Platelet antiaggregate activity

Nicardipine versus nitroprusside for deliberate hypotension during idiopathic scoliosis repair

STUDY OBJECTIVE

To compare coagulation, blood loss, and transfusion requirements between patients receiving nicardipine and nitroprusside for deliberate hypotension during idiopathic scoliosis repair.

DESIGN

Prospective, randomized study.

SETTING

University hospital.

PATIENTS

51 ASA physical status I patients presenting for spine fusion for idiopathic adolescent scoliosis.

INTERVENTIONS

Patients were randomized to two groups to receive nicardipine or nitroprusside to maintain mean arterial pressure (MAP) between 55 and 65 mmHg.

MEASUREMENTS

Blood loss, blood transfusions, and coagulation studies (thromboelastogram and platelet aggregation) before starting vasodilator, 30 minutes and 90 minutes after starting vasodilator, and 30 minutes after stopping vasodilator, were all recorded.

MAIN RESULTS

There was no difference between the groups in blood loss [nicardipine = 1,129 cc (893 to 1,480), nitroprusside = 960 cc (704 to 1,473)] and only one patient required a nonautologous transfusion. There were no differences in prothrombin time (pT, partial thromboplastin time (pTT), platelet count, or platelet aggregation between groups. There were more episodes of severe hypotension (MAP <45 mmHg) in the nitroprusside group (0% vs. 28%, p = 0.0175). On average, patients in the nicardipine group spent 21 minutes less in the recovery room than did the nitroprusside group (p = 0.043).

CONCLUSIONS

Nitroprusside's effect on platelet aggregation produces no increase in blood loss compared with nicardipine. Nicardipine causes less transient severe hypotension than nitroprusside, although both drugs are acceptable choices for obtaining the goals of deliberate hypotension.

Oxidative stress and platelet responsiveness in migraine

The aim of this study is to investigate whether oxidative stress may represent a pivotal determinant of the altered functional features of platelets in migraineurs during the headache-free period. Twenty-three patients with migraine with aura, free of attack, and 23 healthy volunteers were enrolled for the study. The involvement of an oxidative condition appears confirmed by the statistically significant increase (p < 0.001) of plasma levels of thiobarbituric acid-reactive substances which may be considered a marker for oxidative stress and themselves strong-pro-oxidants. Such oxidative status seems to induce in platelets of migraineurs increased membrane rigidity (p < 0.001), reduced cytosolic calcium in the resting condition and after thrombin stimulation (p < 0.001), and decreased aggregatory responses to ADP and collagen. These findings indicate that the "in vitro" anomalous platelet behavior in migraineurs, observed in headache-free periods, may be considered as the transient expression of the exhausted platelets to "in vivo" stimulation and probably related to an increased vulnerability to oxidative stress.

Platelet sensitivity to prostaglandin E1 inhibition is reduced in pre-eclampsia but not in nonproteinuric gestational hypertension

OBJECTIVE

Platelet aggregometry was used to discriminate platelet sensitivity to prostaglandin E1 (PGE1) inhibition, to evaluate whether platelet behaviour in pre-eclamptic women was different in this respect than from that in nonproteinuric hypertensive women.

METHODS

The amount of PGE1 required to inhibit in vitro platelet aggregation induced by arachidonic acid was determined in samples from 60 women: 20 nonpregnant controls, 20 women with normal pregnancies, 10 women with gestational hypertension and 10 with pre-eclampsia.

RESULTS

The response to arachidonic acid was similar among the four groups. Amounts of PGE1 necessary to inhibit platelet aggregation were significantly higher in normal pregnant women compared with nonpregnant controls (P<0.001). Platelets from pre-eclamptic women required significantly higher concentrations of PGE1 to inhibit aggregation than the other groups studied (P<0.001). However, there was no significant difference between normal and nonproteinuric hypertensive pregnant women.

CONCLUSIONS

Our findings support the notion that increased platelet reactivity during late pregnancy is exacerbated in pre-eclamptic women but not in nonproteinuric hypertensive women. This is in agreement with the hypothesis that pre-eclampsia and gestational hypertension are different conditions. Prospective studies are required to confirm if this simple test may be useful in the early identification of pregnant women at risk for pre-eclampsia.

Platelet activation during myocardial ischaemia: a contributory arrhythmogenic mechanism

Experimental and clinical observations of the involvement of platelets in the pathophysiology of myocardial ischaemia indicate the importance of interactions between these formed elements and the heart. The aim of this review is to outline evidence linking platelet activation, myocardial ischaemia and infarction, and to present evidence for a link between platelet activation, arrhythmogenesis and sudden death. A brief review of platelet physiology and pharmacology is provided, with a review of the cardiac electrophysiological effects of ischaemia and the electrophysiological effects of platelet-derived substances. The concept that platelet activation during myocardial ischaemia is a contributory arrhythmogenic mechanism is discussed.

Platelet changes in classic migraine

We investigated some ultrastructural aspects of platelet activity in patients with classic migraine during an attack-free period. We focused on the production of malondialdehyde (MDA), the intracellular concentration of Ca++ and the membrane phospholipid structure using a DPH (1,6 diphenyl-1,3,5 hexatriene) fluorescent probe. Our study comprised 20 patients with classic migraine and 5 healthy controls, from whom 10 cc samples of blood were collected in test tubes containing sodium citrate (1/9 cc). We found no significant differences in MDA production between migraineurs and controls either before or after stimulation with thrombin. The same applies to the concentration of intracellular Ca++ (Ca++i). The membrane lipid composition assessed by DPH fluorescent probe was normal both in migraineurs and in controls. Our findings suggest no intrinsic activation of platelet aggregation.