Shock and Other Inadequate States Flashcards Preview

Cardiology > Shock and Other Inadequate States > Flashcards

Flashcards in Shock and Other Inadequate States Deck (36)
Loading flashcards...

What's the simplest definition of shock?

Acute inadequate oxygen delivery to tissues.
(it doesn't have a 1:1 relationship with pressure etc.)


3 main determinants of tissue perfusion?
Main driving force?

Overall SVR
Distribution of blood flow
Main driving force is blood pressure.


How does a flow directed PA catheter work? What does it measure?

It's threader through RA -> RV -> PA, then occludes of the branch of the PA (like a pulmonary embolism).
Once occluded, the pressure recorded is a pretty good approximation of LA pressure / a good measure of preload / LVEDP.
(this is also called PA wedge pressure - PAWP)
- the same catheter can be used to measure RA and RV and RA pressures.


4 types of shock? (note that multiple types can be happening at the same time)

Hypovolemic (e.g. bleeding out)
Cardiogenic (e.g. acute MI)
Distributive (e.g. sepsis)
Obstructive (e.g. PE)


Primary pathophysiologic derangement in hypovolemic shock? (How do you measure it?)

Decreased preload (measured with PAWP) -> decreased SV and CO.


How does the body compensate for hypovolemic shock?

Symps -> increased HR, contractility, SVR.


4 symptomatic stages of hypovolemia? At about what % volume loss does each occur?

15% loss: resting tachycardia.
20-25% loss: orthostatic hypotension
30-40% loss: hypotension and oliguria
>40% loss: obtundation and circulatory collapse
(probably more important to know symptoms vs. the exact percentages. Note that hypotension occurs later, so you shouldn't wait until you see that to make your Dx)


Primary pathophysiologic derangement in distributive shock?

SVR way too low due to vasodilation with maldistribution -> wastefully increased CO, but not pressure.


2 phases of distributive shock?

Early: Decreased SVR, increased CO
Late: Heart fails, leading to decreased CO and increased SVR.


Causes of distributive shock?

Sepsis is the prototype, but other inflammatory (e.g. anaphylaxis) / endocrine (e.g. Addisonian crisis) conditions can cause it.


Mediators of sepsis?

Endotoxin (LPS from gram neg bacteria in bloodstream)
Interleukins and TNF.


What's the primary pathophysiologic derangement in cardiogenic shock?

Reduction in CO due to heart failure (myocytes can't contract) -> elevated filling pressures and compensatory increase in SVR (to keep pressure up).


Common causes of cardiogenic shock?

Massive MI with >40% loss of LV myocardium.
Acute valvular disease (e.g. ruptured papillary muscle or endocarditis)
Acute interventricular septal defect


How does cardiogenic shock produce a vicious cycle of damage?

decreased CO -> decreased perfusion of heart -> further heart failure -> further decreased CO


How does the PAWP look in cardiogenic shock?

It's increased - there is increased preload / LA pressure because LV can't contract to eject.


Treatment for cardiogenic shock?

Relieve the ischemia.
(as with all of these, you must treat the underlying cause to save the pt)


What's the primary physiologic derangement in obstructive shock?
What will the RA and RV pressure look like?

"Obstruction" to right heart flow, reducing LV preload.
From perspective of the LV, this looks like hypovolemic shock (reduces preload, SV, CO with compensatory increase in SVR), but RA and RV pressure will be increased.


What's the problem in pericardial tamponade?

Impaired diastolic filling due to external force (blood / fluid in pericardium) opposing relaxation.

(not to be confused with cardiac tapenade)


Why is acute tamponade worse than chronic tamponade?

In chronic, the heart has time to increase compliance / otherwise adapt.


What is pulsus paradoxus?
Why does it happen?

Inspiratory drop in systolic BP (a small change is normal, a large change indicates tamponade)
Normally with inspiration, there is an increase in RV filling -> more right preload, but LV has a small drop in preload -> less SV and pressure.

In tamponade, increased RV filling with inspiration makes the RV push on the LV, decreasing LV filling and thus SV and systolic BP.
(note that PP isn't specific for tamponade)


What must be the pressure drop to meet the definition of pulsus paradoxus?

>10 mmHg


What do you see on echo of pericardial tamponade?

A shadow of pericardial effusion ("echo free space").
Collapse of the RV during diastole.


For hypovolemic shock, what are the RA/RV pressure, PAWP, CO, and SVR?
(low, normal, or increased/high)

RA/RV pressure: Low
PAWP pressure: Low
CO: Low
SVR: Increased (compensatory)


For distributive shock, what are the RA/RV pressure, PAWP, CO, and SVR?
(low, normal, or increased/high)

RA/RV pressure: Normal
PAWP pressure: Normal
CO: Increased (compensatory, but ineffective)
SVR: Low


For cardiogenic shock, what are the RA/RV pressure, PAWP, CO, and SVR?
(low, normal, or increased/high)

RA/RV pressure: High
PAWP pressure: High
CO: Low
SVR: High (compensatory)


For obstructive shock, what are the RA/RV pressure, PAWP, CO, and SVR?
(low, normal, or increased/high)

RA/RV pressure: High
PAWP pressure: Low
CO: Low
SVR: High (compensatory)


How does the SVR change in each form of shock?

SVR is always increased as a compensatory mechanism for low CO, unless SVR being too low is itself the source of the shock - as it is in distributive shock.


What happens to metabolism when tissues are hypoxic?

They use glycolysis and make lactate.... but then die.
(Ion pumps don't work, mitochondria damaged, lysozymes burst, complement activates, etc. etc.)


What's the cell death called / first thing to go when hypoxic in each skeletal muscle, GI tract, kidneys, lungs, liver, and heart? (not that important for now, probably)

Skeletal muscle: rhabdomyolysis
GI: mucosal damage
Kidneys: acute renal tubular necrosis
Lungs: alveolar damage, capillary injury, ARDS
Liver: impaired detoxification
Heart: myocardial depression


3 changes in "pre-shock"?
What notably doesn't change at first?

Sympathetic activation leads to...
Increased contractility
Initially blood pressure and CO are maintained. (shock does not equal low blood pressure)