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define a “routine surgery”. who has had a pet through surgery? who has monitored a surgery? what are the technician’s roles during surgery? don’t prove - improve. Anesthetic Depth. Measured by Stages I-IV
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who has had a pet through surgery? • who has monitored a surgery? • what are the technician’s roles during surgery? • don’t prove - improve
Anesthetic Depth • Measured by Stages I-IV • closely monitor the immediate vitals and the developing trend you have recorded, use your teaching and experience to expect what is likely to happen and PREVENT a situation
monitor surgical stimulus • monitor reflexes THROUGHOUT • ensure strong steady, expected HR • ensure rhythmic respiration, PPV prn • ensure average BP • monitor body temp • every animal is different • use your eyes and hands over any machine ever created
Stages of Anesthesia • Stage I • immediately following administration of a drug • voluntary movement • will be disoriented, may U/BM • panting • slight increase HR • decreasing sensitivity to pain • eyes centrally located, normal pupil size and LR • normal muscle tone, normal reflexes • by end of this stage pt is recumbent
Stage II - excitement/involuntary stage • involuntary struggle, vocalize, paddle, chew, yawn • beginning loss of consciousness • irregular respiration (apnea to pant) • likely increased HR • further decreased pain sensitivity • possible nystagmus, possible dilation, present PLR • good muscle tone • exaggerated reflexes
Stage III - Planes I-IV • Pl I - light anesthesia - intubate • RR 12-20, pattern regulating • HR >90, strong pulse • eyes central or rotated ventromedially, possible nystagmus, pupils constricted, yes PLR • good muscle tone • poor/absent swallow reflex • lick, palpebral reflex present • no surgery, yes intubate
Stage III Pl II - Surgical Anesthesia • moderate depth • RR 8-16, more shallow • decreased HR and BP • possible surgical response (increased HR RR) • eyes rotate ventromedially, pupils dilate, sluggish PLR • muscle relaxation • no pedal or palpebral reflex
Stage III Pl III • deep anesthesia • significant cardiopulmonary depression • RR less than 8, may need PPV (Bag) - low tidal volume • HR 60-90 • low BP, weak pulse • CRT 1.5-2 • no surgical response • eyes central, moderate pupil dilation, sluggish/no PLR • flaccid muscle and jaw tone
Stage III Pl IV - anesthetic overdose • very deep • jerky/rocky respiration, abdominal breathing • HR <60 • prolonged CRT • pupils widely dilated, no PLR • dry eyes • DANGER
Stage IV - Dying • no respiration • HR <40 (unexpectedly) • no CRT, no Pulse • cyanotic • resuscitate if possible
WHEN IN DOUBT STOP ANESTHESIA • turn off gas or stop/reverse injectables
Anesthetic Induction • induce anesthesia - bring the animal to the desired plane of unconsciousness. • may also simply need to maintain anesthesia - keep the patent at the desired plane of unconsciousness • no anesthetic agent accomplishes every (and only) effect needed - multimodal pain management and balanced anesthesia
Inhalant v Injectable • Inhalant • adjust depth • eliminated via lungs (primarily) • on oxygen, easy PPV • requires vaporizer setup • slow induction • waste gases • Injectables • no control over depth (once given) • eliminated via liver/kidneys • on room air, must intubate to PPV • only need syringe and drug • slow recovery • possible to inject in wrong area
Injectable Induction • Most common Injectable Induction agent • - Ketamine/Valium Combo • - Propofol • ALWAYS label syringes when drawn up unless giving immediately. • ANESTHESIA IS GIVEN TO EFFECT (titrate)
Ideal injectable • rapid onset induction and recovery • nontoxic • minimal adverse affects to cardiopulmonary system • rapidly and safely metabolized • offers adequate analgesia • offers appropriate muscle relaxation • available, affordable
typically induction agents are given IV • IM doses are usually available, this dose will usually be 3x the calculated IV dose (ketamine, tiletamine, dexmedetomidine) • how will this affect anesthesia? (speed of induction, speed of recovery, control?) • CRI induction agents • oral ketamine
uptake - speed with which the agent is absorbed into the body and begins taking effect • IV drugs do this quickest • IM SQ agents - must be redistributed before affecting CNS • redistribution - the path a drug takes in the body • IV drug is given, travels to the vessel rich brain (takes effect) then travels to muscle and fat, liver for metabolism, excreted by kidney (under perfect circumstance) • as drug is redistributed from brain, pt begins recovering • cumulative drug effect - drug has not left the the redistribution areas before more drug needs to be carried away from the brain - sighthounds
