ANESTHETIC ANESTHETIC MACHINESMACHINES

The primary function of any anesthetic The primary function of any anesthetic machine is to deliver a precise amount of machine is to deliver a precise amount of

oxygen and volatile anesthetic under oxygen and volatile anesthetic under controlled conditions to patients controlled conditions to patients undergoing general anesthesia.undergoing general anesthesia.

ANESTHETIC MACHINEANESTHETIC MACHINE

1)1) Oxygen is be deliveredOxygen is be delivered at a controlled rate at a controlled rate2)2) A A liquid liquid anesthetic is anesthetic is converted to a gasconverted to a gas, ,

then then mixed with oxygenmixed with oxygen, and delivered to the , and delivered to the patientpatient

3) 3) Gases exhaledGases exhaled from the patient are from the patient are disposed disposed of OR re-circulatedof OR re-circulated (after removing the (after removing the CO2CO2))

REMEMBER: You can also use an anesthesia REMEMBER: You can also use an anesthesia machine to machine to deliver oxygen to a patient in deliver oxygen to a patient in distress. DON’T turn the vaporizer on!distress. DON’T turn the vaporizer on! You You do not want to anesthetize these patients!do not want to anesthetize these patients!

COMPONENTS OF THE COMPONENTS OF THE ANESTHESIA MACHINEANESTHESIA MACHINE

Can be broken down into 4 parts:Can be broken down into 4 parts:

Compressed gas supply Compressed gas supply GasGas tanks tanks, their pressure, their pressure gauges gauges, and pressure reducing , and pressure reducing

valvesvalves (may not be visible) (may not be visible)

Anesthetic machineAnesthetic machine Flowmeter, vaporizerFlowmeter, vaporizer

Breathing circuitBreathing circuit Unidirectional Unidirectional valves, hoses, reservoir bag, pop-off valve, valves, hoses, reservoir bag, pop-off valve,

CO2 canister, O2 flush, pressure manometer, negative CO2 canister, O2 flush, pressure manometer, negative pressure relief valvepressure relief valve

Scavenging SystemScavenging System Disposes of excess and waste anesthetic gasesDisposes of excess and waste anesthetic gases

PART 1PART 1

Following the flow of oxygen Following the flow of oxygen

GAS CYLINDERGAS CYLINDER

CarrierCarrier gas gasGas that is compressed Gas that is compressed in a metal cylinderin a metal cylinder and and held under pressureheld under pressureAvailable in various sizesAvailable in various sizes ““E” holds 660 L of oxygenE” holds 660 L of oxygen and is and is attached attached to the to the

anesthesia machineanesthesia machine ““H” cylinders hold 6900 L of oxygenH” cylinders hold 6900 L of oxygen and stand and stand

separate separate from the machinefrom the machine

Tanks are delivered and picked up by the Tanks are delivered and picked up by the oxygen supply companyoxygen supply company

Gas CylinderGas Cylinder

Tanks are color coded for safety and recognitionTanks are color coded for safety and recognition Oxygen tanks: GREEN (U.S.), white (Canada)Oxygen tanks: GREEN (U.S.), white (Canada) Nitrous oxide tanks: blue (U.S.)Nitrous oxide tanks: blue (U.S.) Carbon dioxide tanks: gray (U.S.)Carbon dioxide tanks: gray (U.S.)

Oxygen cannot flow out of the tank unless the Oxygen cannot flow out of the tank unless the outlet valve has been turned to the left. (Righty outlet valve has been turned to the left. (Righty tighty, lefty loosey)tighty, lefty loosey)

Small cylinders Small cylinders attach to the anesthetic attach to the anesthetic machine via a YOKE.machine via a YOKE. Large cylinders are Large cylinders are attached via hoses or pipes. Gas lines may also attached via hoses or pipes. Gas lines may also be used to bring in the gas from another room.be used to bring in the gas from another room.

GAS CYLINDERSGAS CYLINDERS

In addition to color-coded tanks, the In addition to color-coded tanks, the yokes are yokes are gas-specificgas-specific. A nitrous oxide tank cannot be . A nitrous oxide tank cannot be attached to an oxygen yoke. attached to an oxygen yoke. The pin indexing The pin indexing system that is used to attach it is also system that is used to attach it is also specificspecific to its specific gas. to its specific gas.

