Equations Flashcards
Osmolality
Equation for calculated osmolality
number of solute particles (osmoles) in 1 kg of solvent
mOsm/kg
2xNa + BUN/2.8 + BG/18
- 2x NA to account for Cl and HCO3
- Divided to convert from mg/dL -> mmol/L
Osmolarity
number of solute particles (osmoles) per 1L of solvent
mOSm/L
Normal osmolarity in dogs and cats
Dogs: 290-3010 mOsm/L
Cats: 311-322 mOsm/L
Tonicity
Equation for calculated effective osmolality
Only accounts for effective osmoles, i.e. those that don’t freely permeate most cell membranes
2xNa + BG/18
(since BUN is an ineffective osmole)
Osmole gap equation
Osmole gap = measured - calculated osmolality
Gap > 10 mOsm/kg indicates presence of unmeasured solutes
Albumin deficit equation
albumin deficit (grams) = 10 x (desired-patient alb) x BW in kg x 0.3
FFP dose to increase albumin
22.5 mL/kg to raise albumin by 0.5 g/dL
Blood transfusion calculation (2)
90 ml x kg BW x ([desired PCV- patient PCV]/ PCV of donor blood)
1.5 ml x % PCV rise x kg BW
donor PCV usually 70-80%
Old and new Starling’s equation
Old: Jv = Kfc [( Pcap – Pint) – σ (πplasma – πint)]
New: Jv = Kfc [( Pcap – Pint) – σ (πplasma – πisg)]
What is:
- Kf
- σ
Kf= capillary filtration coefficient
-dictates membrane permeability (to water) and membrane surface area.
σ = reflection coefficient
- describes the fact that a small amount of protein leaks from the capillary and depends on the interstitial protein content
- Close to 1 (e.g. BBB) = impermeable to proteins
- Close to 0 (e.g. liver sinusoidal) = freely permeable
reflection coefficient in:
- liver
- kidney
- lungs
Liver: 0
Kidney, brain: 1
Lungs: ~0.5 due to significant leak of protein
-Protein leak decreases as interstitial oncotic pressure rises, limiting further edema formation
Normal Colloid osmotic pressure (COP) in dogs and cats
Dogs 15.3-26.3 mmHg
Cats: 17.6-33.1 mmHg
(20 average for both)
Henderson-Hasselback
pH = 6.1 x log [ (HCO3-) / (0.03 x PCO2)]
6.1 = pKa in body fluids
HCO3 in mEq/L or mmol/L
0.03 = solubility coefficient of CO2 in plasma
PCO2 in mmHg
Carbonic acid equation
CO2 + H2O H2CO3 H+ + HCO3-
Carbonic anhydrase catalyzes first half (intracellularly)
Anion gap
AG = (Na+K) - (Cl+HCO3-)
Not reliable if patient is hypoalbuminemic
Normal anion gap for dogs and cats
Dog: 12-24mEq/L
Cat: 17-31mEq/L
Expected compensation for metabolic disorders
- Metabolic Acidosis ↓1mEq/L HCO3 = 0.7mmHg PCO2↓ +/-3
* Metabolic Alkalosis ↑1mEq/L HCO3 = 0.7mmHg PCO2↑ +/-3
Expected compensation for respiratory disorders
Acute Resp Acidosis ↑1mmHg PCO2 = 0.15mEq/L HCO3↑ +/- 2
Acute Resp Alkalosis ↓1mmHg PCO2= 0.25mEq/L HCO3 ↓ +/- 2
Chronic Resp Acidosis ↑ 1mmHg PCO2 = 0.35mEq/L HCO3 ↑ +/-2
Chronic Resp Alkalosis ↓1mmHg PCO2 = 0.55mEq/L HCO3↓ +/-2
Sodium bicarbonate dose
Sodium Bicarb dose (mmol/L) = 0.3 x BWkg x Base deficit (mmol/L)
Give a fraction to start
8.4%NaHCO3 is hyperosmolar (2000 mOsm/L) therefore must at least dilute 1:3
Stewart’s approach:
- Apparent strong ion difference (SID)
- Effective SID
- Simplified SID
Apparent SID: (Na+ K+ Ca + Mg) – (Cl + other strong anions)
Effective SID: Atot- (albumin, phosphate) + HCO3
Simplified SID = (Na) – (Cl)
Normal: 38-40
Stewart’s approach:
-ATOT
ATOT = Alb + Phos
Stewart’s approach:
- Strong ion gap (SIG)
- Corrected AG for hyperPhos?
SIG = (Na+ K+ Cl + HCO3) – Atot
should be 0
SIG dogs = (alb x 4.9)- AG
SIG cats = (alb x 7.4) - AG
AG corrected = AG + (2.52 - 0.58xPhos)
Semi-quantitative approach:
5 effects
Free water effect, chloride effect, albumin effect, phosphate effect, lactate effect
Semi-quantitative approach:
Free water effect
Free water effect = (Nap - Nan) / 4
Semi-quantitative approach:
Chloride effect
Chloride effect = Cln – Clcorrected
Corrected Chloride = Clp x (Na normal /Na patient)
Semi-quantitative approach:
Albumin effect
Albumin effect = (Albn – Albp) x 4
Semi-quantitative approach:
Phosphate effect
Phosphate effect = (Phosn – Phosp) /2
Semi-quantitative approach:
Lactate effect
Lactate effect = Lact of patient x -1
Semi-quantitative approach:
final equations
what does + and - values mean
Add all effects together = sum
XA (unmeausred) = Base excess - Sum
+ = alkalosis
- = acidosis
Free water deficit
Free water deficit (L) = [ (current Na / normal Na) -1 ] x 0.6 x BWkg
Sodium deficit
Na deficit (mmol) = (Normal Na – Patients Na) x (0.6 x BWkg)
Pseudohyponatremia correction with hyperglycemia
Nacorrected = Nap + 1.6 [(Patient BG – Normal BG )/ 100]
BG>400:
Nacorrected = Nap + 2.4 [(Patient BG – Normal BG )/ 100]
Zinc toxicity
- US pennies minted after 1982
- Canadian pennies minted between 1997-2001
Normals for intraabdominal pressure (IAP)
Normal less than 0-5 cm H2O (0-3.6mmHg)
Normal muscle pressures in dogs
5.7 +/- 5 mmHg
What is Kt/v
Describes efficacy of dialysis with 1.2 as a minimum recognized standard adequacy
K= dialyzer clearance of urea t= dialysis treatment time v= volume of distribution of urea
Urea reduction ratio (URR)
URR = (BUNpre - BUNpost)/BUN pre x 100
URR in %