The effect of morphine on the immune system of ventilated ICU patients

Introduction

Morphine (MO) was shown to depress immune function in animal models and cell cultures [1]. Virtually no data exist regarding the in vivo effect of MO in human beings. MO is often used for sedation of ventilated ICU patients. We therefore evaluated the effect of MO on the immune system of these patients.

Methods

The project was a prospective, self-controlled study. Ventilated ICU patients who were in the Unit > 24 hours and demonstrated no signs of acute infection and considered clinically stable were included. Following exclusive sedation with continuous Midazolam infusion, the first blood sample was taken and MO was added to the regimen, keeping sedation at level 3-4 of Ramsay scale. Twenty-four hours after the addition of the MO, the second blood sample was collected. Leukocytes were analyzed for phagocytosis, oxidative burst and the presence of membrane markers of activation by flow cytometry. Forty-eight and 72-hour blood samples under MO sedation were also analyzed in some patients.

Results

Thirteen patients met the inclusion criteria. The leukocyte membrane activation markers CD11b and CD11c showed significant decrease after 24 hours of MO infusion, 26 ± 13.6% (P = 0.05) and 27 ± 10.0 (P = 0.025), respectively. Other membrane activation markers, CD14, CD18 and oxidative burst, demonstrated a non-significant trend toward decrease in 6 patients with 72 hours exposure to MO.

Conclusions

These human data suggest that MO, which is a standard sedative agent in the ICU, might compromise the immune efficacy of these patients.