A A full tank of oxygenfull tank of oxygen has a pressure of has a pressure of 1900-1900-2200 psi2200 psi. The volume in liters can be . The volume in liters can be determined by multiplying the psi by 0.3 for an E determined by multiplying the psi by 0.3 for an E tank and 1.7 for an H tank.tank and 1.7 for an H tank.     0.3 x psi on gauge  0.3 x psi on gauge  

L/min to be deliveredL/min to be delivered

This formula will allow you to know how long your tank will lastThis formula will allow you to know how long your tank will last

TANK PRESSURE GAUGETANK PRESSURE GAUGE

Display of the pressureDisplay of the pressure of oxygen in of oxygen in the tank. the tank.

Reads Reads zero when it is emptyzero when it is empty, when tank is , when tank is turned off,turned off, and all and all gas has been removed from the machinegas has been removed from the machine

Actual amount in tank is displayed when the tank is Actual amount in tank is displayed when the tank is turned onturned on

Check this gauge Check this gauge BEFOREBEFORE an anesthetic procedure an anesthetic procedure (especially the lengthy ones).(especially the lengthy ones).

TANK PRESSURE GAUGETANK PRESSURE GAUGE

Change when the pressure is no lower Change when the pressure is no lower than 100 psithan 100 psi (some clinics will require (some clinics will require tanks to be changed much earlier). Refill tanks to be changed much earlier). Refill line is at 500 psi.line is at 500 psi.

NITROUS OXIDENITROUS OXIDE

A full E cylinder contains 760 psi.A full E cylinder contains 760 psi.Nitrous oxide is present in liquid and gas Nitrous oxide is present in liquid and gas forms in the tankforms in the tank. When the tank is turned on, . When the tank is turned on, liquid evaporates into a gas as other gas liquid evaporates into a gas as other gas leaves the tankleaves the tank. The . The pressure of the tank pressure of the tank doesn’t changedoesn’t change because of the because of the constant constant replacement of the gasreplacement of the gas until all liquid has been until all liquid has been volitalized. The volitalized. The gauge will not dropgauge will not drop until almost until almost empty.empty.

Anesthetist should change the tank as soon as Anesthetist should change the tank as soon as 500 psi is reached. 500 psi is reached.

PRESSURE REDUCING VALVEPRESSURE REDUCING VALVE

Regulates the pressureRegulates the pressure of the gas of the gas leavingleaving the the tank and tank and going intogoing into the anesthesia machine the anesthesia machine

Allows a Allows a constant flow of gasconstant flow of gas into the machine, into the machine, despite pressure changesdespite pressure changes within the tank within the tank

Reduces the pressureReduces the pressure of oxygen that leaves of oxygen that leaves the tank at 2200 psi to a safer the tank at 2200 psi to a safer 50 psi. 50 psi.

In cases of small tanks and gas lines, the In cases of small tanks and gas lines, the line line pressure is preset at 50 psi. Only the tank pressure is preset at 50 psi. Only the tank pressure gauge is visible.pressure gauge is visible.

PART 2PART 2

Now that the gas is in the machine, it’s job is to Now that the gas is in the machine, it’s job is to mix with the anesthetic and be delivered to the mix with the anesthetic and be delivered to the

patientpatient

FLOW METERFLOW METER

Allows the Allows the flow rate of oxygen traveling through flow rate of oxygen traveling through the machinethe machine to be adjusted by the anesthetist. to be adjusted by the anesthetist. Oxygen does not reach the patient unless this Oxygen does not reach the patient unless this is turned on (neither does the anesthetic gasis turned on (neither does the anesthetic gas..

Calculated in Calculated in Liters per minuteLiters per minuteSeparate Separate flow meters for each gasflow meters for each gas These knobs can be distinguished from one another via These knobs can be distinguished from one another via

labeling, touch, or colorlabeling, touch, or color

FLOWMETER CONT’DFLOWMETER CONT’D

The dial of the flowmeter is turned on and The dial of the flowmeter is turned on and either a either a ball or rotor risesball or rotor rises to the selected to the selected flow rate. flow rate. Read at the center of the ball or top of the Read at the center of the ball or top of the

rotorrotor

Gas travels throughGas travels through the flowmeter the flowmeter

VAPORIZERVAPORIZER

Converts the liquidConverts the liquid anesthetic agent anesthetic agent (usually isofluorane or sevofluorane) (usually isofluorane or sevofluorane) into into a vapor.a vapor.

Adds controlled amountAdds controlled amount of these vapors of these vapors to the to the carrier gascarrier gas

Next stop as oxygen travels from the Next stop as oxygen travels from the flowmeterflowmeter

The flowmeter The flowmeter must be on to deliver must be on to deliver anesthesia to the patientanesthesia to the patient as it needs to as it needs to be mixed with a carrier gas. be mixed with a carrier gas.

