5a. Preanesthetic Work-Up Flashcards
What is the RVT checklist and what are some things that might be on it?
communication of procedures and risk w/ client
consent - written
min. patient database including dx
assess patient anesthetic risk
proper patient fasting
anesthetic and monitoring equipment working
surgical supplies and equipment are ready
Pre-induction patient care - sedation, pre-emptive analgesia, other meds, fluids, temp support, enemas, bandage removal and wound care
What are some communicative do’s?
take time to commune w/ client
know pet/procedure being done
know patient hx and discuss possible complications
get accurate contact info
be honest about cost (include post-op follow up)
keep client informed, esp. if something goes wrong
know what clients wants in event of complications
be thorough about post surgical care reqs (especially post-op home care requirement
What are some communicative dont’s?
NEVER guarantee a cure
Don’t assume that the client understands what is happening, or what is going on - must be able to explain procedures including sedation, anes., sx procedure, home care
Don’t lie to them about s/e and complications, about the cost and cost of complications and that complications/mistakes DO occur
What is the minimum patient database?
- patient signalment
- Patient hx (current/chronic conditions, meds, prior anesthetics/surgeries)
- weight, TPR, mentation
- Complete PE
- Pre-surg pain assessment
- Pre-anes diagnostic workup
What do we grab when we admit a patient and history?
admitting: confirm procedure, cost, contact info, CONSENT, confirm “what if” in case of complication, establish discharge (same day or hospital stay)
Hx: in clinic medical (incl. past labs) and anes hx, patient hx (chronic and acute), current meds, fasting?, water withdrawal?
Why is signalment important?
horses and cats become excited on opioids
dosing requirements diff for every species
horses req dedicated recovery areas to prevent injury
large animals require ventilation support
exotics are handled differently
Why do we care about the breed we’re operating on?
Breed specific MDR1-deficiency (border collies)
sighthounds sensitive to barbiturates
boxers sensitive to acepromazine; terries resistant to it
brachycephalic breed are difficult to intubate; require monitoring during sedation and recovery
Why do we care about the age of the patient we are operating on?
geriatrics often have dec liver and renal functions and overall lowered anesthetic tolerance\neonates and pediatrics have higher fluid reqs, inc risk of hypothermia and diff drug metabolism
Why is sex and repro status important in the patient we’re working on
preg patients always at risk for drug effects to both patient/fetus - inc CV demand, risk of abortion or teratogenicity
Select drugs that do not cross the placenta if possible
avoid acepromazine in stallions
benzodiazepines cause floppy baby syndrome
xylazine can cause abortion in cows/ewes
Why do we perform a PE for premed?
PE and drug order for premed MUST be by the vet
Vet can perform the PE and give order up to 24h before procedure; in event; RVT MUST perform exam immediately (ensure no change in patient) before giving meds
minimal exam immediately before premed (weight, BCS, TPR, MM< hydration status, mentation status, MUST record all values and findings)
What are some PE changes that could occur in 24 hours
hydration - skin tent, sunken eyes
Weight
What normals do we need to memorize?
Temp, HR, RR, CRT, indicators of mild, mod and severe dehydration
record normal for patient
allowances while under anes alter depending on specific patients’ norms
Why is weight/BCS important to know before surgery?
in-clinic patients should be weighed minimum of 124h
ALL anes. patients be weighed on day of
Most important short term weight change is hydration
Must know BCS for ideal BW
if low BCS, need to considered hypoalbuminemia, low body fat, illness
If High BCS, will need to consider lean BW for dosing, underlying cardiac dz, inc resp dep, under GA, fatty liver syndrome in cat post-op
Why is mentation important for surgery?
