TheCVICU

mcs initiation timing for patients in cardiogenic shock

Shock Math

—

by

nvs1
in

Cardiogenic Shock Math

Goal values

Cardiac index (CI): > 2.2 lpm/m2,

Systemic vascular resistance (SVR): 800-1200 dynes/s/cm2,

Central venous pressure (CVP): 8-12 mmHg.

Fick CI/CO Derivation

[math]CI = \frac{VO_2}{C_a-C_v}[/math],

Where, [math]C_a and C_v[/math] are derrived from the Oxygen content equation:

[math]CO_2 = \frac{1.34mLO_2}{gHb} * Hb * SaO_2 + 0.0031*PaO_2[/math],

Hb is in g/dL; to convert to g/L:

[math]CO_2 = \frac{1.34mLO_2}{gHb} * Hb * 10* SaO_2 + 0.0031*PaO_2[/math],

[math]\Longrightarrow[/math]

[math]CO_2 = \frac{13.4mLO_2}{gHb} * Hb * SaO_2 + 0.0031*PaO_2[/math],

The [math]0.0031*PaO_2 [/math] is negligible and can be removed,

[math]\therefore[/math]

[math]CI = \frac{VO_2}{13.4 \times Hb \times (\frac{SaO_2 – SvO_2}{100})}[/math],

[math]CO = CI \times BSA [/math]

BSA = Body surface area, CI = Cardiac index, CO = Cardiac output, CO2 = oxygen content, Ca = oxygen content in artery, Cv = oxygen content in venous system, Hb = hemoglobin, SaO2 = Oxygen saturation in the artery, SvO2 = Oxygen saturation in the venous system, PaO2 = Partial pressure of oxygen in blood, VO2 = Oxygen consumption.

Cardiac Index Calculator

VO2
ml/min/m2
Hb
g/dL
PA Sat
%
Art Sat
%
Height
cm
Weight
kg

Notes

  1. SvO2 is usually the PA Sat obtained from a pulmonary artery catheter. You can also use the SVC or right atrial sat obtained from a central line.
  2. You can use the Art Sat from a pulse oximeter, but the most accurate would be the saturation of arterial blood gas.
  3. Indexed VO2 of 125 ml/min/m2 is an estimated value from Dehmer and colleagues. For the elderly, you can also use 110 ml/min/m2, as demonstrated by Grafton and colleagues.
  4. Limitations of the Fick calculations are predominantly from the estimation of oxygen consumption from nomograms.

Systemic Vascular Resistance (SVR) Calculation

SVR Equation


[math]SVR(dynes/s/cm^{-5}) = 80\times \frac{MAP-CVP}{CO} [/math]

CO = Cardiac output, CVP = Central venous pressure, MAP = Mean arterial pressure, SVR = Systemic vascular resistance.

Notes

  1. Normal values are typically 800 – 1200 dynes/s/cm^-5

SVR Calculator

MAP
mmHg
CVP
mmHg
CO
LPM

Pulmonary Artery Pulsatility Index (PAPi)

PAPi Calculation

[math] PAPi = \frac{PAs – PAd}{CVP} [/math], <br><br>

PAs = Pulmonary artery systolic pressure, PAd = pulmonary artery diastolic pressure, CVP = Central venous pressure.

Notes

  1. PAPi is an indicator of RV function
    • RVSP is an indirect indicator of RV contractile function given a specific afterload condition
    • Higher RAP can suggest a failing RV
  2. PAPi is dependent on loading conditions, i.e., PA capacitance, PA pulse pressure, stroke volume, and RAP
  3. PA capacitance = stroke volume / PA pulse pressure
    • PA Capacitance is a measure of the RV’s ability to accommodate the blood ejected in systole
  4. Further reading: Lim et al.

PAPi Calculator

PAs
mmHg
PAd
mmHg
CVP
mmHg
Figure 1. Society for Cardiovascular Angiography and Interventions (SCAI) stages of cardiogenic shock (CS) differentiated by left ventricular (LV) versus right ventricular (RV) predominance or biventricular shock. pLVAD = percutaneous left ventricular assist device. pRVAD = percutaneous right ventricular assist device. pBiVAD = percutaneous left and right ventricular devices. VA ECMO = venoarterial extracorporeal membrane oxygenator.

pLVAD = percutaneous LVAD such as an Abiomed Impella 5.5/CP

pRVAD = percutaneous RVAD such as a LivaNova ProTek Duo or an Abiomed Impella RP Flex.

  • Oxygenators can be added to the ProTek but not the Impella RP Flex
Figure 2. Society for Cardiovascular Angiography and Interventions (SCAI) stages of cardiogenic shock (CS). Mechanical circulatory support (MCS) should be considered when SCAI stage C shock progresses. It is important to note here, that SCAI shock stages can go forward or backward based on management.
  • Consideration for mechanical circulatory support (MCS) should be triggered when patients who present with classic shock are deteriorating with standard medical therapies (i.e., inotropes, vasodilators, and diuretics).
  • A shock team approach should be considered. Papolos et al.
  • Before initiation of MCS, contraindications and next-step strategies (i.e., bridge to permanent ventricular assist devices, transplant, palliation) should be considered.

Comments

Leave a Reply