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Modern Anesthesia Machines: What you should know

Modern Anesthesia Machines: What you should know. Michael A. Olympio, MD Professor of Anesthesiology Wake Forest University School of Medicine Winston-Salem, North Carolina. ASA 2003 Refresher Course Lecture # 194. Conflict of Interest Statement This speaker has received:.

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Modern Anesthesia Machines: What you should know

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  1. Modern Anesthesia Machines:What you should know Michael A. Olympio, MD Professor of Anesthesiology Wake Forest University School of Medicine Winston-Salem, North Carolina ASA 2003 Refresher Course Lecture # 194

  2. Conflict of Interest StatementThis speaker has received: Educational materials, assistance, and/or courses from: Datex-Ohmeda, Inc., Madison, WI Dräger Medical, Inc., Teleford, PA Mercury Medical, Clearwater, FL Siemens-Elema AB, Solna, Sweden Honoraria from: Datex-Ohmeda, Inc. (total<$2,500) Anesthesia machines and/or monitors on loan from: Datex-Ohmeda, Inc., Madison, WI Dräger Medical, Inc., Teleford, PA

  3. Objectives • Distinguish conventional vs. modern • Recognize limitations and safety issues • Explain how new features operate • Compare representative machines • Consider new concerns • Do not describe every new machine

  4. Principles of Safety Engineering • Monitor and warn • Prevent or attenuate harm • Provide backup devices for 1° failures • Prevent misuse of the equipment • Provide instruction, training, inspection Schreiber P. Safety Guidelines for Anesthesia Systems. Drager Medical, Inc. 1985 Eisenkraft JB. A Commentary on Anesthesia Gas Delivery Equipment and Adverse Outcomes. Anesthesiology 1997;87:731-3.

  5. Machine Morbidity and Mortality • Eichorn JH. (Anesthesiology 1989;70:572-7) • Hypoventilation in 7 of11 accidents • Monitoring could have prevented 100% • Caplan, et.al. (Anesthesiology 1997;87:741-8) • Misuse 3-times more than equipment failure • Monitoring could have prevented 78% • JCAHO. (Sentinel Event Alert 2002;25): Ventilator Deaths/Injury • Healthcare Risk Control 2003;4:1-11: Critical Alarms

  6. Definitions of Conventional and Modern • “Conventional” (no feedback modulation) • Ohmeda • Modulus series and Excel • North American Dräger • Narkomed and GS • “Modern” (feedback modulation) • Datex-Ohmeda • Aestiva/5 (with 7900 ventilator) • Anesthesia Delivery Unit (S/5) • Dräger Medical • Julian • Narkomed 6400 • Fabius GS v1.3

  7. Ten LimitationsofConventional Machines

  8. 1. Numerous External ConnectionsRealize the consequences. Cooper JB, et.al., ‘…Analysis of Major Equipment Failures…’ Anesthesiology 1984;60:34-42 • Breathing circuit/ventilator 43/115 • Leaks, mis- or dis- connections: most frequent critical incident (94/507) • Human error and failure to check were most likely associated factors

  9. Minimal External ConnectionsConsider the advantages. Dräger Julian Datex-Ohmeda Aestiva/5

  10. J. Clin Anesth 1989;1(6):452-6 Potential for barotrauma or hypoventilation with the Drager AV-E ventilator. Eisenkraft JB Revised Dräger AV2+ New Dräger Fabius GS Anesth. Analg 2003; 97:492-3. Inadvertent Positive End-Expiratory Pressure Caused by a Malfunctioning Ventilator Relief Valve. Bourke DL, Tolentino D

  11. 2. Inaccurate Tidal Volume Gas Analyzer Respirometer Compression Settings Leaks Hose Compliance Contributes to VT DON”T FLUSH Operating Principles of Narkomed Anesthesia Systems 1998, Cicman et. al., Dräger Medical, Telford, PA. With Permission.

  12. System compliance: (5ml/cm) x (20cm) = 100ml lost Hose compliance: (2ml/cm) x (20cm) = 40ml lost Leaks/gas analyzer: (4 + 3 ml/sec) x (2sec) = 14ml lost Compression: 3% x 400ml =12ml lost Fresh Gas Flow: (30ml/sec) x (2sec) 60ml gained Summation: VT=400-100-40-14-12+60 Magnitude of VT Discrepancy VT=400, R=10, FGF=1.8 l/min, I:E=1:2, PIP=20 cmH2O Desired VT=400ml Delivered VT=294ml Reported VT=334ml

  13. Electronic flow measurement/control Compliance compensation Fresh gas decoupling Return sampled gas Single-step initiation of mechanical vent Aestiva/5 S5/ADU Leak measurement Reported Never corrected Electronic settings Adjustment to flow sensor data: Fabius GS v1.3 Narkomed 6400 Methods for Accurate Delivery

