Question | Answer |
BP frequency | induction q 1 min
maintenance q 2.5 min
document q 5 min per ASA |
indicator of end-organ perfusion | arterial bp |
what is a good bp depends on | 1. pt baseline, pmh
2. surgical procedure
3. generally w/in 20% of baseline |
SBP | 1. peak pressure during systolic contraction
2. correlates with changes in myocardial O2 consumption |
DBP | 1. trough pressure during diastolic relaxation
2. determinant of coronary perfusion |
MAP definition | 1. time-wt'd avg of arterial pressures during a pulse cycle
2. most useful for assessing organ perfusion |
MAP formula | SBP + 2(DBP) / 3 |
pulse pressure | difference bw systolic and diastolic pressures |
NIBP accuracy depends on | 1. proper cuff size
2. positioning (leaned on, tucked, etc)
3. HR (tachy, brady, irreg. ↓ accuracy) |
proper NIBP cuff size | 1. rubber bladder should be 1/2 way around extremity
2. with 20%-50% > diameter of extremity
~too narrow - over estimate SBP
~too wide - underestimate SBP |
don't place NIBP on | extremities with PIV or vascular abnormalities (fistulas, mastectomy) |
if must place NIBP on arm with PIV | place IV tubing underneath cuff to prevent extravasations |
SBP by Palpation | ~old, unreliable ~no dbp, map ~simple, cheap
1. locate palpable peripheral pulse
2. inflate cuff proximal to pulse til occluded
3. release cuff by 2-3mmHg/beat
4. measure cuff pressure where pulse palpable |
SBP by doppler probe | ~old
1. same as palpation, except with doppler instead of finger.
2. need lube, accurate position above artery |
BP by auscultation | 1. inflate cuff to pressure bw sbp, dbp
2. underlying artery partially collapses and produces korotkoff sounds
3. auscultate w/ stethoscope placed under inflated bp cuff
4. SBP = onset of sounds
5. DBP = disappearance of sounds |
BP by oscillometry | ~preferred ~versatile ~quick ~accurate
1. microprocessor derives SBP, DBP, MAP using an algorithm
2. arterial pulsation causes oscillations in cuff pressure
3. small when cuff > SBP
4. at SBP, markedly ↑
5. at MAP, maximal
6. after MAP, ↓ |
BP by plethysmography | ~peds ~unreliable w/ ↓ perfusion
1. arterial pulsations transiently ↑ blood vol in extremity
2. finger photoplethysmograph consists of light-emitting diode and photoelectric cell |
BP by arterial tonometry | ~@ Christ hospital ~freq calibration ~sensitive to movement
1. measures beat to beat pressure
2. senses pressure required to partially flatten a superficial artery supported by bony structure ie radial |
NIBP limitations | arrythmias |
Art Line - Invasive BP monitoring | GOLD STANDARD |
A line indications | 1. elective ↓ bp (to ↓ blood loss)
2. wide intra-op bp swings (pheochromocytoma)
3. end organ disease necessitating beat to beat pressure regulation
4. multiple ABG's
5. 1 lung ventilation
6. cardiac/major vascular surgery
7. strict bp paramet |
A line contraindications | 1. no collateral blood flow
2. suspicion of pre-existing vascular insufficiency |
radial a line | ~most common site
~superficial location
~collateral flow (5% lack collateral flow) |
test for collateral flow before radial a line insertion | 1. doppler probe
2. plethysmography
3. pulse ox (waveform w/ compressed artery)
4. allen's test (not reliable; need pt cooperation) |
allen's test | 1. exsanguinate hand by pt making fist
2. manually compress radial & ulnar arteries
3. relax hand
4. release pressure over ulnar artery
5. observe return of color
< 5 sec = collateral flow
5-10 sec = inconclusive
> 10 sec = inadequate circulati |
ulnar a line | ~more difficult d/t deeper, tortuous
~do NOT attempt if radial has been tried |
brachial a line | ~large, easily ID'd AC fossa
~less waveform distortion d/t proximity to aorta |
femoral a line | ~last resort
~prone to pseudoaneurysm & atheroma
~↑ infection & thrombosis
~peds complication: aseptic necrosis of femur head |
dp/pt a line | ~distorted waveforms d/t distance from aorta |
axillary a line | ~axillary plexus nerve damage d/t hematoma or traumatic cannulation
~air/thrombi quickly travel to brain during retrograde flusshing of L ax artery |
a line complications | 1. hematoma
2. bleeding
3. vasospasm
4. arterial thrombosis
5. embolization of air bubbles/thrombi
6. necrosis of skin overlying catheter
7. nerve damage
8. infection
9. loss of digits
10. unintentional intra-arterial drug injection |
↑ risk of a line complications | 1. prolonged cannulation
2. HLD
3. repeated insertion attempts
4. female
5. CP bypass
6. pressors
7. prolonged shock
8. pre-existing PVD |
↓ risks of a line complications by | 1. keep ratio of catheter to artery site small
2. heparinized saline at 2-3 ml/hr
3. limit flushing of catheter
4. meticulous attention paid to aseptic technique
5. place pulse ox to monitor perfusion during insertion |
a line pressure system frequency | 1. must exceed natural frequency of arterial pulse
2. most transducers > 200 Hz
3. stopcocks, air, extra tubing ↓ frequency |
a line underdamp | leading to overshoot ~ SBP falsely high (overestimated) |
a line over damp | frequency response too low ~ SBP falsely low (underestimated) |
keys to accurate a line waveform | 1. minimize tubing length
2. eliminate stopcocks
3. remove air
4. low compliance tubing
5. smaller catheters improve underdamped system & ↓ risk for vascular complications |
pressure transducer | 1. contains a diaphgram that is distorted by an arterial pressure wave
2. mechanical energy converted to electrical signal |
strain gauge principle | stretching a wire or silicone crystal changes its electrical resistance ~ pressure transducers based on this |
Wheatstone bridge circuit | pressure transducer sensing elements arranged so voltage output is proportionate to pressure applied to diaphragm |
zero the a line | 1. must move with pt
2. check regularly with position, temp changes
3. when pt is seated - brain arterial pressure differs significantly from LV pressure, so level at the ear, which approximates the Circle of Willis |
a line waveform upstroke | ~contractility
1. faster = ↑ contractility or ↓ SVR
2. slower = ↓ contractility or ↑ SVR |
a line waveform downstroke | peripheral vascular resistance |
a line respiratory variation | hypovolemia |
a line dichrotic notch | ~AV closure ~CO determines position on limb
~↑ = ↑ SV
~↓ = ↓ SV (hypovolemic) |