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Boards Review > Shock Recap > Flashcards

Shock Recap Flashcards

1
Q

Define “shock” (in no more than 6 words, bonus for 4 words).

A

Inadequate cellular energy production

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2
Q

Name/explain the 5 different categories/types of shock and an example of each.

A
  1. Hypovolemic: lack of volume (ex- hemorrhage, severe dehydration)
  2. Cardiogenic: failure of forward flow (ex- CHF, arrhythmia, tamponade)
  3. Distributive: blood not going where it should (ex- sepsis vasodilation, vascular obstruction, GDV)
  4. Metabolic: cells not metabolizing O2 properly (ex- sepsis, hypoglycemia, cyanide)
  5. Hypoxemic: lack of oxygen content in arterial blood (ex- anemia, lung disease, CO toxicity, methemoglobin)
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3
Q

What would be the basic/general treatment strategies for each of the types of shock?

A
  1. Hypovolemic: volume replacement (fluids, blood products)
  2. Cardiogenic: treat CHF (diuretics, inotropes, O2), anti-arrhythmics, pericardiocentesis
  3. Distributive: vasopressors if indicated, remove obstruction (ie heartworms for caval syndrome, anticoagulants/TPA if blood clot, decompress if gastric dilatation)
  4. Metabolic: treat sepsis, O2 supplementation, dextrose PRN
  5. Hypoxemic: oxygen supplementation, transfuse PRN
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4
Q

Fill in the blanks

CO = __ x ____

“Second blank” is dependent on ____ and ___

MAP = CO x __

A

CO = HR x SV (stroke volume)

“Second blank” is dependent on preload and contractility

MAP = CO x SVR (systemic vascular resistance)

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5
Q

Based on what contributes to CO and MAP, what would be the 3 possible broad causes of hypotension?

A
  1. Reduction in preload (hypovolemia)
  2. Reduction in cardiac function (rate or contractility)
  3. Reduction in systemic vascular resistance
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6
Q

What is the body’s physiologic response to acute shock (ie hemorrhage)

A
  • Baroreceptors (in aortic/carotid bodies, JG apparatus) sense decreased BP
  • -> increased sympathetic tone/catecholamine release -> Increased HR and vasoconstriction
  • -> Cortisol release ->many effects including more energy available to cells

-> renin-angiotensin system activation -> Increased fluid retention + vasoconstriction

  • -> vasopressin release -> Increased fluid retention + vasoconstriction
  • All of these help to increase intravascular volume/BP and oxygen delivery- initially can actually have an elevated BP

Eventually, compensatory mechanisms may not be enough (ie ongoing or massive hemorrhage) -> decompensatory shock (bradycardia, impaired contractility, slow CRT, worsened BP, hypothermia, worsened mentation)

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7
Q

Explain the concept of a fluid challenge

A
  • Administer a rapid bolus (20ml/kg of crystalloid or 5ml/kg of colloid) to see if the patient responds appropriately (‘fluid responsive’).
  • Can assess response by a variety of endpoints including BP, clinical perfusion parameters (MM color, CRT, mentation, limb temp), lactate, ScVO2). - If not responding, further fluid boluses are likely not going to be helpfu
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8
Q

Discuss replacement crystalloids in terms of shock resuscitation.

Dose (per bolus in a dog = 1/4 shock):
Duration of action (per JVECC article):
PROS:
CONS:

A

Dose (per bolus in a dog = 1/4 shock): 20ml/kg

Duration of action (per JVECC article): Blood volume sharply decreases as soon as bolus is done, 50% gone by 30 min, 80% gone by 240 min

PROS: Readily available

CONS: Large volume needs to be administered (slower), many neg effects of positive fluid balance (unless were very dehydrated)

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9
Q

Discuss hypertonic saline in terms of shock resuscitation.

Dose (per bolus in a dog = 1/4 shock):
Duration of action (per JVECC article):
PROS:
CONS:

A

Dose (per bolus in a dog = 1/4 shock): 3-5m/kg

Duration of action (per JVECC article): 30% gone at 30 min, 80% gone by 240 min

PROS: Small volume, can be given rapidly, can also help with cerebral edema

CONS: No if pre-existing dehydration, electrolyte imbalances, risk of transient
bradycardia/bronchodilation

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10
Q

Discuss synthetic colloids in terms of shock resuscitation.

