Exam 2 Flashcards
Methods to monitor oxygenation
Pulse oximeter
Blood gas (gold standard)
Cyanosis
Lactate
What does pulse ox monitor?
SaO2 (hgb saturation)
SaO2 numbers to know
- > 95% sat = desired, PaO2 >80 mmHg
- 90-95% sat = mild hypoxemia, Pa 60-80 mmHg
- <90% sat = severe hypoxemia, Pa <60 mmHg
- 70% SaO2 = PaO2 40 mmHg
What does blood gas measure?
PaO2, Pa/vCO2
Allows you to assess O2 exchange at alveoli via A-a gradient, P/F ratio
When does cyanosis occur?
When you already have a problem
PaO2 <40 mmHg
What does Lactate measure?
Indirect measure of anaerobic metabolism
Lactate increases w/ severe hypoxemia
Methods for monitoring ventilation
Capnograph/Capnometer
Blood gas
Acid/base balance
What’s normal end tidal (at end of exhale) Co2
30-45 mmHg
highest point of capnograph, D
What is the difference between blood PCo2 and end tidal CO2?
0-10 mmHg b/c mixes w/ dead space oxygen, Co2 gets diluted slightly
What is the difference between PaCO2 and PvCo2?
PvCo2 ~5 mmHg higher (very small diff)
Arterial and venous blood samples are comparable for ___ but not ___?
comparable for PCO2 but not PO2
should only use arterial samples for accurate PO2 measurement
Why can’t you use a capnograph/nometer for small <5 kg patients?
b/c on a bane circuit so higher O2 flow = further dilution of CO2, inaccurate measurement
What does acid/base balance measure
Indirect measure of Co2 conc b/c CO2 and bicarb are related
Hypoventilation –> high CO2, resp acidosis
Hyperventilation –> low CO2, resp alkalosis
Ways to monitor respiratory activity during anesthesia
Subjective/visually: Resp rate, pattern, rhythm, volume, effort
Respirometer/Ventilometer: tidal vol, minute ventilation
EQ diff’s w/ anesthesia
- maintain a higher PCO2
- greatly affected by position (V/Q mismatch)
- cluster breathing normal, hypoventilation common
- typically maintain lower HR (up to 40% decreased CO under anesthesia)
Cat diff’s w/ anesthesia
- Maintain a lower PCO2
- predisposed to airway obstruction (mucus, small airway)
- hard to intubate
- airways reactive, prone to trauma
Dog diff’s w/ anesthesia
- depressed by opioids
- predisposed to aspiration pneum.
- brachycephalics
Lab animal diff’s w/ anesthesia
- hard to intubate and monitor
- affected by position
- predisposed to airway obstruction (mucus, small airway)
marine mammal/ diver diff’s w/ anesthesia
- diving reflex/breath holding
- may drown w/ anesthesia or during recovery
- hard to intubate
amphibian diff’s w/ anesthesia
- skin breathers
- hard to intubate or monitor
bird diff’s w/ anesthesia
- no alveoli, no diaphragm = ventilation required
- for FRC
- greatly affected by position, airway prone to obstruction (mucus)
- hard to monitor, sensitive to inhalants
- complete tracheal rings
Rum diff’s w/ anesthesia
- hard to intubate
- greatly affected by position
- salivation = predisposed to asp. pneum.
- higher resp rate but smaller tidal vol than EQ
- often hypertensive w/ anesthesia
What’s important about sheep and anesthetic drugs?
alpha 2 agonists will cause hypoxemia
SAC diff’s w/ anesthesia
- hard to intubate (mouths don’t open wide)
- Good oxygenators
- regurge/asp. pneum. risk
Pig diff’s w/ anesthesia
- hard to intubate (90 deg larynx, small airway)
- short necks (can intubate a bronchus)
- unknown underlying dz possible
Oxygen delivery formula
DO2 = CO x CaO2 (oxygen content)
What determines CaO2
hgb conc, PaO2
Cardiac output formula
CO = SV x HR
Factors affecting SV
preload
afterload
contractility
Other factors affecting CO
arterial BP
blood vol
systemic vascular resistance
How can you increase SV during anesthesia?
increase preload (e.g. increase blood vol) but avoid excess (–> edema, pulmonary edema)
increase contractility (inotropic drugs)
decrease afterload (vasodilation) - not recommended b/c decreases BP/perfusion
How to increase HR during anesthesia?
- sympathomimetics (ephedrine)
- parasympatholytics (atropine, glycopyrrolate)
If you wanted to increase CO during anesthesia, would you rather increase HR or SV?
