Effects of posture, hypotension and locally applied vasoconstriction on the middle ear microcirculation in anaesthetized humans

Abstract

Studies by laser-Doppler flowmetry of middle ear microcirculation changes induced by physical and chemical stimuli in the animal have only recently been made. This prospective study, performed in humans, was designed to compare the effects of a postural manoeuvre (headup tilt 30 degrees), hypotension and locally applied vasoconstriction on middle ear blood flow during anaesthesia. Circulatory changes provoked by a headup tilt of 30 degrees, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by locally applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Middle ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O2 and CO2 in arterial blood, pH, arterial lactate concentrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators (nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P < 0.0001, P < 0.0001, P < 0.019, respectively), but did not induce any significant variations in heart rate; variations occurred in middle ear blood flow (P > 0.05, not significant) which were different according to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P < 0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metabolic values, or propofol serum concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Remifentanil and controlled hypotension; comparison with nitroprusside or esmolol during tympanoplasty

“…4 The optic fibre is inserted through the tympanic perforation and is put in place by the surgeon on the mucosa of the promontory of the tympanic cavity. The MEBF was calibrated before the study so that a true zero indicated that the flux was null: MEBF and arterial blood pressure were continuously and simultaneously recorded.…”

“…The MEBF was calibrated before the study so that a true zero indicated that the flux was null: MEBF and arterial blood pressure were continuously and simultaneously recorded. 4 The relative changes in MEBF (*MEBF) and in SABP from their respective baselines C were considered for statistical analysis and comparison between groups. The MEBF autoregulatory responses to controlled hypotension were quantified by the closed-loop gain factor of autoregulation (Ga) calculated from the equation Ga= 1-(%MEBF/ %MABP).…”

“…2 In spite of the arterial pressure being reduced to very low values in many instances, there was no morbidity or mortality which could be ascribed to the technique. Since then, various drugs have been used to facilitate the induction of controlled hypotension for middle ear surgery including vasodilators such as sodium nitroprusside, [3][4][5][6] nicardipine, 4 nitroglycerin, 4 beta-adrenergic antagonists such as propranolol, 5 esmolol, 7 alpha and beta-adrenergic antagonist such as labetalol, 8 and high doses of potent inhaled anesthetics such as halothane. 3,5 Some disadvantages have been reported for these techniques including long postanesthetic recovery for halothane, 3 resistance to vasodilators, 4 tachyphylaxis 9 and cyanide toxicity 1 0 for nitroprusside, or possibility of myocardial depression for esmolol.…”

Controlled Hypotensive Anesthesia in Children Undergoing Nasal Surgery

“…Beta blockers decrease CO and therefore decrease the blood flow to the tissue. So, beta blocker would be appropriate for decreasing the bleeding which result from capillary injury [31][32][33][34][35].…”

Effects of Premedication with Metoprolol on Bleeding and Induced Hypotension in Nasal Surgery

“…It is believed that betablockers are responsible for improvement of the cardiovascular condition and patients' hemodynamic stability via changes in stress related physiological response (5,8). For this purpose we studied the effect of beta-blockers and the patient's position on the surgical table to induce hypotension (9,10). A number of different beta-blockers at different doses have already been tested, but we chose an easily obtained drug, oral metoprolol for this study.…”