Equations Flashcards
(117 cards)
Starling’s forces
Filtration (Jv) = Kf [(Pc-Pif)- σ (πc- πif)]
Kf – capillary filtration coefficient/permeability (capacity of the membrane to filter water at a given net filtration pressure) (ml/min/mmHg)
- Kf is 100x greater in kidney than systemic capillaries
σ – osmotic reflection coefficient (the fraction of the total potential osmotic pressure exerted by the solute in question)
- Glomerular capillary is essentially 1
Pc = capillary hydrostatic pressure
Pif = interstitial hydrostatic pressure
πc =plasma oncotic pressure
πif= interstitial oncotic pressure
Jv = net capillary filtration
Also used to determine GFR (bowman’s space = interstitium)
Free water deficit (L)
0.6 x BW (kg) x ([patient Na+]/[normal Na+] – 1)
Quick formula: 3.7mls/kg/hr of D5W
*calculated to change Na by 1 mEq/hr
If severe (>180meq/L), then replace at a rate of 0.5mEq/L/hr with D5W or oral hourly water administration (if drinking or by NG tube)
Estimated ∆ Na with 1 L fluid
Change in serum [Na]= ([Nafluids]-[Naserum]) / [(0.6 x kg) + 1]
Sodium deficit should be calculated from the minimum safe sodium: 12mEq/L
Na+ deficit in hyponatremia
Na deficit (mmol) = 0.6 x BW (kg) x (Normal Na - Pts Na)
●Sodium deficit should be calculated from the minimum safe sodium : 120 mEq/L
● Do not exceed 0.5 mEq/L/hr or no more than 12 mEq/L/day
● If severe symptoms, may increase sodium more quickly 1.5-2.0 mEq/L/hr for 3-4 hours
Corrected Chloride
Pts Chloride x (Norm Na/Pts Na)
Corrects for free water deficit
Plasma/serum osmolality
Plasma/serum osmolality (mmol/L) = 2(Na + K) + (BUN/2.8) + (glucose/18)
*2 x (Na + K) to account for Cl and HCO3
*Divide to convert between mg/dL to mmol/L
Dog: 290-310 mOsm/kg
Cat: 290-330 mOsm/kg
Effective osmolality
2(Na+K) + (glucose/18)
Because urea is not an effective osmole
Osmolal gap
Measured osmolality – calculated osmolality
- If measured >10mOsm/kg over calculated there are unmeasured solutes present
GFR (ml/min)
(Volume/time)
= Clearance of inulin (filtered but not reabsorbed or secreted)
= Same as clearance, thus saying that the clearance of creatinine equals GFR
- This equation works because there is no tubular reabsorption or section or metabolism of creatinine (-ish) and would work for any other substance like that (inulin)
GFR = (U{Crea} X V ) / P{Crea}
Either inulin or creatinine clearance rate may be used for GFR
U{Crea} = urinary concentration of creatinine
V = urine flow rate
P{Crea} = arterial plasma concentration of Crea
Albumin deficit (grams) = _____________
10 x (desired alb - patient alb) x Kg x 0.3
Or
Using 25% Human serum albumin (HAS) (25g/100mL)
2ml/kg x 2hr then 0.1-0.2mL/kg/hr x 10hr = total 2g/kg
FFP = 3g/100mL
Whole blood = 1.4g/100mL
CSA = variable
Normal COP in dogs and cats:
Plasma: _____
Whole blood: _______
Sick patients: ______ (+ Goal)
Plasma dogs: 21-25mmHg
Plasma Cats: 23-35mmHg
Whole blood Dogs: 10 +/- 2mmHg
Whole blood Cats: 25 +/- 4mmHg
Sick patients: ~14 +/- 3mmHg
Goal of 16mmHg
Henderson-Hasselback Equation
pH= 6.1 x log [ (HCO3) / (0.03 x PCO2) ]
6.1 = pH in bodily fluids
HCO3 -> mEq/L or mmol/K
0.03 = solubility coefficient of CO2 in plasma
PCO2 -> mmHg
Carbonic Acid Equation
CO2 + H2O <—> H2CO3 <—> H (+) + HCO3 (-)
Carbonic anhydrase catalyzes first half (intracellularly)
Base excess
Vs
Base deficit
Base excess = (+) number
Base deficit = (-) number
Corrected Sodium
Na[corrected] = Na[p] + 1.6 [(BG[p] - BG[n]) / 100]
Or
1.6mEq/L decrease in Na for every 100mg/dL increase in glucose or mannitol
