Stats/Equations

Question 1

Qp:Qs

Answer 1

(Ao sat - SVC sat) / (PV sat - PA sat)

Question 2

PVR (woods units)

Answer 2

(mean PA pressure - mean LAP) / Qp

Question 3

Qs:QT or % shunt

measures VQ mismatch

Answer 3

(PV sat - PA sat) / (PV sat - SVC sat)

Question 4

Hardy Weinberg equations

Answer 4

p + q = 1

p^2 + 2pq + q^2 = 1

Question 5

• As the prevalence increases, the PPV ______ and the NPV ______.
• As the prevalence decreases, the PPV ______ and NPV ______.

Answer 5

• As the prevalence increases, the PPV increases and the NPV decreases.
• As the prevalence decreases, the PPV decreases and NPV increases.

Question 6

Variables!

Answer 6

Qualitative variables (categorical)

• • nominal - no order, no magnitude (gender, blood type)
• • ordinal - has order but no set magnitude (ROP, NEC)

Quantitative variables (continuous)

• • interval - equal intervals but no meaningful zero (apgars, temperature)
• • ratio - equal intervals with meaningful zero (birthweight, residuals)

Question 7

between case-control and cohort studies, when do you use RR and when OR?

Answer 7

Use OR with case-control and RR with cohort

Question 8

How do you increase the power (decrease type II error) of a study?

Answer 8

think MASS:

• increase magnitude of difference
• increase alpha
• increase sample size
• decrease std deviation

Question 9

What does changing the p value do to type I and type II errors?

Answer 9

Increasing p value increases chance of type I error (finding a difference when there isn’t one)
Increasing p value decreases the change of type II error (not finding a difference when there is one)

Question 10

KBT?

Answer 10

every % of fetal hemoglobin = 50 mls lost

Eg: 3 fetal cells, 100 maternal cells. 3% = 150 mls lost

Question 11

polycythemia exchange transfusion?

Answer 11

TBV (O-E/O)

Question 12

If infant’s hct drops, how do you calculate EBL?

Answer 12

(change in hct/avg of hcts) x TBV

eg:
If hct went from 55 -> 45 in a 2 kg kid:
10/50 x 180 = 36 mls

Question 13

what is the new hct after a volume of PRBC’s are transfused?

Answer 13

change in hct = (vol PRBC’s x hct PRBC’s)/TBV

eg, give 15 ml/kg of PRBC’s with a hct of 60 to a 2 kg kid:
30 x 60 / 180 = hct will increase by 10

Question 14

If your TV decreases from 6 mls to 3 mls, how much can you expect your CO2 to increase by?

Answer 14

dead space always = 2mls
So TV actually decreased 4 mls to 1 ml

CO2 will go up 4x what it was prior

Question 15

Which one is prevalence, which one is incidence:

• 0.05%
• 5 cases per 10,000 children per year

Answer 15

• 0.05% = prevalence
• 5 cases per 10,000 children per year = incidence

incidence includes cases plus the time “in” which it happens