In microsurgical procedures, visibility of the surgical field is critical to safe and efficient operating. This is particularly true for middle ear surgery (MES), since minimal blood under the magnification of operating microscopes can impair visualization of critical structures and anatomical landmarks. Various anesthetic techniques have been developed to reduce intraoperative bleeding during cases in which any blood can significantly obscure the surgical field. Controlled hypotension has been used for more than half a century, significantly reducing mean arterial pressure (MAP) to decrease intraoperative bleeding and optimize visibility throughout a procedure [1].

Many agents have been used for controlled hypotension, including alpha-2 agonists such as clonidine or dexmedetomidine [2], [3], [4]. Alpha-2 agonists work on presynaptic receptors in the central nervous system (CNS), activating inhibitory neurons and reducing sympathetic output. The main factor in decreased intraoperative bleeding are these sympatholytic properties of dexmedetomidine; loading, or bolus, doses of 1 μg/kg have shown significant reduction in serum norepinephrine and epinephrine levels [5], [6]. Decreased catecholamine levels and sympathetic responses lead to moderate reductions in heart rate (HR), blood pressure (BP), and overall cardiac output (CO). Reduction of these cardiac parameters helps improve surgical field visibility but should be carefully considered and is relatively contraindicated in patients with low ejection fraction (EF) and/or heart block.

Dexmedetomidine has been demonstrated to have approximately 8 times more specificity for alpha-2 adrenoceptors than clonidine [7]. Dexmedetomidine also exhibits high specificity for the alpha-2A subtype, which are primarily responsible for sedative and analgesic activity. The enhanced sedative, analgesic, and anxiolytic properties of dexmedetomidine might allow for decreased analgesic requirements and increased patient satisfaction. Importantly, dexmedetomidine provides analgesia and anxiolysis without consequent respiratory depression (e.g., as with opiates) [7].

Other agents (e.g., propofol, esmolol, remifentanil) have also been used for controlled hypotension intraoperatively. Each of these agents come with unique benefits and potential downsides. Primary additional benefits of dexmedetomidine include its anxiolytic, analgesic, and sedative properties without respiratory depression. Potential negatives, meanwhile, are its reduction of several cardiac parameters (HR in particular) in patients with specific risk factors. Proper patient selection and thorough understanding of agent-specific perioperative implications are essential in selecting a controlled hypotensive agent. In select patient populations without risk factors that may impact agent choice, many options may be suitable for inducing controlled hypotension to improve surgical field visibility in MES. This systematic review and meta-analysis sought to specifically explore dexmedetomidine-induced controlled hypotension for optimizing surgical field visibility and intraoperative bleeding in MES. Through meta-analysis of this agent, the study hoped to synthesize available data to provide a more comprehensive understanding of dexmedetomidine to improve surgical field conditions in MES.