Unit 6 - Respiratory Monitors & Equipment Flashcards
formula for dynamic compliance
Vt / PIP - PEEP
which phase of the capnograph waveform best correlates to V/Q status
phase III
what point of capnograph is EtCO2 measured
point D
what gases can infrared analysis measure
- N2O
- CO2
- volatiles
NOT O2, helium, Nitrogen, or xenon
what gases can infrared analysis measure
- N2O
- CO2
- volatiles
NOT O2
handwritten notes - paco2 to etco2 gradient
what is the Beer Lambert law
relates the intensity of light transmitted through a solution & the concentration of the solute within solution
basis of pulse ox
Airway Resistance =
[P (airway) – P (alveolar)] / Gas Flow Rate
Airway Compliance =
change in volume / change in pressure
factors that influence airway compliance
- muscle tone
- degree of lung inflation
- alveolar surface tension
- amount of interstitial lung water
- pulmonary fibrosis
Dynamic Compliance
compliance of lung/chest wall during air movement
Pressure required to inflate lung to a given volume is a function of air
Dynamic Compliance
compliance of lung/chest wall during air movement
Pressure required to inflate lung to a given volume is a function of air
dynamic compliance is a function of:
both airway resistance and the elasticity of the chest wall
Static Compliance
measures compliance when there is no airflow
Pressure required to keep lung inflated to a given volume is a function
static compliance is a function of:
elasticity of the chest wall only
Peak Inspiratory Pressure
max pressure in pt’s airway during inspiration
what factors affect PIP
airway resistance and chest/lung compliance (Pelastic)
measurement of dynamic compliance
PIP
Dynamic compliance =
Vt / PIP – PEEP
Pressure in small airways & alveoli after target Vt delivered
Plateau Pressure
what conditions decrease pulmonary compliance?
how does this affect the PP and PIP?
- endobronchial intubation
- pulmonary edema
- pleural effusion
- tension PTX
- atelectasis
usually due to reduction in static compliance (PIP and PP increase)
what conditions increase pulmonary resistance?
how does this affect the PP and PIP?
- kinked ETT
- ETT cuff herniation
- bronchospasm
- bronchial secretions
- airway compression
- foreign body aspiration
usually due to reduction in dynamic compliance (increased PIP, PP unchan
phases of capnograph
- I (A-B) = exhalation of anatomic dead space
- II (B-C) = exhalation of anatomic dead space + alveolar gas
- III (C-D) = exhalation of alveolar gas
- IV (D-E) = inspiration of fresh gas that doesn’t contain CO2
A = P elastic
B = P plateau
C = P peak
D = P resistance
what is PIP?
max pressure in pt’s airway during inspiration
what is PIP affected by
airway resistance and chest/lung compliance (Pelastic)
what is plateau pressure
Pressure in small airways & alveoli after target Vt delivered
what does plateau pressure reflect?
elastic recoil of lungs & thorax during inspiratory pause (no gas moving in or out)
plateau pressure assoc. with barotrauma
> 35 cm H2O
complications of increased PP
- VALI
- PTX, pneumomediastinum
- subcutaneous emphysema
how to reduce PP if barotrauma exists
↓ Vt, inspiratory flow, and PEEP (sedation also helpful)
normal static compliance for an adult
35-100 mL/cm H2O
normal static compliance for a child
> 15 mL/cm H2O
what does it mean if ↑ PIP with no change in PP
resistance has increased OR inspiratory flow rate has increased
what does it mean if ↑ PIP + ↑ PP
total compliance has decreased (Pelastic increased) OR Vt has increased
final product of aerobic metabolism
CO2
what is ventilation?
Once CO2 is in alveolus, ventilation is the process by which CO2 is eliminated from body
at what point of capnography waveform is EtCO2 measured?
