What if the Aquarium is in the Intensive Care Unit? Extending the Fish Tank Model to Teach Pharmacokinetics in Critically Ill Patients

OBJECTIVES: This review aimed to explain how the pharmacokinetics of intravenously administered drugs are altered in critically ill patients, using the Fish Tank Model as a conceptual and visual framework. FINDINGS: Critically ill patients experience dynamic pharmacokinetic changes that can be visualized using the Fish Tank Model, where fish (drug molecules) are swimming in a tank of water (the body's volume of distribution) and removed from the tank by a net (clearance). Hypoalbuminemia and altered protein binding are represented by changes in how fish attach to protein structures, affecting the number of freely swimming fish. Systemic inflammation and fluid accumulation expand the tank's volume, lowering concentrations. Hepatic and renal dysfunction can slow clearance, whereas augmented renal function accelerates it, reflected by the size of the net that clears the fish from the tank. Extracorporeal therapies further modify drug behavior: continuous kidney replacement therapy (CKRT) acts like an extra fishing rod to remove fish, whereas CKRT and extracorporeal membrane oxygenation expand the tank, potentially redistributing and sequestering drugs. SUMMARY: The Fish Tank Model, originally developed to illustrate fundamental pharmacokinetic principles, provides a simple yet powerful framework for understanding drug behavior. By extending this model to the intensive care unit, it allows learners and clinicians to visualize complex pharmacokinetic changes, including those induced by extracorporeal therapies such as CKRT and extracorporeal membrane oxygenation, ultimately supporting safer and more individualized drug dosing in critically ill patients.