Statistics, Equations and Pharmacology Flashcards
Laplace’s law and it’s implication/role re: surfactant
P=2T/r (distending pressure, surface tension, radius)
Normally the smaller a sphere is, the higher the pressure needed to distend it or maintain its volume
Surfactant decreases surface tension so helps mitigate that effect (AKA lowers P)
Compliance equation
Change in volume/change in pressure
So compliance is the “slope” on a pressure/volume curve, so greatest in the middle when volume is around FRC
Resistance equation
Resistance = change in pressure/change in flow
Resistance = 8nL/πr4
In neonates primary resistance is airway
Time constant equation
tc = resistance x compliance
Takes 3-5 time constants to allow adequate inspiration/expiration–thus iT is about 0.3-0.45 sec at term
PAO2 equation (alveolar partial pressure of oxygen)
PAO2 = [FiO2 x (barometric pressure-water vapor pressure)] - (PaCO2/R)
Pb (sea level)=760, PH2O=47, R 0.8 or 1 … therefore:
PAO2 = (FiO2 x 713) / (PaCO2/0.8)
Benzodiazepine mechanism of action
Enhances GABA action–benzo binds GABA-receptor
GABA is inhibitory normally, but in preemies is actually excitatory
Theoretical reason for concern about benzodiazepine use
GABA action may induce neuroapoptosis
What kind of tests should you use for data that follow a Gaussian distribution?
Parametric
e.g. t test or ANOVA
(Gaussian is a “normal” bell-shaped distribution)
What test is best used for normally-distributed data comparing two unrelated groups?
t test (it’s parametric AKA best for normally-distributed data)
(A paired t test is used for related groups, such as the same cohort before and after an intervention)
What test is best for abnormally distributed data comparing two UNrelated groups?
Mann-Whitney U test
Name the parametric and nonparametric tests used for comparing two groups that are RELATED
Paired t test and Wilcoxon test
What are the general group names of parametric tests used for comparing 1) two groups and 2) more than two groups?
- t tests (regular if they’re unrelated groups, paired t if they’re related)
- analysis of variance (ANOVA) (one-way ANOVA if unrelated, repeated-measures ANOVA if groups are related)
What are the two nonparametric tests used for comparing two groups of data?
- Mann-Whitney U test if groups are UNrelated
- Wilcoxon test if groups are related
Name some nonparametric tests used for comparing more than two groups
Kruskal-Wallis
Friedman
Spearman
(Nonparametric tests are used when the data distribution is abnormal)
The two tests used for comparing qualitative data, and general difference between the two
X2 (chi squared): all variable options have high frequency
Fisher’s exact: if some results have a very low frequency/number
Number needed to treat (NNT) in words and/or table
NNT= 1/ARR, where ARR=absolute risk reduction
NNT = 1 / [c/(c+d) - a/(a+b)]
Denominator’s positive because more should have the problem who were untreated (c) vs “diseased” who were treated (a)
Relative risk or risk ratio (RR)
(in words and/or from table)
Ratio (i.e. fractional) probability of outcome in the exposed group vs. the probability of outcome in the nonexposed group
RR = (a/[a+b])/(c/[c+d])
Main side effects of bosentan?
Hepatic (transaminitis, hyperbilirubinemia, dysfunction)
Bone marrow suppression (all three lineages)
Sensitivity and specificity __do/do not_ vary with disease prevalence
Do NOT vary with disease prevalence
(Whereas positive and negative predictive value do vary with disease prevalence)
How does phenobarbital improve bilirubin metabolism?
Increases concentrations of ligandin, which is the primary carrier from plasma into hepatocytes
What are the four different types of data, and what’s the difference between ordinal and integer?
