The Anesthesia Machine: Introduction Lucie Filteau (2013), Real GE Aisys Anesthesia Machine [photograpgh]. Retrieved from https://www.flickr.com/photos/luciefilteau/19843830788/in/album-72157654569908142/ By : Didier Mukama

Objectives Know the definition of an Anesthesia Machine Know the different parts of an Anesthesia Machine and their use. Set up and use of anesthetic machine System check out Common Problems and repairs

What is an Anesthetic Machine? At the minimum an anesthesia machine administers anesthetic gases to a patient in a controlled manner A medical equipment used to administer anesthesia to patients. monitors patient and allows the anesthetist/anesthesiologist (user) to make necessary adjustment in order to keep patients under stable state of anesthesia. gives the patient a mixture of anesthetic gas Has incorporated devices that monitors vital signs (HR,BP, Temp, SPO2…) Has alarm systems to allow failsafe operations. Has a protection system that prevents the surgeons, anesthetists… to inhale anesthetic gases.(scavenging system)

What is Anesthetic Gas? Gas used to temporarily keep the patient in total unconsciousness. (General anesthesia) 2 types of anesthetic gases are common: Ether Halogenated (most common):e.g. ISOFLURANE,SEVOFLURANE Non-Ether Halogenated hydrocarbons: e.g. HALOTHANE, CHOLOROFORM Non-Ether Halogenated hydrocarbons are no longer used in developed countries because they are toxic, but are very common in Third World. E.g. HALOTHANE is very common in Rwanda. Other types of anesthetic gases: XENON (costly) The Anesthetic gases are stored in liquid state at room temperature but are very volatile. A vaporizer is used to administer the anesthetic gases to patients

Corrugated tube Oxygen flush valve Ventilator bag Flow meter Vaporizer Different parts of an anesthesia machine- check with engineer to label Vaporizer cabinet Scavenging system Source: Malkin, “Medical Instrumentation in the Developing World” Adapted from: DiverDave (2013), Flow-I anesthesia machine [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Maquet_Flow-I_anesthesia_machine.jpg

System Components APL (Adjustable Pressure Limiting) valve: Pressure limiting valve which releases gas over an adjustable range of pressures on purpose to control system pressure and thus intrapulmonary pressure. Scavenging System: An assembly of specific components that collect excessive exhaled gases and exhausts them out of the operating room to avoid accidental anesthesia of staff. Soda lime: A mixture of sodium and calcium hydroxides that absorbs liquids and gases, especially CO2 from patient exhaled gases Vaporizer: Used to produce an accurate amount of gas from a volatile liquid anesthetic gas. It has a dial or knob to know and to regulate the percentage of anesthetic gases given to the patient.

Homeostasis Control Manual (bag) or assisted (automatic) ventilation Circulation (Blood volume, vasopressor drugs) Neurologic (Autonomous reflex; Anesthetic drugs, relaxant) Thermal regulation (physical; cover, room temperature)

Side effects Drug Toxicity Drug interactions with therapeutic, herbal, abused substances Post-operation Nausea and vomiting

The Anesthesia Machine Mention how the machine is divided into high, intermediate, and low pressure systems Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

High Pressure System Gas from the high pressure cylinders or from a compressor and an O2 plant is supplied via the back of the anesthesia machine (2200 psig for O2) The high pressure side consists of: Hanger Yolk (reserve gas cylinder holder) and seal Check valve (prevent reverse flow of gas) Cylinder Pressure Indicator (Gauge) Pressure Reducing Device (Regulator) Cylinders are not used if there is wall-mounted gas supply. Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Pressure Reducing Device Reduces the high and variable pressures found in a cylinder to a lower and more constant pressure found in the anesthesia machine (45 psig) Reducing devices are preset so that the machine uses only gas from the pipeline (wall gas), when the pipeline inlet pressure is 50 psig. This prevents gas use from the cylinder even if the cylinder is left open (i.e. saves the cylinder for backup if the wall gas pipeline fails)

Intermediate Pressure System Gets gas from the cylinder regulator or the hospital pipeline at pressures of 40-55 psig Consists of: Pipeline inlet connections Pressure gauges Pipes Common gas outlet Master switch Oxygen pressure failure devices Oxygen flush Additional reducing devices Flow control valves Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Pipeline Inlet Connectors Mandatory N2O and O2, usually have medical air and suction ports as well Inlets are non-interchangeable due to specific threading as per the Diameter Index Safety System (DISS) Each inlet must contain a check valve to prevent reverse flow (similar to the cylinder yolk) Ignis (2005), Vaporizer [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Vaporizer.jpg Pipeline inlet connectors (Air, N2O, O2)

