Capnography - Exam 1 (Ericksen) Flashcards
What 3 things does capnography give us information about?
- Ventilation
- metabolism: how effectively CO2 is being produced @ cellular level
- CV: how effectively the CO2 is moving in the vascular system & out of pulmonary system
General Effects of Hypercarbia
- Respiratory acidosis
- increases CBF - increased ICP (vasodilation)
– chemoreceptors in brainstem to help pt blow off CO2 - increases pulmonary vascular resistance (vasoconstricts in the lungs) - increases PA pressures
– NO PULM HTN - potassium shift from intracellular - intravascular (hyperkalemia)
- can be used to get pts to start breathing again
General Effects of Hypocarbia
- respiratory alkalosis
- decreases CBF (low limit of 28mmHg) - vasoconstriction
- decrease pulm. vascular resistance (vasodilation in lungs)
- potassium shifts into the intracellular space
- blunts normal urge to breathe (manual ventialtion or over-breathing)
What other information can capnography tell us?
- pulmonary blood flow
- aerobic metabolism
- placement of ETT/LMA
- integrity of breathing circuit (leaks, disconnects, sample line leak)
- estimates adequacy of CO in CPR
BOHR equation - what is it calculating?
- physiologic DS (anatomic + alveolar)
- Vt
Anatomic DS:
- conducting zones of airway (nose, trachea, bronchi)
Physiological DS:
airway DS + alveolar DS
7 conditions that increase alveolar DS (V/Q mismatching)
- hypovolemia (poor perfusion)
- pulmonary HoTN (poor perfusion)
- PE - obstructed flow
- ventilation of nonvascular airspace (not getting blood)
- obstruction of pre-capillary pulm vessels
- obstruction of pulmonary circulation by external forces
- overdistention of alveoli (PEEP)
What is capnometry?
measurement & quantification of inhaled or exhaled CO2 concentrations
* measured w/ capnometer
What is capnography?
- method of CO2 measurement & a graphic display of time
- detects CO2 breath-breath
- best method to confirm ETT intubation
What is time capnography?
- pressure vs time plot
- most common representation of capnometry
time capnography
High speed
- can interpret info breath-breath
- not looking @ trends
time capnography
slow speed
- looks @ trends
- expired & inspired trend
- waveform looks fast
Side-stream capnography
- aspirates gas sample and analyzes away
- rate of 50-200mL/min
- most common
- transport time delay/rise time is slower
Mainstream capnography
- detected in airway @ circuit
- analyzes gas sample directly in breathing circuit
- no time delay; rise time faster
Where is ETCO2 measured @ in the waveform?
- end of phase III
3 Broad causes of Increased PetCO2:
- increased CO2 production & delivery to lungs
- decreased alveolar ventilation
- equipment malfunction
increased PetCO2
causes of increased CO2 production & delivery to lungs (8)
- increased metabolic rate
- fever
- sepsis
- seizures
- MH
- thyrotoxicosis
- increased CO - CPR, thyroid problems
- bicarb admin - converted to CO2
increased PetCO2
Causes of decreased alveolar ventilation (6)
- hypoventilation
- resp. center depression (drugs)
- partial muscle paralysis
- NM disease
- high spinal anesthesia - knock out resp. drive
- COPD
increased PetCO2
Equipment malfunction causes (4)
- rebreathing - normalish
- exhausted CO2 absorber
- leak in vent circuit (old vents)
- faulty inspiratory/expiratory valve (traps CO2)
Broad causes of decreased PetCO2
- decreased CO2 production & delivery to the lungs
- increased alveolar ventilation
- equipment malfunction
decreased PetCO2
Causes of decreased CO2 production and delivery to lungs (6)
- Hypothermia
- pulmonary hypoperfusion (less delivered)
- cardiac arrest
- PE
- hemorrhage
- hypotension
decreased PetCO2
Increased Alveolar Ventilation
- Hyperventilation - if we are breathing faster for pt or if the pt is breathing faster
decreased PetCO2
Equipment Malfunctions (5)
- ventilator disconnect
- esophageal intubation
- complete airway obstruction
– laryngospasm, tube plugged - poor sampling - breathing too rapid
- leak around endotracheal tube cuff (mixing RA)
What is the normal difference b/w PaCO2 & ETCO2 (PACO2)?
5mmHg
* Ex: ETCO2 35mmHg = PaCO2 40mmHg
Problems that increase the difference b/w PaCO2 & ETCO2 (2)
- V/Q mismatch (PE, endobronchial intubation)
- breathing patterns that fail to deliver alveolar gas to the sampling site
– ex: infants/neonates, COPD (bronchi collapse before alveoli empty), bronchospasm
Problems w/ the capnograph increase the difference b/w ________ & ________.
true ETCO2 & measured ETCO2
* ex: sampling cath leaks, calibration error, side-streaming slow response
Clinical measurement techniques (ETCO2)
- IR light absorption - greater CO2 in sample = less IR hitting detector
- chemical indicator (yellow mellow)
– could still verify esophageal intubation
What are the capnograph monitor requirements?
