Background: Acute renal colic is a common reason for admission to the emergency department (ED) and is associated with severe pain, sympathetic activation and metabolic stress. Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are widely used for analgesia, but their short-term effects on tissue perfusion and respiratory physiology in stable patients are unclear. End-tidal carbon dioxide (EtCO₂) has been suggested as a non-invasive indicator of overall tissue perfusion, but how it behaves during analgesic treatment in stable ED patients is unclear.

Methods: This prospective, randomised study was conducted in an academic emergency department. Adult patients (aged 18-55) presenting with acute renal colic were randomised to receive an intravenous infusion of either dexketoprofen trometamol (50 mg), tramadol (100 mg), or a combination of dexketoprofen trometamol (50 mg) and tramadol (50 mg). Vital signs, oxygen saturation (SpO₂) and EtCO₂ were recorded at baseline and at 30 and 60 minutes. Arterial blood gas parameters, including lactate, were measured at baseline and after 60 minutes. The primary outcome was the change in EtCO₂ over time.

Inclusion Criteria:

• A Glasgow Coma Scale score of 15
• Spontaneous respiration
• The capacity to provide informed consent

Exclusion Criteria:

• Pregnancy or breastfeeding
• Chronic kidney disease,
• Known allergy to study medications,
• Chronic respiratory disease,
• Hemodynamic instability,
• Acute intoxication,
• Uncontrolled epilepsy,
• Recent monoamine oxidase inhibitor use.

The data that support the findings of this study are not publicly available due to privacy and ethical restrictions, as they contain identifiable patient information.