ETCO2 and monitoring things Flashcards
What are the effects of hypercarbia?
- Respiratory acidosis
- Increases cerebral blood flow (CBF): Increases ICP in susceptible patients
- Increases pulmonary vascular resistance
- Potassium shifts from intracellular to intravascular
What are the effects of hypocarbia?
- Respiratory alkalosis
- Decreases CBF
- Decreases pulmonary vascular resistance
- Potassium shifts to the intracellular space
- Blunts normal urge to breathe
What does the bohr equation calculate?
- Calculates physiological dead space
Volume of each breath inhaled that does not participate in gas exchange is?
Dead space
Conducting zones of the airway (nose, trachea, bronchi) is what type of deadspace?
Anatomical deadspace
airway dead space + alveolar dead space =
Physiological deadspace
Portion of the physiologic dead space that does not take part in gas exchange but is within the alveolar space
Alveolar dead space
What are the conditions that increase alveolar dead space (V/Q mismatching)
- Hypovolemia
- Pulmonary hypotension
- Pulmonary embolus
- Ventilation of nonvascular airspace
- Obstruction of precapillary pulmonary vessels
- Obstruction of the pulmonary circulation by external forces
- Overdistension of the alveoli
What is Capnometry?
How is it measured?
- Measurement and quantification of inhaled or exhaled CO2 concentrations
- Measured by a capnometer
What is capnography?
- Method of CO2 measurement and a graphic display over time
- Detection of CO2 breath-by-breath
- Best method to confirm endotracheal intubation
What does the term high speed vs slow speed mean?
- High-speed – user can interpret information about each breath
- Slow-speed – appreciation of the expired and inspired trend
- This is the most common gas sampling system. It aspirates gas sample and analyzes away from airway at a rate of 50 to 200 ml/min.
- This can cause a delay in what?
- Side-stream gas analyzer
- Transport time delay and rise time
What phase on a capnograph will an ETCO2 be measured at?
- ETCO2 measured at the end-point of phase 3.
- Sometimes varies with manufacturers [Value just before inspiration, Largest value, The average at a specific time]
What can increase ETCO2?
- increased CO2 production and delivery to the lungs
- decreased alveolar ventilation
- equipment malfunction
What are examples of increased CO2 production that causes increased ETCO2?
- increased metabolic rate
- fever
- sepsis
- seizures
- MH
- thryotoxicosis
- increased CO2 [during CPR]
- bicarb administration
What are examples of decreased alveolar ventilation that causes increased ETCO2?
- hypoventilation
- respiratory center depression
- partial muscle paralysis
- neuromuscular disease
- high spinal anesthesia
- COPD
What are examples of equipment malfunctions that causes increased ETCO2?
- rebreathing
- exhausted CO2 absorber
- leak in ventilator circuit
- faulty inspiratory or expiratory valve
What is causing this capnograph?
- Esophageal intubation
What can decrease ETCO2?
- decreased CO2 production and delivery to the lungs
- increased alveolar ventilation
- equipment malfunction
What are examples of decreased CO2 production that causes decreased ETCO2?
- hypothermia
- pulmonary hypoperfusion
- cardiac arrest
- PE
- hemmorhage
- hypotension
What are examples of increased alveolar ventilation that causes decreased ETCO2?
- hyperventilation
What are examples of equipment malfunctions that causes decreased ETCO2?
- ventilatory disconnct
- esophageal intubation
- complete airway obstruction
- poor sampling
- leak arount ETT cuff
Difference between PaCO2 and ETCO2 is approx ____ mmHg.
- 5 mmHg
Ex: ETCO2 of 35 mm Hg = PaCO2 of approx. 40 mm Hg
Problems that increase the difference between PaCO2 and ETCO2.
- V/Q mismatching increases the difference between PaCO2 and PACO2 (PE, endobronchial intubation)
- Breathing patterns that fail to deliver alveolar gas at the sampling site, increases the difference between PACO2 and true ETCO2 (alveolar gas) - COPD
- Problems with the capnograph increase the difference between true ETCO2 (alveolar gas) and measured ETCO2 (capnograph)
CO2 measurement most commonly relies on ____ light absorption techniques.
- Infrared (IR)
The greater the CO2 in the sample, the less IR light that reaches the detector
Describe the color change with a CO2 chemical indicator.
