Chapter 21: Anesthesia Principles and Monitoring Flashcards
A small animal’s metabolic oxygen demand is what?
5ml oxygen/kg/min depending on temperature and metabolic factors
Saturated vapor pressure is what?
Point at which the gas of the anesthetic agent is in dynamic equilibrium with the liquid agent
How are vaporizers classified?
Vaporizer output
method of vaporization
location in the circuit
temperature compensation
agent specificity
Name two methods of vaporizer output?
variable bypass or measured flow (rare)
Name three methods of vaporization?
Flow over
bubble through
direct injection (desflurane)
Which method of vaporization is used for desflurane?
direct injection
What is meant by “in-“ or “out of circuit” vaporizer location?
In: within the patient circuit - so dose depends on patient’s minute volume
Out: before the common gas outlet = constant dose of gas regardless of minute volume (most common)
When should CO2 absorbent be changed?
When rebreathing is seen on capnography
Fresh gas flow for a nonrebreathing system is at least ____ times the patients respiratory minute volume (MV)?
3 times MV
Minute volume is tidal volume (15 mL/kg) x resp rate
What should your O2 flow rate be for preoxgenation?
4-5 L/min
What is the I:E ratio min and max?
1:1 to 1:4
** Ideal is 1:2
Regulators on anesthetic machines reduce the carrier gas pressure from that in the tank or wall outlet to what PSI?
45-50 PSI
Initial tidal volume for ventilator setup is calculated as what?
10-15ml/kg for each breath
Which type of ventilator is best for pulmonary disease / patients with changing compliance?
Pressure cycled
What is a general starting peak inspiratory pressure for ventilator setup?
12mmHg
Below what Pa02 - does the oxygen content in blood decrease rapidly?
70mmHg
How do you calculate MAP?
What are normal values?
MAP = DAP + ((SAP-DAP)/3)
Normal pressures are 125/85 (98)
Poor MAP <60mmHg may indicate/cause what?
Poor DAP < 40mmHg may indicate/cause what?
MAP <60 perfusion and O2 delivery unlikely to meet requirements of aerobic metabolism -> prolonged causes brain function alterations or AKI
DAP <40 Poor coronary artery perfusion and may result in cardiac ischemia
In cats the Doppler tends to underestimate the SAP by what?
25mmHg
Is doppler BP affected by tachycardia, or bradycardia or irregular heart beats?
NO
but oscillometric is affected
What is photoplethysmography?
Using SpO2 wave instead of doppler crystal but using cuff - inflate cuff, when wave comes back is SAP
No advantage over doppler
In oscillometric BP - they tend to underestimate what in cats?
In dogs?
Cats - SAP
- Relatively precise for MAP and DAP
Dogs - Underestimate all S/M/D AP
What is needed for direct BP measurement?
Arterial catheter, transducer with wheatstone bridge and monitor for wave form
What mmHg of PaCO2 is termed hypercarbia? Above what mmHg doe we see adverse consequences of hypercarbia
55 mmHg
65mmHg - effects
Why can end tidal (end expiratory) CO2 be used as an accurate reliable continuous estimate of arterial CO2?
at end of expiration should just be alveolar gas only - this effectively mimics that in the pulmonary blood - and approximates the arterial CO2
How do you work around the dilution of ETCO2 in nonrebreathing systems?
Use a side stream monitor so it aspirates a sample more proximal in the ETT
Apart from measuring CO2, what other benefits can ETCO2 be used for?
rapid diagnosis of cardiac arrest
confirm intubation
assessment of CPR effectiveness
Describe the ETCO2 trace for hypoventilation?
For hyperventilation?
A leak in the circuit?
Rebreathing of CO2?
Cardiopulmonary arrest?
hypoventilation - progressive increase in height of the plateau
hyperventilation - progressive decrease of height of plateau
leak - shark fin
rebreathing - progressive elevation of the baseline
Arrest - Sudden decrease in CO - could also be a circuit disconnect
A patient breathing 100% oxygen should have a PaO2 of what?
500mmHg and HGB saturation of 100%
PaO2 of 80mmHg is what SpO2
95%
Anemia will not affect the SpO2 until HCT is less than what %?
