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Spinal or general anaesthesia for surgical repair of hip fracture and subsequent risk of mortality and morbidity: a database analysis using propensity score‐matching

Around 76,000 people fracture their hip annually in the UK at a considerable personal, social and financial cost. Despite longstanding debate, the optimal mode of anaesthesia (general or spinal) remains unclear. Our aim was to assess whether there is a significant difference in mortality and morbidity between patients undergoing spinal anaesthesia compared with general anaesthesia during hip fracture surgery. A secondary analysis examined whether a difference exists in mortality for patients with pre‐existing cardiovascular disease or chronic obstructive pulmonary disease. This was a clinical database analysis of patients treated for hip fracture in Nottingham, UK between 2004 and 2015. Propensity score‐matching was used to generate matched pairs of patients, one of whom underwent each mode of anaesthesia. Data were analysed using conditional logistic regression, with 7164 patients successfully matched. There was no difference in 30‐ or 90‐day mortality in patients who had spinal rather than general anaesthesia (OR [95%CI] 0.97 [0.8–1.15]; p = 0.764 and 0.93 [0.82–1.05]; p = 0.247 respectively). Patients who had a spinal anaesthetic had a lower‐risk of blood transfusion (OR [95%CI] 0.84 [0.75–0.94]; p = 0.003) and urinary tract infection (OR [95%CI] 0.72 [0.61–0.84]; p < 0.001), but were more likely to develop a chest infection (OR [95%CI] 1.23 [1.07–1.42]; p = 0.004), deep vein thrombosis (OR [95%CI] 2.18 [1.07–4.45]; p = 0.032) or pulmonary embolism (OR [95%CI] 2.23 [1.16–4.29]; p = 0.016). The mode of anaesthesia for hip fracture surgery resulted in no significant difference in mortality, but there was a significant difference in several measures of postoperative morbidity.


Introduction
Hip fractures, or fractures of the proximal third of the femur [1], are one of the most common serious injuries that occur in the older population. In 2016, more than 70,000 patients aged ≥ 60 years were treated for a hip fracture in hospitals around the UK, costing the NHS and social care £1 billion (€1.13 billion, US$1.26 billion) annually [2]. Furthermore, one projection indicates that by 2033, despite the incidence of hip fractures in older people decreasing, the increase in the at risk population during the intervening period means around 100,000 patients annually will have a hip fracture fixed surgically in England [3]. The older population account associated with spinal anaesthesia, notably less intraoperative hypotension, avoidance of neurologically active drugs and a possible reduction in early delirium [8].
Decisions regarding anaesthesia are taken on a case-bycase basis; current National Institute of Health and Care Excellence (NICE) guidelines state that patients should be offered the choice between general and spinal anaesthesia following a discussion on the respective benefits and drawbacks [9]. In practice, anaesthetist preference probably plays a central role in this decision-making.
Existing research in this area has not shown clinically significant differences in mortality and morbidity between spinal and general anaesthesia for hip fracture surgery. In part, this may be due to the problem of confounding by indication; people at higher risk of adverse outcomes may be more likely to get one form of anaesthesia than another.
Propensity score-matching is a statistical technique which aims to provide a quasi-experimental analysis where groups are similar across possible confounding factors. The aim of this observational study was to use propensity scorematching to investigate whether there was a clinically relevant difference in outcomes between spinal and general anaesthesia across the population.

Methods
The data were obtained from the Nottingham Hip Fracture and 2015 were included in the study. Patients who underwent epidural anaesthesia were not included. The nature and quality of these data have been described in detail in previous reports [10]. Comorbidities and outcomes are recorded based on the admission clerking and medical records.
The primary exposure was a dichotomy between general and spinal anaesthesia. General anaesthesia included those with and without regional nerve blocks.
Similarly, spinal anaesthesia included those with and without regional nerve blocks.
The postoperative outcome measures of morbidity were recorded if documented in the patient's notes by the treating clinician. Data regarding 30-day mortality are obtained and cross-referenced from hospital data, as well as data from the Office for National Statistics (ONS), as has been described previously [10]. Cross referencing hospital data with ONS data allows identification of all patients who have died in the community, or in other hospitals.
The primary outcome measure was 30-day mortality. These were patients with documented cardiovascular disease (pre-existing cardiovascular conditions including: previous myocardial infarction; ischaemic heart disease; atrial fibrillation; valvular heart disease; or hypertension) and chronic obstructive pulmonary disease (COPD) [11].