Gives indication of underlying illness, CNS status. patients w/ dec mentation have inc risk under GA
Part of distance exam,
lvls: BAR, QAR, lethargic, obtunded, suporous (aroused by painful stimuli), comatose
What are things we MUST report to DVM when doing a PE before giving premeds?
change in weight, hypo/hyperthermia, abnormal HR< rhythm, or murmur; weak, overly strong (bounding) or irregular pulse
inc resp rate or effort: altered lung sounds
delayed CRT; pale, cyanotic or icteric MM
dehydration
cachexia
change in mentation or neurological changes
vomit
What are some additional diagnostics that can be done pre-surgery?
min tests: PCV, TP< BUN, BG
can be done immediately prior to anes or within a reasonable time frame (young patient who is healthy, old patient who is otherwise healthy, patient hit by car 3 d ago)
when testing is declined in whole or part there should be signed consent form
What do we need to record on our anes exam findings?
drug patient is taking
current weight and BCS
TPR, MM, CRT, mentation
anything abnormal
anything examined and found abnormal
also, verbally communicate any abnormalities to VIC
What is the physical status classification
based on minimal patient database
PS1 minimal risk
PS2 low risk
PS3 moderate risk
PS4 high risk
PS5 extreme risk, patient will die w/o procedure
There is NEVER no risk
What is the risk level of PS1? Give the criteria and an example of it
minimal - normal, healthy and not old/very young. Ideal BCS
Young to middle age patients
electives (Spay, neuter)
dental trophy (gr1-2 dental disease)
What is the risk level of PS2, what is the criteria and examples?
low - may have mild systemic dz or slight altered drug metabolism
Neonates, pediatric, geriatric, brachycephalic, mild collapsing
trachea
- Mild chronic liver, renal change, low grade murmur, controlled
hypertension, diabetes
- Mild obesity
- Pregnancy
- Mild dehydration (<3%)
What is the risk level of PS3, the criteria and an example of it
moderate - has severe systemic disease that is well managed
- Moderate dehydration (3-5%)
- Anemia
- Compensated major organ disease (chronic renal disease, controlled
heart failure)
- Moderate-severe collapsing trachea w/ dyspneic episodes
- Addison’s
- FB gastrotomy, cystotomy
What is the risk level of PS4, the criteria and an example of it?
High - has severe systemic disease that is a (constant) threat to life
- Stage 3 heart failure; stage 3 renal disease, liver failure
- Ruptured bladder, pyometra, internal hemorrhage, pneumothorax
What is the risk level of PS5, criteria and an example of it
extreme, survival not likely - MORIBUND. not expected to survive beyond 24h w/o the procedure. Chances of surviving procedure very low
Bleeding out and cannot control blood loss
- Hypothermia
- GVD
- Perforated linear FB with peritonitis
- Stage 4 heart failure, stage 4 kidney failure; end stage liver failure
- Imminent death: multi-organ failure
What is the goal of pre-op stabilizing?
stabalize patient as much as possible prior to any anesthetic/surgical procedure; ensures least patient risk
Depends on whether procedure is elective, required on emergency
Stabilization: fluids to restore dehydration, postpone until ideal BCS, stop bleeding, treat infections, blood transfusions
In event of emergency, many not be able to wait “E” is placed after PS score ex: PS3e
Why are healthy geriatrics considered PS2?
We can see a lot of decline in kidney and liver function before it shows on any diagnostic tests
What are the inherent risks of GA
- CNS depression - suppression of hypothalamic control of temp and other homeostatic func and also dec ability to vasoconstrict in response to any drops in BP
- Dec HR, cardiac output
- Dec RR, tidal volume
- Vasodilation due to gas anesthetics will contribute to hypotension
- Risk of esophageal reflux and aspiration pneumonia
How can we limit the inherent risks of GA?
fasting, temp support, O support, fluids and patient monitoring
What is fasting?
FAST = no food; can have water
NPO = nil per os = no food/water
Fasting is important before anes induction
dec risk associated w/ vomit and regurg during induction, sx and recovery
Job of RVT to instruct client on fasting protocol before surgery date
MUST confirm at time of admitting that patient was fasted - if uncertain, assume patient has not been fasted. may require postponing surgery
What is the standards hours to withold food and water in cats and dogs?
Food: 8-12hrs
Water: 2-4
What are the standard hours to withhold food and water in horses?
Food: 8-12
Water: 0-2
What are the standard hours to withhold food and water in cattle
Food:24-48 hours
Water: 8-12 hours
What are the standard hours to withhold food and water in small ruminants?
Food: 12-18 hours
Water: 8-12 hours
What are the standard hours to withhold food and water in patients <2kg/exotics?
