A Comparison of CoolStick and Ethyl Chloride Spray for the Assessment of Sensory Block to Light Touch and Cold Before Caesarean Section Under Spinal or Combined Spinal-epidural Anaesthesia

In England, up to 35% of deliveries in 2022 were by caesarean section. Current guidelines from NICE recommend that regional anaesthesia is offered for caesarean section. Neuraxial anaesthesia is considered to carry less risk of morbidity than general anaesthesia for both mother and neonate and is performed for approximately 92% of caesarean sections. To ensure the comfort of the mother, and to avoid intraoperative pain that could lead to general anaesthesia conversion, the neuraxial block is tested prior to commencing surgery. In the United Kingdom, the Royal College of Anaesthetists recommend that less than 1% of elective caesarean sections started under regional anaesthesia are converted to general anaesthesia.

Surveys of UK anaesthetists have found a wide range of practices when assessing neuraxial block, including the testing of light touch, temperature, pain and motor block. In a survey of UK anaesthetists, cold has been shown to be the most widely used modality for testing with 92% of respondents testing this modality. This was followed by touch, which 60% of respondents tested for. Recent consensus guidance from the Obstetric Anaesthetists' Association has recommended light touch as the primary testing modality for neuraxial anaesthesia for caesarean section, aiming for a sensory block to the T5 level or above. A second testing modality is recommended in cases where there is doubt over the light touch assessment. In practice, many anaesthetists will consider anaesthesia to be adequate when block to light touch is demonstrated to the T5 level or above and cold to the T4 level or above.

Ethyl chloride spray is the most common piece of equipment for used for testing in the UK. It has been shown that ethyl chloride spray can be used for the assessment of light touch and is equivalent to established methods when assessing adequacy of the block for surgery. However, ethyl chloride has disadvantages: skin irritation and allergic reactions sometimes occur; and containers are expensive, require replacing and carry a carbon footprint. The spray also remains in the atmosphere for up to two months and this can have a deleterious effect on the environment.

Cotton wool has been shown to be as effective at testing light touch when compared to more expensive methods. However, it is not necessarily practical to have multiple pieces of equipment required to assess different block modalities. Given that ethyl chloride is commonly used to test both modalities, a more sustainable and cost-effective approach to testing both light touch and cold would be ideal.

Theophany Limited recently developed the CoolStick for assessment of block height to cold. The CoolStick consists of a stainless-steel head and a plastic handle. It is kept in the fridge before use and is cleaned with an antibacterial wipe between patients. The CoolStick maintains a temperature adequate for cold assessment for up to 10 minutes in ambient theatre temperature and should be kept refrigerated for at least 40 minutes prior to use. It appears to be a more sustainable and cost-effective alternative to ethyl chloride spray; however, there are no studies that demonstrate its clinical application in this setting.