Anesthetic Physiology And Principles Flashcards
What is the cause of rapid reduction in core temperature during the first hour of general anesthesia?
Redistribution of heat from the core to the periphery
What are the 2 mechanisms of undesired heat loss in the OR?
- Impaired thermoregulation secondary to anesthesia
2. Low ambient temperature of the operating theater
What are the 2 main “physic” ways that heat is lost in the OR.
- Radiative (67%)
- Evaporative (17%)
- Conductive and convective (16%)
How can you prevent heat loss from a patient?
By pre-warming them
How much does general anesthesia decrease FRC?
10%
How much is FRC reduced by lying flat?
10-15%
What happens when people go to higher altitude?
Increased respiratory rate to compensate for the decrease in oxygen
Increased cardiac output (returns to normal later)
Increase in Hgb over time (by decrease in plasma concentration, increase in erythropoeitin)
Rightward shift in oxygen dissociation curve ( due to hypoxia, increased 2,3-DPG
Increased hypoxic pulmonary vasoconstriction
What happens to the physiology of the respiratory system when a patient is main stemmed?
Shunting occurs
There is no increase in dead space
What are the 6 factors that influence the level of spinal anesthesia?
- Dose/concentration
- Site of injection
- Baricity of local anesthetic
- Posture of patient
- Volume of CSF
- Density of CSF
In what conditions is the volume of CSF reduced?
Anything that increases intra abdominal pressure: Ascites Obesity Pregnancy Tumor
What is the best clinical sign of reversal?
Sustained head lift
What is the least greatest sign of reversal?
Tidal volume
What are the recommended points of recovery?
Sustained tetany for 5 seconds to a 100 Hz stimulus
Sustained head or leg lift in awake patients
What anesthetic technique has not been associated with exacerbation of symptoms or side effects in MS?
Epidural anesthesia
What are the effects of citrate intoxication?
Hypocalcemia Myocardial depression Hypotension Hypomagnesemia (chelated along with calcium) Coagulopathy
What blood product carries the most citrate.,
FFP and platelets
In what conditions is citrate toxicity more likely?
Hypothermia
Liver disease
Hyperventilating
Pediatrics
What are the signs of citrate toxicity?
Hypotension
Narrow pulse pressure
Increased EDP
Increased CVP
How is citrate metabolized?
Rapidly by the liver
When do ionized calcium levels begin to decrease when transfusing blood?
When blood is given at 6 units/hr
What is the treatment of citrate toxicity?
Calcium
What are the effects of citrate intoxication?
Hypocalcemia Myocardial depression Hypotension Hypomagnesemia (chelated along with calcium) Coagulopathy
What blood product carries the most citrate.,
FFP and platelets
In what conditions is citrate toxicity more likely?
Hypothermia
Liver disease
Hyperventilating
Pediatrics
What are the signs of citrate toxicity?
Hypotension
Narrow pulse pressure
Increased EDP
Increased CVP
How is citrate metabolized?
Rapidly by the liver
When do ionized calcium levels begin to decrease when transfusing blood?
When blood is given at 6 units/hr
What is the treatment of citrate toxicity?
Calcium
What changes would you see with a venous air embolism?
Decreased pulmonary perfusion so decreased ETCO2 with increased PaCO2 due to more dead space
What is the best way to increase FRC in a patient in steel trendelenburg?
Increase PEEP because it increases the volume of air in the lungs
What is citrate used for in blood?
Anti coagulation by binding calcium which prevents calcium from binding to factor IV which prevents coagulation
How long does it take the kidneys to eliminate the bicarbonate from citrate?
3-4 days
Why do infants have a faster rate of induction compared with adults?
Because they have a higher minute ventilation to FRC ratio
Their FRC is lower
At what age does MAC requirement reach a peak
6 months
What does glucagon do to the heart?
Increases contractility by increases camp which increases intracellular calcium so increases inotropy and chronograph
What drug should you avoid using in someone receiving bleomycin?
Lidocaine because it can enhance its cytotoxicity
What should be limited in patients receiving bleomycin?
FiO2 because it can aggravate the pneumonitis
What chemotherapy drugs are not good for doing regional anesthesia?
Vincristine and vinblastine because they cause peripheral neuropathy
How does mannitol work?
Osmotic Diuresis by being freely filtered by the glomerulus but poorly up taken by the vasculature so it sets up a hypertonic gradient drawing fluid into the tubule
How is mannitol renal protective?
Maintains patency of flow and flushes debris from the tubule
Also transiently sets up osmotic gradient in the vasculature so increasing circulating plasma volume
What are the carotid body chemoreceptors primarily responsive to?
Arterial partial pressure of oxygen
When do the carotid bodies start firing?
When PaO2 falls below 60-65 mmHg via the glossopharygneal nerve to increase minute ventilation
How is CO2 transport d in the blood?
As dissolved CO2, bicarbonate and carbamino compounds
Majority = bicarbonate
What is the mechanism by which hyperbaric oxygen works?
