1. Dexmedetomidine Lowers the Concentration of Anesthetic Required during Craniotomies below MAC Garett J. Pangrazzi, BS, Jacob A. Uhler, BA, Prashanth R. Vaadyala, BS, Roger Dzwonczyk, MS and Sergio D. Bergese, MD Presented at the American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL. and Sergio D. Bergese, MD Presented at the American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

2. Background As an α2-adrenergic agonist, dexmedetomidine (DEX) reduces sympathetic outflow by reducing the amount of norepinephrine released in the CNS, especially in the Locus Coeruleus As an α2-adrenergic agonist, dexmedetomidine (DEX) reduces sympathetic outflow by reducing the amount of norepinephrine released in the CNS, especially in the Locus Coeruleus The suggested dose of DEX is a bolus of 0.1 mcg/kg and maintenance dose of 0.2-0.7 mcg/kg/hr, although it has been suggested that higher maintenance doses may be required for adequate sedation The suggested dose of DEX is a bolus of 0.1 mcg/kg and maintenance dose of 0.2-0.7 mcg/kg/hr, although it has been suggested that higher maintenance doses may be required for adequate sedation This review collected data on patients undergoing a craniotomy under general anesthesia by either desflurane (DES, n=132), isoflurane (ISO, n=34) or sevoflurane (SEVO, n=22) with adjuvant DEX This review collected data on patients undergoing a craniotomy under general anesthesia by either desflurane (DES, n=132), isoflurane (ISO, n=34) or sevoflurane (SEVO, n=22) with adjuvant DEX Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

3. Hypothesis A low dose of DEX (<0.4 mcg/kg/hr) will decrease the MAC needed to maintain general anesthesia and minimize adverse hemodynamic events A low dose of DEX (<0.4 mcg/kg/hr) will decrease the MAC needed to maintain general anesthesia and minimize adverse hemodynamic events Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

4. Methods Accepted MAC levels Accepted MAC levels –DES: 7.3% –ISO : 1.15% –SEVO: 2.1% More than 1 MAC is typically used during general anesthesia to ensure patient's tolerance of the different noxious stimuli associated with surgery and blunting of memory and awareness More than 1 MAC is typically used during general anesthesia to ensure patient's tolerance of the different noxious stimuli associated with surgery and blunting of memory and awareness The intra-operative minimum and maximum concentrations of inhaled anesthetic were collected for each patient after surgical incision and throughout the duration of DEX administration The intra-operative minimum and maximum concentrations of inhaled anesthetic were collected for each patient after surgical incision and throughout the duration of DEX administration Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

5. In order to monitor for hemodynamic changes during the craniotomies, data was collected on blood pressure (BP) and heart rate (HR) at three times: In order to monitor for hemodynamic changes during the craniotomies, data was collected on blood pressure (BP) and heart rate (HR) at three times: –five minutes before incision (t = -5) –during incision (t = 0) –five minutes after incision (t = 5) A hemodynamic status change was defined as: A hemodynamic status change was defined as: –a change in systolic BP above 140 mmHg (hypertension) –or below 90 mmHg (hypotension) –or a change in HR above 100 bpm (tachycardia) –or below 60 bpm (bradycardia) Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL. Methods

6. Only those patients with hemodynamic status changes occurring during both the incision and after incision and having vitals within normal limits for preoperative baseline and before incision were included as having an adverse hemodynamic event Only those patients with hemodynamic status changes occurring during both the incision and after incision and having vitals within normal limits for preoperative baseline and before incision were included as having an adverse hemodynamic event Those patients that did not fall within normal ranges for BP and HR during the preoperative baseline and before incision were not included in our assessment for hemodynamic status change Those patients that did not fall within normal ranges for BP and HR during the preoperative baseline and before incision were not included in our assessment for hemodynamic status change Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL. Methods

7. MAC data for each inhaled anesthetic are expressed as median values with 25th and 75 th percentiles MAC data for each inhaled anesthetic are expressed as median values with 25th and 75 th percentiles Results: MAC Data Minimum MAC (%)Maximum MAC (%) Anesthetic Agent (N)Median25th %ile75th %ileMedian25th %ile75th %ile DES (132)4.03.04.05.04.16.0 ISO (34)0.60.50.81.00.91.0 SEVO (22)1.0 1.22.01.02.0 Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

8. Results: Hemodynamic Findings Anesthetic AgentHypertensiveHypotensiveTachycardicBradycardic DES7/1280/1281/12120/121 ISO2/301/301/323/32 SEVO5/210/21 3/21 Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.

9. Discussion The review showed that patients undergoing craniotomies with low doses of adjuvant DEX required less than 1 MAC for each inhaled anesthetic to ensure an adequate level of general anesthesia The review showed that patients undergoing craniotomies with low doses of adjuvant DEX required less than 1 MAC for each inhaled anesthetic to ensure an adequate level of general anesthesia From these results, low doses of DEX may increase patient intraoperative hemodynamic stability and reduce patient exposure to inhaled anesthetics and their associated complications From these results, low doses of DEX may increase patient intraoperative hemodynamic stability and reduce patient exposure to inhaled anesthetics and their associated complications Pangrazzi, G.J., et. al. American Society of Anesthesiologists (ASA) 2008 Annual Meeting. October 18–22, 2008, Orlando, FL.