Intubation and Anesthetic Machines

Intubation and Anesthetic Machines

Endotracheal Intubation
Types of endotracheal tubes Plain Used in birds Occasionally used in cats A plain tube does not form an airtight seal within the trachea Will allow secretions, blood or gastro-intestinal fluid to enter the lungs

Types of endotracheal tubes Cuffed Used in all species Cuff is inflated with air to produce a leak proof seal A pilot balloon is used to estimate degree of inflation Alternatively the cuff is filled until no leak of air can be heard when the lungs are inflated to 25 cm H2O pressure

Types of endotracheal tubes Cole Originally designed for babies The tube has excellent pressure-flow characteristics and provides less resistance to breathing Absence of cuff allows insertion of a larger tube A cole tube is commonly used for cats "Shoulders" of the tube form an airtight seal at the entrance to the larynx

Size of endotracheal tube Choose an endotracheal tube as large as possible without forming a "push-fit‘ Check the tube length alongside the animal The tip of the tube must be beyond the larynx but not extend past the thoracic inlet

Size of endotracheal tube Tube sizes refer to the internal diameter of the part of the tube residing in the trachea A few manufacturers print both internal and external diameters on their endotracheal tubes Purchase tubes with thin walls especially when they are to be used on cats and small dogs A thin wall allows a tube with a larger lumen to be used

Technique of intubation Orotracheal Intubation Dogs and Cats Open the dog or cat's mouth and view the larynx Use a bright overhead light or a laryngoscope There is no excuse for doubt when inserting an endotracheal tube You can see where it is -- in the trachea or in the esophagus

Technique of intubation Orotracheal Intubation Dogs and Cats Pull the tongue forward gently in the dog and cat to move the larynx more rostral . Do not pull hard on the tongue or it will could lacerated or have nerve damage Do not put your fingers inside the mouth (jaw tone and the ability to reflexively close the jaws persists into light anesthesia) A plastic or metal stilette can be used inside an endotracheal tube to stiffen it This is to improve control of the direction of the tip of the tube, not so that you can force the tube into the larynx Make sure that the tip of the stilette is not sharp and does not extend beyond the end of the tube, where it might lacerate the trachea

Technique of intubation Orotracheal Intubation Dogs and Cats If you use a laryngoscope Place the tip of the blade over the tongue and under the epiglottis Placing it on the epiglottis will distort the laryngeal opening and make it harder to intubate Tracheal intubation can be performed with the animal on its side, sternum, or back The position may be dictated by the animal's condition (e.g., with GI obstruction always intubate the animal in sternal position, with the head up) or by personal preference of the surgeon

Technique of intubation Orotracheal Intubation Pigs and small ruminants Technique used is the same for dogs and cats The anatomy of the pharynx and larynx of these species differs Adult Cattle Intubation can be performed using a laryngoscope with an extra long blade Intubation most frequently accomplished without viewing the larynx You introduce your hand and arm into the mouth to palpate the laryngeal opening and to guide the tip of the endotracheal tube into the trachea Horses Intubation performed "blind", without viewing the larynx and without palpation.

Nasotracheal Intubation
Dogs, cats, pigs and ruminants Not performed Horses Easy to insert a tube from the nares through the ventral nasal meatus, into the trachea Used in some foals to administer halothane or isoflurane to induce anesthesia Used in adult horses during recovery from anesthesia to relieve nasal obstruction from mucosal swelling

Pharyngostomy Intubation
Tracheal intubation through a pharyngostomy Dogs and cats May be used in dogs and cats requiring oral surgery, e.g., repair of fractured jaw, cleft palate repair, lacerations of hard palate Allows the surgeon greater access to the surgical field

Exotics Reptiles – Most reptiles can be intubated if large enough.
Avian – Endotracheal intubation sometimes used. High incidence of mucous blockage in tubes due to very small tracheal openings and high mucous production. Most avian veterinarians prefer air sac cannulization. This is a surgical procedure when a tracheal tube is inserted directly into an air sac near the leg.

