Anesthesia Machines. Inhaled Anesthetic Agents

Transcription

1 Anesthesia Machines Key Points Anesthesia Machines: - basic components of the generic machine understand how the gasses and agent-mixing part of the machine connects to the patient breathing circuit - know what gasses are used in a three-gas anesthesia system - basic components of the CO 2 absorber circuit - 3 basic monitors of anesthesia machine function; delivered O 2 %, airway press. flow - function of the OFPD or Fail Safe Valve (Oxygen Fail Protection Device) - function of the ORMC or Hypoxic Guard (Oxygen Ratio Monitor Controller) - function of the vaporizer lockout - understand how CO2 absorbent works and why we use it - the four aspects of anesthesia: - Anesthesia / unconsciousness (no consciousness / awareness) - Analgesia (no pain) - Amnesia (no recall) - Immobilization / muscle relaxation (no movement) D. J. McMahon rev cewood identify the commonly used anesthetic agents today: DESfluorine, ISOfluorine, SEVfluorine (in vaporizers) and Propofol (IV) Anesthesia is a state of induced unconsciousness. Anesthesia can be obtained by an inhaled agent through an endotracheal tube, or can be obtained by an IV drug infusion. Categories: > Local, often Local Monitored Anesthesia Care (LMAC) > Regional - spinal - epidural - nerve block specific Inhaled Anesthetic Agents > Many are ethers (general formula R O R ) > First was diethyl ether > First vaporizer-delivered agent was halothane (1960 s) > Later agents were in vogue but were discontinued due to serious side effects ( enflurane, Fluoromar, methoxyflurane ) > General, which includes: - Anesthesia / unconsciousness (no consciousness / awareness) - Analgesia (no pain) - Amnesia (no recall) - Immobilization / muscle relaxation (no movement) The drugs used to achieve anesthesia have varying effects in each of these areas.

2 The vast majority of inhaled general anesthetics today (2015) are given with one of three agents: - isoflurane ( Forane, Zeneca Labs generics) purple - sevoflurane ( Ultane, Abbott Labs Baxter generics) yellow - desflurane ( Suprane, Baxter) blue Propofol - first injectable non-opioid general anesthetic - occasionally halothane ( Fluothane ) red Each is metabolized differently, so each has advantages and risks associated with the heart, liver, or kidney. The choice of agent is a clinical judgment made by the anesthesia provider, based on the type of surgery, the patient s age, the patient s medical history, etc. Original trade name: Diprivan Portable ( table-top ) anesthesia machines -- The essential requirements of an anesthesia machine: > Oxygen-carrying gas mixture - could be room air, but usually ~50% O 2 > Anesthetic agent, vapor or IV medication - metered-out very precisely > Ability to create positive airway pressure - necessary for respiratory gas exchange

3 no flow oxygen anesthetic agent backup cylinders oxygen anesthetic agent nitrous oxide oxygen anesthetic agent nitrous oxide medical air all gases connects to pt. breathing circuit

4 Three machine hazards and their solutions: 1: Oxygen supply failure, leaving anoxic gas supply - the Fail-Safe Valve or Oxygen Failure Protection Device (OFPD) Shuts off all gas flows if the oxygen pressure fails 2: Hypoxic or anoxic mixtures from the flowmeters - the Hypoxic Guard or Oxygen Ratio Monitor-Controller (ORMC or ORC) Assures that at least 25% oxygen is delivered 3: More than one agent vaporizer turned-on - Vaporizer Lock-out Mechanism; Allows only one vaporizer to be enabled Pressure Regulator Gas Supply Check Valve Flowmeter Tubes in Series; not additive; read the left (fine) until it maxes out, then read the right (coarse)

5 Digital flowmeters - Dräger Fabius GS Measure gas flow based on the mass of the gas rather than by earlier methods. Flowmeter Needle Valve Blue: Nitrous Oxide (N 2 O) Yellow: Medical Air Green: Oxygen (O 2 ) Typical screen - Dräger Fabius GS Medical air or N 2 O Medical air or N 2 O Medical air or N 2 O O 2 failure shutoff valve ( FailSafe Valve ) Oxygen Failure Shutoff Device

6 Oxygen ratio controller (Dräger) Oxygen ratio controller (Ohmeda) min 25% O 2 Delivering the volatile anesthetic Generic Flow-Over Anesthetic Vaporizer: Better Generic Flow-Over Vaporizer: Problems: Problems: -- Intended for multiple agents -- Non-linear output -- variable output at different flows -- variable output with temperature changes -- Dangerous for several reasons not for high flow needs 'choke' for low flow vapor is temperature sensitive

7 Modern Agent-Specific Vaporizer, OFF Modern Agent-Specific Vaporizer, ON adjusts from 2-3% anesthetic agent to start down to.5-1% as case proceeds Patient s lungs Essential Monitors of the Anesthesia Machine: (These monitor the machine, not the patient) > Delivered oxygen percentage > Airway pressure > Airway gas flow From machine CO 2 Absorber Assembly - schematic Adjustable Pressure Limiting Valves

8 CO 2 absorbent: > Chemically removes CO 2 from the patient s respiratory gases. > Consists of NaOH, KOH, and Ca(OH) 2, which react with CO 2 to form carbonates and water in two separate reactions. > Includes a dye which changes to purple when the CO 2 absorbing capacity is exhausted. > Major brands: SodaSorb, Baralyme, Amsorb Adjustable Pressure Limiting (APL) Valve comes from gasses agent mixing circuit

9 Manual Ventilation: Manual Ventilation: Mechanical Ventilation: Mechanical Ventilation:

10 Scavenging of Waste Anesthesia Gas (WAG) : > Required by NIOSH / OSHA > NIOSH allows < 25 ppm of N 2 O (8-hour average) > Gases must be actively drawn out of the local air > Scavenging is integrated into the anesthesia machine > Testing should be done at least annually > Can be measured with dosimeters from a commercial lab, or with an IR detector made for air testing. Most common troubleshooting issues: > Leaks in the absorber circuit and/or patient circuit > Inadequate volume delivered from ventilator > Water accumulated in ventilator tubing > Flow meter inaccuracy or failure Get factory service training! Be pro-active: - Know how to do a pre-op machine checkout. - Get the book out and check the troubleshooting tables. Major Players in Anesthesia Machines: > North American Dräger > GE-Datex-Ohmeda > Mindray Great tutorial on anesthesia machines: Minor Players: > Spacelabs > DRE, Oceanic (compact types)

11 Virtual Anesthesia Machine: > Univ of Florida, Dept of Anesthesiology > From the Home Page, click on the Simulation Workbook tab > Requires one-time free registration