Oxygen Pressure Monitors An anesthesia machine is designed such that it sounds an alarm whenever the oxygen supply pressure falls below normal range. (O2 concentration should not be below 19%) Some machines have and electronic as well as a mechanical low O2 supply alarm. In this case one would be a beeper/buzzer and the other would be an air powered whistle

Oxygen Pressure Failure Devices A Fail-Safe valve is found in each gas line supplying the flow meters. This valve shuts off or proportionately decreases the supply pressure of all other gasses with the decrease in O2 supply pressure. 2 kinds of fail-safe valves exist: Pressure sensor shut-off valve (e.g. Ohmeda) Oxygen failure protection device (e.g. Drager)

Oxygen Pressure Fail Device Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Pressure Sensor Shut-Off Valve Oxygen supply pressure opens the valve as long as it is above a pre-set minimum value (e.g.. 20 psig). If the oxygen supply pressure falls below the threshold value the valve closes and the gas in that limb (e.g.. N2O), does not advance to its flow-control valve.

Oxygen Failure Protection Device (OFPD) Based on a proportioning principle rather than a shut-off principle The pressure of all gases controlled by the OFPD will decrease proportionately with the oxygen pressure Not able to reproduce electronically- draw?

Oxygen Flush Valve Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer) Machine standard requires that the flow be between 35 and 75 L/min in flush mode The ability to provide jet ventilation Hazards May cause barotrauma

O2/N2O System with CO2 Absorber Source: Developing Anesthesia: Guidelines for Anaesthesia in Developing Countries Version 1.6.

Second-Stage Reducing Device Located just upstream of the flow control valves Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to 26 psig for N2O and 14 psig for O2 Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure

Low Pressure System It goes from the flow control valves to the gas outlet and consists of: Flow meters Vaporizer mounting device Check valve Common gas outlet

Flowmeter assembly When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float Rschiedon (2007), Flowmeter [drawing]. Retrieved from https://commons.wikimedia.org/wiki/File:Flowmeter.jpg

Proportioning Systems Mechanical integration of the N2O and O2 flow-control valves Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1 Found source- Universidade Technologica Federal Do Parania- not sure if ok to reproduce, looks like no according to their website.

Limitations of Proportioning Systems Machines equipped with proportioning systems can still deliver a hypoxic mixture under the following conditions: Wrong supply gas Defective pneumatics or mechanics Leak downstream (e.g. worn/broken o-rings or leaking pipe fittings) Inert gas administration: Proportioning systems generally link only N2O and O2

Vaporizers A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow Ignis (2005), Vaporizer [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Vaporizer.jpg

Classification of Vaporizers Methods of regulating output concentration Concentration calibrated (e.g. variable bypass) Measured flow Method of vaporization Flow-over Bubble through Injection Temperature compensation Thermocompensation Supplied heat

Generic Bypass Vaporizer Flow from the flowmeters enters the inlet of the vaporizer The function of the concentration control valve is to regulate the amount of flow through the bypass and vaporizing chambers Splitting Ratio = flow though vaporizing chamber/flow through bypass chamber The concentration control dial may be located in the bypass chamber of the outlet of the vaporizing chamber Mention that the machine standard requires that all vaporizers on the anesthesia workstation be concentration calibrated (aka variable bypass, direct reading, dial-controlled, automatic plenium, percentage-type, tec-type vaporizers, and vaporizer chamber bypass arrangements Virginia Reid (2015), Vaporizer [diagram]

Factors That Influence Vaporizer Output Flow Rate: The output of the vaporizer is generally less than the dial setting at very low (< 200 ml/min) or very high (> 15 L/min) flows Temperature: Automatic temperature compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures Back Pressure: Intermittent back pressure (e.g. positive pressure ventilation causes a higher vaporizer output than the dial setting) C’ = concentration at the new atmospheric pressure C = the concentration at the old atmospheric pressure (i.e. the concentration dialed into the vaporizer) P’ = the barometric pressure for which c’ is being established P = the barometric pressure for which the vaporizer is calibrated (i.e. at the old atmospheric pressure)

Factors That Influence Vaporizer Output Atmospheric Pressure: Changes in atmospheric pressure affect variable bypass vaporizer output as measured by volume % concentration, but not (or very little) as measured by partial pressure (lowering atmospheric pressure increases volume % concentration and vice versa) Carrier Gas: Vaporizers are calibrated for 100% oxygen. Carrier gases other than this result in decreased vaporizer output.

