Pre anesthetic work up Flashcards
RVT checklist with pre anaesthetic work up
Communication of procedures and risk with client
Consent- written
Minimum patient database including diagnostics
Asses patient anaesthetic risk
Proper patient fasting
Anesthetic and monitoring equipment are ready
Pre-induction patient care
Sedation, preemptive analgesia, other medication, fluids, temp support, enemas, bandage removal and wound care
Communications dos with anesthetic
Take the time to communicate with your client
Know their pet and the procedure they are coming in for
Know the pets history
Discuss possible complications
Get accurate contact info
Be honest about cost (include postop follow ups)
Keep client informed, esp if something goes wrong
Know what client wants in event of complications
Be thorough about post surgical care requirements (especially postop home care requirements)
Communication donts for anesthetic work ups
NEVER guarantee a cure
Don’t assume that the client understands what is happening
You must be able to explain procedures including sedation, anesthesia, surgical procedure, home care
Don’t lie to them
Side effects/complications that may occur
complications/mistakes that do occur
Cost and cost of complications
Patient admiting
Confirm procedure, cost, contact info
Consent (written is always best option)
Confirm “what if” in the case of complication
Establish discharge (same day or hospital stay)
Patient history
In clinic medical (incl. Past labs) and anaesthetic history
Client history (chronic and acute)
Current medication
Fasting? Water withdrawal?
Minimum patient database
Patient signalment
Patient history (current and chronic conditions, medications, prior anaesthetics/surgeries)
Weight, TPR, mentation
Complete physical examination
Presurgical pain assessment
Preanesthetic diagnostic workup
Why is species important with anesthesia
Horses and cats become excited on opioids
Dosing requirements different for every species
Horses require dedicated recovery areas to prevent injury
Large animals require ventilation support
Exotics are handled differently
Why is the breed important for anesthesia
Breed specific MDR1-deficiency
Sighthounds are sensitive to barbituates
Boxers are sensitive to acepromazine; terriers are resistant to acepromazine
Brachycephalic breeds are difficult to intubate; require monitoring during sedation and recovery
WHy is the age important for anesthesia
Geriatrics often have decreased liver and renal functions and overall lowered anaesthetic tolerance
Neonates and pediatrics have higher fluid requirements, increased risk of hypothermia and different drug metabolism
Why is sex and reproductive status important for anesthia
Pregnant patients are always at increased risk for drug affects both to patients and fetus
Increased cardiovascular 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 and ewes
Why is a PE important before doing GA
PE and drug order for premed must be done by the vet
Vet can perform the PE and give order up to 24 h before procedure; in this event, RVT must perform exam immediately (ensure there is no change in patient status) before administering medication
Minimal exam immediately before premedication
Weight, BCS
TPR, MM, hydration status, mentation status
Must record all values and findings
Why is BCS important before GA
In clinic patients should be weighed a minimum of q24h
All anaesthetic patients to be weighed on the day of
Most important short term cause of weight change is hydration
Must know BCS in order to
Ideal BCS ⅗, 5/9
If low BCS, will need to consider hypoalbuminemia, low body fat, illness
If high BCS, will need to consider lean body weight for dosing, underlying cardiac disease, increased resp depression under GA, fatty liver syndrome in a cat on the postop period
Why is mentation important
Gives indication of underlying illness, CNS status. Patients with decreased mentation have increased risk under GA
Part of distance exam- always include distance exam
What is the normal resp rate of cats and dogs
<32
What is anormal TPR for a foal
T: 38.3-39.5
P: 80-120
R: 24-40
What is a normal TPR for an equid
T: 37-38.5
P: 24-40
R: 8-16
What is a normal TPR for a calf
T:38.4-39.5
P:60-100
R:20-50
What is a normal TPR in a bovid
T:37.8-39.2
P:60-80
R:10-30
What is in a qualitative exam
Heart sounds
Pulse quality
Lung sounds
Hydration status
Mentation
What is in a Quantitative exam
TPR
RR
mm
CRT
You must report these PE findings to the DVM before giving premeds
Change in weight
Hypothermia or hyperthermia
Abnormal HR, rhythm, or murmur; weak, overly strong (bounding) or irregular pulse
