1 Introduction

Postoperative pain management is a crucial part of surgical care, directly influencing patient recovery and outcomes. In Brazil, healthcare disparities [1, 2] may impact postoperative results, making it essential to explore the role of opioids in this setting. Despite being the primary analgesic for surgical pain [3], opioids are consumed at lower rates [4] in Brazil compared to developed countries. This discrepancy highlights the need to investigate the effects of opioid use on patient recovery, particularly in economically and healthcare-constrained environments.

Our study, conducted at the University Hospital Onofre Lopes (HUOL) in Natal, Brazil, examines how opioid use affects the length of hospital stay and mortality rates among post-surgical patients. These indicators are critical for assessing the implications of opioid management on recovery and safety [5, 6]. By examining these factors, we aim to provide insights that can inform the development of improved pain management protocols.

2 Methods

2.1 Study design and population

This is a transverse observational study, which included participants aged 18 years or older who underwent abdominal surgery between January 1st and December 31st, 2023. Eligibility extended to patients treated by surgical teams specialized in general, gastrointestinal, or oncologic surgery and who had undergone either general or regional anesthesia. Patients who died during surgery and those who remained hospitalized at the end of data collection period were not included in the study.

Our primary aim was to delineate the epidemiological profile of opioid usage among patients undergoing surgery during the year 2023 and any impact on the convalescence period.

We used the STROBE cross sectional checklist when writing our report [7].

2.2 Data collection

We systematically gathered data from medical records, starting from the immediate postoperative period up to the point of medical discharge. This data collection included detailed records of analgesic therapy such as the types of opioids prescribed, the duration of opioid usage, daily dosages, and the use of any adjuvant analgesic drugs. We also recorded demographic and epidemiological information, including the patient's sex, age, and the surgical team involved.

2.3 Statistical analysis

We performed statistical analyses using JAMOVI software. Specific statistical tests are detailed in the table legends. Continuous variables were tested for normal distribution and summarized using means, standard deviations, medians, and interquartile ranges as appropriate. Categorical data were expressed as frequencies and percentages. Associations between opioid use and various patient characteristics were evaluated using logistic regression models, adjusting for potential confounders identified in the preliminary analysis.

3 Results

3.1 Characteristics of participants

Eligibility criteria returned 406 entries with abdominal surgeries. Three patients were excluded for being under 18 years old, five were excluded for being hospitalized when the data collection period ended and 13 refused to participate. Thus, we analyzed opioid consumption among 385 surgical patients at the HUOL throughout 2023 (Table 1). The cohort was predominantly female (61.2%) with 43.4% aged 41–60 years. Detailed demographic characteristics are provided in Table 1, which includes distributions by sex, age, and type of surgery. The general surgery team performed the largest portion of surgeries (41.3%), predominantly prescribing tramadol as the most robust analgesic during recovery. The median duration of hospital stay was two days, with an interquartile range of 5 days.

Table 1 Patient demographic characteristics
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3.2 Opioid usage analysis

A significant majority of the patients (89.6%) used opioids during their postoperative hospital stay (Table 1). Tramadol was overall the most frequently administered opioid, followed by nalbuphine and morphine. A small subset of patients (10.4%) did not receive any opioids.

In the analysis of daily opioid requirements (Table 2), we observed that the morphine dosage varied significantly by age, with older patients aged 61–94 requiring higher doses (median 10 mg, range 3–12 mg) compared to other age groups (p = 0.01). There were no significant differences in nalbuphine and tramadol dosages across genders, with medians around 80 mg morphine equivalent (MME) (range 36.2–160 MME) for nalbuphine and 60 MME (range 60–80 MME) for tramadol. Regarding surgical type, bariatric surgery patients required the lowest median morphine dose at 4 mg, while the same group needed higher tramadol doses, consistently at 80 MME. Conversely, oncological surgery was associated with the lowest nalbuphine doses (median 30 MME, range 30–40 MME), significantly lower than those for gastrointestinal surgeries (p < 0.001). These findings indicate distinct opioid requirements based on patient age and type of surgery, suggesting the need for tailored pain management approaches.

Table 2 Daily opioid dose
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3.3 Hospital stay and opioid use

The length of hospital stay varied significantly depending on the type of opioid used (Table 3). Patients treated with morphine had a notably longer median stay (15.5 days) compared to those who received weaker opioids like nalbuphine or tramadol (2 days). However, the variation in hospital stay between patients receiving weaker opioids and those not receiving any opioids was not statistically significant.

Table 3 Hospital length of stay (LOS)
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Furthermore, linear regression revealed significant associations between opioid type and length of hospital stay (Table 3). Specifically, each additional milligram of morphine administered was associated with a nearly 7-h increase in hospital stay. Patients older than 50 experienced a hospital stay 28% longer than those younger than 50.

