Abstract
ObjectivesTo investigate the effects of isoflurane and propofol on mean arterial pressure (MAP), cochlear blood flow (CoBF), distortion-product otoacoustic emission (DPOAE), and the ultrastructure of outer hair cells (OHCs) in guinea pig cochleae.MethodsForty-eight male guinea pigs were randomly assigned to one of six treatment groups. Groups 1 to 3 were infused (i.v.) with a loading dose of propofol (5 mg/kg) for 5 min and three maintenance doses (10, 20, or 40 mg kg−1·h−1, respectively) for 115 min. Groups 4 to 6 were inhaled with isoflurane at concentrations of 1.15 vol%, 2.30 vol% or 3.45 vol% respectively for 120 min. CoBF and MAP were recorded prior to and at 5 min intervals during drug administration. DPOAE was measured before, immediately after, and 1 h after administration. Following the final DPOAE test, cochleae were examined using scanning electron microscopy.ResultsPropofol treatment reduced MAP in a dose-dependent manner. CoBF and DPOAE showed increases at propofol maintenance doses of 10 and 20 mg kg−1·h−1. Inhalation of isoflurane at concentrations of 2.30 vol% and 3.45 vol% reduced MAP and CoBF. DPOAE amplitude increased following inhalation of 1.15 vol% isoflurane, but decreased following inhalations of 2.30 vol% and 3.45 vol%. Cochlear structure was changed following inhalation of either 2.30 vol% or 3.45 vol% isoflurane.ConclusionsPropofol could decrease MAP and increase both CoBF and DPOAE without affecting OHC structure. Inhalation of isoflurane at concentrations >2.30 vol% decreased CoBF and DPOAE, and produced injury to OHCs.
Highlights
During middle ear surgery, it is important to maintain a relatively blood-free surgical field, and this can be achieved by decreasing systemic blood pressure to a level of controlled and stable hypotension[1]
Anesthetics must be used with caution, because hypotension may result in decreased cochlear blood flow (CoBF), leading to cochlear damage
Effects of propofol on mean arterial pressure (MAP), CoBF, and distortion-product otoacoustic emission (DPOAE) Compared with baseline values, the different doses of propofol caused decreases in MAP and increases in CoBF, and the changes became stabilized after a 20 min infusion time
Summary
It is important to maintain a relatively blood-free surgical field, and this can be achieved by decreasing systemic blood pressure to a level of controlled and stable hypotension[1]. Several pharmacological agents can be used for this purpose, and include vasodilators, alpha 2A adrenergic agonists, beta adrenergic antagonists, magnesium sulphate, and anesthetics[1,2,3]. Among those choices, the use of anesthetics to achieve controlled hypotension is convenient and welcomed by anesthesiologist[4,5]. Anesthetics must be used with caution, because hypotension may result in decreased cochlear blood flow (CoBF), leading to cochlear damage. Several studies have suggested that CoBF has an autoregulation similar to that involved in brain blood flow [7,8]. It has been shown that both isoflurane and desflurane impaired cerebral autoregulation at minimum alveolar concentrations (MAC)
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