outline from 2012 Flashcards
Triad of general anesthesia
- Narcosis: sleep, unconsciousness
- Muscle relaxation
- Analgesia: reflex
Premedication
Give patient sedative +/- analgesic and the patient is still conscious
Induction
Loss of consciousness with administration of inhalant, injectable
Maintenance
maintaining unconsciousness with inhalant, injectable, or combo
Balanced anesthesia
Can be accomplished by use of combo of neuromuscular blocking drug to produce muscle relaxation, an opioid to produce analgesia, and low concentration of injectable agent or inhalant to maintain unconsciousness
Advantage of balanced anesthesia
- allows lighter plane of anesthesia
- results in more stable cardiovascular and pulmonary function
- good for very ill patients
ASA class I
- Def
- normal healthy patient w/o systemic dz
- ex
- neutering
- tail docking
- elective procedures
ASA class II
- Def
- mild systemic disease w/ no functional limitations
- Examples
- minor fractures
- slight dehydration
- obesity
- ear infection
- heart murmurs
ASA class III
- Def
- moderate to severe systemic disturbance with some functional limitation
- Example
- chronic heart disease
- anemia
- open/severe fracture
- hyperthyroidism
ASA class IV
- Def
- severe systemic disturbance which poses a constant threat to life and is incapacitating
- Example
- ruptured bladder
- pyometra
- internal hemorrhage
- pneumothorax
ASA class V
- Def
- not expected to survive without intervention
- example
- severe shock
- organ failure
Primary function of anesthetic machine
- O2 delivery
- blend and deliver anesthetic gas mix
- remove CO2
- support ventilation
O2 is color coded
Green
Open breathing system
- no reservoir for anesthetic gas mixture and no rebreathing of expired gas
- liquid inhalant on a cotton ball in a cage or on cloth
Semiopen breathing system
- reservoir for anesthetic gas mixture
- no rebreathing of expired gas
- no CO2 absorption
*non-rebreathing
Semiclosed breathing system
- reservoir for liquid anesthesia
- partial rebreathing and absorption of CO2
*circle
Closed breathing system
- Reservoir for liquid anesthesia
- complete rebreathing
- CO2 removed
*circle
Main breathing system used in vet med
(patient < 7-10 kg)
Non-rebreathing system - semiopen
Main breathing system used in vet med
patient > 10 kg
circle breathing system - semiclosed
Exhausted soda lime is
- hard and chalky
- turns purple
- stays cool
- slightly salty
Fresh soda lime is
- canister will feel hot b/c it’s an exothermic rxn
- white
- crumbles easily
Unidirectional valves
- one way flow of gas
- inspiratory and expiratory side
- prevents rebreathing of CO2
- make sure the disks are seated horizontal and working properly
- can cause hypercapnia if valve doesn’t work
Pop-off valve
(adjustable pressure limiting valve)
- releases excess gases to environment
- source of most anesthetic mishaps
Non rebreathing systems
- less dead space
- less/no resistance
- DO NOT O2 FLUSH
Advantages of non-rebreathing systems
- low resistance
- less dead space
disadvantages of non-rebreathing systems
- inspired gas not humidified
- greater loss of body heat
- more environmental pollution
- more $$$ in long-run
Airway preop considerations
PE
- Full PE
- Head and neck
- open mouth without pain
- loose teeth
- upper airway obstruction
- nasal/oral secretions
- masses
advantages of tracheal intubation (7)
- ensures patient airway
- prevents aspiration, especially in regurgitation prone patients
- enables ventilation if needed
- maintain airway in problematic poistioning
