Ch01-2-4-9781975113285
Useful Formulae
4
Thomas M. De Fer
INTRODUCTION
• The most important formula for the intern year:
(discharges + transfers) (admissions + cross cover) 2
Sleep (h) =
× number of interns
• Many of these formulae can be found on applications for your electronic devices or on Web sites. A-a O 2 GRADIENT
− Pa O
A-a gradient = PA O 2
2
2 × 713) − (PaCO 2
PAO
= (FiO
/0.8)
2
( all units in mm Hg )
• Estimate for upper limit of normal in room air (in mm Hg) by age (years) = (age/4) + 4. • Causes of increased A-a gradient: V/Q mismatch, intrapulmonary right-to-left shunt, intracardiac right-to-left shunt, impaired diffu- sion (room air only) ANION GAP (SERUM)
AG = [Na + ] − ([Cl − ] + [HCO 3 – ])
( all in mmol/L )
• Normal = 8 to 12 mmol/L • See Chapter 15, Acid-Base Disorders, for differential diagnosis.
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