quick guide to understand univentricular parallel circulation

1. Dr.AbhinavAgarwal

2.  Cardiac output affected by
 Preload
 Afterload
 Rate
 Rhythm
 Contractility
 AP shunts
 Regional Resistance
 Neurohumoral Factors (Inflammation, sympathetic
nervous system)
 Local Factors (Autoregulation)

3.  Redistribute Blood flow to brain and heart
 Mesentric and splanchnic circulation- silent ischemia during
compensated shock
 Baroreflex - Contractility, HR, SVR & decreases venous
capacitance
 Often body impairs systemic flow in face of myocardial
dysfunction (regional ischaemia due to high SVR)
 Ischaemic organ damage can occur even in presence of normal
global oxygen economy
 Regional Ischaemia →MODS→Death

4.  In series/ Normal circulation Qp=Qs=Qt
 In parallel circulation Qt= Qp+Qs
 At same Qt if Qp increases, Qs Decreases and vice a versa
 Pulmonary artery = Systemic artery= SaO2
 If Qs low = Sa-vO2 is high
 If Qs High = Sa-vO2 is low

5. 200
At Increased Qs
At decreased Qs
150
2070
50
50
100
50
50
SvO2 decreases
SvO2 increases
O2 delivered = Qs*O2 content of blood
At fixed O2 content and
at fixed O2 Extraction (suppose 50)
Oxygen delivered will depend on Qs

6.  Increased O2 demand:
 SvO2 reduces
 SaO2 will reduce
▪ (Vicious Cycle)
 SVR depends on many
factors

7.  Optimal systemic oxygen delivery occurs at
 Qp:Qs = 1 with
 lowest Qt (total cardiac output)
Fick Principle:
Equality of systemic
oxygen consumption
and pulmonary
oxygen uptake

8.  At Normal
extraction =25% &
SpvO2 = 100%
(No lung issue)
 Pulse ox (SaO2)=
75%
 SvO2 = 50%
 Qp:Qs = 1
75%
75%
75%
50%
100%

9.  At same saturation (75%)
 Any Qp:Qs is possible depending on Qt (PARRCA)
 Sa-vO2 (Extraction) = <25% : Qs high, Qp low,
Qp:Qs low at high Qt
 Sa-vO2 (Extraction) = >25% : Qs low, Qp high
Qp:Qs high at low Qt

10.  At same Sa-vO2: (Systemic flow is fixed)
 Any SpO2 is possible depending on Qt (PARRCA)
 If SaO2 High: Qp is high and Qp:Qs = 2 at high Qt
 If SaO2 Low: Qp is low and Qp:Qs = 0.5 at low Qt

11.  At same Qt (Total cardiac output)
 Any Qp: Qs can exist
 At Qp: Qs = 2
▪ Qp increases: SaO2 increases
▪ Qs reduces: Sa-vO2 increases
 At Qp:Qs = 0.5
▪ Qp decreases : SaO2 decreases
▪ Qs increases: Sa-vO2 decreases

12.  At same Qp:Qs = 1
 Many SpO2 are possible depending on Qt
(PARRCA)
 At high Qt :
▪ both systemic and pulmonary blood flow is high
▪ SpO2 high, SvO2 high & Sv-aO2 < 25%
 At low Qt :
▪ Both systemic and pulmonary blood flow is low
▪ SpO2 low, SvO2 low & Sv-aO2 > 25%
▪ Tissue oxygen utilization is impaired if SvO2<50%

13.  At constant Qt moderate alteration in Qp:Qs balance will have minimal effect on SaO2
 At fixed Qp:Qs, Increase in Qt can deliver more oxygen to tissue
 As tissue cannot utilize oxygen if SvO2<50%, so body has very less O2 reserve to maintain
increased O2 demand in parallel circulation.
 Body has more oxygen reserves at high Qt but at an expense of myocardial oxygen demand
 Another way to increase O2 delivery is by Increasing Hb

15.  Optimization of SaO2 alone will result in acute hemodynamic
collapse unexpectedly in an apparently stable child.

16.  Gas manipulation of PVR
 Inspired CO2: Increased PVR, decreased SVR, Increased O2 delivery
(esp. brain)
 Subatmospheric FiO2: Raises PVR
 Controlled PPV while avoiding hypervenilation (PEEP)
 O2 can be used if:
 Respiratory pathology is present
 Restrictive communications
 Control of elevated SVR was more effective than increasing PVR
 Inotropes increase SVR at high doses
 Inodilators preferred (while preventing significant hypotension)
 Morphine reduces Sympathetic outflow
 Regional saturations of brain, liver, kidney, gut and muscle can be
measured to rule out regional ischaemia
 Increase Hct > 50% increases O2 carrying capacity

17.  Pulmonary venous SpvO2 = 100%
 Variablity in Arteriovenous saturation
difference
 Not possible to obtain true sytemic venous
mixed venous saturation

18.  Thank you