In firefighting, pump physics is one of the most critical things an engine company officer must understand. How do we “get the wet stuff on the red stuff” in sufficient quantity without sacrificing penetrating power? The inverse ratio between volume and pressure (as the water pressure increases, volume decreases) has befuddled many a rookie lieutenant.
The same, I think, is now true in health care, by virtue of numbers alone. If we equate the fire officer’s “volume” with the medical practitioner’s “presence” (as in patients seen per hour) and “pressure” with the sum total of medical knowledge and capability, the analogy becomes more apropos, the similarities more apparent. Since failure is not an option in medicine or firefighting, let’s examine how the fire service has solved this conundrum and determine whether health care might do likewise.
In the fire service, the problem has been successfully addressed with something called the changeover valve. To understand how this works, we must first examine the terms “series” and “parallel.” Most large pumps have two sets of impellers (pinwheel gears) that either work together in a series, with impeller #1 pushing water into impeller #2 to produce high pressure, or spin separately to produce less pressure but more total volume.
Still there? OK, just a few more terms: static pressure (water main baseline), nozzle pressure (tip of the nozzle), residual pressure (what’s left when we subtract nozzle pressure from static pressure). Now, on with the show.
The fire officer takes a quick look at static pressure when the engine is hooked-up to a hydrant with a supply line. The changeover valve is pre-set to “pressure.” When the first fire attack line is charged and the nozzle opened, a large gauge on the pump panel indicates residual pressure, then does the same with each additional attack line. When residual pressure drops to less than half of static pressure, the officer, or the engineer, operates the changeover valve moving the pump vanes into a “volume” setting. In some fire departments, this is done routinely after the third attack line has been established, regardless of the various pressure readings.
So there it is. “What?” you ask. “The answer,” I reply. Health care desperately needs some sort of changeover valve. Some standard way to reduce pressure when it becomes necessary to increase volume. It might be as simple as a standardized patient rating system with regard to degree of difficulty, although that in itself could be a challenge initially.
Also needed: Agreed-upon standard operating procedures. And these should be written by practicing health care providers.
Here’s a final, important note: fire pumps, and the firefighters who use them, are protected from extreme pump pressures by something called a pressure relief valve. Health care should have one as well.
Rob Burnside is a retired firefighter and paramedic.