By David Harrington, PhD
The vast majority of biomeds are very good at problem solving and doing repairs with minimal test equipment. While this is a key part of your day-to-day work, how the questions are written on the certification exam can present problems to some people. Here are some examples of potential problem questions that I found in the study guide.
One question on problem solving involved an ECG recorder with a heated stylus. The question stated that the waveform appeared to be overdamped and asked the reason. The potential answers included mismatched electrodes, a bad cable, the tension on the stylus was too high, or a gain problem. Many of you would go right to the tension on the stylus, but in a sampling of potential test takers, more than 30% had never worked on an ECG recorder with a heated stylus.
Another version of this question involved a wide baseline with tension replaced by heat too high and no ground replacing the gain. Remember that the inputs of the ECG amplifier are isolated from ground, so a missing ground would not give you a wide baseline. Mismatched electrodes would cause the baseline to wander, as would the bad cable, so the answer must be the heat is too high.
A common problem in the past on ECG recorders was that the wrong paper was used—specifically, paper designed for thermal print heads used on stylus machines. The problem was that the paper burned through or the wax/clay paper used on thermal print head machines, and segments would not print out because the “dots” were covered with wax/clay and did not touch the paper. This is a rare occurrence in the 21st century, but it could still happen in a physician’s office or clinic where the recorder is seldom used.
Another question in the problem solving was on the output of a defib with a Lown waveform. Several things bothered me on this question; foremost that the Lown waveform was on only the American Optical defibs and they have been out of production for more than 25 years. The question said that when testing the unit, the BMET noted that the energy displayed on the unit was 400 but the tester showed only that 280 was delivered, and then asked the reason why. Simply, it was the loss in the cables and circuits, but the big problem that I have with the question is that in 1978 all manufacturers came out with modifications where the stored energy—what was displayed on the unit—would be within +/- 10 of the energy delivered to the tester. If you find a unit like this during your testing—where the energy shown on the dial/display is upward of 30%—the unit does not meet current standards of care and is dangerous. Please, either update it or take it out of service.
As a side note, some of these older defibrillators from various manufacturers would actually increase their stored energy as they aged. I once found a unit made in the 1960s that stored more than 500 joules and delivered close to 400 joules. Just to be on the safe side, I suggest that you review the Heart Association guidelines for defibs, pacing, and AEDs, published in the August 7, 2006, issue of Circulation. It is probably available in your hospital library.
Another series of questions on invasive and noninvasive blood pressure also had some interesting points that you need to remember.
One question asked why the invasive blood pressure was higher than the cuff pressure. The answers presented did not really answer the question: operator error, noncalibrated systems, cuff size, and it is normal. The fact is that systolic pressure increases as you measure farther away from the heart; the second reason is that the cuff should not be on the same arm that has the catheter for the invasive pressure. It is not uncommon to have a 10- to 15-mmHg difference between direct and indirect arterial blood pressures.
Several questions on blood pressure cuffs also were a little less than crystal clear. So remember that if the cuff is too small for the patient, it could cause a higher than actual pressure to be determined, and if the cuff is too large, it could indicate a lower pressure. What was not mentioned is that some cuffs are designed for the left arm and others for the right; these are generally the two tube models, where the inflation bladder does not completely cover the artery that it is supposed to occlude.
In many hospitals invasive blood pressures are not common, so many biomeds may have problems with the questions on blood pressure monitoring. Take a look at this article online for a couple of examples.
David Harrington, PhD, is a health care consultant, Medway, Mass, and is a member of 24×7’s editorial advisory board. For more information, contact.
The arterial waveform appears to be damped. What should be done to correct the problem?
- Adjust the amplifier gain
- Move the transducer
- Flush the line
See the answer
The pulmonary artery (PA) waveform on the scope will go to a flat line every few seconds. What is the cause?
- Noncalibrated amplifier
- The PA line is too far in
- The transducer needs to be replaced
- The display is not calibrated
See the answer