Injectable Induction Agents • Barbiturates • Cyclohexamines - dissociatives • Neuroleptanalgesics • Propofol
Pharmacodynamics • Ionization - polar (ionized) or non-polar (nonionized) forms - only non polarized compounds can pass through cell membranes at the brain. when pH is normal (7.4) this happens easily and as expected. • if acidotic - compounds can diffuse in brain and exaggerate response (may require less dry to anesthetize)
Protein Binding - compounds are either freely circulating in plasma or bound to proteins. only unbound compounds can enter brain, proteins inhibit • if hypoproteinemic (TP > 3g/dL) - much more drug is available to enter brain, can easily be fatal
brain is highly lipid • Lipid Solubility - tendency of a compound to dissolve in fats/oils. aka partition coefficient • highly lipid soluble compounds cross into brain easily and are quickly redistributed
Redistribution • vessel rich group - brain (CNS) heart liver kidney endocrine system • VRG - 10% body mass, 75% blood flow • muscle - 50% mass, 20% bldflw • fat - 20% mass, 5% bldflw • compounds go to the brain first, high/low concentration carries compounds away from brain to rest of VRG, onto liver for metabolism and kidney for excretion
as compound is redistributed away from the brain the pt recovers • low lipid soluble compounds diffuse way from the VRG and store in muscle and fat longer - this affects the high/low concentration and drugs are not carried away from the brain as quickly (especially if having to redose) - cumulative affect • ultrashort acting barbiturates - thiopental, methohexital
Barbiturates • used for anesthesia but more for anticonvulsants and euthanasia • losing popularity to newer generation anesthetics • all controlled • stimulates GABA - inhibitory transmitter to depress CNS/cause loss of consciousness
Barbiturate Classification • classified on chemical structure, duration of action • Ultra-Short Acting • Short Acting • Intermediate Acting • Long Acting
alternate names • thiobarbiturates - ultra-shorts like thiopental sodium, methohexital • oxybarbiturates - phenobarbital, pentobarbital, thiomyalal • pentobarbital - B-Euthanasia D (the pink stuff)
Ultra-short acting barbiturates • used for general anesthesia • rapidly absorbed and redistributed (ultra-short acting) • onset 30-60 sec • duration 5-20 min • recovery depends on pt (sighthounds)
possible decreased in CO, BP, RR (possible severe), bradycardia, arrhythmia (including PC and bigeminy) coughing, laryngospasm, salivation, tidal, VT • why is decreased tidal volume dangerous? • no significant analgesia • poor muscle relaxation • must be IV - perivascular sloughing (esp thiopental) • thiopental can stimulate PNS - can cause sensitivity to epinephrine - if given can cause arrhythmia (VPC, bigeminy, tachy/bradycardia, AV block - caution using in stressed or cadiac pt
Short Acting Barbiturates (imedazole derivatives) • etomidate • guaifenesin
etomidate - sedative/hypnotic for small animal anesthesia • not controlled • minimal change to cardiopulmonary function • decreases intracranial/intraoccular pressure • excellent for pt with shock or heart dz • wider therapeutic range than thiopental and even propofol • good muscle relaxation • not common due to price and adverse effects
no analgesia • V, muscle movement, excitement during induction/recovery, sneezing, suppresses adrenocortical function (use premeds) • possible phlebitis on injection though must be given IV • rapid injection or repeat doses can cause hemolysis • inj via IV line can help
Guaifenesin GG (glycerol guaiacolate) • as an injectable - sedative and muscle relaxer • used mostly in large animal (combined with other agents for induction/recovery) • also used (far more in companion animal medicine) as an expectorant (Cough Tabs) • minimal changes to cardio/resp/gi systems • irritating to tissues perivascularly • hemolysis in LA
Intermediate Acting Barbiturate - pentobarbital • Pentobarbital sodium • used in lab animal medicine IP for euth, concentrated for SA euth
Long Acting Barbiturate • Phenobarbital - used mostly as anticonvulsant, can be used in sedation • chloramphenicol can increase effect of phenobarbital • barbiturates cross the placenta (decreased respiration for fetus on delivery) • barbiturates enhance neuromuscular block effect of muscle relaxer • chronic use of barbiturates (phenbarb) increase hepatic activity (can increase resistance and shortening of opioid and other meds metabolized by liver
