how to survive a gas attack
DESCRIPTION
Slides for a short talk on some tips and tricks for trainees when interpreting ABGs (arterial blood gases). Talk given at the free registrar's day at Bedside Critical Care 2013 in the Whitsunday Islands.TRANSCRIPT
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How to Survive a
GAS ATTACK!in 10 minutes…
A Talk by Chris Nickson
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No $
Photo by Misserion
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Overview
A-a GradientCompensation
Strong IonsAnion Gap
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All aboutA-a gradients(not really…)
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A-a gradient = PAO2 – PaO2
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PAO2 = FiO2 (PB – PH20) – (PaCO2/R)
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Quick check:expected PaO2 = %FiO2 x 5
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Caveats:high PaCO2
A-a gradient varies with age and FiO2
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Rule of thumb:expected A-a gradient =
(age/4) + 4
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Be aCompensation
King (or Queen)
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Respiratory compensation = rapid
Metabolic compensation = slow
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Metabolic compensation
The 1-2-3-4-5 Rule
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1
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12
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12
HCO3
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1 42
HCO3
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1 42 5
HCO3
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1 42 5
HCO3
acute chronic
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1 42 5
HCO3
acute chronic
10 mmHg
PaCO2
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Respiratory compensation
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PaCO2 = 1.5 x HCO3 + 8 (+/-2) if metabolic acidosis
PaCO2 = 0.7 x HCO3 + 20 (+/-5) if metabolic alkalosis
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Rule of thumb:If pH = 7.xy then
PaCO2 ≈ xy
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Strong ions… WTF?
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The real determinants of pH are:
Strong ionsWeak acids [ATOT]
PCO2
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Strong Ion difference:
Na – Cl
<38 = NAGMA>38 = metabolic alkalosis
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EMCrit by Scott Weingart http://emcrit.org/podcasts/acid-base-i/
Acid-Base Physiology by Kerry Brandishttp://www.anaesthesiamcq.com/AcidB
aseBook/ABindex.php
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High Lactate withNormal Anion Gap… WTF?
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Anion gap
Na – (HCO3+Cl)
Normal = 8-12 mM
LTKR
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Anion gap is only ~50% sensitive
for lactic acidosis
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What causes a low anion gap?
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Low Anions: Albumin
High Cations
Bromism
Analytical error
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Correcting for low albumin is essential
AGadj = AGobs + 0.25 x (42 - Albobs)
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THE END
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THE END
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