This observational cohort study studies two aspects of perioperative depression.

First, it examines the postoperative morbidity and mortality among patients with preoperative depression.

Secondly, in a subset of patients without signs of preoperative depression, the investigators describe the riskfactors for development of de-novo postoperative depression.

BACKGROUND With over 300 million surgeries performed yearly, the impact of perioperative morbidity weighs heavily on society[1]. Multiple studies have highlighted cardiac-[1], renal-[2], pulmonary-[3] and neurological complications[4] as well as other compound metrics of outcome.[5] Postoperative complications, if survived, sometimes result in major impact on function and quality of life.[6] Whilst somatic complications after major surgery are being increasingly investigated, the research field has scarce data on psychological outcomes such as postoperative depression. Most studies use specific surgical cohorts. These include studies of meningioma surgery[7] and glioma patients[8]; both with elevated risk of postoperative depression. In contrast, no significant difference in antidepressant use was found after vestibular schwannoma surgery.[9] When comparing spinal surgery to coronary artery bypass grafting, hysterectomy, cholecystectomy, chronic obstructive pulmonary disease, congestive heart failure exacerbation, and uncomplicated vaginal delivery, the former had the highest risk for postoperative depression.[10] Etiology of major depressive disorder (MDD) is poorly understood, and diagnosis is difficult.[11, 12] Many who experience a first episode of MDD will go on to suffer from recurrent episodes.[13, 14] When compared to equally disabling somatic disorders treatment for depression is less prevalent, indicating under-treatment of the condition.[15] Additionally, individuals with MDD are at elevated risk of cardiovascular disease and all cause-mortality.[16]

HYPOTHESIS The investigators hypothesize that surgery is a stressful event, potentially triggering depression. The investigators further hypothesize that in selected high-risk patients, postoperative new-onset depression is more common and potentially avoidable.

METHODS The investigators plan to use perioperative data from the surgical planning tool, Orbit. The Orbit cohort at Karolinska University Hospital in Solna and in Huddinge, two separate large university hospitals includes Swedish personal identity number (PIN), patient demographics, American Society of Anesthesiologists (ASA) physical status classification, type, date and duration of anesthesia and surgery. NOMESCO classification can be used to subgroup surgical procedures into sixteen categories; neuro, endocrine, ophthalmic, ear, nose and throat, oral and maxillofacial, cardiac, vascular, thoracic, breast, gastrointestinal, urologic, gynecologic, obstetric, orthopedic, dermatologic and minor surgery. The Orbit cohort is cross-matched with electronical medical records (EMR) allowing us to characterize the patients in the cohort based on pre- and postoperative ICD-codes (diagnoses, co-morbid conditions) and pre- and postoperative ATC-codes (medications). Hospital length of stay, readmissions and dates of death can also be retrieved from the EMR.

By merging Orbit data with EMR-data as described above it effectively allows us to investigate short- and long-term outcome for patients developing (new-onset) postoperative depression; this can be achieved by removing patients with depression diagnoses (using ICD-codes from the EMR) and/or patients with collected antidepressants (using ATC-codes from the EMR) in the years prior to surgery. What is the short- and long-term mortality for these patients? How do they far in terms of overall morbidity and health care utilization? The investigators can also characterize the short- and long-term outcome for patients with preoperative depression, focusing specifically on the patients excluded in the study two. How do these patients fare in term of risks for mortality, morbidity and health care utilization?

Inclusion Criteria:

*Adult patients (18 years or older) undergoing surgery at Karolinska University Hospital in Solna or in Huddinge

Exclusion Criteria:

*Patients under the age of 18.

This cohort is fully comprised of adult patients undergoing surgery at Karolinska University Hospital in Solna or in Huddinge

Individual participant data, may be shared to researchers that provide a methodological sound proposal