Increased 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 common additional diagnositics before surgery
Minimum testing is usually: PCV, TP, BUN, BG
Can be done immediately prior to anesthesia; or within reasonable time frame
When testing is declined in whole or part there should be a signed consent form
Your anesthetic record must include your pre anesthetic exam findings such as
Drugs patient is taking
Current weight, BCS
TPR, MM, CRT, mentation
Anything is abnormal
Anything that was examined and found normal
Also verbally communicate any abnormalities to the VIC
5 classes of patients based on anaesthetic risk
PS1 minimal risk
PS2 Low risk
PS3 moderate risk
PS4 high risk
PS5 extreme risk; patient will die without procedure
Physical status classification is
Based on minimal patient database
5 classes of patients based on anaesthetic risk
There is NEVER no risk
What is the goal of preop stabilization
Goal: stabilise patient as much as possible prior to any anaesthetic/surgical procedure; this ensures least patient risk
Depends on whether procedure is elective, required or emergency
What does preop stabilization look like
Fluids to restore dehydration
Postpone until ideal BCS
Stop bleeding, treat infections, blood transfusions
In the event of an emergency, you may not be able to wait and “E” is placed after PS score. Example: PS3E
What are some inherent risk of GA
CNS depression
Suppression of hypothalamic control of temp and other homeostatic functions
Also decreases ability to vasoconstrict in response to any drops in blood pressure
Decreased HR, cardiac output
Decreased RR, tidal volume
Vasodilation due to gas anaesthetics will contribute to hypotension
Risk of esophageal reflux and aspiration pneumonia
How to limit risk of GA
Fasting
Temp support
O2 support
Fluid support
Patient monitoring
What is fasting and why
Fast = no food, can have water
NPO= nil per os= nothing per mouth= no food or water
Fasting is important before anesthetic induction
Decreases risk associated with vomit and regurgitation during induction, surgery and recovery
Job of RVT to instruct client on fasting protocol BEFORE surgery date
Must confirm at time of admitting that patient was fated
If the client is uncertain, assume the patient has not been fasted. May require postponing surgery
How long do you fast a dog or cat
Food: 8-12h
Water: 2-4h
How long to fast a horse
Food: 8-12h
Water: 0-2h
Horses have risk of gastric ulceration if empty stomach; OK if horse gets small mount of hay if anaesthetic is short
How long to fast cattle
Food: 24-48h
water; 8-12h
How long to fast small ruminants
Food: 12-18h
Water: 8-12h
Do not use standard fasting protocols on the following; consult with VIC for special instructions
Patients less then 2 kg
Neonates <8 weeks
Exotics
Diabetics- also need to instruct on insulin
Patients with cachexia or less than ideal BCS
There is an increased risk of hypoglycemia in all of the above groups
Emergency anesthesia and fasting
Emergent cases may not have time to fast
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
Complications of not fasting
Esophageal reflux
Esophageal trauma
Aspiration pneumonia
What is esophageal reflux
Different from vomiting
Gastroesophageal sphincter relaxes under GA→ when patient is in lateral, there is passive flow of stomach contents into the esophagus
Risk of reflux increases if not fasted
Occurs intraop and recovery (risk until patient can swallow and hold head)
Esophageal trauma and GA
Complication of esophageal reflux
Stomach acid enters esophagus and causes damage to the esophageal lining
Clinical signs: vomit, nausea, dysphagia, post op anorexia
If severe enough, this could eventually lead to esophageal stricture- scar tissue develops where trauma occurred
Aspiration pneumonia and GA
Complications of esophageal reflux
Stomach contents flow into oral cavity and from the oral cavity, enter the airways while patient is recumbent
high risk during recovery
What causes aspiration pneumonia
Filling of alveoli with fluid (acute airway obstruction)
Infection and inflammation of the lungs (24-72 h post op)
Can be very severe, fatal
How to diagnose aspiration pneumonia
Crackles on auscultation
Decreased oxygenation; cyanosis
Fluid oral cavity
Fluid from nares
Post op ADR, fever, increased resp sounds, tachypnea
Preventing aspiration pneumonia
Fasting
Keep ETT cuff inflated until patient swallows
Stomach tube
Patient positioning
If patient has not aspirated yet but is at risk
Lateral?
If patient has aspirated and is unconscious
Sternal?
