A chemical used to join plastic medical device components is the target of a tough new report from engineering researchers at Johns Hopkins University.
The researchers report a chemical commonly used in the joining of PVC parts for medical plastic equipment can impair heart function in rats. These findings, the scientists say, suggest a possible new reason for some of the common side effects, such as loss of taste and short-term memory loss, from medical procedures that require blood to be circulated through plastic tubing outside the body.
"We have tested primarily devices made from PVC, either soft or hard," says Artin A. Shoukas, Director of the Center for BioEngineering Innovation and Design at the Johns Hopkins University-School of Medicine. "(These include) cardiopulmonary bypass equipment (heart lung machine), dialysis equipment, ECMO and IV bags." ECMO stands for extracorporeal membrane oxygenation, a technique that provides oxygen to blood for newborns with inadequate lung function.
In a press release issued by Johns Hopkins, the scientists state: "These new findings also have strong implications for the future of medical plastics manufacturing."
In addition to loss of taste and memory, the Johns Hopkins researchers say coronary bypass patients often complain of swelling and fatigue. These problems usually resolve within a few months after surgery, but they are troubling and sometimes hinder recovery. These symptoms generally go away, according to the researchers.
Dr. Shoukas's personal experience with coronary bypass surgery propelled his search for a root cause for the loss-of-taste phenomenon. "I'm a chocoholic, and after my bypass surgery everything tasted awful, and chocolate tasted like charcoal for months," he says. Shoukas and Caitlin Thompson-Torgerson, a postdoctoral fellow in anesthesiology and critical care medicine, say they suspected the trigger for these side effects might be a chemical compound.
The researchers took liquid samples from IV bags and bypass machines and analyzed the fluids in another machine. They found cyclohexanone leaching from these devices. All fluid samples contained at least some detectable level of the chemical. Cyclohexanone is commonly used joining PVC components in medical tubing and devices.
The researchers then injected rats with either a salt solution or a salt solution containing cyclohexanone and measured heart function. Rats that got only salt solution pumped approximately 200 mL of blood per heartbeat and had an average heart rate of 358 beats per minute, while rats injected with cyclohexanone pumped only about 150 mL of blood per heartbeat with an average heart rate of 287 beats per minute.
The team calculated cyclohexanone caused a 50-percent reduction in the strength of each heart contraction. They also found the reflex that helps control and maintain blood pressure is much less sensitive after cyclohexanone exposure. Finally, the team observed increased fluid retention and swelling in the rats after cyclohexanone injections.
"We would never recommend that patients decline this type of treatment if they need it," says Shoukas. "On the contrary, such technologies are life-saving medical advances, and their benefits still far outweigh the risks of the associated side effects. As scientists, we are simply trying to understand how the side effects are triggered and what the best method will be to mitigate and ultimately remedy these morbidities."
This study was funded by the Bernard A. & Rebecca S. Bernard Foundation, the American Heart Association, the W.W. Smith Foundation, the National Institutes of Health, the Pulmonary Vascular Research Institute, the American College of Cardiology, the Shin Chun-Wang Young Investigator Award, the American Physiological Society, the Joyce Koons Family Cardiac Endowment Fund and funds from Dr. Shoukas.
A spokesman for the American Chemistry Council had no comment on the report. A spokesman for the Society of Plastics Industry (SPI) says, "We see this as a non-issue. These are life-saving devices."