- control in patients with upper airway disease
- admin of inhalent when face mask not possible
- route for suctioning trachea
Ace in premed
- tranquilization/sedation
- known antiarrhythmic
- reduces afterload which dec workload of heart
- antiemetic
- antihistaminic
Ace premed contraindications
- anemia
- will dec PCV by splenic sequestration
- shock
- bleeding problem
- interferes with platelet aggregation
- splenectomy
- hepatic insufficiency
- prolonged effect
- Hypothermic
- vasodilation
*NOT OLD AGE
When giving Ace IM instead of IV
reduce dose by half
Morphine
- cheapest
- vomiting
- long duration
- efficacious for severe pain
- IM or IV slow, possible histamine release
Hydromorphone
- vomiting
- long duration
- IM injection
Methadone
- less vomiting
- blocks NMDA receptors in addition to opioid receptors
Meperidine
- synthetic full agonist
- no vomiting
- does not decrease HR
- shorter duration of action (45 min)
- causes massive histamine release when given IV
- negative inotropic effects => decreases contractility
Buprenorphine
- partial agonist, high affinity at mu-opioid receptor
- competes with full agonists: morphine, hydro, methadone
- duration: 4-8 hrs
- less painful procedures
- no vomiting
- mydriasis in cats
Fentanyl + remifentanil
- short duration
- around 15 min
- mainly used as CRI during balanced anesthesia
- hepatic metabolism
Butorphanol
- agonist-antagonist
- less efficacious than full agonist
- used for non-painful diagnostic procedures
- prominent sedation, especially with acepromazine
- short duration: about 1 hr
If ace is contraindicated
- neuroleptanalgesia: BZDs + opioid
Diazepam
not soluble, can only mix with ketamine
Midazolam
water soluble given any route
BZDs
- has minimal CV depressant effect
- good for sick patients
- don’t use on agitated or BAR patients
- paradoxical agitation
Opioid only for premed
- can cause sedation
- more predictable when patients are sick or depressed
Nothing for premed
- can be feasible in very sick patients
- induction can proceed without premed
Premed for aggressive dogs
- dexmedetomidine + an opioid
- Alpha 2 agonist
- hydro, morphine, or butorphanol
Premeding cats
- ace + opioid creates less sedation than in dogs
- Ketamine creates more sedation
- contraindicated in HCM
- Dexmedetomidine in aggressive cats
- CV effects tolerated by HCM cases
- Opioids cause hyperthermia
- monitor body temp closely
Premeding horses
- alpha-2s are main drugs
- effects
- sedation, analgesia, muscle relaxation
- examples
- zylazine, detomidine, romifidine, dexmedetomidine
- effects
- Opioid for analgesia after alpha-2 agonist to prevent excitement
- butorphanol or morphine
- Ace before premed possiblity
- penile prolapse in stallions
Categories of injectable anesthetic agents
- Barbiturates (MOA at GABA receptors)
- thiopental
- Non-barbiturates
- propofol
- dissociative agents: ketamine, tiletamine
- Etomidate
- Alfaxan
Thiopental
- ultra short acting barbiturate (inc affinity for GABA)
- leakage from vein hurts
- CNS: minimal changes in ICP, dec CBF and metabolic rate/O2
- Respiratory: apnea, dec cough and gag
- CV: dec BP, slows hepatic metabolism, metabolites excreted in urine
Thiopental
contraindications
- greyhounds/sighthounds
- CV compromised patients
- pre-existing arrhythmias
Propofol
- Interacts with GABA, short acting phenolic hypnotic agent
- CNS: dec ICP, oxygen requirement
- Resp: depression, apnea, dec cough and gag
- CV: myocardial depression, dec BP
Propofol
Metabolism
- metabolized by hepatic cP450 enzymes
- may have extra hepatic uptake and metabolism
