capnography Flashcards
Effects of Hypercarbia
Respiratory acidosis
Increases cerebral blood flow (CBF)
Increases pulmonary vascular resistance by causing vasoconstriction
Potassium shifts from intracellular to intravascular
Effects of Hypocarbia
Respiratory alkalosis
Decreases CBF
Decreases pulmonary vascular resistance
Potassium shifts to the intracellular space
Blunts normal urge to breathe
Bohr equation
calculates physiologic dead space
(VD/VT) = (PACO2 -PECO2) / PACO2
Volume of each breath inhaled that does not participate in gas exchange
dead space
anatomic or physiologic
airway dead space + alveolar dead space
Physiologic dead space
portion of the physiologic dead space that does not take part in gas exchange but is within the alveolar space
alveolar ds
Measurement and quantification of inhaled or exhaled CO2 concentrations
Capnometry
Conditions that increase alveolar dead space (V/Q mismatching)
-Hypovolemia- poor CO = less bf to ventilating area
-Pulmonary hypotension= not good flow
-Pulmonary embolus= blocking bf
-Ventilation of nonvascular airspace
-Obstruction of precapillary pulmonary vessels
-Obstruction of the pulmonary circulation by external forces
-Overdistension of the alveoli
Detection of CO2 breath-by-breath
Capnography
Best method to confirm endotracheal intubation
user can interpret information about each breath
High speed time capnography
appreciation of the expired and inspired trend
Slow-speed time capnography
Aspirates gas sample and analyzes away from airway at a rate of 50 to 200 mL/min
Side-stream
most common but slower
Analyzes gas sample directly in the breathing circuit
Main-stream
No time delay; rise time is faster
Measured at end-point of Phase III
End-Tidal CO2
Causes of increase PETCO2
MH
sz
inc metabolic rate
thyrotocisosis,
inc CO
Bicarb admin
Causes of decreased alv ventilation
resp center depression
paralysis
nm dz
high spinal
COPD
Causes of dec PETCO2
hypothermia
pulm hypoperf
cardiac arrest
PE
hemm
hypotens
Difference between PaCO2 and ETCO2 is approx…
5mmhg
V/Q mismatching increases the difference between
PaCO2 and PACO2
Breathing patterns that fail to deliver alveolar gas at the sampling site, increase the difference between……
PACO2 and true ETCO2 (alveolar gas)
Ex: neonates and infants; COPD, bronchospasm
Problems with the capnograph increase the difference between______
true ETCO2 (alveolar gas) and measured ETCO2 (capnograph)
Ex: sampling catheter leaks, calibration error, slow response time relative to breathing pattern
Color change of pH sensitive paper
Purple – No CO2
Yellow – CO2
Sensitive to low levels of CO2
Capnography 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
ETCO2 phase 1
respiratory baseline (should be 0)
Exhalation of anatomic dead space and the apparatus
no CO2
1/3 to vt exits
ETCO2 phase 2
expiratory upstroke
CO2-rich alveolar gas
Sampling of alveolar gases
Normally steep
ETCO2 phase 3
Alveolar plateau
Normally representative of CO2 in the alveolus
Can be representative of ventilation heterogeneity, slight increasing slope
ETCO3 phase 0
inspiratory downstroke
Sometimes called phase IV
Inspiration of fresh gas, remaining CO2 washed out
Downstroke returns to baseline
Occasional Phase IV
A sharp upstroke in PCO2at the very end of phaseIII
Upstroke probably results fromthe closure of lung units with lower PCO2
Allows for regions with higher CO2to contribute to more of the exhaled gas sample
Seen in pregnant and obese pts
Decreased FRC and lung capacity
Alpha angle
Separates phase II and phase III
100 – 110 degrees
Angle increases with an expiratory airflow obstruction
Beta angle
Separates phase III and phase 0
90 degrees
Angle increases with malfunctioning inspiratory unidirectional valves, rebreathing, and low tidal volume with rapid respiratory rate
Obstruction COPD, bronchospasm, or kinked ETT causes what to ETCO2
short phase 2
increases alpha angle
Rise in phase 3 but not plateaued
Shark fin
Faulty inspiratory valve causes…
Wider beta angle and the inspiratory down stroke is wider
Malfunctioning inspiratory valve = extension of the downslope and if the pt rebreaths because they aren’t down to 0.
Never return to baseline – rebreathe thought the inspiratory limb
Sample line leak causes…
Occasional phase 4.
Only getting half the et coming out -> small wave form
Hyperventilation causes…..
decrease in ETCO2
Hypoventilation causes…..
increase in ETCO2
Causes of rebreathing
soda-lime exhaustion
Co2 getting back to inspiratory limb because not scavenged
Incompetent expiratory valve
Flutter valves need flipped
ETCO2 doesnt go back to 0.
Curare cleft
muscle relaxants wearing off
spont breath during a mechanically ventilated breathe
overbreathing
spont breathe between mechanical breathe
Esophageal intubation
decreased ETCO2, poor waveform
