MathPad Formulas
To get these into Mathpad:
Airway:
Difficult Intubation Risk
Version 1.3 Harms & Stranges 2001, with slight modification by
R. Prasad
--Input--
"All the factors predicting difficult oral intubation risk need to
be assigned either a 1 (if present) or a 0 (if absent), except oropharyngeal
(Mallampati) class, which must be 1, 2, 3, or 4."
Mallampati Class<- 3
ShortNeck: 1
RecedingMandible: 1
Protruding Maxillary Incisor: 0
--Ouput--
Probability-> 52 % will be a difficult or failed intubation.
RelativeRisk-> 366 times the risk of an uncomplicated MP Class One airway.
---Reference article---
Relative Risk Analysis of Factors Associated with Difficult Intubation
in Obstetric Anesthesia, by Rocke et al. Anesthesiology 77:67-73,
1992
--Calculation of Probability--
Probability=Round(100*(Exp(-4.43+MPFactor+1.612*(ShortNeck)+2.27*(RecedingMandible)+2.076*(Incisor))/(1+Exp(-4.43+MPFactor+1.612*(ShortNeck)+2.27*(RecedingMandible)
+2.076*(Incisor)))))
MPFactor->0.62
MPFactor=Choose(Class;-1.4;-0.23;0.62;1.01)
--Calculation of Relative Risk--
RelativeRisk=Round(Exp(MPFactor+1.612*(ShortNeck)+2.27*(RecedingMandible)+2.076*(Incisor)+1.4))
---License---
GPL
---Output---
HeightCM<-
APDiameterMM-> 14.7
TransverseDiameterMM-> 14.7
APDiameterFrench-> 44.1
TransverseDiameterFrench-> 44.1
LengthCM-> 11.8 "cords to carina"
UseMaxFrenchDLT-> 35
DepthCM-> 28.5
APDiameterMM/10=Round(100*Exp(-6.65)*HeightCM**1.37)/100
TransverseDiameterMM/10=Round(100*Exp(-5.88)*HeightCM**1.22)/100
APDiameterFrench/3=APDiameterMM
TransverseDiameterFrench/3=TransverseDiameterMM
LengthCM=Round(10*Exp(-3.8)*HeightCM**1.22)/10
"Dimensions based on 90 patients of age 9 days - 20 years and height
~55-190 cm.
Griscom & Wohl, Am Rev Resp Dis 1985; 131: 840-4"
MinDimen->14.7
MinDimen=If(APDiameterMM<TransverseDiameterMM;APDiameterMM;TransverseDiameterMM)
UseMaxFrenchDLT=If(MinDimen>18;41;If(MinDimen>16;39;If(MinDimen>15;37;If(MinDimen>14;35;If(MinDimen>12.5;32;0)))))
DepthCM=Round(10*(29+(HeightCM-175.26)/10.16))/10
"Recommendations based on J Kent Garman's page"
Cardiac Risk Assessment for Noncardiac Surgery
"From Gauss et al, Anesth 2001, 94(1):38-46."
---Input---
"Major surgery: Aortic repair, aortoiliac or iliac endarterectomy,
gastric, liver, pancreatic, small bowel, colonic, rectal
0-false, 1-true"
CAD<-
MajorSurgery<-
ExerciseEKG<-
"Exercise EKG: 0-not done, 1-normal, 2-abnormal
Abnormal = ST depression greater than baseline by 0.1mV or more 60ms
after J-pt (if within T-wave, then at J+40msec) seen in 3 consecutive beats
without baseline variation. ST elevations 0.2mV or more unless in leads
with signs of previous MI.
