Lecture 8 (Hypotension)-Exam 3 Flashcards
What is hypotension? What are the values?
- Hypotension is a decrease in systemic blood pressure below accepted low values
- While there is not an accepted standard hypotensive value, pressures less than 90/60 are recognized as hypotensive
- It may be absolute with changes in systolic blood pressure to less than 90 mm Hg or mean arterial pressure of less than 65 mm Hg
How do we calculate MAP?
2/3 diastolic pressure + 1/3 systolic pressure
Blood pressure is continuously regulated via what?
via the autonomic nervous system as a balance of the sympathetic nervous system and the parasympathetic nervous system.
How does parasympathetic and sympathetic nervous system act on the BP?
- The sympathetic nervous system acts to raise blood pressure by increasing heart rate and constricting arterioles.
- The parasympathetic nervous system lowers blood pressure by decreasing heart rate and relaxing arterioles to increase vessel diameter.
Blood pressure modulation
* Blood pressure is modulated by what 2 primary mechanisms?
CO and total peripheral vascular resistance
How do you calculate CO and SVR?
- Cardiac output = Stroke Volume x Heart Rate
- Systemic Vascular Resistance = 80 x (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output
Blood pressure modulation:
* Disease states that reduce stroke volume or heart rate will decrease what?
will decrease the total cardiac output of the heart, functionally decreasing the ability to generate blood pressure
Various medications are also capable of inducing hypotension via what?
via augmenting these biologic parameters
* Disease states that reduce stroke volume or heart rate will decrease the total cardiac output of the heart, functionally decreasing the ability to generate blood pressure
What are disease states that modulate BP? (6)
Disease states include arrhythmias, valvular regurgitation, valvular stenosis, diastolic or systolic heart failure, large volume losses of blood, and cardiac tamponade
What is poiseuille’s law?
- Where L equals the length of the vessel and n equals the viscosity of blood. Functionally, vessel length is not subject to change in the body and viscosity does not rapidly adjust and can be accepted as standard value in most cases. Therefore, the only modifiable physiological value is the radius of the vessel.
- A decrease in arteriolar caliber increases the resistance to blood flow, thus increasing blood pressure. Conversely, increasing the diameter of terminal arterioles will decrease resistance to blood flow, thus decreasing blood pressure.
- Total peripheral vascular resistance is primarily controlled via autonomic neuronal responses to modulate fluctuations in blood pressure
- The natural state for arteriolar smooth muscle tone is to be relaxed with dilated arterioles. Therefore, the absence or blunting of autonomic input by medications or disease states will lead to hypotension.
Blood pressure modulation
* Both cardiac output and total peripheral vascular resistance function as what?
* When cardiac output decreases, peripheral resistance should what? How?
* When peripheral resistance decreases, cardiac output will do what?
- Both cardiac output and total peripheral vascular resistance function as feedback compensation mechanisms for the other in healthy individuals.
- When cardiac output decreases, peripheral resistance should increase via constriction of terminal arterioles to decrease vessel caliber to maintain blood pressure
- When peripheral resistance decreases, cardiac output will increase via increased heart rate to maintain blood pressure.
A decrease in arteriolar caliber increases what? increasing the diameter of terminal arterioles will what?
- A decrease in arteriolar caliber increases the resistance to blood flow, thus increasing blood pressure.
- Conversely, increasing the diameter of terminal arterioles will decrease resistance to blood flow, thus decreasing blood pressure.
Total peripheral vascular resistance is primarily controlled via what?
via autonomic neuronal responses to modulate fluctuations in blood pressure
The natural state for arteriolar smooth muscle tone is what?
is to be relaxed with dilated arterioles. Therefore, the absence or blunting of autonomic input by medications or disease states will lead to hypotension
What are different types of hypotension?
- Cardiogenic
- Orthostatic
- Vasovagal
What is going on with orthostatic hypotension?
- In orthostatic hypotension, a combination of the blunting of the autonomic nervous system and mild hypovolemia from dehydration is the culprit.
- When lying flat, there is even distribution of fluid throughout the body.
- However, on standing heart rate fails to increase appropriately and peripheral resistance fails to increase appropriately leading to a rapid, transient decrease in blood pressure that improves with postural changes. This is classically symptomatic with dizziness and syncope.
Cardiogenic hypotension/shock
* What is it?
* What are some sxs?
* What labs?
- Cardiogenic shock is a failure to achieve sufficient cardiac output with maintained total peripheral resistance.
- Sxs: decrease BP, edema syncope
- Labs: EKG, lactic acid
Defining Cardiogenic Shock
* Defined as what?
Cardiogenic shock is defined as a primary cardiac disorder that results in both clinical and biochemical evidence of tissue hypoperfusion
Defining Cardiogenic Shock
* What is the clinical criteria?
Clinical criteria include a systolic blood pressure of less than or equal to 90 mm Hg for greater than or equal to 30 minutes or support to maintain systolic blood pressure less than or equal to 90 mm Hg and urine output less than or equal to 30 mL/hr or cool extremities
Defining cardiogenic shock:
* Hemodynamic criteria include
Hemodynamic criteria include a depressed cardiac index (less than or equal to2.2 liters per minute per square meter of body surface area) and an elevated pulmonary-capillary wedge pressure greater than 15 mm Hg
Cardiogenic shock:
* What is the MCC cause?
* What are the mechanical defects?(5)
- Acute myocardial ischemia (most common)
- Mechanical defect: acute mitral regurgitation (papillary muscle rupture), ventricular wall rupture (septal or free wall), cardiac tamponade, left ventricular outflow obstruction (hypertrophic obstructive cardiomyopathy [HOCM], aortic stenosis [AS]), Left ventricular inflow obstruction (MS, atrial myxoma)
Cardiogenic shock causes:
* What are contractility defects? (5)
* What can happen (clot)?
* What _ _ failure?
* What can happen to the aorta?
- Contractility defect: ischemic and non-ischemic cardiomyopathy, arrhythmias, septic shock with myocardial depression, myocarditis
- Pulmonary embolus (right ventricular with or without left ventricular failure)
- Right ventricular failure
- Aortic dissection
Cardiogenic shock:
* What are other causes?(4)
Other causes include cardiotoxic drugs (doxorubicin), medication overdose (beta/calcium channel blockers), metabolic derangements (acidosis), electrolyte abnormalities (calcium or phosphate)
Pathophysio of cardiogenic shock dt MI
* Ischemia to the myocardium causes what? What happens in return?
- Ischemia to the myocardium causes derangement to both systolic and diastolic left ventricular function, resulting in a profound depression of myocardial contractility.
- This, in turn, leads to a potentially catastrophic and vicious spiral of reduced cardiac output and low blood pressure, perpetuating further coronary ischemia and impairment of contractility.