Food: should be fasted for shorter tims or not at all
Water: for shorter times
What is one reason that we might be able to still give a small amount of hay to horses that may need to be fasted?
Horses has risk of gastric ulceration if empty stomach
What special patient groups require special fasting requirements
Patients less than 2kg
Neonates <8wks
Exotics
Diabetics - also need to instruct on insulin
Patients w/ cachexia or less than ideal BCS
There is an increased risk of hypoglycemia in ALL of above groups
In what times might fasting simply not be an option? What can do we instead?
Emergencies - need to weigh risk of postponing surgery against possible complications
options: increase monitoring, use positioning of body to decrease risk of aspiration, can induce vomit, can place stomach tube
What are the complications of not fasting?
esophageal reflux, esophageal trauma/esophagitis, aspiration pneumonia,
Other common ones: nausea, V/D (s/e of hydro and/or GA), filled intestines and bladder (dec accessibility to abdominal organs, inc risk of contam, longer sx times), bloating in ruminants -require a stomach tube to release rumen gasses even if they have been fasted
What is esophageal reflux
different from vomiting
gastroesophageal sphincter releaxes under GA > when patient is in lateral, there is passive flow of stomach contents into the esophagus
risk of reflus inc if not fasted
occurs intra-op AND recovery (risk until patient can swallow AND hold up head
what is esophageal trauma
esophagitis
complication of esophageal reflux
stomach acid enters esophagus and causes damage to the esophageal lining
clinical signs: vomit, nausea, dysphagia, post-operative anorexia
if severe enough, this could eventually lead to esophageal stricture - scar tissue develops where trauma occurred
What is aspiration pneumonia
complication of esophageal reflux
stomach contents flow into oral cavity and from the oral cavity, enter the airways while patient is recumbent
Causes: filling of alveoli with fluid (acute airway obstruction), infection and inflam of the lungs (24-72 h post-op), can be very severe, fatal
Highest risk is recovery - in sx, airway is protected by cuff, but after it is not
How do we diagnose aspiration pneumonia?
crackles on auscultation
decreased oxygenation; cyanosis
fluid from oral cavity
fluid from nares
post-op ADR, fever, increased resp sounds, tachypnea
How do we prevent aspiration pneumonia
fasting, keep ETT cuff inflated until patient swallows
stomach tube
patient positioning
If patient has NOT aspirated yet but is at risk - position head up body down to prevent aspiration
If patient has aspirated and is unconscious - head down so gravity drains fluid
What is thermoregulation? What is core heating and cooling caused by?
homeostatic process controlled by the hypothalamus
core heating: shivering, muscle contraction, inc metabolic rate, vasoconstriction of peripheral blood vessels
Cooling: dec metab rate, vasodilation of peripheral blood, panting, salivation, sweating
What are the major causes of temperature drop during GA?
- depression of hypothalamus (thermoregulatory centre)
- decreased metabolic rate
- Muscles don’t cntract/loss of shiver
- vasodilation (especially acepromazine and inhalants)
- Cold 100% oxygen
- Open body cavity (especially if open abdomen)
- Evaporation of alcohol during surgical prep
- Conduction loss to stainless steel
What are some factors that might affect heat loss
intrinsic (patient) factors that can’t be altered - BCS, size of animal (smler have higher surface area to body mass so lose heat faster, neonatres and geriatrics have less thermoregulation)
Extrinsic(external) factors that CAN be altered: drug selection (some cause more vasodilation than others), ambient temperature, duration of GA - longer procedure = colder, degree of shaving and type/volume of surgical scrub
How might we monitor core body temp?
know temp BEFORE pre-meds
From time of induction, monitor every 15m until patient is recovered
after recovery, monitor every 30m until patient can sustain temp >37.4
methods: esophageal thermometer - most accurate
Rectal thermometer - most convenient
Axillary/ear is not accurate enough
What is the normal temperatures for a dog, cat, horse and bovine?
Dog: 37.5-39.5
Cat: 37.5-39.5
Horse: 37.0-38.5
Bov: 37.8-39.2
Expect a slight drop in body temperatures
36-38 - allowable range under GA
>38.4 - patient can allow own temp; do not heat
36-37 - must provide active heating support
<36 - must inform DVM
<33 - dying
What are the complications from low body temp?