Complications of endotracheal intubation If the internal diameter of the endotracheal tube is too small in relation to the animal There will be increased resistance to breathing Hypoventilation will result If the cuff is over inflated, or if it is inflated for too long The tracheal mucosa, and sometimes the cartilage, will die and slough Later the animal will show signs of tracheitis Only inflate the tube cuff with enough air to prevent a leak when the animal's lungs are artificially inflated If you have a device to measure intra-cuff pressure, inflate the cuff to 25 cm H2O pressure If the duration of surgery is long, provided that regurgitation has not occurred, the cuff should be deflated and the tube repositioned every 2 hours

Complications of endotracheal intubation If the tube is too long A primary bronchus may be intubated One lung will collapse Cyanosis may develop Delivery of inhalation anesthetic is impaired The animal may wake up Endotracheal tubes can cause airway obstruction They become twisted or kinked The bevel of the tube lies against the tracheal wall The cuff is over inflated and squashes the tube lumen The cuff bulges over the end of the tube K-Y lubricant is allowed to dry inside the tube Mucus and secretions accumulate during anesthesia (especially cats and small dogs) or are allowed to dry inside the tube (improper cleaning after anesthesia).

Complications of endotracheal intubation Trauma of the larynx and trachea Can produce laryngitis/tracheitis which will last for several days Laryngeal trauma may also predispose the animal to laryngospasm or to granuloma formation at a later date Mucosal swelling in the recovery period may cause partial or complete airway obstruction Preferably do not cause trauma, but if swelling occurs, inject dexamethasone IV and provide supportive treatment (oxygen, reintubate) until the swelling is reduced Irregular heart rhythm Laryngoscopy causes bradycardia Tracheal intubation causes tachycardia and, sometimes, ventricular premature depolarizations Atropine premedication should prevent bradycardia Lidocaine, 2 mg/kg, applied directly to the larynx or injected intravenously before intubation should modify or prevent tachycardia Lidocaine is used when tachycardia is anticipated to cause deterioration of the patient.

Complications of endotracheal intubation Leak in the cuff preventing an airtight seal and controlled ventilation Always check the cuff for leaks before inducing anesthesia Transfer of infection Clean tubes thoroughly, inside and outside, between patients Use a bristle brush and betadine (or similar) solution If ethylene oxide (ETO) sterilization is used, adequate aeration is needed to eliminate irritant residues

Endotracheal intubation
Complications of endotracheal intubation Bracycephalic syndrome (short nose breeds) Stenotic nares Everted layrngeal saccules Elongated soft palate Hypoplastic trachea Airways can collapse easily after extubation Wait until the dog has a good gag reflex before extubating Preoxygenate for 5 minutes before induction in case of a difficult intubation

Complications of endotracheal intubation Cats Can be very difficult to intubate due to laryngeal spasms Small amount of lidocaine swabbed on larynx can numb it long enough to intubate Many need to use a stylet in endotracheal tube to help pass it

Complications of endotracheal intubation Collapsing trachea Genetically weak trachea Preoxygenate severe cases Intubate as gently as possible as not to irritate the trachea

Procedure for tracheal extubation in dogs and cats Leave tube in place until swallowing reflex returns Remove blood clots from nasopharynx Deflate the cuff before extubation Exceptions: When bleeding into the nose and mouth has occurred Excessive salivation has occurred Regurgitation has occurred Prevent the animal biting the tube while it is being removed Cost prohibitive Animal (dog or cat) can easily inhale or swallow pieces of tube

Parts of an Anesthetic Machine
Gas cylinders Oxygen and nitrous oxide are contained in compressed gas cylinders Found as E cylinders that are usually attached to the machine via yokes that are equipped with a specific pin system Tanks also come in large G and H cylinders

Gas cylinders Pressure gauge attached to the cylinder indicates the pressure of the gas in the tank Pressure in a full O2 cylinder is 2200 psi Oxygen tanks should be changed when pressure drops below 500 to 600 psi The volume of O2 in an E cylinder can be calculated by multiplying the psi by 0.3 A full tank of 2200 psi will contain 660 L of O2

Gas cylinders Nitrous tanks are stored at lower pressures A full tank is 770 psi Nitrous tanks should be changed when pressure gauge drops below 500 psi Both liquid and gas states are present but the gauge reads only the gas state Liquid evaporates to gas as soon as the gas leaves the tank so the pressure in the tank will not change until all the liquid state has evaporated

O2 cylinder, pressure releasing valve, pressure gauge

Pressure releasing valve (regulator) Reduces the high pressure of the O2 or nitrous leaving the tank to a low pressure of 50 psi

