Hideo Hirakata

Sevoflurane inhibits human platelet aggregation and thromboxane A2 formation, possibly by suppression of cyclooxygenase activity

Background Halothane increases bleeding time and suppresses platelet aggregation in vivo and in vitro. A previous study by the authors suggests that halothane inhibits platelet aggregation by reducing thromboxane (TX) A2 receptor-binding affinity. However, no studies of the effects of sevoflurane on platelet aggregation have been published. Methods The effects of sevoflurane, halothane, and isoflurane were examined at doses of 0.13-1.4 mM. Human platelet aggregation was induced by adenosine diphosphate, epinephrine, arachidonic acid, prostaglandin G sub 2, and a TXA2 agonist ([+]-9,11-epithia-11,12-methano-TXA2, STA2) and measured by aggregometry. Platelet TXB2 levels were measured by radioimmunoassay, and the ligand-binding characteristics of the TXA2 receptors were examined by Scatchard analysis using a [sup 3 Hydrogen]-labeled TXA2 receptor antagonist (5Z-7-(3-endo-([ring-4-[sup 3 Hydrogen] phenyl) sulphonylamino-[2.2.1.] bicyclohept-2-exo-yl) heptenoic acid, [sup 3 H]S145). Results Isoflurane (0.28-0.84 mM) did not significantly affect platelet aggregation induced by adenosine diphosphate and epinephrine. Sevoflurane (0.13-0.91 mM) and halothane (0.49-1.25 mM) inhibited secondary platelet aggregation induced by adenosine diphosphate (1-10 micro Meter) and epinephrine (1-10 micro Meter) without altering primary aggregation. Sevoflurane (0.13 mM) also inhibited arachidonic acid-induced aggregation, but not that induced by prostaglandin G2 or STA2, although halothane (0.49 mM) inhibited the latter. Sevoflurane (3 mM) did not affect the binding of [sup 3 H]S145 to platelets, whereas halothane (3.3 mM) suppressed it strongly. Sevoflurane (0.26 mM) and halothane (0.98 mM) strongly suppressed TXB2 formation by arachidonic acid-stimulated platelets. Conclusions The findings that sevoflurane suppressed the effects of arachidonic acid, but not those of prostaglandin G2 and STA2, suggest strongly that sevoflurane inhibited TXA2 formation by suppressing cyclooxygenase activity. Halothane appeared to suppress both TXA2 formation and binding to its receptors. Sevoflurane has strong antiaggregatory effects at subanesthetic concentrations (greater than 0.13 mM; i.e., approximately 0.5 vol/%), whereas halothane has similar effects at somewhat greater anesthetic concentrations (0.49 mM; i.e., approximately 0.54 vol/%). Isoflurane at clinical concentration (0.84 mM; i.e., approximately 1.82 vol/%) does not affect platelet aggregation significantly.

Delayed discharge and acceptability of ambulatory surgery in adult outpatients receiving general anesthesia

PurposeDelay in discharge after ambulatory surgery impairs its cost-effectiveness. However, it is not self-evident that prolonged postoperative stay is associated with low quality of care and patient acceptability of ambulatory surgery. The aims of this study were to document factors affecting delay in discharge, recovery profiles, and patient acceptability in adult outpatients.MethodsPerioperative data were collected prospectively on consecutive 726 adult same-day surgical patients receiving general anesthesia. Factors that affected home-readiness, discharge, and unanticipated admission were noted. Patients were followed up 24 h after discharge using a standardized questionnaire to identify postdischarge symptoms, patient’s self-rated resumption of normal activity (RNA) level, and preference of outpatient procedure.ResultsEighty-two percent of patients were discharged home <270 min after operation, 16% were delayed (≥270 min), and 2% required unanticipated admission. Delayed patients reported postdischarge pain more frequently (53%) and a lower 24-h postoperative RNA level (7.2 ± 1.8) and preference ratio (76%) than no-delay patients (34%, 8.0 ± 1.9, 87%, respectively; P < 0.001). Delay in home-readiness (≥165 min) was mainly due to an adverse symptom, and delay in discharge after reaching home-readiness (≥150 min) was mainly due to a persistent symptom (58%) or a social/system problem (34%). Causes of admission were perioperative complications (80%) or social reasons (20%).ConclusionDelays in discharge are mainly due to adverse symptoms or social/system problems. Delayed discharge is associated with increased postdischarge pain, lower RNA level, and patient acceptability. Appropriate care of postoperative symptoms and system management could prevent delay in discharge and improve patient RNA level and acceptability.