"
---Output---
% CardiacRisk-> 5
"Risk of cardiac mortality and morbidity during first 30 POD's. Cardiac
death, perioperative MI or minor cell injury (elevated troponin-T), CHF"
CardiacRisk=Choose(CAD+MajorSurgery+1;0;Choose(ExerciseEKG+1;7;5;13);Choose(ExerciseEKG+1;27;10;47))
"Surgenor et al. Anesth Analg 2001; 92:596-601
Heart failure is most common cause of death after CABG. 80% of variation
in risk of death is due to HF. Therefore, predicting risk of fatal HF may
help direct aggressive preemptive therapy.
Ravindra Prasad, MD"
---Input---
"Enter 1 if true, 0 for false."
Age<-
Female<-
PriorCABG<-
Urgent<-
Emergent<-
ThreeVDisease<-
EFLessThan40<-
Diabetic<-
PVD<-
RenalFailure<-
---Output---
"Remember: overall risk of death in the study population was 4.48%;
death from HF, 2.88%."
% Risk->
---Calculations---
odds->
odds=Exp((.4259*(Age>=70&&Age<80))+(1.0066*(Age>=80))+(.5204*Female)+(.5023*PriorCABG)+(1.8337*Emergent)+(0.659*Urgent)+(.8528*EFLessThan40)+(.3545*ThreeVDisease)+(.4443*Diabetic)+(.8598*PVD)+(1.0439*RenalFailure)-4.8963)
Risk=100*odds/(1+odds)
"EABL is the Estimated Allowable Blood Loss, assuming slow steady blood loss with maintenance of intravascular volume with RBC-free solutions.
For MathPad by Ravindra Prasad, MD
Formula: Ward et al. Anesth 1980; 53: S126"
--Input--
"Leave one blank"
ml EABL<-
starting Hgb HgbStart<-
accepted Hgb HgbEnd<-
weight (kg) Wt<-
Blood volume BV: 70
"For Blood volume (cc/kg), use:
Adult Pediatric
obese, thin, normal infant 80
60 , 65 ,
70 neonate 90
muscular 75 premie 100
female -5
"
EABL=Round(BV*Wt*Ln(HgbStart/HgbEnd))
"The usually used formula, EABL= BloodVol * (HgbStart-HgbTarget) / HgbAverage, is a close approximation of this, the real formula."
EBL Calculation
Calculates estimated blood loss based on starting and current Hgb levels.
You need to estimate current blood volume as a fraction of baseline.
By Ravindra Prasad, MD
---Output---
EBL-> 2,900 ml
---Input---
"For Blood/kg, use:
male-70 infant-80
female-60 neonate-90
premie-100"
Patient weight kg: 90
Baseline Hgb Base: 11.5
Current Hgb Now<-
PRBCs given Units: 4
Blood/kg in ml: 70
BV (frac of baseline) BV: 1.1
---Variables, Formulas---
HgbBase->724.5
HgbNow->651.42
HgbPRBC->230
GramsEBL->303.08
HgbBase=((ml*kg)/100)*Base
HgbNow=((ml*kg)/100)*Now*BV
HgbPRBC=Units*2.5*23
GramsEBL=HgbBase+HgbPRBC-HgbNow
EBL=Round(100*GramsEBL/((Base+Now)/2))
Fluid Replacement
"By Ravindra Prasad, MD"
--Input--
"Calculates fluids to give. Assumes NPO since YESTERDAY, incision TODAY."
