Listen to Audio cylinder gas delivery system hospital gas delivery system oxygen-pressure-failure-device oxygen flush valve flow control valve flowmeters fresh gas outlet spirometers breathing circuit pressure gauge Vaporizer copper kettle vaporizer measured-flow vaporizer agent-specific vaporizer Tec 6 vaporizer electronically controlled vaporizer variable bypass vaporizer ventilator disconnect alarms waste-gas scaveging system oxygen analyzers humidifiers nebulizers Cylinders Gas Delivery System : PISS -pin index safety system (PISS) connection to the anesthetic machine -cylinders are a high-pressure source of medical gas which is attached to the machines hanger yoke assembly hanger yoke assembly includes: -index pins (PISS) -washer -gas filter -check valve Cylinders are under large values of pressure therefore need to be measured and regulated: Bourdon pressure gauge: allows measurement of pressure within the cylinder Pressure regulator: pressure within the cyliner is regulated to less than 50 psig to ensure safety Hospital Pipeline Gas Delivery System DISS -diameter index safety system (DISS) connection to the anesthetic machine -pipeline gases supplied at a pressure between 45 - 55 psig therefore does not need a pressure regulator -pipeline gases flow through a pressure gauge and check valve then combine and share a common gas pathway w/ cylinder gases Oxygen-Pressure-Failure-Device -nitrous oxide and air supply travels directly to the flow meter -oxygen passes through a pressure-failure device, oxygen flush valve, and ventilator power outlet -if the pressure of oxygen < 25 psig then the fail safe valve automatically closes -fail safe valve automatically closes the gas lines to nitrous oxide and air -fail safe valve closes gas lines to other gases other than oxygen in order to prevent hypoxic gas mixtures -fail safe valve does not ensure safety from other causes of hypoxic mixtures since it is measuring pressure vs concentration of 02 Oxygen Flush Valve -allows for high flow of oxygen approx. 35 - 75 liters per minute directly into the common gas outlet -potential for barotrauma to the lung due to high flow rates with no pressure regulator -therefore extreme caution must be used when using oxygen flush valve as the patient is connected to the breathing circuit Flow Control Valves -determines the gas flow rate -counter clockwise direction increases the gas flow rate -valves are touch and color coded to allow better identity for each gas flow rates being controlled Flow Meters -measure gas flow rate -constant-pressure variable-orifice flowmeters: are the ones obtained on the anethetic machine -indicator of measured flow rates may be: ball, bobbin, or float Flowmeters are callibrated for specific gases which are affected by gas properties with differing patterns of flow low laminar flows: affected by gas viscosity high turbulent flows: affected by gas density Malfunction of flowmeters may be due to: -dirt in the flow tune -nonvertical alignment of the tube -sticking of the float at the top of the tube -hypoxic mixtures are possible if a leack develops within or downstream of the 02 flowmeter -risk of hypoxic mixture is reduced if the 02 flow meter is positioned downstream from other gases Spirometers -measures tidal volume delivered to the patients -many spirometers use a turbine principle to measure both minute ventilation and tidal volume -pneumotachograph is a form of fixed-orifice flowmeter that may function as a spirometer Inaccurate measurements of exhaled tidal volumes can be from: -circuit leaks -disconnection -ventilator malfunction -inertia, friction, and water condensation in wright respirometers Significant differences between the volume of gas delivered to the circuit and the volume of gas reaching the patient may be due to: -long compliant breathing tubes -rapid respiratory rates -high airway pressures Breathing Circuit Pressure Gauge -generally measures the pressure within the expiratory and inspiratory unidirectional valves -generally reflects airway pressure Increase in airway pressure may indicate: -decrease in pulmonay compliance -increas in tidal volume -obstruction within the breathing circuit Decrease in airway pressure may indicate -increase in pulmonary compliance -decrease in tidal volume -possible leak within the breathing circuit peak airway pressure: = dynamic compliance which involves movement of gas flow (ex. mucous plug/ kinking of ETT) plateau airway pressure:= static compliance which does not involve moment of gas flow ( ex. decreased lung compliance) -generally in normal ventilation in a normal lung: peak airway pressure is equal to plateau pressure peak airway pressure may be slighty higher than plateau pressure as well Increase in peak airway pressure and plateau pressurecan be from: -decreased lung compliance -increased tidal volume Increase in peak airway pressure and no change in plateau pressure can be from: -increased airway resistance -increased inspiratory gas flow rate Vaporizers Four types: copper kettle vaporizer measured flow vaporizer agent specific vaporizer variable bypass vaporizer -vaporizes liquid states of anesthetic agents into a gaseous state of anethetic agent -vapor pressure of anethetic agent: created by the collisional forces of anesthetic molecules upon the walls of the container -high temperature is associated with high vapor pressure Copper Kettle Vaporizer -considered a measured-flow or flowmeter-controlled vaporizer -copper used because of a high specific heat and high thermal conductivity -mainly used in veterinarian anesthesia -dedicated thorpe tube flow meter determines the amount of carrier gas passes through the vaporizer -vaporizer-circuit flow-control valve divides the vaporizer circuit from the standard oxygen and nitrous oxide flowmeters -relationship between copper kettle flow, total gas flow, and anesthetic concentration which exits 1ml liquid anesthetic = approximately 200 ml anesthetic vapor after having passed through the vaporizer Measured Flow Vaporizer ex. copper kettle vaporizer vapor output: (carrier gas to vaporizer) x (vapor pressure of anesthetic agent) /(barometric pressure) -vapor