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Formulas & Norms

WillWallace Fomulas & Norms

a/A ratio PaO2/PAO2 norm is 90%, >35%=weaning, reflects efficiency of oxygenation as a percentage, <74%=shunt, V/Q mismatch or diffusion defect
A-aDo2 A-a gradient, norm 5-10 mmHg on .21, 30-60 on 100%, >350=mech support, <350 weaning. Represents potential to Oxygenate vs. the amount of O2 in the artery. Every 50mmHg is approx. 2 percent shunt above norm of 2-5%
Alveolar Air Equation (pb-47)FIO2-(PaCO2x1.25), norm 80-100mmHg (can reach 675 on 100%), press of O2 in the Alveoli at any given Pb, represents potential for arterial oxygen
BP norm 120/80 (90-140/60-90), <90/60 or >180/110 is inconsistent with weaning
CaO2 norm 16-20 vol% (Hbx1.34)SaO2 + (PaO2x.003) total amount of O2 carried in 100ml of blood, combined content of O2 carried on Hb and dissolved in plasma, (can be reduced by <Hb, anemia or <CO)
CcO2 Content of pulm capillary blood oxygen at 100% FIO2, (Hbx1.34)1 + (PAO2x.003) used in shunt equation
CD dynamic compliance, aka CLdyn, norm is 0.03-0.04L/cmH2O (30-40mL/cmH20), calc is Vt(L)/(PIP-PEEP) Changes in CD indicate changes in CL or elastance. Up with decreased elasticity (emphysema, down with with stiff (ARDS).
CI cardiac index, 2.5-4 L/min, <2.1 inconsistent with weaning
Cs (CVAE) static compliance, norm for vent pt is .035-.055L/cmH20 or 35-55mL/cmH20, calc is Vt/(Pplat-PEEP), represents the combination of lung elasticity and chest wall recoil while on vent. Down with stiff lungs, >35ml/cnH2O weaning
*Ct Tube compliance aka compressible volume, volume lost to pt circuit, approx 3ml/cmH20 x PIP, deduct from VT to find actual delivered tidal volume. VT-(PIP x 3) equals actual VT.
CvO2 (Hb x 1.34)SvO2 + (PvO2 x .003) norm is 15 vol%, represents the value of O2 in blood returning to the right side of the heart after tissues have oxygenated.
CVP central venous pressure, norm 2-6 mmHg, 2-6 weaning
Deadspace ventilation in excess of perfusion (pulm emboli)
DO2 O2 Delivery, (CaO2 x CO) x 10, norm is 1000mL/O2/min
FIO2 for weaning <40-50% weaning
Flow (VT/IT) x 60 or VE x (I+E)
Flow required for a 1 second I-time and a VT of 750cc? .750 equals L/sec x 1 or .750L/sec flow. To convert to L/min .750 x 60 equals 45L/m, this is the vent flow setting to deliver a VT in 1 second I-time.
Hb 12-16 g/100ml of blood, (no anemia or >10g for weaning)
HCO3 22-26 torr
HCT 40-50%
HR norm 60-80, 60-120 weaning
I:E ratios/% 1:2=33%, 1:3=25%, 1:4=20% (add the ratio parts, then figure what percent is the sum of the parts, 1+4 is 5 and 1/5 of 100% is 20%)
IBW F 105+5/lb over 60"
IBW M 106+6/lb over 60"
I-time represents relationship for volume (Liters), flow (L/sec) and time (seconds). V eq F x T or F eq V/T
Low press on vent look for leak, cuff or humidifier will be first place
MAP Mean arterial pressure, norm 90 (80-100), 70-130 weaning
MIP/NIF Max Inspiratory Press, norm -80 - -100, > -20 support indicated, <-20 weaning (remember that negative numbers are larger as they become less, -25 < -20)
PaCO2 35-45 torr, >55 indicates support, <50 weaning
PaCO2 to increase with pt on mech vent <PIP, <RR, >PEEP
PaCO2(d) CO2 desired, CO2 is adjusted by changing Resp rate so (VExCO2)/CO2d=VEd or (RRset x CO2)/CO2d=RRd, always round down and go slightly acidic as tissue will oxygenate better.
