E1 Flashcards
What is pulse oximetry dependent on to obtain a measurement?
Pulsatile expansion
Automatic BP standards and important considerations
Average difference +/- 5 mmHg
In reality
• Large variances
• Underestimate MAP during HTN
• Overestimate MAP during HoTN
• Ankle, thigh, calf cuffs never validated
Averaging/trending for measurements reliability
What information is provided by EtCO2
PRIMARY= ventilation
- Pulmonary blood flow
- Aerobic metabolism
- Placement of endotracheal tube/LMA
- Integrity of breathing circuit
- Adequacy of cardiac output
- Dead space (VD) to tidal volume (VT)
Causes, solutions, and description of overdampened system
•↓ SBP=underestimated •↑DBP=over estimated • No dicrotic notch •↓ pulse pressure •Loss of detail d/t • System too rigid • System too short Fix= extension • Problem w/ Fluids/pressure bag Not enough pressure on bag Bag is empty Fix=change bag; ↑ pressure • Air bubbles Fix=remove bubbles from system
What is the law of absorption
Beer-Lambert equation
• If a known intensity of light illuminates a chamber of known dimensions
• then the concentration of a dissolved substance can be determined
Mechanism of metabolic alkalosis
increase PCO2
What are causes of respiratory alkalosis
Increased minute ventilation Over ventilation Abnormal CNS ventilation pulmonary insult (PE) Liver failure sepsis pregnancy
Abnormal renal [hco3] reabsorption and [h] elimination is…
Metabolic acidosis or alkalosis
Characteristics of Oxyhgb dissociation curve in lungs vs tissues/capillaries
O2 uptake in lungs
• Bloody nearly saturated
• Across large range of tensions (LEFT shift)
During passage through systemic capillaries
• Large amount of O2 released (RIGHT shift)
• Relatively small drop in tension
As long as blood is saturated
What is the diagnostic accuracy of invasive BP monitoring?
About 80% accurate
• For color change at 5 second
Pulse oximetry, Doppler doesn’t improve
Describe waveforms of art-line
1: systolic upstroke • Pulsatile flow down artery 2: systolic peak pressure • As ventricle repolarizes 3: systolic decline • Begin diastole 4: dicrotic notch • Produced by blood pushing back on aortic valve • Diastole 5: diastolic runoff • Atrial contraction 6: end-diastolic pressure • DBP
Causes of increased PetCO2 d/t decreased alveolar ventilation
Hypoventilation Resp center depression NM disease High spinal anesthesia COPD
Drawback to sidestream EtCO2 measurement
analyzers have a delay time and rise time
the concept being similar to other expired gas analysis
What determines pH in ECF?
A-B balance between [HCO3] and [CO2]
What physiologic action alters CO2?
Why is this important?
- lung ventilation
- Can help correct respiratory disorders quickly
AANA monitoring standards
Oxygenation
Ventilation
CV
Oxygenation Clinical observation Pulse oximetry ABG’s as indicated Ventilation Auscultation Chest excursion ETCO2 Pressure monitors as indicated Cardiovascular ECG Auscultation as needed BP and HR q 5minutes
Disadvantages of automatic BP. Rationales
Unsuitable in rapidly changing situations Patient discomfort Clinical limitations • Extremes of heart rate, pressure Can cause trauma d/t frequent recycling • Coagulopathies • Peripheral neuropathies • Arterial/venous insufficiency • Compartment syndrome
What is the degree of weak acid dissociation determined by?
What are examples of weak acids?
pH
Temperature
Examples:
albumin, phosphate
What are symptoms of respiratory acidosis
vasodilation
narcosis
cyanosis
Arterial line complications
Distal ischemia or pseudoaneurysm Hemorrhage, hematoma Arterial embolization Local infection Peripheral neuropathy • Nerves and vessels in close proximity
What is the Stewart approach to A-B balance interpretation?
