Maker's Study Guide (Week 2)

Actual weight < IBW

Use actual weight

actual weight > IBW but < 130% IBW

Use actual weight

If actual weight > 30% of IBW

Use Adjusted Body Weight

IBW(kg, men)

50 + 2.3(inches over 5 ft)

IBW(kg, women)

45.5 + 2.3(inches over 5 ft)

Adjusted BW (kg)

IBW + 0.4(Actual weight - IBW)

Cockcroft Gault equation

((140-age) x kg) / (72 x SCr)) x 0.85 for women.

CG equation ____ CrCl and is used for ___

estimates, drug dosing

Is it appropriate to round SCr

NO

In overweight individuals, actual BW tend to ___ CrCl and IBW tend to ___ CrCl

overestimate, underestimate

CrCl-24 hr urine collection ___ CrCl, and is used in ___

measures, inpatient setting when more accurate estimate of renal function is needed in a clinical setting.

CrCl-24 hr urine collection

CrCl (mL/min) = (Urine (mL)/1440 min) x Ucr/Scr

CKD-EPI is used for

nephrologists to stage patients with CKD

Serum Creatinine increases with ______ and decreases with ______

muscle mass, protein intake, obesity, sex(M), CKD //

elderly and limb amputation

___ is more accurate than SCr but recommended to use both in CKD EPI

Cystatin C

In GFR Calculator, we leave standardized assay checked off as "yes", because labs are supposed to utilize

IDMS

CKD-EPI is adjusted for BSA

mL/min/1.73m^2

Assume CrCl<10 mL/min if

dialysis, anuria (urine production less than 50-200 mL in 24 hours), severe AKI

Special Pop: Infants, normal SCr:__

GFR very low (20 mL/min/1.73m^2) in newborns

reaches "normal" levels after first year of life.

Normal SCr = 0.2-0.4mg/dL

Estimating Renal Function in Children: Modified Schwartz formula

GFR (ml/min/1.73 m2 ) = 0.413 x ht (cm)/Scr

Special Pop: Unstable Renal Fxn

In AKI/critical illness, difficult to estimate GFR due to Scr fluctuations

CG or CKD-EPI equations in AKI?

NOOOOOOO

Special Populations: Renal Transplants

no unique formula, because of fluctuating SCr. great emphasis on following Scr trends.

Long term, many patients will have eGFR of _____

<60 ml/min/1.73 m2

acidemia

pH < 7.35

alkalemia

pH > 7.45

primary disorder

Process causing alteration in blood pH. Metabolic or respiratory

compensation (secondary response)

attempts to correct HCO3-/pCO2 ratio toward normal & mitigate the change in pH

Role of Lungs

CO2 elimination is directly related to the rate and depth of air moving in and out of the lungs

If a person is hypoventilating, pCO2 is ___

increased

Respiratory alkalosis is caused by

hyperventilation (exhale too much co2, blowing it off)

If a person is hyperventilating, pCO2 is ____

decreased

Respiratory acidosis is caused by

hypoventilation (exhale too little CO2; RETAIN it)

Role of Kidneys

Maintain concentration of HCO3 at 24 meq/L by reabsorption of filtered bicarb in the proximal tubule (catalyzed by carbonic anhydrase), H+ secretion, NH4+ excretion

pH range

7.35-7.45

pco2

35-45 mmHg

pO2

80-100 mmHg

HCO3

22-26 meq/L

O2 sat

>95% sat

base excess or deficit

+/- 2 mEq/L

base excess

Amount of acid which would need to be added or subtracted from a substance in order to return the pH to normal

A base excess > +2 mEq/L

metabolic alkalosis

A base excess < -2 mEq/L

metabolic acidosis

ABG short form

pH/pCO2/pO2/HCO3-/O2 sat

Primary Disorder

pH < 7.35 → acidosis

pH > 7.45 → alkalosis

HCO3-

<22 mEq/L → metabolic acidosis

>26 mEq/L → metabolic alkalosis

pCO2

<35 mmHg → respiratory alkalosis

>45 mmHg → respiratory acidosis

A patient with metabolic alkalosis is expected to have:

a) pH 7.55, HCO3 15 mEq/L

b) pH 7.55, HCO3 32 mEq/L

c) pH 7.55, pCO2 50 mmHg

d) pH 7.25, pCO2 31 mmHg

b

In respiratory alkalosis the primary issues are ____

high pH and low pCO2

In respiratory alkalosis,

kidneys compensate by decreasing bicarbonate to lower pH

metabolic acidosis (low pH, low HCO3-)

compensatory mech: lungs increase pH and lower pCO2

metabolic alkalosis (high pH and high hCO3-)

compensatory mech: lungs compensate by decreasing pH and increasing pCO2

respiratory acidosis (low pH and high pCO2)

compensatory mech: lungs compensate by increasing pH and HCO3-.)

respiratory alkalosis (high pH, low pCO2)

compensatory mech: lungs lower pH and HCO3-

anion gap

unmeasured anions in plasma

normal AG

8-12 mEq/L

increased anion gap generally caused by

metabolic acidosis

AG equation

AG = Na+ - Cl- - HCO3-

AG needs to be corrected in patients with hypoalbuminuria (Alb < 4g/dL)

Every 1g/dL decrease in albumin will decrease AG by about 2.5 mEq/L.

Corrected Ag

Add 2.5 to the AG for every 1g/dL decrease in albumin

Ex: Pt with albumin of 3g/dL and AG of 14 will have corrected AG of

16.5mEq/L

If AG is > 12 mEq/L, patient has

AG metabolic acidosis.

AG < 12 mEq/L

No underlying A/B disorder

Respiratory Acidosis Causes

central depression of respiratory center (sedative/opioid OD, neuromuscular blockers/disorders, paralytics)

Respiratory Alkalosis Causes

Increased central stimulation of respiration (anxiety, pain, salicylate toxicity)

Metabolic Acidosis (pH low, hco3 low) has 2 kinds

1) anion gap

2) hyperchloremic

AG Metabolic Acidosis common causes include

renal failure (AKI/CKD), ketoacidosis (uncontrolled diabetes/excess alcohol), lactic acidosis, drugs, toxins, OD

Hyperchloremic Metabolic Acidosis (normal range AG) common causes include

intestinal HCO3- losses, diarrhea, fistula, surgical drains, very large amounts of normal saline

Severe hyperchloremic metabolic acidosis tx (pH <7.1-7.2)

dialysis and IV Sodium bicarb (GOAL TO INCREASE PH NOT CORRECT)

Hyperchloremic metabolic acidosis tx

Na/K bivcarb, K citrate PO

Chronic metabolic acidosis

very common in patients with CKD (avoid K+ if CKD)

Tx: oral bicarb supplement

Use CO2 as surrogate marker for HCO3-0

No need for ABGS

pCO2 is NOT the same as

CO2

Metabolic Alkalosis

-saline responsive

-saline resistant

"Saline responsive" metabolic alkalosis TX

* Intravascular volume depletion (NG suctioning, vomiting, diuretics)

* volume depletion: 0.9% NaCl IV

alt to volume: acetazolamide 500-1000 mg PO bid

* severe: IV HCl (PREFERRED) / IV NH4Cl

Severe metabolic alkalosis TX (HCO3 > 50 mEq/L, pH>7.55) tx

ICU patients

IV HCl (PREFERRED), IV NH4Cl

Goal is PARTIAL CORRECTION (pH=7.5) to prevent overcorrection

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