Categorical, ordinal, integer (ie. interval), and continuous
Ordinal is like stages or grades, ie. ranking–the order means something; integer/interval data have a set value difference between each data point
What are the three “measures of central tendency” (ie. average)
Mean: literally the average (the sum divided by the number of data points)
Median: the value that’s in the middle (50% data points are above and below)
Mode: most common value
Median is used more in studies because it’s less influenced by outliers than the mean
How much of a data set is above (or below) 2 standard deviations “of the norm”
2 standard deviations equals 2.3% of the data
So if you’re 2 SDs smarter than the average bear, you’re smarter than 97.7% of the population (the 2.3% that are 2 SDs below, plus all 95.4% of the chumps in the middle)
What is a type 1 error (and give two synonyms)
Alpha error, “p-value”
The chances of finding a difference when there is none (like a false-positive result)
When you’re an alpha, you think you’re hot shit even when you’re not
What is the power of a statistical test
The “power” of your study is essentially how likely are your results to be correct
Power = 1 - beta error
Type 2 (beta) is chances of saying there’s no difference when there actually is
What is the difference between a case-control study and a cohort study
Case-control is retrospective (you compare a group with an outcome with one that did not)
Cohort is prospective (you compare group with an exposure to group that did not)
What’s the difference between relative risk reduction and absolute risk reduction
Relative risk reduction is by what proportion is it decreased
Absolute reduction is by what actual amount
If something happens 8% in control and 4% in test group, the RRR is 50% but ARR is 4%
Draw the statistics box to help with calculating measures of effect
Outcome goes ON top
(When talking about an exposure vs. outcome, OUTcome on top; when talking about treatment vs. disease, disease goes on top)
What’s the difference between relative risk and odds ratio
The relative risk is how having an exposure affects your chances of an outcome compared to its frequency in the non-exposed
Odds ratio is the ODDS that the outcome will happen in the exposed group compared to the odds of it happening in the control group
They are the same when the prevalence of the outcome is low
Oxygen consumption equation
O2 consumption = CO in dL/min x 1.34 x [Hb] x (SaO2-SvO2 in decimals)
A.K.A. =CO x (CaO2-CvO2)
=cardiac output x (arterial oxygen content - venous oxygen content)
(mL/g Hb and Hb concentration can be pulled out of CaO2 and CvO2)
When is the odds ratio NOT equal to the relative risk, and in which direction will it be inaccurate
When an outcome is common (eg. disease is prevalent), odds ratio with OVERestimate the effect of an exposure
When you play the odds, you may THINK you’ve won when you haven’t
Definition of sensitivity vs. positive predictive value (PPV)
Frequency of true positive (how good is the test at detecting disease)
If test is positive, how likely are you to have disease
Denominator is different, for sensitivity it’s the total number who are actually positive and for PPV it’s the total who tested positive
What’s the difference between specificity and negative predictive value
Specificity: true negative / (true negative+false positive)
AKA how many of those without disease did the test accurately diagnose
NPV: true negative / (true negative+false negative)
AKA how many that tested negative were actually disease-free
Anion gap calculation
(Na+K)-(Cl+HCO3)
Normal 10-16
Oxygen carrying capacity equation
O2 bound to Hb + O2 dissolved and unbound
(1. 34 x [Hb] x SpO2) + (0.003 x PaO2)
* This is the same as oxygen content but DIFFERENT than oxygen consumption which is affected by cardiac output*
Oxygen content calculation
O2 content = Hb-bound O2 + unbound O2
= (1.34x[Hb}xSpO2) + (0.003xPaO2)
- 1.34mL/g is how many mL of O2 each g Hb can carry*
- Oxygen content is the same as the carrying capacity (how much can your body hold) but DIFFERENT from oxygen consumption (how much do you use up)*
