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We have explored systemic and regional tolerance to haemodilution during anaesthesia with two different synthetic colloids. Eighteen dogs undergoing mechanical ventilation during anaesthesia with ketamine were submitted to progressive normovolaemic haemodilution with either gelatin (GEL; n = 9) or hydroxyethylstarch (HES; n = 9) administered on a 1:1 ratio. Systemic oxygen delivery was calculated from measurement of thermodilution cardiac output and arterial oxygen content, while systemic oxygen consumption was determined from expired gas analysis. Mesenteric oxygen delivery and consumption were determined using ultrasonic flow measurements, and arterial and mesenteric venous oxygen contents. The critical haemoglobin concentration (i.e. the haemoglobin value below which oxygen consumption becomes oxygen delivery dependent) was mean 3.6 (SD 0.8) g dl-1 in the GEL and 3.5 (1.5) g dl-1 in the HES group. The mesenteric critical oxygen extraction ratio (O2ER) (GEL 50.1 (12.1)%; HES 48.5 (13.4)%) was significant lower than the systemic critical O2ER (GEL 66.1 (8.4)%; HES 67.7 (7.1)%). There were no significant differences between the GEL and HES groups for any of these variables, or in the amount of colloid administered. During the study, oxygen delivery decreased almost linearly with reduction in haemoglobin, indicating a lack of cardiac output response to anaemia during ketamine anaesthesia.

† A prospective randomized controlled trial tested the effects of a single dose of dexamethasone at the induction of anaesthesia on postoperative nausea, vomiting, and pain in children after tonsillectomy † Dexamethasone reduced the incidence of postoperative nausea, vomiting, and pain in children at both doses tested. Background. The efficacy of dexamethasone (DEX) to reduce morbidity after paediatric tonsillectomy remains controversial. We evaluated the effect of 0.15 and 0.5 mg kg 21 DEX on the incidence of postoperative nausea and vomiting (PONV) and on pain intensity after paediatric tonsillectomy. Methods. A total of 147 children aged 2–8 yr undergoing elective tonsillectomy were included in this prospective randomized double-blind study. At the induction of anaesthesia, subjects received 0.15 mg kg 21 (DEX 0.15), 0.5 mg kg 21 (DEX 0.5) DEX, or an equivalent volume of saline solution (placebo). Anaesthetic and surgical techniques were standardized. The incidence of PONV and the need for anti-emetic drugs and additional analgesia (tramadol and/or morphine) were recorded. Postoperative pain was assessed using the Children’s Hospital of Eastern Ontario Pain Scale, the visual analogue scale, and the postoperative pain measure for parents. Results. The incidence of early PONV (primary outcome variable) was lower in both DEX groups (DEX 0.15: 21%; DEX 0.5: 22%; placebo: 49%; P¼0.001). The incidence of severe pain was reduced in the DEX groups on the second postoperative day (DEX 0.15: 20%; DEX 0.5: 5%; placebo: 47%; P,0.001). The study was not powered to assess a difference between the two DEX dose groups. Conclusions. A single i.v. injection of DEX at the induction of anaesthesia was effective in reducing the incidence of early and late PONV and the level of pain on the second postoperative day. A 0.15 mg kg 21 DEX dose appeared to be as effective as a 0.5 mg kg 21 dose to reduce the incidence of PONV.