point D
what does it mean if you see a small peak just before inspiration on capnograph waveform
reflects emptying of alveoli with longer time constants and higher CO2 concentrations
V/Q during phases II & III of EtCO2 waveform
II = increased V/Q in apex
III = decreased V/Q in bases
where is the alpha angle of capnograph waveform measured
point C
normal alpha angle of capnograph
100-110 degrees
causes of increased alpha angle
expiratory airflow obstruction (COPD, bronchospasm, kinked ETT)
where is beta angle measured in capnograph waveform
point D
angle of beta angle
90 degrees
cause of increased beta angle
rebreathing caused by faulty inspiratory valve
CO2 analysis that provides faster response time
mainstream (in-line)
which type of CO2 analysis increases apparatus dead space
mainstream (in-line)
why is the response time for a sidestream (diverting) CO2 analysis usually slower than mainstream
Pumping mechanism continuously aspirates gas sample from breathing circuit
what does this EtCO2 waveform represent
airflow obstruction
ex - COPD, bronchospasm, kinked ETT
EtCO2 waveform with airway obstruction
prolonged upstroke with increased alpha angle
what does this EtCO2 waveform represent
cardiac oscillations
caused by heart beating against lungs
what does this EtCO2 waveform represent
cardiac oscillations
caused by heart beating against lungs
what does this indicate if seen during spontaneous ventilation
inadequate muscle relaxant reversal
what does this EtCO2 waveform represent & what causes it
low EtCO2 - plateau phase well below normal
Caused by hyperventilation, ↓ CO2 production, ↑ alveolar dead space
examples of increased dead space that can cause this waveform
hypotension
PE
low EtCO2
what does this waveform represent
increased EtCO2 with normal plateau
Caused by ↑ CO2 production or ↓ alveolar ventilation
- Ex ↑ CO2: MH, sepsis, fever, hyperthyroid
- Ex ↓ ventilation: hypoventilation, narcotics
what does this waveform represent
increased EtCO2 with normal plateau
Caused by ↑ CO2 production or ↓ alveolar ventilation
- Ex ↑ CO2: MH, sepsis, fever, hyperthyroid
- Ex ↓ ventilation: hypoventilation, narcotics
what does this waveform represent
inspired CO2 - baseline doesn’t return to 0, indicates rebreathing
causes of an EtCO2 baseline that doesn’t return to zero
- exhausted absorbent
- incompetent expiratory valve
- hole in inner tube of Bain
- inadequate FGF with Mapleson
- rebreathing under drapes (not intubated)
what does this waveform represent
incompetent inspiratory valve
EtCO2 waveform changes seen with incompetent inspiratory valve
Decreased slope during inspiratory phase (widened beta angle)
Waveform may or may not reach 0 (depends on FGF)
EtCO2 waveform changes seen with incompetent inspiratory valve
Decreased slope during inspiratory phase (widened beta angle)
Waveform may or may not reach 0 (depends on FGF)
what does this represent
leak in sample line during PPV
EtCO2 changes with leak in sample line during PPV
- Beginning of plateau is low - alveolar gas is diluted when atmospheric air is aspirated into sample line
- Positive pressure during inspiration pushes CO2-rich gas through sample line - results in peak at the end of the plateau
patient populations you might see this waveform in
obese and pregnant patients
when can this waveform be seen
after single-lung transplant
* First peak is alveolar gas from transplanted lung (normal time constant)
* Second peak is alveolar gas from diseased lung (air trapped in sick lung = longer time constant)
Also reported with severe kyphoscoliosis
4 requirements for EtCO2 to be detected
- CO2 must be produced during metabolism
- Must be adequate pulmonary blood flow to deliver CO2 to lungs for elimination
- Must be adequate ventilation to transport CO2 to breathing circuit
- Must be intact sampling system
what 2 things should be considered to answer a question about changes in EtCO2
- what is the cause
- does this affect the PaCO2-EtCO2 gradient
causes of wide PaCO2 to EtCO2 gradient
suggests V/Q mismatch or equipment malfunction
normal PaCO2 to EtCO2 gradient
2-5 mmHg
causes of increased EtCO2 r/t increased CO2 production and delivery to lungs
- increased BMR (↑ VO2)
- MH
- thyrotoxicosis
- fever
- sepsis
- seizures
- laparoscopy
- tourniquet or vascular clamp removal
- bicarb admin
- shivering
- increased muscle tone (NMB reversal)
- medication side effect
causes of increased EtCO2 r/t decreased alveolar ventilation
- hypoventilation
- CNS depression
- residual NMB
- COPD
- high spinal
- neuromuscular disease
- metabolic alkalosis (if SV)
- medication side effect
3 changes that affect EtCO2
- CO2 production and delivery to lungs
- alveolar ventilation
- equipment
equipment malfunctions that increase EtCO2
rebreathing, CO2 absorbent exhaustion, unidirectional valve malfunction, increased apparatus dead space
decreased EtCO2 r/t decreased CO2 production and delivery to lungs
- decreased BMR (↓ VO2)
- ↑ anesthetic depth
- hypothermia
- ↓ pulmonary blood flow
- ↓ CO
- hypotension
- PE
- V/Q mismatch
- medication side effect
- pain/anxiety (if breathing spontaneously)
equipment malfunctions that cause decreased etco2
ventilator disconnect, esophageal intubation, poor seal with LMA or ETT, sample line leak, airway obstruction, apnea
what wavelengths of light are emitted by a pulse ox
red light (660 nm) and near-infrared light (940 nm)
Beer Lambert law applied to pulse ox
relates intensity of light transmitted through a solution and concentration of solute within the solution
solution = blood, solute = Hgb
red light is preferentially absorbed by:
deoxyhemoglobin (venous blood has relatively more than arterial)
Near-infrared light is preferentially absorbed by:
oxyhemoglobin (arterial has more)
which has a higher wavelength and higher amount of bound O2: red or near-infrared light?
