Cardiopulmonary recirculation in dialysis. An underrecognized phenomenon

Area of Science:

• Nephrology
• Cardiovascular Physiology
• Medical Diagnostics

Background:

• Access recirculation is a common complication in hemodialysis, affecting treatment efficiency.
• Current methods to detect access recirculation involve injecting cold saline and monitoring blood temperature or water concentration.
• These methods assume that observed changes are solely due to recirculation within the dialysis access.

Purpose of the Study:

• To investigate transient blood cooling and hemodilution phenomena observed after cold saline injection in the absence of access recirculation.
• To identify the underlying physiological mechanism responsible for these transient changes.
• To assess the impact of this phenomenon on the accuracy of urea kinetic modeling and access recirculation calculations.

Main Methods:

• Four hemodialysis patients were studied under controlled conditions designed to prevent access recirculation.
• A bolus of cold saline was injected into the venous line of the dialysis circuit.
• Blood temperature and water concentration at the dialyzer inlet were continuously monitored.

Main Results:

• Transient blood cooling and hemodilution were observed in all patients, even when access recirculation was impossible.
• These effects were attributed to the passage of injected saline through the heart and pulmonary circulation.
• A portion of the cooled blood returned to the vascular access, bypassing systemic capillaries.

Conclusions:

• The phenomenon termed "cardiopulmonary recirculation" can mimic the effects of access recirculation.
• This can lead to inaccurate urea kinetic modeling and erroneous calculations of access recirculation.
• Clinical interpretation of cold saline tests requires consideration of cardiopulmonary recirculation to avoid misdiagnosis.