VAPORIZERVAPORIZER

Similarly, the Similarly, the vaporizer must be on to deliver vaporizer must be on to deliver any anesthesiaany anesthesia to the patient. Otherwise, only to the patient. Otherwise, only the carrier gas will be deliveredthe carrier gas will be delivered

The mixture of the anesthetic gas and carrier The mixture of the anesthetic gas and carrier gas is known as FRESH GAS.gas is known as FRESH GAS.

Once mixed, Once mixed, fresh gas cannot return to the fresh gas cannot return to the vaporizer. vaporizer.

Use the correct anesthetic with the correct Use the correct anesthetic with the correct vaporizer! (Don’t put sevo in the iso machine)vaporizer! (Don’t put sevo in the iso machine)

VAPORIZERVAPORIZER

Amount of anesthetic liquid left in Amount of anesthetic liquid left in vaporizer is visible in the vaporizer is visible in the indicator indicator windowwindow. Check BEFORE your surgery to . Check BEFORE your surgery to see if it needs refilling!see if it needs refilling!

If for some reason the If for some reason the vaporizer vaporizer

is tipped overis tipped over (usually the (usually the

whole machine), turn the whole machine), turn the

vaporizer off and run oxygen vaporizer off and run oxygen

onlyonly through the machine for through the machine for

15 minutes15 minutes to flush it out. to flush it out.

PRECISION VS. NONPRECISION PRECISION VS. NONPRECISION VAPORIZERSVAPORIZERS

Precision vaporizers Precision vaporizers delivers a precise, delivers a precise, controlled amount of anestheticcontrolled amount of anesthetic to the patient to the patient

Expressed as a % which is chosen based on an Expressed as a % which is chosen based on an anesthetic’s MAC and the patient’s requirementsanesthetic’s MAC and the patient’s requirements

$$ Commonly used anesthetics can reach Commonly used anesthetics can reach

concentrations as high as 30% + if they are not concentrations as high as 30% + if they are not controlledcontrolled

PRECISION VS. NONPRECISION PRECISION VS. NONPRECISION VAPORIZERSVAPORIZERS

Nonprecision vaporizers are simple, Nonprecision vaporizers are simple, cheaper, and are typically used for cheaper, and are typically used for anesthetics with low vapor pressure such anesthetics with low vapor pressure such as methoxyfluoraneas methoxyfluorane

PART 3PART 3

BREATHING CIRCUITBREATHING CIRCUIT

The system that The system that brings the fresh gas brings the fresh gas from the vaporizer to the patient and from the vaporizer to the patient and takes the expired gases from the takes the expired gases from the patientpatient

May contain unidirectional valves, May contain unidirectional valves, reservoir bag, pop off valve, CO2 canister, reservoir bag, pop off valve, CO2 canister, O2 flush, negative pressure relief valve, O2 flush, negative pressure relief valve, pressure manometer. pressure manometer.

UNIDIRECTIONAL VALVESUNIDIRECTIONAL VALVES

One-way valvesOne-way valves that that allow the flowallow the flow of fresh gas to of fresh gas to enter the inhalationenter the inhalation valve and valve and exit the exhalationexit the exhalation valve. valve.

Valve is either a Valve is either a rigid disk or a flaprigid disk or a flap that flutters as gas that flutters as gas flows past itflows past it

Inhalation valve opens as patient inhalesInhalation valve opens as patient inhales, anesthetic , anesthetic enters the hose, then the endotracheal tube and the enters the hose, then the endotracheal tube and the patientpatient

CO2 and anesthetic gases are then CO2 and anesthetic gases are then exhaled, travel exhaled, travel down the hose and through the unidirectional down the hose and through the unidirectional exhalation valve. This valve prevents the expired exhalation valve. This valve prevents the expired gases from traveling back to the patient before the gases from traveling back to the patient before the CO2 is removedCO2 is removed

RESERVOIR BAGRESERVOIR BAG

Also called a Also called a rebreathing bagrebreathing bag

Fills as gases enter the circuit or patient Fills as gases enter the circuit or patient exhales, exhales, deflates as patient inhalesdeflates as patient inhales

FUNCTIONSFUNCTIONS

1)1) StoresStores gas gas

2)2) Helps in determining correct Helps in determining correct endotracheal endotracheal tube placement. Movement of bag with tube placement. Movement of bag with breaths = tube in tracheabreaths = tube in trachea

3)3) Allows assessmentAllows assessment of respiratory rate and of respiratory rate and depthdepth

4) 4) Allows “bagging”Allows “bagging” of the patient of the patient- reverse atelectasis if present- reverse atelectasis if present-removal of CO2 and anesthetic that builds -removal of CO2 and anesthetic that builds up when respirations have decreased in up when respirations have decreased in volumevolume