Dose (per bolus in a dog = 1/4 shock):
Duration of action (per JVECC article):
PROS:
CONS:

A

Dose (per bolus in a dog = 1/4 shock): 5ml/kg

Duration of action (per JVECC article): BV continues to increase at 30 min after bolus, stable at 240 min

PROS: Smaller volume, can be given rapidly, longer-lasting effect, oncotic support

CONS: Side effects- coagulopathy, renal damage. No survival benefit over crystalloids in human studies, more expensive

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11
Q

Discuss Human albumin in terms of shock resuscitation.

Dose (per bolus in a dog = 1/4 shock):
PROS:
CONS:

A

Dose (per bolus in a dog = 1/4 shock): variable

PROS: Smaller volume, oncotic support without negative effects of synthetic colloid, protects glycocalyx

CONS: Reaction risks in animals, no survival benefit over crystalloids for use in “routine resuscitation” (unsure in hypoalbuminemia)

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12
Q

Discuss whole blood in terms of shock resuscitation.

Dose (per bolus in a dog = 1/4 shock):
PROS:
CONS:

A

Dose (per bolus in a dog = 1/4 shock): variable

PROS: Most physiologic, especially for hemorrhage, contains platelets/clotting factors

CONS: Reaction risks, “massive transfusion” risks

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13
Q

What is an impedence threshold device?
How might it be helpful for shock or CPR?
What would be a contraindication to use?

A
  • A valve that attaches to an ET tube that makes the intrathoracic pressure more negative (opposite of PEEP). This improves venous return to the heart (preload).
  • There are 2 different “cracking pressures”- higher for CPR (12mmHg), lower used for shock resuscitation (7mmHg).
  • AVOID if pulmonary disease (could worsen edema).
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14
Q

What is “dampening”?

A

Dampening is the influence within the system that reduces oscillations from the natural frequency.

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15
Q

Explain how to test the “dampening” of a direct arterial (or CVP) monitoring system.

A
  • Easier method: want 1-2 oscillations after the square wave, each no more than 1/3 of the previous wave’s amplitude.
  • More oscillations = underdamped
    - May overestimate systolic pressure (falsely high)
  • Less oscillations = overdamped
    - May underestimate systolic pressure (falsely low)
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16
Q

List possible causes of over-dampening.

A

long tubing, very stiff tubing, hypothermia, arrhythmia or significant tachycardia

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17
Q

List possible causes of under-dampening.

A

clot in catheter, air bubble in tubing, over-compliant tubing, narrow tubing, loose connections, kinks, arterial spasm

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18
Q

Explain pulse pressure variation and how this can be used to guide shock treatment.

A
  • There are normally minor variations between BP during spontaneous and mechanical ventilation due to changes in intrapleural pressure
  • Hypovolemia magnifies this effect, because the heart and intrathoracic vessels become more collapsible
  • Respiratory associated variation in arterial pressure can be used as an indicator of volume responsiveness
  • If spontaneously breathing, more negative intrathoracic pressure at insipiration (so higher arterial pressure)
  • If under positive pressure ventilation, more positive intrathoracic pressure at inspiration (so lower arterial pressure)
  • Correlates better with volume responsiveness compared to SPV
  • > 15% PPV is more likely to respond to volume than <15% PPV
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19
Q

Pulse pressure variation equation

A

PPV (%) = 100 x [ (PPmax – PPmin) /
(PPmax + PPmin)/2] = mean PP

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20
Q

Label the CVP waveform below and describe what each point correlates to.

A
  1. a-wave: generated by atrial contraction, usually highest point, correlates to just after P-wave on EKG. Mean of a-wave is used to estimate the CVP.
  2. c-wave: may or may not be visible, secondary peak following a-wave, corresponds to bowing of the tricuspid valve into the RA during early RV systole (just after QRS on EKG)
  3. x-descent: decrease in RA pressure caused by atrial relaxation/RV emptying
  4. v –wave: indicates back pressure from atrial diastolic filling, correlates to just after the T-wave on the EKG
  5. y-descent: indicates atrial emptying (opening of the TV, blood flows into ventricle during diastole)
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21
Q

Draw a pulmonary artery catheter and label the parts.

A
22
Q

What does the Proximal Port (CVP Port) of a pulmonary artery catheter do and where does it sit in the patient?

