Physiology review Q Flashcards
(14 cards)
Phenylephrine is a ___________ -acting sympathomimetic that exerts its systemic blood pressure effects principally by stimulating ______________________.
direct // alpha-adrenergic receptors
A 32-year-old male presents eight years after an IED blast traumatically amputated his left extremity above the knee. Six hours into an eight hour osseointegration case, the patient’s ETCO2 is 45 mmHg and the patient’s nasal temperature is 37.5 oC. The attending asks you for an estimate of the P50 on this patient’s oxyhemoglobin dissociation curve. Which of the following is reasonable?
*
A. 20 mm Hg
B. 27 mm Hg
C. 35 mm Hg
D. 55 mm Hg
C. 35 mm Hg
The P50 of the oxyhemoglobin dissociation curve represents the partial pressure of oxygen (PO2) at which hemoglobin is 50% saturated with oxygen. The normal P50 for adult hemoglobin at standard conditions (pH 7.4, PCO2 40 mmHg, temperature 37°C) is approximately 26.6-27 mmHg.
Several factors can shift the oxyhemoglobin dissociation curve, thereby affecting the P50. These are often remembered by the mnemonic “CADET, face Right!” for factors that cause a right shift (increased P50, meaning hemoglobin has less affinity for oxygen and releases it more easily to tissues):
Carbon dioxide (increased PCO2)
Acidosis (decreased pH)
DPG (2,3-Diphosphoglycerate, increased)
Exercise (increased metabolism leads to increased CO2, acid, temperature)
Temperature (increased temperature)
Conversely, the opposite of these factors causes a left shift (decreased P50, meaning hemoglobin has greater affinity for oxygen and holds onto it more tightly).
The P50 of the oxyhemoglobin dissociation curve represents the partial pressure of oxygen (PO2) at which hemoglobin is 50% saturated with oxygen. The normal P50 for adult hemoglobin at standard conditions (pH 7.4, PCO2 40 mmHg, temperature 37°C) is approximately _________________.
26.6-27 mmHg
A 32-year-old male presents eight years after an IED blast traumatically amputated his left extremity above the knee. Six hours into an eight hour osseointegration case, the patient’s ETCO2 is 45 mmHg and the patient’s nasal temperature is 37.5 oC. The attending asks you for an estimate of the P50 on this patient’s oxyhemoglobin dissociation curve. Why would their PO2 be 35 instead of the normal 26.6-27?
Since both the CO2 and temperature are slightly elevated, they would both contribute to a right shift in the oxyhemoglobin dissociation curve, meaning the P50 would be increased from the normal range of 26.6-27 mmHg.
How does ETCO2 impact the oxyhemoglobin dissociation curve?
Right shift
How does temp impact the oxyhem diss curve?
right shift
Mixed venous oxygen saturation measured from a pulmonary artery catheter would be expected to be increased in which disease state?
A. Cardiogenic shock
B. Cyanide poisoning
C. Hemorrhagic shock
D. Status epilepticus
B. Cyanide poisoning
What is the best initial vasopressor in the treatment of shock, particularly cardiogenic or vasodilatory?
A. Epinephrine
B. Norepinephrine
C. Dopamine
D. Vasopressin
B. Norepinephrine
Mechanism: Primarily a potent alpha-1 agonist, causing significant vasoconstriction (increasing systemic vascular resistance and blood pressure). It also has moderate beta-1 effects, providing some inotropy (increased heart contractility) with minimal effect on heart rate at typical doses.
Advantages: It is effective at increasing mean arterial pressure (MAP) and systemic vascular resistance (SVR) and has been shown to have fewer dysrhythmias compared to dopamine.
Mech: norepi
Primarily a potent alpha-1 agonist, causing significant vasoconstriction (increasing systemic vascular resistance and blood pressure). It also has moderate beta-1 effects, providing some inotropy (increased heart contractility) with minimal effect on heart rate at typical doses.
mech: epi
Strong alpha-1, beta-1, and beta-2 adrenergic effects. It causes vasoconstriction, increases heart rate, and increases contractility.
mech: dopamine
Dose-dependent effects. At low doses, it primarily affects dopaminergic receptors (renal vasodilation). At moderate doses, it has beta-1 effects (inotropy and chronotropy). At high doses, it primarily has alpha-1 effects (vasoconstriction).
mech: vasopressin
Acts on V1 receptors in vascular smooth muscle, causing vasoconstriction independent of adrenergic receptors. It also has antidiuretic hormone effects (V2 receptors).
Why would we use norepi over epi?
Epi is secondline: While highly effective, its strong beta-1 effects can cause significant tachycardia and increase myocardial oxygen consumption, which can be detrimental in certain forms of shock, especially cardiogenic shock where the heart is already compromised. It’s often used as a second-line agent or in specific situations like anaphylactic shock (where it’s first-line for its bronchodilatory and anti-allergic effects) or in cardiac arrest.
Epi runs the risk of tachycardia while norepi increases MAP and SVR with lower arrythmia risks
The condition that is most detrimental for the patient with coronary artery disease under anesthesia is:
a. Bradycardia (HR 50)
b. Tachycardia (HR 115)
c. Hypotension (BP 92/48)
d. Hypertension (BP 190/90)
b. Tachycardia (HR 115)
Tachycardia (HR 115): This is highly detrimental for two main reasons:
Increased Myocardial Oxygen Demand: A faster heart rate significantly increases the workload of the heart, leading to a higher demand for oxygen.
Decreased Myocardial Oxygen Supply: Tachycardia dramatically shortens the duration of diastole (the relaxation phase when the heart fills with blood and the coronary arteries primarily perfuse the myocardium). This significantly reduces coronary blood flow and thus oxygen supply to an already compromised heart. The combination of increased demand and decreased supply makes tachycardia a major precipitant of myocardial ischemia and infarction in CAD patients.
