Clinical Monitoring 1 - Exam 1 Flashcards
When would we have ventilatory pressure monitoring?
- with invasive ventilation - LMA/ETT
- Ex: PEEP/PIP
What pt population & surgeries require strict temp monitoring/thermoregulation?
- children & elderly
- major surgeries, long surgeries w/ temp changes
What does a Left shift in the oxyhemoglobin curve mean?
What 6 things cause a left shift in the oxyhemoglobin curve?
- that Hb’s affinity for O2 is increased - not as much O2 released to tissues
1. alkalosis (increased pH)
2. Hypocarbia (low CO2)
3. Hypothermia
4. Decreased 2,3 DPG (metabolic byproduct)
5. COHb
6. Fetal Hb
What does a right shift in the oxyhemoglobin curve tell us?
What 4 things can cause a right shift?
- Hb’s affinity for O2 is lower - O2 released easier & used by tissues
1. Acidosis (low pH)
2. Hypercarbia (high CO2)
3. Hyperthermia
4. Increased 2,3 DPG
O2 saturation of Hb
PO2 60mmHg = ____ O2 sat
90%
O2 saturation of Hb
PO2 40mmHg = ____ O2 sat
75%
O2 saturation of Hb
PO2 27mmHg = ____ O2 sat
50%
What 3 things happen to light as it goes through matter?
- transmitted
- absorbed
- reflected
What is the Beer-Lambert Law of Absorption?
relates transmission of light through a solution to concentration of solute
- light absorption measured at wavelengths proportional to # of solutes
Beer-Lambert
What happens w/ low concentration Hb?
- the solutes are not absorbing all of the wavelengths
Beer Lambert
What happens w/ high concentration Hb?
There are way less wavelengths getting through
* the concentrated solutes blocks most of the light
Beer-Lambert
What happens w/ less light path length? What is the example of this?
- normal/constricted vessel - more light gets through
Beer-Lambert
What happens w/ more light path length? What is the example of this?
- Dilated artery/vein - more light is absorbed & less gets through
What are the types of Hb that could be circulating in adult blood?
- Oxyhemoglobin
- Deoxyhemoglobin
- Methemoglobin (Fe3+)
- Carboxyhemoglobin
- Sulfhemoglobin
What is Sulfhemoglobin?
- stable green pigment molecule
- made through oxidation of iron in Hb from sulfa containing drugs
What type of oximetry is the gold standard for measuring carboxyhemoglobin?
Co-oximetry
* regular pulse-ox demonstrates falsely elevated O2 sat
Wavelength Chart
Red light wavelengths
660nm
Infrared light wavelengths
940nm
Deoxyhemogobin (deO2Hb) absorbs more ____ light.
Red light (660nm)
Oxyhemoglobin (O2Hb) absorbs more ____ light.
Infrared (940nm)
What estimates SaO2?
pulsatility of arterial blood flow
What is pulse-ox light transmitted through?
- Skin
- soft tissue
- venous blood
- arterial blood
- capillary blood
- different tissue/solutes
What is the ratio of AC/DC light absorption?
the pulsatile component divided by the non-pulsatile component for each wavelength
- the more tissue your pt has or the more vasodilated = more light absorption
What is DC?
Direct current
* non-pulsatile
* deO2Hb
What is AC?
Alternating Current
* pulsatile
* O2Hb
Carboxyhemoglobin vs. Oxyhemoglobin
COHb absorbs as much light in 660nm (red) range as O2Hb
- falsely elevated SpO2
- Left shift in O2Hb curve - less release of O2
Each ____ increase in COHb will increase SpO2 by ____.
What % COHb do smokers have?
- 1% - 1%
- > 6% in smokers (6% falsely high SpO2)
What 6 things can interfere w/ the pulse-ox read out?
- Ambient light
- Low perfusion (low CO, shock, vasoconstricted)
- Venous blood pulsations = altered AC (pulsatile)
- Additional light absorbers (methylene blue)
- Additional forms of Hb (fetal Hb, COHb)
- Nail Polish
When would you have pulsatile venous blood flow?
- infant - transposition of great vessels
- alteration in R heart return
- AV fistulas
What types of surgeries would methylene blue be administered?
- Renal cases
- Cysto cases
- bladder cases
- in ICU for other indications (vasoplegia)
What happens w/ a pulse-ox reading in response to methylene blue admin?
- falsely low until methylene blue circulates & gets out of system
Pulse-ox and CO measurement
- pulse ox may indicate CO status
- looks like A-line waveform = GREAT CO
- Dampened = POOR CO
look for trends
Where is a good spot to place a pulse-ox in someone w/ an epidural?
On their toes - vasodilated w/ epidural
Why should a pulse-ox not be placed on the index finger?
- when pts wake up they stab themselves in the eye (corneal abrasion)
What areas of the body are less affected by vasoconstriction and will reflect desaturation quicker?
- Tongue, Cheek, Forehead
What produces korotkoff sounds?
- turbulent flow beyond the partially occluded cuff
Korotkoff Sounds
Phase I:
Phase II:
Phase III:
Phase IV:
phase V:
- most turbulent/audible (SBP)
- softer & longer
- crisper & louder
- softer & muffled
- sounds disappear (DBP)
Formula for MAP
MAP = DBP + 1/3(SBP-DBP)
What are 5 limitations to BP Auscultation?
- decreased peripheral flow
- changes in vessel compliance (edema, atherosclerosis)
- incorrect cuff size
- obesity
- kids
Appropriate Cuff Bladder
- 40% of arm circumference
- 80% length of upper arm
- center over the artery
Automatic BP
What BP measurement has the least agreement w/ invasive BP monitor?
SBP
* esp. in critically ill/elderly
What conditions produce errors w/ automatic BP monitoring?
