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AS 421


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Uses for Anesthesia
Restraint, Examination, Maniulation, Surgery, Control of convulsive seizures, Euthansia
Block-Failure of brain to receive impulses initiated by sensory stimuli. Analgesia
Block-Failure of arriving sensory impulse to pass on into memory storage. Amnesia
Block-Failure of arriving sesnory impules to evoke an effect-no response.
A state of controled and reversible unconscious
Animal will not respond to stimuli. Animal immobile. Varying degrees of muscular relaxation occur. certain reflexes are abolished. Analgesia should be complete. Amnesia should be complete.
Most drugs have shortcomings, therefore it requires several agents in combination to produce
Balanced Anesthesia
Slight depression, patient awake
Greater depression, patient is asleep but can be awakend
Patient asleep, can be awakened, but returns to sleep. Usually implies good analgesia.
some sedation and hypnosis, but mainly alters behavior and the animal's reaction to its environment. Usually implies very little or no analgesia
Determination of Anesthetic Protocol
Specie and breed, age, pranesthetic condition (healthy or sick), nature of operation (minor to major), Equipment available, skill of anesthesitist.
Anesthetic procedure divided into four components
Pre-anesthesia, induction, Maintenance, recovery
Obtain Hx, perform exam. lab workup. maybe give pre-anesthetic drugs.
Shows incoordination or excitement followed by relaxation and unconsciousness. Progressive loss of some protective reflexes occurs (swallow and cough) and the onset of analgesia occurs.
Skeletal muscle relaxation occurs, movement ceases. Further loss of protective reflexes (palpebral), mild respiratory and cardiovascular depression.
Occurs when anesthetic concentration in brain begins to decrease. 1.Injectable metabolized in liver, metabolites excreted in kidney or excreted unchanged by kidney or redistributed to other tissues (short acting thiobarbiturate) 2. Inhalation Eliminated by the respiratory tract 3.Specific reversing agents-for opiods, xylazine
Safety-General anesthesia is not without risks. CNS depressants may depress vital centers controlling cardiovascular, respiratory and thermoregulatory centers. Death can occur
Monitor HR and Pulse quality, ventilation, MM color, through all parts of anesthesia. Preanesthetic drugs are safer, decrease dose needed of general anesthesia, less stressful. Minimum doses of drug "given to effect" this is called titration. Can't predict exact dose for induction and maintencance varies between animals. Recovery still dangerous: watch for vomiting, laryngospasms, convulsions, hypothermia.
Minimum doses of drugs "to effect"
Stages of anesthesia
Stage I (no planes). Stage II (no planes). Stage III (4 planes). Stage IV (no planes).
Stage I
Immediately after administration of agent. Animal is conscious but disoriented. Respiration and heart rate normal. All reflexes present.
Stage II
Begins w/ loss of consciousness. All reflexes present, may even be exaggerated. Can chew and swallow, yawning common. Pupils dilated, but constrict w/ bright light. Higher centers release voluntary control and animal may appear to be “fighting” the anesthetic-rapid limb movement, vocalization, struggling; breathing irregular or animal holding breath. In reality, this is due to anesthetic selectively depressing neurons in the brain the normally inhibit and control motor neurons. Stage II ends when muscle relaxation begins, slower resp. rate and decreased reflex activity. To reduce or avoid Stage II, may want to increase administration of anesthetic. With some preanesthetics, you may not see stage II, also when using injectable agents in premedicated animals
Stage III plane I
Plane 1-resp. pattern regular, involuntary limb movements cease. Eyeballs rotate ventrally, pupils partially constricted, diminished PLR. Gagging and swallowing reflexes reduced enough to allow endotracheal tube to be passed. Palpebral reflex present but less brisk than stage II. Reacts to painful stimulus
Stage III plane II
2. Plane 2-medium depth, suitable for most surgical procedures. May see increased heart rate or resp. rate, but patient unconscious and immobile. PLR is sluggish, eyeballs central or rotated, pupils slightly dilated. Respirations regular but shallow, between 12-16/breaths per minute dog (higher cat). Heart rate and blood pressure mildly decreased. More muscle relaxation. Loss of pedal and palpebral reflexes.
Stage III plane III
Plane 3-deeply anesthetized. Significant circulatory and respiratory depression present. Considered excessively deep for most surgical procedures. Resp. rate < 12 breaths/minute (dog) and shallow. Ventilation may be desirable (bagging or mechanical ventilator). Decreased heart rate and blood pressure. CRT 1.5-2sec. PLR poor or absent. Eyeballs central, pupils moderately dilated. Reflex activity almost totally absent. Jaw tone is slack.
Stage III plane IV
Plane 4-see spasmodic, jerky ventilatory pattern (“rocking boat”)-caused by lack of coordination of the intercostals and abdominal muscles and diaphragm. Pupils fully dilated, PLR absent. Muscle tone flaccid. Obvious cardiovascular depression-marked drop in heart rate and bp, pale mucous membranes and prolonged CRT. TOO DEEPLY ANESTHETIZED.
