To the Editor:
I read with great interest the article by Wigmore et al.1 at the Royal Marsden Hospital (London, United Kingdom), which suggested that total intravenous anesthesia (TIVA) is associated with improved cancer survival when compared to volatile inhalational anesthesia. The study has caused a great deal of excitement among many, and with good cause, demonstrating a 50% greater risk of mortality in the volatile group compared to TIVA.
I noticed that even after propensity matching, there was a statistically significant difference in transfusion rates between groups, there being an almost 50% higher rate of blood transfusion in the group receiving a volatile anesthetic (150 vs. 110 patients, P = 0.011). The reason for this difference is unclear; it may be that patients undergoing TIVA have lower rates of perioperative anemia, have less bleeding intraoperatively, or simply that anesthetists who use TIVA also have more conservative thresholds for blood transfusion.
It is recognized that conservative blood transfusion strategies may offer survival benefit,2 and reducing the use of allogenic blood transfusion may improve mortality.3 In fact, blood transfusion has been reported to worsen a variety of outcomes4 in cancer surgery including increasing incidence postoperative infections and increasing disease recurrence in addition to increasing mortality.4,5 Perioperative blood transfusion may influence immunomodulation in a number of ways,6 including potentiating postoperative levels of the cytokine interleukin-6 and interleukin-6–inducible tumor growth factors such as hepatocyte growth factor and vascular cell adhesion molecule 1.5 So potentially both blood transfusion and use of volatile may have contributed to reduce survival in the inhalational group via their impact on immunomodulation, thereby increasing cancer cell growth.
The magnitude of the TIVA survival benefit seen in the Royal Marsden study1 can clearly not be explained by the differences in transfusion rates alone. In absolute terms, there were 190 more deaths in the propensity-matched volatile group, but only 40 more patients in that group underwent blood transfusion. However, I believe differing transfusion rates between groups may be an important confounding factor, which was not mentioned by the authors in their discussion. It is increasingly recognized that many aspects of anesthetic care,7 including perioperative transfusion, use of opioid analgesia, and regional anesthesia, may all alter the immune response and influence cancer recurrence and thus survival. Clearly the situation is far more complex than the headline; I do hope when prospective research is undertaken, it takes these wide-ranging aspects of perioperative care into account.
The author declares no competing interests.