caridac output monitoring and oxygen delivery Flashcards Preview

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Flashcards in caridac output monitoring and oxygen delivery Deck (22)
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1
Q

how do you calculate oxygen consumption (VO2)?

A

VO2= (FiO2 - FeO2) x Vm/ weight in kg

2
Q

with an FiO2 of 93%, FeO2 (EtO2) of 89%, Vm 6.5 L, and pt wt of 75 kg calculate the VO2

A

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

3
Q

how is O2 delivery (DO2) calculated?

A
  • 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
4
Q

-75 kg pt.
-HR 70 bpm
-Hct .39
-Sat 100%
-FiO2 .93
est. CO 5 L/min
what is the DO2?

A

-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

5
Q

does 100% O2 really have a dramatic impact on the amount of oxygen delivered to the tissues?

A

NO

6
Q

does CO have a dramatic impact on the amount of oxygen delivered to the tissues?

A

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

7
Q

does hgb have a dramatic impact on the amount of oxygen delivered to the tissues with a normal CO?

A

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
8
Q

what is beneficial of CO monitoring?

A
  • 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
9
Q

what effect does a significant drop in CO have on the capnography?

A

rise drops almost to 0

10
Q

what are determinants of CO?

A
  • 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)
11
Q

what affects preload?

A
  • fluid volume status
  • valve efficiency
  • vena cava obstruction
  • pulmonary vascular resistance
12
Q

what affects afterload?

A
  • valvular obstruction
  • HTN
  • tourniquet use
13
Q

what affects contractility?

A
  • myocardial oxygen supply and demand (ischemic state)

- inotropic drugs

14
Q

describe invasive methods of CO monitoring?

A

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
15
Q

what are minimally invasive methods of CO monitoring?

A
  • esophageal Doppler
  • partial CO2 rebreathing
  • arterial pressure waveform [lithium indicator dilution/pulse power (LiDCO); pulse contour (PiCCO); Flo Trac (no invasive manual calibration needed]
16
Q

what is a non invasive method of CO monitoring?

A

thoracic bioimpedance

17
Q

what are errors in thermodilution?

A
  • rapid fluid boluses
  • respiratory variations
  • post bypass pump temperature drift
  • right heart valvular regurgitation (tricuspid)
  • high levels of PEEP
  • intracardiac shunts
  • low flow states
18
Q

describe continuous thermodilution CO monitoring

A
  • uses small heat signal instead of cold
  • updated CO averages every 30 seconds
  • averages readings over 3-6 minutes
  • respiratory variations removed
  • rapid central venous IV infusions and post bypass pump fluid decrease accuracy of measurement
  • with averages an approx. 10 minute delay can cause acute changes to be inaccurate
19
Q

describe arterial pressure waveform analysis for CO monitoring

A
  • provides a beat to beat CO measurement
  • calculation of SV from area under waveform
  • measurement based on calculation algorithm
  • calibration accounts for vascular resistance, compliance, impedance, wave reflectance
  • require well defined arterial waveform (dicrotic notch defines end-systole)
  • frequent dysrhythmias and tachycardia can result in low SV and affect accuracy
  • affects of respiratory variations on SV can provide usable info on fld. vol. status
20
Q

describe partial O2 rebreathing for CO monitoring

A
  • ETCO2 measured reflects pulmonary capillary blood flow
  • requires tracheal intubation and mechanical ventilation
  • semi-continuous measurements
  • must be blood that participates in gas exchange (shunted blood not involved in gas exchange)
  • if no PAC or art line, use ETCO2 and HR
21
Q

describe esophageal Doppler monitoring of CO

A
  • measures velocity of aortic flow
  • probe size of NGT inserted lower esophagus
  • flow through descending thoracic aorta
  • calculates flow velocity using moving red blood cells
  • contraindicated in esophageal pathology, coagulopathy
22
Q

describe thoracic bioimpedance monitoring of CO

A
  • thoracic resistance (aka bioimpedance) changes as thoracic volume changes
  • four pairs of electrodes inject microcurrents and sense bioimpedance
  • accuracy of results are affected by:
  • electrical interference
  • incorrect placement of electrodes
  • previous heart surgery
  • aortic valve disease