Ketamine Suppresses Platelet Aggregation Possibly by Suppressed Inositol Triphosphate Formation and Subsequent Suppression of Cytosolic Calcium Increase

Background Ketamine has been shown to suppress platelet aggregation, but its mechanisms of action have not been defined. The purpose of the current study is to clarify the effects of ketamine on human platelet aggregation and to elucidate the underlying mechanisms of its action. Methods Platelet aggregation was measured using an eight-channel aggregometer, and cytosolic free calcium concentration was measured in Fura-2/AM–loaded platelets using a fluorometer. Inositol 1,4,5-triphosphate (IP3) was measured with use of a commercially available IP3 assay kit. To estimate thromboxane A2 (TXA2) receptor binding affinity and expression, Scatchard analysis was performed using [3H]S145, a specific TXA2 receptor antagonist. TXA2 agonist binding assay was also performed. The membrane-bound guanosine 5′-triphosphatase activity was determined using [&ggr;-32P]guanosine triphosphate by liquid scintillation analyzer. Results Ketamine (500 &mgr;m) suppressed aggregation induced by adenosine diphosphate (0.5 &mgr;m), epinephrine (1 &mgr;m), (+)-9,11-epithia-11,12-methano-TXA2 (STA2) (0.5 &mgr;m), and thrombin (0.02 U/ml) to 39.1 ± 30.9, 46.3 ± 4.3, −2.0 ± 16.8, and 86.6 ± 1.4% of zero-control, respectively. Ketamine (250 &mgr;m–1 mm) also suppressed thrombin- and STA2-induced cytosolic free calcium concentration increase dose dependently. Although ketamine (2 mm) had no effect on TXA2 receptor expression and its binding affinity, it (1 mm) suppressed intracellular peak IP3 concentrations induced by thrombin and STA2 from 6.60 ± 1.82 and 4.39 ± 2.41 to 2.41 ± 0.98 and 1.90 ± 0.86 pmol/109 platelets, respectively, and it suppressed guanosine triphosphate hydrolysis induced by thrombin (0.02 units/ml) and STA2 (0.5 &mgr;m) to 50.3 ± 3.2 and 67.5 ± 5.5%versus zero-control, respectively. Conclusion Ketamine inhibits human platelet aggregation possibly by suppressed IP3 formation and subsequent suppression of cytosolic free calcium concentration. The site of action of ketamine is neither TXA2 nor thrombin binding sites but possibly receptor-coupled mechanisms, including G-protein.

Platelet aggregation is impaired during anaesthesia with sevoflurane but not with isoflurane