Understanding how strong ion difference (SID), weak acid concentration [Atot] and PaCO2 affect AND explain A-B balance
What is SaO2
A ratio of reduced (deoxygenated) Hb to all Hb
What are limitations and their causes to auscultating BP
↓ peripheral flow • Shock • Intense vasoconstriction Changes in vessel compliance • Severe edema • Calcific arteriosclerosis Shivering incorrect cuff size
What is systolic pressure variation represent and why does it occur
SV changes btwn LH and RH
D/T increased intrathoracic pressure and lung volumes
INC LH and DEC RH SBP d/t end-exp pressure
What happens when lung volume increases from increased intrathoracic pressure to left ventricular preload, afterload, SV
INC LV preload
DEC LV afterload
INC LV SV
Invasive BP monitoring sites
Radial Brachial Posterior tibial Axillary Dorsalis pedis Femoral
Describe the stepwise approach of the traditional A-B analysis. 7 steps
- Is patient hypoxic?
- Is the pH normal?
- Is it respiratory or metabolic? and What are PaCO2 and HCO3 levels?
- Simple or mixed?
- Compensated, partially or uncompensated?
- Suspected or actual cause?
- Treatment?
How is systolic pressure variation measured? Effects of mechanical ventilation
Min pressure, compared to Max pressure
In mechanically ventilated patients
• Normal = 7-10mmHg total
Treatment of respiratory acidosis
Increase Vm
Ventilator setting changes = increase RR or Vt
Treat cause
How are arterial waveforms made?
Summation of sine waves
Fundamental wave + harmonic wave = typical pressure wave
•Fundamental wave = Expansion & contraction of vessel in response to pressure wave
• Systolic
•Harmonic wave = “echo” or “ripple” effect of wave
• Diastolic
What happens when lung volume increases from increased intrathoracic pressure to right ventricular preload, afterload, SV
DEC RH preload/VR
INC RH afterload
DEC RH SV
Distal pulse difference in waveforms in periphery
As pressure wave moves TO periphery: • Arterial upstroke steeper • Systolic peak higher • Dicrotic notch later • Seen later in waveform Longer distance for sine wave to travel • End-diastolic pressure lower • Wider pulse pressure
What are the 3 major causes of decreased PetCO2
Equipment malfunction
Decreased CO2 production and delivery to lungs
Increased alveolar ventilation
Acidic or alkalotic?
[H+] > [OH-]
[OH-]>[H+]
[H+] > [OH-] = acidic
[OH-]>[H+] = alkalotic
What is the bohr equation
(Vd/Vt) = [(PACO2 - PeCO2)/PACO2)
What happens to dissociation curve if blood poorly saturated
• Small amounts of O2 released
• LARGER drop in tension
Steep slope of dissociation curve
What is the treatment for respiratory alkalosis?
Decrease minute ventilation
Make ventilator changes (dec RR or Vt)
Treat cause
What are 3 rules of A-B balance
- Electrical neutrality
- Dissociation equilibriums
- Mass conservation
4 types of adult hb
- Oxyhemoglobin (HbO2)
- Reduced Hb (deoxy)
- Methemoglobin (metHb)
- Carboxyhemoglobin (COHb)
Pulse pressure variation equation
PPV=[(PPmax-PPmin)/(PPmax + PPmin)/2] x100
EtCO2 monitor requirements
CO2 reading within +/- 12% of actual value
Manufacturers must disclose interference caused by ethanol, acetone, halogenated volatiles
Must have a high CO2 alarm for inhaled and exhaled CO2
Must have an alarm for low exhaled CO2
What are Korotkoff phases?
Phase 1 • the most turbulent/audible (SBP) Phase II-III • sound character changes Phase IV-V • muffled/absent (DBP)
How does HbCO compare to HbO2 at 660 and 940? How does HbCO affect SpO2, especially in smokers?
Absorbs as much light in the 660 nm range as oxyhemoglobin does
Falsely elevates SpO2
Each 1% ↑ COHb will ↑ SpO2 1%
Many smokers have >6% COHb
What is SVV
Computer analysis of arterial pulse pressure waveform
Area under the waveform
Correlates resistance and compliance
based on age, gender
computes SV
Describe the Allen’s test
Compresses radial and ulnar arteries Patient makes a tight fist • Exsanguinating the palm Patient opens hand Release ulnar artery • Color of palm should return in < 10 seconds
SV pressure curve and contractility
slope directly r/t contractility
High slope = high contractility
INC stretch = INC contractility = INC CO/SV
Low slope = low contractility
Less stretch = low contractility = dec CO/SV
d/t dec preload
What occurs to substances with polar bonds in water
They dissolve or dissociate into component parts
Degree of H2O dissociation and [H+] is affected by what 3 things
Strong ions
Weak Acids
CO2
How is light absorption affected by solute concentration?