SV
Increasing just HR decreases filling time, but increases work - only increases CO a bit
How to increase BP during anesthesia?
Modulate chatecholamine receptors
support blood volume
Catecholamine receptors actions
a1 - vasoconstriction (increase SVR)
a2 - vasoconstriction (increase SVR), bradycardia (decreased HR)
b1 receptors - tachycardia & increased contractility (increase CO)
b2 receptors - vasodilation (decrease SVR)
CV complications during anesthesia
Bradycardia Tachycardia Decreased contractility Rhythm disdurbances Vasomotor (blood vessel) tone change
Treat bradycardia
Fix cause of problem Give anticholinergic (atropine, glycopyrrolate)
What drugs cause bradycardia
opioids
alpha 2 agonists
anticholinesterases
What drugs cause tachycardia
ketamine
anticholinergics (glyco, atropine)
Treat tachycardia
fix cause of problem
Beta-blockers as last resort (Esmolol)
Treat for decreased contractility
decrease anesthetic plane
Inotropes to increase contractility (Dobutamine, Dopamine, ephedrine)
How to diagnose an arrhrythmia?
ECG
What drugs cause vasodilation?
Propofol
Isoflorane
Acepromazine
What drugs cause vasoconstriction?
alpha 2 agnoists
ketamine
Treat vasodilation
Increase blood vol or CO
Give a vasopressor (vasoconstrictor) - Dopamine, phelephrine
Treat vasoconstriction
Reverse or stop vasopressors
Give vasodilator - Ace, sodium nitroprusside, hydralazine, amlodipine
PE indicators of cardiovascular function
- demeanor, activity level, temp
- dyspnea d/t decreased DO2 or pulmonary edema from heart failure
- Pulse rate, rhythm, quality
- mucus mem color
- CRT
- hydration status
- ascultate
Considerations about pulse pressure
- not the same as BP
- measures difference btwn systolic and diastolic pressures (similar P’s = weak pulse, big diff = strong pulse)
- pulse may be absent when MAP <40 mmHg (hypotensive) but pulse pressure could still be nx
Normal amount of water in the body & where it lives
60-80% of bodyweight
60% is intracellular
40% is extracellular (10% in extravascular, 30% interstitial)
normal blood volume in the body
5-9% of bodyweight
Ways to assess hydration
- skin turgor
- tacky mm
- hemoconcentration (increased PCV, TP)
- increased Cr, BUN (if severe), concentrated urine, low urine output
- tachycardia
- decreased bw, depression, lethargy
Ways to monitor CV function during anesthesia
- direct CO monitoring (gold standard)
- HR
- Arterial BP (important, early indicator of trouble)
Blood Pressure formula
BP = CO x SVR (systemic vascular resistance)
Normal SAP (systolic arterial pressure)
100-140 awake
>90 SA, >100LA anesthetized
Normal MAP (mean arterial pressure)
80-120 awake
>60 SA, >70 LA anesthetized
Normal DAP (diastolic arterial pressure)
60-80 awake
>50 anesthetized
Ways to measure BP
Direct: arterial catheter (gold standard)
Indirect: doppler, oscilometric
Cuff width for accurate estimate of BP
needs to be 40% limb circumference
too small width = overestimation, too big = underestimate
Doppler vs. oscilometric
Doppler - has crystal, gives SAP only
Oscilo - no crystal or sphygmomanometer, SAP, MAP, & DAP given
Why is hypotension bad?
oxygen delivery likely decreased
Consequences of mild but prolonged hypotension
CNS damage
Renal & hepatic damage/failure
GI & muscle tissue necrosis
Consequences of severe hypotension
severe CNs damage
severe myocardial damage
acute death
Treat hypotension
Try to increase CO & tissue perfusion first (to maintain DO2)
Vasoconstriction could increase SVR, but could also decrease perfusion more - tricky
Treat hypovolemia
Restore blood volume by crystalloids, colloids, blood products
Risk of a too long ET tube
increased dead space
goes into a bronchus –> hypoxemia, hypoventilation, decreased anesthetic plane (common in pigs)
Proper cuff inflation
Inflate cuff until don’t hear leak when squish bag to ~10-15 cmH2O PIP (SA, 20-30 for LA)
Should hear safety leak if squish bag to 20-30 cmH2O
Consequences of cuff overinflation
trauma –> tracheal rupture, pneumothorax & pneumomedastinum
LA - trachea will collapse ET tube
ET tube obstructs itself
Indications for mechanical ventilation
hypoventilation
hypoxemia
increase inhaled anesthetic depth
logistics
With mechanical ventilation, how do you adjust inspiratory time?
larger animal = longer time
smaller animal = shorter time
What’s normal tidal vol? Minute ventilation?
