Lecture 7: Shock (Exam I) Flashcards
For a normal person, how much can CO increase when needed?
What if the person trains?
What if the person is a world-class athlete?
- 23 - 25 L/min (400% increase)
- 30 - 35 L/min
- 40 - 45 L/min (600% increase)
What expands cardiac reserve?
What diminishes it?
- Exercise expands cardiac reserve whilst pathology diminishes it.
What two disease processes result in no cardiac reserve?
- Severe valvular disease
- Severe MI
Describe what is occurring in this graph.
- A myocardial infarction has detrimentally impacted someone’s cardiac output curve resulting in A.
- B - E are body’s attempt to maintain CO by increasing volume (RAP).
- F is eventual fluid overload resulting in worsening CO & death.
In the figure below, which state would pulmonary edema be most likely to develop in?
F
Describe what is occurring in the graph below.
- Severe MI leads to inadequate CO initially.
- Inadequate CO is overcome with volume retention and autonomic compensation.
- Either recovery of cardiac tissue or pharmaceutical help.
What curve shift would be seen from a digoxin-treated heart post severe myocardial infarction?
Left shift
Can MAP be utilized alone to determine tissue perfusion? Why or why not?
Gap between MAP and CO demonstrates lack of tissue perfusion despite decent MAP.
What is the gold standard for CO measurement? What are other ways it can be measured?
- Swan-Ganz catheter
- Flo-track (meh)
- Blood gasses
- Manual CO w/ cold injectate
- SvO₂
- Impedance changes
- Echocardiogram
When assessing cardiac output via manual cold saline injectate, what would a more diluted sample at the sensor indicate?
- A higher CO
slow dilution = ↓CO
fast dilution = ↑CO
What is the formula for the Fick equation?
CO = (O₂ absorbed per min by lungs mL/min)
÷
(Arteriovenous O₂ difference mL/dL of blood)
How many mL/dL of O₂ return to the heart from systemic circulation?
- 15 mL/dL
How many mL/dL of O₂ leave the heart?
- 20 mL/dL
Calculate cardiac output from the following parameters:
- V̇O₂ = 240 mLO₂
- Arterial O₂ = 20 mLO₂
- Venous O₂ = 14 mLO₂
4 L/min
What is V̇O₂?
How is it measured?
- O₂ absorbed per minute by the lungs.
- Via spectrometer (gas in vs gas out)
How does coronary ΔO₂ (essentially O₂ consumption) compare to that of systemic?
- Coronary consumption of O₂ is much greater than that of systemic with ΔO₂ = 15mL/dL
Below is a CO measurement obtained from ultrasonic flowmeter. What is indicated by the green circle?
- Retrograde perfusion as the aortic valve closes funneling blood into the coronary arteries.
Below is a CO measurement obtained from ultrasonic flowmeter. What general concept is important to note from this graph?
Disregard the green circle for this question
Pulsatile nature of CO (CO isn’t a steady state of 5 L/min, its formed from pulses up to 20 L/min with periods of ~ 0 L/min).
When is an echocardiogram most useful in the assessment of cardiac output?
- Best for monitoring changes in CO over time.
How many heart beats are in a normal respiratory cycle?
- 8 beats per respiratory cycle.
What is the normal pulse pressure variation noted with the respiratory cycle called?
- Pulsus paradoxus
What would a systolic blood pressure drop of greater than 10mmHg during inspiration indicate?
- Hypovolemic status (the patient needs a bolus or passive leg raise).
Increasing preload will have what effect on PPV (pulse pressure variation)?
- ↑ preload = ↓ PPV
What component of shock results in direct cardiac depression?
- Toxin release from tissue ischemia
What occurs when capillaries become ischemic?
- Necrosis via lysosomes resulting in loss of colloids and edema.
How is capillary necrosis secondary to shock treated?
- Prevention
- Steroids (↓necrosis)
What are the treatment options for shock?
- Pressors (preserving perfusion to VRGs)
- Inotropes
- Steroids
- Fluid replacement
- Colloids
- Positioning
- O₂ (not super helpful, Hgb is usually saturated)
What will eventually happen with colloid replacement for shock?
- Colloid overload will stress the kidneys and eventually just become excreted.
What stimulates SNS reflexes?
- Poor perfusion to the medulla of the brain stem.
What organ is a reservoir of Hgb?
Where is the largest reservoir of blood?
- Spleen
- GI tract
What is the strongest CV reflex in the body?
- CNS Ischemic Response - all blood vessels squeeze to maintain perfusion to the brainstem.
Which capillary pressure forces favor filtration?
- PCAP
- PISF
- πISF
Which capillary forces disfavor filtration?
πCAP
How would arterial NFP (net filtration pressure) be calculated?
NFP = (PCAP + PISF + πISF) - πCAP
Which capillary force changes when talking about the capillary forces on the venous end of the capillary beds?
How does it change?
How does this affect NFP?
- PCAP changes from 30 to 10.
- NFP becomes -7. Filtration becomes disfavored
