Chronic Pain After Intensive Care Unit: Clinical Predictors

Over the past two decades, improved intensive care practices have significantly reduced in-hospital mortality. However, a growing number of survivors experience a range of long-term complications, collectively known as Post-Intensive Care Syndrome (PICS). A key but underexplored component of PICS is chronic pain, defined as persistent pain lasting beyond 12 weeks or beyond the expected healing time following trauma or surgery.

Existing data suggest that up to 73% of ICU survivors report moderate to severe pain one year after discharge, with the shoulder being the most commonly affected anatomical region. Retrospective studies estimate the prevalence of chronic pain among ICU survivors to be as high as 44%. Identified risk factors include advanced age and severe sepsis; however, there is limited evidence regarding the true impact of chronic pain on activities of daily living (ADLs), its intensity, and clinical predictors.

This prospective observational study is conducted at the Intensive Care Unit of Attikon General University Hospital in Athens, Greece, and includes both medical and surgical ICU patients, including cardiothoracic surgery cases. The aim is to assess the prevalence, anatomical distribution, and intensity of chronic pain in ICU survivors, examine its interference with daily functioning, and explore associations between chronic pain and clinical or laboratory data collected during ICU admission, hospitalization, and discharge.

Patients are evaluated at three timepoints: ICU admission, ICU discharge, and three months post-ICU discharge. The inclusion criteria are age ≥18 years and ICU stay of at least 24 hours.

Detailed data collection includes:

Demographics and Lifestyle: Age, sex, educational level, occupation, weight, height, Body Mass Index (BMI), weekly physical activity.

Pain History and Characteristics: Prior history of chronic or acute pain, anatomical localization, intensity with Visual Analogue Scale score (VAS score), and pain qualities assessed using the validated Greek version of the Short-Form McGill Pain Questionnaire.

Medical History: Hypertension, dyslipidemia, arrhythmias, coronary artery disease, Chronic Obstructive Pulmonary Disease (COPD), Asthma, Obstructive Sleep Apnoea (OSA), chronic kidney disease, Gastro Esophageal Reflux Disease (GERD), peptic ulcer, thyroid disorders, diabetes, stroke, migraine, epilepsy, musculoskeletal/rheumatologic conditions, psychiatric disorders, surgical history, and opioid use.

ICU Parameters: Duration of stay, use of vasopressors, sedatives, opioids, presence of sepsis, mechanical ventilation,Acure Respiratory Distress Syndrome (ARDS), surgical procedures, and regional anesthesia.

Laboratory Data at ICU Admission and Discharge: Hematocrit, hemoglobin, White Blood Cell count (WBC), platelets, International Normalized Ratio (INR), C-reactive protein (CRP) ,fibrinogen, procalcitonin, creatinine, urea, potential of hydrogen (pH), Partial pressure of carbon dioxide (pCO₂), Partial pressure of oxygen (pO₂), Bicarbonate (HCO₃-), potassium, sodium, calcium, phosphorus, magnesium, chloride, Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), Gamma-Glutamyl Transferase (GGT), Alkaline Phosphatase (ALP), total bilirubin, albumin, and Thyroid-Stimulating Hormone (TSH).

The study's overarching goal is to better characterize the burden of chronic pain among ICU survivors and to inform the development of targeted preventive and therapeutic strategies. Ethical approval has been granted by the Institutional Ethics Committee of Attikon University Hospital, and all participants provide written informed consent.