Spinal Anesthesia and Tumor-promoting Effects of Surgery. Bar-Yosef et al. (page 1066)
Bar-Yosef et al. wanted to determine whether spinal blockade, which attenuates the neuroendocrine stress response, might lessen perioperative immunosuppression and thus reduce the tumor-promoting response observed in animal studies after surgery. The group used an animal model that was used previously to study the influence of surgical stress on metastatic development. After laparotomy under halothane anesthesia, Fischer-344 male rats were intravenously inoculated with DNA-radiolabeled MADB106 adenocarcinoma cells. This selected variant cell line is obtained from pulmonary metastasis of a mammary adenocarcinoma chemically induced in inbred F344 Fischer rats. The cells are retained, and metastases develop only in the lung.
The researchers assigned animals to one of 7 groups: a control group, which remained undisturbed in their cages; one of three subgroups undergoing anesthesia without surgery; or one of three subgroups undergoing anesthesia with surgery. Anesthetic regimens included halothane only, halothane with systemic morphine, or halothane with spinal block. Analgesic effects of morphine and spinal block had been previously validated in a pilot study. Animals were used for only one experiment each. In the first experiment, MADB106 cells were injected 4–5 h after induction of anesthesia, and the animals’ lungs were removed 24 h after tumor inoculation for assessment of lung tumor retention. Animals’ lungs were removed 3 weeks after tumor inoculation for the second experiment. In the third, researchers drew blood 4–5 h after induction of anesthesia and assessed the number and activity of natural killer cells in vitro .
In this study, laparotomy produced a 17-fold increase in lung tumor retention, and addition of spinal block to halothane anesthesia reduced this effect by 70%. Systemic morphine also reduced the tumor-promoting effects of surgery but to a lesser extent. Activity of natural killer cells was suppressed by surgery and by anesthesia alone. The clinical significance of attenuating postoperative immunosuppression by regional anesthesia is unclear, and the authors urge consideration of a controlled clinical study to assess whether metastatic development could be decreased during the susceptible postoperative period, when immunosuppression reduces the activity of natural killer cells.