3. Injectable Anesthetics Flashcards
What are the 3 sections of the body anesthetics affect
Affects the brain and/or spinal cord and/or peripheral nerves and cause loss of sensation/pain
What are the 3 classes of anesthesia?
local
regional
general - injectable, inhalant
What is general anesthesia?
state of reversible unconsciousness produced by general anesthetic agents
central-acting, coma-like state (absence of pain sensation over entire body and is not aware of stimulus, amnesia) (varying degrees of muscle relaxation, immobility)
Always see changes in CV and pulmonary function
Temporary, so long as drug is active
What are the 4 stages of general anesthesia?
Stage 1 - Voluntary excitement/conscious fear response
Stage 2 - Involuntary (unconscious) excitement
Stage 3 - Unconsciouss (surgical anesthesia)
- Plane 1: light unconsciousness (goal of induction)
- Plane 2: Mod unconsciousness (surgical plane)
- Plane 3: deep uncon. (early OD)
Stage 4 - anesthetic overdose
What happens with Stage 1 anesthesia?
Voluntary excitement; conscious fear response
still conscious, but losing consciousness
Fear, excitement; fight-or-flight
disorientation, struggling, ic HR, inc muscle tension, inc RR, inc BP
urination, defecation, panting and/or breath-holding
What happens with Stage 2 anesthesia?
involuntary unconsciousness excitement
Unconscious fightorflight
loss of voluntary control - twitching, paddling, moaning, tremors, rigid limbs; dilated pupils, irregular breathing
Towards the end of stage 2, muscles relax, dec reflexes, slowing HR/RR
What is the goal of induction?
to get the patient through stages 1 & 2 as quickly as possible to minimize stress and to intubate
Stage 3, plane 1
What happens with stage 3 anesthesia?
unconsciousness, surgical plane of anesthesia
dec cardiopulmon func and dec response to stimulus, dec sympathetic func, breathing is regular, 3 planes of unconsciousness within stage 3
What happens with stage 3 plane 1 anesthetic?
Light surgical plane
light unconsciousness, dec muscle tone; dec reflexes; dec sensation but still react to painful stimulus (HR, RR, BP will inc if painful stimulus applied)
Movement is possible
Goal of induction
Can intubate and prep patient
inadequate for surgery
What happens with stage 3 plane 1 anesthesia?
Moderate unconsciousness, surgical plane
Adequate, ideal degree of unconsciousness for surgery, depressed CV function and resp
Vitals are steady and stable
Minimal muscle tone, no reflexes, no reaction to most painful procedures (if pulling on viscera, ex. ovarian ligament, may still see transient inc in HR, RR, BP)
What happens with stage 3 plane 3 of anesthesia?
Deep unconsciousness (aka early OD)
extensive CNS depression
significant CV, resp depression
NO muscle tone, no reflexes; limp
Early warning patient is no stable - TOO MUCH ANESTHETIC
may need to manually support ventilation; will need to support BP
What is stage 4 anesthesia?
Anesthetic OD
brainstem paralysis, CV, pulmonary collapse (aka shock)
initially will see fight or flick response (dilated pupils, inc HR/RR); rapidly followed by shutdown of CV and resp functions (Rapid dec in HR, RR, BP, MM go white)
Death will ensue in 1-5 mins if you do nothing
Stop anesthetic. Start CPR
What are the 3 parts to performing anesthesia?
Induction, maintenance, recovery
What is induction?
The process where patients move thru stages 1-2 and enters stage 3
Ie. moving from conscious to uncon
Induction should always be rapid as stage 1/2 are not nice for anyone
Induction is typically with a general anesthesia
Injectable GA provides fast induction so stage 1/2 never noticed
Stage 1 can be achieved by OD on a sedative, recall patient is still conscious in stage 1
What is maintenance in regards to anesthesia?
Where patient is consisten at stage 3 - consistent depth of unconsciousness; CNS depression. Consistent CV and resp func
If painful procedures are being performed; then the patients should be in plane 2
most commonly, patients are maintained with an inhalant anesthetics - occasions where maintenance is with an injectable anesthetic
What is recovery in regards to anesthestic?
After anesthetic turned off or no longer being administered, patient stages reverse
like induction, slow recovery can be rough
smooth recoveries are typically fast and controlled
patient returns to state of consciousness - typically, use return of vitals to pre-anesthetic normas and sternal recumbency as end of recovery period
Why is knowing drugs and how to monitor important? What can we prevent by knowing this?
Anesthetic accidents are devastating and can result in permanent injury, death, loss of license, lawsuits
Majority can be prevented by knowing drugs, proper dosing and admin, knowing patient, appropriate monitoring (know normals), accurate communication b/w vet and tech, using highest standards of care
Always keep meticulous records
What are some unique things about injectable general anesthetics?
drugs given by IV route
centrally-acting depressants (all of them) - must reach brain to work properly, designed to cross BBB; usually very lipophilic
Used as part of balanced anesthetic, with or w/o an inhalant anesthetic
require inactivation/elim by liver/kidneys
Why are injectable anesthetic drugs the preferred method of induction
Preferred for all species over gas - more rapid onset of stage 3 and considered standard in all med to lg dogs and LA. Except in small exotics, cats and very sm dogs where inducing inhalation anesthetic may be considered acceptable in specific situations
may be single or combo of drugs
always given IV to effect - except in lg animals where entire calculated dose should be given (a lg animal that is not fully anesthetizes is dangerous)
What are the limitations for injectable anesthetics
- cause CNS, CV and resp depression - always risk of debilitating or fatal OD, must monitor HR, ventilation and BP
- Do not provide (sufficient) analgesia - MUST use w/ analgesics for painful procedures
- Do not provide muscle relaxation - combine w/ muscle relaxants, inhalant anesthetics
- Very low TI; no error for mistakes - must dose accurately for the individual patient
- Cannot be reversed/removed
- Have longer recovery period than inhalants - reqs liver metab and/or elim, have more excitement and/or hallucinations
What are the steps to using injectable anesthetics?
- Always dose for lean body weight
- Always administer “to effect” IV (SA)
- Do not administer too rapidly
- Always use a catheter
- Can use alone for short procedures
- Check and double-check doses
What is the purpose of administering to effect iv (SA?)
calculate & draw up the full dose for the patient
using IV cath, only give 1/4-1/2 of total dose > flush > watch for effect. If more drug needed give 1/4 of total dose > flush > watch for effect, repeat until animal is in stage 3 then stop
Purpose: only give as much drug is req; dec risk of OD
Why do we not want to administer injectable anesthetics too fast?
giving too fast can cause arrhythmias and induction apnea (breath holding)
Wait 15-90 after each increment
What will we always use a catheter with injectable anesthetics?
Can give to effect easier
ensures venous access since drugs will cause some degree of hypotension