3.4 Mortality

There were 14 instances of mortality. The logistic regression analysis identified 3 predictors of increased mortality risk with statistical significance. In our analysis, morphine use was significantly associated with increased mortality risk (odds ratio [OR] = 16.85, standard error [SE] = 0.831, 95% confidence interval [CI]: 3.30–85.91, p < 0.001). For every additional day of hospitalization, the odds of mortality increased by 6.4% (OR = 1.064, SE = 0.022, 95% CI: 1.019–1.110, p = 0.005). Additionally, patients above the median age of 50 years were 8.23 times more likely to die compared to those below the median age (OR = 8.23, SE = 0.910, 95% CI: 1.38–48.92, p = 0.021).

4 Discussion

Our analysis reveals that administering opioids, specifically morphine, significantly prolongs hospital stay. Patients treated with morphine experienced notably longer median stays compared to those receiving weaker opioids like nalbuphine or tramadol. This finding is consistent with other studies [8, 9] that have reported both chronic and sporadic opioid use during hospitalization being associated with increased duration of stay and a higher number of readmissions within 30 days.

Prolongation of hospital length of stay (LOS) linked to opioid use stems from a range of morbid effects associated with these substances. Impacts on the immune system [10] and an elevated predisposition to acute infectious diseases [11,12,13] have been reported. Furthermore, opioids are associated with extended durations in intensive care stay, including delayed extubation times, as seen in previous studies [14].

Logistic regression analysis has shown that morphine use significantly increases mortality rates, indicating a critical need for careful opioid prescription. The academic debate on this association remains unresolved, with some studies confirming our results [15] and others reporting no such link [16,17,18]. Factors such as underlying health conditions, the reasons for opioid prescriptions, and treatment management are significant contributors that might confound direct associations with mortality. Regarding LOS, the data demonstrated a dose-dependent relationship between morphine administration and a substantial increase in LOS, along with additional factors such as advanced age that may influence recovery time and the need for extended care.

The increase in LOS associated with morphine use compared to weaker opioids is multifactorial. Patients requiring higher doses or more potent analgesia likely had a broader clinical background, necessitating longer assistance time [19, 20]. With respect to age treatments are more complex in older patients. This population typically presents a higher incidence of comorbidities and physiological changes that impact drug effects. Increased consumption or use of more potent opioids by older patients is hazardous, as this population often has reduced hepatic and renal function, leading to prolonged drug circulation and decreased blood volume, concentrating the dose in a smaller volume of blood [19, 20].

In addition, research indicates that endogenous opioids are essential for pain modulation and stress responses. Furthermore, gonadal steroid hormones, particularly estrogen, are associated with reduced pain during periods of elevated blood concentration [21]. The complex pain signaling cascade begins in the spinal cord, ascends to the cortex, and involves various neural components, such as neurons, microglia, inflammatory reactions, and neurotransmitters [22]. A higher consumption among women was expected, given that this cascade performs differently between males and females, as men are less sensitive to pain and respond more intensely to opioids than women [22]. However, in our study, there was no statistically significant difference in the consumption of opioids between females and males, which contrasts with other studies [23, 24]. This suggests that although research indicates women are generally more sensitive to pain than men, the discrepancies observed are not always uniform, especially sex hormones and their immunological, inflammatory and neural activities [22]. We also noted a statistically significant association between opioid use and age, indicating a predilection of adults ≤ 60 years for analgesia with nalbuphine. There are various explanations and theories for this association. From a neurobiological point of view, it is common for older people to have higher pain thresholds and reduced sensitivity to pain, which can result in a lower demand for opioids [25]. The use of simple analgesics and non-steroidal anti-inflammatory drugs (NSAIDs) as adjuvants to opioids plays a crucial role in the management of postoperative pain [26]. These adjuvants are often prescribed to complement pain control and they can also reduce the need for high-dose opioids, thus minimizing the potential associated side effects, such as sedation, nausea, constipation, and the risk of addiction [27]. Our data showed a clear preference for dipyrone as an adjuvant analgesic, present in 85.2% of the prescriptions analyzed (supplementary file). There is a notable divergence in analgesic drug preferences between different countries, with Brazil standing out for its predominant use of dipyrone, while in other nations, paracetamol and NSAIDs are more common [28, 29]. These variations in use can be attributed to availability, cost, perceived effectiveness, and medical and cultural preferences. These findings support physicians in considering age, gender, and adjuvant analgesics in managing patients' postoperative pain, helping to direct resources appropriately and including a more targeted approach to improve patient comfort, but can also have significant benefits in terms of safety and postoperative recovery.

The findings of this study should be interpreted with caution; there are several limitations. The observational nature of the survey constrains our ability to deduce the causality between opioid consumption and increased mortality or prolonged hospital stays. Furthermore, the analysis did not fully adjust for potential confounders such as baseline health conditions and the indications for prescribing opioids. The absence of complete medical histories, particularly previous opioid use, may have influenced outcomes. Additionally, applicability of our results is limited by the specific demographic of HUOL and potentially may not reflect broader populations. Lastly, the dependency on hospital records for data extraction might have introduced bias due to possible inaccuracies or incompleteness.

5 Conclusion

Our findings indicated that nearly all patients used opioids in the postoperative period following abdominal surgeries. Weak opioids, tramadol, and nalbuphine were most commonly used. The use of morphine was associated with increased hospital stay and mortality. Strategies to reduce opioid use should be implemented for this patient group.