New anticoagulant drugs: monitoring and perioperative strategies.

Arterial and venous thromboses are major causes of mortality and morbidity. In Western countries, more than 1% of the population takes an antithrombotic agent. Many of these patients will need to undergo surgery and decisions need to be made regarding whether to continue their antithrombotic medication and risk increased bleeding or to stop it and potentially increase the risk of thrombosis. Anaesthesiologists, therefore, need to be aware of the basic pharmacology of the available agents as well as their individual indications, contraindications, and adverse effects. In this review we will discuss these aspects, and also discuss new antithrombotic agents that are currently being developed to improve efficacy and to increase safety in comparison with conventional agents. New coagulation monitoring devices will also be discussed.

Plasma substitution effects of a new hydroxyethyl starch HES 130/0.4 compared with HES 200/0.5 during and after extended acute normovolaemic haemodilution.

BACKGROUND: The volume expansion effect of a recently introduced hydroxyethyl starch, HES 130/0.4, was compared with the commonly used HES 200/0.5 after rapid infusion of a single large dose (up to 2 litres) administered during acute normovolaemic haemodilution (ANH). METHODS: This prospective, randomized, double-blind study included 40 patients scheduled for major abdominal surgery with no contraindication to ANH. Patients were randomized to undergo ANH with either HES 130/0.4 (n=20) or HES 200/0.5 (n=20). Blood was collected to reach a target haemoglobin level of about 8.0 g dl(-1) and simultaneously replaced by the same volume of colloid (HES 130: 1825 [SD 245] ml; HES 200: 1925 [183] ml). Heart rate, mean arterial pressure, cardiac filling pressure, and cardiac output were measured before induction of anaesthesia (baseline), 10 min after completion of ANH, before surgery, at the end of surgery and on the following morning (postoperative day 1; POD1). ANH blood was systematically retransfused during surgery or before POD1. RESULTS: Exchange of about 40% of blood volume resulted in similar haemodynamic changes in both groups. Filling pressures increased significantly, while cardiac index remained unchanged (HES 130: from 3.3 [0.4] to 3.2 [0.7] litre min(-1) m(-2); HES 200: from 3.0 [0.6] to 3.1 [0.7] litre min(-1) m(-2)). Need for crystalloids and colloids was similar between the groups during surgery and on POD1. Total blood loss (HES 130: median 2165 ml, range 660-2970 ml; HES 200: median 2464 ml, range 640-19 380 ml) and amount of allogeneic red blood cells transfused (HES 130: median 0, range 0-4 units; HES 200: median 0, range 0-18 units) were comparable in the two groups. CONCLUSIONS: This study demonstrates a good immediate and medium-term plasma volume substitution effect of HES 130 compared with HES 200. HES 130 could represent a suitable synthetic colloid for plasma volume substitution during extensive ANH.

Tropisetron in the prevention of postoperative nausea and vomiting.

STUDY OBJECTIVES: To evaluate the efficacy of tropisetron, a selective 5-HT(3) receptor antagonist, in preventing nausea and vomiting in high-risk inpatients undergoing various surgical procedures. DESIGN: Prospective, open, nonrandomized, observational, interventional study. SETTING: Postanesthesia care unit, and surgical wards of the University Hospital Center, Charleroi. PATIENTS: A total of 1,132 elective surgical inpatients (>15 years of age) in two separate surveys. The first prospective survey covered all surgical adult inpatients (n = 671) after various surgical procedures over a 3-month period. A new 3-month survey was performed to assess the effectiveness of the preventive measure and included another 461 patients. INTERVENTIONS: Risk factors associated with nausea and vomiting were recorded in the first survey and used to establish an antiemetic policy. This consisted in the administration of tropisetron 2 mg intravenously after anesthesia induction, if two patient-related risk factors associated with high-risk surgery and general anesthesia were present. MEASUREMENTS AND MAIN RESULTS: Nausea frequency and intensity, assessed every 4 hours using a visual analog scale (VAS), frequency and times of vomiting episodes and the need for rescue medication were recorded for 72 hours postoperatively. Nausea was experienced by 18.8% and vomiting by 9.8% of the patients in the first survey (211 high risk-patients of 671). In the second survey, 137 patients of 461, considered at high-risk received prophylactic tropisetron. The proportion of patients having nausea decreased to 11.1% (p,178 0.01) and vomiting episodes to 2.8% (p < 0.001). Twenty-six of the tropisetron-treated patients (19%) suffered subsequent postoperative nausea and vomiting (PONV). Patient satisfaction with tropisetron was high. CONCLUSION: Prophylactic tropisetron can reduce the incidence of PONV in selected high-risk inpatients undergoing various types of surgical procedures.

Cardiovascular and metabolic response to acute normovolemic anemia. Effects of anesthesia.

BACKGROUND: The maintenance of adequate tissue oxygenation during acute anemia depends on an increase in both cardiac output and tissue oxygen extraction. This study tested the hypothesis that anesthesia blunts the cardiac output response associated with acute normovolemic hemodilution. METHODS: Forty patients undergoing major abdominal surgery were prospectively randomized to undergo acute normovolemic hemodilution (ANH) either awake (awake group, n = 20) or with fentanyl-nitrous oxide-isoflurane anesthesia (anesthetized group, n = 20). Radial and pulmonary artery catheters were placed in all patients. After hemodynamic measurements were taken, patients in the two groups underwent hemodilution to decrease their hemoglobin concentration from 13 to 8 g/dl. A total of 1,875 +/- 222 ml (mean +/- SD) of blood was collected and simultaneously replaced by the same volume of medium molecular weight hydroxyethylstarch in both groups. RESULTS: In the awake group, ANH resulted in a significant increase in cardiac index (from 3.1 +/- 0.5 to 4.8 +/- 1.0 l. min-1. m-2) related to both an increase in heart rate and stroke index. Oxygen delivery remained unchanged, but oxygen consumption increased significantly, resulting in an increase in oxygen extraction ratio. In the anesthetized group, ANH resulted in a significantly smaller increase in cardiac index (from 2.3 +/- 0.5 to 3.1 +/- 0.7 l. min-1. m-2) related solely to an increase in stroke index. Oxygen delivery decreased but oxygen consumption was maintained as oxygen extraction increased. CONCLUSIONS: Anesthesia significantly reduces the cardiac output response associated with ANH. This could be related to the effects of the anesthetic drugs on the autonomic and the cardiovascular systems.