pressure of anesth. agent = (CG) x (VP) / BP - VP anesthetic concentration vapor output / total gas flow within the circuit Agent Specific Vaporizer -delivers a constant concentration of anesthetic agent despite temperature changes or flow through the vaporizer -also known as variable-bypass vaporizer -counterclockwise motion allows for an increasing percentage of gas flow to enter into the vaporizing chamber vs bypass chamber -gases from vaporizing chamber and bypass chamber combine together and mix with gases from co2 absorber to form fresh gases -vaporizers are agent specific therefore must not be mixed accidently with a wrong and noncorresponding anesthetic agent -excessive tilting of vaporizer may lead to high anesthetic concentrations which may be hazardous to the patient "pumping effect" may occur at low flows during positive pressure ventilation and entails a reverse flow of gas into the vaporizer Tec 6 -heat blended vaporizer (ex.desflurane vaporizer) -electrically heated to 39 degrees C -vapor pressure of 2 atm -no FGF through desflurane sump -pure desflurane vapors mixes with fresh gas just before exiting the vaporizer -dial control and FGF rate determine the amount of desflurane vapor is released -does not automatically compensate for in elevation ex. high elevations: anesthesiologist must manually increase the conc. dial Variable-bypass Vaporizer -recommended location outside the circle system -vaporizer between the flowmeter and common gas outlet allows less chances of dramatic inc in conc. with 02 flush valve use recommended order of vaporizers based on vapor pressure and potency of anesthetic agents (upstream to downstream): desflurane, methoxyflurane, enflurane, sevoflurane, isoflurane, halothane Electronically Controlled Vaporizers -may be integrated with an electronic flow-control Flow-control helps to separate the gas flow into: bypass flow liquid chamber flow : agent-specific cassette (Aladin cassette) which vaporizes the anesthetic agent -the flow leaving the saturated anesthetic liquid chamber combines with the bypass flow to join before leaving the fresh gas outlet -altering the ratio between the ratio between the bypass flow and liquid chamber flow changes the concentration of the anesthetic -software determines the fresh gas concentration of the anesthetic agent depending on the output pulses from the agent wheel -liquid chamber flow is calculated dependant on desired fresh gas concentrations and determined cassette gas concentration agent-specific cassette (Aladin cassette): -does not contain a bypass channel -anesthetic liquid cannot escape while handing (ex. filling) -cassette can be carried in any position without concern of 'tilting' are related concern of resultant hazardous vapor output -the flow leaving the saturated anesthetic liquid chamber combines with the bypass flow to join before leaving the fresh gas outlet -altering the ratio between the ratio between the bypass flow and liquid chamber flow changes the concentration of the anesthetic -sensors in the cassette measure pressure and temperature which helps calculate the exiting anesthetic agent concentration Ventilators -create a pressure gradient from the proximal airway to the alveoli -newer models create positive pressure ventilation (vs old models using negative pressure ex. iron lungs) Four phases of ventilation: -inspiration -transitional period between inspiration to expiration -expiration -transitional period between expiration to inspiration Mechanical Ventilators generate a tidal volume by producing a pressure gradient which directs as flow Termination of inspiratory phase occurs by preset limit of: -time duration ex. Time-cycled ventilators allows variation of tidal volume and peak inspiratory pressures -inspiratory pressure ex. Pressure-cycled ventilators reached preset pressure allows for the cycle from insp to exp phase -tidal volume ex. Volume-cycled ventilators preset volume creates a varying inspiration duration and insp pressure Modes of ventilation: -controlled ventilation -assisted ventilation -intermittent ventilation -synchronized intermittent mandatory ventilation Waste Scaveging System -vented gases from breathing circuits are disposed of by a waste-gas scavenging system -pressure release valve allows for the transfer of gases from the breathing circuit into the scaveging system -reducing inhalational anesthetic levels to trace levels accepted by NIOSH is accomplished with a functional scaveging system -NIOSH = national institute of Occupational Safety and Health -passive scaveging:scaveging system leading to directly to the outside environment -active scaveging : scaveging system leading to the hospital's vacuum system Humidifiers relative humidity: ratio of mass of water present in a volume of gas absolute humidity Upper respiratory tract -100% relative humidity which is approximately 47 mm H20/L at 37 degree C -normally warms inhaled gases Inhaled gases via ETT bypass the upper respiratory tract may cause: -dehydration of musosa -altered function of respiratory cillia -inspissations of respiratory tract secretions -atelectasis possibly leading to V/Q mismatch Humidifiers: -reduce water loss -reduce heat loss Designs: -condenser humidifier -heat and moisture exchanger traps exhaled humidification and releases the humidity in the next inhalation Nebulizers -suspend water particles into a spray in which the droplet size depends on the methodology of nebulization Method of nebulizing water droplets: high-pressure jet nebulizers 5 - 30 um diameter droplets ultrasonic nebulizers 1- 10 um diameter droplets Oxygen Analyzer low-level alarm which is activated when turning on the analyzer placed in the inspiratory limb or expiratory limb of the circle system breathing circuit not to placed in the fresh gas flow line measurement of oxygen concentration can be done as follows: -electrochemically -paramagnetic analysis -mass spectrometry Electrochemical sensors -galvanic cell -polarographic cell paramagnetic sensors -self callibrating -no consumable parts -rapid response time which allows for differentiation of inspiratory and expiratory oxygen concentrations