- prolongs anesthetic recovery and general recovery (especially in cats)
- predisposes patient to anes overdose - due to dec metabolism of drugs and can maintain cool patients on lower anes dose
- shivering during recovery will increase O demands
- below 33, brainstem is depressed and there is cardiac malfunction
How could we minimize heat loss during GA?
stabilize room temp prior to premed (turn up heat, especially in winter)
Prudent use of alcohol and scrub water (don’t drown your patient; remove excess scrub/alcohol)
Place barrier btw patient and table top
Warm IV fluids to ~37.5, same for saline used for abdominal flushes
Blankets, circulating warm water blanket; forced warm air blanket (bair huggers), warm water bottles
minimize surgical and GA times
What are some heating items to avoid?
electric heating pads and lamps - poor control and get too fast, sedated/anes patient can’t move away, cause contact area burns (even if mild heat for a prolonged time), especially cats (genetic predisposition), ~1 week to appear; can cause sepsis
Aggressive heating of exterior body surface - causes peripheral vasodilation (body thinks its too hot)> vasodilation of surface capills > cooled blood from surface goes to core and drops temp further
What is hyperthermia under GA?
> 39C, most often seen just before/during recovery
Common causes: excessing external heat source (too much warming), cat that reacts to mu-agonists (hydromorphone, fentanyl), malignant hyperthermia (rare, more common in pigs)
Management: remove heat source; fans, reverse drug if possible, cold iv fluids, turn up 100% O flow
What are some factors that cause hypoxia
decreased RR and tidal volume occur w/ mu-agonists, A2 agonists (all species but severe in ruminants), ALL GA
Propofol, alfaxalone cause induction apnea
iso suppresses CO2drive
depressed ventilation results in less O uptake and decreased CO exhaustion
also dec ability to move O and CO around body
How can we give O support?
patients under GA require a minimum of 33 O to maintain O saturation of blood
room air is 21% O; not sufficient to meet tissue demands whenc combined w/ depressed resp function
must have 100% O source to achieve maximum O saturation of blood
How might weight affect respiratory function?
tidal volume already decreased under GA
Increased weihgt requires more effort to expand and expel lungs; especially if animal is recumbent - dependant lung areas (“down” side of patient in lateral) mayd develop atelectasis where they’ll partially collapse in area due to poor inflation
Applies to morbidly obese animals and LA
may require manual/automatic ventilation
WHat do we need to be aware of with our favorite breed, the brachycephalics
risk of soft palate collapse. If anim also has stenotic nares, entire airway could be cut-off
watch for resp distress, inc lethargy, cyanosis
continuous monitoring from time of sedation until completely recovered
worst risk is sedation and recovery (ie. not intubated)
When intubated, will breathe better then they ever have before. may keep ETT in even after recovered (Do not pull with swallow); release cuff so anim can pull it out on their own
be aware, patient may also have collapsing trachea and size ETT appropriately
What is normal BP with no meds?
120/80 (94) - varies with age, species, health status and situation
What combination maintains BP?
HR, cardiac output, degree of vascular contraction, oncotic pressure (presence of albumin and colloids in plasma keep water in the blood vessels), fluid volume
adequate BP required for delivery of O2 and nutrients to cells; removal of CO2 and waste products
What is our BP under GA?
always a drop under GA
degree of hypotension depends on drugs used (inhalants, acepromazine, A2’s), patient stability (underlying CV/renal dz, hydration, geriatrics and neonates), duration of GA
Any blood loss will contribute to hypotension
WHat are some factors causing hypotension in anesthetized patients?
- decreased cardiac function
- vasodilation
- evaporative losses
- perioperative hemorrhage
How does decreased cardiac function and Evaporative affect hypotension in anesthetized patients?
Dec cardiac func: dec HR + cardiac output, less V of blood moved per unit time, most severe depression by A2-agonists, inhalants and injectable anes, if severe enough can cause cardiogenic shock
EVAPORATIVE: open body cavities, dry gases, real loss of fluid volume
How does vasodilation and perioperative hemorrhage affect hypotension in anesthetized patients?
