The global volume of surgery is large and growing, with approximately 312.9 million operations performed in 2012 [1]. Based mostly on in-hospital evidence, data suggest that up to 80% of patients experience pain after surgery, with over 70% of these patients describing their pain as moderate to severe [2,3]. With advances in surgical and anesthetic techniques and attempts to reduce costs and hospital-acquired morbidity, the duration of hospital stays after surgery continues to decrease [4,5]. In fact, it is estimated that ambulatory surgeries constitute over 60% of all surgeries in the United States, as well as in other countries [6-8]. Shorter hospital stays after surgery shift the onus of adequate pain management from the hospital staff to the patient and their family caregivers. However, discharge instructions provided to patients regarding pain management self-care may be inadequate, unclear, or forgotten by the patient, potentially explaining previous reports of higher pain levels (moderate to severe) following hospital discharge compared with time spent in hospital [4,9].

Adequate pain control after surgery is imperative for successful recovery, and poorly controlled pain can have devastating impacts on patients’ physical functioning, mental health, relationships, and productivity [10,11]. In addition to causing unnecessary suffering, the pain-induced release of catecholamines can cause cardiac complications such as myocardial ischemia and cardiac failure [12]. Pain can also result in chest and abdominal wall splinting, resulting in hypoxemia and alveolar collapse [12]. These complications are associated with an increased economic burden resulting from increases in readmissions, emergency room visits, and the workload of community staff [7,13]. Furthermore, undertreated acute postoperative pain increases the risk of developing chronic postsurgical pain (CPSP) [14,15]. CPSP is estimated to affect 10% to 40% of surgical patients, and given the growing burden of surgical diseases and global volume of surgery, the negative impacts of CPSP are large [16,17]. CPSP is similar to other chronic pain conditions and thus is associated with a severe symptom burden and large economic impact and requires a comprehensive multidisciplinary approach to treatment [18-20].

The goal of relieving acute postoperative pain after hospital discharge must be carefully balanced with the competing goals of managing the adverse effects of analgesic treatments and minimizing other risks, such as the development of persistent opioid use [17]. In addition to acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs), opioids are the mainstay of postoperative pain management [21]. As has been long recognized, adverse effects of commonly used nonopioid analgesics (eg, hepatoxicity with acetaminophen; bleeding, impaired bowel anastomosis healing, and renal toxicity with NSAIDs) necessitate careful prescribing and follow-up, and may limit their use and consequently their opioid-sparing effect [21]. With respect to postoperative opioids after hospital discharge, reports suggest that they are frequently prescribed in excess, with potentially inadequate instructions and prescriber follow-up [18,22]. This is particularly concerning given reports of high rates of persistent opioid use after surgery, even in opioid-naïve individuals [23-25]. In addition to these clinical concerns surrounding acute pain management, postsurgical patients may also experience surgical complications (eg, bleeding, and wound infection or dehiscence) and other postoperative cardiorespiratory problems. Since perioperative clinicians (eg, surgeons and anesthesiologists) are generally more focused on higher acuity in-hospital patient care and general practitioners may be uncomfortable managing complex postsurgical patients while they’re recovering at home, the early postdischarge postoperative period may be a vulnerable period, leaving patients’ pain inadequately managed.

Appropriate pain management for surgical patients after hospital discharge is of great importance. The majority of studies focusing on postoperative pain have been conducted on inpatients or ambulatory surgery patients before discharge, whereas the period after discharge appears to be much less investigated. Thus, we aim to perform a systematic review to investigate this period for patients in regard to postoperative pain to quantify the extent of this problem and identify future research needs.

The objective of this review is to synthesize the available evidence on the prevalence of moderate-to-severe postoperative pain within the first 1 to 14 days after hospital discharge and compare the findings in patients who underwent ambulatory surgery (same day) with those who underwent inpatient surgery (at least 1-night hospital stay). We will also describe the adverse outcomes that participants experienced that are attributable to poor pain control after hospital discharge, including readmission to hospital, emergency room or other unplanned medical visits, and decreased quality of life.