PurposeHalothane suppresses platelet aggregationin vitro and ex vivo, and prolongs bleeding time. In a previous invitro study we demonstrated that sevoflurane had a more suppressive effect on platelet aggregation than did halothane. The present study investigated whether the clinical use of sevoflurane affected platelet aggregationex vivo.MethodsThirty-eight patients undergoing minor elective surgery were divided randomly into sevoflurane and isoflurane groups. Anaesthesia was induced with thiopentoneiv, and was maintained with sevoflurane or isoflurane with nitrous oxide. Blood was collected to measure platelet aggregation induced by adenosine diphosphate (ADP) and epinephrine. The first (control) blood collection was performed in the operating room before induction of anaesthesia, and the second 5–10 min after tracheal intubation but before the start of surgery, when the end-expiratory sevoflurane or isoflurane concentrations had stabilised at 1–1.5 times the minimum alveolar concentration (MAC) and mean artenal pressures were between 80–120% of preanaesthetic values.ResultsIn all samples obtained dunng sevoflurane anaesthesia (n= 15), ADP and epinephnne could not induce secondary aggregation, although they did induce pnmary aggregation. In contrast, in the isoflurane group, both primary and secondary aggregation were observed in 14 out of 15 patients, and secondary aggregation was abolished in only one of the samples obtained dunng anaesthesia.ConclusionSevoflurane, but not isoflurane, alters platelet aggregation in the clinical situation, possibly by suppression of thromboxane A2 formation.RésuméObjectifL’halothane inhibe l’agrégation plaquettairein vitro etin vivo et prolonge le temps de saignement. Nous avons anténeurement démontré que le sévoflurane avait un effet inhibiteurin vitro plus important sur l’agrégation plaquettaire que l’halothane. La présente étude a pour but de vérifier si l’usage clinique du sévoflurane affecte l’agrégation plaquettairein vivo.MéthodesTrente-huit patients soumis à une chirurgie élective mineure répartis au hasard en groupe sévoflurane et groupe isoflurane participaient à l’étude. L’anesthésie était induite au thiopentaliv, et entretenue au sévoflurane ou à l’isoflurane avec du protoxyde d’azote. Du sang était recueilli pour la mesure de l’agrégation plaquettaire induite par le diphosphate d’adénosine (ADP) et l’épinéphnne. Le premier échantillon sanguin (contrôle) était recueilli en salle d’opération avant l’induction de l’anesthésie et le second, 5–10 min après l’intubation trachéale et avant le début de l’intervention après stabilisation des concentrations télé-expiratoires de sévoflurane et d’isoflurane à 1–1,5 fois la concentration alvéolaire minimale (MAC) de même que de la pression arténelle moyenne à 80–120% des valeurs préanesthésiques.RésultatsMalgré une agrégation primaire, l’ADP et l’épinéphnne n’ont induit l’agrégation secondaire dans aucun des échantillons recueillis sous anesthésie au sévoflurane (n = 15). Par contre, on a observé dans le groupe isoflurane une aggrégation tant primaire que secondaire chez 14 des 15 patients, l’agrégation secondaire n’ayant été abolie que chez un seul des patients.ConclusionEn clinique, le sévoflurane contrairement à l’isoflurane altère l’agrégation plaquettaire possiblement par suppression de la formation de thromboxane A2.

The effect of inhaled anesthetics on the platelet aggregation and the ligand-binding affinity of the platelet thromboxane A2 receptor.

The mechanism by which anesthetics suppress platelet aggregation has not been elucidated.We determined the effects of halothane, enflurane, and isoflurane on human platelet aggregation induced by adenosine diphosphate (ADP), epinephrine, and a thromboxane A2 (TXA2) analog, and on ligand binding to the platelet TXA (2) receptor. Halothane (2.6 mM) strongly suppressed ADP- and epinephrine-induced secondary aggregation of platelets, without significant alteration of primary aggregation. Platelet aggregation induced by a specific TXA2 agonist, (+)-9,11-epithia-11,12-methano-TXA (2) (STA2), was suppressed by halothane, enflurane, and isoflurane in a concentration-dependent manner; the concentration of halothane, enflurane, and isoflurane which induced 50% inhibition (IC50) were 3.2, 12.3, and 15.7 mM, respectively (or 4.7, 9.8, and 24 minimum alveolar anesthetic concentration [MAC], respectively). The binding of a specific TXA2 receptor antagonist,3 H-S145, was significantly reduced by halothane (14-28 mM), but not by enflurane (20 mM) and isoflurane (20 mM). Scatchard analysis revealed that halothane (14 mM) increased Kd from 0.53 nM to 14.3 nM but did not alter Bmax significantly. These results indicate that halothane has a stronger suppressive effect on platelet aggregation than enflurane and isoflurane, and that the effect of halothane on platelet aggregation is due to reduction of the ligand-binding affinity of the platelet TXA2 receptor. (Anesth Analg 1995;81:114-8)

Propofol has both enhancing and suppressing effects on human platelet aggregation in vitro.