near-infrared
where is the greatest amount of blood in tissue sample at pulse ox trough
venous
where is the greatest amount of blood in tissue sample at pulse ox peak
arterial
SpO2 =
SpO2 =
pulse ox sites that are fast, middle, and slow
- Fast = ear, nose, tongue, esophagus, forehead
- Middle = finger
- Slow = toe
pulse ox placements that can cause venous engorgement and falsely decreased SpO2 in trendelenburg
head or esophagus
when is SpO2 monitoring most useful
when the patient’s PaO2 aligns with steep portion of oxyhgb dissociation curve
causes of oxyhgb dissociation curve LEFT shift
- ↓ temp
- ↓ 2,3-DPG
- ↓ CO2
- ↓ H+
- ↑ pH
- ↑ HgbMet
- ↑ HgbCO
- ↑ Hgb F
left = love (increased affinity for O2)
causes right shift of oxyhgb dissociation curve
- ↑ temp
- ↑ 2,3-DPG
- ↑ CO2
- ↑ H+
- ↓ pH
right = release (decreasd affinity for O2)
SpO2 90, 80, 70 = PaO2 ?
60, 50, 40
Methods to improve SpO2 signal
digital block, warm extremity, protect from ambient light, apply vasodilating cream, administer arterial vasodilator
a pulse ox is a noninvasive monitor of what 3 things
- Hgb saturation
- HR
- Fluid responsiveness (pulse pressure variation)
1st branch off aortic arch
Brachiocephalic (innominate) artery
3rd branch off aorta
1st branch off aortic arch
Brachiocephalic (innominate) artery
3rd branch off aorta
SpO2 in severe anemia
pulse ox may overestimate - SpO2 does not quanitify amount of Hgb or dissolved O2 in blood
where can pulse ox be placed to monitor perfusion during mediastinoscopy
right extremity
perfusion index & waveform quality will be affected if brachiocephalic artery is compressed by scope
alveolar ventilation in a patient hypoventilating on room air
According to alveolar gas equation, will have increased alveolar PCO2 and decreased alveolar PO2
alveolar oxygen calculation
alveolar oxygen calculation
T/F pulse ox is a reliable measure for detecting bronchial intubation
false
if a high inspired O2 concentration is used, it’s possible SpO2 will be
T/F pulse ox is a reliable measure for detecting bronchial intubation
false
if a high inspired O2 concentration is used, it’s possible SpO2 will be
best assessments of bronchial intubation
Better assessed by bilateral breath sounds, CXR, and/or fiberoptic visualization of carina
margin of error for SpO2
+/- 2-3% when SpO2 70-100%
3% when SpO2 50-70%
required to diagnose methemoglobin or carboxyhemoglobin
co-oximeter
SpO2 with methemoglobin
- absorbs 660 nm and 940 nm equally - 1:1 absorption ratio is read as 85%
- Falsely underestimates SpO2 if O2 sat > 85%
- Falsely overestimates SpO2 if O2 sat < 85%
SpO2 in carboxyhemoglobin
- absorbs 660 nm to same degree as OxyHgb
- Co-Hgb & Oxyhgb look the same to the pulse ox
- Reads sum of Co-Hgb + Oxyhgb (overestimates SpO2)
how does nail polish affect SpO2
black, blue, and green affect accuracy
red & purple do not
dyes that can affect spo2 accuracy
methylene blue
indocyanine green
indigo carmine
NOT fluorescein
determines concentrations and identities of all the sample gases simultaneously
Infrared Absorption Spectrophometry
does oxygen absorb infrared light
nope
how is exhaled oxygen measured
must be measured by electrochemical analysis (galvanic cell or Clark electrode) or paramagnetic analysis
what is mass spectometry
- Bombards a gas sample with electrons creating ion fragments
- All particles become charged & can be separated and identified based on their mass
Uses a high-power argon laser to produce photons
Raman Scatter Spectrometry
New tool that can detect inspired, expired, and breath to breath changes of a particular gas by incorporating a lipid layer on the crystal
Piezoelectric Crystals
Lipid layer responds to individual gases as they make contact and get ab
New tool that can detect inspired, expired, and breath to breath changes of a particular gas by incorporating a lipid layer on the crystal
Piezoelectric Crystals
Lipid layer responds to individual gases as they make contact and get ab
why are Piezoelectric Crystals impractical in the clinical setting
Unable to identify multiple gases at once
how does hypocapnia affect oxyhgb dissociation curve
left shift
how does hypercapnia affect oxyhgb dissociation curve
right shift
what can infrared absorption spectrophometry measure? what can’t it measure?
CAN measure CO2, N2O, volatiles
CAN’T measure O2, helium, nitrogen, xenon
most likely cause of acute decrease in EtCO2
hypovolemia (increased dead space)
ex - hemorrhage
most likely cause of acute decrease in EtCO2
hypovolemia (increased dead space)
ex - hemorrhage
relationship between PaCO2-EtCO2 gradient and dead space
increased gradient = increased dead space