Flow meter Measure O2 or nitrous in L/min Allows the anesthetist to set the O2 or nitrous oxide flow rates that will be delivered to the animal As the gas passes through the flow meter gas pressure is reduced further to 15 psi

Flow meter

Vaporizer Converts the liquid anesthetic into a gas state Controls the amount of vaporized amount of vaporized anesthetic mixed with the carrier gas

Sevoflurane vaporizer

Check valves Inhalation/Exhalation flutter valves Insures a uni-directional flow of gas to and from the patient when delivering a circle system Y connector Connects the endotracheal tube to the inspiratory and expiratory tubes of a circle system

Rebreathing bag (reservoir bag) Allows the animal to breath easier from a reservoir of gas Can be used to deliver O2 (with or without anesthetic gas) and manually assist respirations, bagging Bags should have a minimum volume of 60 ml/kg of patient weight

Carbon dioxide absorber Soda lime canister Used in rebreathing systems to remove CO2 from the expired gases Exhaust gases enter a canister containing soda lime or barium hydroxide Na+, K+, Ca2+ and Ba2+ hydroxide reacts with the exhaled CO2 and water to form carbonate Heat is liberated and the pH decreases

Carbon dioxide absorber Soda lime canister A pH color indicator turns blue on consumption When the soda lime or barium hydroxide granules turn color or the granules become hard instead of crumbly, they are saturated with CO2 and should be replaced When in use, the granules will produce heat and condensation within the canister The color reaction is time limited Exhausted crystals should be removed immediately and replaced with new granules

Carbon dioxide absorber Soda lime canister Should be changed after 6 to 8 hours of use depending on the size of the animal and the gas flow rate If machines are left standing for longer than 30 days, granules should be replaced before using machine

Exhaust valve Also called the pop-off valve, or pressure relief valve Exhaust gases leave the system via the exhaust valve entering the scavenger system Valve can be fully or partially open when a patient is using the machine Valve is closed for leak tests or when filling the reservoir for assisted respirations

Manometer Measures the pressure in the system in mm Hg or cm H20 Generally calibrated form -30 to +50 cm H20 Gauge thus reflects the pressure of gas in the animal’s airways and lungs The pressure should be at 0 and never more than 15 cm H20 (11 mm Hg) When providing positive assisted ventilation, the pressure should not exceed 15 to 20 cm H20 (11 to 15 mm Hg)

Oxygen flush valve O2 bypasses vaporizer, delivering 100% O2 to breathing system Enables the anesthetist to flush the system with pure O2 Fills the reservoir and system for leak test Also flushes the anesthetic gases out of the circuit and replaces with pure oxygen Never use O2 flush valve with a Bain circuit in a small animal because it produces too much pressure

Scavenger system Attached to the exhaust valve Consists of tubing that collects gases and directs them outside the building or to a charcoal canister Can be active or passive

Negative pressure relief valve Some newer machines have this safety feature Valve opens in response to a negative pressure situation in the system Allows room air into the circuit Negative pressure could be due to an active scavenger system or a low oxygen supply

Maintenance Oxygen tanks must be turned off to prevent excess pressure on the regulator Flush the remaining O2 to minimize damage to the pressure gauge and reducing valves Turn flowmeter off to prevent sudden rush of O2 into the flowmeter when O2 is turned back on Don’t over tighten because the knobs can be easily twisted off

Maintenance After each anesthesia induction, removable machine parts and anesthetic equipment that come in contact should be washed in a mild, soapy solution, soaked in a cold disinfectant, thoroughly rinsed and dried The dome valves and absorbent canister should be disassembled and wiped dry. Flutter valves need periodic removal and cleaning with a disinfectant to prevent adherence to the machine housing

Maintenance Vaporizers should be turned off when not in use and periodically emptied to prevent buildup of the preservative and other residue Best to clean and recalibrate by authorized personnel every 6 to 12 months Isoflurane does not contain a preservative

Maintenance Barium hydroxide or soda lime granules found in the CO2 absorbers need replacing when the granules have changed color or cannot be easily crumbled Do not tightly pack and leave about 1 cm (1/2 inch) of air space Avoid having dust enter tubing or hoses of the machine Rubber items will likely need to be replaced after prolonged use

