Chemistry Flex Bench Flashcards
contribute most to serum osmo
Na
Glucose
Urea
purpose of osmo
kidney’s concentration ability
typical causes for ↑ osmo
dehydration
kidney issues
osmo equation
1.86(Na) + (glu/18) + (BUN/2.8) + 9
osmo normal ranges
serum – 275-300 mOsm/kg
urine – 50-1200 mOsm/kg
osmo gap equation
measured osmo - calculated osmo
normal <10
causes of ↑ osmo gap and ↑ anion gap
- PO4, SO4 (renal failure)
- acetone, BHOB (DKA)
- alcohol
- lactate (tissue hypoxia)
- ethylene glycol (antifreeze)
- ANION gap – salicylate (aspirin OD)
anion gap (no K) equation and RR
Na - Cl + tCO2
RR: 7-16 mEq/L
RR with K: 10-20 mEq/L
excess anions/acids
↑ anion gap
sample size for osmo (in pipette)
20 μL
the osmo sample must be…
(size)
slightly longer than it is wide
no convex meniscus
osmo procedure for pts
run in duplicate
must be within 2 mOsm
1000 mOsm/kg depresses FP by…
-1.86° C
steps of FP osmometer
- fast cool
- reaches 0° – slow cool
- mechanical pulse freezes sample
- heat of fusion – asymptotically warms sample to its freezing point – temp approaches equilibrium
- plateau – osmolality is read
automated multi-wavelength spectrophotometric method used on ABG instruments
co-oximetry
test method for co-oximetry
1 μL blood heated to 37° and sonically hemolyzed by vibrating the cuvette walls at 30 kHz
Beer’s law is used to measure components
fractions of total Hgb are given
↑ Hgb affinity for O2
↑ pH
↓ pCO2
↑ pO2
↓ 2,3-DPG
↓ temp
↓ Hgb affinity for O2
↓ pH
↑ pCO2
↓ pO2
↑ 2,3-DPG
↑ temp
corrected barometric pressure
BP value - 47 mmHg [VP of water] = corrected BP
calibrate BP for gas content
corrected BP(% gas) = mmHg
ABG sample requirements
- tightly stoppered
- balanced heparinized syringe
- on ice (2 hr) – 30 min no ice
- no bubbles
- perform ASAP
non-balanced heparin effects…
electrolytes, especially cCa2+
lipid therapy affects…
OXI measurements (Beer’s law)
opposite arrows vs same arrows on either side of HH equation
opposite – respiratory
same – metabolic
calibration for electrode drift
one-point
calibration for electrode slope changes
two-point
HH equation for blood gases
pH = 6.1 + log[HCO3/(pCO2)(0.03)]
pKa for blood gases
6.1
normal pH, HCO3, and pCO2
pH – 7.35-7.45
HCO3 – 22-26 mEq/L
pCO2 – 35-45 mmHg
alkalosis/acidosis with normal pH
fully compensated
P/F ratio equation and ranges
pO2/% inspired O2 = P/F
mild resp distress – 200-300
moderate – 100-200
severe – <100
room air is 21% O2
indicates ARDS or resp failure
—–% O2 saturation for a capillary specimen is acceptable
> 70
as pH ↓, iCa —-, because…
↑
decreasing pH causes less Ca to be protein-bound
iCa sample
dark green (heparinized plasma) tube with no gel
on ice (4hr) or not on ice (30 min)
half full
WB
released with iCa to account for false changes
pH
— iCa causes seizures, cardiac arrest
↓
— iCa causes nausea, constipation, kidney failure
↑
if osmo gap is >25…
suspect ingestion of substance
high osmo gap with HAGMA
high anion gap metabolic acidosis
MEELK
- methanol
- ethylene glycol
- ethanol
- lactic acidosis
- ketoacidosis
high osmo gap without HAGMA
high anion gap metabolic acidosis
- isopropyl alcohol
- mannitol
- sorbitol
- glycine
- maltose
glycine, sorbitol, mannitol used for transurethral resection of prostate
hyponatremia + euvolemia
- SIADH
- adrenal insufficiency
- hypothyroidism
hyponatremia + hypovolemia
- diuretics
- osmotic diuresis
- vomiting
- diarrhea
hyponatremia + hypervolemia
- kidney failure
- cardiac arrest
- cirrhosis
- nephrotic syndrome
↓ serum osmo
↓ serum Na
↑ urine output
↓ urine osmo
water overload
↑ serum osmo
↑ serum Na
↑ urine output
↓ urine osmo
DI
↓ serum osmo
↓ serum Na
↓ urine output
↑ urine osmo
SIADH
causes of water overload
psychogenic/primary polydipsia
- hypothalamic disease
- drugs
- altered mental status/psychiatric disease
polyuria + polydipsia
>2.5 L/day urine output
crave water/ice
extreme fatigue, muscle weakness
DI
2 types of DI
central – failure of pituitary to secrete normal ADH
nephrogenic – renal resistance to action of ADH
fluid overload/weight gain
low urine output with high SG
SIADH
causes of SIADH
- malignant production of vasopressin
- diseases of CNS
- pulmonary disorders
- side effects of drugs
