Dear Editor,

Both Drs. Bhambhani and Richmond miss an important point in discussing methods to avoid syringe dead space errors in diluting medications for neonatal dosing. The assumption that volumes as small as 0.02 cc can be accurately measured with a 1 cc syringe is erroneous. A number of years ago I was investigating the etiology of wildly erratic gentamicin levels and learned that the syringe manufacturer only guarantees that the volume measured with a 1 cc syringe is accurate to +/- 0.01 cc. If one draws up 0.02 cc, whether to inject into another syringe, or by adding 0.02 cc to diluent already in the syringe, one actually will be drawing up anywhere between 0.01 cc and 0.03 cc (this is assuming the human eye is absolutely accurate at measuring 0.02 cc).

To avoid this type of error, one needs to abandon the idea of trying to accurately draw up volumes of less than 0.1 cc. We eliminated our problem with gentamicin levels (and other dilution errors) by instituting a policy that our nurses and pharmacists never made dilutions using medication volumes of less than 0.1 cc. To make the dose of digoxin mentioned by Dr. Bhambhani (5 mcg from a 250 mcg/ml solution), one would make a dilution by adding 0.1 cc of digoxin to 4.9 cc of diluent, thus yielding a solution of 25 mcg/5cc. One would then administer 1 cc of this solution to give 5 mcg.

Dear Editor,

I agree with you that there can be overdosage while administrating IV medications in neonates. These are few of the precautions we take in our neonatal unit to avoid medication errors.

1. The required quantity of diluent is first drawn in the syringe and then the required amount of the drug is drawn in the syringe and quantity measured in the middle part of the syringe.

2. Required quantity of the drug is measured from the shoulder of the syringe, leaving the nozzle empty and then diluent is taken.

3. When very small quantity of the drug needs to be withdrawn -first more drug is taken, diluted and then the extra quantity is discarded keeping only the quantity required.( e.g. drug dose required 0.01ml -- Draw 0.1 ml in a syringe prefilled with diluent 1ml measured from the shoulder of the syringe. Mix it well and then discard 0.9 ml leaving 0.1 ml in the syringe. this can be further diluted to 1 ml before administration)

Dr. Anjali Bangalore

Dear Editor,

There is a simpler solution to the problem of the syringe dead space when diluting drugs which was raised by Dr Bhambani et al. and that is to draw some of the diluent into the syringe first. Perhaps I may be allowed to quote from the section on neonatal drug administration on page 5 of the Neonatal Formulary (4th edition, 2003 - www.neonatalformulary.com).

"Many drugs have to be diluted before they can be used in babies because they were formulated for use in adults. In addition, dilution is almost always required when a drug is given as a continuous infusion. Serious errors can occur at this stage if the dead space in the hub of the syringe is overlooked. Thus, if a drug is drawn into a 1ml syringe up to the 0.05 ml mark, the syringe will then contain between 1.14 and 1.18 ml of drug. If the syringe is then filled to 1 ml with diluent the syringe will contain three times as much drug as was intended.

To dilute any drug safely, therefore, draw some of the diluent into the syringe first, preferably until the syringe is about half full, and then add the active drug. Mix the drug and diluent if necessary at this stage by one or two gentle movements of the plunger, and then finally make the syringe up to the planned total volume with further diluent. In this way the distance between two of the graduation marks on the side of the syringe can be used to measure the amount of active drug added.

While this may be adequate for 10-fold dilution, it is not accurate enough when a greater dilution than this is required. In this situation it is necessary to use two syringes linked by a sterile three way tap. The active drug is drawn up into a suitable small syringe and then injected into the large syringe through the side port of the tap. The tap is then turned so as to occlude the side port and diluent is added to the main syringe until the desired volume is reached."

Sam Richmond