurate tidal volumes produced by one of his institution’s newer machines. “Older ventilators had air and oxygen proportional valves built into a single assembly, but this particular problem ventilator has these valves separated,” Wright says. “Consequently, each valve has its own controller board, which in turn is controlled by a main controller board—a total of four boards involved. I was able to identify the problem as originating with one of the four controller boards. It had gone bad, but which one it was I could not be sure.”
The easy way to have dealt with this conundrum would have been simply to order four new controller boards, then remove the old ones and install in their place the new set. However, Wright saw that as being fiscally wasteful, since each board carried with it a not-inconsequential price tag. “I did not want to just throw circuit boards at a system,” he says. Acting on advice he obtained from the manufacturer’s technical support arm, Wright ordered just one board and, when it arrived, began swapping it with each installed board until he found the bad one. This took more time, but Wright believes it was the right course. In addition to saving his institution some money, he also helped cement in the minds of his customers that the biomed department is a valuable resource.
A nice thing about ventilators is they often come with a built-in device checklist intended for use by their operators.
“After pressing the power on button, the machine boots up and then presents the clinician with the option of stepping through a protocol that checks the functionality of the vent, including an airtight check for leaks,” McKenna says.
Wright calculates that most of the ventilator service calls he receives are the result of respiratory therapists or nurses improperly conducting these performance tests. “Ventilators calculate airway circuit compliance and resistance, which are the basis of the tidal volume numbers that show up on the display screen,” he says. “It’s possible to produce strange readings if the numbers don’t match up with system performance.”
Humphrey believes a role for the clinical/biomedical engineering department would be to work with clinicians on the design of a preuse performance test procedure. “Biomeds—knowing the equipment as they do—would be in a good position to suggest components that ought to be tested but that clinicians might not necessarily think to check, such as the integrity of the oxygen cell,” he says.
At Wright’s hospital, this has been addressed by “making sure techs are properly trained in conducting those performance tests,” he says. “After I wrote and conducted a performance testing training program for our respiratory therapists and equipment techs, my vent service calls dropped by about 90%. A key element of the training program sought to explain what all the bells and whistles on these machines really do. There are so many advanced modes on today’s vents that it’s very easy for a user to create programming conflicts and completely confuse the vent as to what it’s supposed to do. Biomeds can make an important contribution to alarms management by educating respiratory therapists and equipment techs about what each alarm means, why it pops up, and what can be done to reduce the incidence of false alarms.”
Over and Above Requirements
Biomeds also continue the quest to reduce service calls in general, given the life-critical nature of ventilators. Accordingly, biomed departments typically place extra emphasis on preventive maintenance (PM).
“Each manufacturer has its own recommended intervals for parts replacement, recalibration, electrical safety check, and verification of operation and performance,” Humphrey says. “Some of the recommendations are calendar based, where they call for inspections every 6 months or 12 months. Others are based on machine hours. You’re advised to PM the vent after maybe 2,500, 5,000, or 10,000 hours of operation. We have our own risk-classification guidelines that we follow. So, for instance, if the vent is used in a critical care environment, we PM it twice a year even if the manufacturer recommends only annual care.”
Wright employs a computerized program that generates a list of all required PM procedures for each ventilator in the fleet at Christus St Michael. Typical tasks outlined on that customizable list include making sure warning labels are present and readable, changing out the filters, replacing the diaphragms and exhalation valves, verifying battery condition, replacing batteries as needed (usually once every 2 years), confirming that correct tidal volumes are generated, and calibrating the PEEP valve. “It takes about 2 hours to complete a full PM on one ventilator,” Wright says, adding that locating ventilators due for inspection can at times be daunting. “We’re looking into tagging each of our ventilators with a radio frequency identification chip,” he says. A potential drawback to such tagging is possible interference with sensitive wireless devices, such as monitoring equipment.
Signal interference was unknown and certainly unimagined by ventilator pioneer George Poe Jr. His concern rested with developing a machine that would breathe reliably and without fail on behalf of adults and children. Today’s breed of ventilators is operationally the best ever, but they are not trouble free. Biomeds know this and are ready to step in at a moment’s notice to put things right when problems surface.
Rich Smith is a contributing writer for 24×7. For more information, contact .