Lecture 3 - Perioperative Hypertension Flashcards
What organ systems do HTN effect?
All of ‘em
What are the 3 components that impact blood pressure?
Cardiac ejection
Intravascular volume
Vascular elasticity/tone
Where does systolic blood pressure originate? How about diastolic blood pressure?
Systolic pressure represents how stiff our arteries are (resistance to LV ejection)
Diastolic pressure represents the elastic property of our arteries during recoil. (relaxation after arterial wall stretch)
What is the general effect of age on our blood pressures? Why?
Aging leads to higher systolic pressure, but normal or lower diastolic pressure.
Higher systolic pressure: our vascular system stiffens as we age. Elastic tissue is replaced by stiffer fibers and artherosclerotic plaques, leading to higher resistance during systole.
Normal to lower diastolic pressure: lack of recoil due to decreased elasticity
(diastolic may stay the same because stiffer arteries would require less recoil since they distend less)
In normal situations, our bodies’ blood pressures will increase in response to noxious stimuli.
Is this cause for concern in the peri-operative setting?
It depends.
In normal patients, autoregulatory functions maintain BP in a narrow range.
In elderly patients (and other susceptible groups), autoregulation is not as robust and so the range of BP will be much higher which can be detrimental to perfusion, etc, etc..
What are the respective weaknesses of using mechanical measurement and automated measurement of blood pressures?
Mechanical (Korotkoff sounds): human error
Auto-NIBP: profound BP changes may impact accuracy due to automated range adjustment
What does the dichrotic notch of an arterial pressure reading represent? How about the peak and the trough?
Dichrotic notch: point at which aortic valve closes (@ end of cardiac ejection) to prevent blood from leaking back into the heart ; upward stroke (increased pressure) comes from elastic recoil of the artery
Peak: systolic
Trough: diastolic
Why is excessively high BP dangerous?
Chronically high BP in the perioperative setting (outside of patient’s normal hemodynamic range) may lead to:
- scarring/inflammation of end organs
- high pressure on end organs leading to pathologies (ESRD, CHF)
Why is excessively low BP dangerous?
Chronically low BP perioperatively may lead to hypoperfusion of organs, hypo-oxygenation of organs –> organ failure / damage (esp the brain)
What can happen if we drop a patient’s BP too quickly?
Acute hypoperfusion of end organs, especially the brain (may cause light-headedness or unconsciousness)
Mean arterial pressure equation is..
MAP = [2(DBP) + SBP]/3
DBP = diastolic BP, SBP = systolic BP
What does MAP represent?
Estimation of how much total blood volume is being ejected per LV stroke
What may happen if we increase vascular bed resistance too much through vasoconstricting meds?
Heart failure from overwork (strain due to resistance)
Damage to vessel walls can cause artherosclerosis (scarring of vessel walls) or end organ damage
What is the pulse pressure indicative of?
It is a measure of the difference/gradient between SBP and DBP.
It is proportional to the amount of blood ejected per cardiac cycle.
Can also be used as an indicator of the patient’s volume status.
What is the pulse pressure equation?
PP = SBP - DBP
What does an increase in systolic pressure without a significant change in diastolic pressure usually mean?
Blood volume of cardiac ejection increased with minimal change to the vascular tone
How would vasodilitation effect your blood pressure reading if ejection fraction remained relatively constant?
Lower diastolic pressure.
Ejection fraction may go up due to increase in vascular pool due to dilitation.
(May need peer review on this one)
BP signs of pre-hypertension.
Systolic: 120-139 mm Hg
Diastolic: 80-89 mm Hg
Mean pressure < 93 mm Hg
*Considered high-end normal/pt is at risk
BP signs of hypertension stage 1.
Systolic > 140 mm Hg
Diastolic > 90 mm Hg
Mean pressure > 93 mm Hg
BP signs of hypertensive crisis.
Systolic > 180 mm Hg
Diastolic > 110 mm Hg
When does a hypertensive crisis escalate into a hypertensive emergency?
Organ dysfunction or damage.(must lower BP ASAP!)
What are the categories of hypertension? Describe them.
> Essential hypertension: HTN caused by autoregulation of smooth muscle walls; effected by electrolyte fluxes
> Chemical hypertension: HTN due to vascular volume and electrolyte retention in body; will effect vascular tone of the body
> Renal-vascular hypertension: HTN caused by autoregulation of renal perfusion + fluids and electrolytes at the level of the kidney; can cause excessive BP elevations
How do hypertensive patients differ from non-hypertensive patients in the autoregulation of their BP and HR? Why is this concerning to anesthetists?
HTN pts have an exaggerated BP rise in response to peri-op stimulation.
Their BP can fluctuate up to ~90 mm Hg (VS 20-30) and HR can also reflexively fluctuate up to 40 beats (VS 15-20).
We need to be concerned about this because wide hemodynamic swings can lead to excessive stress on heart and end organs
How should we manage the BP of a HTN patient?
Ensure that their BP is well-controlled (usually with beta blockers) for a certain period of time prior to surgery.
We want to maintain a narrow BP range to minimize wide hemodynamic swings at/around their baseline hemodynamic range.
We don’t want to induce what we believe to be ‘normal’ BPs because their hearts are used to autoregulating its own rhythm and maintaining end organ perfusion at these hypertensive states.
End organs will also learn how to autoregulate its own perfusion to provide adequate feedback to the heart in this chronic baseline range so we don’t want to induce stress by taking the pt too far out of that range.
What are possible (and often seen) effects of anesthesia on physiological components that effect BP?
Baroreceptor response blunting
Intravascular reduction due to dehydration and blood loss
Sympathetic inhibition
Vasodilation
Cardiac depression
Hemodynamic expectations during induction
Elevated BP due to vasoconstriction in response to meds and stimulation
Tachycardia
(Symp NS activation, Parasymp NS blockade)
Hemodynamic expectations during emergence
Elevated BP due to pain, bladder distention, fluid overload
Restoration of vascular tone can also elevate BP (decrease in vessel compliance –> vascular pool (think diastolic) decreases –> more resistance against LV contraction)
Hypoxia and hypercarbia can also lead to higher BP
Normal tensive vs well-controlled hypertensives: how should we manage their hemodynamics?
You don’t really have to manage them differently peri-operatively.
They will both respond similarly to medication. However, do think about what medications HTN pts are on.
What are the threshold BP that indicates a pt is in a poorly controlled state and should not proceed with elective surgery?
Systolic > 170
or
Diastolic > 110
or both (including 170/110)
We need to get these pts on some meds or therapy to better control their BP prior to surgery.