What are some common complications with not fasting animals for GA
Nausea
V/D
Side effect of hydro and/or GA
Filled intestines and bladder
Decreases accessibility to abdominal organs
Increased risk of contamination
Longer surgery times
Bloating in ruminants
Require a stomach tube to release rumen gasses even if they have been fasted
Core body temp support is
Thermoregulation is a homeostatic process controlled by the hypothalamus
Core heating is by
- Shivering, muscle contraction, increased metabolic rate, vasoconstriction of peripheral blood vessels
Core cooling is by
- Decreased metabolic rate, vasodilation of peripheral blood vessels, panting, salivation, sweating
Major causes of temp drop during GA are
Depression of the hypothalamus (thermoregulatory centre)
Decreased metabolic rate
Muscles don’t contract/loss of shiver
Vasodilation (especially acepromazine and inhalants)
Cold 100% O2
Open body cavity (especially if open abdomen)
Evaporation of alcohol during surgical prep
Conduction loss to stainless steel
What are some factors that affect heat loss
Intrinsic (patient) factors that cant be altered
- BCS
- Size of animal – smaller animals have higher surface area to body mass so lose heat faster
- Neonates and geriatrics have less thermoregulation
Extrinsic (external) factors that can be altered
- Drug selection – some cause more vasodilation than others
- Ambient temp
- Duration of GA – longer procedure = colder
- Degree of shaving and type/volume of surgical scrub
How to monitor core body temp
Know temp BEFORE premedicating
From the time of induction, monitor every 15 minutes until patient is recovered
After recovery, monitor every 30 min until patient can sustain temperature >37.4 °C
Methods:
Esophageal thermometer - most accurate
Rectal thermometer – most convenient
Axillary/ear is not accurate enough
What are the important temps under GA
36-38 °C – allowable range under GA
>37.4 °C – patient can maintain own temp; do not heat
36-37 °C – must provide active heating support
<36 °C – must inform DVM
<33 °C – dying
Complications from low body temp
Prolongs anaesthetic recovery and general recovery (especially in cats)
Predisposes patient to anaesthetic overdose
Due to decreased metabolism of drugs
Can maintain cool patients on lower anaesthetic dose
Shivering during recovery will increase oxygen demands
Below 33*C, brainstem is depressed and theres is cardiac malfunction
How to minimize heat loss under GA
Stabilize room temperature prior to premedication (turn up heat, especially in winter)
Prudent use of alcohol and scrub water (don’t drown your patient; remove excess scrub/alcohol)
Place barrier between patient and table top
Warm IV fluids to ~37.5°C; same for saline used for abdominal flushes
Blankets, circulating warm water blanket; forced warm air blanket (Bair huggers); warm water bottles
Minimize surgical and general anesthetic times
Things to avoid for heating under GA and why
Electric Heating pads and Lamps
- Often poor control and get too hot
- Sedated/anesthetized 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 it is too hot vasodilation of surface capillaries cooled blood from surface goes to core and drops temp furthe
Causes of Hyperthermia under GA
> 39 °C
Most often seen just before/during recovery
Causes from most to least common:
Excessive external heat source (too much warming)
Cat that reacts to mu-agonists (hydromorphone, fentanyl)
Malignant hyperthermia (rare, more common in pigs)
Management of hyperthermia under GA
Remove heat source; fans
Reverse drug if possible
Cold IV fluids
Turn up 100% oxygen flow
Factors that cause hypoxia
Decreased RR and tidal volume with
Mu-agonsits
Alpha-2 agonists (all species; most severe in ruminants)
ALL general anesthetics
Propofol, alfaxalone cause induction apnea
Isoflurane suppresses CO2 drive
Decreased ventilation results in less O2 uptake and decreased CO2 exhaustion
Also decreases ability to move O2 and CO2 around body
Oxygen for patients under GA
Patients under GA require a minimum of 33% O2 to maintain oxygen saturation of blood
Room air is 21% O2; not sufficient to meet tissue demands when combined with depresses resp function
Must have 100% O2 support to achieve maximum oxygen saturation of blood
Weight and resp function with GA
Tidal volume already decreased under GA
Increased weight requires more effort to expand and expel lungs: especially if animal is recumbent
Dependant lung areas (“down” side of patient in lateral) may develop atelectasis
Alveoli partially collapse in this area due to poor inflation
Applies to
Morbidity obese animals
Large animals (Eq, Bovine)
May require manual/automatic ventilation
Brachycephalic’s and oxygen support under GA
Risk of soft palate collapse. If animal also has stenotic nares, their entire airway could be cut-off
Watch for resp distress, increasing lethargy, cyanosis
Continuous monitoring from time of sedation until completely recovered
Worst risk is sedation and recovery (i.e., 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 animal can pull out on own when they want
Be aware patient may also have collapsing trachea and size ETT appropriately
What is a normal BP
Normal BP (no medications): 120/80 (94)
Varies with age, species, health status, and situation
Blood pressure is maintained by a combination of:
