Frozen succinylcholine

Abstract

We wish to report an unusual problem we encountered with the use of succinylcholine. An emergency Caesarean section was arranged under general anaesthesia for persistent fetal bradycardia. After pre-oxygenation, the patient was given thiopental 375 mg. However, the succinylcholine in a 2 ml syringe could not be injected, even with substantial pressure on the plunger. On closer inspection, the solution was found to be frozen inside the syringe. A second succinylcholine syringe was quickly prepared and used without delay. The patient was intubated without oxygen desaturation and surgery proceeded uneventfully. It is usual practice in our hospital to draw up and store emergency anaesthetic drugs in a drug fridge. Our fridge is a Dometic RA 122 H (Dometic Ltd, Luton, UK). The temperature of the fridge is maintained at 2–4 °C by a thermostat. The temperature inside the fridge is measured by a thermometer and is displayed digitally. The drugs are replaced every 24 h. Immediately after the incident, the temperature reading was noted to be 1–2 °C. Our hospital pharmacist measured the freezing point of succinylcholine to be − 0.62 °C. The syringe had been stored on the middle shelf in the fridge for approximately 6 h. The refrigerator was serviced and was found to be in perfect working condition. It is therefore possible that, in everyday use, parts of the fridge may be at temperatures lower than that displayed on the thermometer. Only two cases of anaesthetic drugs freezing have been reported previously [1, 2]. Does succinylcholine need to be refrigerated at all? Suxamethonium stored at room temperature can remain stable [3] and sterile [4] for up to 8 days if the pH is not changed. Driver et al. cultured 756 syringes left over a period of 8 days and none of the syringes grew organisms. They concluded that the probability of drug sterility after 8 days would be 0.9961. Although freezing of succinylcholine in a syringe is a rare event, the consequences could be disastrous. Other drugs may also have the potential to freeze when stored in a refrigerator. Following this case, we recommend close inspection before use of any liquid drug stored in a refrigerator and consideration be given as to whether it is feasible to avoid storing drugs that are required in an emergency in a refrigerator.