Anaesthetic safety of the macintosh® oral laryngeal spray device

Primary hypothesis: A single, maximal hand squeeze of the Macintosh® laryngeal spray atomiser bulb may deliver a toxic dose of local anaesthetic to the oral mucosa of small infants. Method: Two anaesthetists, A and B, completed 10 single maximal bulb squeezes per individual Macintosh® atomiser (five for each anaesthetist). Seven atomisers in daily use at a children's hospital were tested. Spray volumes were compared between devices and individual anaesthetists, using a repeated measures analysis of variance model. Results: The mean volume ± standard deviation of 2% lignocaine spray delivered per single maximal squeeze of the seven Macintosh® atomiser bulbs by anaesthetists, A and B, was 0.54 ± 0.7 ml, and 0.31 ± 0.4 ml, respectively. The range was 0.025-2 ml. This is equivalent to 10.8 mg ± 14 mg and 6.2 mg ± 8 mg of lignocaine, respectively. The difference between the two anaesthetists was statistically significant (p-value < 0.0001) and ranged from a maximum of 1.0 ml to a minimum of 0.05 ml. Conclusion: There is a difference in the amount of local anaesthetic delivered when two anaesthetists use a single maximal squeeze of the Macintosh® spray atomiser bulb from the seven Macintosh® spray devices tested. The dose delivered was not dependent upon the user. In order to prevent a toxic dose being administered, it is recommended that the plastic chamber of the atomiser is filled with a safe dose of local anaesthetic calculated for each child, particularly small infants, before the upper airway is sprayed.