NPO yest (HH.MM) NPO: 22.00
Incision (HH.MM) Start: 13.00
Weight (kg)
kg: 60
Fluid loss (cc/kg/hr) Evap: 10
Est. blood loss (cc) EBL<-
cc Colloid: 500 cc Cryst: 0
units PRBC: 0< units FFP: 0
"Above are fluids given ALREADY"
--Output--
EvapTime-> 4.5 hrs
EvapLoss-> 2,700 cc
NPO Deficit-> 1,950 cc
Maintenance-> 100 cc/hr
Crystalloid to give-> 3,750 cc
Blood to transfuse-> 4.2 Units
OR fluid rate-> 700 cc/hr
---Calculations---
Now Time0-> 17.5
NPO Time1-> 22
Incision Time2-> 13
NPO Hrs-> 19.5
first10-> 40
next10-> 20
over20-> 40
Time0=Hour(Now())+Minute(Now())/60
Time1=Hours(NPO)
Hrs=Round((Time0+24-Time1)*10)/10
first10=If(kg>10;10;kg)*4
next10=If(kg<=10;0;If(kg>20;10;kg-10))*2
over20=If(kg<=20;0;kg-20)*1
Maintenance=first10+next10+over20
Deficit=Round(Maintenance*Hrs)
Time2=Hours(Start)
EvapTime=Round((Time0-Time2)*10)/10
EvapLoss=Round(Evap*EvapTime*kg)
"DefReplac=Deficit"
give=Deficit+EvapLoss-Cryst+(EBL-Colloid-(250*(FFP+PRBC)))*3
rate=Maintenance+(Evap*kg)
transfuse=Round(give/90)/10
---Input---
"Calculates volume of droperidol to give for desired µg/kg dose."
mg/ml DropConc: 2.5
µg/kg Dose: 10
kg Weight<-
---Output---
cc Volume-> 0.26
Volume=Weight*Dose/1000/DropConc
Incidence - 24 hrs Sinclair
"Anesth 1999;91:109-18"
Adapted by: Ravindra Prasad, MD
---Input---
(years) age<- (1 is male) sex<-
(hours) duration<-
(Below, 1 is yes)
smoker: 0 PONV: 0
GA: 1 ENT: 0 ophth: 0
plastic: 0 (not D&C) gyn: 0
(ortho)
knee: 0 shoulder: 1 other: 0
---Output---
PercentPONV-> 56.4
"Prasad Inpatient Prophylaxis.
For outpatient general anesthetics, decrease threshold by one level.
(modified from Watcha)
<10% None
10-30% Drop 0.625mg
30-60% Drop 0.625mg AND Steroid
>60% Drop 0.625mg AND Steroid
AND Ond 4mg
Steroid = dexamethasone 1 mg/kg,
up to 8 mg.
Rescue
<60% Ond 1 mg
>60% Metoclopramide,
phenothiazine, or other"
---Calculation---
PercentPONV=Round(1000/(1+Exp(5.97+0.014*age+1.03*sex+0.42*smoker-1.14*PONV-0.92*duratn-2.36*GA-1.48*ENT-1.77*ophth-1.90*plastic-1.20*gyn-1.04*knee-1.78*shoulder-0.94*other)))/10
"max 3hrs"
duratn-> 3
duratn=If(duration>3;3;duration)
Incidence - 24hrs Apfel (simple)
"Anesth 1999;91:693-700"
Adapted by: Ravindra Prasad, MD
---Input---
(1 if true)
female<-
nonsmoker<-
Motion sickness or PONV<-
Postop opioids<-
---Output---
PercentPONV-> 61
"Prasad Inpatient Prophylaxis.
For outpatient general anesthetics, decrease threshold by one level.
(modified from Watcha)
<10% None
10-30% Drop 0.625mg
30-60% Drop 0.625mg AND Steroid
>60% Drop 0.625mg AND Steroid
AND Ond 4mg
Steroid = dexamethasone 1 mg/kg,
up to 8 mg.
Rescue
<60% Ond 1 mg
>60% Metoclopramide,
phenothiazine, or other"
---Calculation---
PercentPONV=Choose(1+female+nonsmoker+PONV+opioids;10;21;39;61;79)
Incidence - PACU Junger
"Anesth 2001;92:1203-9
Adapted by: Ravindra Prasad, MD"
---Input---
years Age<-
minutes Duration<-
"Below, 1=yes"
Female<-
N2O<-
IntraopOpioids: 0
Smoker: 0
PropofolMAC: 0
---Output---
PercentPONV-> 11.8
"Prasad Inpatient Prophylaxis.