-assist or control ventilation – esp if in -assist or control ventilation – esp if in respiratory arrestrespiratory arrest

Volume of bag should be minimally Volume of bag should be minimally 60mL/kg (round up) See pg 119 for 60mL/kg (round up) See pg 119 for reference chartreference chartSizes range from ½ L to 30 L (1,2,3L Sizes range from ½ L to 30 L (1,2,3L commonly used on small animals)commonly used on small animals)

SIGNS THAT YOUR RESERVOIR SIGNS THAT YOUR RESERVOIR BAG IS NOT THE RIGHT SIZE:BAG IS NOT THE RIGHT SIZE:

OverinflatesOverinflates rapidly if too small. If rapidly if too small. If overinflated, animal will have problems overinflated, animal will have problems exhalingexhaling

Bags should consistently be ~ ¾ fullBags should consistently be ~ ¾ full

Very little movement of bag with breaths if Very little movement of bag with breaths if too bigtoo big

POP-OFF VALVEPOP-OFF VALVE

AKA AKA pressure reliefpressure relief valve valve

Allows excess Allows excess gas to leavegas to leave the breathing the breathing circuit and circuit and be scavengedbe scavenged

Prevents the build-upPrevents the build-up of excess gas or of excess gas or pressure within the circuit. If the pressure pressure within the circuit. If the pressure were allowed to build up (forgot to open were allowed to build up (forgot to open pop off valve), the pop off valve), the alveoli in the lungs alveoli in the lungs could rupturecould rupture

KEEP the pop-off valve OPEN unless KEEP the pop-off valve OPEN unless you are bagging the patient (or if you you are bagging the patient (or if you have a low-flow/closed system)have a low-flow/closed system)

POP OFF VALVEPOP OFF VALVE

In some instances, the degree that the pop In some instances, the degree that the pop off valve is opened changes with the flow off valve is opened changes with the flow rate and how full the reservoir bag israte and how full the reservoir bag is

CO2 ABSORBERCO2 ABSORBERGases that don’t exit the machineGases that don’t exit the machine via the pop off valve go via the pop off valve go into the CO2 canister and are then returned to the patientinto the CO2 canister and are then returned to the patientCO2 canister usually contains CO2 canister usually contains soda lime that removes CO2soda lime that removes CO2 from other gases breathed out. from other gases breathed out. ““Exhaused” soda lime granules no longer absorb CO2.Exhaused” soda lime granules no longer absorb CO2.

HOW DO I KNOW WHEN THE GRANULES ARE EXHAUSTED?HOW DO I KNOW WHEN THE GRANULES ARE EXHAUSTED?Color Color change to violet, off-white or pink depending on the change to violet, off-white or pink depending on the brand. Based on pH.brand. Based on pH.CO2 saturated granules are CO2 saturated granules are hard and brittlehard and brittle, new ones can be , new ones can be chipped and crumbledchipped and crumbledOnce color becomes abnormal, it is possible that it changes Once color becomes abnormal, it is possible that it changes back to normal within hoursback to normal within hours

CO2 CANISTER WITH SODA CO2 CANISTER WITH SODA LIMELIME

O2 flushO2 flush

When activated, When activated, O2 bypasses the O2 bypasses the flowmeter and vaporizer and enters the flowmeter and vaporizer and enters the circuitcircuit

High flow rate (up to 75L/min!)High flow rate (up to 75L/min!)

Never use with a non-rebreathing systemNever use with a non-rebreathing system

Can use to fill the bag, help a critical Can use to fill the bag, help a critical patient, dilute the anestheticpatient, dilute the anesthetic

PRESSURE PRESSURE MANOMETER/GAUGEMANOMETER/GAUGE

Measures Measures pressures of gas within the pressures of gas within the circuit in cm H20circuit in cm H20

Eyes on this while baggingEyes on this while bagging your patient your patient

DO NOT GO ABOVE DO NOT GO ABOVE 20 CM H2020 CM H20!!

NEGATIVE PRESSURE RELIEF NEGATIVE PRESSURE RELIEF VALVEVALVE

When an active scavenging system is When an active scavenging system is utilized, if negative pressure is detected in utilized, if negative pressure is detected in the circuit, this valve opens and allows the circuit, this valve opens and allows room air in.room air in. Particularly in instances when there is Particularly in instances when there is

excessive suctionexcessive suction Also in instances where the O2 flow rate is Also in instances where the O2 flow rate is

too low or the tank runs out of oxygentoo low or the tank runs out of oxygenBetter for the patient to breathe room air than no Better for the patient to breathe room air than no airair