  14. Flow Sensor Technology: Anemometer • Constant temperature • Variable current • Thermal conductivity adjustment for Desflurane • Low resistance to flow • Not reverse flow • Caution: ignition source Dräger Spirolog®

  15. Fire in the Breathing Manifold • Xylocaine® pump spray (AstraZeneca, London, UK) • Ethanol is explosive at 3.5-15% in AIR @ 363° C • 100% Oxygen was in use • Platinum wire 140°-900° C • Ceramic expiratory disc valve destroyed • Flame of burning ethanol drawn backwards to ETT • Instruction manual prohibited use with flammable agent A Combustive Destruction of Expiration Valve in an Anesthetic Circuit. Kanno TA, Aso C, Saito S, Yoshikawa D, Goto F. Anesthesiology 2003;98:577-9

  16. Flow Sensor Technology: Ultrasound • Flow alters time of flight • Up or downstream • Reverse flow detected • Independent of gas mixture or density • No moving parts • Resolution: +/- 20ml

  17. Frontal v. back pressure Pressure differential proportional to (flow)2 Directional flow Need density and viscosity corrections Flow Sensor Technology: Pitot tube Datex-Ohmeda D-Lite® Sensor

  18. Turbulent flow Pressure differential Flow is inversely proportional to the square root of density He << O2, N2, N2O, CO2 Determines direction Resolution +/- 20ml Flow Sensor Technology: Variable Resistor

  19. Humidity Problems Resolved • Tubing of nondistensible, narrow diameter • Not humidity, but condensed water • False positive “Exp. Reverse Flow” alarm • Use HME instead of heated humidifiers • Redesigned flow sensor Ventilatory Failures with the Datex-Ohmeda 7900 SmartVent. Cantillo J, Domsky R, Gratz I, Goldberg M. Anesthesiology 2002;96:766-8. In Reply: Mitton M, Datex-Ohmeda, North America. Anesthesiology 2002; 96:768. Ambietn O.R. Temperatures and Datex-Ohmeda 7900 SmartVent Malfunction. Blinder JL. Anesthesiology 2002; 97:1645. In Reply: Cantillo J, Gratz I, Domsky R, Goldberg ME. Anesthesiology 2002; 97:1645.

  20. Measures energy loss through a resistor Pressure differential Laminar flow Only viscosity matters Independent of density Integrate flow vs time Known, constant gas Hagen-Poiseuille Law Heated and re-zeroed Fresh Gas Flow Sensors:Pneumotachometer (Fleish) Image from Raemer DB, Monitoring Ventilation, in Anesthesia Equipment 1993 Mosby, Ehrenwerth and Eisenkraft, Eds. With permission.

  21. Management of Fresh Gas Flow

  22. S/5 ADU Electronic Gas Flow Display Measured / Calculated gas flows, concentration Desired concentration

  23. S/5 ADU Monitoring Display Mixed All Measured Photo courtesy of Datex-Ohmeda, Inc., Madison, WI., with permission.

  24. Failures of O2/N2O Flow Controls • Broken chain (Ohmeda Link 25) • freewheeling nitrous dial: hypoxic mixture • Faulty set screw (Ohmeda Link 25) • turning on the oxygen dial caused the delivery of nitrous oxide only! (loose set screw) • turning the oxygen dial dragged nitrous along (set screw too tight) • Faulty stop pins (Narkomed) • oxygen could not be turned on Paine GF, Kochan JJ. Failure of the Chain-Link Mechanism of the Ohmeda Excel 210 Anesthesia Machine. Anesth Analg 2002; 94:1365-76

  25. S/5 ADU O2/N2O Ratio Controller • O2 and N2O flow measured • Ratio is calculated • N2O is limited by the proportional valve, if necessary • N2O further limited by volatile % • 100 ml oxygen before N2O • N2O cut-off if no O2 pressure Diagram courtesy of Datex-Ohmeda, Inc., Madison, WI., with permission.

  26. User sets FiO2 and 2nd gas User sets total flow Unit meters ratio Unit controls FGF valve Dräger Julian Julian Electronic FGF Control Diagram courtesy of Rob Clark, Dräger Medical, Telford, PA., with permission.

  27. FGF Interruption Caused Vaporizer Malfunction • Datex-Ohmeda “D-Tec Plus” desflurane vaporizer • NOT the original Tec-6 • Dräger Julian Anesthesia Machine (VCV only, not PCV) • “No Output” warning was accurate • Proper response to alarms emphasized • Software modified to prevent problem With Technology Comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer. Kimatian SJ. Anesthesiology 2002; 96:1533-34. In Reply: Feldman JM, Draeger Medical, Inc. Anesthesiology 2002; 96:1534. In Reply: Mitton M. Datex-Ohmeda, NA. Anesthesiology 2002; 96:1534-5.

  28. Reporting Gas Consumption Narkomed 6400 calculates fresh gas consumption. Offers alarms. S/5 ADU calculates fresh gas and volatile agent consumption.