For outpatient general anesthetics, decrease threshold by one level.
(modified from Watcha)
<10% None
10-30% Drop 0.625mg
30-60% Drop 0.625mg AND Steroid
>60% Drop 0.625mg AND Steroid AND Ond 4mg
Steroid = dexamethasone 1 mg/kg, up to 8 mg.
Rescue <60% Ond 1 mg
>60% Metoclopramide,
phenothiazine, or other
"
---Calculation---
PercentPONV=Round(1000/(1+Exp(4.9682-0.8949*Female+0.6294*Smoker+0.917*PropofolMAC-0.8078*N2O-1.4301*IntraopOpioids+0.005*Age-0.0051*Duration)))/10
"Combined 2 formulas that had no reason for combining ... just playing around."
---Input---
(years) Age<-
(hours) Duration<-
"(Below, 1=yes)"
Male<-
Smoker<- PONV: 0
GA: 1 N2O: 0
PropMAC: 0 IntraopOpioids: 1
ENT: 0 ophth: 0
plastic: 0 (not D&C) gyn: 0
(ortho)
knee: 0 shoulder: 0 other: 0
---Calculation---
PercentPONV=Round(1000/(1+Exp(5.97+0.014*Age+1.03*Male+0.42*Smoker-1.14*PONV-0.92*duratn+0.917*PropMAC-2.36*GA-0.8078*N2O-1.4301*IntraopOpioids-1.48*ENT-1.77*ophth-1.90*plastic-1.20*gyn-1.04*knee-1.78*shoulder-0.94*other)))/10
"max 3hrs"
duratn-> 3
duratn=If(Duration>3;3;Duration)
---Output---
PercentPONV->
"Prasad Prophylaxis Regimen.
For outpatients, decrease threshold by one level (modified from Watcha).
<10% None
10-30% Drop 0.625mg
30-60% Drop 0.625mg AND Steroid
>60% Drop 0.625mg AND Steroid
AND Ond 4mg
Steroid = dexamethasone 1 mg/kg,
up to 8 mg.
Rescue
<60% Ond 1 mg
>60% Metoclopramide,
phenothiazine, or other"
---Output---
Depth to space-> (mm)
Bolus volume-> (cc)
MaxBupiv-> (mg/hr)
MaxMSO4-> (µg/hr)
---Input---
years.months Age<-
weight kg<-
block # of segments<-
---Calculation---
age->
age=Int(Age)+Frac(Age)*100
space= 10 + 2*age
volume=0.05*kg*segments
MaxBupiv=kg*(0.5-0.25*(age<2/12))
MaxMSO4=8*kg
"Meds:
Fent 2mcg/Bupiv 0.1%
Epid/Caud Gtt Rates
Bupiv 0.1%
Infant <=2 mo age, max = 0.25 mg/kg/hr (for 48 hrs max)
Infant > 2 mo age, max = 0.5 mg/kg/hr
Morph 15 mcg/cc
Bolus: 0.03-0.05 mg/kg
Gtt: usual range: 3-8 mcg/kg/hr
Fent
Bolus: 0.5-1.0 mcg/kg
Gtt: usual range: 0.5-1 mcg/kg/hr
"
Epidural - Depth by Paramedian Approach
(IARS abstract)
Depth to lamina x<-
Depth to space L->8.09
Degrees from horizontal caudal: 45
L=(x+.72)/Cos(caudal)
Paravertebral Block
kg<-
mm from midline-> 15.5
mm depth-> 39.8
midline=kg*.12+10.2
depth=kg*.48+18.7
---Output---
pHCorrected->
mEq/L BaseDeficit->
mEq HCO3toGive->
---Input---
"Calculates Base Balance, and how much HCO3 to give (if you're going
to give it at all!).
