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Flashcards in Capnography Deck (67):

What is average O2 consumption in ml/(kg min)?

3.5 ml/(kg min)

~250 for 70kg pt

Note: The rate of O2 consumption increases as pt weight decreases but the obese pt. consumes more O2 overall.


What are the respiratory quotients from least to greatest?

Fat metabolism RQ = 0.71

Protein: 0.835

Mixed: 0.82 - 0.85

Carbohydrate: 1

Lipogenesis: 1 - 1.2

Note: 8-10 hrs after a meal, carbohydrate metabolism becomes minimum and fat dominates.


What is :


a graph of gaseous CO2 concentration as a function of time

an instrument for measuring gaseous concentrations (numerical)

the practice of measuring and recording concentrations (numerical)



Identify the parts of the capnogram:


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I: Dead space + fresh gas

II: Dead space + alveolar gas

III: Alveolar gas plateau

IV: Inspiration

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During phase ___, exhaled gas from the large a/w has a PCO2 of 0.



During phase __, is the transition between a/w and alveolar gas.



Phase III is normally flat, but in the presence of VA/Q mismatching, it has a ______ slope.



What occurs to the slope of the capnogram as a result of a kinked tube?

increased slope


Where is the alpha angle measured and what is its approximate value?

within point C curve in Phase II

~ 100º

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Where is the beta angle measured and what is its approximate value?

angle within curve between phase III and IV

Beta ~ 90º


What occurs with respect to the alpha angle in COPD?

The alpha angle increases

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What occurs with respect to the beta angle in COPD with rebreathing?

the beta angle increases

Note: Another possible cause of increased beta angle is a prolonged response time compared with the respiratory cycle time.


Normal CO2 levels is ___-___ torr



How does a mainstream sampling device operate?

Infrared light beam is passed through the airway device

Note: Side stream readings are delayed.  Also alpha angles are sharper in mainstream devices.  


What error can occur with colorimetric CO2 detectors?

If stomach acid is regurgitated, false positive results may occur when the ETT is in the esophagus.  

Also, the color change may be permanent.


The sidestream capnogram is about ___ breath out of phase with actual activity.

1/2 breath


What changes occur to the alpha and beta angles in sidestream analyzed waveforms?

both are more rounded due to fresh gas flow dilution


Where should you place the sample line and why?

Closest to the ETT as possible to avoid dilution by fresh gas.

If close to the y-piece, readings with be diluted.


What are the advantages of side stream analysis?

  • More robust
  • Cheaper to maintain
  • Weight of sensor on ETT is not a factor
  • Not limited to CO2 and N2O
  • No added dead space to the breathing circuit


What are the advantages of main stream analysis?

  • No "leak in circuit"
  • Measure high ventilatory rates
  • Decreased artifact such as cardiogenic oscillations


Identify the capnograms:

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Kinked ETT


If there is a slow rise in phase III that does not appear to reach a plateau, what is the capnogram suggesting?

  • emphysema, asthma
  • suggestive of large A-a CO2 gradient
  • morphology suggests dilution of alveolar gas with dead space gas


What are expected ETCO2 - PaCO2 gradients:

Slightly abnormal
Moderately abnormal
Markedly abnormal

0-7 mmHg





In a pt with COPD, what gas exchange units empty first? Poorly ventilated or well ventilated?

Well-ventilated units empty first, then the poorly ventilated ones which result in the progressive increase of capnogram caused by asynchronous exhalation.


What factors determine ETCO2?

Composition of the alveolar gas

  • CO2 production: metabolism, temperature
  • Gas transport to alveolus
  • Gas exchange
  • Inspired gas composition
  • Composition of mixed venous blood

Emptying of alveolus

  • A/w resistance
  • Compliance
  • Alveolar volume




What causes increased PETCO2?

Increased CO2 production--fever, sepsis, giving bicarb, increased metabolic rate, seizures

Decreased alveolar ventilation--COPD, muscular paralysis, hypoventilation, respiratory center depression

Equipment malfunction--rebreathing, exhausted CO2 absorber, leak in circuit


What causes decreased PETCO2?

Decreased CO production and delivery to lungs--hypothermia, hypoperfusion, cardiac arrest, pulmonary embolism, hemorrhage, hypotension

Increased ventilation

Equipment malfunction--ventilator disconnect, esophageal intubation, complete a/w obstruction, poor sampling, leak around ETT cuff


What causes increased P(a-ET)CO2?

  • Pulmonary hypoperfusion
  • Pulmonary embolism
  • Cardiac arrest
  • Positive pressure ventilation
  • High rate, low tidal volume


During endobronchial intubation, how can we maintain normocapnography?

minute ventilation

Note: 2 lungs may need tidal volume at 600ml, but if ventilating only 1 lung, change your tidal volume to about 1/2 and change frequency of breaths.


Shunt eventually leads in what changes in ETCO2?



If there is a pulmonary embolus, lung becomes ______.

dead space


What occurs to EtCO2 when there is a pulmonary embolus?


etCO2 ~20


What ventilator valve issue creates this problem?

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expiratory valve from seating properly

Note: Think of rebreathing.


What ventilator valve issue creates this problem?

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Correct with turning up FGF

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How do you calculate EtCO2 from % to mmHg?

