Dosage des isoformes cardiaques des troponines T ou I : intérêt en cardiologie et en anesthésie–réanimation

Measurement of cardiac troponin I or T in serum (highly specific for the myocardium) have replaced classical markers, such as creatine kinase MB. Cardiac troponins are preferred markers because of their high specificity and sensitivity. This had led to modifications of the original World Health Organization criteria for acute myocardial infarction. Furthermore, the place of the troponins as superior markers of subsequent cardiac risk in acute coronary syndrome has now become firmly established, for both diagnostic and risk stratification purposes. The use of C-reactive protein and/or other inflammatory biomarkers may add independent information in this context. After non cardiac surgery, the total cardiospecificity of cardiac troponins explains why other biomarkers of necrosis should no longer be used. Recent studies suggest that any elevation of troponin in the postoperative period is indicative of increased risk of long-term cardiac complications. This prognostic value has been previously demonstrated in other clinical settings such as invasive coronary intervention (surgical myocardial revascularization and percutaneous coronary intervention) and after heart valve surgery. Increases of troponin indicate cardiac damage, whatever the mechanism (ischemic or not). Other causes of cardiac injury include: pulmonary embolism, myocarditis, pericarditis, congestive heart failure, septic shock, myocardial contusion. In most cases, elevation of troponins has been shown to be associated with a bad outcome.

[Anesthesia of hypertensive patients]

Hypertension is a frequent condition among adults. It is one of the major risk factors of atherosclerotic diseases. Anesthetologists are frequently confronted to the management of treated or untreated hypertensive patients whose major risk during that period concerns the potential association with coronary artery disease. Therefore, the preoperative assessment should be insured of an adequate control of blood pressure, the presence of potential target organ damage and especially the detection an underlying coronary disease and its importance. The risk of cardiovascular complications and consecutively the preoperative check-up depend of the type of surgery scheduled. Preoperative systolic blood pressures (SBP) below 180 mmHg and diastolic blood pressures (DBP) below 110 mmHg are recommended. Due to their efficacy, tolerability and the easiness of their use, dihydropyridins and beta-blockers are the most frequent drugs used in the peri-operative period. Many studies evidenced the benefit of beta-blocking agents in patients with definite or potential coronary artery disease during the immediate period of major surgery, with not only a decrease of serious cardiac complications and post-operative mortality but also an improvement of mid- and longterm prognosis. There is no evidence to privilege any type of anesthesia. A respect of hemodynamic conditions (avoidance of severe hypotension and tachycardia) reduces the incidence of ischemic complications. The hemodynamic stability is obtained with an adapted anesthesia and the use of intravenous vasoconstrictive or vasodilator agents as well as beta-blockers (esmolol). The diagnosis of perioperative myocardial infarction is based on the measurement of seric concentrations of cardiac Troponin isoforms (TnI or TnT).

Utility of cardiac troponin measurement after cardiac surgery

Postoperative cardiac failure due to myocardial necrosis remains a major complication in cardiac surgical procedures and its diagnosis is still difficult. In fact, cardiac enzymes, electrocardiogram and echographic signs are often misleading. The prognostic valve of troponin I after coronary artery bypass or conventional value surgery has been evaluated in 500 adult patients. Postoperative troponin I concentrations after cardiac surgery represent an independent variable associated with mortality (in-hospital death) and morbidity (low cardiac output and acute renal failure).

Dose of prophylactic intravenous ephedrine during spinal anesthesia for cesarean section

STUDY OBJECTIVE

To compare the incidence of maternal hypotension associated with spinal anesthesia for cesarean section when 10-, 15-, or 20-mg prophylactic boluses of intravenous (IV) ephedrine are used.

DESIGN

Prospective observational study.

SETTING

Teaching hospital.

PATIENTS

108 women admitted for elective cesarean section.

INTERVENTIONS

Spinal anesthesia was performed using hyperbaric bupivacaine 10 mg, sufentanil 2 microg, and morphine 0.2 mg (volume 4 mL). Ephedrine (10, 15, or 20 mg) was administered 2 minutes after the intrathecal injection. Maternal blood pressure was checked every 2 minutes. Hypotension was promptly treated with 5-mg ephedrine boluses.

MAIN RESULTS

Incidence of hypotension was significantly higher in women receiving a 10-mg prophylactic dose of ephedrine than in those receiving either a 15-mg or a 20-mg prophylactic dose of ephedrine [23/36 in the 10-mg ephedrine group vs. 13/36 and 10/36 in the 15-mg and 20-mg ephedrine groups, respectively (p< 0.05)].

CONCLUSION

In the conditions of this study, a single bolus of IV ephedrine with doses of either 15 or 20 mg decreased significantly the incidence of maternal hypotension as compared to a single 10-mg bolus of ephedrine.