By Ravindra Prasad, MD"
pH<-
PCO2<-
kg<-
pHCorrected=pH+(PCO2-40)/10*.08
BaseDeficit=Round((7.4-pHCorrected)/.15*100)/10
HCO3toGive=Round(kg*BaseDeficit*0.3/2)
Air LPM Calculator
---Input---
"Calculates LPM air, since most anesthesia ventilator air flowmeters
are not marked precisely.
By Ravindra Prasad, MD"
O2LPM<-
Percent FiO2<-
Percent FiGas<-
AirLPM-> 0.2
---Calculations---
FiO2/(100-FiGas)=(O2LPM+0.21*AirLPM)/(AirLPM+O2LPM)
"Fairly good approximation. Assigns PO2=100 for all saturations >= 97.4%. Assumes linear relationships between PO2 and SO2 between every 10 PO2."
Enter % Sat<-
Approximate PO2-> 100
PO2=Round(if(Sat<13.5;0+(Sat-0)/(13.5-0)*10;if(Sat<35;10+(Sat-13.5)/(35-13.5)*10;if(Sat<57;20+(Sat-35)/(57-35)*10;if(Sat<75;30+(Sat-57)/(75-57)*10;if(Sat<83.5;40+(Sat-75)/(83.5-75)*10;if(Sat<89;50+(Sat-83.5)/(89-83.5)*10;if(Sat<92.7;60+(Sat-89)/(92.7-89)*10;if(Sat<94.5;70+(Sat-92.7)/(94.5-92.7)*10;if(Sat<96.5;80+(Sat-94.5)/(96.5-94.5)*10;if(Sat<97.4;90+(Sat-96.5)/(97.4-96.5)*10;100)))))))))))
Exclude patients with other lung surgery or severe lung disease. Predicts
minimum PaO2 at 100% O2, 10 cc/kg x 10, i:e set at 1:1.
(IARS 2000 abstract)
---Output---
PaO2->
---Input---
Age yr<-
Height cm<-
Weight kg<-
Lung ventilated (1 left, 0 rt) side<-
PaO2=432-3*yr-5.3*(cm*cm/10000/kg)+36.6*side
"An estimate only, but probably a fairly good one. Assigns 100% saturation for all PO2>400. Assumes linear relationships between PO2 and SO2 between every 10 PO2 from 0-100, and from 100-400."
PAO2<-
SAO2-> 92.33
SAO2=If(PAO2<10;0+(PAO2-0)/10*(13.5-0);If(PAO2<20;13.5+(PAO2-10)/10*(35-13.5);If(PAO2<30;35+(PAO2-20)/10*(57-35);If(PAO2<40;57+(PAO2-30)/10*(75-57);If(PAO2<50;75+(PAO2-40)/10*(83.5-75);If(PAO2<60;83.5+(PAO2-50)/10*(89-83.5);If(PAO2<70;89+(PAO2-60)/10*(92.7-89);If(PAO2<80;92.7+(PAO2-70)/10*(94.5-92.7);If(PAO2<90;94.5+(PAO2-80)/10*(96.5-94.5);If(PAO2<100;96.5+(PAO2-90)/10*(97.4-96.5);If(PAO2<400;97.4+(PAO2-100)/300*(100-97.4);100)))))))))))
--Input--
Enter height (in) ht<-
Enter weight (lb) wt<-
Enter height (cm) htcm<-
Enter weight (kg) wtkg<-
htcm=ht*2.54
wtkg=wt/2.2
BMI=Round(wtkg/((htcm/100)*(htcm/100)))
--Output--
BMI-> m2
" Normal 19-24
Overweight 25-29
Obese 30-39
Morbid Obesity >39
"
--Input--
Enter height (in) ht<-
Enter weight (lb) wt<-
Enter height (cm) htcm<-
Enter weight (kg) wtkg<-
htcm=ht*2.54
wtkg=wt/2.2
BSA=sqrt((ht*wt)/3131)
--Output--
BSA-> 1.82 m2
Drips Calc: Convenient Mixture
--Input--
"Calculates how much drug (mg) to add to specified fluid volume so
that the patient gets the desired dose (µg/kg/min) running at the
desired rate (cc/hr)."
