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These studies indicate that surgery depresses immune function because both anesthetic agents and physical trauma cause circulating levels of all lymphocyte subsets to decline after surgery with general anesthesia causing a panlymphocytopenia. Lymphocyte function, independent of cell number, is inhibited whether measured in vitro by lymphocyte responses to mitogens, antigens or homologous lymphocytes or measured in vivo by loss of response to skin testing. Lymphocyte functional inhibition may be related to disproportionate declines in T cell subsets or related to the appearance of immunosuppressive serum factors which inhibit lymphocytes. Transfusion potentiates whatever mechanism is responsible for lymphocyte inhibition; surgery accompanied by transfusion is followed by more profound decreases in lymphocyte numbers and in lymphocyte functional activity than surgery without transfusion. It is difficult to extrapolate these observations to retrospective clinical studies linking transfusion to increases in risk of infection or recurrence of malignancy. The study by Jensen et al.(9) suggests that use of leukocyte-free blood will prevent transfusion-associated adverse clinical phenomena, but this study needs to be replicated. The data certainly favors avoiding the use of homologous blood. BLOOD TRANSFUSION AND INFECTION The hypothesis that transfusion causes immune suppression leading to infections is confounded by the observation that the magnitude of the injury directly correlates with the degree of immune suppression and the necessity for transfusion. Potential confounders must be considered in any study of infections following surgery: confounders in one clinical situation are not significant or non-existent in another. Each field of surgery has its own risk factors for infection which are often associated with transfusion as well as with infection. The contribution of transfusion to the risk of infection independent of variables reflecting tissue destruction and bacterial contamination can be calculated statistically using stepwise logistic regression (13). This type of analysis is commonly used in medical studies, ignoring the basic precept that the independent variables must be truly independent. The independent variables are not genuinely independent: the magnitude of the procedure, the duration of surgery, the blood loss and the tissue damage are all related to one another and all are related to the number of units of blood given as well as to the risk of infection. The analysis is useful as long as one is aware that all conclusions drawn are subject to limitations. This analysis has been applied to 23 populations of patients undergoing procedures ranging from bone marrow harvesting to coronary artery bypass graft. In 22 studies transfusion was a statistically significant risk factor for infection and in 17 of the 23 it was the most significant determinant of infectious complications in stepwise logistic regression. In 14 studies the p value for the relationship between transfusion and infection was 0.001 or less. Non-operative site infections are increased following blood transfusion, indicating that transfusion's association with infection is independent of the operative trauma (14-16). Several studies have demonstrated a dose-response relationship between transfusion and infection risk but the greatest increment in risk is noted between no transfusion and one unit of blood (14,16-19). Transfusion is a potent predictor of infection after controlling for variables reflecting tissue destruction and contamination.
DOI link for These studies indicate that surgery depresses immune function because both anesthetic agents and physical trauma cause circulating levels of all lymphocyte subsets to decline after surgery with general anesthesia causing a panlymphocytopenia. Lymphocyte function, independent of cell number, is inhibited whether measured in vitro by lymphocyte responses to mitogens, antigens or homologous lymphocytes or measured in vivo by loss of response to skin testing. Lymphocyte functional inhibition may be related to disproportionate declines in T cell subsets or related to the appearance of immunosuppressive serum factors which inhibit lymphocytes. Transfusion potentiates whatever mechanism is responsible for lymphocyte inhibition; surgery accompanied by transfusion is followed by more profound decreases in lymphocyte numbers and in lymphocyte functional activity than surgery without transfusion. It is difficult to extrapolate these observations to retrospective clinical studies linking transfusion to increases in risk of infection or recurrence of malignancy. The study by Jensen et al.