Hemodialysis often causes patients to feel cold. This sensation is not just due to a chilly clinic environment; it is a direct and expected physiological side effect of the treatment itself. Hemodialysis cleans the blood and removes excess fluid when the kidneys are no longer able to perform these functions effectively. Understanding the science behind the temperature drop can help patients manage the discomfort.
Why Hemodialysis Causes Temperature Drop
The mechanical process of hemodialysis involves circulating a patient’s blood outside the body, exposing it to a cooler environment. Approximately two cups of blood flow through the extracorporeal circuit, including the dialyzer, tubes, and machine, at any given moment. This circulation outside the body’s insulated core facilitates heat loss to the surrounding air.
The dialyzer, often called the artificial kidney, is a primary site of heat exchange. Blood flows against the dialysate fluid, which is typically set around 37 degrees Celsius (98.6 degrees Fahrenheit) or sometimes lower. Even though the dialysate is body-temperature-warm, the process efficiently removes heat from the patient’s blood, resulting in a net heat loss.
Even when the dialysate matches the patient’s core temperature, the volume of blood passing through the cool machine components and tubing reduces the patient’s overall body heat. This acute cold sensation is predominantly a phenomenon of in-center hemodialysis, unlike peritoneal dialysis (PD) where the cleaning fluid remains inside the body. The machine’s constant flow and the dialysate’s temperature create a thermal gradient that pulls heat away from the patient.
The Body’s Physiological Reaction
The sensation of coldness is amplified by the body’s internal responses, which are triggered to maintain stability during dialysis. A common compensatory mechanism is peripheral vasoconstriction, where the body narrows blood vessels in the extremities, such as the hands and feet. This action attempts to conserve warmth by redirecting blood flow toward the core organs, intensifying the feeling of coldness in the limbs.
The removal of excess fluid, known as ultrafiltration, is a significant factor contributing to coldness and shivering. Ultrafiltration can lead to a drop in blood pressure (hypotension). Low blood pressure triggers the body’s thermoregulatory system, causing shivering to generate heat and compensate for reduced circulation. The difference between the temperature threshold for shivering and vasodilation is very small—only 0.3 to 0.8 degrees Celsius—meaning a minor change can cause a major physiological reaction.
The perception of cold is also influenced by an intentional reduction in core body temperature. Low dialysate temperatures, sometimes set between 34 and 35.5 degrees Celsius, are utilized to improve hemodynamic stability and prevent drops in blood pressure. While this cooled dialysis benefits blood pressure, it directly contributes to the feeling of being cold, with up to 70% of patients reporting discomfort or shivering.
Practical Ways to Stay Warm During Treatment
Patients can take proactive steps to manage the cold sensation and maintain comfort throughout their session. Dressing in layers is an effective strategy, allowing patients to adjust clothing as their body temperature fluctuates during the multiple-hour treatment. Wearing warm accessories like thick socks, a hat, or a scarf helps prevent heat loss, as significant heat can escape from the head and feet.
Many dialysis facilities provide heated blankets, and patients should ask the staff for one to use during their session. If the cold is persistent, patients can discuss adjusting the dialysate temperature with their healthcare team, as machines can be set to individual temperature profiles. Specialized clothing is also available, featuring openings that expose only the vascular access site while keeping the rest of the body covered and warm.
The cold sensation is often most pronounced later in the session, after a large volume of fluid has been removed. Patients should notify the staff immediately if they experience severe, uncontrollable shivering or if the coldness is accompanied by symptoms like dizziness or nausea. These symptoms could indicate an exaggerated drop in blood pressure or a potential infection, requiring prompt attention.