Observation of snakebite victims: is twelve hours still necessary?

To determine the period of observation required to exclude elapid envenoming following presentation with suspected or definite snakebite in South-east Queensland.

Two part case series of patients presenting with a snakebite to a regional hospital in South-east Queensland. A snakebite assessment protocol was established for a prospective phase with the same data collection tool used for retrospective cases. The time of onset of clinical features, and abnormal investigations consistent with envenoming were recorded for each feature. 'Time zero' was set at the time of removal of effective first aid or, time of presentation in the absence of effective first aid.

A total of 360 presentations of snakebite were identified with envenoming diagnosed in 34 cases (9%). Seventy-three percent of clinical features and investigation abnormalities were present at, or before, time zero with 95% present within 6 h. All abnormalities, which commenced beyond 6 h, occurred in patients where the diagnosis of envenoming had already been established.

Six hours of assessment appears adequate to exclude elapid envenoming in asymptomatic patients in South-east Queensland. Evidence in the literature of delayed onset of envenoming in completely asymptomatic patients is difficult to find.