Week 7 - Math

Question 1

A-a gradient

Answer 1

1. % air x 713 (760-47)
2. PaCO2/0.8

1-2 =PAO2

PAO2 - PaO2

A = calculated alveolar oxygen pressure
a = measured arterial blood oxygen pressure

PAO2 = (PB-PH2O)xFiO2-PaCO2/R

PB = barometric pressure at sea level 760
PH20 = pressure of water
47
R = respiratory quotient
0.8

Normal 5-15mmHg

Question 2

RER resting energy requirement

Answer 2

30 x BW + 70 =

Question 3

Rehydration volume

Answer 3

% dehydrated x BW =
X 1000 to get mL

Question 4

Osmolality

Answer 4

2 x (Na + K) + Glu/18 + BUN/2.8

Question 5

Effective osmolality

Answer 5

2 x Na + Glu/18

Ref: 290-310 mOsm/kg

Question 6

Daily maintenance fluid rate

Answer 6

65-75ml/kg/day or 2-4ml/kg/hr

(70xBW^0.75)/24
(<2kg or >40kg)

(30xBW+70)/24
(Mid range weight)

Question 7

Rehydration volume

Answer 7

% dehydration x BW x 1000 = mL

Question 8

Dehydration %

Answer 8

<5% - not dehydrated
5-6% - tacky mm’s
6-8% - decreased skin turgor/dry mm’s
8-10% - retracted globe within orbit
10-12% - persistent skin tent/dull cornea/evidence of hypovolemia
>12% - hypovolemic shock/death

Question 9

Sodium bicarbonate

Answer 9

BWx0.3x(12-HCO3)x0.5

Base excess

Question 10

Corrected Na

Answer 10

Na measured + 1.6 x (Glu-100/100)

Question 11

Anion gap

Answer 11

(Na + K) - (Cl-HCO3)

Cations - anions

Normal: 4-12 mmol/L

Question 12

Hypoxemia with normal A-a gradient

Answer 12

Hypoventilation

Question 13

Hypoxemia with elevated A-a gradient

Answer 13

Pneumonia

Question 14

K-max

Answer 14

0.5mEq/kg/hr

Unless patient is on cardiac monitoring

Question 15

Na deficit

Answer 15

(Target Na-Patient Na)(0.6xBW)

Question 16

Free water deficit

Answer 16

(Patient Na/Normal Na-1) x (0.6 x BW) (in L)

Decrease Na by 1mmol/hr - acute
Decrease Na by 0.5mmol/hr - chronic

Question 17

Total body water

Answer 17

0.6xBW (in L)

Question 18

MAP

Answer 18

Systolic + 2 x Diastolic/3