Critical Care - Misc Subjects (Eisenberg)

Question 1

What is nitric oxide (endogenous) produced by?

Answer 1

NO synthase

Question 2

What are 4 isoforms of NO found in our body?

Answer 2

Neuronal NO synthase: smooth muscle dilation of respiratory tracts

Inducible NO synthase: found in cytokines and inflammatory/mast cells (pro/anti inflammatory - currently uncertain)

Mitochondrial NO synthase: leads to cardiac response to hypoxia

Endothelial NO synthase: dilation of pulmonary and systemic vasculature

Question 3

Dead space VS shunt

Answer 3

Dead space: no perfusion (V/Q ratio of infinity)

Shunt: no ventilation (V/Q ratio of zero)

Question 4

Would you use NO as a possible therapy for a shunt or dead space?

Answer 4

Use it for a shunt b/c it can vasodilate unshunted areas that ARE ventilated which takes blood away from the shunted area, increasing V/Q ratios in regions that are still effectively engaging in gas exchange (decreases pulmonary HTN)

Question 5

What does a shunt look like on a CXR?

Answer 5

White solid mass

Question 6

What are some properties of NO?

Answer 6

Odorless

Colorless

Toxic (from cars, cigarettes, and power plants)

Is a free radical that can form NO2

Question 7

When given NO for pulmonary HTN, what limitations will it have on physiologic effects? (oxygenation vs vascular relaxation)

Answer 7

NO will vasodilate as much as it can, but there is a point of vasodilation at which oxygenation will no longer improve (so pt can be at 85% and be stuck there despite continual improvement in pulmonary HTN)

Question 8

Indications for NO..

Answer 8

ARDS

Intraop pulmonary HTN

Heart transplants

LVAD placement (decreases RV work and increases LV preload)

Question 9

It is most beneficial for what population of pts?

Answer 9

critically ill babies with PPHTN (persistant pulmonary HTN)

Question 10

What are some possible side effects of NO?

Answer 10

Increased bleeding time from platelet interactions (animal studies only)

Nephrotoxicity (NO controls glomerular and tubular functions; more research needed)

Formation of NO2 (possible for alveolar damage, PE; uncommon though; alarms are set to inform you of high levels)

Methemeglobinemia (measure 4 hrs after, then once daily)

Rebound* (abrupt withdrawal can cause acute hypoxemia)

Question 11

What is an absolute contraindication to NO?

Answer 11

Methemeglobin reductase deficiency

Question 12

What should your flows be when giving NO? (Remember this is NOT N2O/nitrous oxide)

How should you dose NO?

Answer 12

Minimum flow, no more than your pts minute ventilation

10-20 ppm for hypoxia up to 40 ppm for improvement in pulm HTN

Question 13

How should you wean your pt off NO? Why should you do this?

Answer 13

Go to 10 ppm for 30 minutes

Then go to 5 ppm and go down 1 ppm every 10 minutes

Question 14

What is the main purpose of cardiac balloon pumps?

Answer 14

Optimize myocardial O2 supply and reduce cardiac demand to optimize ventricular performance

Question 15

When does the balloon pump inflate and deflate in the aorta? What effects does it have when it does?

Answer 15

Inflates upon diastole (as soon as aortic valve closes) to increase diastolic pressure (increases coronary artery perfusion)

Decreases afterload when it deflates (when aortic valve opens) during end of diastole (deceases ventricular work and increases CO)

Question 16

Indications for balloon pumps

Answer 16

Failing hearts (there’s a bunch lol but that’s really the common thread)

Question 17

What are absolute contraindications to aortic balloon pumps?

Answer 17

Aortic regurgitation (balloon will increase backflow)

Aortic dissection

Aortic stents (balloon may stretch the stents)

End-stage heart disease with no anticipation of recovery

Question 18

Relative contraindications to aortic balloon pumps

Answer 18

Uncontrolled sepsis

Abdominal aortic aneurysm

Tachyarrhythmias

Question 19

Where should the balloon pump be placed? What happens if it is placed too inferiorly?

Answer 19

Tip should be distal to left subclavian artery @ 2nd to 3rd intercostal space (can be visualized b/c its radio-opaque)

If placed too low, it can impede renal artery flow

Question 20

What does the display ratio (IAB frequency) indicate in an IAB pump?

Answer 20

It represents assistance rate.

1:X means every X beat is assisted.

Question 21

How come you can only depend on the MAP on the display panel to gauge the effect of your IAB pump?

Answer 21

The machine cannot tell the difference between systolic and diastolic augmentation.

Question 22

What is the rule of thumb to detecting early inflation of an IAP pump?

Answer 22

Pressure of when the balloon pump kicks in is much higher than dichrotic notch peak. (it should only be a beat higher)

Question 23

What characterizes optimal inflation?

Answer 23

Dichrotic notch should disappear as soon as balloon inflates.

Dichrotic notch peak should coincide with pressure at which assisted systole begins (or be close)

Question 24

What are the physiological effects of early inflation?

Answer 24

Premature closure of aortic valve, causing increases in LVEDP and PCWP (backlogging)

Increased afterload and LV wall stress

Aortic regurg (due to back pressure)

Increased cardiac O2 demand as heart tries to pump against inflated balloon

Question 25

What is the rule of thumb in detecting late inflation of an IAB pump?

Answer 25

You can still see a dichrotic notch right before balloon inflates (absence of sharp V)

(Balloon inflates too late so you can still see a shadow of the dichrotic notch, or a full one depending on how late it goes off)

Question 26

What is the physiological effect of late IAB pump inflation?

Answer 26

sub-optimal coronary artery perfusion

Question 27

What is the rule of thumb in detecting early deflation of an IAB pump?

Answer 27

If you see that the assisted systole is the same as the unassisted systole (may also see the same for diastole)

Question 28

How can you assess optimal deflation of an IAB pump?

Answer 28

Assisted distole and systole are lower than unassisted diastole and systole.

(Difference more pronounced in diastole)

Question 29

What are the physiologic effects of early deflation?

Answer 29

Suboptimal coronary perfusion

Potential retrograde coronary blood flow (possible angina)

Sub-optimal afterload reduction

Increased cardiac O2 demand

Question 30

What is the rule of thumb in detecting late deflation of an IAB pump?

Answer 30

unassisted diastole (trough after dichrotic notch) is lower than assisted diastole (should be opposite way around)

diastolic augmentation may appear widened (Assisted diastole takes longer)

Question 31

What are the physiological effects of late deflation of an IAB pump?

Answer 31

No afterload reduction

Increased cardiac O2 demand due to LV ejecting against greater resistance (the balloon) - due to increased afterload from the balloon being there

Question 32

What are the indications for controlled ventilation?

Answer 32

Protect airway (eg aspiration risk)

Obstruction

Ventilation needed

Secretions (clearance of bronchial secretions)