Inhalation and airway management Flashcards
Advantages to endotracheal intubation
-airway remains protected with seal
-good seal provides more stable anesthesia
-can ventilate lungs
-minimal workspace pollution
Disadvantages to endotracheal intubation
-technical failures
-can become obstructed if not clean or very small diameter airway (birds)
-laryngeal trauma
-mucosal irritation or pressure necrosis
Principles of intubation
- Surgical plane- removes laryngeal reflexes
-Risk of aspiration is high during this period
-intubation at light depths promote regurgitation (ruminants, dogs, cats) - Secure tubes in place
3.Use gentle technique
Methods that can be used to check placement
-Water vapor in tube
-Air flow (test with hair)
-Palapte neck
-Auscultate both sides of the thorax with IPPV
-Capnogram
Cuffed Endotracheal Tube
-Used in almost all patients to ensure good seal is obtained. Not used in birds because they have complete tracheal rings
-Bevel allows tube to slip between vocal cords
-Size- Want diameter to be very close to trachea size. Size indicated is inside diameter
-Murphy Eye- safety measure to ensure airflow even if occlusion occurs. Careful not to occlude murphy eye
**lube of tube used to increase seal of cuff
Tube types and apparatus
-cuffed and non-cuffed tubes
-red rubber (prone to kinking so not used often) and clear tubes
-high volume/low pressure cuff or opposite
-select largest diameter and correct length
**always check tubes are serviceable before use
Correct placement of tube
Choose correct diameter and length prior to anesthesia
-can use laryngeal scopes
-Palpate trachea to select between 3 possible diameters
-Pre-measure fro thoracic inlet to the incisors
-ET tube appropriate length
Where to tie kling with tube?
-Right around the connector, however tube could slip off and be swallowed if disconnected.
VS
-Directly onto tube- Tying on tube can cause some obstruction.
Problems with endotracheal tubes
-kinked tubes with neck flexion
-damaged tubes
-endobronchial intubation
-tracheal damage
Steps to inflate cuff
**inflate as soon as you can
1.Ventilate lungs (10-15 cm H2O) with O2
2. Listen for leaks around cuff
3. Inflate cuff until you cannot hear a leak with IPPV
4. Turn on anesthetic vapourizer
Deflate cuff
**prior to extubation
-Swallow in a dog
-Ear flick/palpebral reflex in a cat
-Wait to see muscle tone for brachycephalics
V-gels: Supraglottic airway device
-Designed for rabbits and cats; have to be sized correctly for each individual
-Need special lube
*Problems with poor fitting and potential for obstruction if moving the animal. Need a capnogram
Pollution of workplace
-Avoid chronic exposure to trace amounts of anesthetic gases
-Intubate patient when possible
-Check for leaks before every anesthetic
Anesthetic agent uptake
- Depth of anesthesia is related to the partial pressure of the inhalant within the brain
-control partial pressure of agent with the vapourizer
-Changes the alveolar and blood partial pressures - Rapid induction/recovery
-Less lipophilic=high MAC (less potent)
Order of anesthetic inhalants??
