Download - How to survive a gas attack
How to Survive a
GAS ATTACK!in 10 minutes…
A Talk by Chris Nickson
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Photo by Misserion
Overview
A-a GradientCompensation
Strong IonsAnion Gap
All aboutA-a gradients(not really…)
A-a gradient = PAO2 – PaO2
PAO2 = FiO2 (PB – PH20) – (PaCO2/R)
Quick check:expected PaO2 = %FiO2 x 5
Caveats:high PaCO2
A-a gradient varies with age and FiO2
Rule of thumb:expected A-a gradient =
(age/4) + 4
Be aCompensation
King (or Queen)
Respiratory compensation = rapid
Metabolic compensation = slow
Metabolic compensation
The 1-2-3-4-5 Rule
1
12
12
HCO3
1 42
HCO3
1 42 5
HCO3
1 42 5
HCO3
acute chronic
1 42 5
HCO3
acute chronic
10 mmHg
PaCO2
Respiratory compensation
PaCO2 = 1.5 x HCO3 + 8 (+/-2) if metabolic acidosis
PaCO2 = 0.7 x HCO3 + 20 (+/-5) if metabolic alkalosis
Rule of thumb:If pH = 7.xy then
PaCO2 ≈ xy
Strong ions… WTF?
The real determinants of pH are:
Strong ionsWeak acids [ATOT]
PCO2
Strong Ion difference:
Na – Cl
<38 = NAGMA>38 = metabolic alkalosis
EMCrit by Scott Weingart http://emcrit.org/podcasts/acid-base-i/
Acid-Base Physiology by Kerry Brandishttp://www.anaesthesiamcq.com/AcidB
aseBook/ABindex.php
High Lactate withNormal Anion Gap… WTF?
Anion gap
Na – (HCO3+Cl)
Normal = 8-12 mM
LTKR
Anion gap is only ~50% sensitive
for lactic acidosis
What causes a low anion gap?
Low Anions: Albumin
High Cations
Bromism
Analytical error
Correcting for low albumin is essential
AGadj = AGobs + 0.25 x (42 - Albobs)
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