This protocol was developed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) checklist [26] (Multimedia Appendix 1) and has been registered in the PROSPERO database (registration number CRD42020194346). The systematic review will be carried out in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [27] and the Meta-analyses Of Observational Studies in Epidemiology (MOOSE) checklist [28].

We will conduct a detailed search on MEDLINE and EMBASE from their inception until the date the searches are run. The search will include terms relating to postoperative pain, the time frame following hospital discharge, and search filters for epidemiological studies. The search strategies for MEDLINE (Multimedia Appendix 2) and EMBASE (Multimedia Appendix 3) were developed in consultation with a librarian with expertise in literature searches. We will also review the bibliographies of any studies identified for relevance. We will not be contacting experts or searching the grey literature to identify additional studies.

The review will include postoperative pain epidemiological observational studies with postsurgical patients that assessed postoperative pain at home (ie, after hospital discharge). Studies with fewer than 100 participants will be excluded.

We will include studies with adults aged 18 years and over that underwent a surgical procedure.

Two trained reviewers (RP and MM) will independently evaluate studies for eligibility. Screening will be performed on titles and abstracts using Covidence software [29]. Citations will be stored in EndNote software (Clarivate Analytics). Full-text screening will be performed on citations felt to be potentially eligible. Disagreements between reviewers will be resolved by discussion and consensus, and if necessary, a third reviewer will be consulted (IG). The screening and selection process will be presented using a PRISMA flowchart, and reasons for exclusion will be reported.

Data from included studies will be extracted using standardized extraction forms specifically designed for this review. These forms will capture information about the surgical procedure (eg, total knee arthroplasty), total number of participants before and after dropouts, patient inclusion and exclusion criteria, patient characteristics (eg, age, medical diagnoses), time points for pain intensity measurements, primary and secondary outcome measures, and other study characteristics (eg, date of publication).

Our primary outcome will be the proportion of patients reporting moderate-to-severe postoperative pain at rest or with movement, or both, within the first 1 to 14 days after hospital discharge. We chose this time frame because the first couple of weeks after surgery are most commonly associated with pain of the highest severity and most functional consequences [30,31]. We will preferentially use 4/10 (numerical rating scale), 40/100 (visual analog scale), or ≥moderate pain (category scale) as the bottom threshold for moderate pain. However, if those specific data are not available and if a study provides pain prevalence estimates using their own definition of moderate pain, we will use those data as provided.

Our secondary outcomes will include the following: (1) a comparison of the proportion of participants reporting moderate-to-severe postoperative pain within the first 1 to 14 days after discharge between those who underwent ambulatory surgery (same day) and those who underwent inpatient surgery (at least 1-night hospital stay); and (2) adverse outcomes experienced by participants within the first 1 to 14 days after discharge that are attributable to poor pain control, including readmission to hospital, emergency room or other unplanned medical visits, and decreased quality of life.

Only similar studies (eg, similar surgical procedures, similar postoperative days, and outcomes measured) will be combined for analysis in order to avoid clinical heterogeneity. Extracted data will be compiled in Microsoft Excel for analysis. Analysis will be performed using Review Manager (RevMan) software (version 5.3; The Nordic Cochrane Centre, The Cochrane Collaboration). We plan to use a random-effects model for meta-analysis for primary and secondary outcomes if it is deemed appropriate to combine heterogenous studies.

If inappropriate to combine studies, a descriptive approach will be used to report the primary and secondary outcomes. The findings will be organized and presented by type of surgical procedure.

Risk of bias for each study will be independently assessed by 2 reviewers (RP and MM). We will use the risk-of-bias tool for prevalence studies developed by Hoy et al [32], which includes 10 items plus a summary assessment (Multimedia Appendix 4). Items 1 to 4 assess the external validity of the study, and items 5 to 10 assess the internal validity. Disagreements between reviewers will be resolved with discussion and consensus. If necessary, a third reviewer (IG) will be consulted.

Heterogeneity will be evaluated using the I² statistic. When the I² value is higher than 50%, we will consider possible explanations for it.

We plan to conduct a sensitivity analysis where we combine data from all studies that focused on any degree of postoperative pain after discharge rather than only the studies that focused on moderate-to-severe pain.