Vasoplegia/LV/RV Failure Flashcards
What is the definition of vasoplegia?
Low SVR in the presence of normal or high cardiac output; SVR < 800 dynes with CI > 2.2 L/min/m2
Where does central regulation of vascular tone occur?
Locus ceruleus (SNS) and the hypothalamic-pituitary adrenal axis in the paraventricular nucleus
What are the receptors for vascular tone?
Adrenergic (epi, norepi, DA, phenylephrine) + vasopressin + angiotensin receptors
What occurs at the cellular level with vasoplegia?
Desensitization of the adrenergic, vasopressin, and angiotensin receptors via phosphorylation of the G-protein coupled receptors
How is vascular tone regulated at the intracellular level?
Via nitric oxide; NO synthetase expression is enhanced -> increased NO production -> vasodilation
What receptors does epi hit? Norepi? Phenylephrine?
Epi = alpha1, beta1, and beta 2; Norepi = alpha1 and beta1; Phenylephrine = alpha1
How does methylene blue work for vasoplegia?
Inhibits nitric oxide synthetase (for less NO) and inhibits guanylate cyclase (normally inhibits GMP buildup and promotes smooth muscle vasodilation)
Which patients should you avoid methylene blue in?
Patients with G6PD deficiency -> can cause serotonin syndrome when used with other meds that increase serotonin (i.e. SSRI, TCA, fentanyl, tramadol, cocaine)
How does hydroxycobalamin work in vasoplegia?
Inhibits NO synthetase, nitric oxide, and hydrogen sulfate
What are the side effects of hydroxycobalamin?
Chromaturia (orange/red urine) + erythema + headache + photosensitivity for 2 weeks + abnormal lab values
What abnormal lab values can you see with hydroxycobalamin?
Transient hypokalemia (usually in patients with B12 deficiency) + elevated hemoglobin and basophils (12-16 hours) + elevated creatinine, glucose, and alk phos (24 hours) + LDH, PTT, INR/PT are unreliable (24 hours)
How does angiotensin II work with vasoplegia?
It inhibits renin; hyperreninemia is associated with hemodynamic instability post bypass and replacing angiotensin II can help with vascular tone
What should you dilute methylene blue with?
Anything but normal saline as it can cause precipitation and decreased solubility
How much methylene blue should you give for vasoplegia?
1-2 mg/kg bolus followed by 0.25-0.5 mg/kg/hr infusion
How much hydroxycobalamin should you give for vasoplegia?
5mg bolus and can repeat if needed
What is dromotropy?
Looking at conduction velocity
How do catecholamines work?
Activates beta1 receptors (increased chronotropy, dromotropy, and release of renin)
How does dobutamine work?
Beta1 and beta2 agonist + increases myocardial O2 consumption
How does dopamine work?
Intermediate doses activates beta1 receptors (3-10 mcg/kg/min) while higher doses (10-20 mcg/kg/min) activates alpha1 receptors
How does epinephrine work?
Alpha1, beta1, and beta2 receptor agonist + increased coronary blood flow (via increased diastolic pressures and local cardiomyocyte vasodilators) + increased pulmonary blood flow (via pulmonary vasoconstriction)
How does isoproterenol work?
Beta1 and beta2 agonist + potent systemic vasodilation + mild pulmonary vasodilation
How does norepinephrine work?
Potent alpha1 agonist with some beta1 effects + power vasoconstrictor + increased coronary blood flow (via increased diastolic pressure and local vasodilators in coronaries)
What is the mechanism of action for milrinone?
Phosphodiesterase inhibitor -> increases cAMP by inhibiting PDE -> increases contractility and CO + decreases SVR/PVR + decreased myocardial wall tension
How does levosimendan work?
Augments sensitization of troponin C to calcium + increases coronary perfusion via coronary vasodilation + increases contractility without increasing O2 demand
What are risk factors for postop low cardiac output syndrome?
Age > 65 + LVEF < 50% + on-pump CABG + DM + CKD + CPD duration + emergency surgery + incomplete revascularization
What are some echocardiographic findings of RV failure?
RV free wall hypokinesia + RV dilation + TAPSE < 16mm
What are some causes of chronic RV dysfunction?
Left-sided heart disease (most common) + chronic lung disease + pulm HTN + congenital heart disease + right-sided valvular disease + cardiomyopathies
How can a properly placed LVAD cause RV dysfunction?
The LVAD can uncover preexisting RV dysfunction by increasing venous return to the RV + LV size decreases so the IV septum shifts
How does bosentan and ambrisentan work?
Endothelin receptor antagonists which can help with pulmonary vasodilation; taken as an oral pill
How do inhaled pulmonary vasodilators help with RV function?
Reduces RV afterload (decreased PVR) + improved V/Q mismatch (blood flow increases to well-ventilated areas only)
How does inhaled nitric oxide work?
Increases cellular cGMP -> vasodilates smooth muscle
Why does iNO have such a short half life?
NO is scavanged by hemoglobin as soon as it diffuses into the blood
What are possible side effects of iNO?
Methemoglobinemia (inhaled NO combines with hemoglobin to form nitrosylhemoglobin which is oxidized to metHb) + tachyphylaxis + thrombocytopenia (10% of patients) + lung injury from nitrous dioxide formation + increased risk of lung infection
Can iNO cause AKI?
A meta-analysis suggests only at higher doses (>20ppm) for prolonged periods of time (>7 days)
How does inhaled epoprostenol work?
Synthetic prostacyclin -> stimulates adenyl cyclase -> vasodilation
What is the normal starting dose of iNO? Of inhaled epoprostenol?
iNO = 20 ppm; Inhaled epoprostenol = 50 nanograms/kg/min
What is the half life of inhaled epoprostenol?
2-5 min
What pulmonary artery pulsatility index value is concerning for RV failure?
PAPi < 1.85
What RV stroke work index value is concerning for RV failure?
RVSWI < 400 mmHg*mL/m2