The Circuit: Circle System Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed: Unidirectional valves between the patient and the reservoir bag Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve

Circle System Advantages: Disadvantages: Relative stability of inspired concentration Conservation of respiratory moisture and heat Prevention of operating room pollution PaCO2 depends only on ventilation, not fresh gas flow Low fresh gas flows can be used Disadvantages: Complex design = potential for malfunction High resistance (multiple one-way valves) = higher work of breathing The final three points of the advantages section are meant to contrast with the Bain circuit

The Adjustable Pressure Limiting (APL) Valve User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system Bag-mask Ventilation: Valve is usually left partially open. During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve. Mechanical Ventilation: The APL valve is excluded from the circuit when the selector switch is changed from manual to automatic ventilation

Patient Rebreathing Circuit Protects the breathing circuit or ventilator from excessive positive or negative pressure. Mention that the ventilator relief valve is the same thing as the overflow valve mentioned in the previous slides Developing Anesthesia: Guidelines for Anaesthesia in Developing Countries Version 1.6 (2007). Retrieved from linrary.ewh.com

Patient Rebreathing Circuit with Scavenger Output Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480. Malkin, R. (2006). Medical instrumentation in the developing world (p. 65). Memphis, Tenn.: Engineering World Health.

Checking Anesthesia Machines Categories of checks: Gas supply/High pressure system Low-Pressure system APL valve and Scavenging system Breathing system Manual and automatic ventilation system Monitors Final configurations Any emergency ventilation equipment located in the OR Check any gas analysis found on the machine For more details on checking out the anesthesia machines please visit (copy and paste in web browser): http://books.google.rw/books?id=HXZ0WdMuUpgC&pg=PA932&lpg=PA932&dq=anesthesia+check+out+system&source=bl&ots=KvKZeGJHtP&sig=aCDalB2xrnCmR4wowHsXyWMlPy0&hl=en&ei=HLWwTIqGGseH4gb_4MWHBg&sa=X&oi=book_result&ct=result&resnum=6&ved=0CCYQ6AEwBQ#v=onepage&q=anesthesia%20check%20out%20system&f=false

Patient Monitoring Clinical Signs – not automatic measured Anesthesia Movement, Pupil dilation, Sweating, Heart and lung sounds Anesthesia Neuromuscular Relaxation- Evoked response - accelerometers, EMG Sedation, Hypnosis Blood concentration - Expired inhaled anesthetic agent concentration Spontaneous EEG - Compressed Spectral, BiSpectral analysis; Entropy Evoked EEG responses -- Somatic, Auditory, Optical Analgesia (no pain) -- ??

Patient Monitoring Respiration Ventilation - Spirometry (Respiratory rates, tidal volumes, minute ventilation), Airway pressures Gas Exchange - FiO2 (inspired oxygen), Pulse oximetry, FeCO2 (Capnography - expired carbon dioxide) Kalumet (2005), Narkosemonitor [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Narkosemonitor.jpg

Patient Monitoring Circulation Temperature Electrocardiogram (ECG) Blood Pressures Non-invasive blood pressures (NIBP) Invasive Blood Pressures Arterial, Venous Atrial, Ventricle, Pulmonary Artery, Pulmonary pressures Cardiac Output Temperature Pflegewiki-User Würfell (2007)., Medical Monitor [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Monitor_(medical).jpg

Patient Safety Fail Safe Mechanism against Hypoxia - O2/N2O mechanic connection, O2 monitor, pulse oximetry Apnea, Leaks, disconnect, occlusion - low minute ventilation, high/low pressure, CO2 monitor Excessive airway pressure - redundant pressure relief valves Over/Under Anesthetic deliver -Vaporizer interlock, concentration monitor

Patient Safety Mandatory preanesthesia checkout Alarm System - a dilemma Intended for vigilance Result: Excessive alarms noise

Common Problems Sticky rotameters needle valves Power supply User error Leaks Gases leak may affect staff and are flammable Sticky rotameters needle valves Flush with alcohol Mintz I Flow Meter (2013). Retrieved from https://en.wikipedia.org/wiki/Anaesthetic_machine

Preventive Maintenance O2 sensor contacts cleaning with alcohol Batteries replacement Mark.murphy (2005), Diving oxygen analyser [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Diving_oxygen_analyser.JPG ClckrFreeVectorImages (2015), Battery [drawing. Retrieved from Pixabay

Preventive Maintenance CO2 absorber replacement Przemysław Jahr (2012), Drägersorb® Soda Lime [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Dr%C3%A4gersorb_Soda_Lime.jpg