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A continuous infusion of aminophylline, 40 mg per hour, was ordered for an elderly man with asthma. The nurse prepared a concentration of 1 gram of aminophylline in 250 ml D5W (40 mg per 10 ml) and hung the bottle. She then attached a nonvolumetric (dropcounting) infusion controller (not to be confused with an infusion pump) to the intravenous tubing.
At change of shift, the nurse mentioned in report that more than 200 ml of solution remained in the bottle, enough to last well through the next two shifts. But at the end of the second shift, another nurse noticed that the I.V. bottle was empty. She quickly checked the controller; it was set at 10 drops per minute (the correct rate for a microdrip I.V. set that delivers 60 drops per ml). Then she discovered that the infusion was flowing through macrodrip tubing, which delivers 20 drops per ml. As a result, the patient was receiving 30 ml per hour instead of the prescribed 10 ml per hour.
The nurse called the doctor, who ordered the infusion discontinued and blood drawn for analysis. The patient complained of severe nausea, a result of the aminophylline overdose.
This error was not the fault of the machine but rather of the user. A drop-counting infusion controller is a precision instrument when used correctly. But because it accommodates any size I.V. tubing, errors like this one can occur.
To avoid similar errors, be sure you understand completely how a drop-counting controller works. Make sure you attach the correct size tubing.
Check the drip rate visually to see if it's running too fast; don't rely only on the controller. Time-taping the I.V bottle can help you monitor the rate.
Ask your pharmacist to prepare a chart showing the correct flow rates and tubing to be used for standard concentrations of frequently infused drugs. Keep the chart handy for easy reference.
Volumetric gravity-dependent rate controllers are set in ml per hour, not drops per minute. This controller eliminates the need for calculating a drop rate. Also, only the tubing specifically intended for the machine can be attached to it.