- good choice for hepatic patients
- may have extra hepatic uptake and metabolism
- Repeated boluses don’t excessively prolong recovery
- good choice for maintenance for prolonged procedures
- Ok for preggos
- rapidly cleared from puppies
Propofol
Contraindications
- caution in cats - heinz body formation and oxidative damage
- CV compromised patients
- pancreatitis patients
Ketamine
- Dissociative agent
- CNS: hallucinations, agitation, confusion in humans; inc CBF and ICP, inc O2 demand
- Resp: apneustic breating, maintain respiratory drive
- CV: stim of sympathetic nerv syst (inc HR, CO, BP), arrhythmias
- Only induction agent with analgesic properties
- action at NMDA receptors
Ketamine
Metabolism
- Dogs: hepatic
- Cats: excreted mostly in urine unchanged
Ketamine
Contraindications
- intracranial masses, head trauma, eye trauma, glaucoma
- cardiac disease and arrhythmias
- cats with kidney disease
Etomidate
- CNS: dec CBF, ICP, O2 requirement, IOP
- Resp: maintain drive, gag and cough reflex
- CV: produces minimal changes even in hypovolemic dogs
- good choice for patients with primary heart disease
- Endocrine: dec in cortisol function
- Hemolysis: propylene glycol formation
- metabolism: hepatic
Etomidate
contraindications
- abnormal adrenal function
- septic shock
- long-term use
Summary drugs
Thipental
Propofol
Ketamine
Etomidate
Alfaxalone
- thiopental
- Good: lower ICP, IOP, gag, use in brain dz
- Bad: perivascular sloughing if out of vein (high pH), ventricular bigeminy
- Propofol
- Good: Short lasting, used in hepatic dz
- Bad: apnea, vasodilation, hypotension
- Ketamine
- Good: analgesic properties, Can be used IM
- Bad: lower adrenal resp to stress, hemolysis
- Etomidate
- Good: Maintain BP and blood flow, good in cardiac dz
- Bad: lower adrenal response to stress, hemolysis
- Alfaxolone
- Good: can be used IM
- Bad: not avail in US
CV dz
Good/bad
- Good: Etomidate
- Bad: Propofol
Resp dz
Good/bad
- Good: Etomidate
- Bad: Propofol, thiopental
CNS dz
Good/bad
- Good: Thiopental, Propofol
- Bad: Ketamine
Hepatic dz
Good/bad
- Good: Propofol
- Bad: Thiopental
Preggos
Good/bad
- Good: propofol
- Bad: Thiopental
gas definition
gas at room temp and ambient temp
Vapor definition
liquid at room temp and ambient temp
MAC
- minimum alveolar concentration is the percentage of agent present in alveoli that will prevent 50 % of population from moving in response to noxious stimuli
- measure of potency
The lower the MAC the greater the
potency
Cats tend to have a higher MAC for
volatile agents
MAC Methoxyflurane
0.24
MAC of Halothane
0.87-1.04
MAC Isoflurane
1.28-1.63
MAC Sevoflurane
2.1-2.58
MAC Desflurane
7.2-10.32
Facters that Dec MAC
- severe acidosis
- hypothermia
- pregnancy
- advanced age
- premeds
- induction agents
- local anesthetics
- severe anemia
- severe hypoxemia
- sepsis
Factors that inc MAC
- Hyperthermia
- Hypernatremia
Def: delivered concentration of the anesthetic
percent setting on vaporizer
Def: inspired or inspiratory conc
- conc that the patient inhales
- equal to vaporizer setting if using non-rebreathing system
- less than delivered if using a circle rebreathing system because of dilution by expired gas
Def: expired concentration
- concentration at end of expiration
- reflects alveolar concentration
Def: Alveolar concentration
- reflects amount of anesthetic in brain
Factors affecting inspiratory concentration
- fresh gas flow rate
- volume of circle breathing system
- absorption by machine or circuit (rubber)
- time constant
Factors affecting alveolar concentration
