Introduction
Discussion
References

 

 

 

 

 

 

 

Introduction

It is estimated that there are 70,000-75,000 fractured neck of femurs sustained in the UK every year. Around 10% of these patients will die within one month and around one third will die within one year.1, 2

Alongside an increased risk of mortality and physical morbidity, there are a large number of patients every year that are admitted with a fractured neck of femur that have an intercurrent diagnosis of cognitive impairment or dementia. Indeed, dementia is a recognised risk factor for hip fracture3 and it has been shown that cognitive limitations increases the risk of morbidity and mortality in such patients who fracture their hip.4, 5

It would, therefore, seem logical to try and limit any potential iatrogenic causes that may induce or worsen cognitive impairment. Berggren et al described that post-operative confusion was as prevalent as 44% of elderly patients after surgery for fractured neck of femur,6 with other studies suggesting the incidence of post-operative cognitive impairment in elderly patients for any surgery in general is around 37%.7 However, the incidence may be even higher with some studies suggesting that post-operative cognitive dysfunction (PCOD) is underdiagnosed by nurses and clinicians.7

Despite this association it still remains unclear if anaesthesia plays a role in the onset of cognitive impairment8 in post-operative patients. There is some literature available supporting the notion that general anaesthesia can be a predisposing factor for post-operative cognitive impairment9 with a meta-analysis by Mason et al also advocating use of regional anaesthesia over general anaesthesia due to this potential increased risk of PCOD, but they
identified no obvious link with development of post-operative delirium.10

Anaesthetists may base their choice of anaesthesia for fractured neck of femur surgery, partially, on the patients cognitive state, avoiding general anaesthetic where possible in patients with impairment. However, the literature on the matter appears at times contradictory with multiple studies stating that the use of general anaesthesia has, in fact, no effect on PCOD.11-15 One paper has even stated that, by reducing the ‘surgical stress’ of an operation by undergoing general versus regional anaesthesia, that general anaesthesia may actually provide a neuroprotective effect in the post-operative period.16

A systematic review performed by Davis et al found that three studies they analysed showed a difference in cognitive function between regional anaesthesia, whilst 13 did not.17

There are multiple potential mechanisms by which general anaesthesia has been thought to cause or worsen cognitive impairment, including; oligomerization and cytotoxicity of amyloid peptides18, 19 increasing tau protein phosphorylation20 and altering transmission of neurotransmitters.21, 22

In addition, studies have looked at whether anaesthetic type has an impact on clinical outcomes, including length of stay and mortality, with no differences found between differing types of anaesthesia.23, 24

The aim of this study was therefore to assess whether anaesthesia, specifically the use of ‘general anaesthesia’ versus ‘no general anaesthesia,’ had an impact on cognitive dysfunction given the inconsistent nature of the current literature.

The method and results of the study are covered in further detail in the first part of this article published in the May edition, available online here.

 

Discussion

This study looked at, primarily, the relationship between the use of general anaesthetic or alternative anaesthesia and change in abbreviated mental test score (AMTS), calculated from their pre and post-operative AMTS. This was used as a proxy for presence of POCD.

The change in AMTS was not statistically significantly different for the group that received a general anaesthetic versus the group that did not.

Finally, this study looked at whether operation type influenced the choice of anaesthesia that patients received. The authors note a statistically significant difference in whether patients received a general anaesthetic, or not, based on their operation type. Patients were more likely to receive ‘no general anaesthetic’ if they were having an arthroplasty procedure (Hemiarthroplasty/total hip replacement) and more likely to receive a ‘general anaesthetic’ if they were having a fixation procedure (cannulated screws/dynamic hip screw/intramedullary nail).

To ascertain why this was the case the study went on to look at potential differences between the different operative groups. Looking at pre-operative AMTS (as an anaesthetist would only be able to speculate as to the potential for AMTS change pre-operatively when deciding on anaesthetic) and operation type received, there was statistically significant difference between groups, with the hemiarthroplasty group having the lowest mean of ranks value, indicative of lower pre-operative AMTS and hence increased prevalence of preoperative cognitive impairment in this group. This suggests, patients in the hemiarthroplasty group are preferentially having ‘no general anaesthetic’ based on this increased prevalence of pre-operative cognitive dysfunction, for those requiring a hemiarthroplasty.

The authors recognise that patients in the total hip replacement group would unlikely receive their anaesthetic type because of concerns around pre-operative cognitive impairment. This is because one of the requirements for them being eligible for this operation is no significant pre-existing cognitive impairment.1 They are, hence, more likely to receive ‘no general anaesthetic’ for another reason and literature would suggest this may be due to its perceived use for anaesthesia as well as analgesia.25 However, even when the total hip replacement  group were removed, a sub analysis still showed a statistically significant difference.