A

Sits in the right atrium, measures RA pressure (aka CVP)

Place to bolus cold fluid for cardiac output measurement

23
Q

What does the Distal Port of a pulmonary artery catheter do and where does it sit in the patient?

A

At very tip of catheter, after balloon

Sits in the pulmonary artery- can collect mixed venous blood samples

With balloon deflated, gives pulmonary artery pressure

With balloon inflated, gives pulmonary capillary wedge pressure

Pulmonary capillary wedge pressure is a indirect measurement of left ventricular diastolic pressure (preload)

24
Q

What does the Thermistor Port of a pulmonary artery catheter do and where does it sit in the patient?

A

connected to patient monitor, measures temperature in the pulmonary artery (just proximal to the balloon)

25
Q

Where in the heart are each of these pulmonary artery catheter pressure tracings located?

A
  1. RA or jugular vein
  2. Right ventricle
  3. Pulmonary artery
  4. Pulmonary artery wedge (surrogate for LA pressure)
26
Q

List possible complications of a pulmonary artery (Swann-Ganz) catheter?

A
  • Arrhythmias/heart block
  • Infection/sepsis/endocarditis
  • Knotting/inability to remove
  • Pulmonary infarct, thrombosis, air embolism
  • Pulmonary artery rupture/hemorrhage (particularly if balloon is overinflated)
  • Valve damage -> regurgitation
27
Q

Briefly explain the concept of the Thermodilution method of cardiac output monitoring including type of instrumentation needed for each.

A
  • Instrumentation: PA catheter
  • Cold saline of known temperature and volume is injected into the cranial vena cava or right atrium (via the proximal port)
  • The blood passes through the ventricle and into the pulmonary artery, temperature is measured at the pulmonary artery
  • The change in temperature is used to calculate the flow (cardiac output)
28
Q

Briefly explain the concept of the Lithium dilution method of cardiac output monitoring including type of instrumentation needed for each.

A
  • Instrumentation: Central venous catheter (or peripheral?), arterial catheter
  • The lithium sensor is attached to the arterial catheter and the cardiac output computer.
  • A dose of lithium is injected into the jugular catheter and the sensor measures the amount of lithium at the arterial catheter, calculating the cardiac output.
  • The same technique can potentially be performed with a peripheral venous catheter, but may be less accurate in dogs.
29
Q

Briefly explain the concept of the Fick method of cardiac output monitoring including type of instrumentation needed for each.

A
  • Instrumentation: central venous catheter or PAC, arterial catheter (or art stick), intubated patient
  • Calculates cardiac output by an equation that uses the oxygen consumption by the lungs and the arteriovenous difference in oxygen
  • CO = oxygen consumption/ AV oxygen content difference
  • CO = V02/ (CaO2–CvO2)
  • Oxygen consumption is calculated by the difference between inspired tidal volume and oxygen concentration and expired tidal volume and oxygen concentration
  • The AV difference is calculated by measuring arterial and mixed venous (from pulmonary artery catheter) blood oxygen and hemoglobin levels
  • This method can also be used with carbon dioxide as the indicator gas
    - CO = CO2 elimination by lungs/ (CaCO2–CvCO2)
30
Q

Briefly explain the concept of the Pulse contour methods (PiCCO2 LiDCO) method of cardiac output monitoring including type of instrumentation needed for each.

A
  • Instrumentation: arterial catheter
  • The area under the pulse pressure waveform has some correlation to stroke volume.
  • An algorithm is applied to the pulse pressure waveform (taking into account arterial impedence, compliance, and resistance) to calculate the CO.
31
Q

Briefly explain the concept of the Transthoracic impedence method of cardiac output monitoring including type of instrumentation needed for each.

A
  • Instrumentation: electrodes
  • Uses 4 paired electrodes to measure changes in transthoracic impedence over the cardiac cycle, then calculates and estimate of stroke volume
32
Q

Define Free radical

A

atom, molecule, or ion that has unpaired valence electrons

33
Q

Define Reactive oxygen species

A

oxidizing agent (usually a free radical) which reacts with biological molecules

34
Q

Define Ischemia

A

period of lack of blood flow/oxygen and lack of energy production

35
Q

Define Reperfusion

A

tissue damage caused when blood supply returns to the tissue after a period of ischemia

36
Q

Define Antioxidant

A

molecule that inhibits oxidation of other molecules/free radical formation

37
Q

Which causes more damage- ischemia or reperfusion?

