Effects of dexmedetomidine on kidney and brain tissue microcirculation and histology in ovine cardiopulmonary bypass: a randomised controlled trial.

Cardiac surgery requiring cardiopulmonary bypass is associated with postoperative acute kidney injury and neurocognitive disorders, including delirium. Intra-operative inflammation and/or impaired tissue perfusion/oxygenation are thought to be contributors to these outcomes. It has been hypothesised that these problems may be ameliorated by the highly selective α2 -agonist, dexmedetomidine. We tested the effects of dexmedetomidine on renal and cerebral microcirculatory tissue perfusion, oxygenation and histology in a clinically relevant ovine model. Sixteen sheep were studied while conscious, after induction of anaesthesia and during 2 h of cardiopulmonary bypass. Eight sheep were allocated randomly to receive an intravenous infusion of dexmedetomidine (0.4-0.8 µg.kg-1 .h-1 ) from induction of anaesthesia to the end of cardiopulmonary bypass, and eight to receive an equivalent volume of matched placebo (0.9% sodium chloride). Commencement of cardiopulmonary bypass decreased renal medullary tissue oxygenation in the placebo group (mean (95%CI) 5.96 (4.24-7.23) to 1.56 (0.84-2.09) kPa, p = 0.001), with similar hypoxic levels observed in the dexmedetomidine group (6.33 (5.33-7.07) to 1.51 (0.33-2.39) kPa, p = 0.002). While no differences in kidney function (i.e. reduced creatinine clearance) were evident, a greater incidence of histological renal tubular injury was observed in sheep receiving dexmedetomidine (7/8 sheep) compared with placebo (2/8 sheep), p = 0.041. Graded on a semi-quantitative scale (0-3), median (IQR [range]) severity of histological renal tubular injury was higher in the dexmedetomidine group compared with placebo (1.5 (1-2 [0-3]) vs. 0 (0-0.3 [0-1]) respectively, p = 0.013). There was no difference in cerebral tissue microglial activation (neuroinflammation) between the groups. Dexmedetomidine did not reduce renal medullary hypoxia or cerebral neuroinflammation in sheep undergoing cardiopulmonary bypass.

Orthotopic liver transplantation in two patients with hypertrophic obstructive cardiomyopathy.

Orthotopic liver transplantation (OLT) in patients with end-stage liver disease is a procedure associated with high cardiac output, low systemic vascular resistance (SVR), coagulopathy and the potential for significant blood loss. A feature of hypertrophic obstructive cardiomyopathy (HOCM) is left ventricular outflow tract obstruction which may be exacerbated by reduced SVR, reduced filling pressures, tachycardia and positive inotropy. We report two cases of OLT in patients with HOCM. Our anaesthetic technique involved the use of halothane and vecuronium and avoidance of drugs causing tachycardia and positive inotropy. Management was aided by intraoperative transoesophageal echocardiography which showed that filling pressures poorly reflected end-diastolic volumes. Volume administration, vasoconstrictors and avoidance of inotropes and chronotropes reduced the outflow tract obstruction which was particularly severe in the reperfusion period.

Prediction of the mediastinal drainage after coronary artery bypass surgery.

Using multiple correlation and linear regression approaches, we investigated the association between the amount of mediastinal drainage for the first 24 postoperative hours and clinical variables as well as multiple haematological tests performed at three time points: before anaesthesia induction, 10 minutes after protamine administration and just after skin closure, on 46 patients undergoing primary coronary artery bypass grafting. Three models from the three times were then developed to predict mediastinal drainage. The number of internal mammary grafts, the total number of grafts and plasma fibrinogen concentration were useful predictors of mediastinal drainage at all three times. The platelet count taken only after skin closure was found to provide additional predictive information. Each regression model explained approximately 60% of the variation in postoperative mediastinal drainage. The information obtained from these predictive models is useful in defining high-risk populations.

Patterns of coagulopathy during liver transplantation: experience with the first 75 cases using thrombelastography.

Using both conventional laboratory clotting profile and thrombelastography, coagulation status was monitored intraoperatively during liver transplantation in the first 75 cases performed at the Austin Hospital between June 1988 and October 1992. Superimposed on a baseline coagulopathy due to liver disease is a specific pattern of coagulation disturbance which occurs during a liver transplant. Fibrinolysis occurs in the anhepatic stage, worsens with early reperfusion and then spontaneously resolves. In addition reperfusion is associated with a transient clotting defect. If blood loss is excessive, coagulopathy due to massive transfusion may compound the situation. Thrombelastography is a measurement technique allowing rapid on-site assessment of functional clotting status. It is particularly useful in liver transplant surgery. In combination with clinical bleeding assessment it facilitates selective use of component therapy (fresh frozen plasma, platelets and cryoprecipitate) and specific drug treatment only when it is appropriate. It also acts as a liver function test, being especially useful in assessing the graft after reperfusion.

Blood loss and transfusion requirements in liver transplantation: experience with the first 75 cases.

The blood loss data and transfusion requirements including blood bank, salvaged washed red cells, fresh frozen plasma and cryoprecipitate were analysed for the first 75 cases of liver transplantation performed at the Austin Hospital between June 1988 and October 1992. The mean blood loss was 8.8 litres (standard deviation 14.1) with a median value of 4.0 litres. Blood product use expressed as mean number of units (SD) was bank red blood cells 7.1 (12.7), washed red blood cells 3.9 (5.9), fresh frozen plasma 7.1 (9.1), platelets 5.1 (7.4), and cryoprecipitate 1.7 (5.1). These results demonstrate that liver transplantation can be performed without imposing excessive demands on blood transfusion services. Management should include surgical techniques to minimize bleeding and use of autologous transfusion. Use of component therapy (FFP, platelets and cryoprecipitate) should not be empirical. It should be selective on the basis of clinical bleeding assessment and guided by results of the laboratory coagulation profile and changes in thrombelastographic (TEG) parameters.