Enter pt weight(kg) wt<-
Enter dose (µg/kg/min) dose<-
Enter rate (cc/hr) rate<-
Enter cc mixing into cc: 50
--Output--
Add-> 15 mg into your volume
Add=0.06*dose*wt*cc/rate
"By Ravindra Prasad, MD
From Smith's, and various."
---Output---
HRlow-> 60 SBPlow-> 80
HRhigh-> 90 SBPhigh->120
RRlow-> 30 WeightLow-> 15
RRhigh-> 30 WeightHigh-> 19
"Weights (in kg) are calculated for males; females slightly less."
---Input---
weeks: 0
months: 0
years<-
---Calculations---
Age->4
Age=weeks/52+months/12+years
HRlow=If(Age<0.25;80;If(Age<2;70;If(Age<10;60;50)))
HRhigh=If(Age<0.02;160;If(Age<0.25;200;If(Age<2;120;90)))
SBPlow=If(Age<0.084;50;If(Age<0.5;60;If(Age<2;65;If(Age<3;75;If(Age<5;80;If(Age<12;92;100))))))
SBPhigh=If(Age<0.084;70;If(Age<0.5;110;If(Age<2;115;If(Age<3;125;If(Age<9;120;If(Age<12;130;140))))))
RRlow=If(Age<0.1154;45;If(Age<2;40;If(Age<6;30;If(Age<10;25;20))))
RRhigh=If(Age<0.1154;60;If(Age<2;40;If(Age<6;30;If(Age<10;25;20))))
WeightLow=If(Age<0.084;3.4;If(Age<0.5;4;If(Age<1;8;If(Age<2;10;If(Age<3;13;If(Age<6;15;If(Age<9;21;If(Age<12;28;45))))))))
WeightHigh=If(Age<0.084;3.4;If(Age<0.5;4;If(Age<1;8;If(Age<2;10;If(Age<3;13;If(Age<6;19;If(Age<9;25;If(Age<12;40;62))))))))
"For any pt, PCO2*TV*RR is constant (K). To change PCO2 to new level (PCO2Goal), NewMV=K/PCO2Goal."
AlveolarTV=(TV-2.2*wtkg)
AlveolarTV-> 614 ml
AlveolarMV=AlveolarTV*RR
AlveolarMV-> 3,684 ml/min
K=PCO2Now*AlveolarMV
K->147,360
NewAlveolarMV=K/PCO2Goal
NewAlveolarMV-> 4,912 ml/min
NewAlveolarMV=NewAlveolarTV*RR
NewAlveolarTV-> 818.66666666667 ml/min
NewAlveolarMV=AlveolarTV*NewRR
NewAlveolarTV=(NewTV-2.2*wtkg)
NewRR=Round(10*NewRR)/10
NewTV-> 972.66666666667ml/min
NewRR->8
IfOldTVNewRR=Round(10*NewRR)/10
IfOldRRNewTV=Round(NewTV)
---Input---
TV<-
RR<-
wtkg<-
PCO2Now<-
PCO2Goal<-
---Output---
IfOldRRNewTV->
IfOldTVNewRR->
"By Ravindra Prasad, MD"
Cortisone=1.25*Hydrocortisone
Hydrocortisone=4*Prednisone
Prednisone=Prednisolone
Prednisolone=1.25*Methylprednisolone
Methylprednisolone=Triamcinolone
Triamcinolone=4/0.7*Betamethasone
Decadron=0.75/4*Triamcinolone
---Input---
Cortisone<-
Hydrocortisone<-
Prednisone<-
Prednisolone<-
Methylprednisolone<-
Triamcinolone<-
Betamethasone<-
Decadron<-
"Enter command-i, then one value: calculates equivalent steroid doses."