Stem cell harvest

Once a sufficient number of stem cells are present in the blood, they are collected by a process known as apheresis as shown in Figure 1.

The day prior to procedure venous access should be assessed. If so, on the day of harvest, a catheter or needle is inserted into a vein in each arm. Blood is drawn from one arm into the apheresis machine which separates and collects the stem cells from the other blood components. The remaining blood is returned into the patient’s other arm. The whole process takes approximately four to five hours. The stem cells are mixed with the cytoprotectant, dimethyl sulphoxide (DMSO), and stored in liquid nitrogen tanks.

The minimum number of stem cells needed for a transplant is two million stem cells per kilo of body weight. However, the aim almost always is to collect enough stem cells for two transplants, even though most patients only receive one. This is because after the high-dose therapy it is much more difficult to mobilise enough stem cells for a second transplant, should this be an option.  Local hospital policy will dictate whether stem cells can be stored or not, and, if so, for how long.

During apheresis, the most common side-effect is a cramping or tingling sensation in the hands, feet or around the mouth. This is usually an indication of a drop in calcium levels caused by the introduction of anticoagulant into the blood when it is returned to the patient. This can be simply corrected by drinking a glass of milk.

Nurses should ensure that patients are aware of these potential side-effects and that they are as comfortable as possible during the long process.