The customer reported that a patient was undergoing a therapeutic plasma exchange (tpe) procedure and a concurrent treatment of extracorporeal membrane oxygenation (ecmo).During the procedure, they received an air alarm and the nurse noticed air bubbles in the return tubing line.The nurse stopped and aborted the procedure with partial rinseback.Per the customer, approximately 30 to 45ml of blood was not returned to patient.No medical intervention was required for this event and the patient is 'fine'.The customer declined to provide patient identifier (id).The tpe set is not available for return because it was discarded by the customer.
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This report is being filed to provide additional information.Investigation: the customer stated that the operator noticed air bubbles in the return line past the rlad.The run data file (rdf) was analyzed to determine the alarms and signals from the return line air detector (rlad) in the optia.The rlad is situated at the exit of the return pump and is the last point of air detection in the optia circuit.There was no air alarm and all of the rinseback was successfully completed.Signals in the rdf also indicated that air was detected by the optia return line air detector (rlad) during rinseback after the procedural run was initiated, however, the cumulative air was less than the 1.0 ml needed to trigger an rlad alarm.The patient showed no symptoms or signs attributable to air embolism.Per terumo bct's internal risk documentation, outgassing of cold replacement fluids can occur when the fluids are warmed through the blood warmer in tpe procedures.When blood warmer tubing is connected to the return line, any air bubbles could be infused into the patient.Based on the calculation of the maximum rate of air generated, a low level health hazard risk from outgassing in the reported case is expected.The absence of reported clinical symptoms when outgassing has been noted and supports this contention.Root cause: during tpe procedures on spectra optia, the replacement saline, albumin or plasma may be cold.If they are not allowed to warm to room temperature, and if the return blood is warmed, air bubbles may form.The reason for this "outgassing" is that gasses are more soluble in liquids at low temperatures than at higher temperatures.If at a low storage temperature air is available to dissolve in a fluid (albumin, plasma, etc.) and approaches its equilibrium solubility at that temperature, when the fluid is warmed the air will come out of solution, because its solubility is exceeded at the higher temperature.It is usually described as chains of very small bubbles or foam, which tend to rise toward the top of the tubing.The small bubbles may coalesce to form larger bubbles.Because cold ffp was used as part of the replacement fluid in the tpe procedure, the operators used an astotherm blood warmer in the return line in each of the procedures.The astotherm blood warmer consists of a length of tubing wrapped around a heated mandrel.Heat is transferred to the return-line blood to prevent the sensation of cool return blood.The root cause for the reported air in return line was due to outgassing of small bubbles out of solution due to cold replacement fluid being warmed.The system operated as intended.
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