HE, Me, and the FBI. by Gary Grist RN CCP Emeritus
The title is not a typo. The HE stands for ‘heat exchanger.’ The Me stands for me, myself, and I. And FBI stands for…the FBI.
In the late 1980’s I was using one of the first disposable pediatric membrane oxygenators. It had a combined venous reservoir and cardiotomy reservoir. This was of great advantage in volume management. When using bubble oxygenators, it was necessary to use a separate cardiotomy reservoir to ensure that nitrogenous bubbles generated by the field suckers and ventricular vent would not enter the bubble column. Another feature was an efficient heat exchanger (HE). It was a flexible, corrugated stainless steel tube coiled at the base of the venous reservoir. The corrugations improved the heat exchange efficiency as the venous blood flowed into and out of the reservoir. The HE was visible when the reservoir was filled with clear fluid. But it was hidden if the reservoir was blood-filled.
A Sudden Leak
After completing one particular case, I was recirculating the pump waiting for the surgeon to close the patient’s chest. Suddenly, the venous reservoir began to fill with fluid quickly. I suspected a leak causing the heater/cooler (H/C) to pump water into the venous reservoir. I immediately turned the H/C off and clamped the water lines. Sanguineous fluid slowly percolated out of the HE, filling one of the clamped off water lines. I informed the surgeon that the pump could not be used if it was needed to go back on bypass. I set up another circuit that was not required.
A Big Split
Upon draining the circuit, I found that the HE tube had split along one of the corrugated creases. The vertical rend was about ¾” long and ¼” wide. I guessed that the stainless-steel tubing had some stress that caused a large hole similar to a spontaneous mechanical failure in an automobile radiator. Fortunately, the failure occurred after bypass was terminated and there was no patient injury. I had never returned a disposable membrane oxygenator to a manufacturer before. We did not have a risk management department back then to give me advice on what to do. I never had a disposable bubble oxygenator failure of any kind during use. So I rinsed the oxygenator as best as I could with a bleach solution to decontaminate it. (This was a mistake. I admit it!) I double bagged the oxygenator and later gave it to the manufacturer’s representative along with my verbal story about what happened. I thought that this was a freak failure and continued to use that oxygenator model.
About two months later, I received a phone call from Human Resources saying that an FBI agent wanted to talk to me. I arranged to meet him in an empty family discussion room, having no clue as to why the FBI wanted to speak to me. When we met, he flashed his credentials at me as he introduced himself. He said that he was investigating a case of industrial sabotage for the FDA. Before 1991 when the FDA established its own Office of Criminal Investigations, FBI agents were tasked with this. The returned oxygenator manufacturer was accusing me of deliberately damaging the HE with a caustic chemical to damage their company. They had to report such a catastrophic failure to the FDA by law. There was a risk that they would have to recall their oxygenators, which could cost them millions of dollars and damage their sales unless they could prove that the HE failure was a deliberate act of sabotage.
The agent questioned me extensively, looking for a motive for my actions. I denied any motivation to harm the oxygenator company and explained to him precisely what happened. I guess he believed me because after he departed, I never heard anything else about the incident. I don’t remember if there was a recall of any kind by that manufacturer for HE related problems. Soon after that, I switched to a different make of disposable pediatric membrane oxygenator.
Since my encounter with the FBI, I have not sent any defective oxygenators or any other defective disposable product back to the manufacturers. I would dispose of the defective units and simply tell the manufacturer’s representative what I found. When my hospital finally set up a risk management department, I would give the defective product to them and let them handle the issue.
I am surprised that in the 21st century, there are still reports of oxygenator HE failures (1,2,3,4). Despite manufacturer quality control efforts, HEs can still have dangerous leaks. HE leaks can injure or kill a patient and result in litigation involving millions of dollars. Even though HE leaks are a manufacturing defect, a perfusionist may still be held responsible on the premise that the pump set up procedure did not detect the leak before use. So, I would like to make some suggestions on making HEs safer by making H/Cs safer.
