Model SRPM Room Pressure Monitor - PRESSURE TRANSDUCER: Opening Doors in the Operating Room

Openings Doors in the Operating Room

New Room Pressure Monitor Avoids Problem of Lint Accumulation

In the summer of 2008, a major Boston-area hospital sought help to resolve a thorny problem in its operating rooms. Nurses were complaining about how difficult it was to open and close the doors in the facility’s 23 operating rooms, five of which had just been built. They couldn’t understand why they had to pull so hard to open the doors. A veteran hospital HVAC engineering and design consultant did some sleuthing and eventually pinpointed the problem as the effects of airborne lint on the sensors controlling OR pressurization.

Yes, lint, the ubiquitous clinging bits of fiber and fluff that fall off fabrics on such products as hospital scrubs and patient linens, was fouling up instruments that measure operating room differential space pressures. As lint accumulates on the sensing elements of these instruments, they begin to under-report space differential pressure. Pressure is increased to the degree that it becomes difficult to push open the doors to enter and exit the ORs.

The most obvious solution was to clean the existing instruments more frequently. However, the sensors on the existing lint-accumulating space differential pressure instruments are very small and are easily damaged during cleaning.

Further sleuthing uncovered the new SRPM (Setra Room Pressure Monitor) by Setra Systems, Inc., whose sensors do not come in contact with the air in the conditioned spaces being monitored and, therefore, do not need frequent lint removal or any other frequent servicing. Nearly a year after installing the new SRPM in one operating room, the problem has been completely eliminated. As funds become available, the hospital intends to install the new monitors in all the ORs, as well as infectious isolation rooms, and other spaces where lint build up is a problem.

Airborne lint problem an issue in a variety of hospital spaces

“There is a surprising amount of airborne lint in hospitals, even inside operating rooms that receive highly filtered supply air,” remarks Paul Lindberg, a mechanical engineer from Advanta Consulting Engineering, a hospital HVAC engineering, design and troubleshooting firm that has worked in more than forty New England hospitals.

According to Lindbergh, who has done work for this particular one million square foot medical center for more than twenty years, the lint originates from “scrub” clothing, operating suite gowns, patient “johnnies,” bed linens, and in other fabrics common to hospitals.

He notes that ORs have one of the highest concentrations of airborne lint of any hospital spaces, probably because ten or twelve people on a surgical team may be in the OR at the same time, each of whom is producing lint. However, other hospital spaces in which these fabrics are found also generate substantial amounts of airborne lint, for example, infectious isolation rooms. He believes it is important to use space differential pressure instrumentation that is not susceptible to fouling by airborne lint in the hospital setting generally.

“In an operating room, air is highly filtered and there is positive pressure, since you do not want air to come into the operating room from the outside,” said Lindberg. The code requirement for pressure is 0.01 inches water gauge. This is a very small amount of pressure, one that can barely be felt by the palm of the hand. If there is that much pressure on the inside of the OR door, one can be certain that the airflow is going from the OR to the outside space, and not vice verse. “If the controls malfunction, and pressure is pumped up much higher, say, .05 inches, that is when one would begin to have difficulty with the door, feeling pressure against you as you try to push it open.”

Part of the problem stems from the design of the existing instrument, which contains tubes of about an inch and a half in diameter, in which small sensors (with the diameter of a toothpick) protrude into the tube, over which air passes. With such a narrow space, just a couple of fibers on the sensor can throw off the readings significantly.

After determining that the lint was building up on the instruments and causing incorrect readings, Lindbergh looked at whether frequent cleaning might correct the problem. “Cleaning was definitely a viable option – the medical center could send an instrument technician around to clean the units, say monthly,” he says.

“But there’s a risk when you clean these sensors, even with the most delicate of tools, because the sensors are fragile and there is a good chance you’re going to damage them.” Also, the instruments quickly begin to lose accuracy again soon after the lint build up is removed. In as little as a month, their accuracy was reduced by about 20-30 percent, as lint particles begin to accumulate on the instrument sensors.

Lindberg was not convinced that cleaning was a good alternative, even if they were willing to invest in monthly cleaning, so he recommended that the hospital opt for a different type of instrument that would not be susceptible to reduction in accuracy due to airborne lint.

Search for the solution leads to SRPM

To find another option, Lindberg consulted the controls contractor that maintains the hospital’s environmental control systems. The contractor suggested he contact Boxborough, Massachusetts-based Setra Systems, Inc., a leading manufacturer and designer of pressure measurement instrumentation. The controls contractor had experience using Setra instruments for industry clean room solutions.

“After contacting Setra, their factory representatives sent information on the SRPM (Setra Room Pressure Monitor) instrument for space differential, and I was immediately interested in the fact that the sensors within the instrument are not exposed to environmental air, so airborne lint can’t disrupt them,” said Lindberg.

According to Michael Saracco, Setra’s North American Sales Manager, “The SRPM is designed for pharmaceutical, hospital, semiconductor, clean rooms, research laboratories, and critical low differential pressure applications that require stringent pressure monitoring and alarming.”

The SRPM monitors the positive or negative pressure in protected environments and airborne infection isolation rooms in accordance with Centers for Disease Control guidelines. It measures and displays highly accurate pressure readings to 0.001 inches of water column resolution.

In addition to the enclosed design that protects it from airborne lint, the SRPM has a large, easy to see graphic RGB backlit touch-screen display, allowing fingertip access to menus that guide the user through room setup, application, security and calibration. It features a green LED to indicate normal conditions, and a red LED, audible alarm, and single pole, double throw (SPDT) relay for remote annunciation, to signal unsatisfactory room pressure status.

The medical center conducted a trial, installing an SRPM in one of its five new operating rooms. “The unit has been in place for a year, and has given excellent, reliable information, with no maintenance required,” said Lindberg.

He adds that he has checked the accuracy of the output of the new SRPM instrument five or six times over the past year with a very accurate portable differential pressure meter. The SRPM has agreed with the portable instrument to within 0.001-inch water gage during each check. “At the same time, I checked the readings on the other instruments, and found them to be inaccurate, giving me a good view of how well SRPM performs in comparison to other instruments.”

In addition to the fact that the instrument works precisely as planned, Lindberg found it easy to swap over from the existing instrument to the new one. He was also impressed with the company’s willingness to get involved in the project even though the hospital was purchasing only one instrument.

Although interested in changing over the instruments in all the ORs and other spaces within the hospital that are adversely affected by airborne lint, the hospital is currently holding off on its plans until the funding picture is brighter.

According to Paul Lindberg, “The unit has definitely met my expectations and I will definitely consider recommending Setra Systems, Inc.’s SRPM instruments for my next design job for OR suites or infectious isolation areas.”

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