Propofol, currently available as a lipid emulsion (Intralipid loo/), is widely used for induction and maintenance of general anaesthesia [ 11. We have recently evaluated the effects of total intravenous anaesthesia with propofol on the immune response during minor surgery [2] and found increased percentages of T helper lymphocytes in the blood after propofol anaesthesia but not after conventional balanced anaesthesia with thiopentone and nitrous oxide. T helper cells are a subset of T lymphocytes pivotal in augmenting both cell-mediated [3] and humoral immunity [4]. Major surgery causes changes in the immune response which are related to the extent of surgical trauma [5] and the neuroendocrine stress response [6]. In this study we compared the effects of propofol infusion anaesthesia and combined isoflurane anaesthesia on the immune response to abdominal hysterectomy. Patients and methodsWe studied 30 women (median age 47 years; range 36-65 years), ASA grades 1 or 2 scheduled for elective abdominal hysterectomy. The patients were allocated randomly to two groups. Patients with immunosuppressive treatment, malignant disease or marked obesity (weight exceeding the ideal body weight by 30% or more) were not studied.

SummaryWe have earlier found increased percentages of T helper cells (CD4-positive lymphocytes) in the blood circulation after propofol infusion anaesthesia. Cytokines interferon-g (IFN g ) and interleukin-4 (IL-4) are important in the differentiation of T helper cells into subtypes T helper type-1 (Th1) and type-2 (Th2). To study the effects of propofol emulsion, its solvent Intralipid ® and thiopentone on Th1/Th2 balance, measurements of IFN g and IL-4 production by mononuclear leucocytes were carried out in vitro. As IL-2 has a central role in immune responses to surgery, its production was also measured. Concanavalin A-stimulated mononuclear cells were cultured in the presence of propofol emulsion at 3.5 or 10 mg.ml ¹1 , Intralipid ® 35 or 100 mg.ml ¹1 , or thiopentone 3 mg.ml ¹1 . Cytokine production was measured from the conditioned media of mononuclear cell cultures. Decreased IFN g (p < 0:001) and IL-4 concentrations (p < 0:01) were found in the presence of thiopentone, but IL-2 production was unaffected. By contrast, propofol emulsion or Intralipid ® had no effects on IFN g , IL-2 or IL-4 concentrations. Propofol 10 mg.ml ¹1increased the IFN g /IL-4 ratio from the control value median 243 (162-562) (25th-75th percentile) to 363 (195-1028) (p < 0:01), but thiopentone decreased it to 145 (60-214) (p < 0:01). These findings show that propofol and thiopentone have different effects in vitro on Th1/Th2 balance and suggest that they have different modulating effects on the immune response.