PaCO2-to decrease with pt on mech vent >PIP, >RR, <PEEP
PaO2 80-100 torr, >60 mmHg on <60% weaning
PaO2 <80 on FIO2 <60 V/Q mismatch
PaO2 <80 on FIO2 >60 shunt, refractory hypoxemia or venous admixture
PaO2 desired PaO2 (desired) x FIO2 (current)/PaO2 (current)=FIO2 required to bring PaO2 to desired level. Example of pt on 40% FIO2, PaO2 of 53 and wanting PaO2 of 80, calc is (80x.4)/53 equals .60, so increase FIO2 to 60%
PaO2/FIO2 PaO2/FIO2, norm 350-450mmHg, <300 indicates acute lung injury, <200 indicates ARDS, >200=weaning, measures o2 efficiency
PaO2-to decrease while pt on mech vent <PIP, <RR, <PEEP, or <FIO2
PaO2-to increase while pt on mech vent >PIP, >RR, >PEEP, or >FIO2
PAP pulmonary artery pressure, norm 25/10 (20-35/5-15), >35/15 is inconsistent with weaning, pulm hypertension, left vent fail, fluid overload
PCWP pulmonary artery wedge pressure, norm 5-10 mmHg, >18 is inconsistent with weaning, left vent failure, fluid overload
PEEP positive end expiratory pressure above baseline of 0, norm 3-5 (5-8/ARDS)
PH Norm 7.35-7.45, <7.20 indicates support, >7.35 weaning
PIP Peak pressure, norm is <50cmH2O, the press required to overcome both compliance and resistance
PvO2 40 torr
QS/QT Pulmonary Shunt equation (CcO2-CaO2)/(CcO2-CvO2) Norm 2-3%, >20% vent indication, <20% weaning, >30% is life threatening. Measures % of QT not exposed to ventilation, shunts caused by atelectasis, edema, pneumonia, pneumothorax, obstructions
QT cardiac output, norm 5L/min (4-8)
RAW (RIAF) Airway Resistance norm is 5-12cmH2O/L/Sec for intubated pt, (PIP-Pplat)/(flow in min/60 sec). Increase in RAW reflects an issue with airways, bronchospasm, secretions, edema etc.
Refractory hypoxemia hypoxemia that does not respond to O2 therapy
RR respiratory rate, norm 12-20, >35 indicates support, 6-30 weaning
RSBI Rapid shallow breathing index, RR/VT, <105 weaning, must be calculated during spont breathing, press support reduces predictive value
RV Residual Volume 1.2 L
SaO2 97-100%
Shunt perfusion in excess of ventilation
SvO2 75vol%
TC Time constant, (Raw x CS)e, where e represents volume exhaled as a percent, 1 is 63%, 2 is 86%, 3 is 95% and 5 is 100% exhaled. TC <3 leads to air trapping.
TCT total cycle time, 60 sec/RRset, amount of time for a single breath cycle both I and E. If I:E is 1:2 then TCT is 3
TLC total lung capacity 6L
VA Alveolar ventilation, (VT-VD) x RR, represents sum of breaths taking place in gas exchange, norm 4-5 L/min
VC Vital capacity, 65-75 mL/kg, <10mL/kg indicates support, >15 mL/kg for weaning
VD Deadspace volume, VD=(VT-VA), norm is 33% of VE, 1 mL/lb IBW or 2.2mL/kg (approx 150 ml)
VD/VT Ratio Deadspace to VT ratio, norm 24-40%, >60 indicates support, <60% wean, increase (w/no change in VE) indicates decreased blood flow to alveoli, usually caused by emboli, excessive PEEP, or emphysema
VE Minute ventilation, VE=VT x RRset, flow of expired gas in one minute, norm 5-8L/min, < 10 weaning
VEspont VEtot-(VTset x RRset), norm 5-6 L/min,
VO2 O2 consumption, norm is 250mL/O2/L/min, [C(a-v)O2 x QT] x 10, the amount of O2 consumed by the body per liter of blood per minute.
VTspont VEtot-(VTset x RRset)/(RRtot-RRset) Measured when machine in SIMV mode, represents what the patient is actually breathing on his/her own.
VT norm is 5-8 mL/kg (400-600 cc), <5mL/kg indicates support, >5 weaning.
Created by: williamwallace
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