  29. Compliance Compensation • System compliance of 6 ml/cm; Set VT = 600ml • First cycle: Pplat = 20 cm; Total comp = 30 ml/cm • Next cycle adds: 6 ml/cm x 20 cm = 120 ml • Thus: 720 @ 24; Then: 744 @ 24.8; 749 @ 24.9 Dräger Julian Diagram courtesy of Dräger Medical, Telford, PA.

  30. 3. Excess Volume Delivery • FRESH GAS DECOUPLING: a mechanism which compensates for, or prevents fresh gas flow contribution to tidal volume • Types offered: • Feedback adjustment: Aestiva/5 • Pre-emptive adjustment: S/5 ADU • Intermittent FGF: Julian • FGF re-direction: Narkomed 6400 Fabius GS

  31. Conventional mechanical ventilation. (Representing Dräger Narkomed AV2+)

  32. Servo-controlled volume ventilation; Electronic PEEP. (Representing Datex-Ohmeda Aestiva/5)

  33. Decending bellows and fresh gas decoupling; Intermittent fresh gas flow. Compliance compensation. FIGURE 13 (Representing Dräger Julian)

  34. Fresh gas distal to I-valve; preemptive decoupling. Compliance compensation. FIGURE 5 Representing Datex-Ohmeda S/5 ADU. Higuchi H, et. Al. Carbon Dioxide Absorption Capacity. Anesth Analg 2001;93:221-5.

  35. Addition of a piston ventilator; Relocation of the reservoir bag. FIGURE 7

  36. Fresh gas decoupled through reservoir bag; Piston ventilation. Exhalation mode. FIGURE 9 A M/S-E (Representing Dräger Narkomed 6400)

  37. Relocation of the piston to the inspiratory limb; Fresh gas decoupling. PEEP/Pmax default open APL Bypass default closed (Representing Dräger Fabius GS) FIGURE 11

  38. Clamped Fabius GS PEEP/Pmax

  39. Advantages of a Piston Ventilator • No unintentional PEEP • Non-compliant • top dead center in VCV • Universal size • Mechanical precision • 10 ml x 80 bpm • No gas consumption • Isolated or exposed to patient gas Narkomed 6400 Divan Ventilator Bellows

  40. PCV Comparisons for Infant ExtremesNAD 6000 v. Aestiva 3000 v. Servo 900C PCV-30/60; PEEP-0/10/15; I/E-1:3/1:1, R-10/20/40; C=1-3ml/cm (“severe”) • Aestiva: lowest Vt (ΔP), flows; most accurate set P and PEEP (above mandatory) • NAD: highest flow; most accurate Vt measurement (+13%, after adjustment) • Servo: pressure overshoot Stayer SA, et. al. Anesth Analg 2000:91:1145-50

  41. VCV Comparisons in InfantsNAD 6000 v. Servo 900C SET: Vt 21; RR 25; PEEP 3.6; I:E 1:2 • Randomized crossover in 20 infants <5kg • NAD: improved ventilation, higher flow • pCO2: 43 v. 47 mmHg • ETCO2: 34 v. 37 mmHg • Vt (actual): 12.9 v. 11.3 ml • Vt (reported): 20.0 v. 19.0 ml • NAD: higher MAP • MAP 9.7 v. 8.6 cmH2O Stayer SA, et. al. Anesth Analg 2001;92:76-9

  42. 4. Excess Airway Pressure • Location of pressure sensor • Inverse ratio ventilation (IRV) • APL valves • Pressure controlled ventilation • Electronically controlled PEEP • Open scavenger systems (without valves) • Preset/electronic inspiratory pressure limiters • Protection from O2 flush during CMV

  43. Pressure/Volume Flow/Volume Loops Compliance Leaks Obstructions PEEP Resistance Trending Spirometry

  44. 5. Advanced Ventilation Features ACTUAL patient values (Aestiva/5) MAP Increased by IRV

  45. MAP, Vt Increased by PCV MAP, Vt Increased by PEEP Same patient. ACTUAL values

  46. Circuit pressure Set Pi Flow Fast 10% Medium 50% Slow 90% Inspiratory Flow Adjustment in PCV Is selection of “Inspiratory Rise” consistent with PCV? Default to Fast in the USA, Medium in Europe. Courtesy of Datex-Ohmeda, Inc., Madison, WI., with permission.

  47. Limitations of Mechanical PEEP • Mechanical/magnetic system • Several moving parts • Susceptible to friction • PEEP adjustment monitored only during exhalation • Takes time to adjust Operating Principles of Narkomed Anesthesia Systems. Second Edition, 1998. Cicman, et. al., eds., North American Drager, Telford, PA., with permission.

  48. Conventional Variable Resistor APL Valve Operating Principles of Narkomed Anesthesia Systems. Second Edition, 1998. Cicman, et. al., eds., North American Drager, Telford, PA., with permission.

  49. CPAP During Spontaneous Ventilation Circuit pressure is directly related to flow, because APL is a resistor. E = I x R

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