9. Blood Pressure Monitoring Flashcards
hypotension problems
causes decreased tissue organ perfusion
- stroke, MI, renal failure
postoperative delerium
causes of hypotension (8)
vasodilation
- anesthetic induced
hypovolemia
pt positioning
- head up (reverse trend, beach chair)
vagal response
chronic steroid pts
decreased cardiac contractility/EF
- decr CO
too large BP cuff
lateral decubitus
hypovolemia causes
dehydration/NPO status
blood loss
bowel prep
(reqs 1000-1200mL to replace fluid loss)
hypotension treatments (6)
IV fluids and/or blood products
- volume replacement takes time
vasoconstrictors
- treats anesthetic induced vasodilation
lighten anesthetic
change pts position
- trendelenberg
ionotropes
- improve contractility
stress dose steroids
most common cause of hypotension during surgery
anesthetic induced hypotension
is there any reason to believe low BP isn’t just vasodilation from the anesthetic?
reverse trendelenburg?
high blood loss?
too large BP cuff?
lateral decibutus position?
poor EF?
vagal response after incision?
vasoconstrictors primarily act on
peripheral arterioles
vasoconstrictors mechanism
decr blood flow in peripherals
incr blood flood to vital organs
hypertension problems
LV pumps against greater resistance
incr strain on heart = more O2 consumption
incr strain on cerebral vasculature
–intracerebral hemorrhage and stroke
hypertension etiologies
chronic:
- aging
- poor lifestyle (diet, sedentaty, etc)
Acute:
- pain
- light anesthesia
hypertension treatments
increase depth of anesthesia
narcotics (works if pt is in pain)
vasodilators
blood flow/perfusion and blood pressure
blood flow is proportional to blood pressure
incr BP: incr perfusion
decr BP: decr perfusion
autoregulation of blood flow
ability for an organ to maintain constant blood flow over a wide range of blood pressures
brain
heart
kidneys
cerebral autoregulation range
MAP: 60-160mmHg
renal autoregulation range
MAP: 80-180mmHg
coronary autoregulation range
MAP: 50-120 mmHg
if pt is hypotensive, cerebral blood vessels will
vasodilate
increases cerebral perfusion
if pt is hypertensive, cerebral blood vessels will
vasoconstrict
prevents too much blood flow going to the brain
prevents increase in ICP
cerebral autoregulation curve: Right Shift
chronically hypertensive pts
takes higher than normal BP to keep blood flow to the brain constant
lower autoreg level is higher than normal
renal glomerular filtration rate ceases below what level
MAP 40-50mmHg
what threshold should we keep pt’s BP within during surgery?
20-30% of baseline (preop) MAP value
systolic BP during anesthesia
> 90mmHg
diastolic BP during anesthesia
> 50mmHg
MAP during anesthesia
> 65mmHg
pulse pressure during anesthesia
> 35mmHg
“controlled hypotension”
surgeon request
decreases bleeding at surgical site
caution during “controlled hypotension” requests
sick/chronically hypertensive pts
beach chair position
communicate concerns w/surgeon
If BP falls below autoregulatory range
autoregulation organs receive blood flow, just not as much
If BP rises above autoreg range
autoreg organs receive more blood flow than they should
BF is proportional to blood pressure
autoregulation ability impairement
ischemia
hypercarbia
acidosis
stroke
high end tidal concentration of volatile agent
(>2 MAC)
auscultation is aka
sphygmomanometry
korotkoff sounds disappear (first time)
when artery is completely compressed
no blood flow through compressed artery
korotkoff sounds appear
when artery is partially compressed
blood flow is turbulent in partial compress state
korotkoff sounds disappear (2nd time)
when artery is completely open
blood flow is laminar
systolic BP manual measurement
appearance of korotkoff sound
diastolic BP manual measurement
disappearance of korotkoff sound
NIBP cuff uses
oscillometry
oscillometry
arterial pulses cause oscillations of varying amplitudes in the cuff as it is inflated and deflated
BP cuff above systolic
pulse amplitude is low
cannot be felt
BP cuff at systolic
pulse amplitude increases
can be felt
BP cuff at mean arterial pressure
pulse amplitude at maximum
pulse maximally felt
BP cuff at diastolic pressure (and below)
pulse amplitude decreases
cannot be felt
NIBP cuff determines
systolic
diastolic
MAP
separate readings
oscillometry is accurate w/
regular rhythms
oscillometry is inaccurate w/
irregular rhythms
NIBP cuff sizing: width
20-50% greater than extremity diameter
BP cuff too large
underestimates BP
has to squeeze harder to flatten artery
BP cuff too small or loosely placed
overestimation of BP
has to inflate to higher pressure to compress artery
systolic leg BP
10-20mmHg greater than arm BP
diastolic leg BP
equal (or lower) to BP in arm
MAP in leg
higher in leg than arm
NIBP cuff accuracy
only accurate with adequate distal perfusion
causes of innacurate BP readings
kinked blood pressure tubing
leaning on cuff
defective cuff/cable
limited blood flow to extremity
diagnose false BP readings
move monitoring site
signs low BP is more likely
low EtCO2
lack of SpO2 waveform
clinical causes of hypotension
- induction
- large blood loss
when to be suspicious of false High BP reading
really high diastolic
very narrow pulse pressure
NIBP cuff should not be placed
on operative arm
side of mastectomy or lymph node removal
- lymphedema risk
arm w/AV fistular or AV graft
dialysis
excess waster and fluid removed from blood in pts w/renal failure
2 types of dialysis
hemodyalysis (HD)
peritoneal dialysis (PD)
hemodialysis (HD)
vein/artery access (fistula, graft, central line)
machine draws blood
machine purified blood
machine returns blood to vein
AV fistula
artificial connection between artery and vein
larger vain so pt can tolerate dialysis
vein swells bc under higher (arterial) pressure
MAC anesthesia for surgery
AV graft
artificial tube that connects artery to vein
mature faster than fistulas
higher infection rate/clot risk
central line dialysis
subclavian vein access
short term solution
12 or 14F
peritoneal dialysis
solution infused into peritoneal cavity
waster products diffuse across peritoneum into solution
solution w/waste is drained
renal failure pt management
anemic
restrict fluids
- 500mL bag w/microdrip
cautious of serum [K+] increase
- sux contraindicated
- LR not contraindicated
higher measuring site BP impact
lower BP reading
lower measuring site BP impact
higher BP reading
lateral decibitus BP
dependent arm (lower): BP overestimated
independent arm (upper): BP underestimated
sitting/reverse trendelenberg BP reading
BP in arm will be higher than BP in brain
BP in brain will be lower than the monitor BP reading
phlebostatic axis
4th intercostal space
along mid axillary line
external location of right atrium
only place in a standing pt where blood pressure readings are not affected by gravity
phlebostatic axis
what valve aligns with the phlebostatic axis?
tricuspid
where should blood pressure readings be taken
at the level of the heart
sitting position BP reading
BP in brain is lower than BP in cuff
brain BP estimation
distance from middle of cuff to the external auditory meatus (ear)
every 1 cm above cuff, MAP decreases by 0.77mmHg