Light absorption must be measured at wavelengths equal to the number of solutes
• More solutes = more light absorbed
• Less solutes absorbs less light
What are symptoms of respiratory alkalosis?
Vasoconstriction, lightheadedness, visual disturbances, dizziness, possible hypocalcemia
Physiologic cause of metabolic alkalosis
Net loss of H+
addition of HCO3-
Causes, solutions and description of underdampened system
•↑ SBP = exaggerated •Square wave Too much oscillation •System TOO responsive (↑ resonance) d/t: • Longer tubing Transmits extra waveforms Fix=Decrease tubing length • Tubing too distensible Fix=Use stiffer tubing
What is the traditional and stewart interpretation of respiratory
Traditional = increased PaCO2 and decreased pH
Stewart = increased PaCO2
What factors are considered in the Stewart approach?
- PaCO2
- Strong ion difference (SID)
- Total weak acid concentration [Atot]
Principles of distal pulse amplification
Arterial pressures measured at different sites
will have different morphologies
• Due to impedence changes along vascular tree
Causes of hypocarbia
Respiratory alkalosis
Decreases CBF
Potassium shifts to the intracellular space
Blunts normal urge to breath
Equation for SVV
SVV= SV max – SV min / SV mean
Inflation and bladder standards for BP
Maximum cuff pressure • 300mm Hg for adults • 150mm Hg for neonates To prevent extended inflation Cuff bladder • 40% of arm circumference • 80% of length of upper arm
Expected PCO2 compensation in metabolic alkalosis
PaCO@ = (0.7 x HCO3-) +20
What is normal range of PaO2 pH PaCO2 HCO3 Anion Gap
PaO2= 80-100 mmHg (90) pH= 7.35-7.45 (7.4) PaCO2= 35-45 mmHg (40) HCO3= 22-26 mEq/L (24) Anion Gap= 14-18 mEq/L (16)
What does and increased SPV indicated? How should it be addressed?
indicates= early hypovolemia
Give fluid
SpO2 limitations (10)
Failure to determine sat Poor function with poor perfusion Difficulty in detecting high partial pressures Delayed hypoxic event detection Erratic performance with dysrhythmias Inaccuracy with different hgb Inaccuracy with dyes Optical interference Nail polish and coverings Motion artifact
Causes of hypercarbia
Respiratory acidosis
Increases cerebral blood flow
Increases ICP in susceptible patients
Increased pulmonary vascular resistance
Potassium shifts from intracellular to intravascular
How are SID and Atot related?
Inversely
Acidosis = DEC SID/INC Atot
Alkalosis = INC SID/DEC Atot
How is light transmitted when measuring SpO2
Via Skin Soft tissue Venous blood Arterial blood Capillary blood
How do changes in SID affect A-B balance?
What is normal ECF SID?
- Changes in SID cause changes in [H] and [OH]
- INCREASED SID = alkalosis
- DECREASED SID = Acidosis
-Normal = 40-44 mEq/L
Advantages of automatic BP
Automaticity Simplicity Noninvasive Reliable Monitor integration • Pulse ox doesn’t alarm if BP monitor inflates
First knowledge of pulse?
First recorded BP ?
First sphygmomanometer?
Ancient China and India had some knowledge of pulse
1st recorded blood pressure: 1733 by Reverend Hales on a horse
1st sphygmomanometer: 1881 invented by Samuel von Basch
What are the signs of acute and chronic respiratory alkalosis compensation
Acute = HCO3 will decrease
2 mEq/L for q 10 mmHg decreased CO2 (down to 20)
Chronic = HCO2 will decrease
5 mEq/L for q 10 mmHg decreased CO2 (down to 20)
Traditional and stewart interpretation of respiratory alkalosis
Traditional = decreased PCO2 and increased pH Stewart = Decreased PCO2
Accuracy of SpO2 compared to ABG
Accurate (+/- 2%)
• when measured against ABG’s (sat > 70%)
• Not as accurate w/ sat<70%
How does peripheral vasoconstriction affect SpO2 and what can lead to it.