10%
What can affect a pulse oximeter reading?
vasoconstriction - pain, alpha 2 agonist, hypothermia
profound anemia
profound hypoxemia
Can pulse oximeter be normal in a hypotensive, anemic and hypoventilating patient?
yes - so cannot be relied on for assessment of respiration, can be normal in hypoventilation
When should you reverse nerve blockage?
Do not reverse until all 4 of the twitch responses on your train of four stimulator have returned.
- This signifies that the level of the drug at the neuromuscular junction is low enough that it may be overcome by increasing acetylcholine at the junction (ACHesterase inhibitors)
What is normal central venous pressure in mmHg and cmH20?
0-5 mmHg
0-8 cmH20
Response to a fluid bolus is more indicative of volume status than a CVP measurement. What is the response to a fluid bolus:
when there is hypovolemia ?
when there is hypervolemia?
Hypovolemic: a bolus of 5-10 ml/kg might not change CVP
Hypervolemic: CVP will increase by 3-4mmHg and very slowly if at all return to baseline
How does a thermodilution catheter work for CVP?
Does it give continuous readings?
A thermistor-tipped catheter is placed in the pulmonary artery via the jugular - then a saline bolus is administered, the heart pumps it out and a temperature change is noted -> a curve is formed and CO is area under the curve
No, not continuous. Reads only when the saline injection is given.
Cardiac output monitoring techniques?
Thermodilution
lithium dilution CO
pulse contour analysis
Noninvasive CO device
Name three ways of determining anesthetic depth?
Clinical signs
ETCO2
Brainwave activity - electroencephalogram - not good for dogs or cats
Which receptors do opioids work on?
Mu (μ), kappa, delta
μ is most analgesic
k is also analgesic
delta is modulating of μ
How do opioids work?
Bind to receptor which are all G-coupled proteins - decreasing the release of substance P and glutamate
activation = influx of K+ and calcium into the presynaptic cell and causes hyperpolarization of the post synaptic cell - resulting in a net decrease in neuronal activity and transmission of pain signals
How much can opioid pain relief reduce anesthetic inhalant requirements?
40-60%
Why might opioids increase regurgitation?
May increase pyloric sphincter tone/ileus
Which opioids cause histamine release -> causing vasodilation, tachycardia and hypotension more often?
Meperidine and morphine lesser extent
Potency compared to morphine?
- hydromorphone
- oxymorphone
- meperidine
- methadone
- Fentanyl
- Buprenorphine
- hydromorphone 8x
- oxymorphone 10x
- meperidine 1/10th (morphine is 10x meperidine)
- methadone 2x
- Fentanyl 100x
- Buprenorphine 40x
Therapeutic plasma concentrations are achieved in dogs in how long after fentanyl patch placement?
18-24 hours
Remifentanil is unique in the way it is metabolized, how is it metabolized?
Metabolized by plasma esterases - so does not need hepatic or renal to be metabolized
What can occur rarely with fentanyl or its derivates?
Chest wall rigidity - “wooden chest” - treat with naloxone
What is serotonin syndrome and which opioids can it be seen in and with use of what drugs?
Meperidine and tramadol
when used with monoamine oxide inhibitors (MAOIs) or TCAs (Trazodone)
Result of excess serotonin in the body -> anxiety, hyperthermia and in more severe cases shock, rhabdomyolysis and subsequent renal failure
What is Acepromazine?
phenothiazine tranquilizer depressing dopamine activity in the RAS - acts as an alpha 1 receptor antagonist
Alpha 2 antagonists result in decreases of what?
Adverse effects?
norepinephrine
hyperglycemia, respiratory depression, vasoconstriction
hypertension then hypotension due to bradycardia and decreased central sympathetic output
side effects usually seen due to peripheral effects on alpha 1
What is trazodone?
A phenylpiperazine antidepressant - serotonin antagonist and reuptake inhibitor
peak plasma concentration after oral admin is 7 hours
What does etomidate induce?
Adrenal suppression which can last for 6 hours - risk of adrenal insufficiency e.g. septic shock patients
- if must be used can give a physiological dose of corticosteroids in postop period
MAC for surgically anesthetized patients is?
1.2-1.5x published MAC
What is electromechanical dissociation?
Pulseless electrical activity on your EKG - A plausible wave form on monitor but actually no coordinated muscular contraction by the heart.
ETCO2 and Doppler are better for assessing actual circulation of blood by the heart.