A

Reperfusion

38
Q

What tissues are most prone to damage by free radicals?

A

Lipids (cell membranes, brain)

39
Q

What are possible methods to reduce or treat ischemia/reperfusion injury?

A
  • Block formation of ROS (NAC, vitamin C, vitamin E, ubiquonol, calcium channel blockers, allopurinol)
  • Scavenge ROS after they are formed (Lidocaine, superoxide dismutase, catalase, deferoxamine, DMSO, nitric oxide, adenosine)
  • Block neutrophils
  • Prevent platelet aggregation
  • Quickly restore circulation (ie GDV)
  • Remove organs without reperfusing them (ie splenic or mesenteric torsion)
  • Prophylaxis is generally more effective than therapy after the fact
40
Q

What are the current guidelines as far as order of beginning CPR?

A
  1. Identify collapsed/non-responsive patient (apneic or agonal)- do not confirm pulse
  2. Chest compressions
  3. Intubate/begin ventilation
  4. IV access, consider reversal agents, other drugs
41
Q

What happens during a basic “cycle” of CPR?

A
  • Continuous compressions at 100-120bpm, compress 1/3-1/2 the width of the chest
  • Continuous ventilation at 10 bpm
  • 2 minutes per compressor without stopping for anything
  • Reassess rhythm between each cycle
    - Epinephrine (or vasopressin) administered every other cycle if in asystole
    - Defibrillate if in V-fib between cycles
42
Q

Explain the cardiac pump theory/technique for chest compressions

A

hands placed directly over the heart, direct compressions of the heart.

Used for cats, small dogs, thin/keel chested dogs.

43
Q

Explain the thoracic pump theory/technique for chest compressions

A

use changes in chest volume/pressure to pull blood into the heart (vacuum), hands placed at widest part of the chest to get maximal change in volume.

Used for larger dogs, less compressible chests.

44
Q

What would be the negative effect of a high ventilation rate during CPR?

A

Increased intrathoracic pressure -> decreased venous return (without enough blood flow to the heart, will not regain spontaneous circulation)

45
Q

Explain the pros/cons of low dose vs high dose epinephrine.

A

High dose has higher return of spontaneous circulation but lower survival to discharge (due to negative effects on organs), so high dose is only recommended for refractory CPR (>10 min).

46
Q

What is the evidence/recommendation for use of atropine during CPR?

A

There is no known benefit for routine use in CPR in human or veterinary studies.
Reasonable to try it every other cycle (alternating with epiphephrine), could routinely use if high vagal tone is suspected (brachycephalic, GI disease).

47
Q

What are indications for use of vasopressin during CPR?

A

As an alternative to epinephrine for routine CPR (no additional benefit or harm compared to epi)

Preferred to epinephrine in severe acidosis

48
Q

True or False?
Explain reasoning for your choice.

Epinephrine should be automatically administered to patients every other CPR cycle regardless of the rhythm assessment (V-fib versus asystole).

A

FALSE- epi should be routinely administered for asystole, but only for refractory V-fib not responding to multiple defibrillation attempts.

49
Q

True or False?
Explain reasoning for your choice.

Administering a single defibrillation shock at a time is preferred to administering “stacked” shocks.

A

TRUE- need perfusion to the heart for the SA node to resume after defibrillation, so further shocks are less likely to be effective than the first one, no benefit to multiple shocks in a row.

50
Q

True or False?
Explain reasoning for your choice.

Defibrillation should be performed immediately in all patients as soon as V-fib is detected.

A

FALSE- immediately only if V-fib detected within 4 minutes of arrest, otherwise should have at least 2 minutes of chest compressions prior to defibrillation (and between defib attempts)

51
Q

True or False?
Explain reasoning for your choice.

All patients receiving CPR should receive a bolus of IV fluids.

A

FALSE- Only if pre-existing hypovolemia. Excessive IVF increases intrathoracic pressure (decreasing return to heart).

52
Q

What is the evidence for the use of therapeutic hypothermia post arrest in humans?
What is the current recommendation in veterinary medicine?

A

Most human studies show significant survival and neurologic outcome improvement when therapeutic hypothermia is initiated during or immediately after CPR.
This is considered standard of care in humans (various techniques including external and core cooling, generally require sedation/mechanical ventilation).

Not routinely performed in veterinary medicine- avoid active rewarming (VERY SLOW if done) and avoid hyperthermia at all costs.

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