2.1

Study design

This is a prospective observational study where preoperative, intraoperative and anesthesia recovery variables were examined. The report of the present study followed the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines for observational studies .

2.2

Location, sample, and sampling

This study was conducted in the surgical processes area of a public, general, and major university hospital, integrated into the Unified Health System (in Portuguese, SUS), in Belo Horizonte, Minas Gerais, Brazil. In 2019, an average of 700 surgeries per month were performed.

The sample size was defined by calculating the minimum number of patients necessary for a study with multiple regression analysis. To test a multiple regression consisting of 10 predictor variables, a sample size of 118 patients would be adequate to detect an effect size of at least 0.15, statistical power level of 0.80, and significance level of 0.05.

A simple random sampling method was used to select patients for this study. The sample consisted of patients who underwent elective surgery, selected randomly from the hospital’s surgical schedule. Each patient had an equal chance of being chosen. The sample comprised patients who fulfilled the inclusion criteria and willingly consented to participate in the research.

2.3

Inclusion criteria

We included patients over 18 years old, belonging to the elective surgery program of the study hospital, undergoing general anesthesia and with American Society of Anesthesiology (ASA) clinical status classification I and II.

2.4

Exclusion criteria

During the preoperative phase, we excluded patients who had a previous record of psychiatric problems, cognitive impairment, or persistent pain. During the postoperative period, we excluded patients who were given postoperative neuraxial analgesia or peripheral nerve blocks (to eliminate the potential influence of additional methods of pain control), patients who were transferred to the intensive care unit for postoperative care, and patients who experienced neurological alterations after surgery (which would interfere with the assessment of pain using the selected scale).

2.5

Instruments and data collection

A specific instrument was created to obtain clinical and sociodemographic characteristics. The instrument included patient health information and possible covariates associated with postoperative pain, including data from preoperative period (sex, age, race, psychological stress, and preoperative pain levels), intraoperative period (type of surgery, duration of surgery, dose of opioids in the operating room) and the anesthesia recovery period (dose of opioids in the PACU and adequacy of pain management).

The instrument was evaluated by three judges with the following characteristics: judge 1- nurse, with a doctorate degree, six years of clinical experience in perioperative nursing, thirteen years of experience in clinical research; judge 2- nurse, with a doctorate degree, twelve years of clinical experience in perioperative nursing, twenty-five years of experience in clinical research; judge 3- nurse, with a doctorate degree, thirteen years of experience in perioperative nursing, twenty-two years of experience in clinical research. The judges evaluated the face and content validity and found no need for modifications.

To evaluate the performance of the interviewers and verify the adequacy of the questionnaires to the characteristics of the study population, a pilot study was carried out in 30 patients (non-sampled group), between October and December 2018. According to this process, no changes needed to be made.

We employed the Hospital Anxiety and Depression Scale (HADS) to evaluate symptoms of anxiety and depression within the past week. This scale comprises a total of 14 items, which are answered using a 4-point Likert scale. The HADS includes two subscales: HADS-A (7 items) and HADS-D (7 items), which assess anxiety and depression, respectively. On a scale ranging from 0 to 21, a score of 9 or higher on each subscale reflects symptoms of anxiety and depression. The literature demonstrates the validity and reliability of HADS in Brazilian hospital clinical contexts. ^, The scale demonstrated satisfactory internal consistency to assess anxiety and depression, with Cronbach coefficients of 0.68 and 0.67, respectively. The assessment using the HADS was conducted during the immediate preoperative phase, upon arrival at the Surgical Center (SC).

Pain was assessed with the Verbal Numerical Scale (VNS). This is a unidimensional ordinal instrument that quantifies the severity of pain using numerical values that correspond to the level of pain experienced. The numerical scale ranges from 0, indicating the absence of pain, to 10, signifying the most severe pain ever experienced. Nine moments of pain assessment were carried out. The first assessment was in the preoperative period, at the SC reception. There were seven moments of evaluation in the postoperative period, in the PACU, as follows: time 0 – at the patient’s admission (considered time 0 min), time 1 – 15 min, time 2 – 30 min, time 3 – 45 min, time 4 – 60 min, time 5 – 90 min and time 6 – 120 min, which corresponds to the assessment routine in the PACU at the study site. Also, pain was assessed upon discharge from the PACU.

The opioid dosage was obtained by aggregating the total amount of opioids given to the patient and converting this total into morphine-equivalent doses (measured in milligrams of morphine). We executed the computation using an internet-based opioid conversion calculator. Previous research in perioperative environments has utilized this calculator. ^, Opioid doses were collected from patients’ medical records. Opioids administered in the Operating Room (OR) and during hospitalization in the PACU were included.