- solubility in blood of inhaled anesthetic
- cardiac output / alveolar blood flow
- ventilation
- partial pressure diff between alveolar gas and venous blood
Summary of main factors influencing onset of anesthesia
- inspired concentration
- alveolar ventilation
- cardiac output
- blood solubility
Cardiac effects of inhalants
- arrhythmogenicity
- cardiac depression (dose-dependent) = dec CO
- dec in systemic vascular resistance = vasodilation
Respiratory effects of inhalents
- respiratory depression
- dec in tidal volume
Drugs that can be used to dec MAC
- BZDs
- sedatives
- opioids
- lidocaine infusions
Apnea
- Most common during induction
- barbiturate or propofol induction
- check pulse, make sure it’s not cardiac arrest
- control ventilation and O2 until spontaneous breathing
- 2-3 breaths/minute
- Mechanical stimulation safer than drugs
- ie: doxepram
Airway obstruction
- Signs: dyspnea, stridor, jerky movements, reduced reservoir bag
- Causes: kinked ET tube, overinflated cuff, mucus/blood
- suction if blood, mucus, vomit
- use armored tube if neck in extreme flexion
Hypoventilation (hypercapnea)
- Signs: dec RR/tidal volume, High pCO2
- Causes: CNS depression, limited thoracic movement, exhausted soda lime
Cardiovascular problems
- Cardiac arrest
- Hypotension
Causes of cardiovascular probs
- drug effects
- hypovolemia
- shock
- animal in deep plane of anesthesia
Signs of cardiovascular probs
- tachycardia
- weak pulse
- good pulse: means systolic/diastolic diff is good, not indicative of adequate blood pressure
Treatment/prevention of cardiovascular probs
- check pulse
- dec anesthetic plane
- admin fluids
- crystalloids 10 mL/kg over 10 minutes (bolus)
- positive inotropic agents if no response to both of above
- dobutamine - LA
- dopamine - SA
- epinephrine
PVC id on EKG
- no associated P wave
- wide and bizarre QRS complex
Causes of PVC
- hypoxia
- hypercapnia
- traumatic myocarditis
- GDV
TX/prev PVC
- lidocaine
- thiopental
- for bigeminy (alternating sinus and PVC)
Causes of bradycardia
- excessive vagal tone
- eyeball traction
- laryngeal surgery
- abdominal exploration
- drugs
- opioids
- alpha2 agonists
- hypothermia
- wont respond to atropine
Tachycardia and EKG
- P wave present = sinus tachycardia
- No P wave = supraventricular
Causes of tachycardia
- LIGHT ANESTHESIA: #1 cause
- hypovolemia
- hypercapnia
- shock
- sepsis
Human error
- wrong drug/concentration/body weight
- O2 tank off/O2 flowmeter off
- suction too high/off
- Closed pop-off valve
- wrong anesthetic
requirements of recovery area
- quiet, not too bright, temp control
- Oxygen, drugs, and resuscitation equiptment
- heat
- supervision
Patient can leave OR IF
- patent airway
- adequate ventilation
- hemodynamically stable
Pain control:
Consequences of pain
- stim of sympathetic n.s. => tachycardia + peripheral vasoconstriction
- respiratory acidosis and hypoxemia => inc RR
- dec GI motility
- stim of ADH => changes in body fluid balance
- excitement, violence, self-mutilation
Signs of pain
- change in behavoir
- stimulation of SNS
- dilated pupils
- tachycardia
- hypertension
- inc RR
Strategies for pain control
- opioids
- NSAIDS
- adjuct drugs sedation/tranq
- nerve blocks, epidural
- ice, acupuncture
- Distractions
Use of opioids
- Can be given before full consciousness regained
- some may require sedation also
- ace, diazepam
- dec drug dose in depressed patient IV
- closely monitor RR
If animal become apneic post-op, rule out (3 things)
- cardiac arrest => check pulse
- cerebral injury during anesthesia => eye fixed and dilated?