It increases PaO2 thereby increasing the oxygen content of the blood by increasing the amount dissolved in plasma
Because the amount dissolved in plasma = paO2 X .003
At what level of PaO2 is the saturation of oxygen 100%?
100 mg
How much oxygen do tissues at rest extract?
5-6 ml/dL
At what FiO2 and atmospheric pressure do you get sufficient O2 requirement without contribution from hemoglobin?
FiO2 of 100% at 3 am
What is Henry’s law?
At a constant temperature, the amount of gas dissolved in liquid is proportional to the partial pressure of the gas
What is Boyle’s law?
At a constant temperature, the volume of gas is inversely proportional to the pressure
This is how hyperbaric oxygen therapy works in air embolism
What mediates bradycardia?
Carotid sinus barorerceptor stimulation causing SNS inhibition
How does the carotid sinus work?
Afferents nerves go to glossopharygneal nerve (activated by stretch)
Activation leads to signaling to nucleus solitarius which inhibits sympathetic innervation from spinal cord and stimulates PNS to stimulate vagus nerve
When is the RV perfused in the cardiac cycle?
Diastole and systole due to the lower right heart pressures
What does angiotensin II do to GFR?
It increases it by constricting the efferent arteriole in states of hypovolemia
What does renin cause?
Cleavage of angiotensinogen to angiotensin I
What is myotonic dystrophy?
Delayed muscle relaxation after contraction
Other associations:
Gastric atony, thyroid dysfunction, cardiac conduction abnormalities, myopathy, MVP, diabetes, adrenal insufficiency
What are the symptoms that occur due to autonomic activity during ECT?
Increased ICP
Increased PSNS initially after seizure followed by a sympathetic surge
In myasthenia gravis, how do you need to change your succinylcholine dose?
It will need to be increased due to a decreased number of functional acetylcholine receptors
In MG, what will you need to do to your NMB dose?
Decrease it
In Lambert-Easton syndrome, what will you need to do to your succinylcholine dosing?
Decrease it because patients are sensitive to muscle relaxants
(Decreased Ach release so increased extrajunctional receptors due to low calcium influx all the time and therefore low Ach release)
How much more affinity does CO have for hemoglobin than oxygen?
200-300 times
How does CO shift the oxygen-hemoglobin dissociation curve?
Leftward
What kind of ph abnormality does CO cause?
Anion gap metabolic acidosis due to lactic acidosis from leftward shift of curve
Why is tachypnea a late sign in carbon monoxide poisoning?
Because the carotid bodies respond to PaO2, which is not affect in CO
What are the cardiac effects of CO?
Direct depression because CO binds to cardiac myoglobin even more than hemoglobin
What is PaO2 a function of?
Alveolar O2 (therefore FiO2, atmospheric pressure, and DLCO)
In what conditions is PaO2 normal?
Methemoglobinemia
Carbon monoxide poisoning
Severe anemia
What is a common pulse ox reading in methemoglobinemia?
85%
What are strong ions?
Sodium Chloride Potassium Magnesium Calcium (Lactate, sulfate, ketoacids, nonesterified fatty acids)
What is the concept of the strong ion difference?
It proposes that plasma ph is determined by 3 independent factors: PCO2, SID, Atot (total plasma concentration of nonvolatile buffers)
What are the nonvolatile buffers in the body?
Albumin
Globulins
Inorganic phosphates
What is the strong ion differences?
It represents the difference between the charge of plasma strong cations (sodium, potassium, calcium magnesium) and anions
What is the normal strong ion difference?
40-44 mEq/L
What happens with rapid administration of normal saline?
Hyperchloremic non anion gap metabolic acidosis and a decrease in SID
What other condition can cause hyperchloremic metabolic acidosis?
Severe diarrhea (loss of isotonic fluid rich in bicarbonate)
Loss of bicarbonate is counteracts by an increase in chloride
What are the classic lab findings in SIADH?
Low sodium with a urine sodium greater than 20 and increased urine osmolarity, decreased plasma osmolarity
Why is urine sodium high in SIADH?
The kidney attempts to excrete the excess fluid through increased natriuresis in response to the decreased plasma osmolarity
What is the haldane effect?
The relationship between carbon dioxide dissociation curve and oxyhemoglobin
What is the Bohr effect?
The binding effect of H to Hemoglobin chains and the oxygen release and dissociation thereafter
What does Gs do?
GDP binds GTP then dissociates and stimulates adenylyl cyclase to convert ATP to cAMP which binds subunits that release subunits of protein kinase A which stimulates release of calcium from the sarcoplasmic reticulum
Which hormones work by Gs?
Glucagon Beta adrenergic a Dopamine V2 Anterior pituitary hormones Prostacyclin can receptor that inhibits platelet aggregation
What does increased cAMP cause?
Bronchodilation Vasodilation Increased contractility Lipolysis Glycogenolysis
What does ECT do to cerebral blood flow and ICP?
Increases them
How does ECT work?
Delivers an electrical stimulus to induce a seizure of at least 25 seconds