Local Instrumental Variable Methods to Address Confounding and Heterogeneity when Using Electronic Health Records: An Application to Emergency Surgery

Background

Electronic health records (EHRs) offer opportunities for comparative effectiveness research to inform decision making. However, to provide useful evidence, these studies must address confounding and treatment effect heterogeneity according to unmeasured prognostic factors. Local instrumental variable (LIV) methods can help studies address these challenges, but have yet to be applied to EHR data. This article critically examines a LIV approach to evaluate the cost-effectiveness of emergency surgery (ES) for common acute conditions from EHRs.

Methods

This article uses hospital episodes statistics (HES) data for emergency hospital admissions with acute appendicitis, diverticular disease, and abdominal wall hernia to 175 acute hospitals in England from 2010 to 2019. For each emergency admission, the instrumental variable for ES receipt was each hospital’s ES rate in the year preceding the emergency admission. The LIV approach provided individual-level estimates of the incremental quality-adjusted life-years, costs and net monetary benefit of ES, which were aggregated to the overall population and subpopulations of interest, and contrasted with those from traditional IV and risk-adjustment approaches.

Results

The study included 268,144 (appendicitis), 138,869 (diverticular disease), and 106,432 (hernia) patients. The instrument was found to be strong and to minimize covariate imbalance. For diverticular disease, the results differed by method; although the traditional approaches reported that, overall, ES was not cost-effective, the LIV approach reported that ES was cost-effective but with wide statistical uncertainty. For all 3 conditions, the LIV approach found heterogeneity in the cost-effectiveness estimates across population subgroups: in particular, ES was not cost-effective for patients with severe levels of frailty.

Conclusions

EHRs can be combined with LIV methods to provide evidence on the cost-effectiveness of routinely provided interventions, while fully recognizing heterogeneity.

Highlights

Effectiveness of emergency surgery for five common acute conditions: an instrumental variable analysis of a national routine database

The effectiveness of emergency surgery vs. non-emergency surgery strategies for emergency admissions with acute appendicitis, gallstone disease, diverticular disease, abdominal wall hernia or intestinal obstruction is unknown. Data on emergency admissions for adult patients from 2010 to 2019 at 175 acute National Health Service hospitals in England were extracted from the Hospital Episode Statistics database. Cohort sizes were: 268,144 (appendicitis); 240,977 (gallstone disease); 138,869 (diverticular disease); 106,432 (hernia); and 133,073 (intestinal obstruction). The primary outcome was number of days alive and out of hospital at 90 days. The effectiveness of emergency surgery vs. non-emergency surgery strategies was estimated using an instrumental variable design and is reported for the cohort and pre-specified sub-groups (age, sex, number of comorbidities and frailty level). Average days alive and out of hospital at 90 days for all five cohorts were similar, with the following mean differences (95%CI) for emergency surgery minus non-emergency surgery after adjusting for confounding: -0.73 days (-2.10-0.64) for appendicitis; 0.60 (-0.10-1.30) for gallstone disease; -2.66 (-15.7-10.4) for diverticular disease; -0.07 (-2.40-2.25) for hernia; and 3.32 (-3.13-9.76) for intestinal obstruction. For patients with 'severe frailty', mean differences (95%CI) in days alive and out of hospital for emergency surgery were lower than for non-emergency surgery strategies: -21.0 (-27.4 to -14.6) for appendicitis; -5.72 (-11.3 to -0.2) for gallstone disease, -38.9 (-63.3 to -14.6) for diverticular disease; -19.5 (-26.6 to -12.3) for hernia; and - 34.5 (-46.7 to -22.4) for intestinal obstruction. For patients without frailty, the mean differences (95%CI) in days alive and out of hospital were: -0.18 (-1.56-1.20) for appendicitis; 0.93 (0.48-1.39) for gallstone disease; 5.35 (-2.56-13.28) for diverticular disease; 2.26 (0.37-4.15) for hernia; and 18.2 (14.8-22.47) for intestinal obstruction. Emergency surgery and non-emergency surgery strategies led to similar average days alive and out of hospital at 90 days for five acute conditions. The comparative effectiveness of emergency surgery and non-emergency surgery strategies for these conditions may be modified by patient factors.

403 The Difficulties of Managing Trauma in Elderly Patients in a West of Scotland Trauma Unit

Aim

An increasing number of elderly patients require admission to Trauma & Orthopaedic units throughout Scotland with admissions often complex and lengthy. We aimed to assess the current standard of care within a west of Scotland trauma unit against the 2019 British Orthopaedic Associations Standard of Care (BOAST) - “The care of the older or frail orthopaedic trauma patient” and devise a multi-disciplinary quality improvement strategy.

Method

All patients over the age of 65 admitted to the Trauma & Orthopaedic department of the University Hospital Wishaw between the 1st-14th of August 2020 were included. Online medical records were assessed and compared to the BOAST guideline. Results were presented to Orthopaedic and Care of the elderly (COTE) team and postgraduate teaching before being re-audited from 1st-14th May 2021. Data was analysed using Chi- Squared test.

Results

Cycle one vs Cycle two:

Falls risk assessment was carried out in 50/57(87.7%) vs 49/57(86.0%); Nutritional assessment carried out in 53/57(93.0%) vs 50/57(87.7%); Delirium assessment carried out in 54/57(94.7%) vs 47/57(82.5%). More patients were reviewed by Acute Care of the Elderly nurses 24/57(42.1%) vs 30/57(52.6%). No significant improvement was seen in the percentage of patients reviewed by a COTE consultant:15/57(26.3%) vs 17/57(29.8%) (P = 0.68).

Conclusions

Both cycles show good concordance with the BOAST criteria, including physiotherapy reviews, falls and delirium assessment, however significant deficiencies exist, including the provision of COTE input. This has prompted a reconfiguration of orthogeriatric input for trauma patients, with significant investment in the recruitment of COTE medical staff.

Extra-thoracic, extra-meningeal solitary fibrous tumours - A case series and service review

BACKGROUND

Solitary fibrous tumours (SFT) are a type of mesenchymal tumour. Whilst the majority of cases follow an indolent course a significant proportion of patients suffer metastases or disease recurrence post-surgical excision. Due to the unpredictable clinical course follow up duration and intensity remains contentious.

AIMS

We aimed to determine current outcomes of management of this tumour, apply and assess current risk recurrence models to determine if our standard of care could be improved upon.

METHODS AND PATIENTS

A prospective database of patients treated at a regional musculoskeletal oncology service was assessed. Only extra-pleural, extra-meningeal SFTs were included in the study. Surgical outcome and post-operative investigations were scrutinised and the Pasquali and Demicco recurrence risk models were applied and assessed.

RESULTS

From 2009 to 2019 12 patients were identified, 8 female and 4 males. Their age at diagnosis ranged from 21 to 76 years. 11 patients underwent surgery with curative intent and no patient suffered disease progression or recurrence, with a mean follow up time of 41 months. One patient presented with metastatic disease and was managed palliatively.

CONCLUSIONS

Following this review of our case series and utilising risk recurrence models published in the literature we have changed our follow up protocol. In new cases of SFT the Pasquali prognostic model, with the addition of the presence or absence of necrosis, will be utilised. If a patient has benign features on initial biopsy we propose to not perform staging. Furthermore, if biopsy and final pathology results remain concordant, with no concerning features, and the patient has undergone complete excision reduced intensity follow up could be considered.Level of evidence Level IV, retrospective case series.