Impact of Anesthesia Maintenance Methods on Long-term Survival Rate

It is estimated that 234.2 million major surgical procedures are undertaken every year worldwide. Surgery is one of the major treatment methods for patients with malignant tumor. And, alone with the ageing process, more and more elderly patients undergo surgery for malignant tumor. However, evidence emerges that choice of anesthetics, i.e., either inhalational or intravenous anesthetics, may influence the outcome of elderly patients undergoing cancer surgery.

A. Effects of anesthetics on immune function after surgery

The choice of general anesthetics might influence human's immune function after surgery. An international multicenter team (NCT00418457) investigated the effects of propofol-paravertebral anesthesia vs sevoflurane-opioid anesthesia on the immune function in patients after breast cancer surgery. In a small sample size (n = 32) randomized controlled trail published in 2010, postoperative serum concentrations of interleukin (IL)-1 (protumorigenic cytokine) and matrix metalloproteinases (MMP)-3/9 (associated with cancer cell invasion and metastasis) were significantly lower (P = 0.003 and 0.011, respectively), whereas that of IL-10 (antitumorigenic cytokines) was significantly higher in the propofol group than in the sevoflurane group (P = 0.001). In another small sample size (n = 10) randomized controlled trail published in 2014, serum obtained from patients who received propofol anesthesia led to greater human donor natural killer (NK) cell cytotoxicity in vitro when compared with serum from those who received sevoflurane anesthesia. In a recent small sample size (n = 28) randomized controlled trial, the levels of NK and T helper cell infiltration in breast cancer tissue were significantly higher in patients receiving propofol anesthesia than those receiving sevoflurane anesthesia (P = 0.015 and 0.03, respectively).

Similar findings were reported in patients with other malignant tumors. In a small randomized controlled trial, 30 patients with non-small-cell lung cancer randomly received either propofol or isoflurane anesthesia. The results showed that cluster of differentiation (CD)4+CD28+ percentage (P < 0.0001) and the ratio of interferon-gamma:interleukin-4 (P = 0.001) all increased significantly with propofol but no change with isoflurane anesthesia; indicating that propofol promotes activation and differentiation of peripheral T-helper cells. In another randomized controlled trial, 60 patients undergoing surgery for tongue cancer surgery randomly received total propofol, mixed (propofol induction and sevoflurane maintenance) anesthesia or total sevoflurane anesthesia. The results showed that the percentages of CD3+, CD3+CD4+, and NK cells and the ratio of CD4+/CD8+ were significantly decreased in the two sevoflurane groups, but not in the total propofol group; suggesting that propofol has less effects on cellular immune response than sevoflurane. There are also studies that reported neutral results.

The above studies suggest that, when compared with inhalational anesthesia, propofol intravenous anesthesia may have favorable effects on the immune function in patients after cancer surgery. However, care must be taken when explaining these results: (1) the sample sizes of the available studies were small; (2) the relationship between postoperative immune function changes and long-term outcomes remains unclear.

B. Effects of anesthetics on invasiveness of malignant tumor

The effects of anesthetics on invasiveness of tumor cells were mainly tested in the experimental studies, i.e., tumor cells were incubated with anesthetics in the in vitro environment. In this aspect, propofol shows somewhat favorable effects. The results of Miao et al. showed that propofol stimulation decreased the expression of MMP-2 and -9 and subsequently decreased the invasive activity of human colon cancer cells, possibly via extracellular signal-regulated kinase 1/2 (ERK1/2) down-regulation mediated through the gamma-aminobutyric acid (GABA)-A receptor. The study of Wang et al. reported that propofol inhibited invasion and metastasis, and enhanced paclitaxel-induced apoptosis of ovarian cancer cells, possibly by suppressing the Slug expression. Ecimovic et al. also reported that propofol reduced migration in both estrogen receptor-positive and -negative breast cancer cells, possibly by suppressing the Neuroepithelial Cell Transforming Gene 1 (NET1) expression.

The reported effects of various inhalational anesthetics are conflicting. Huang et al. compared the effects of propofol and isoflurane on prostate cancer cells. The results showed that propofol, at clinical relevant concentration, inhibited the activation of hypoxia-inducible factor (HIF)-1 alpha, and partially reduced cancer cell malignant activities; whereas isoflurane raised HIF-1 alpha expression, and increased the probability of proliferation and migration. The study of Benaonana et al. reported similar results, i.e., isoflurane up-regulated the expression of HIFs, and increased the growth and malignant potential of renal cancer cells. On the other hand, sevoflurane and desflurane show opposite effects. Multiple studies found that sevoflurane inhibited the proliferation and migration, and induced apoptosis of lung cancer cells. Müller-Edenborn et al. also reported that volatile anesthetics (sevoflurane and desflurane) reduced invasion of colorectal cancer cells through down-regulation of matrix metalloproteinase-9.

So far, the clinical significance of anesthetics on the invasiveness of malignant tumors is still lacking.

C. Effect of anesthetics on long-term outcome after cancer surgery

Studies in this aspect are very limited. In the study of Enlund et al., 2838 patients who underwent breast cancer or colorectal cancer surgery were retrospectively analyzed, among them 1935 received sevoflurane anesthesia and 903 propofol anesthesia. The 1-year and 5-year survival rates were higher in propofol-anesthetized patients than in sevoflurane-anesthetized ones (differences in overall survival rate were 4.7%, P = 0.004 and 5.6%, P < 0.001, respectively). However, the differences were not statistically significant after adjusting for confounding factors. In a recent study, Wigmore et al. retrospectively investigated 11,395 patients after cancer surgery. After exclusions and propensity matching, 2,607 patients remained in each of the inhalational anesthesia group or total intravenous anesthesia group. The results showed that, after a median follow-up duration of 2.66 years (95% confidence interval [CI] 2.62-2.69), volatile inhalational anesthesia was associated with a higher risk for death after both univariate (HR 1.59, 95% CI 1.30-1.95) and multivariable analysis (HR 1.46, 95% CI 1.29-1.66).

However, in this aspect, long-term follow-up results of randomized controlled trials are still lacking. Prospective studies exploring the effect of anesthetic choice on long-term survival in cancer surgery patients are urgently needed.