TV: 10-20 ml/kg
MV: 100-250 ml/kg/min
How do neuromuscular blockers work?
block ACh receptors –> paralysis
Good for orthopedic, ophthalmic, CNS procedures or EQ deep abdomen procedures
neuromuscular blocker drugs
Cis-atracurium, atracurium, vecuronium
Key component for neuromuscular blockade
assisted ventilation & monitoring of paralysis
Reversals for neurmuscular blockers
Edrophonium
Neostigmine (mg diagnostic)
suggamadex-Rocuronium
Physiostigmine (mg treatment)
Risk w/ poor padding/placement during surgery
ischemia, post-op pain
nerve damage
rum - asp. pneum.
EQ - edema
Why is thermoregulation important w/ anesthesia
decreases metabolic rate, thus heat –> hypothermia
occurs faster in younger (less E stores) or smaller animals (more SA)
Consequences of hypothermia
prolonged recovery, prolonged drug metabolism
decreased MAC
Impaired coag, delayed wound healing
increased mortality rate
When do you pull the ET tube
SA - strong swallow
Rum - sternal, holding head up
EQ - standing
Brachycephalics - as late as possible
How do crystalloids treat dehydration
restore water & electrolytes, increase extracellular vol
Types of crystalloids
LRS
physiologic saline (0.9% NaCl)
normosol
plasmalyte
Water is normal daily water intake?
1-5 ml/kg/hr or 20-120 ml/kg/day
lower side for larger animals
How much crystalloid is given to anesthetized patients (as a guideline)?
1-10 ml/kg/hr
Usually a conservative bolus first - 10-20 ml/kg
Expect it to move from intravascular to extravascular space in 30-45 mins
How much of a bolus do you give for shock?
50-100 ml/kg
Why would you use colloids over crystalloids
colloids have high oncotic pull, so stay in vasculature longer (6-48 hrs vs. <1 hr) BUT can fluid overload and other issues, so limit dose
Types of colloids
Hetastarch, Dextran, Albumin, Oxyglobin
When do you usually give blood products & how much do you give?
PCV <20 ot TP <3.5
Give 1-5 ml/kg/hr (faster if active bleed)
how do you treat acidosis in an emergency
bicarbonate
bicab = bs x base deficit x 0.3
How do you treat alkalosis in an emergency
physiologic saline
How do you treat hypoglycemia
1-5% dex as needed
required glu = bs x 0.3 x (desired glu - current glu level)
How do you treat hyperglycemia
insulin
Expectations of resp func in EQ under anesthesia
hypoventilation - mechanical ventilation required
V/Q mismatch (impacted by recumbency)
leave ET tube in until STANDING (w/in 1 hr post anesthesia)
EQ common protocol for sedation
alpha 2 agonist (Xylazine, detomadine, ___dine)
Ace - take edge off early on
+/- butorphanol or morphine
EQ common induction protocol
Ketamine + diazepam/midazolam +/- guaifenesin
no propofol - wierd behaviors
EQ common maintenance protocol
<1 hr = total IV: Triple Dip (XDK) or G/MKX
>1 hr = G/MKX, then CRI of K & X, then inhalant
Monitoring EQ during inhaled anesthesia
- must measure arterial BP (MAP should be >70 mmHg)
d/t decreased CO & hypotension –> myopathy - must treat hypotension
- ideally, ECG
- take periodic blood gas (esp. w/ inhaled anesthetics) b/c pulse ox & capnograph less reliable in EQ
Options for systemic EQ pain management
- Alpha 2’s used commonly
- opioids (but combined b/c cause excitation, ileus)
- maybe lidocaine or ketamine CRI to decrease anesthetic requirement (and Ketamine improves CO)
Options for local/regional blocks in EQ
local anesthetics for distal extremities only
Opioids (combined w/ alpha 2) - longer lasting
NSAIDs - traditionally used
Why are opioids so commonly used in combo w/ other drugs for anesthesia?
analgesia
peri-operative sedation
large margin of cardiovascular safety
shorter acting drugs (e.g. fentanyl) decrease dose of IA needed & decrease risk of drug accum
Who should you use opioids very cautiously in?
Horses
behavioral issues & ileus, inconsistent effects
When would you use a ketamine CRI in combo w/ IA’s for anesthesia?
- reduces windup
- reduces anesthetic requirement of IA’s
hypercapnea causes
vasodilation and tachycardia
