Transcript Capnography for the intensivist

Capnography for the intensivist
Sarah Philipson
THE END.
THE END.
Questions?
What
CO2 is
capnography?
physiology
Questions?
What is
capnography?
Questions?
CO2
physiology
What is
capnography?
How is it
used?
Questions?
CO2
physiology
What is
capnography?
How is it
used?
Questions?
CO2
physiology
Do I care?
What are
the
problems
with it?
Capnography
• Measurement of CO2 vs time
• Infrared spectroscopy measures the fraction
of energy absorbed and converts this to a
percentage of CO2 exhaled
• Normal capnogram
I – inspiratory baseline
II – expiratory upstroke
III – alveolar plateau
IV – inspiratory downstroke
Capnography
• Measurement of CO2 vs time
• Infrared spectroscopy measures the fraction
of energy absorbed and converts this to a
percentage of CO2 exhaled
• Normal capnogram
I – inspiratory baseline
II – expiratory upstroke
III – alveolar plateau
IV – inspiratory downstroke
Capnography
• Measurement of CO2 vs time
• Infrared spectroscopy measures the fraction
of energy absorbed and converts this to a
percentage of CO2 exhaled
• Normal capnogram
I – inspiratory baseline
II – expiratory upstroke
III – alveolar plateau
IV – inspiratory downstroke
Normal EtCO2 = 38-40mmHg
A-B: Dead space
B-C: Dead space
+ alveoli
C-D: Alveoli
D: ETCO2
D-E: Inspiration
How we measure CO2
Physiology – “ICU is easy!”
Carbon Dioxide
PRODUCTION
AT TISSUES
Carbon Dioxide
PRODUCTION
AT TISSUES
TRANSPORT IN BLOOD
Carbon Dioxide
PRODUCTION
AT TISSUES
TRANSPORT IN BLOOD
REMOVAL VIA
VENTILATION
Carbon Dioxide
PRODUCTION
AT TISSUES
TRANSPORT IN BLOOD
REMOVAL VIA
VENTILATION
Carbon Dioxide
PRODUCTION
AT TISSUES
TRANSPORT IN BLOOD
REMOVAL VIA
VENTILATION
Carbon Dioxide
PRODUCTION
AT TISSUES
TRANSPORT IN BLOOD
REMOVAL VIA
VENTILATION
CO2 production
• Produced in tissues through cellular
respiration – glycolysis, Krebs cycle,
phosphorylation
CO2 production
CO2 up
CO2 down
Increased metabolic rate
-Sepsis
- Hyperthermia
-Burns
-Trauma
-Hyperthyroidism
-Shivering
-Malignant hyperthermia
-Neuroleptic malignant syndrome
Decreased metabolic rate
-Hypothermia
-Starvation
-Drugs for hyperthyroidism
Metabolic acidosis
CO2 transport
• Diffuses across capillary membranes and is transported to lungs through
the venous system
– ~7% transported dissolved in blood
– ~20% as carbaminohaemoglobin (reaction between carbon dioxide
and the amine radicals of the haemoglobin molecule)
– ~70% as bicarbonate and hydrogen ions from dissociation of carbonic
acid
CO2 transport i.e. cardiac output
• Diffuses across capillary membranes and is transported to lungs through
the venous system
– ~7% transported dissolved in blood
– ~20% as carbaminohaemoglobin (reaction between carbon dioxide
and the amine radicals of the haemoglobin molecule)
– ~70% as bicarbonate and hydrogen ions from dissociation of carbonic
acid
CO = SV x HR
CO2 transport
CO2 up
CO2 down
Tourniquet release
Arrest
Shock
Drugs
- Carbonic anhydrase inhibitor
(acetazolamide) – prevents CO2 transport
Shunting eg. PE
CO2 removal i.e. ventilation
• Ventilation = rate, volume, diffusion
CO2 removal i.e. ventilation
CO2 up
CO2 down
Low RR
- Drugs – sedatives, opiates
- Neurological causes
High RR
-Acidotic
-Psychological
-Ventilator settings
Diffusion impaired
-Chronic lung disease
-Inflammation – infection/inflammatory
process
Impaired ventilation
-APO
-Intrapulmonary shunt: atelectasis,
collapse, haemo/pneumothorax, effusion
Low volumes
-Ventilator settings
-Poor compliance
-Equipment – leak, tube placement
High volumes
- Ventilator settings eg. PS too high
ETCO2 - Why is it useful?
Reflects changes in:
- Ventilation
- Can predict impending respiratory failure
- Provides early warning of airway compromise
- Transport
- Can be used as a predictor of fluid responsiveness – found
to be proportional to CI in measuring response to passive
leg raise in patients with stable metabolic and respiratory
conditions
- Production
- Metabolism
Have I convinced you?
Problems with capnography
- Only reliable(?) in patients with stable
metabolic and respiratory states
- Abnormal Aa gradients make EtCO2 not a good
predictor of PaCO2, but can still use trend
- Needs to be a trend, not a one-off measure
- Detects, does not diagnose – more tests!
- Difficulty with equipment – easily clogged
with water droplets
- Normal capnogram can occur with glottic
intubation – still need an XR
Convinced?
• Capnography
• CO2 physiology
– Production
– Transport
– Ventilation
• The capnography curve and what it can tell us
• Problems with capnography
KEEP CALM
AND
WATCH THE
CO2