BACKGROUND Volatile anesthetics are known to suppress platelet aggregation. In contrast, there is conflicting information regarding the effect of propofol on platelet function. The present study was designed to clarify the effects of propofol on platelet function and the mechanisms underlying these effects. METHODS Propofol or an equivalent volume of 10% Intralipos (as a control) was added to test tubes 5 min before the induction of each reaction. Platelet aggregation induced by epinephrine, arachidonic acid (AA), prostaglandin G2 (PGG2), or STA2 (a thromboxane A2 [TXA2] analog) was measured using an eight-channel aggregometer. To determine type 1 cyclooxygenase activity, AA (0.5 mM) was added to an assay mixture containing type 1 cyclooxygenase, and the concentration of the final product, malonaldehyde, was measured by spectrophotometry. Epinephrine-, adenosine diphosphate-, AA-, and PGG2-induced TXA2 formation was measured using a commercially available radioimmunoassay kit. To estimate TXA2 receptor-binding affinity, 3H-S145, a specific TXA2 receptor antagonist, was added, and the radioactivity of receptor-bound 3H-S145 was determined using a liquid scintillation analyzer. Inositol 1,4,5-triphosphate formation was measured in STA2-stimulated platelets using a commercially available inositol 1,4,5-triphosphate assay kit. RESULTS Propofol (40 microM) enhanced, whereas 100 microM suppressed, adenosine diphosphate- and epinephrine-induced secondary aggregation without affecting primary aggregation. Propofol (40 microM) also enhanced, but 100 microM suppressed, AA-induced aggregation. Propofol (100 microM) enhanced PGG2- and STA2-induced aggregation. Propofol (100 microM) suppressed AA-induced TXA2 formation but did not alter that induced by PGG2. Propofol (30-100 microM) suppressed AA-induced malonaldehyde formation, indicating inhibition of type 1 cyclooxygenase activity. Propofol did not alter TXA2 receptor-binding affinity. Propofol (30 and 100 microM) augmented inositol 1,4,5-triphosphate formation in STA2-stimulated platelets. CONCLUSIONS The present findings clearly indicate that high concentrations of propofol suppress the activity of type 1 cyclooxygenase, the enzyme that converts AA to PGG2. Furthermore, propofol also enhanced STA2-induced inositol 1,4,5-triphosphate formation. These results may explain the inconsistent findings of previous investigators.

Anesthesia with sevoflurane, but not isoflurane, prolongs bleeding time in humans.

AbstractPurpose. Halothane has been shown to suppress platelet aggregation in vitro and ex vivo and to prolong bleeding time. In a previous in vitro study, we demonstrated that sevoflurane had a stronger suppressive effect on platelet aggregation than halothane. The present study investigated whether clinical use of sevoflurane affects bleeding time in vivo. Methods. Thirty-four patients undergoing minor elective surgery were randomly assigned to sevoflurane or isoflurane. Anesthesia was induced with intravenous thiopental and maintained with sevoflurane or isoflurane with nitrous oxide. Bleeding time was measured by the Duke method. An initial (control) measurement was obtained in the operating room before the induction of anesthesia, and a second was obtained 5–10 min after endotracheal intubation but before starting the operation, when the end-expiratory concentration of sevoflurane or isoflurane had been stabilized at 1–1.5 times the minimum alveolar concentration (MAC), and the mean arterial pressures were between 80% and 120% of the preanesthetic values. Results. Bleeding time was increased from the preanesthetic value of 2.07 ± 0.82 min to 2.83 ± 0.93 min (n = 15) in the sevoflurane group (P < 0.01) but was not significantly altered in the isoflurane group. Conclusion. Sevoflurane alters bleeding time in the clinical situation.

Halothane and isoflurane preferentially inhibit prostanoid-induced vasoconstriction of rat aorta

