Lecture 3 - Intraoperative Hypertension

Question 1

Cardiac output equation

Answer 1

CO = HR x SV

Question 2

Systemic vascular resistance equation

Answer 2

SVR = (MAP-CVP) x 80 / CO

Question 3

General causes of hypotension and how to measure them

Answer 3

• Preload = Measure w/ LVEDV
• Contractility = Measure w/ ECHO
• Afterload = Measure w/ SVR
• Heart rate = Important in infants (fixed SV)
• Rhythm = Afib, especially in aortic stenosis (needs good atrial kick)

Question 4

Mean arterial pressure equation

Answer 4

2/3 DBP + 1/3 SBP

Question 5

Definition and causes of narrow pulse pressure

Answer 5

SBP-DBP < 25. Aortic stenosis, coarctation, tension pneumothorax, MI, shock, dampening of the system

Question 6

Definition of widended pulse pressure and causes

Answer 6

SBP-DBP >40. Aortic regurgitation, atherosclerotic vessels, PDA, high output states (thyrotoxicosis, AVM, pregnancy, anxiety)

Question 7

Causes of intraoperative hypotension

Answer 7

• Excessive anesthesia: Induction agent, volatile, or narcotic
• Inadequate preload:
  
  • Hypovolemic shock (hypovolemia, anemia)
  • Increased intrathoracic pressure (PEEP, I:E ratio, PTX) or pneumoperitoneum
  • Spinal anesthesia (affects both preload and afterload)
• Reduced afterload
  
  • Vasodilated states (liver failure, sepsis/SIRS/shock, anaphylaxis)
  • Depleted catecholamine states (adrenal suppression, methamphetamines, cocaine)
• Diminished afterload: Acute MI, non-perfusing arrhythmia, cardiomyopathies, valvulopathies

Question 8

Treating hypotension

Answer 8

• Temporize w/ fluids
• Increase preload = EBL, UOP. Consider CVP, PAC, or TEE
• Ventilation = Reduce PEEP, decrease I:E ratio, rule out pneumothorax
• Metabolic = Treat acidosis and hypocalcemia
• Increase afterload = Decrease volatile anesthetic
• Pharmacologic agents

Question 9

Phenylephrine - Mechanism of action, when to use it, and dosing

Answer 9

• a1 agonist
• Use in vasodilated states w/ tachycardia (can cause bradycardia)
• 100 mcg IV q2-3 min

Question 10

Ephedrine - Mechanism of action, when to use it, and dosing

Answer 10

• a1, b1, b2 (less) agonist
• Direct & indirect-acting agent by releasing endogenous catecholamines
• Increases HR, BP, contractility
• Use in vasodilated, bradycardic, low CO states
• 5-10 mg IV q3-5 min

Question 11

Epinephrine - Mechanism of action, when to use it, and dosing

Answer 11

• a1, a2, b1, b2 agonist
• Used for profound hypotension
• Direct-acting catecholamine on alpha/beta receptors
• Increases vasoconstriction, contractility, HR
• 10 mcg IV q-35 min
• Up to 1mg in code blue situations

Question 12

Dopamine - Mechanism of action, when to use it, and dosing

Answer 12

• Usually used as an infusion
• 5 mcg/kg/min IV (up to 20)
• Increases contractility and HR

Question 13

When to use steroids for hypotension and what dose

Answer 13

Consider 100mg hydrocortisone if steroids used in the past 6 months

Question 14

Causes of intraoperative hypertension

Answer 14

• Light anesthesia, pain, chronic hypertension, cocaine, meth, hypervolemia, drug contamination
• Hypermetabolic state = MH, thyrotoxicosis, NMS, pheochromocytoma
• Elevated ICP = Cushing triad w/ bradycardia and irregular respirations
• Autonomic hyperreflexia = Paraplegic / quadriplegic -> reflex arc (e.g. distended bladder). Spinal cord lesion >T5 or <T10

Question 15

Treatment of hypertension

Answer 15

• Opioids = Treat pain and deepen anesthetic
• Propofol = Quickly sedates light patient, also vasodilation
• Volatile anesthetics = Causes vasodilation while deepening anesthetic
• Beta-blockers = Esmolol, metoprolol, labetalol
• Vasodilators = Hydralazine, NTG, nitroprusside