Oxygenation index equation
OI = (MAPxFiO2) / PaO2
OI is usually used to decide if ECMO is warranted (>40 is suggested)
Side effects to know for the two antireflux medications erythromycin and metoclopramide
Erythromycin: pyloric stenosis
Metoclopramide: tardive dyskinesia which is irreversible
How many calories in intralipids (IL), carbohydrates (CHO) and amino acids (AA)
20% IL: 9kcal/kg
CHO: 3.4kcal/kg
AA: 4kcal/kg
And remember D___ means ___g/100mL (so D10 is 10g/100mL)
Glucose infusion rate calculation (GIR or DDR)
GIR = volume (mL/kg/day) x Dex % x 0.007
eg. 80mL/kg/day x 10 x 0.007 = 5.6 g/kg/min
Two most common drugs that cause thrombocytopenia
1) Indomethacin
2) Heparin
FeNa calculation
FeNa= [(uNa x sCr) / (sNa x uCr)] x 100
Easy to remember, definition is how much you excrete so [uNa] must go in numerator, and you always pair urine with serum (so it follows sCr also goes in numerator)
Plasma osmolarity calculation
Osm (in mOsm/L) = 2[Na] + (gluc/18) + (BUN/2.8)
Normal is 270-300 mOsm/L
The smaller the molecule the more it contributes
GFR equation (estimation using Schwartz)
GFR= (k x height)/sCr
- k*=0.45 in term
- k*=0.33 in preterm
(Height is in cm)
Location of action for furosemide
Loop of Henle (thus loop diuretics)
Thick ascending limb
Location of action for acetazolamide (Diamox)
Proximal convoluted tubule
Remember _P_CT is where you _P_ee out bicarb
(Acetazolamide increases HCO3 excretion, such as when trying to correct contraction alkalosis)
Sodium deficit equation
Na+ deficit = ([sNa]-desired [Na]) x weight x 0.6
Most drugs experience what order of kinetics
First order
(Means a certain percentage of concentration is excreted in a certain amount of time; AKA the premise of a half-life)
What are the y- and x- axes for the pressure-volume loops in respiratory and cardiac physiology
Respiratory: Pressure is x, volume is y
CV: Volume is x, pressure is y
Remember “beaking” on ventilators, and that CV has inversed axis
Label A-D
A: mitral valve opens (phase IV-ventricle relaxed but empty [while atrium filled], ie “isovolumetric relaxation”)
B: end-diastolic volume (phase I-ventricle filled, ie diastole)
C: aortic valve opens (phase II-ventricle contracted but AV closed, ie “isovolumetric contraction”)
D: end-systolic volume (phase III-ventricle emptied, ie systole)
Most “basic” cardiac output equation
CO = SV x HR
cardiac output = stroke volume x heart rate
- Remember CO is a “volume per minute”, so can equate to Flow (Q)*
- Therefore another equation is Q = P/R*
Cardiac output equation using its definition as Flow (Q)
CO = flow, ie Q
Q = Pressure/Resistance
CO = SBP / (8nL/πr4)
- SBP is systolic blood pressure*
- 8nL/πr4 is systemic vascular resistance*
Which antihypertensive group is contraindicated when <36 weeks and why?
Angiotensin-converting enzyme inhibitors (ACEI)
In-utero (and therefore in premature infants) nephrogenesis is driven by RAAS, so inhibiting that system can impair nephrogenesis that continues through 36 weeks
What type of ratio comparing outcomes is most frequently used for case control studies (relative risk or odds ratio)
Odds ratio
_O_dds ratio is better when looking at _O_utcome to define groups, and then retrospectively at risk/exposure (AKA when _O_utcome is rare so starting there)
Is it better for the area under the curve in an ROC (receiver operator characteristic) curve to be high or low?
Better to be HIGH, meaning the sensitivity and specificity were both high
Three medications that induce (increase) P450 activity
Dexamethasone
Phenobarbital
Phenytoin
How much (% wise) does 1 standard deviation cover
68.2%
vs. classic 95% covered by 2 SD
Highly protein-bound drugs have a __higher/lower__ volume of distribution?
Lower
Because more of it’s trapped in plasma (bound) than getting put into tissues
Drugs with a larger volume of distribution (Vd) generally have a ______ half-life
Longer
Because they’re distributed (i.e. hiding) in more tissues
Equation for volume of distribution (Vd)
Vd = [total drug] / ([drug in plasma] x body weight)
Neonates have higher Vd because of decreased protein binding, and preemies even more so
