What is nitric oxide (endogenous) produced by?
What are 4 isoforms of NO found in our body?
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
Dead space VS shunt
Dead space: no perfusion (V/Q ratio of infinity)
Shunt: no ventilation (V/Q ratio of zero)
Would you use NO as a possible therapy for a shunt or dead space?
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)
What does a shunt look like on a CXR?
White solid mass
What are some properties of NO?
Toxic (from cars, cigarettes, and power plants)
Is a free radical that can form NO2
When given NO for pulmonary HTN, what limitations will it have on physiologic effects? (oxygenation vs vascular relaxation)
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)
Indications for NO..
Intraop pulmonary HTN
LVAD placement (decreases RV work and increases LV preload)
It is most beneficial for what population of pts?
critically ill babies with PPHTN (persistant pulmonary HTN)
What are some possible side effects of NO?
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)
What is an absolute contraindication to NO?
Methemeglobin reductase deficiency
What should your flows be when giving NO? (Remember this is NOT N2O/nitrous oxide)
How should you dose NO?
Minimum flow, no more than your pts minute ventilation
10-20 ppm for hypoxia up to 40 ppm for improvement in pulm HTN
How should you wean your pt off NO? Why should you do this?
Go to 10 ppm for 30 minutes
Then go to 5 ppm and go down 1 ppm every 10 minutes
What is the main purpose of cardiac balloon pumps?
Optimize myocardial O2 supply and reduce cardiac demand to optimize ventricular performance
When does the balloon pump inflate and deflate in the aorta? What effects does it have when it does?
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)
Indications for balloon pumps
Failing hearts (there's a bunch lol but that's really the common thread)
What are absolute contraindications to aortic balloon pumps?
Aortic regurgitation (balloon will increase backflow)
Aortic stents (balloon may stretch the stents)
End-stage heart disease with no anticipation of recovery
Relative contraindications to aortic balloon pumps
Abdominal aortic aneurysm
Where should the balloon pump be placed? What happens if it is placed too inferiorly?
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
What does the display ratio (IAB frequency) indicate in an IAB pump?
It represents assistance rate.
1:X means every X beat is assisted.
How come you can only depend on the MAP on the display panel to gauge the effect of your IAB pump?
The machine cannot tell the difference between systolic and diastolic augmentation.
What is the rule of thumb to detecting early inflation of an IAP pump?
Pressure of when the balloon pump kicks in is much higher than dichrotic notch peak. (it should only be a beat higher)
What characterizes optimal inflation?
Dichrotic notch should disappear as soon as balloon inflates.
Dichrotic notch peak should coincide with pressure at which assisted systole begins (or be close)
What are the physiological effects of early inflation?
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
What is the rule of thumb in detecting late inflation of an IAB pump?
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)
What is the physiological effect of late IAB pump inflation?
sub-optimal coronary artery perfusion
What is the rule of thumb in detecting early deflation of an IAB pump?
If you see that the assisted systole is the same as the unassisted systole (may also see the same for diastole)
How can you assess optimal deflation of an IAB pump?
Assisted distole and systole are lower than unassisted diastole and systole.
(Difference more pronounced in diastole)
What are the physiologic effects of early deflation?
Suboptimal coronary perfusion
Potential retrograde coronary blood flow (possible angina)
Sub-optimal afterload reduction
Increased cardiac O2 demand
What is the rule of thumb in detecting late deflation of an IAB pump?
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)
What are the physiological effects of late deflation of an IAB pump?
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
What are the indications for controlled ventilation?
Protect airway (eg aspiration risk)
Secretions (clearance of bronchial secretions)