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
Blood pressure UNDER GA looks like and depends on
There is always a drop in BP under GA
Degree of hypotension depends on
Drugs used (inhalants, acepromazine, alpha-2)
Patient stability (underlying cardiovascular/renal disease; hydration status; geriatrics and neonates)
Duration of GA
Any blood loss will contribute to hypotension
Factors causing hypotension in anesthetized patients
Decreased cardiac function
- Decreased HR, decreased cardiac output
- Less volume of blood moved per unit time
- Most severe depression by alpha-2 agonists, inhalants, injectable anesthetics
- If severe enough, can cause cardiogenic shock
Vasodilation
- Inhalant anesthetics, acepromazine
- Causes a relative decrease in fluid volume; with time, fluid moves from interstitial space to vascular space
- If severe enough, could result in vasogenic shock
Evaporative losses
- Open body cavities, dry gasses
- Real loss of fluid volume
Perioperative hemorrhage
- Can be minimal to severe
- Real loss of fluid volume
IV catheterization benefits
It is best to IV catheterize patients under heavy sedation and/or GA
Benefits
Can deliver IV fluids to maintain blood volume & support blood pressure
Can be hard to get IV access later due to low BP
Rapid administration for emergency drugs
Used to administer CRI’s
Reduces the risk of perivascular injection
Can administer a number of IV drugs one after another with flushing between each one (trauma)
Acceptable BP under GA
Dog, cat: 110-160/50-70 (60-90)
Eq: >80/>50 (60-90)
When to report BP under GA
Dog, cat Systolic <90; MAP <70; Diastolic <40
Eq Systolic <90; MAP <80; Diastolic <40
Surgical fluids are determined by
Amount of fluids required to maintain BP in the presence of drugs that cause cardiac depression and vasodilation
ALWAYS recommended
Isotonic cystalloids (LRS, Normosol, Plasmalyte) appropriate for most patients
Administer via IV catheter
When do you administer surgical fluids
From time of induction until patient is recovered
Any dehydration is corrected BEFORE general anesthesia (not part of surgical rate)
Return to appropriate maintenance rate after recovery to prevent fluid overload
Must record fluid type, rate, total volume(or start and stop times), any changes in fluid rate as they occur
What are the common surgical fluid rates by species
Surgical fluid rate in otherwise healthy patient:
CATS: 2-3 ml/kg/h
DOGS: 3-5 ml/kg/h
Large animal: 5-10ml/kg/h
This rate is used on its own!
Adjust with changes in BP, lungs sounds, HR, bleeding….
Know THIS rate for exam purposes!
FLuid bolus for surgical fluids is used for
Given when patients are hypotensive (despite surgical fluid rate) or bleeding profusely
I.e., when the surgical fluid rate is not enough
Start with a SINGLE crystalloid bolus
10 ml/kg over 15 min
Can repeat up to 3-4 times if necessary
Check with the vet before administering
Reasons fro surgical fluids
Offsets causes of hypotension (vasodilation and decreased 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 electrolyte and acid-base imbalances (commonly occur under GA and with pathology)
Supports renal drug elimination
Volume overload can occur from
Too much fluid (excessive total volume infused)
Too fast fluids - Giving fluids too fast prevents them from entering into the extracellular fluid volume properly
Given the appropriate rate and volume to the wrong patient
Hct <20
Low albumin
Patients < 5 kg
Heart failure
Renal disease
Physiological effects of volume overload
Hypertension
Very bad if pre-existing heart disease; causes heart to work harder and can cause cardiac overload
Increases blood loss
Fluids move to 3rd spaces in the body (abdomen, pleural space, pulmonary spaces)
Pulmonary edema
Cerebral edema
Can dilute oxygen carrying capacity of blood
SIgns of volume overload
Increased Lung sounds/Crackles
↑respiratory rate and dyspnea
Coughing and restlessness if patient is awake
Tachycardia
Increased BP
Hemodilution (decrease the relative PCV)
Ocular and nasal discharge, chemosis
Subcutaneous edema
Neurological signs
How to prevent volume overload
Know your calculations
Use an appropriate-sized fluid bag (ex. 100 ml for cat spay)
Clamp off the line when transporting patients
Check IV line and rate hourly. Caution: most drip sets will alter their rate slowly over time.
Ideally, use an infusion pump
Monitor equipment
Monitor patient
How to treat volume overload
No definitive therapy
Main treatments:
Discontinue fluids
Start on diuretics
Provide oxygen support
Best to prevent fluid overload rather than treat it!
What are some tips to use when calculating fluid volumes
Convert weight to kilograms
Calculate the hourly rate
ml/h (SA); L/h (LA)
Always enter this value into the medical notes
Then, calculate the drip rate from the above
Whole drops per whole seconds
Drip sets :
>10-15 kg: 10 drop/ml set
<10 kg: 60 drop/ml set (aka “pediatric” set)
Double check your numbers and make sure that they MAKE SENSE. For example, you would never give 50 ml/h to a cat
Mark your fluid bag with “Start” and “End” so you know how much fluid your patient has received = total volume infused.
Be aware that certain patients will have altered rates. Heart failure and renal disease may require decreased fluid rates; fever and younger animals require high rates, etc. If in doubt, ask.