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(760 - 47 mmHg) * EtCO2 in %



What does this waveform indicate?

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The pt is trying to breathe while being mechanically ventilated.

This is an indication of inadequate ventilation rather than inadequate muscle relaxant.

Solution: Increase minute ventilation.


What is this waveform also known as?

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Curare Cleft

However, the capnogram does not reveal the circumstance of the inspiratory effort.

Clinician must decide to adjust the ventilator (minute ventilation), level of anesthesia, degree of muscle relaxation, metabolic state, and impact of external stimuli require consideration.


What does a curare cleft, or notch, indicate when the pt is spontaneously breathing?

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Lack of synchronous action between the intercostal muscles and the diaphragm, most commonly caused by inadequate muscle relaxant reversal.  

As the relaxant is reversed, the curve becomes normal in shape.  The notch can be seen in pts with cervical transverse lesions, flail chest, hiccups, and pneumothorax.


What could be causes for this capnogram?

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Inadequate paralysis

Severe hypoxia

Pt waking up


What is the cause of this waveform?

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Incomplete scale has clipped the waveform.

While inspired CO2 is elevated above normal (normal = 0%), it is not elevated enough to be rebreathing. Hypoventilation is responsible for this level of EtCO2.


Name the waveform:

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Cardiogenic oscillations --common in pediatric pts

Contributing factors include:

  • negative intrathoracic pressure
  • low respiratory rate
  • diminished vital capacity:heart size ratio
  • low tidal volumes

Might be able to correct by adjusting:

  • increase FGF
  • ventilator rate/flow
  • tidal volume
  • place sample line behind the HME to increase dead space



Why would cardiogenic oscillations not match ECG reading?

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Different sweep speeds


What may occur to readings as a result of cardiogenic oscillations?

Falsely high respirations may be calculated on less sophisticated capnometers.

Also EtCO2 may be miscalculated.


What is pneumocardiography?

Change in volume of the heart causes a change in the lung volume--> can calculate CO


What factors increase EtCO2?

  • Lap procedures
  • Injection of sodium bicarbonate
  • Pain, anxiety, shivering
  • Increased muscle tone, due to reversal perhaps
  • Convulsions
  • Hyperthermia
  • Upper airway obstruction
  • Rebreathing
  • Release of tourniquet


What factors decrease EtCO2?

  • Hypothermia
  • Increased depth of anesthesia
  • Use of muscle relaxants
  • Hypovolemia
  • Pulmonary embolus
  • Increased pt dead space


Detecting ______ in early stages is one of the most important reasons for routinely monitoring CO2.

MH, malignant hyperthermia

Note: You still get MMR with NMB.  Also, you will more often see increase HR. Treat with dantrolene.


What factors relating to equipment increase EtCO2?

Increased apparatus dead space

Expiration obstruction





What factors relating to equipment decrease EtCO2?

Leak in sample line

Low sampling rate

Too high sampling rate

Inadequate seal around tracheal tube


What are several causes for the waveform?

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Incompetent expiratory valve

Exhausted absorbent in the circle system

Problems with the inner tube of a coaxial system

An incompetent inspiratory valve


What does this waveform indicate?

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Incompetent inspiratory unidirectional valve

Note: During inhalation, increased respiration of CO2.


What does this waveform indicate?

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Wet droplets on exhalation valve that seated properly following some breaths, but not others.


What does this waveform indicate?

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Or, deadspace ventilation due to lack of blood supply, not shunt.


What does this waveform indicate?

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Return to spontaneous ventilation.


What does this waveform indicate?

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Variations between lungs.

If the compliance, a/w resistance, or V/Q differ substantially from the other lung.

Has been reported in a pt with severe kyphoscoliosis and following single-lung transplantation.



What does this waveform indicate?

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Contamination of the expired gas sample

Large leak above.

Small leak below.

Note: Contamination may be caused by placing the sampling site too near the fresh gas inlet or too high a sampling flow rate as well.


What does this waveform indicate?   

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Mr. Biggs said assume loss of blood supply to lungs unless o/w indicated.

  • Pulmonary emboli
  • Extubation
  • Complete breathing system disconnect
  • Ventilator malfunction
  • Plugged sampling tube
  • Totally obstructed tracheal tube


 What does this waveform indicate?

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Poorly fitting anesthesia mask


 What does this waveform indicate?

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  • Massive blood loss
  • Obstruction of major blood vessels
  • Circulatory arrest with continued pulmonary ventilation
  • Pulmonary embolism


What does this waveform indicate? 

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Air embolism


What does this waveform indicate?

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Hyperventilation, or

Wide arterial-alveolar CO2 gradient due to excessive dead space.


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May be partial airwaay obstruction

Rising body temperature

Hypoventilation due to a partial leak in the breathing circuit.


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If balloon inflated too long, see decrease in CO2


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Tourniquet release


Capnometer responds well at low ventilatory rates.

It cannot respond well to:

  • high ventilatory rates
  • excessive line lengths
  • excessive resistance
  • low sampling flow rate
  • water in the sample line


Increasing respiratory rate leads to what with respect to the capnogram?

sine wave appearance and mean CO2 reading

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Frequency response increases with increasing _______ into the analyzer.

gas flow rate