caridac output monitoring and oxygen delivery Flashcards
how do you calculate oxygen consumption (VO2)?
VO2= (FiO2 - FeO2) x Vm/ weight in kg
with an FiO2 of 93%, FeO2 (EtO2) of 89%, Vm 6.5 L, and pt wt of 75 kg calculate the VO2
VO2 = FiO2 - FeO2 x Vm/ wt
0.93 - 0.89 x 6500 ml / 75 kg
0.04 x 86.67 ml/kg
= 3.4 mls O2/kg/min
how is O2 delivery (DO2) calculated?
- first calculate O2 content (CaO2)
- (hgb x oxyhgb x 1.39) + (.003 x PaO2)
- hgb is hct divided by 3
- oxyhgb is FiO2
- PaO2 = FiO2(# not %) x 5
- DO2 = CaO2 (mls/dL) x CO (mls/min) / kg /100
- estimated CO is 5 L/min
-75 kg pt.
-HR 70 bpm
-Hct .39
-Sat 100%
-FiO2 .93
est. CO 5 L/min
what is the DO2?
-CaO2 = (hgb x oxyhgb x 1.39) + (.003 x PaO2)
= (13 x .93 x 1.39) + (.003 x {93 x 5})
= 16.8051 + 1.395
= 18.2 mls O2/dL
-DO2 = CaO2 x CO/kg/100
= 18.2 x 5000/75/100
= 12.1 mls/O2/kg/min
does 100% O2 really have a dramatic impact on the amount of oxygen delivered to the tissues?
NO
does CO have a dramatic impact on the amount of oxygen delivered to the tissues?
Yes, CV system is the limiting factor in delivery of O2 to tissues
*if CO dropped to 2500 ml DO2 drops to 6.0 mls/O2/kg/min; if drop to 1000 ml, DO2 drops to 2.4 mls/O2/kg/min
does hgb have a dramatic impact on the amount of oxygen delivered to the tissues with a normal CO?
Yes
- hgb 13, CaO2 18.2, DO2 12.1
- hgb 8, CaO2 1.7, DO2 7.8
- hgb 5, CaO2 5.7, DO2 3.8
what is beneficial of CO monitoring?
- helps to provide a global picture of overall circulatory status
- used to guide therapy and evaluate response to clinical interventions
- yields information regarding oxygen delivery and consumption
- CO is the primary compensatory mechanism that responds to an oxygenation challenge
- can help the clinician with assessment of vascular resistance and fluid status
what effect does a significant drop in CO have on the capnography?
rise drops almost to 0
what are determinants of CO?
- SV x HR (volume over time)
- stroke volume: amount blood pumped per beat
- preload: cardiac filling
- afterload: systemic vascular resistance
- contractility: myocardial ventricular force
- HR: beats per minute (chronotropic)
what affects preload?
- fluid volume status
- valve efficiency
- vena cava obstruction
- pulmonary vascular resistance
what affects afterload?
- valvular obstruction
- HTN
- tourniquet use
what affects contractility?
- myocardial oxygen supply and demand (ischemic state)
- inotropic drugs
describe invasive methods of CO monitoring?
thermodilution
- averages 2-3 measurements
- requires PAC
- 2.5-10 ml of room temp or iced saline
- CO based on RV which normally reflects LV
- degree of temp change is inversely proportional to CO
- temp change is minimal when flow is high
- temp change is great when flow is low
- thermodilution curve is produced (area under curve is high when CO is low)
- tricuspid regurg and shunts give invalid results
what are minimally invasive methods of CO monitoring?
- esophageal Doppler
- partial CO2 rebreathing
- arterial pressure waveform [lithium indicator dilution/pulse power (LiDCO); pulse contour (PiCCO); Flo Trac (no invasive manual calibration needed]