In a previous study, we demonstrated that halothane and isoflurane inhibit binding of thromboxane A2 to its receptors on human platelets and thus inhibit prostanoid-induced aggregation strongly. The aim of this study was to determine whether volatile anaesthetics inhibit prostanoid-induced vasoconstriction preferentially. Rat isolated aortic rings were mounted in organ baths and their isometric tension was measured. They were contracted with STA2 (a stable thromboxane A2 analogue), prostaglandin F2α (PGF2α), phenylephrine, and 20 mM KCl, and then exposed to halothane (0.5–3%), isoflurane (0.5–3%), and sodium nitroprusside (SNP, 10−9−3 × 10−7 M). Halothane (2–3%) and isoflurane (2–3%) induced greater relaxation of aortic rings precontracted with STA2 and PGF2α than of those precontracted with phenylephrine (P < 0.01). Halothane induced greater relaxation of rings precontracted with KCl than phenylephrine only at 3%, whereas isoflurance relaxed rings precontracted with KCl more than those with phenylephrine at 0.5, 2 and 3% (P < 0.05). In contrast, SNP relaxed rings precontracted with PGF2α, KCl and phenylephrine equally, but induced smaller relaxations of those precontracted with STA2 (P < 0.05). We conclude that halothane and isoflurane inhibit prostanoid-induced vasoconstriction preferentially, possibly by interacting with prostanoid receptors.RésuméLors d’une étude antérieure, nous avons démontré que l’halothane et l’isoflurane inhibaient la liaison de la thomboxane A2 avec ses récepteurs situés sur les plaquettes humaines et inhibaient fortement ainsi l’agrégation induite par les prostanoïdes. Cette étude vise à déterminer si les anesthésiques volatils inhibent la vasoconstriction induite par les prostanoïdes de façon préférentielle. Des anneaux isolés d’aorte de rat sont introduits dans des bains organiques et leur tension isométrique est mesurée. On les fait a’abord contracter avec du STA2 (un analogue stable de la thomboxane A2), de la prostaglandine F2α (PGF2α), de la phényléphrine, et 20 mM de KCl, et on les expose ensuite à l’halothane (0,5% à 3,0%), l’isoflurane (0,5%–0,3%) et au nitroprussiate de soude (SNP, 10−9−3 × 10−7 M). Vhalothane (2–3%) et l’isoflurane (2–3%) produisent une plus grande relaxation des anneaux aortiques précontractés avec la phényléphrine (P < 0,01). L’halothane produit, mais seulement à 3%, te plus grande relaxation des anneaux précontractés avec le KCL qu’avec la phényléphrine, alors que l’isoflurane aux concentrations de 0,5 2 et 3% relaxe les anneaux précontractés avec le KCl plus que ceux contractés avec la phényléphrine (P < 0,05). Par contre, le SNP relaxe également les anneaux précontractés avec la PGF2α, le KCl et la phényléphrine, mais produit une relaxation moins grande sur ceux qui ont été précontractés avec du STA2 (P < 0,05). Nous concluons que lhalothane et l’isoflurane inhibent la vasoconstriction induite par les prostanoïdes de façon préférentielle, possiblement par interaction avec les récepteurs prostanoïdes.

Bidirectional effects of dexmedetomidine on human platelet functions in vitro

Platelets express the imidazoline (I)-receptor, I1 and I2, as well as the α2-adrenoceptor. Although dexmedetomidine, a selective α2-adrenoceptor agonist with some affinity for the I-receptor is expected to affect platelet function, the effects of dexmedetomidine on platelet functions remain unclear. In the present study, we investigated the effects of dexmedetomidine on human platelet functions in vitro. The effects of dexmedetomidine on platelet aggregation were examined using aggregometers. The formation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in platelets was measured by an enzyme immunoassay. In addition, P-selectin expression in platelets was estimated by flow cytometry. We showed that dexmedetomidine enhances platelet aggregation. But in the presence of yohimbine, an α2-antagonist, dexmedetomidine suppressed platelet aggregation. Efaroxan, an I1-antagonist, and methylene blue, a soluble guanylate cyclase inhibitor, abolished the suppressive effect of dexmedetomidine, whereas idazoxan, an I2-antagonist, showed no effect. Dexmedetomidine suppressed cAMP formation and enhanced P-selectin expression in platelets, and these effects were inhibited by yohimbine. Dexmedetomidine increased cGMP formation in platelets in the presence of yohimbine, and this increase was suppressed by efaroxan. These results demonstrated that dexmedetomidine has both enhancing and suppressive effects on human platelet functions through its action on the α2-adrenoceptor and on the I1-imidazoline receptor, respectively.