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Am J Obstet Gynecol. 2019 Jul 13. pii: S0002-9378(19)30902-0. doi: 10.1016/j.ajog.2019.07.018. [Epub ahead of print]

Risks of pre-operative anemia in women undergoing elective hysterectomy and myomectomy

Murji A¹, Lam M², Allen B², Richard L², Shariff SZ², Austin PC³, Callum J⁴, Lipscombe L⁵.

^{1 Department of Obstetrics and Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada. Electronic address: ally.murji@sinaihealthsystem.ca.}

^{2 ICES Western, London, Ontario, Canada.}

^{3 Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; ICES Toronto, Toronto, Ontario, Canada.}

^{4 Department of Laboratory Medicine and Molecular Diagnostics, Sunnybrook Health Sciences Centre and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.}

^{5 Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada; ICES Toronto, Toronto, Ontario, Canada; Department of Medicine, Women’s College Hospital, Toronto, Ontario, Canada.}

Abstract

BACKGROUND: Hysterectomy is one of the most common surgeries performed worldwide. Identification of modifiable risk factors for complications or re-admissions could lead to targeted interventions to improve patient care and reduce healthcare costs. Pre-operative anemia has been identified as a risk factor for adverse post-operative outcomes following non-cardiac surgery. However, studies have not focused on young and healthy surgical populations, such as women undergoing gynecologic surgery for benign indications.

OBJECTIVE(S): The purpose of this study was to evaluate if pre-operative anemia in women undergoing elective hysterectomy or myomectomy for benign indications was associated with increased 30-day post-operative morbidity and mortality.

STUDY DESIGN: In this retrospective population-based cohort study, we followed adult women (≥18 years of age) who underwent elective hysterectomy or myomectomy (laparoscopic/laparotomy) between the years 2013 and 2015 for benign indications in Ontario, Canada. We used linked administrative data from a government administered single-payer provincial healthcare system using Canadian Classification of Health Interventions (CCI) intervention codes, International Classification of Diseases 10^th Revision (ICD-10) diagnostic codes, physician billing codes and laboratory data from both community and hospital laboratories across the province. Our exposure of interest was pre-operative anemia, defined as a hemoglobin value <12g/dL on the complete blood count measured closest to the date of surgery. Our primary outcome was the composite of 30 day post-operative morbidity and mortality. Secondary outcomes, were five individual components of the primary outcome: death, transfusion, surgical site infection, veno-thromboembolism, and return to hospital within 30 days. To adjust for confounding, we generated a propensity score using a multiple logistic regression model in which the presence of anemia was regressed on all baseline characteristics. We matched anemic to non-anemic patients on the logit of the propensity score. Using an unadjusted log-binomial model estimated using generalized estimating equations (GEE) to account for the matched pairs, we calculated the relative risk (RR), 95% confidence intervals (CI) and p-values to evaluate the effect of anemia on outcomes.

RESULTS: Of the 16,218 women in the cohort, 3,664 (22.6%) had anemia. After propensity matching, standardized differences in all baseline characteristics (N=3,261 per group) were <0.10. In the matched cohort, the primary outcome (death, complications, or re-admission) occurred in 41.2% of anemic patients and 36.2% of non-anemic patients (RR 1.14, 95%CI 1.07 – 1.21, p<0.0001; absolute risk reduction (ARR) 5.03%, 95%CI 2.70 – 7.36; number needed to harm (NNH)=20). The risk of transfusion was significantly higher in anemic patients (RR 3.25 95%CI 2.67 – 3.95, p<0.0001; ARR 8.34%, 95%CI 7.06 – 9.63; NNH=12). There was no difference in other secondary outcomes. In a subgroup analysis (women >55 years versus ≤55, N=736), older women were at increased risk of the primary outcome (RR 1.40, 95%CI 1.12-1.76, p=0.004), transfusion (RR 4.20, 95%CI 1.65-10.72, p=0.003), surgical site infection (RR 1.35, 95%CI 1.01-1.81, p=0.04), and return to hospital (RR 2.36, 95%CI 1.54-3.62, p<0.0001).

CONCLUSION(S): Pre-operative anemia in women undergoing elective hysterectomy/ myomectomy was common and is an independent risk factor for 30-day post-operative adverse outcomes, especially in older women.

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