Environmental concerns
Environmental pollution can be minimized through proper equipment use and scavenging of the gases Safe exposure limit for inhalant anesthetic agents has been set at 2 p.p.m. in room air Everyone, especially pregnant women, should avoid high levels of waste anesthetic gases Much of the anesthetic levels are because of leaks in anesthetic machines

Vaporizers and CO2 absorbers should be filled with minimal personnel in a well ventilated area while wearing gloves and masks Do not turn the vaporizer on and off until or while, the patient is connected to the machine During recovery, keep patient in a well ventilated area and on the machine until expired gases are scavenged

Use active scavenging systems whenever possible to ensure waste gases are drawn out of the area If passive scavenging is used, keep the hose as short as possible and have it travel downward toward the exhaust If it is not possible to install scavengers in all rooms where machines are used, either use an activated charcoal cartridge that must be replaced after 12 hours or substitute injectable anesthesia

Before anesthesia, the machine should be checked for both high and low pressure leaks Leakage of nitrous is the major environmental concern A high pressure system test monitors NO2 and O2 leakage A low pressure system leak is in the anesthetic machine itself

Low pressure system test A low pressure system leak occurs between the flowmeter and the patient Turn the tank on, close the pop-off valve, and occlude the end of the hose so the gas should have nowhere to escape Adjust the flowmeter to at least 2 L/min of O2 allowing the bag to fill gradually and then turn off the flowmeter If there is no escape of air when the bag is gently squeezed, then there is no low pressure system leakage

Low pressure system test System can also be checked by occluding as above and using the flowmeter to allow the system to pressure at 30 cm H2O Turn off the flowmeter The pressure should be maintained for at least 10 seconds One can also listen for the hiss of escaping air or use a detergent solution as described earlier

Breathing Systems Rebreathing systems Circle systems
Rebreathing refers to breathing a mixture of expired gases and fresh gases The amount of CO2 in inhaled gases depends on Whether the rebreathing system has a CO2 absorber The flow rate of fresh gases (the higher the fresh gas flow rate, the more expired gas is pushed out the scavenger and not rebreathed Depending on the flow rate of fresh gas, the system is classified as a closed system (total rebreathing of expired gases) or semi-closed system (partial rebreathing of expired gases)

Breathing Systems Closed rebreathing systems
With closed systems the fresh gas flow rate is does not exceed the patient’s metabolic O2 consumption of 5 to 10 mL/kg/min The system may be used with a closed pop-off valve and a fresh gas flow rate of 5 to 10 mL/kg/min Expired gases are recirculated (after CO2 removal) with incoming fresh gases

Danger of increased CO2 accumulation if CO2 absorber not working efficiently It is economical and there is minimal pollution It takes longer to change planes of anesthesia O2 depletion and N2O buildup are common, so do not use N2O with this system Requires constant monitoring to ensure pressures do not build up in the system if the O2 flow delivered exceeds the metabolic requirement

It can be dangerous to run a rebreathing system with the pop-off valve closed, if the pop-off valve does not have a safety release at high pressures It is recommended that the pop-off valve be left partially open to prevent increases in pressure in the system and to adjust the O2 flow rate accordingly to prevent the rebreathing bag from collapsing If the bag does not collapse you can be confident that sufficient O2 is being delivered to meet the patients metabolic requirements

Breathing Systems Semi-closed or partial rebreathing systems
With semi-closed systems, the fresh gas is delivered in excess of metabolic consumption at 25 to 50 mL/kg/min (suggested economical flow rate) The gas escapes through the pop-off valve to the scavenger or after having the CO2 removed by the soda lime and then recirculated with the fresh gases Higher flow rates can be used Less rebreathing will occur N2O buildup is less of a concern with higher flow rates Important to flush the system to prevent nitrogen buildup from the expired gases

Breathing Systems Non-rebreathing systems
There is no mixing of inhaled and exhaled gases and no rebreathing of expired gases; all expired gas goes to the scavenger CO2 absorber not required Fresh gas flow rates required at 200 to 300 mL/kg/min Fresh gas flow rates required at 130 to 200 mL/kg/min with the Bain system May be some rebreathing of exhaled gases if a reservoir bag and low flow rate

Breathing Circuits Many kinds of breathing circuits available
Circle system Universal F-circuit Bain system (Coaxial)