(9) suggests that use of leukocyte-free blood will prevent transfusion-associated adverse clinical phenomena, but this study needs to be replicated. The data certainly favors avoiding the use of homologous blood. BLOOD TRANSFUSION AND INFECTION The hypothesis that transfusion causes immune suppression leading to infections is confounded by the observation that the magnitude of the injury directly correlates with the degree of immune suppression and the necessity for transfusion. Potential confounders must be considered in any study of infections following surgery: confounders in one clinical situation are not significant or non-existent in another. Each field of surgery has its own risk factors for infection which are often associated with transfusion as well as with infection. The contribution of transfusion to the risk of infection independent of variables reflecting tissue destruction and bacterial contamination can be calculated statistically using stepwise logistic regression (13). This type of analysis is commonly used in medical studies, ignoring the basic precept that the independent variables must be truly independent. The independent variables are not genuinely independent: the magnitude of the procedure, the duration of surgery, the blood loss and the tissue damage are all related to one another and all are related to the number of units of blood given as well as to the risk of infection. The analysis is useful as long as one is aware that all conclusions drawn are subject to limitations. This analysis has been applied to 23 populations of patients undergoing procedures ranging from bone marrow harvesting to coronary artery bypass graft. In 22 studies transfusion was a statistically significant risk factor for infection and in 17 of the 23 it was the most significant determinant of infectious complications in stepwise logistic regression. In 14 studies the p value for the relationship between transfusion and infection was 0.001 or less. Non-operative site infections are increased following blood transfusion, indicating that transfusion's association with infection is independent of the operative trauma (14-16). Several studies have demonstrated a dose-response relationship between transfusion and infection risk but the greatest increment in risk is noted between no transfusion and one unit of blood (14,16-19). Transfusion is a potent predictor of infection after controlling for variables reflecting tissue destruction and contamination.
These studies indicate that surgery depresses immune function because both anesthetic agents and physical trauma cause circulating levels of all lymphocyte subsets to decline after surgery with general anesthesia causing a panlymphocytopenia. Lymphocyte function, independent of cell number, is inhibited whether measured in vitro by lymphocyte responses to mitogens, antigens or homologous lymphocytes or measured in vivo by loss of response to skin testing. Lymphocyte functional inhibition may be related to disproportionate declines in T cell subsets or related to the appearance of immunosuppressive serum factors which inhibit lymphocytes. Transfusion potentiates whatever mechanism is responsible for lymphocyte inhibition; surgery accompanied by transfusion is followed by more profound decreases in lymphocyte numbers and in lymphocyte functional activity than surgery without transfusion. It is difficult to extrapolate these observations to retrospective clinical studies linking transfusion to increases in risk of infection or recurrence of malignancy. The study by Jensen et al.(9) suggests that use of leukocyte-free blood will prevent transfusion-associated adverse clinical phenomena, but this study needs to be replicated. The data certainly favors avoiding the use of homologous blood. BLOOD TRANSFUSION AND INFECTION The hypothesis that transfusion causes immune suppression leading to infections is confounded by the observation that the magnitude of the injury directly correlates with the degree of immune suppression and the necessity for transfusion. Potential confounders must be considered in any study of infections following surgery: confounders in one clinical situation are not significant or non-existent in another. Each field of surgery has its own risk factors for infection which are often associated with transfusion as well as with infection. The contribution of transfusion to the risk of infection independent of variables reflecting tissue destruction and bacterial contamination can be calculated statistically using stepwise logistic regression (13). This type of analysis is commonly used in medical studies, ignoring the basic precept that the independent variables must be truly independent. The independent variables are not genuinely independent: the magnitude of the procedure, the duration of surgery, the blood loss and the tissue damage are all related to one another and all are related to the number of units of blood given as well as to the risk of infection. The analysis is useful as long as one is aware that all conclusions drawn are subject to limitations. This analysis has been applied to 23 populations of patients undergoing procedures ranging from bone marrow harvesting to coronary artery bypass graft. In 22 studies transfusion was a statistically significant risk factor for infection and in 17 of the 23 it was the most significant determinant of infectious complications in stepwise logistic regression. In 14 studies the p value for the relationship between transfusion and infection was 0.001 or less. Non-operative site infections are increased following blood transfusion, indicating that transfusion's association with infection is independent of the operative trauma (14-16). Several studies have demonstrated a dose-response relationship between transfusion and infection risk but the greatest increment in risk is noted between no transfusion and one unit of blood (14,16-19). Transfusion is a potent predictor of infection after controlling for variables reflecting tissue destruction and contamination.
ABSTRACT