Evaluation of Fentanyl Transdermal Patch Absorption in Hemodynamically Unstable ICU Patients.

This is a single-center, pharmacokinetic study evaluating fentanyl absorption from transdermal patches in critically ill patients admitted to the surgical intensive care unit (ICU). A total of 40 patients will be recruited and divided into two groups. Both groups will receive a transdermal fentanyl patch for pain management. The grouping is based on hemodynamic status: 20 patients will be classified as hemodynamically unstable, defined by the need for intravenous norepinephrine infusion (≥5 drops/hour of a 4 mg/50 mL solution) to maintain a mean arterial pressure (MAP) of at least 65 mmHg. The other 20 patients will be considered hemodynamically stable, maintaining a MAP ≥ 65 mmHg without norepinephrine infusion. Patients who require very high doses of norepinephrine (over 20 drops/hour), with or without vasopressin, will be excluded. The objective is to determine whether hemodynamic instability affects the systemic absorption of fentanyl from transdermal patches. Blood levels of fentanyl will be measured every 4 hours for the first 48 hours following patch application. The area under the concentration-time curve (AUC) will be calculated for each participant. The primary outcome is the difference in AUC between the stable and unstable groups. Secondary variables include clinical and physiological factors that may influence fentanyl absorption, such as age, sex, body mass index (BMI, as a proxy for adiposity), body temperature, and liver function. To ensure appropriate pain control in all participants, supplemental analgesia (non-fentanyl-based) will be administered during the first 24 hours after patch application and again at 48-72 hours, as needed. The ICU nursing team will routinely assess pain using validated tools such as the Behavioral Pain Scale (BPS), in accordance with standard unit practice.