Capnography for the intensivist Sarah Philipson. THE END.
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Transcript of Capnography for the intensivist Sarah Philipson. THE END.
Capnography for the intensivist
Sarah Philipson
THE END.
THE END.
Questions?
Questions?CO2
physiologyWhat is
capnography?
Questions?What is
capnography?CO2
physiology
Questions?What is
capnography?CO2
physiology
How is it used?
Questions?What is
capnography?CO2
physiology
How is it used? 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 capnogramI – inspiratory baselineII – expiratory upstrokeIII – alveolar plateauIV – 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 capnogramI – inspiratory baselineII – expiratory upstrokeIII – alveolar plateauIV – inspiratory downstroke
Normal EtCO2 = 38-40mmHg
Capnography
• Measurement of CO2 vs time• Infrared spectroscopy measures the fraction
of energy absorbed and converts this to a percentage of CO2 exhaled
• Normal capnogramI – inspiratory baselineII – expiratory upstrokeIII – alveolar plateauIV – inspiratory downstroke
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 up CO2 down
Increased metabolic rate-Sepsis- Hyperthermia-Burns-Trauma-Hyperthyroidism-Shivering-Malignant hyperthermia-Neuroleptic malignant syndrome
Decreased metabolic rate-Hypothermia-Starvation-Drugs for hyperthyroidismMetabolic acidosis
CO2 production
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 transportCO2 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. ventilationCO2 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 CALMAND
WATCH THE CO2