The effect of patient-controlled analgesia on coadministered red blood cells

Patient-controlled analgesia (PCA) provides effective pain control. The possibility of administrating opioids in the same line as red blood cells (RBCs) for patients with poor venous access has been entertained. The literature on this approach is not extensive, but generally cautionary.

Standard concentrations of morphine, hydromorphone (Dilaudid), and meperidine (Demerol) were used to determine the effect on RBCs. Three in vitro approaches were used: 1) continuous low-dose opioid infusion with a single bolus, 2) continuous infusion with multiple boluses, and 3) assessment of RBCs with different concentrations of opioids in test tubes. Samples were assayed for hemoglobin (Hb), mean corpuscular volume (MCV), plasma Hb, potassium, and lactate dehydrogenase, and a peripheral blood smear was made.

Addition of each drug as a single or multiple bolus(-es) with continuous infusion showed the same effects as normal saline. In vitro exposure of Demerol at a 1:2 ratio (drug:blood) increased the MCV (110 fL), at 1:1 the MCV was 120 fL, and there was 4.5 percent hemolysis. At 2:1, hemolysis increased to 9.2 percent. Both morphine and Dilaudid had similar effects as normal saline.

Morphine, Dilaudid, and Demerol, given as a bolus in the intravenous line, have the same effects as those seen with saline. When mixed directly with the blood for more than 1 hour, however, Demerol caused increasing RBC swelling and at high, nontherapeutic concentrations, caused hemolysis. Our study suggests that analgesia delivered via PCA may be safely coadministered with RBCs. Further clinical study is warranted.