DK2985_C000 1..28 - AlSharqia Echo Club

300 Transesophageal Echocardiography80Group A: Propofol 1.5 mg/kgGroup B: Thiopental 4 mg/kgGroup C: Propofol 2.5 mg/kgGroup D: Thiopental 6.5 mg/kgSlope of E In7060500Mean SEMp < 0.05 within the groupp < 0.05 between group A and Bp < 0.05 between group C and D5 10 15MinutesFigure 13.18 Changes in left ventricular elastance (Eln) (mmHg/mL) as a parameter of contractility after successive single-bolusintravenous injections of 4.0 and 6.5 mg/kg of thiopental and 1.5 and 2.5 mg/kg of propofol. [Reproduced with permission fromMulier et al. (31).]resistance. Effects on pulmonary arterial pressure may begreater than on systemic arterial pressure. Higher dosescan result in paradoxical effects, with predominanthemodynamic depression instead of stimulation. (Cardiovascularpharmacology of anesthetics. In: EstafanousFG, ed. Cardiac Anesthesia: Principles and Clinical Practice.2nd ed. Chapter 10. Lippincott Williams & Wilkins,2001.)EtomidateEtomidate produces the fewest hemodynamic changesamong the sedative–hypnotic agents. The inotropiceffects of etomidate are mild. Dose-dependent decreasesin sympathetic tone, venous return, preload and cardiaccontractility can occur with etomidate but are typicallyless obvious than with thiopenthal. Arterial blood pressureusually remains stable. (Cardiovascular pharmacology ofanesthetics. In: Estafanous FG, ed. Cardiac Anesthesia:Principles and Clinical Practice. 2nd ed. Chapter 10.Lippincott Williams & Wilkins, 2001.)3. Effect of Intravenous Anesthetic Agents onDiastolic FunctionLittle data is available on the effect of intravenous anestheticagents on diastolic function. Recently, Gare et al.(33) studied the effects of sedative doses of midazolamand propofol in patients with normal and mild diastolicdysfunction (relaxation abnormalities), using transthoracicmitral inflow pulsed-wave (PW) Doppler and annulartissue Doppler imaging. Their results suggest that sedationwith midazolam or propofol does not affect the indices ofleft ventricular diastolic performance in the two groups.C. Nonanesthetic Drugs Commonly UsedDuring Cardiac Surgery1. Positive Inotropic DrugsEndogenous CatecholaminesEPINEPHRINE. Epinephrine is a potent a- andb-adrenoreceptor agonist. In the heart, epinephrine is apotent stimulant of myocardial inotropy, has significantarrhythmogenic potential and increases stroke volume(SV), coronary blood flow and HR. Doses of 0.01–0.03 mg kg per min provide low-dose epinephrine in whichb-agonist effects predominate. However, at a higher dose(maximum 0.1 mg kg per min), the a-agonist effect tendsto predominate, inducing vasoconstriction.NOREPINEPHRINE. Norepinephrine, predominantly,stimulates the a-adrenoreceptors although concurrentstimulation of the b 1 -adrenoreceptors occurs to a lesserextent. Thus, blood pressure increases as a result ofincreased SVR; this in turn tends to decrease the HR dueto vagal reflex pathways which overcome the direct stimulationof myocardial b 1 -adrenergic receptors. b 1 -mediatedincrease in myocardial contractility do occur, so norepinephrineis considered a positive inotropic agent particularlyat low doses where the b 1 effects predominateover the peripheral a effects. The overall cardiac effectsof norepinephrine include increased SV, coronary bloodflow, and arrhythmogenic potential while there isminimal change in CO and a potential decrease in HR.