Lange Ch22 Flashcards
How much is physiologic dead space? Per weight?
1 cc per lb. so average physiologic dead space is 150cc
Bohr equation for dead space to tidal volume ratio Vd/Vt
Vd/Vt = (PACO2 - PeCO2) / PACO2. Avg ratio is 33% for 150/450. PeCO2 is mixed expired
Relationships of Pa, Pv, and PA in the 3 lung zones
Zone 1: PA > Pa > Pv, high V/Q
Zone 2: Pa > PA > Pv
Zone 3: Pa > Pv > PA, low V/Q
Ventilation and perfusion improve in dependent areas
How to calculate PAO2?
PAO2 = FiO2*(760-47) - (PCO2 / 0.8)
PAO2 ~ FiO2 * 6
MC mechanism of hypoxemia
Increased A-a gradient caused by R->L shunt, V/Q mismatch, low MvO2 (low cardiac output, high O2 consumption, anemia)
Venous admixture (physiologic shunt) equation
Qs/Qt = (CcO2 - CaO2) / (CcO2 - CvO2)
Normal shunt is 5%
Total oxygen delivery (DO2) equation
DO2 = cardiac output * arterial O2 content
Oxygen consumption VO2 equation
VO2 = cardiac output * (arterial O2 content - mixed venous O2 content)
Oxygen content equation
(O2sat * hgb * 1.31) + (PO2 * 0.003)
Mixed venous oxygen content equation
CvO2 = CaO2 - (VO2 / Qt)
VO2 oxygen consumption ~ 250 mL/min
Qt cardiac output
Basic breathing rhythm originates from what part of brain?
Medulla
Effect of anesthesia on peripheral ventilatory response to hypoxemia
Abolished response