Air Pressure Test
Each H/C should have a built-in air pressure test mechanism to test the HE before the water enters it (5). The pressure generated should be in the range of four atmospheres: about 3000 mmHg or 60 pounds. This would detect any existent leak and generate enough pressure to cause any weak spot in the HE to fail before use. Sixty pounds of pressure would be expected if ‘wall water’ was being used instead of a H/C. So HEs should be robust enough to tolerate such pressure.
Aspirated Water Flow
H/Cs should use aspirated water flow through the HE instead of positive pressure flow. If there is a spontaneous HE leak (like the one I described above) after a successful pressure test, it is safer for blood to be drawn out rather than water to be forced into the blood path of the oxygenator HE.
Blood Leak Detector
A blood leak detector is a simple device that uses a ridged tube about one foot long and two inches in diameter. The longer the tube, the more sensitive it will be. The caps on each end have lenses, one with a photocell and the other with an adjustable light source. The H/C water aspirated from the oxygenator HE would enter and exit the ridged tube by side manifolds at opposite ends of the detector tube. If any blood enters the recirculating H/C water, it will be detected. These units are so sensitive that they can detect blood in amounts so small as to be invisible to the naked eye. The blood detector would also detect biofilm buildup within the H/C with which nontuberculous mycobacteria and other microbes are associated (6).
Integrated Heat Sterilization
H/Cs should have a system to recirculate hot water heated by the H/C internal heater between uses. This is a decontamination method that has been used in artificial kidney machines to kill the microbes within their tubing and components that could generate pyrogens (7). Pyrogens are endotoxins produced by bacteria such as E. coli that can cross the hemodialyzer membrane and harm the patient. Recirculating water within the H/C at 158F for 30 minutes between uses would kill most pathogens that could enter the blood through a HE leak or enter the environs by aerosolization. Even though it is resistant to heat decontamination to a certain degree, the numbers of nontuberculous mycobacteria present can be significantly reduced with each heat cycle. If only sterile distilled water is used initially to fill the system and added to the H/C to replace spillage, this is particularly true. Heat decontamination would also reduce or eliminate biofilm buildup and the need for harsh chemical decontamination, which requires the need for draining and repeated rinsing of the H/C with specially filtered water (8,9). Heat decontamination could be performed after every use, whereas chemical decontamination would be performed much less frequently.
Ultraviolet lights over the main water reservoir in the H/C could not decontaminate the system as well as hot water. But it would inhibit microbial growth on a continuing basis when the H/C is not in use (7).
A disposable gross air intake filter would remove lint generated from sterile drapes and wraps and other atmospheric detritus. Keeping lint and other particulate material from depositing on the dry internal surfaces of the equipment would probably extend the life of the H/C. The exhaust air should be filtered through a disposable high-efficiency particulate air (HEPA) filter. HEPA filters have pore sizes small enough to remove bacteria and other microbes as air passes through these filters, nearly sterilizing it. This would prevent the aerosolization of nontuberculous mycobacteria and other bacteria. It would be unnecessary to vent the unit outside of the room.
Frankly, this may not be practical, but at least one manufacturer has developed a H/C that eliminates water as the heat transfer medium, using glycol instead. Glycol inhibits bacterial growth. This H/C must be used with special, disposable, sterile heat exchangers, which must still be assessed for leaks. The hazards of glycol to blood compartment leaks are unknown. In addition, the H/C itself requires charging from a separate industrial chiller system (10). Whether or not this will be a practical system only perfusionists and the free market can determine.
Hope For The Future
I hope manufacturers will make these H/C improvements to protect future patients from physical harm and future perfusionists from legal damage. I understand these improvements would increase the cost of H/Cs. Eliminating the time-consuming, labor-intensive process and exposure to harsh chemicals used by current decontamination methods would motivate perfusionists to purchase the higher cost units. And making the H/Cs safer would motivate institutions to pay more for them.