- CO2 reading w/i +/- 12% of actual value
- Manufacturers disclose interference from ethanol, acetone, halogenated volatiles
- must have a high CO2 alarm for inhaled & exhaled CO2 (rebreathing)
- must have an alarm for low exhaled CO2
What can we interpret when looking at a time capnogram?
- CO2 values
- approximate blood CO2 levels
- pulmonary blood flow
- alveolar ventilation
Differential diagnoses of loss of exhaled CO2 – things we want to rule out/possible causes
- esophageal intubation
- accidental extubation
- disconnection or failure of sampling/device (leak, failure of sampling pump)
- apnea (drugs), bronchospasm (loss of exhaled CO2), cardiac arrest
Normal Capnograph
Phase I
- baseline should be 0mmHg - unless rebreathing
- represents exhalation of anatomic DS & apparatus
- essentially no CO2
Normal Capnograph
Phase II
- expiratory upstroke
- CO2 rich alveolar gas being expired
- sampling of alveolar gases
- normally steep
Normal capnograph
Phase III:
- plateau phase
- representative of CO2 in the alveolus
- ventilation heterogeneity - alveoli closing @ diff times
- gives the slight increasing slope
Normal capnograph
Phase 0
sometimes called phase IV
* inspiration of fresh gas - remaining CO2 washed out
* downstroke returns to baseline
Normal Capnograph
Occasional Phase IV
different from phase 0
* sharp upstroke in PCO2 @ end of phase III
* resulting from closure of lung units w/ lower PCO2
* allows for regions w/ higher CO2 to contribute more to exhaled sample
Who is the occasional phase IV seen in?
Why?
- pregnant & obese
- decreased FRC & lung capacity
- things are emptying & last little bit goes “pewwww”
- also called phase IV’
What is the alpha angle?
- separates phase II & III
- 100-110 degrees
What causes the alpha angle to increase?
- expiratory airflow obstruction
- end of the alveoli obstruct & close before emptying
- give shark fin appearance & the angle widens
COPD, bronchospasm, kinked ETT
What is the beta angle?
- separates phase III & 0
- 90 degrees
What causes the beta angle to increase?
- malfunctioning inspiratory unidirectional valves
- rebreathing of CO2
- low Vt w/ rapid RR (fast & shallow)
Mechanical Ventilation Capnograph
Spontaneous Ventilation Capnograph
- sometimes see all phases
- sometimes see bumps/hills
Inadequate seal around ETT capnograph
- B angle opens and widens
- RA is also entering
- Phase III cut short b/c its going out around the lost seal as well
Faulty Inspiratory Valve Capnograph
- inspiratory valve gets stuck - causes rebreathing of CO2
- expiratory valve can also get stuck
- phase I now starts @ 5-8mmHg instead of 0mmHg
- this capnograph also has the little step up @ the end of phase 0!!!!
Sample Line Leak Capnograph
- atmospheric air being aspirated into sampling line
- dilutes ETCO2 & decreases the value
- has a peak that looks like phase IV’ but it is not
- this capnograph does not reach 40mmHg for phase III
Hyperventilation Capnograph
- decrease in ETCO2
- @ least 3 capnographs decreasing in size or trend going down
- Causes: decreased anesthesia/metabolic acidosis
Hypoventilation Capnograph
- Increase in ETCO2
- cause: hypoventilation, fever, narcotics
- capnograph waves are getting bigger and trend is going up
Airway Obstruction Capnograph
shark fin
* phase II & III connected
* alpha angle pretty much gone (opened up)
Cardiogenic Oscillations Capnograph
- seen in peds - Heart close to trachea & beating against lungs
– causes emptying @ different times of lung regions - see at end of exhalation as flow decreases to 0
- age this goes away - depends on anatomy as they get bigger (8-10)
Rebreathing/Soda Lime Exhaustion Capnograph
- cannot get back to baseline
- this does not have the step up like faulty inspiratory valve
- baseline gets higher & higher
- phase 0 does not change - gets as low as it can
- inspiratory baseline higher but valve not broken
NMBD wearing off capnograph
- Curare cleft
- little divot at the end of phase III
- can we flip off the vent & let them breathe or do we need to reparalyze?
Overbreathing Capnograph
- getting mechanical breath but taking own spontaneous breath as well
- weaker vs. stronger
- can let them breathe - feel bad and give PS by closing APL valve a little
- titrate narcotics to RR
Esophageal Intubation Capnograph
- spontaneous looking waveform that goes away
- if mechanically ventilated wave that goes away = accidental extubation/kink/self-extubation
