The Duration of Spinal Anaesthesia - a Prospective, Observational Cohort Study

With the increasing health care cost and the scarcity of nursing staff, there is considerable focus on providing surgery in an ambulatory setting. Total hip and knee arthroplasty (THA and TKA) are now procedures where selected patients are sent home on the same day after the procedure. Therefore, knowledge of key factors affecting the length of stay is important. One factor is the method of anaesthesia used for the operative procedure.

Spinal anaesthesia is often used for THA and TKA and has several advantages compared to general anaesthesia. However, spinal anaesthesia also has drawbacks, because it reduces the force in the legs, hindering early mobilisation. There are no good data on the duration of spinal anaesthesia. Compared to the past, there has been a shift towards using lower doses of local anaesthetic (LA) injected into the subarachnoid space. Theoretically, this should result in a shorter duration of anaesthesia, and this would be of value in an ambulatory setting. However, if the variation in the duration is high and therefore not predictable for the individual patient, spinal anaesthesia has limitations in the ambulatory setting.

The objective of the present study is to prospectively collect data on the type and dose of LA injected into the subarachnoid space and the duration of spinal anaesthesia in participants scheduled for orthopaedic surgery in spinal anaesthesia. We hypothesise that the mean duration of spinal anaesthesia is positively correlated to the dose of LA injected into the subarachnoid space.