- Purple – No CO2
- Yellow – CO2
Sensitive to low levels of CO2
ETT placement still needs verification by alternative means
Information that can be interpreted from a time capnograph?
- Interpreting CO2 values
- Approximate blood CO2 levels
- Pulmonary blood flow
- Alveolar ventilation
- Differential diagnosis of loss of exhaled CO2 (esophageal intubation, cardiac arrest)
What are the inspiratory and expiratory segments of a normal capnograph?
- Inspiratory – Phase 0
- Expiratory – Phases I, II, and III
Describe Phase I of a normal capnograph.
- Baseline
- Exhalation of anatomic dead space and the apparatus (ETT, LMA)
- Essentially no CO2
- 1/3 of tidal volume is exhaled
Describe Phase II of a normal capnograph.
- Expiratory upstroke begins (CO2-rich alveolar gas)
- Sampling of alveolar gases
- Normally steep uprise
Describe Phase III of a normal capnograph.
- Alveolar Plateau phase
- Normally representative of CO2 in alveolus
- Can be representative of ventilation heterogeneity, slightly increasing slope
Describe Phase 0 of a normal capnograph.
- Sometimes called phase IV
- Inspiration of fresh gas, remaining CO2 washed out
- Downstroke returns to baseline
Describe the Occasional Phase IV (Phase IV Prime) of a capnograph.
- A sharp upstroke in PCO2 at the very end of phase III
- Upstroke probably results from the closure of lung units with lower PCO2
- Allows for regions with higher CO2 to contribute to more of the exhaled gas sample
- Seen in pregnant and obese pts d/t Decreased FRC and lung capacity
Describe the alpha angle of the capnograph.
- Separates phase II and phase III
- 100 – 110 degrees
- Angle increases with an expiratory airflow obstruction
- Ex: COPD, bronchospasm, or kinked ETT
Describe the beta angle of the capnograph.
- Separates phase III and phase 0
- 90 degrees
- Angle increases with malfunctioning inspiratory unidirectional valves, rebreathing, and low tidal volume with rapid respiratory rate
Describe the capnograph
- Normal Capnograph
- Mechanical Ventilation
Describe the capnograph
- Normal Capnograph
- Spontaneous Ventilation
What is the issue with this capnograph?
- Inadequate Seal around ETT
Additional:
* beta angle is widened
* P3 is cut short bc whatever is going out is leaving around the ETT too.
What is causing this capnograph?
- H: faulty inspiratory valve, resulting in a slower downslope, which extends into the inhalation phase (phase 0) as CO2 in the inspiratory limb is rebreathed
- J: faulty inspiratory valve.
Miller pg 1311
What is causing this capnograph?
- Sample line leak
Take note that this a small wave form and that ETCO2 does not even reach 40 mmHg
S27
Miller: dual plateau in phase III, suggesting the presence of a leak in a sidestream sample line. Early portion of phase III abnormally low due to dilution of exhaled gas with ambient air. The sharp increase in CO2 at the end of phase III reflects a diminished leak resulting from the increased circuit pressure at the onset of inspiration
What is causing this capnograph?
- Hyperventilation
- Gradually decreasing waveforms
What is causing this capnograph?
- Hypoventilation
- Gradually increasing waveforms
What is causing this capnograph?
- Airway obstruction on inspiration
Additional:
* Shark Fin
* Alpha angle: Basically gone
* P2 & P3 are basically one.
S30
Miller: increased upslope of phase III, as may occur during bronchospasm (asthma, chronic obstructive pulmonary disease), or partially obstructed endotracheal tube/breathing circuit
What is causing this capnograph?
- Cardiac oscillation
- Often seen in pediatric patients, the heart is close to the trachea
Millers Definition: cardiogenic oscillations at the end of exhalation as flow decreases to zero and the beating heart causes emptying of different lung regions and back-and-forth motion between exhaled and fresh gas;
What is causing this capnograph?
- Re-breathing soda lime exhaustion
Take note that rebreathing is occurring. The capnograph does not return to baseline.
Millers: rebreathing of CO2, as may occur with faulty expiratory valve or exhausted absorber system
What is causing this capnograph?
- NMBD’s wearing off
- Presence of a “curare cleft”
What is causing this capnograph?
- Over-breathing
- Notice the spontaneous breath between the mechanical breath