The Pain Management Index (PMI) was calculated as a strategy to evaluate the adequacy of pain management. The PMI assesses the adequacy of pain management by reflecting the balance between the most potent class of analgesics used/prescribed and the intensity of pain reported by the patient. For calculation, pain intensity was classified as 0 = No pain (VNS: 0), 1 = mild pain (VNS: 1, 2 and 3), 2 = moderate pain (VNS: 4, 5 and 6) and 3 = severe pain (VNS: 7, 8, 9 and 10). ^, For analgesics, values were assigned according to the World Health Organization (WHO) pain ladder, as follows: 0 = no prescribed analgesia, 1 = non-opioid analgesic, 2 = weak opioid and 3 = strong opioid. ^, The index was constructed by subtracting the level of maximum pain felt in the PACU from the level of analgesia prescribed in the PACU, acquiring values between −3 and 3. Negative scores on the PMI indicated inadequate treatment and positive scores were considered an approximation of acceptable treatment. ^, Although PMI was originally designed to assess the adequacy of pain management in cancer patients, its validity to use in patients with acute pain, including postoperative patients, has been well established.

The data were collected by three research assistants, with the following characteristics: research assistant 1 – nurse, master’s student in nursing with postgraduate training in perioperative nursing, with >5 years of experience in a surgical center. Research assistant 2 – nurse, master’s student in nursing, with postgraduate training in perioperative nursing, with >7 years of experience in a surgical center. Research assistant 3 – nurse, master’s degree in nursing, doctorate student in nursing, with >6 years of experience in clinical and surgical center. Before conducting interviews, the research assistants undergo training and were provided with comprehensive information regarding the study protocol, definitions, and the DCI.

2.6

Ethical considerations

This study is a component of a larger research project named “Pain in the post-anesthesia recovery room: incidence and predictive factors”, which has been approved under the number 14,531,419.8.0000.5149. Participants in the study were provided with the opportunity to voluntarily participate by signing the Informed Consent Form. Participants were comprehensively briefed on the study’s goals. Moreover, the researchers explicitly stated that the participants’ involvement carried no potential risks and that they had the freedom to withdraw from the study at any time without experiencing any negative repercussions.

2.7

Data analysis

Data were analyzed using the R software version 4.3.2. Firstly, a descriptive analysis of the data was carried out to characterize the sample. Qualitative variables are displayed using frequency distributions and percentages. Measures of central tendency, such as mean (M) and standard deviation (SD), represent the quantitative variables. For descriptive analysis of pain assessments in the PACU, frequency distributions and percentages were presented. A Friedman test was then performed to determine whether there were significant differences between pain ratings over time, with Conover post-hoc analysis. Pain levels upon patient admission to the PACU, maximum pain felt in the PACU and pain upon discharge from the PACU were compared. Data normality was tested with the Shapiro-Wilk test and was considered to have non-parametric distribution. The association between variables was estimated using an ordinal regression model (also known as a cumulative logistic model). Ordinal regression is a regression model for cumulative logits that allows changes to be evaluated ordinally, as is the case with pain assessment scales. ^, The strength of association was presented using odds ratio (OR) with 95 % confidence intervals (CI) and p-value <0.05 was considered statistically significant.

3.1

Characteristics of patients in the preoperative, intraoperative and anesthesia recovery periods

During the preoperative period, a total of 281 participants consented to take part in the study. In the postoperative phase, we excluded 55 patients. The study excluded 21 patients who received either regional or local anesthesia during surgery, two who experienced neurological alterations in the post-anesthesia recovery room, and 32 who were transferred to the intensive care unit after surgery. There were a total of 226 patients in the final sample. Table 1 displays the categorization of patients based on their preoperative, intraoperative, and anesthetic recovery features.

All 226 (100 %) patients who were seen at the SC reception during the preoperative period claimed that they did not experience any pain (VNS = 0) and had not been administered any opioids in the 48 h leading up to the surgery. During the intraoperative period, Fentanyl was the most administered opioid in the OR, accounting for 65.0 % of cases. Morphine was the second most frequently used opioid, with a usage rate of 27.9 %. A total of 16 patients (7.1 %) did not get any opioids throughout their time in the OR. During anesthesia recovery, the most used opioid in the PACU was Morphine (15.9 %), followed by Fentanyl (1.3 %), and 187 (82.8 %) did not receive analgesics, opioid or non-opioid, in the PACU. Patients in this study did not receive multimodal analgesia.

3.2

Pain assessments and pain control in the post-anesthesia care unit

The overall incidence of pain (VNS > 0) in the PACU was 72 (31.9 %) patients. The average time of onset of pain in the PACU was 33.1 ± 24.9 min after admission. Upon admission to the post-anesthesia care unit, 5.8 % of patients reported moderate to severe pain (VNS ≥ 4). The assessment time at which they reported the most intense pain was time 5, 90 min after admission, where 34.7 % of patients reported moderate to severe pain (VNS ≥ 4). However, at the time of discharge, 50 (22.1 %) of patients reported moderate to severe pain (VNS ≥ 4). Table 2 presents pain assessments of patients in the PACU.

Table 2

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