2002 OPEN FORUM Abstracts
MONITORING NEONATES RECEIVING NITRIC OXIDE THERAPY: EFFECTS OF MALFUNCTIONING HEMOLYZER ON METHEMOGLOBIN RESULTS.
Robert J. Rogness, RRT, CPFT, Jamie Clink, BS, RRT, RN, Michael Trevino, MS, RRT, Gary Weinstein, MD, FCCP, Thomas Pullano, MD, Presbyterian Hospital of Dallas, Dallas, Texas.
Introduction: Nitric oxide (NO) therapy is used in neonatal intensive care to treat Persistent Pulmonary Hypertension of the Newborn (PPHN). Toxicity of inhaled NO is extremely low when administered appropriately. However, even at normal clinical doses (1-20 parts per million), careful monitoring of the effects of NO is necessary to ensure the safety of the patient. Rare cases of methemoglobinemia have been reported as a result of NO therapy. It is the practice of our institution to routinely measure methemoglobin (metHb) in infants on NO therapy.
Case Summary: Two term infants in the Neonatal Intensive Care Unit (NICU) were receiving NO therapy at 20 PPM, initially with metHb levels of 1-2%. Over the next few days, both of their metHb levels steadily increased to 8-9% despite improvement in clinical status. Pulmonary laboratory staff was called to verify the accuracy of the analyzer, an Instrumentation Laboratories (IL) 482 CO-Oximeter. Preventive maintenance was performed, and three levels of controls were run with results in range. New blood samples were obtained and analyzed, but metHb levels remained >5%. Technical support at IL was called for further direction; however, even after further diagnostic troubleshooting, the machine appeared to be in working order. Pulmonary laboratory staff still suspected that the results were incorrect, and therefore asked IL to send a field technician to inspect the machine. After IL performed annual preventive maintenance and three levels of controls were run, blood was again analyzed for metHb. The results were still >5%. This time however, the specimens were saved and analyzed on an IL 482 at a different facility. The metHb levels in these specimens were normal. IL was asked how the two machines could be measuring the two samples so differently. Further investigation revealed that the analyzer?s hemolyzer was not functioning properly, resulting in inaccurate metHb measurements despite normal controls.
Discussion: Quality control
materials are used to validate the accuracy and precision of an analyzer. In
this situation however, the machine was giving erroneous information despite
acceptable control values. On the IL 482, as well as the IL 382 and IL 682 CO-Oximeters,
there is no alarm to alert the user that the hemolyzer is not functioning properly.
Since the controls were already hemolyzed, expected values were normal, while
whole blood samples were being measured incorrectly. Potentially, this could
be a serious problem for the treatment of any patient whose
management is being guided by the metHb results produced by this series of CO-Oximeter.
While these machines are no longer in production, hundreds are still in use
nationwide. Clinicians should be aware that verification of machine accuracy
in this IL CO-Oximeter series is not necessarily confirmed by
acceptable quality control.