VASODILATION: inhalant anesthetics, acepromazine, causes a relative dec in fluid V; w/ time, fluid moves from interstitial space to vascular space - if severe enough, could result in vasogenic shock
PERIOP HEMORR: can be minimal to severe, real loss of fluid volume
What are the benefits of IV catheterization?
best to IV catheterize patients under heavy sedation and/or GA
1. can deliver IV fluids to maintain blood volume + support BP
2. Can be hard to place IV later bc of low BP
3. Rapid admin for emerg drugs
4. used to admin CRI’s
5. Reduce risk of perivascular injection
6. Can admin a # of IV drugs one after another w/ flushing btw each one to dec trauma
What are some acceptable values under GA for BP. When must we report?
Ideal values: D/C 110-160/50-70 (60-90)
Eq: >80/>50 (60-90)
Report: D/C systolic <90; MAP <70;diastolic <40
Eq: systolic <90; MAP <80: diastolic <40
What are surgical fluids?
amount of fluids req to maintain BP in the presence of drugs that cause cardiac depression and vasodilation
Always recommended
How long do we give surgical fluids? what must we record?
isotonic crystalloids (LRS, normosol, plasmalyte) appropriate for most
admin IV cath
from time of induction > recovery - any dehydrated is correct BEFORE GA, return to appropriate maintenance after recovery to prevent fluid overload
Must record fluid type, rate, total V (or start and stop times), any changes in fluid rate at they occur
What is the surgical fluid rate in otherwise healthy patient in cats, dogs and LA?
Cat: 2-3ml/kg/h
Dog: 3-5ml/kg/h
LA: 5-10ml/kg/h
Rate is used on its own
Adjust w/ changes in BP, lung sounds, HR, bleeding
know THIS for exam purposes
What is a fluid bolus?
given when patients are hypotensive (despite surgical fluid rate) or bleeding profusely
ex. when the surgical fluid rate is not enough
Start w/ a SINGLE crystalloid boilus - 10ml/kg over 15m, can repeat up to 3-4 times if necessary
check w/ vet before administering
What are some reasons for surgical fluids?
offsets causes of hypotension (vasodilation and dec cardiac output)
treats fluid loss
Supports tissues that receive the most blood flow: kidneys >brain > heart. Even mild hypotension can result in post-anesthetic renal damage
also corrects elyte and acid-base imbalances (commonly occur under GA and w/ pathology)
Supports renal drug elim
What is volume overload?
can occur from too much fluid (excessive total volume infused or too fast fluids - giving fluids too fast prevents them from entering into the extracellular fluid V properly
Given the appropriate rate and volume to the wrong patient
HCT <20, low albumin, patients <5kg, heart failure, renal dz
What are the physiological effects of volume overload?
- hypertension -vry bad if pre-existing heart dz; causes heart to work harder and can cause cardiac overload - inc blood loss
- fluids move to 3rd spaces in the body (abdomen, pleural space, pulmon spaces) - pulmonary/cerebral edema
- can dilute O carry capacity of blood
What are the signs of fluid overload?
inc lung sounds/crackles
inc RR and dyspnea
coughing and restlessness if patient is awake
Tachycardia
inc BP
hemodilution (dec relative PCV)
ocular and nasal discharge, chemosis
SQ edema
neuro signs
How can we prevent volume overload?
know your calculations
use appropriate-sized fluid bag (100ml for cat spay)
clamp off line when transporting patients
check IV line and rate hourly. caution: most drip sets will alter rate slowly over time
ideally, use an infusion pump, monitor equipment, monitor patient
How do we treat volume overload?
no definitive therapy
maintain txs: discontinue fluids, start on diuretics, provide O support
best to prevent rather than tx
What are some tips on fluid calculations?
- convert weight to kgs
- Calculate hrly rate - ml/h (SA); L/h (LA) and ALWAYS enter this value into medical notes
- then, calculate drip rate from above in whole drops per whole seconds
Drip sets: >10-15kg: 10drop/ml, <10kg: 60gtt/ml set (aka. pediatric set) - Double check 3’s, make sure they make sense. Ex. neger give 50ml/hr to a cat
- mark fluid bag w/ start/end for total volume infused
- be aware that certain patients have altered rate. heart/renal may need dec fluid rates; fever in yg animals req high rates. in doubt, ask