- atherosclerosis (low SBP & high DBP = narrowed PP)
- edema
- obesity
- chronic HTN
BP cuff size & BP measurement
cuff too large =
cuff too small =
large = low BP
small = high BP
BP machines - problems w/ estimation
- underestimate MAP during HTN
- overestimate MAP during HoTN
- underestimate SBP/overestimate DBP
Possible complications of automatic BP measurement
- Compartment Syndrome
- Pain (Raynaud’s)
- Peteichiae/ecchymoses
- limb edema
- Venous stasis & thrombophlebitis
- peripheral neuropathy
When should we use caution w/ automatic BP?
- severe coagulopathies
- peripheral neuropathies
- arterial/venous insufficiency
- recent thrombolytics
What are 4 indications for invasive BP monitoring?
- continuous, real time measurement needed
- planned pharmacologic manipulation
- repeated blood sampling
- determination of volume responsiveness
Monitoring sites for invasive BP monitoring
- Radial: most common
- Ulnar
- Brachial: impedance of flow
- Axillary
- Femoral - hidden hematoma
- Posterior Tibial
- Dorsalis pedis
How to perform Allen’s Test:
- occlude radial & ulnar arteries
- pt makes a fist - exsanguination of palm
- release of ulnar artery
- color should return in seconds
- poor predictive value!
Seldinger’s Technique for A-line insertion
- Prop the wrist on a towel & tape fingers back
- 30-45 degree angle - go in w/ needle
- thread guidewire
- remove needle
- place cath & take guidewire out
Transfixion Technique for A-line placement
- same positioning & prep as Seldinger’s
1. front & back walls punctured intentionally
2. needle removed
3. needle removed
4. cath withdrawn until pulsatile blood flow appears - then advanced
What anatomic location is the A-line leveled at?
Aortic root
What 3 things can we do to maximize the A-line waveform?
- limit stopcocks
- limit tubing length
- non-distensible tubing
What is 1 labeling?
Systolic Upstroke
* right after the R wave in EKG
What is 2 labeling?
Systolic peak pressure
What is 3 labeling?
Systolic Decline
What is 4 labeling?
Dicrotic notch (aortic valve closing)
What is 5 labeling?
Diastolic runoff - valves are closed & blood is running back in
What is 6 labeling?
End-Diastolic Pressure
What will the arterial waveform look like closer to the aortic arch?
Further from the aortic arch?
- closer - more crude
- Further (pedal/femoral) - more smooth
Characteristics as arterial pressure wave moves to periphery
- arterial upstroke steeper
- systolic peak higher
- dicrotic notch later (Aortic Valve)
- End-diastolic pressure lower
How are arterial pressure waveforms made?
- summation of sine waves
- fundamental wave + harmonic wave = arterial pressure wave
6 - 10 harmonics needed for most arterial pressure waves
________ ________ is analysis of the summation of multiple sine waves and gives us the projection on the screen.
Fourier Analysis
Arterial Waveform
What does a distinct dicrotic notch suggest?
the system has good resolution @ higher frequencies
* not overdamped
Arterial Waveform
How many oscillations should follow after a fast flush in the square wave test?
- no more than 2
- amplitude should be no greater than 1/3 of previous oscillation
- time interval b/w the 2 <30msec = 33Hz
What is an underdamped arterial waveform?
- multiple oscillations after fast flush
- SBP overestimated
- several dicrotic notches
What is an overdamped arterial waverform?
- pressure tracing does not oscillate after fast flush
- dicrotic notch lost
- SBP decreased & falsely narrowed PP
Arterial BP monitoring
What 5 things can cause Pressure Gradient Changes
- age (less compliance = SBP higher & DBP lower = increased PP)
- atherosclerosis
- peripheral vascular resistance changes
- septic shock
- hypothermia
What are 5 possible Arterial line complications?
- distal ischemia/pseudoaneurysm
- hemorrhage/hematoma
- arterial line emboli
- local infection
- peripheral neuropathy
What is the purpose of pressure waveform analysis?
to identify the presence of residual preload reserve
* assess to see if pts will tolerate a fluid bolus
What does pressure waveform analysis look at?
cyclic arterial BP variations d/t respiratory induced changes in intrathoracic pressure
BP changes w/ PPV
- BP goes up on inspiration (increased LV preload and decreased LV afterload)
- BP goes down on expiration (LV preload reduced b/c decreased venous return)
What is Systolic Pressure Variation (SPV) looking at?
cycle of increasing & decreasing SV and arterial BP in response to end-expiratory pressure
Normal SPV (swing) in mechanically vented pts
7-10mmHg
Normal change up in SPV (inspiration)
2-4mmHg
Normal change down in SPV (swing) - expiration
5-6mmHg
what is increased SPV indicative of?
The pt will be volume responsive or have residual preload reserve
- critically ill - dramatic increase in SPV is usually from the down component (> 5-6mmHg)
What is PPV (pulse pressure variation) looking at?
- maximum and minimum pulse pressures over the entire respiratory cycle
- also assess fluid status of the pt (high is dry)
What is normal PPV?
< 13-17%
b/w 13-17% or > will have positive response to vol. expansion
PPV 14% = give volume
SVV (stroke volume variation) correlates ________ and ________ based on age and gender.
- resistance
- compliance
Formula for SVV =
SVV = (SV max - SV min)/SV mean
SVV normal
10-13%
* > 10-13% positive response to volume expansion
What 6 things are necessary to have an accurate assessment of BP variation?
- mechanical ventilation (Vt 8-10mL/kg)
- PEEP > or = 5mmHg
- regular cardiac rhythm
- normal intra-abdominal pressure (closed cavity)
- Closed chest
- pt positioning