xRead - Nasal Obstruction (September 2024) Full Articles

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situations, and anesthesiologist comfort play a large role. Intraoperative opiates may also impact blood loss and is an uncontrolled confounder in many studies. The use of remifentanil infusion should be considered. Surgeons and anesthesiolo gists should jointly agree on the optimal plan fore ach patient. Policy Level: Recommendation. Intervention: The use of TIVA in functional ESS is recommended where possible in conjunction with anethesiologist preference. Value judgments and costs should also be taken into consideration. XII.A.4.b. Hypotensive Anesthesia Obtaining an excellent surgical field improves opera tive technique and surgical outcome with a shorter operating time. A significant amount of research has been conducted into determining which anesthetic tech nique is best to achieve this and whether total intra venous anesthesia (TIVA) or inhalational anesthesia (IA) is preferable. 1827,1829,1831,1835,1836,1838,1841,1843,1844,1847 Inmany of these articles the authors state that controlled hypoten sion (defined as a MAP between 50 and 70 mmHg) is an important element in achieving the best operative field 1829,1831,1843,1844,1847,1850,1853–1856 but there is little known about what mean arterial pressure (MAP) is best for ESS, 1853,1854 what considerations need to be taken into account when choosing which drugs to use to achieve this MAP, and what MAP is safe. 1853,1854 It is well described that prolonged hypotension can result in patients hav ing post-operative cerebral ischemic effects such as mem ory loss, neurological deficits and even death. 1853,1854 The brain has a built-in protective mechanism to help prevent cerebral ischemia by adjusting the blood flow when vari ations in blood pressure occur. This is termed cerebral autoregulation and allows the brain to adjust the blood flow to match the cerebral metabolic needs. It is generally accepted that the ischemic threshold for the anesthetized brain is about 50% of those of the awake patient due to the lower metabolic requirements of the anesthetized brain. In the systemic reviews on TIVA vs IA 1829,1835,1836 there was significant variation in the studies as to what MAP was aimed for with some studies having a MAP above 70 mmHg so although these patients had TIVA there was no attempt to induce controlled hypotension. One of the factors that contribute to significant bleed ing in the surgical field is disease load. 1838,1847 Patients with extensive sinus disease and polyps have a greater degree

of vascularity and will usually bleed more than patients with minimal disease. 1838,1847 Even though interventions in this patient group are more likely to result in a differ ence in surgical field than interventions in low disease load patients, this is seldom addressed in any of the published studies. In an RCT Brunner et al. 1838 compared TIVA and IA in nasal polyp patients with a high Lund and Mackay score (high disease load) and showed that TIVA was signif icantly better than IA in controlling the surgical field. Even though TIVA was shown to give a better surgical field, the MAP that they aimed for in both patient groups was 70 80 mmHg. In a study by Ha et al. 1854 the patients served as their own control so the bleeding for a specific disease load was studied at both a high and a low MAP. In this study the bleeding scores did track the MAP emphasizing the need to address the MAP in patients with a poor surgical field. There have been a number of studies comparing TIVA with IA where the target MAP was 50 to 60 mmHg 1855,1856 but it is unclear from these studies what MAP is most effective in ESS and what MAP is safe. Ha et al. in 2 studies 1853,1854 correlated MAP with cerebral perfusion by placing a Doppler probe on the temporal region over the middle cerebral artery and measuring flow through the artery. At the same time the MAP and cardiac output were measured by an arterial line. In the first study 1853 there was a strong correlation between the MAP and the cerebral blood flow through the middle cerebral artery (V MCA )with a correlation between the MAP and the bleeding scores. In the second study 1854 the MAP was intentionally var ied throughout the ESS procedure with the bleeding score observations blinded to the MAP. The V MCA was measured at the same time point. The correlation between MAP and V MCA was again demonstrated, with both the MAP and the cardiac output tracking the bleeding score. It was also demonstrated that to maintain the V MCA at above 50% of the baseline for 90% of the anesthetic time the MAP needed to be kept above 60 mmHg. This was confirmed by a study by Farzangan et al. 11 who used Near Infra-Red Spectrome try (NIRS) to measure cerebral oxygenation and confirmed that cerebral oxygenation was maintained with a MAP > 55 mmHg. In summary, controlled hypotension is an important part of optimizing the surgical field 1855,1856 but a safe MAP of between 60 and 70 mmHg needs to be part of the anesthetic protocol. The target MAP is best achieved with a combination of TIVA, 1827,1829,1836,1847,1850,1853-1856 alpha receptor agonists (clonidine or dexmedetomidine) 1841 and B-blockers. 1844,1850,1853–1856