Difference between revisions of "Estimating VO2"
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* https://pubmed.ncbi.nlm.nih.gov/26976237/ | * https://pubmed.ncbi.nlm.nih.gov/26976237/ | ||
* From a [https://aeitechnologies.com/wp-content/uploads/2022/12/MOXUS-CARDIAC-OUTPUT-Option.pdf white paper] about the Moxus metabolic cart cardiac output estimation methods: | * From a [https://aeitechnologies.com/wp-content/uploads/2022/12/MOXUS-CARDIAC-OUTPUT-Option.pdf white paper] about the Moxus metabolic cart cardiac output estimation methods: | ||
| − | ** CO2 rebreathing Fick method. Q = VCO2 | + | ** CO2 rebreathing Fick method. Q = VCO2 / (CaCO2 - CvCO2) |
** VCO2 is "easily measured"... how? | ** VCO2 is "easily measured"... how? | ||
** CaCO2 is estimated with EtCO2 if the subject has healthy lungs and the EtCO2 is peaking, otherwise PaCO2 from an ABG can be used | ** CaCO2 is estimated with EtCO2 if the subject has healthy lungs and the EtCO2 is peaking, otherwise PaCO2 from an ABG can be used | ||
Revision as of 05:40, 17 August 2024
- An automated machine check could calculate the amount of machine leak you have in the circuit, separate from any patient leak. Just occlude the Y-piece and run the vent while comparing your VTI - VTE. Average 20 breaths or so and likely there is a delta of a few ml with each breath accounting for air lost from circuit connections, internal machine leaks, tubing, etc. Variability may also be due to measurement error from the flow meters used.
- Once connected to the patient, VTI - VTE gives the total volume lost per breath. Subtract the machine leak found above and this gives you the patient side leaks (air lost from around the ETT cuff, volume lost to chest tubes, etc)
- FiO2 * FGF = V̇O2
- You can calculate the V̇O2 using the Fick equation: <math chem>\ce{\dot VO2} = Q \times\ (C_a\ce{O2} - C_v\ce{O2})</math>, where Q is the cardiac output.
- Reference values for V̇O2 max
- In 2016, the AHA published a scientific statement recommending that CRF – quantifiable as V̇O2 max/peak – be regularly assessed and used as a clinical vital sign; ergometry (exercise wattage measurement) may be used if V̇O2 is unavailable. source
- V̇O2 max is correlated with reduced all-cause mortality. source
- https://pubmed.ncbi.nlm.nih.gov/8565545/
- https://pubmed.ncbi.nlm.nih.gov/26976237/
- From a white paper about the Moxus metabolic cart cardiac output estimation methods:
- CO2 rebreathing Fick method. Q = VCO2 / (CaCO2 - CvCO2)
- VCO2 is "easily measured"... how?
- CaCO2 is estimated with EtCO2 if the subject has healthy lungs and the EtCO2 is peaking, otherwise PaCO2 from an ABG can be used
- CvCO2 is estimated by allowing rebreathing a fixed concentration of expired CO2 for up to 10 seconds (any longer and the additional inhaled CO2 has time to recirculate and affect your mixed venous value), the inhaled CO2 should rapidly equilibrate with the alveolar and mixed venous CO2.
- Tidal volumes should be at least 2x dead space.
- 10 breaths should be ignored after rebreathing for re-equilibration.
- Rebreathing bag volume should be 1.5x the tidal volume.
- Calibrate the best guess of CvCO2 by using the EtCO2 and adding 4-6 mmHg
- A paper from 2010 showing a Fick rebreathing technique continuous CO monitor applied to both ICU and OR environments.