Results
In total, 8144 patients were included in the initial analysis, all of whom had a propensity score calculated (Fig. 1 , Figure 1 Flowchart to indicate inclusion/exclusion throughout the study.

Discussion
In this study, the mode of anaesthesia did not affect 30-or incorporating 2152 participants [14]. The same systematic review also found no difference in mortality at 3 months based on five studies and 953 participants [14]. This is concordant with another systematic review including 14 studies [15] and a large American study (> 50,000 patients) [16] that both showed that anaesthetic technique had no effect on 30-day mortality.  There are a number of potential explanations for this finding. It is possible a true relationship between spinal anaesthesia and requirement for postoperative blood transfusion exists. A study found that patients undergoing spinal anaesthesia for hip arthroplasty were 35% less likely to require a postoperative transfusion, and the authors postulated that spinal anaesthesia led to lower intraoperative blood pressure and therefore a reduction in blood loss [17]. However, the findings of the anaesthetic sprint audit of practice suggested that intra-operative arterial blood pressure was lower with general anaesthesia in patients having hip fracture surgery [6]. In addition, our results are concordant with a meta-analysis of 66 randomised controlled trials that found the mean difference of estimated blood loss to be 335 ml lower with spinal compared with general anaesthesia in a variety of surgical procedures [18]. It is also possible that a degree of residual confounding may have led to this finding as no data were available to match patients based on existing coagulopathy; this condition is a relative contra-indication to spinal anaesthesia, due to the increased risk of vertebral canal haematoma and subsequent spinal cord compression [19].
Given that patients with an existing coagulopathy have an increased likelihood of requiring a postoperative transfusion [20], and are also more likely to be deemed unsuitable for a spinal anaesthetic, it is possible that this had a confounding effect. which is notoriously unreliable. Positive dipstick tests in a patient who is catheterised may be ascribed less importance than if the patient was not catheterised.
We found that patients who received spinal anaesthesia were significantly more likely to suffer from DVT or PE postoperatively. A systematic review found no significant difference in the incidence of DVT when chemoprophylaxis was used [14], a practice which is now commonplace [23] and routine in our institution; however, the study did show that spinal anaesthesia increased the risk of postoperative PE although this was dependent on the type of statistical analysis performed [14]. It is possible that patients who were at greater risk of VTE (due to baseline risk or comorbidities reducing mobilisation) were more likely to be given spinal anaesthesia. There may, therefore, be support within the current evidence for an association between spinal anaesthesia and an We could not find any convincing evidence of this benefit.
As with all non-randomised studies, we cannot exclude residual confounding, particularly regarding severity of COPD.
There were limitations to this study which should be  [27,28]. Until routine data collection allows analysis of how anaesthesia was delivered, these questions are likely to remain unanswered. Finally, but perhaps most importantly, we may be simply measuring the wrong outcomes [29]. If clinical outcomes are unaffected by mode of anaesthesia, then addressing softer outcomes such as patient satisfaction, quality of life and operating theatre efficiency may be more important.
Despite these limitations, there is a major strength: with the power of an 8000-patient dataset, and data on a multitude of outcomes, we were unable to demonstrate clinicallyrelevant differences between modes of anaesthesia. For individual clinicians to state that his or her favoured technique is optimal based on incomplete data involving only tens or hundreds of patients is an unprovable claim.
There are four ongoing randomised controlled trials of spinal vs. general anaesthesia [30][31][32][33]. We await the results of these with interest. In the meantime, it would seem the decision to use a particular mode of anaesthesia for a patient undergoing hip fracture surgery is primarily based around patient choice and the inclinations of individual practitioners [34], rather than a standardised approach. We suggest that future research should be directed towards how anaesthesia is delivered, rather than mode of anaesthesia per se.