 

Table 1 – Statistical analysis for comparison of pre-operative AMTS for each operation type

Analysis of pre-operative AMTS and subsequent operation type
Category Mean of Ranks

Hemi

656.3

THR

896.0

Cannulated screws

861.3

DHS

675.1

IM nail

732.1

p=0.000021

 

The strengths of this retrospective cohort study are its sample size and the objective measurement of ‘change in AMTS’ used. The authors believe that this is a more objective measure of change in a patient’s cognition between the pre and post-operative period and also allows for homogenicity as the overall change in AMTS negates the differences in patients pre-existing cognitive dysfunction. Numerous other publications often use DSM criteria for diagnosis of post-operative delirium or cognitive dysfunction, with no account of inter or intra observer variability when making these diagnoses.11, 26

The authors do, however, recognise one of the major limitations of this study, which is, that there was no way of identifying, whether patients, in the ‘no general anaesthesia’ group, had any sedative or opiate medications that may have had implications with respect to the patients cognitive function. Indeed, it has been identified that benzodiazepines, opioids, dihydropyridines and antihistamines may all result in cognitive dysfunction in elderly patients and some of these may be used in such patients.27

Moreover, there is evidence to suggest that the use of lighter sedation alongside a spinal anaesthetic results in less PCOD than with larger doses.28 Alongside this, the study was performed at a single site and there were no standardised protocols for differing types of anaesthesia, particularly poignant when looking at the ‘general anaesthesia group,’ where the potential for specific drugs to result in PCOD could not be identified.

The authors also recognise that AMTS is not the most robust way to measure the presence of cognitive impairment, but there is currently nothing else available in the National Hip Fracture Database (NHFD) that records pre and post operative cognitive function. We feel that, further data collection around this area would be beneficial for investigating the link between anaesthetic type and development of POCD in the future. We hope this paper would encourage and facilitate discussion around data collection for the NHFD to ensure we are gathering sufficient information on our patients.

The findings within this study seem to differ with those found in some similar studies,29, 30 but there are others that report similar findings11-13 and the authors note that the literature around this topic can appear, somewhat, inconsistent.

This study would support the hypothesis that type of anaesthesia does not significantly effect PCOD, when considering this with respect to change in AMTS. Despite this, patients appear to be having their anaesthetic type influenced by the presence of pre-existing cognitive impairment.

           

Table 2 – Statistical analysis for comparison of ASA for each operation type

ASA Operation Type and ASA        
 

Hemi

THR

Cannulated screws

DHS

Nail

 
1

6
8.80
( 0.89)

0
0.64
( 0.64)

2
0.45
( 5.40)

10
7.34
( 0.96)

1
1.77
( 0.34)

19

2

101
109.77
( 0.70)

14
7.99
( 4.53)

11
5.57
( 5.29)

92
91.57
( 0.00)

19
22.10
( 0.44)

237

3

377
364.51
( 0.43)

23
26.52
( 0.47)

13
18.50
( 1.64)

299
304.07
( 0.08)

75
73.40
( 0.04)

787

4

106
106.99
( 0.01)

6
7.78
( 0.41)

4
5.43
( 0.38)

91
89.25
( 0.03)

24
21.54
( 0.28)

231

5

1
0.93
( 0.01)

0
0.07
( 0.07)

0
0.05
( 0.05)

1
0.77
( 0.07)

0
0.19
( 0.19)

2

 

591

43

30

493

119

1276

X2  =  23.320,     df  =  16,    X2/df  =  1.46 ,         p  =  0.1054

* 1 patient in each group was listed as “other” – operation not known

expected values are displayed in italics

individual X2 values are displayed in (parentheses)

 

The authors recognise, however, that there are other potential factors that could have influenced the results of this study and others looking at similar outcomes, largely the lack of rationalisation to specific protocols for comparing groups and not identifying which patients may have had exposure to other medications that may result in cognitive impairment. This paper is intended to show that there is no difference between anaesthetic types and that there is insufficient data collected which may be inappropriately influencing findings.

For this reason, the authors feel there is a role for a prospective randomised control trial. Within such a study, a standardised assessment tool could be used prospectively to identify, via multiple methods (which could include change in AMTS and DSM diagnostic criteria), the presence of PCOD and delirium, allowing for better capture of post-operative problems.

A prospective study would also allow for comparable use of anaesthesia and medications,
and allow for some control of medication effects within in each group, hence facilitating better comparison of potential risk factors for development of PCOD.

In addition to this, the study reveals that, the data in the NHFD is useful for such retrospective analysis’ as performed in this study, but it also suggests that there are some deficiencies in data collection, specifically around the nature of anaesthetic and perioperative drugs patients are receiving. The authors, therefore, feel that increasing the amount of data captured in NHFD should be considered, using additional proforma collection tools. A prospective study at a local or regional level may be useful as a pilot in potentially instigating change in the acquisition of data in this area.

 

Mark Sohatee, County Durham and Darlington NHS Foundation Trust, University Hospital of North Durham

Hannah Wilkinson, County Durham and Darlington NHS Foundation Trust, University Hospital of North Durham

Andrew Gower, County Durham and Darlington NHS Foundation Trust, University Hospital of North Durham

 

Conflict of interest: None declared

Acknowledgements: Helen Brar – Consultant Anaesthetist, County Durham and Darlington NHS foundation trust, University Hospital of North Durham who reviewed the paper prior to submission/advisor around writeup content from anaesthetic perspective.

 


References

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