Stage IV
stops breathing, circulatory colapse then DEATH
IV injection
standard dose calculated administered "to effect" Allow E-tubing, gas anesthesia
IM injection
Calculated doses are 2-3 times greater than that required for IV injection. MUST give entire dose. Onset of anesthesia and recovery slow.
mask induction
a. ↑ waste anesthetic gas to personnel. b. Struggling may cause epinephrine release, predisposing to cardiac arrhythmias. c. Technique-Give 100% O2 for 2-3 min. Begin administering 0.5% isoflurane or halothane. Increase by 0.5% q 30 sec., up to 3-4%. O2 rate should be 30 x’s the patient’s tidal volume, with a minimum of 3-4 L/min. (higher flow rates help speed induction).
a. Disadvantage-difficult to monitor patient b. Also, ↑ waste gas to personnel c. Technique-Begin introducing 4-5% isoflurane or halothane, and 3-5 L/min of O2
brachycephlic patient. if patient has not been fasted. Respiratory problems (edema...etc...)
Endotracheal Intubation -advantages-
1. Allows for more efficient delivery of anesthetic gas to patient 2. Decreases “dead space” within respiratory passages a. Dead space-those portions of breathing passages which contain air, but in which no gas exchange occurs. This includes the mouth, nasal passages, pharynx, trachea, and bronchi. 3. Allows O2 delivery when respiration needs to be assisted. a. Intermittent positive pressure ventilation (IPPV) –squeezing of reservoir bag to deliver O2 or gas anesthetic mixture to patient. 4. Decreases risk of aspiration-vomitus, blood, saliva
endotracheal intubation -problems-
1. May stimulate vagus nerve causing increased parasympathetic tone. a. bradycardia, hypotension and cardiac arrhythmias (more so in dog). Atropine prevents. 2. Difficulty in certain ages (pediatrics), breeds, and specie3. Damage to tissues from overzealous efforts-laryngospasm 4. Exotics, lab animals-“blind intubation” 5. Advancing endotracheal tube into bronchus Measure from incisor teeth to between larynx and thoracic inlet 6. Excessive dead space with some tubes (human use) 7. Pressure necrosis-low pressure cuffs best 8. Tracheal tears-always disconnect prior to turning, support head and neck when carrying. 9. Obstruction of tube-saliva, mucus, blood, kinked tube, end occluded against wall of trachea 10 Biting of tube-intubate when deep enough, extubate when begins to swallow 11. Disinfection-may cause irritation 12. May cough due to irritation despite all precautions.
Maintenance: needs to be-
Deep enough to perform sx not any deeper. Too light = pain may awake during procedure. Too deep: slow recovery or overdose
Key is adequate monitoring:
Assess every 3-5 minutes unless high risk anesthetic. high risk monitor continuously.
Monitor: HR, RR, CRT, MM, Color, BP, PSO2...etc...
Vital signs
parameters that indicate the response of the animal’s homeostatic mechanisms to anesthesia-including heart rate, respiratory rate, and CRT. Indicates how well the animal is maintaining basic circulatory and respiratory function during the anesthetic
Heart rate and rhythm
i. minimum acceptable rate-dog- 60 bpm, cat- 100 bpm ii. decreased rate a result of anesthetic (CNS depressants) iii. increased rate as a result of atropine, ketamine, tiletamine iv. inform doctor of any rhythm abnormalities (halothane, xylazine) v. can take pulse, use stethoscope or esophageal stethoscope vi. electronic monitoring devices available
Give 1 benefit and 1 disadvantage of endotracheal intubation.
Benefits: decrease risk of aspiration. Decrease "dead space". Allows for more efficient delivery of gas to patient (O2 and ISO) Disadvantages: may stimulate vagus nerve increases parasypathetic tone. Damage to trachea: pressure necrosis-low pressure cuffs, obstructions of tube, biting...etc...
What is the difference between a vital sign and a reflex?
Vital sign is used to measure the animals life signs, HR, RR, CRT ...etc... Reflex can be used to measure depth of anesthesia.
In general, heart and respiratory rates tend to increase with increased anesthetic depth. T/F
At what stages/planes of anesthesia is the eye position central?
Stage III Plane III and IV. Plane II eyes can be central or rotated. Stage IV
Recovery is the time period between discontinuation of anesthetic administration and the removal of the endotracheal tube. T/F
Describe etubation in a brachycephalic dog.
Patient on O2 until swolling, in strenal recubency make sure pet can lift its head on its own
Minimum accepted heart rates during anesthesia are
60 bpm for canine 100 bpm for feline
State 2 reason for hypothermia in the anesthetized patient.
Muscles not moving. Shaving, cleaning, decreased metabolic rate, open body cavity, vasodilation, drugs.
minimum accepted breaths per minute during anesthesia are
why is timing of extubation in the feline so important?
Lyrangospasms, may result in death.

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