Breathing Circuits Circle system CO2 absorber
Inspiratory and expiratory unidirectional valves (check valves or flutter valves) Two breathing hoses connected with a Y-piece to the patient Rebreathing bag Pop-off valve (exhaust valve) scavenger

Breathing Circuits Circle system
Can be used as a non-rebreathing system (200 mL/kg/min) Can be used as a partial rebreathing system (25 to 50 mL/kg/min) Can be used as a total rebreathing system (5 to 10 mL/kg/min)

Breathing Circuits Circle system
An advantage is the mixture of expired gases with incoming gases Humidifies and warms the incoming gases Main disadvantages of the circle system occur with smaller patients Excess weight and bulk of the hoses Excess dead space Resistance to breathing caused by the unidirectional valves

Breathing Circuits Universal F-circuit
Basically a modified circle system where the inspiratory hose is placed within the expiratory hose Still requires a CO2 absorber, rebreathing bag, unidirectional valves, pop-off valve and scavenger

Breathing Circuits Universal F-circuit
Incoming fresh gas is warmed also by expired gases The advantage is lighter weight and less bulk Disadvantage is that if the system is stretched, the end of the inspiratory hose pulls away from the end of the expiratory hose Considered a safety feature so that the hoses don’t break Increases the dead space within the circuit Even when not stretched, the dead space is equivalent to the circle system

Breathing Circuits Bain system Consists of one tube inside the other
Fresh gases flow through the inner tube Unused and exhaled gases flow through the outer tube There also is a rebreathing bag with a clip on the tubing between the reservoir bag and scavenger connection but no CO2 absorber Between breaths, the fresh gases flow through the inner tube toward the patient and then back through the outer tube toward the scavenger

Breathing Circuits Bain system
When the patient inspires, the gases are drawn from the inner tube, which will be 100% fresh gases or a mixture of fresh gases and expired gases, depending on the fresh gas flow rate This system can be used as a non-rebreathing system with a fresh gas flow rate of 200 to 300 mL/kg/min The high flow rate pushes exhaled gases away down the outer tube so there is no rebreathing of exhaled gases By changing the flow rate to 130 to 200 mL/kg/min the system acts as a partial rebreathing system Most of the gases get pushed away but there is partial rebreathing of some exhaled gases

Breathing Circuits Bain system Ideal for small patients (<7kg)
Lightweight Minimal dead space Little resistance to breathing Good for all small animals in general but is not economical when the patient weighs in excess of 10kg Limiting factor is the size of the patient The O2 flowmeter must provide flow rates required for a partial or non-rebreathing system (130 to 300 mL/kg/min) Total volume of the Bain hose must be greater than the tidal volume of respiration of the patient to effectively prevent rebreathing

Breathing Circuits Bain system
Good for procedures involving the head (less tubing in the way) Good for procedures with much manipulation (i. e. radiography, because there is less weight pulling on the head) Warming and humidification are minimal with partial rebreathing Requires a precision vaporizer

Vaporizers Vapor pressure is characterized by the amount of vapor related to its liquid in a closed container The pressure exerted by the gas is called the vapor pressure and will increase with increases in temperature Most anesthetics vaporize at a concentration higher than necessary for clinical anesthesia So a vaporizer is used to deliver diluted anesthetics to patients

Vaporizers Precision vaporizer
Enables delivery of controlled concentrations of anesthetic vapor independent of time, temperature and fresh gas flow rate Temperature and flow rate are compensated for by the vaporizer or manually by the anesthetic technician

Vaporizers VOC (vaporizer out of circle)
Vaporizer is added to the system between the O2 flowmeter and the circle The circle consists of the inspiratory and expiratory valves, breathing hoses,CO2 absorber, pop-off valve, scavenger and rebreathing bag

Vaporizers VIC ( vaporizer in circle)
Vaporizer is placed inside the breathing system, usually between the inspiratory valve and the patient VIC’s are always non-precision The carrier gas passes over the surface of the anesthetic liquid or past a wick Incoming gases mix with warm exhaled gases in the system Better vaporization of liquid is obtained when low fresh gas flows are used High flows cool liquid and reduce vaporization Are also safest when used with agents with low vapor pressure (e. g. methoxyflurane)

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