Chronic AT1-receptor blockade does not alter cerebral oxygen supply/demand ratio during cardiopulmonary bypass in hypertensive patients.

BACKGROUND: The angiotensin II receptor type 1 antagonist candesartan has been hypothesized to alter vasopressor requirements and brain-blood flow by changing cerebrovascular autoregulation. Therefore, we assessed the effects of a pre-anaesthetic treatment course with candesartan on cerebral arterial-jugular bulb oxygen content difference, middle cerebral artery blood velocity, and vasopressor requirements in hypertensive patients undergoing elective on-pump coronary artery bypass graft surgery. METHODS: In a randomized, double-blind, placebo-controlled study, we evaluated the effects of candesartan (8 mg po/d, given for 6-8 days before surgery) in 35 hypertensive patients. The mean arterial pressure was maintained above 60 mmHg by bolus administration of phenylephrine, if required, and dosages were recorded. RESULTS: Candesartan did not significantly alter oxygen content difference across the cerebral circulation, mean middle cerebral artery blood velocity during cardiopulmonary bypass, or phenylephrine requirements either before (0.0067 microg/kg/min+/-0.0042 vs. 0.0056 microg/kg/min+/-0.0049, P=0.48) or during cardiopulmonary bypass (0.0240 microg/kg/min+/-0.0240 vs. 0.0250 microg/kg/min+/-0.0190, P=0.97) compared with placebo. CONCLUSION: Thus, a 6-8-day treatment course with candesartan does not alter global cerebral perfusion and oxygen supply/demand ratio during cardiopulmonary bypass, or vasopressor requirements in hypertensive patients undergoing on-pump coronary artery bypass graft surgery, and no deleterious consequences of AT1-receptor blockade were detected.

Minimally invasive endoscopic port-access intracardiac surgery with one lung ventilation: impact on gas exchange and anaesthesia resources.

Minimally invasive endoscopic intracardiac surgery including one lung ventilation has been proposed to decrease surgical trauma but its impact on oxygenation and resource consumption has not been reported. We compared effects on gas exchange, induction, total anaesthesia time, staffing costs, and complications in 42 consecutive patients to a matched group undergoing similar surgery conventionally. Use of endoscopic compared to conventional surgery evoked a decrease in the P(a)o(2)/F(I)o(2) ratio (mean (SD) 24.1 (14.9) vs 48.9 (14) kPa, p < 0.05) following termination of bypass with one lung ventilation (10 patients showed a P(a)o(2)/F(i)o(2) below 13.3 kPa (100 mmHg)). There was also an increase of anaesthesia induction time (47 (13) vs 31 (9) min, p < 0.05), and an increase by 156 min of total anaesthesia time (474 (89) vs 321 (69) min, p < 0.05). Anaesthetist staffing costs increased by 300%. Thus, minimally invasive endoscopic intracardiac surgery consumes many more anaesthesia resources than conventional surgery and can result in hypoxaemia, but overall can be considered feasible provided that extensive continuous monitoring is employed.

Disseminated intravascular clotting associated with Fc-receptor IIa-mediated platelet activation in a patient with endocarditis after aortic valve replacement.

This report describes fatal disseminated cardiovascular thrombosis associated with Fc-receptor IIa-mediated platelet activation during surgery for aortic valve replacement in a patient with endocarditis. The patient's serum contained antibodies which strongly activated platelets via the Fc-receptor IIa. Antibodies did not bind to platelet factor 4 or aprotinin and binding was independent of heparin. The mechanisms and differential diagnosis for such a complication are discussed. Our data show for the first time in a patient with endocarditis that, beside HIT, other immune complexes can induce massive intravascular coagulation via platelet Fc-receptor IIa activation.

[Mechanisms of tachyphylaxis in regional anesthesia of long duration]. / Mechanismen der Tachyphylaxie bei langdauernden Regionalanästhesien.

Tachyphylaxis to local anesthetics is defined as a decrease in duration, segmental spread or intensity of a regional block despite repeated constant dosages. However, there is disagreement about the incidence of tachyphylaxis. In contrast to tachyphylaxis, pseudotachyphylaxis denotes time dependent variations in pain or circadian changes in the duration of local anesthetic action. Tachyphylaxis appears neither to be linked to structural or pharmacological properties of the local anesthetics nor to the technique or mode of their administration. The mechanisms underlying tachyphylaxis are open to debate and include changes in pharmacokinetics or pharmacodynamics. Considering pharmacokinetics, local edema, an increased epidural protein concentration, changes in local anesthetic distribution in the epidural space or a decrease of perineural pH could result in decreased diffusion of the local anesthetics from the epidural space to their binding sites at the sodium channel. Increased clearance of local anesthetics from the epidural space may be caused both by increased epidural blood flow or increased local metabolism. Considering pharmacodynamics, antagonistic effects of nucleotides or increased sodium concentration, increased afferent input from nociceptors or receptor down regulation of the sodium channels have been implicated. However, none of these theoretical considerations is supported strongly enough by data to explain tachyphylaxis. A new possibility to maintain for a longer time neural blockade is the design of new ultralong-acting local anesthetics. Liposomal formulations of local anesthetics also appear suitable to provide longer lasting regional anesthesia. The recent observation that NMDA-antagonists as well as NO-synthase-inhibitors prevent the development of tachyphylaxis suggests involvement of the nitric oxide pathway in the development of tachyphylaxis. Accordingly, NMDA-antagonists or NO-synthase-inhibitors may prevent tachyphylaxis.