Cyclohexamines(Dissociatives) • most common - ketamine • dissociatives disrupt nerve transmission (inhibit some, stimulate others). n-methyl d-aspartate (NMDA) inhibited to prevent wind-up • wind-up - exaggerated response to low intensity pain stimulus (worsened post-op pain) • onset - IV 90 sec, IM 2-4 min, PO 5-10 min • dogs IV PO, cats IM PO • duration 30-60 min • recovery 2-6 hr
great for immobilizing for brief procedures (local blocks, BCM) • catalepsy - not surgical, awake but no response to surroundings - premed premed premed • often combined with opioids and tranquilizers (ie telazol) • VTI - KAG w/ buprenorphine (can cause hyperthermia post-op) • telazol - tiletamine/zolazepem(diazepam) - lasts 14 days in fridge - can cause hypothermia • see also ket/val • oral ketamine - 100 mg/kg (ie fractious cat)
open eyes, central dilated pupils,possible nystagmus, intact reflexes • increased HR and BP w/o decrease CO • arrhythmia • hypersalivation, V, vocalization, jerking movements/tremors, prolonged recovery • increase intraoccular and CSF pressures • superficial analgesia (no visceral analgesia) • respiratory depression/apneustic breathing (long pause, inhale, short pause, exhale) • metabolized by liver, excreted by kidneys • IM burns - no necrosis expected (like thiopental) • can cause amnesia • DO NOT USE with seizures • possible behavior changes for hrs/days afterward
responsible for tachycardia, vasoconstriction, increased BP • apneustic breathing pattern • increased salivation • increased CSF and intraoccular pressure • muscle rigidity • can cause urinary obstruction
Ket/Val • ketamine/diazepam • one of the most popular agents • combined at equal volumes - 1.2mL Ket/1.2ml Val (for example) • onset 30-90 sec • duration 5-10 min • recovery 30-60 • minimal cardiac depression • good muscle relaxation • smooth recovery • some analgesia • controlled
Tiletamine • reconstituted - 4 days room temp, 14 days refrigerated • used in variety of species IM SQ IV • IM only in dogs/cats • poor visceral analgesia • pt maintains palpebral, corneal, laryngeal, pedal reflexes • increased salivation • long/hard recovery, tremors, seizure, hyperthermia • hypersensitive post-op
Propofol • ultra-short acting non-barbiturate • phenolic compound unlike all other anesthetics • used once to induce, repeatedly prn for maintenance, or CRI • onset 30-60 sec • duration 2-10 min • recover in ~10, standing in 15-30 mins • appetite stimulant in low doses
lists 30 min recovery in cat - many practices do not use this drug in feline medicine - toxicity • NOT controlled • rapid redistribution, not cumulative (still prolonged recovery in sighthounds) • the slower you give it the less you need to use (can be given too slow)
wide safety agent- mild sedation to general anesthesia • decreases intracranial and intraoccular pressure • provides muscle relaxation • antiemetic and anticonvulsant • can be used with valium
no significant analgesia • highly protein bound • severe respiratory distress/ acute apnea especially if given quickly • bradycardia and decreased contractile strength • if too slow - excitation, tremors, paddling, nystagmus • ONLY milky white agent to EVER be given IV (too date) • must be given IV
decreases blood pressure (worse if given rapidly) - do not use in hypotensive pt • possible seizure like activity/reaction - rare • expires quickly - 6 hrs at room temp - contain soy oil and egg lecithin • Propofol 28 - benzyl alcohol • mix all drugs well before use • can keep expired propofol for use during euthanasia • cost is often an issue in practice
Morphine • opioid • onset 15-60 sec • duration 3-6 hr • recovery 2-4 hr • controlled • typical V w/i 15-20 min • popular as CRI • epidural
metabolized by liver, excreted by kidneys • post analgesia can be reversed • possible dysphoria - a feeling of uneasiness and anxiety • decreased GI motility, vasodilation, hypotension (possible hypertension) significant resp depression, pupil constriction
Fentanyl • opioid • very popular analgesic • can be used with valium/midazolam for induction • onset 1-2 min • duration 20-30 min (inj) • profound sedation
bradycardia, sensitive to sound • controlled • reuptake from storage sites, metabolized by liver, excreted by kidneys • also used in CRI • available as transdermal patch (last 3-5 days) (clip fur, wipe with water (no alcohol), apply directly to skin, hold to melt adhesive, wrap lightly, label label label)