Haemodynamic Effects of Low-dose Spinal Anaesthesia for Hip Fracture Surgery.

A Retrospective, Observational, Single-centre, Cohort Database Analysis of the Haemodynamic Effects of Low-dose Spinal Anaesthesia for Hip Fracture Surgery.

Approximately 65, 000 hip fractures occur in the United Kingdom (UK) each year, and more than 99% are repaired by surgery. Roughly half of patients receive spinal anaesthesia, where a small amount (usually less than half a teaspoonful) of local anaesthetic is injected into the lower back, around the nerves that go to and from the hip.

Low blood pressure is very common during surgery (at least > 30%, depending on definition), and appears to be linked to a greater chance of death within a month after surgery.

There are 2 main ways of managing low blood pressure during surgery: treatment and prevention. Treatments (fluids, drugs) have side effects in the older, frailer population with hip fracture. Prevention involves giving anaesthesia at lower doses. National guidelines recommend that lower doses are given, but this recommendation is based on historical research selectively involving younger, fitter people having hip fracture surgery. Importantly, these studies did not record blood pressure either accurately or often enough.

The Anaesthesia Sprint Audit of Practice (ASAP) 2 study suggested that a safe level of low blood pressure occurs when only 1.5 mls of spinal anaesthesia is given, and the investigator has been using this amount in Brighton since 2011. Recently, the investigator has reported a way of transferring vital signs data from anaesthetic monitors to storage computers for medicolegal purposes (e.g. in Coroner's investigations: approximately 4000 people in the UK die annually within a month of hip fracture surgery).

However, analyzing such observational data should also allow the investigator to describe accurately how blood pressure changes around the time of surgery, and in patient groups that are normally excluded from prospective research (e.g. the very old, the very frail, people with dementia). By comparing this data to published national data from the ASAP 1 study, the investigator hopes to determine whether lower doses of spinal anaesthesia are linked with a lower rate of low blood pressure during surgery, potentially improving people's survival and recovery after hip fracture.

Approximately 65, 000 hip fractures occur in the UK each year, and more than 99% are repaired by surgery. Roughly half of patients receive spinal anaesthesia, where a small amount (usually ~ 2.5mls) of local anaesthetic is injected into the lower back, around the nerves that go to and from the hip.

The investigator has found that low blood pressure (hypotension) is very common during surgery (occurring in at least > 30%, depending on the definition of hypotension), and appears to be significantly linked to a greater chance of death within a month after surgery (~3% rise in mortality/5 mmHg fall in SBP).

There are 2 main ways of managing low blood pressure during surgery: treatment and prevention. Treatments (fluids, drugs) have side effects in the older, frailer population with hip fracture, including fluid overload with heart failure, and cardiac/kidney/gut ischaemia.

Prevention involves giving anaesthesia at lower doses. UK national guidelines recommend that lower doses are given (< 2mls 0.5% hyperbaric bupivacaine), but this recommendation is based on historical research selectively involving younger, fitter people having hip fracture surgery. Importantly, these studies did not record blood pressure either accurately (i.e. invasively) or often enough (i.e. > every 5 minutes).

The ASAP 2 study suggested that a safe level of low blood pressure occurs when only 1.44 mls 0.5% hyperbaric/normobaric spinal anaesthesia is administered, and the investigator has been using this amount (1.5mls) in Brighton since 2011.

Recently, it has become possible to transfer vital signs data from anaesthetic monitors to storage computers for medicolegal purposes (eg in Coroner's investigations - approximately 4000 people in the UK die annually within a month of hip fracture surgery).

However, analyzing such observational medicolegal data should also allow accurate description of how blood pressure changes around the time of surgery, and in patient groups that are normally excluded from prospective research (eg the very old, the very frail, people with dementia). By comparing this data to published national data from the ASAP 1 study, it should be possible to determine whether lower doses of spinal anaesthesia are linked with a lower rate of low blood pressure during surgery. By merging individuals' data with that held on the Brighton Hip Fracture Database, it should be possible to determine whether prevalence (and/or depth+duration of hypotension) are correlated with outcomes (survival, length of inpatient stay) after hip fracture repair.

Inclusion Criteria:

1. Adults (over 18 years) who have sustained a unilateral hip fracture and received surgery (hemiarthroplasty, dynamic hip screw, cortical screws, proximal femoral nail) under low dose spinal anaesthesia (1.3 mls 0.5% hyperbaric bupivacaine) after fascia iliaca block + sedation, administered by the Chief Investigator (CI) between 3rd March, 2017 and 1st January, 2020 at the Princess Royal Hospital, Hayward's Heath (E Sussex).
2. For whom crude vital signs data have been stored in pseudo-anonymised electronic form on secure hospital computers, for medico-legal reference

Exclusion Criteria:

1. People with hip fracture receiving conservative management during the study period;
2. People with hip fracture requiring total hip arthroplasty (for whom larger volumes of spinal anaesthesia are used);
3. People with hip fracture administered spinal anaesthesia other than 1.3 mls 0.5% hyperbaric bupivacaine;
4. People meeting inclusion criteria for whom vital signs could not be stored electronically due to equipment failure.