- Cold or exogenous catecholamines
* Decrease in pulsatile strength
Causes of metabolic alkalosis
Common = GI loss (excess GI suction and Cl- loss) Diuretics Diarrhea Third spacing bleeding hypokalemia
What is dampening in the art-line system
- Decreases system resonance
* Prevents exaggerated waveforms
Treatment of metabolic alkalosis
Hypoventilation
Fluid replacement
treat cause
What is the ratio of ratios
R= (AC 660/DC 660) / (AC 940/DC 940)
Abnormal CO2 levels primarily causes…
Respiratory acidosis or alkalosis
Describe the function of automatic flush, zeroing and leveling the invasive BP monitor
Automatic flush
• 1-3ml/hr
• prevents thrombus formation
Zeroing
• References pressures against atmospheric air
Leveling
• Typically aortic root
• midchest/midaxillary line
• Level where you want to monitor
Traditional and stewart interpretation of metabolic alkalosis
Traditional= Increased HCO3 and increased pH
Stewart= Increased SID, Cations > anions
How is [Atot] related to A-B balance?
Increased [Atot] = acidosis
Decreased [Atot]= alkalosis
Causes increased PetCO2 due to increased CO2 production/delivery
INC metabolic rate Fever/sepsis Sz MH Thyrotoxicosis Inc CO HCO3 admin
How does equipment malfunction cause decreased Petco@
Vent disconnection
Esophageal intubation
Complete airway obstruction
leak around ETT
Describe the square wave test & purpose
Fast flush • Waveform becomes square • Flush pressure high matching pressure on bag Release of fast flush • Produces oscillations • No more than 2 oscillations • Subsequent oscillations = 1/3rd height of previous This indicates presence of dampening
What does degree of dissociation of a substance in water determine?
If the substance is a strong acid or base
Causes of increased PetCO2 d/t equipment failure
Rebreathing
Exhausted SODA lime
Faulty ins/exp valves
What does the pulse oximeter actually measure and how
Pulsatile expansion of the artery
• ↑ length of light path
• ↑ absorbency
How is EtCO2 clinically measured
Most commonly relies on IR absorption techniques
The greater the CO2 in the sample, the less IR that reaches the detector
Samples are extracted by one of two methods…
- Mainstream (non-diverting)
- Sidestream (diverting)
EtCO2 chemical indicator
Semi-quantitative
Color change of pH sensitive paper (Litmus)
A type of capnoMETER
What is the automatic non-invasive BP technique
Based on oscillometry • The maximal amplitude is MAP • SBP and DBP calculated from algorithm • SBP usually 25-50% of MAP amplitude • DBP is least accurate Roughly to directly measured arterial pressure • When MAP = 75 mmHg
When would monitoring SpO2 on toes be appropriate?
- may be more reliable with epidural blocks
* Vasodilation from block improves pulsatile flow
difference in capnometry and capnography
Capnometry
-The measurement and quantification of inhaled/exhaled CO2
Capnography
-The method of measurement but also a graphic display or time
What does increased and decreased SID indicate
Increased = presence of unmeasured ANIONS
Decreased = presence of unmeasured CATIONS
What are the major causes of increased PetCO2
Increased CO2 production/delivery to lungs
Decreased alveolar vent
Equipment malfunction
Tips for monitoring SpO2 on fingers
• Dark polish or synthetic nails inhibit transmission
Absorbs or redirects light
• Detection of desaturation and resaturation is slower peripherally
• Don’t put on index finger
High use = ↑ artifact
• sensitive to vasoconstriction
How does decrease alv vent cause decreased PetCO2
Hyperventilation
Indications for invasive BP monitoring
Continuous needed, real-time Planned pharmacologic manipulation Repeated blood sampling Determination of volume responsiveness Timing of IABP counterpulsation
What is pulse oximetry
Absorbance of light Light through matter
• Transmitted, absorbed or reflected
What are the signs of acute and chronic respiratory acidosis compensation?