Anion Gap =
Anion Gap = (Na + K) - (Cl + HCO3)
= UA (variable) - UC (not variable)
- not reliable if patient is hypoalbuminemic
Dogs: 12-24mEq/L
Cat: 17-31mEq/L
AG alb (dog) = AG + 0.42 x (3.77 - alb)
AG alb (cat) = AG + 0.41 x (3.3 - alb)
AG phos = AG + (2.52 - 0.58 x Pi)
Expected compensation for simple acid base disorders:
Acute Resp Acidosis: ⬆️ 1mmHg PCO2 = 0.15mEq/L HCO3 ⬆️ +/- 2
Acute Respiratory Alkalosis: ⬇️ 1mmHg PCO2 = 0.25 mEq/L HCO3 ⬇️ +/- 2
Chronic Respiratory Acidosis: ⬆️ 1mmHg PCO2 = 0.35 mEq/L HCO3 ⬆️ +/- 2
Chronic Respiratory Alkalosis: ⬇️ 1mmHg PCO2 = 0.55mEq/L HCO3 ⬇️ +/- 2
*Metabolic Acidosis: ⬇️ 1mEq/L HCO3 = 0.7mmHg PCO2 ⬇️ +/- 3
*Metabolic Alkalosis: ⬆️ 1mEq/L HCO3 = 0.7mmHg PCO2 ⬆️ +/- 3
- Not really a thing in cats
Sodium Bicarb Dose =
NaHCO3 (mmol/L) = 0.3 x kg x Base deficit (mmol/L)
= 0.3 x kg x (normal HCO3 - patient HCO3)
0.3 is approximate distribution of bicarb
This dose will return bicarb to normal, so only give a fraction
8.4% NaHCO3 = 2000mOsm/L so dilute 1:3 with water for injection
Don’t push or risk hypovolemia/Increased ICP
Stewart Approach
Strong ion difference (SID) = Na + K + Ca + Mg - (Cl + other strong anions)
Most simplified SID = (Na) - (Cl)
ATOT (aka total of weak acids) = Alb + Phos
* SIG = SID - (HCO3 + ATOT)
*its like AG for traditional, but less effected by albumin
*Normal SIG should be zero
Steward Semi-quantitative approach
Shorthand formulas:
N= normal value
P= patient or measured value
1) Free water effect = (Na[p] - Na[n]) / 4
Hypernatremia -> alkalosis
Corrected chloride = Cl[p] x (Na[n] / Na[p])
2) Chloride effect = Cl[n] - Cl[corrected]
3) Albumin effect = (Alb[n] - Alb[p]) x 4
Hypoalbuminemia -> alkalosis
4) Phosphate effect = (Phos[n] - Phos[p]) / 2
5) Lactate effect = Lact[p] x (-1)
Add all together to = Sum
XA (unmeasured) = Base excess - Sum
(+) value is alkalosis
(-) value is acidosis
Na Deficit example:
20kg dog with a Na of 120mmol/L (normal 145mmol/L)
Calculate the Na deficit.
Give plan to correct over 10hrs.
Na deficit (mmol) = (145-120) x (20 x 6)
Na deficit = 300mmol Na
Correct over 10 hr:
30mmol Na/hr
If you use 3% HTS = 513mmol Na/L or 0.513mmol Na/mL
30/0.513 =58ml/hr of 3% HTS
Or
1) Calculate: Change in serum sodium = (Fluid Na - Patients Na) / [(0.6 x kg) + 1]
- Fluid Na options include: 3% HTS = 513mmol/L, 5% HTS = 856mmol/L, 7.2% HTS = 1283mmol/L, 23.4% HTS = 4004mmol/L
- JVECCs Review suggests adding K into the equation bc any K supplementation will activate NaKATPase and will cause Na to leave the cell and increase Na -> change in serum sodium = [(Fluid Na + K) - Patients Na] / [(0.6 x kg) + 1]
2) Determine: fluid rate (ml/hr) = (1000 x rate of Na correction in mmol/L/hr)/Change in serum sodium
- Rate of Na correction should be 0.4mmol/L/hr (= 9.6mmol/L in 24 hr)
- so that you do not correct > 10mmol in 24 hr.
3) Throw away: Na deficit calculation -> you don’t need it
Pseudohyponatremia
Na dilution due to increased osmolality, most often hyperglycemia (also retained mannitol)
For every 100mg/dL increase in glucose above normal = 1.6-2.4meq/L decrease in Na
Not linear relationship, more hyperglycemia, larger the Na drop
Phosphate
3.1mg/dL = 1mmol/L = 1.8mEq/L
APP = _____
Abdominal perfusion pressure (mmHg) = MAP - IAP
Goal APP > 60mmHg
IAP = Intra-abdominal pressure
IAH = intra-abdominal hypertension (sustained pressure > 12mmHg)
ACS = abdominal compartment syndrome (sustained increase > q-mmHg that is associated with new organ dysfunction or failure)
1mmHg = ~ 1.4cmH2O