- residual neuromuscular blocking drug
If animal is intubated w/chest movement and no air movement in trachea
- check for obstruction of ET tube = blood clot, mucus plug
- inflate lungs by breathing bag and feal resistance
- pull and place new tube as quick rule-out
If patient has check movement but no air movement after extubation
- OPEC: open mouth, pull tongue rostrally, extend head and neck, clear airway
- place animal in sternal recumbency
- r/o nasal edema in horses - phenylephrine
- r/o laryngospasms in cats, small ruminants, pigs
- bandages circling neck
- tracheostomy if needed
If patient has jerky or abnormal respiratory movements after extubation
- r/o partial obstruction - OPEC
- r/o pain
- r/o circulatory failure
- r/o pulm path: red froth, ascult chest
- r/o resid neuromuscular blocking drug
- r/o cyanosis
- aspirate chest tube
Signs of shock
- weak palpable pulse
- tachycardia or bradycardia (terminal)
- inc CRT, pale MM, cyanosis
- cold extremeties
- hypotension
- unresponsive to stim
Management of shock
- Oxygen
- Fluids
- positive ionotropes
- dopamine
- dobutamine
Hypothermia more of a concern in
smaller animals
First reflexes to return as animal wakes up
ocular reflexes
spontaneous movement
Light plane of anesthesia
- central eye ball position
- nystagmus in horses
- no limb movement to possible infrequent spontaneous movement
- good muscle tone
- reflexes in response to sx
- moist cornea
- pedal, palpebral, conjuctival, and corneal reflex
medium plane of anesthesia
- no spontaneous movement
- no reflexes
- no hemodynamic response to sx stim
- moderate muscle tone
- no palpebral reflex
- ventromedial rotation of eye and smaller pupil
Deep plane of anesthesia
- further dec in tidal volume
- more abdominal breathing
- eyes fixed centrally w/dilated pupil
- no palpebral, pedal, corneal reflexes
- no spontaneous movement
- hyptension/bradycardia
esophageal stethoscope is a poor indicator of
adequacy of circulation
Direct measurement of BP
- arterial catheter
- standard of care in horses
- good for critically ill patients
- invasive and time consuming
Indirect measurements of BP
- sphygomomanometry
- width of cuff: 40% around patient leg
- bigger cuff: underestimates BP
- smaller cuff: overestimates BP
- width of cuff: 40% around patient leg
- Oscillometric
- 60 mmHg
Pulse ox
- measures arterial oxygen saturation
- detects hypoxemia: spO2 < 90 or B Gas PaO2 of 60
- monitors HR
- placed on tongue or nasal septum
Pulse ox measures light absorption at two different wave lengths
- Reduced HB absorbs more red light
- Oxygenated HB absorbs more infrared light
Capnography
- Measures end-tidal and inspired CO2 tension
- useful to determine
- hypo/hyper ventilation (inc/dec CO2)
- apnea (zero CO2)
- Resp obstruction
- pulm embolism
- rebreathing of CO2
Body temp should stay above/equal to
- 94 degrees
- Below 94
- anesthetic requirements reduced
- prolonged recovery likely
- depressed cardiopulmonary function
- above normal: rule out malignant hyperthermia
- Below 94
Cardiac dz and anesthesia
- prone to: arrhythmias and fluid overload
- most anesthetic agents depress CV
- low oxygen delivery
- Drugs
- opioids and midazolam
- etomidate
- low inhalent delivery
Pulmonary dz and anesthesia
- most drugs dec ventilation
- pre-oxygenate
- drugs
- low dose opioid
- propofol
- assist ventilation
Liver disease and anesthesia
- Concerns
- low metabolism, dec prot prod, dec glucose stores, hypoxia
- use reversible, short-acting drugs
- drugs
- opioids +/- midazolam
- propofol
- remifentanil + isoflurane
- fluid: FFP, hetastarch, glucose
Brain disease and anesthesia
- concerns: high CO2, BP and low O2
- avoid drugs that cause: vx, sedation (hypoventilation), inc ICP (ketamine, halothane)
- Drugs
- low dose opioid IV
- thiopental, diazepam
- isoflurane/sevoflurane
- hyperventilate
- recovery: keep head elevated, low sedation
Renal dz and anesthesia
- electrolyte abnormalities
- avoid hypotension and hpoperfusion
- avoid drugs that dec MAP, CO, cause vasoconstriction
- drugs
- opioid +/- low dose ace
- dopamine CRI - promote blood flow
- propofol?
- fluid therapy
- low inhalents
Most inhalation and IV anesthetics will……
- dec CO => less blood flow to tissue => metabolic acidosis
- dec resp => respiratory acidosis
principles of fluid admin prior to anesthesia
- correct
- dehydration
- electrolyte imbalances
- acid-base imbalances
