Patients with COVID undergoing hip fracture repair have high mortality rates. If spinal anesthesia is associated with decreased rates of mortality, this study could provide hypothesis generating data for prospective studies. Investigators hypothesize that spinal anesthesia (SA) is associated with decreased mortality compared to general anesthesia (GA) for patients undergoing hip fracture surgery. The primary objective is to determine for patients undergoing hip surgery with COVID-19 infection, whether SA, as compared to GA, is associated with a lower rate of mortality 30 days postoperatively. The secondary objective is to determine whether SA, as compared to GA, is associated with a lower rate of morbidity 30 days postoperatively. Investigators will be analyzing a data set provided by the National Surgical Quality Improvement Program (NSQIP). Descriptive statistics will be performed. Multivariable logistic regression will be performed for the primary and secondary objectives.

Background: Patients with hip fracture have poor outcomes, attributed to risk factors that include advanced age and higher rates of underlying chronic comorbidities. COVID-19 infection is an independent risk factor for increased mortality in hip fracture patients in the perioperative period. A recent meta-analysis demonstrates COVID-19 infection is associated with higher than seven-fold increase in risk of mortality. Recommended management of hip fracture includes timely surgical repair, multimodal pain control, and multidisciplinary follow-up, to facilitate return to mobility and independent function.

Anesthesia for hip fracture surgery can be achieved by either general anesthesia (GA) or spinal anesthesia (SA). The potential advantages of SA include opioid-sparing effects, lessened impacts on the respiratory and gastrointestinal systems, and reduction in rates of adverse outcomes such as pneumonia, mechanical ventilation, intensive care unit (ICU) admission, venous thromboembolism (VTE), myocardial infarction (MI), stroke, transfusion, readmission, and prolonged postoperative length of stay. However, a recent randomized control trial found no difference between SA and GA for older adults undergoing hip fracture surgery for the primary outcome of survival and recovery of ambulation at 60 days.

While emerging evidence shows COVID-19 infection increases mortality after hip surgery, there is a lack of research examining whether the choice of anesthetic technique modifies the postoperative mortality and morbidity of hip fracture patients with COVID-19 infection. This is particularly important due to the high mortality (35% in COVID-positive patients, vs. 2% in patients without COVID), with the potential for SA to modify this risk by circumventing the need for airway interventions. SA may also offer superiority over general anesthesia for limiting aerosol generation and exposure of operating room staff during the pandemic. While SA may reduce the risk of pulmonary morbidity by reducing the need for airway interventions, its motor block on accessory muscles and the need for sedation may adversely impact ventilation. Investigators hypothesize that spinal anesthesia (SA) is associated with decreased mortality compared to general anesthesia (GA) for patients undergoing hip fracture surgery.

Study Design: The requirement for written informed consent will be waived for use of deidentified data. Patient information will be obtained for the retrospective cohort analysis using the NSQIP® (general dataset linked with the Hip Fracture Procedure Targeted Dataset), a prospectively-collected multicentre dataset with more than 150 clinical variables within 30 days after surgery. The setting of this study will be patient data obtained from the multicentre generated NSQIP Hip Fracture Procedure Targeted Dataset. The period of patient data obtained will include from January 2017 through December 2021. We will omit the data from January 2020 to December 2020 given there was no reporting of COVID status during this period. Data will only be obtained from patients undergoing hip surgery with mortality and morbidity gathered for 30 days postoperatively. In this study, the investigators goal is to evaluate the adjusted association between anesthesia technique and mortality and morbidity after hip fracture surgery for patients who tested positive for COVID-19.

The primary objective is to determine for patients undergoing hip surgery with COVID-19 infection, whether SA, as compared to GA, is associated with a lower rate of mortality 30 days postoperatively.

Our secondary objective is to determine whether SA, as compared to GA, is associated with a lower rate of morbidity 30 days postoperatively. To provide context for interpretation, we will describe the epidemiology of the following rates during versus before the 2020 COVID-19 pandemic (January to December 2021, compared to 2017 to 2019): 1) SA versus GA uti-lization for hip fracture surgery, and 2) mortality and morbidity for hip surgery patients without COVID-19 infection. Finally, we will quantify the mortality and morbidity for pa-tients with versus without COVID-19 infection undergoing hip fracture surgery, stratified by SA and GA.

Purpose: The purpose of this study is to evaluate the adjusted association between anesthesia technique and mortality and morbidity after hip fracture surgery

Population cohorts: The study will be divided into three cohorts: those undergoing hip surgery 1) without COVID-19 infection January to December 2021, 2) with COVID-19 infection January to December 2021, and 3) pre-pandemic from January 2017 to December 2019.

Due to the variable duration of asymptomatic period that can precede symptoms and diagnosis, COVID-19 infection status will be classified as follows.

In the primary analysis, COVID-negative patients will be defined as no preoperative COVID (within 14 days before surgery) and no postoperative COVID, and COVID-positive patients will be defined as yes (lab-confirmed) preoperative COVID and no postoperative COVID. In NSQIP, preoperative COVID status denotes within 14 days be-fore surgery, and patients with preoperative COVID are always coded "No" for postopera-tive COVID. NSQIP does not have previous history of COVID prior to 14 days, which is a major limitation given the increased mortality of patients with recent COVID undergoing surgery (24).

In NSQIP, preoperative COVID status denotes within 14 days before surgery, and patients with preoperative COVID are always coded "No" for postoperative COVID. NSQIP does not have previous history of COVID prior to 14 days, which is a major limitation given the increased mortality of patients with recent COVID undergoing surgery.

As patients with postoperative COVID-positive status are difficult to interpret due to variable incubation period and the possibility of COVID-19 contraction while in hospital postoperatively, investigators will perform sensitivity analysis using alternative definitions for the COVID-positive cohort, including 1) laboratory confirmed preoperatively or postoperatively, 2) laboratory confirmed or symptomatic preoperatively, and 3) suspected and laboratory confirmed anytime preoperatively or postoperatively).

Data analysis: Investigators will be analyzing a data set provided by the National Surgical Quality Improvement Program (NSQIP). Descriptive statistics will be performed. Multivariable logistic regression will be performed for the primary and secondary objectives.

Inclusion Criteria:

• Sampled in the NSQIP Hip Fracture Procedure Targeted Dataset from January 2017 through December 2019 and from January 2021 to December 2021.
• undergoing surgical fixation of hip fractures using either general and/or spinal anesthesia.
• In case of reduced Procedure-Targeted data collection during the COVID-19 pandemic, investigators will also create a total open hip fracture cohort using relevant Current Procedural Terminology codes (27244, 27245, 27269, 27236, or 27248)

Exclusion Criteria:

• Primary or secondary anesthetic technique listed as local anesthesia alone, local anesthesia with intravenous sedation, epidural, and those with no reported anesthesia technique
• American Society of Anesthesiologists (ASA) Physical Status (PS) V (defined as "5-Moribund"), and
• Ventilator-dependence preoperatively.
• Platelet counts less than 80,000/mm3 within 90 days before surgery,
• International normalized ratio (INR) greater than or equal to 1.5, or
• Partial thromboplastin time (PTT) greater than 35 seconds (likelihood of being ineligible for SA)

The study will include all patients 19 years or older who are sampled in the NSQIP Hip Fracture Procedure Targeted Dataset from January 2017 through December 2019 and January 2021 to December 2021 undergoing surgical fixation of hip fractures using either general and/or spinal anesthesia.