Acute = increase 1 mmHg for q 10 mmHg (>40)
Chronic= increase 4 mEq/L for q 10 mmHg (>40)
What information does EtCO2 give and how does it correlate w/ PaCO2
informs us about PACO2
Approximates PaCO2 about 4 mmHg
If EtCO2 is 36 mmHg what is PaCO2 estimate
PaCO2 = ~40 mmHg
Disadvantages of invasive BP monitor at brachial, DP, and femoral sites
Brachial • Not used much d/t poor collateral flow Dorsalis Pedis • Much smaller Femoral • Easy to access • Better in emergency situations • Problems • Much more positional • Infection complications • Ligament injury
How does dec CO2 production/delivery to lund cause dec PetCO2
Hypothermia Arrest PE Hemorrhage HoTN
What are normal up and down variations for SPV
Normal UP= 2-4mmHg
Normal DOWN= 5-6mmHg
What is strong ion difference (SID)
SID = strong cations - strong anions
SD=(Na + K + Ca2 + Mg2) - (Cl- + lactate)
What are causes of SpO2 signal artifact and how are they corrected?
-Ambient light solved by alternating red/infrared -Low perfusion if signal amplified, artifact is too -venous blood pulsation Longer signal, slower change -Additional lights IV dyes, New pulse ox w/ 8 wavelengths filters dye -Additional forms of Hb
What are symptoms of metabolic alkalosis
Widespread vasoconstriction
lightheadedness
tetany
paresthesia
What does SVV calculation rely on?
What is normal SVV
Assumes SR, Vt 8 ml/kg, stable respiration
normal = 13%
Difference between uncompensated, partially compensated and fully compensated A-B disorders?
uncompensated= abnormal pH and CO2/HCO3
Partially compensated = pH abnormal and both CO2 and HCO3 are adjusting in same direction.
Fully compensated = pH normal, CO2 and HCO3 abnormal and adjusted in same direction
Causes of respiratory acidosis
Primary = lungs fail to eliminate CO2-hypoventilation
Drug related resp depression/OD
Neuro injury
Lung injury/disease (COPD, ARDS etc)
NMBD
What is the best method to confirm endotracheal intubation
Detection of carbon dioxide breath-by-breath the
Which SpO2 monitoring sights are most sensitive and why
Tongue, Cheek, Forehead
• less affected by vasoconstriction
• reflects desat quicker
How is hydrogen ion concentration measured?
pH (negative log of H concentration)
Invasive BP placement techniques
1st: Seldinger’s Technique
• Use of guidewire passed through needle
2nd: Transfixion Technique • Same positioning and preparation • Front and back walls are punctured intentionally • Needle removed • Catheter withdrawn until pulsatile blood flow appears and then advanced • Difficult with Long caths Small & stiff caths Low BP may not be as pulsatile -not associated w/ more complications
What pathology can alter art-line waveform (7)
Age: lack of distensibility Atherosclerosis • ↑SBP; ↓DBP? Embolism • Clot on cath Arterial dissection Shock Hypothermia Vasopressor infusions
What is an abnormal pulse pressure variation and what does it indicate?
How should it be addressed?
abnormal = >17%
Decrease preload and increased intravascular volume
Fix= volume resus
How can invasive BP monitoring waveform be maximized
•Limit stopcocks •limit tubing length • ↑s waveform falsely ↑ BP •non-distensible tubing • Prevents pulsatile expansion So that waveform isn’t amplified by tubing
Advantages of SpO2 (10)
Accurate Not affected by gas Noninvasive continuous Can indicate decreased CO Convenient Tone modulation Probe variety Battery operated Economical
What are Korotkoff sounds?
Series of audible frequencies
Produced by turbulent flow beyond partially occluding cuff
Describe weak acid dissociation in H2O?
Partially dissociates in H2O
Degree of dissociation determined by: pH and temp
How is pulse pressure measured and what does it indicate?
What is normal
utilizes max and min pulse pressures over entire respiratory cycle
Normal <13% ∆
Maximal difference in arterial pulse pressure
Divided by average of max & min pulse pressures
Normal 13-17%
AANA monitoring standards Thermoregulation Neuromuscular Positioning and protection Additional Omission
-Thermoregulation
When significant ∆ in body temp are anticipated or suspected
-Neuromuscular
When NM blocking agents are administered
-Positioning and protective measures
Except aspects performed exclusively by other providers
Note no involvement, or check yourself
-Additional means
depending on needs of patient, surgical technique or procedure
-Omission with reason must be charted
Reason why monitoring wasn’t done
What is the Boston approach to A-B analysis?
A-B maps and relationship between CO2 and HCO23
What is AC and DC
AC = pulsatile DC = non-pulsatile
Why analyze waveform
Hemodynamic resuscitation = begins w/ adequate preload
Who would benefit from ↑ preload ”reserve”
