The influence of preoperative anxiety on postoperative pain in patients undergoing cardiac surgery

This study aims to identify the influence of preoperative anxiety levels on the predisposition to postoperative pain in patients undergoing cardiac surgery based on analgesic needs, as well as to explore the relationship between preoperative anxiety, postoperative pain and sex.

study design

This prospective cohort study of patients undergoing cardiac surgery assessed preoperative anxiety levels as a factor influencing immediate postoperative pain.


Patients over the age of 18 undergoing elective cardiac surgery at a tertiary hospital run by the Regional Health Management Board of Castile and León, Spain, between January and April 2020. The following types of cardiac surgery were covered: coronary revascularization (a graft using the mammary artery or saphenous vein) and/or valve surgery (repair or replacement). All with sternotomy and cardiopulmonary bypass. Patients who did not consent to participate in the study after receiving information about it were excluded. A total of 13 patients were excluded: 1 exitus occurred within the first 24 hours after surgery, 8 patients could not complete the preoperative anxiety test due to last-minute changes to the operative schedule, and 4 patients provided incomplete data on postoperative pain. A total of 116 patients meeting the inclusion criteria were finally included. The optimal sample size was set at 113 participants with a 95% confidence interval, a precision of 0.5 units and a standard deviation of 2.5 units for mean postoperative pain. The replacement rate was set at 15%.

Data gathering

Data were collected on: (a) socio-demographic variables: age and sex; (b) most frequent comorbidities and toxic habits during the last month (smokers: more than 5 cigarettes per day and alcoholics: daily consumption of more than 60 g of alcohol in men and more than 40 g in women or occasional consumption of more than 60 g of alcohol in a single drink.); (c) type of cardiac surgery (coronary, valvular or mixed) and cardiopulmonary bypass time (minutes); (d) psychological variables: SA/TA level (score from 0 to 60 for each subscale); (e) analgesic requirements in the postoperative period: milligrams of morphine hydrochloride required to maintain pain below 4 on the Verbal Numerical Rating Scale (vNRS), which ranges from 0 (no pain) to 10 (pain maximum) and, (f) body surface area calculated with height and weight. Regarding analgesic needs, it is known that weight or body surface area makes a difference in morphine dosage recommendations. Drugs administered during surgery (fentanyl and etomidate or propofol and rocuronium bromide) were not considered as they were used according to protocol.


In the 24 hours preceding the intervention, patients hospitalized in cardiac surgery meeting the inclusion criteria were informed of the objectives of the study and asked for their informed consent. After signing the informed consent form, the patients completed the Spanish version of the State-Trait Anxiety Inventory (STAI). This psychometric questionnaire includes two scales measuring different facets of anxiety: state and trait anxiety. The STAI contains 40 elements. Half of the items belong to the State subscale, which is made up of sentences describing how the respondent is feeling at that precise moment. The other half belongs to the traits subscale, which includes sentences describing how the respondent usually feels. The Spanish adaptation of the questionnaire has good internal consistency at 0.90–0.93 (Cronbach alpha) for the State subscale and 0.84–0.87 (Cronbach alpha) for the Trait subscale. In the Spanish version, the direct scores corresponding to the sum of the items have been converted into percentile and sten scores, which are obtained according to the sex and age indicated by the authors of the Spanish adaptation.16. Percentile scores were used in this study. Patients were asked to respond to items on the SA scale, which ranges from 0 (not at all) to 3 (a lot), and the TA scale, which ranges from 0 (almost never) to 3 (almost always). The minimum direct score was 0 and the maximum was 60 for both subscales, and this score was then converted to the corresponding percentile. Two members of the research team administered the questionnaires in all cases, giving patients the same instructions for completing the questionnaire to reduce potential bias17.

After their surgery, the patients’ pain was assessed and monitored in the Cardiac Recovery Unit throughout the first 48 hours post-operatively. The first 48 hours after surgery was selected as the follow-up period to measure patients’ pain, as several studies have identified it as the most painful period after cardiothoracic surgery.2.18.

Postoperative pain assessment was performed once patients had been extubated and were able to verbalize their pain. The vNRS scale was used to measure their pain (0: no pain and 10: maximum pain). Pain intensity was recorded every two hours in two daily shifts: morning (8 a.m. to 3 p.m.), evening (3 p.m. to 10 p.m.) and night (10 p.m. to 8 a.m.). Patients’ sleep was respected during the night shift, with at least two measurements taken at 00:00 and 06:00. Maximum pain values ​​recorded at each shift throughout the 48-h monitoring period were used for the study.

The postoperative pain management protocol for cardiac surgery patients in the Cardiac Recovery Unit offered two options based on medical criteria: (A) Analgesic combination of 1 g of paracetamol every 8 hours and 50 mg of dexketoprofen every 8 h given alternately and (B) 1 g paracetamol every 8 h and 2 g metamizole magnesium every 8 h given alternately. In addition, whenever patients expressed pain greater than 4 on the vNRS scale, IV boluses containing 3 mg of morphine hydrochloride were administered as “rescue doses”. The variable “analgesic needs” was measured by calculating the total number of milligrams of morphine hydrochloride required by the patients over the 48 h period.

Ethics approval

The study was conducted in accordance with the principles set out in the Declaration of Helsinki. Permission to conduct the study was approved by the Clinical Research Ethics Committee of the Eastern Valladolid Health Region (reference number: GR-19-1253).

statistical analyzes

Data was analyzed using IBM SPSS Statistics for Windows, version 24.0. Armonk, NY: IBM Corp. Quantitative variables were expressed as means and standard deviations. Qualitative variables, in terms of their frequency distribution. The normality assumption was assessed using the Kolmogorov-Smirnov test. Associations between qualitative variables were explored using Pearson’s chi-square test. When more than 20% of the cells had expected values ​​less than 5, Fisher’s exact test or the likelihood ratio test for variables with more than two categories was used. Students you-test was used to compare two groups of quantitative values ​​and ANOVA was used to compare more than two groups of quantitative values. To analyze the degree of association between the quantitative variables, the Pearson correlation coefficient was used. A univariate linear regression model was performed to identify the factors related to the dose of morphine received by each patient. Variables found to be statistically significant at the 0.1 level in previous analyzes were entered into a multivariate linear regression model. The association performance of the model was calculated with the coefficient of determination R squared (R2). The statistical significance level for all tests was set at p

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