Poison down the Tubes

31. July 2009

Infusion bags, catheters, kidney dialysis and heart-lung machines often are life-sustaining. But they create special problems as well. If blood circulates outside the body, it might lead to serious malfunctions of organs. A potential cause is the chemical cyclohexanone.

It is impossible to imagine modern medicine without extracorporal blood circulation for example for kidney dialysis or bypass surgeries. The temporary take-over of functions of vital organs saves the lives of millions of patients. But extracorporal blood circulation entails a number of own risks such as heart function problems with reduced cardiac output and cardiac arrhythmias. Some patients suffer from loss of memory or appetite, organ swellings or fatigue.

Plastic materials contain cyclohexanone

Artin Shoukas and Caitlin Thompson-Torgerson at the Johns Hopkins University Medical School now found a potential reason for the afflictions of some patients which sometimes vanish only months after the surgery (American Journal of Physiology – Heart and Circulatory). They found cyclohexanone (CHX) in plastic tubes, an organic solvent which is used during the production of medical devices made of polyvinylchloride (PVC). It is a component in infusion bags and in extracorporal circulation systems. It travels from tubes and connections with the contacting fluids – including blood. After intravenous administration of fluids via PVC bags and i. v. tubes, CHX can be detected in urine samples of newborns.

Shoukas and his team already suspected chemicals originating from plastic components in medical devices to be the cause for side effects after some medical procedures. The researcher had made very personal experience after a bypass surgery: “As a ‘chocoholic’ stroke me that everything I ate tasted horrible – and for months chocolate tasted like charcoal.”

Chemical strikes the heart

The scientists analyzed crystalloid fluid samples from unused extracorporal tubings and i. v. bags with the aid of gas chromatographic mass spectroscopy to determine clinical CHX exposition values and to discover the CHX contamination in the collected fluids. Those fluids contained from 9.63 to 3,694 micrograms CHX per liter. Afterwards they examined comprehensively the effects of an i. v. infusion with saline solution plus CHX and only saline solution in 49 rats. They checked the cardiovascular function by cardiac output, heart frequency, stroke volume, vascular resistance, arterial pressure and ventricular contractility. They also examined the sensibility of the baroreflex and the formation of edema.

The hearts of those rats which had only received saline solution pumped nearly 200 microliters of blood per heart beat with an average stroke frequency of 358 per minute. Rats with CHX infusion only “made” 150 microliters blood per heartbeat and a heart frequency of 287 per minute. Not only the pump function of the heart was affected, animals with CHX also had a reduced contractility of the heart muscle. According to the researchers, CHX causes a 50% reduction of the strength of each and every heart contraction. The baroreflex which participates in control and preservation of the blood pressure was reduced after CHX exposition and reacted less sensible. Another observation showing in the animals with a CHX infusion was increased fluid retention and swellings.

Benefits of extracorporal treatment remain undisputed

The data provides estimates about the CHX contamination of the most frequently commercially available i. v. bags and extracorporal circulation systems, says Shoukas. In clinically relevant CHX exposition the animals show cardiovascular impairments similar to the observed side effects on humans during clinical applications. This fact confirms the researchers’ hypothesis: CHX adds to cardiovascular insufficiency for example after heart surgeries. Nonetheless the scientists do not recommend refusing a necessary procedure due to the diagnostic findings. Those technologies often are life-saving thus the benefits prevail the risks for sure.

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