Factors affecting minimal alveolar concentration
-Sedation and powerful opioid analgesics lower the amount of anesthetic required (especially in dogs)
-Body temp (hypothermia causes CNS depression)
-Species variation
-Age (older animals require less anesthetic)
Factors affecting anesthetic uptake
- delivered concentration
- blood solubility of agent
- lipid solubility of agent
- lung ventilation
- Cardiac output
Delivered concentration affecting anesthetic uptake
-set vapourizer high=faster uptake
-promotes movement of drug from breathing system to lungs
Blood solubility of agents affect on anesthetic uptake
-Have larger blood compartment
-slower onset- takes longer to reach equilibrium
Lipid solubility of agents affect on anesthetic uptake
-Fat soluble agents have slower uptake
-Will go to fatty tissues
Lung ventilation affects on anesthetic uptake
-more alveolar ventilation enables more drug to enter and leave
Cardiac outputs affect on anesthetic uptake
The higher the CO= the slower the uptake
-hard to mask down excited patients
-sick animals with hypovolemia require less anesthetic
Setting the vapourizer dial
Ask whether you are inducing or maintaining anesthesia? Assess depth of anesthesia
-know MAC values, whether anesthetic sparing
1.Rebreathing systems
-dilute fresh gas input because of low oxygen flows and recycled exhaled gases
- Non-breathing systems
-what you dial up is what they get
Assessing depth of anesthesia
-Eye- will roll ventral medial
-Muscle tone
-Palpebral
Measuring anesthetic agents
-Rely on experience and vapourizer settings
-assess depth of anesthesia
>only give volatile agent that animal needs, no more
>alveolar exhaled % most accurate measurement
-monitors can measure gas composition (expensive)
Isoflurane
Colour= Purple
-rapid induction and recovery
-good muscle relaxation
-questionable analgesia
-0.2% metabolized by liver
-most commonly used; many species
MAC Isoflurane
Dog= 1.28
Horse=1.31
Cat=1.71
Isoflurane Cardiopulmonary effects
-Dose dependent cardiopulmonary depression
-most respiratory depressant of all inhalational drugs
-little effect on ANS
-direct relaxation of smooth muscle in blood vessels (interference with calcium)
-vasodilation more pronounced compared to myocardial depression (hypotension likely to occur)
-little myocardial sensitization to catecholamines
-stable HR
Acepromazine with isoflurane
-tends to produce more hypotension (both vasodilate blood vessels)
Clinical use of isoflurane
Induce with 2-4%
Maintain with 1-2% (but actual value will depend on other anesthetis sparing drugs used)
May need to ventilate lungs because of respiratory depression
Sevoflurane
Colour= Yellow
-rapid induction and recovery
-not as irritating to airways/mucous membranes as isoflurane
-Metabolism produces few FI- ions
-used in many species; exotics
-expensive (3x more than isoflurane)
-minimal advantages compared to isoflurane
MAC of sevoflurane
Dogs= 2.4%
Sevoflurane and CO2 absorber form
Compound A and carbon monoxide
-Will result in these toxic byproducts accumulating in rebreathing systems with low O2 flow
Sevoflurane cardiopulmonary effects
-comparable to isoflurane
-dose dependent cardiopulmonary depression
-vasodilation is greater than myocardial depression (hypotension likely)
-hepatic blood flow preserved
-minimal respiratory depression (animals breath well spontaneously)
Sevoflurane clinical use
Induce with 3-7%
-usually well tolerated, sweet smell
Maintain with 2-4%
-actual values depend on anesthetic sparing drugs
Sevoflurane metabolism
Rapid elimination from lungs reduces amount available for metabolism
Sevoflurane metabolism into Fluoride ions?
Fluoride can be nephrotoxic in high amounts
-Enzyme (P450-2E1) used for sevoflurane FI- metabolism BUT not enough is present in the kidney to cause nephrotoxicity
**Sevoflurane is NOT associated with clinical renal problems
CO2 absorbers and sevoflurane degradation
CO2 absorbers contain hydroxide bases to remove CO2
-Mono-valent hydroxides (Na, K) cause more breakdown of inhalant compared to di-valent hydroxides (Ca)
**Special di-valent CO2 absorbers is used for sevoflurane
Soda lime absorber
Has Na-OH and some K-OH (mono-valent)
Barium hydroxide lime
Has K-OH
-produces high operating temperatures and more sevoflurane breakdown
CO2 absorbers and heat
**Exothermic Rxn
-CO2 absorber canister temperatures normally are 25-45 degrees BUT high temperatures (80degrees) can occur if you use very low O2 flow and very dry absorber
Sevoflurane and FIRE
Sevoflurane creates the most heat and can cause canister fires
Ev. 2.4% sevoflurane and very dry absorber= 300 degrees C
**ensure fresh absorber… will crumble when pinched
Partial intravenous technique (PIVA)
IH drugs have little anesthesia and can depress the cardiovascular system (dose dependent).
-Use other drugs as infusion or bolus to help reduce IH concentration needed
-Anesthetic sparing effect
**useful for debilitated animals or animals undergoing invasive procedures
