The Value of Continuous
ScvO2 Monitoring in PICU
Caulette Young, RN, BSN
Pediatric Clinical Nurse Consultant
Edwards Lifesciences, LLC
Disclaimers
• Paid consultant for Edwards Lifesciences, LLC
• Pediatric critical care products
• Provide education, in-services, research &
technical advice
Objective
The goal in PICU is to maintain a balance
between oxygen delivery and consumption.
Continuous ScvO2 allows the clinician to
assess oxygen delivery and consumption in
real-time. Imbalances can rapidly be identified
and treated earlier with improved outcomes.
What is our main goal for patients in ICU?
• Adequate
oxygenation & tissue
perfusion
How can we achieve this?
• Ensure
a balance between oxygen
delivery & oxygen consumption
How can we assess for this?
• Continuous
monitoring ScvO2
Reflection vs Transmission
Spectrophotometry
74
Receiving fiber
Transmission fiber
SVC
LED photo detector
Benefits of Continuous vs. Intermittent
• Real-time, no waiting for analysis results
• Decrease risk for infection
• Decrease risk for transfusions
• Early warning
– Identification of DO2/VO2 imbalance
– Traditional hemodynamic monitoring unreliable
• Cost savings
– Financial
– Resources of staff
– Prevention
Using continuous ScvO2 monitoring
to evaluate tissue oxygenation at
the bedside enables the clinician to
detect early alterations in oxygen
balance.
(Goodrich 2006 Crit Care Nurs Clin N Am)
“Oxygen delivery does not provide
information about the adequacy of
tissue oxygenation.”
Curley & Harmon
Critical Care Nursing of Infants and Children 2nd Ed
Uncorrected imbalances
• Shift in dissociation curve: left or right
• Hypoxia / hypoxemia
• Acidosis
• Redistribution or maldistribution of blood
• MODS
• Pulmonary hypertension
• Cardiovascular collapse / cardiac arrest
• Necrosis & irreversible cell death
• Death
What is
ScvO2?
Central venous oxygen saturation
measured at the SVC-RA junction
Indicative of balance between
oxygen delivery & consumption
Trends well with SvO2
SVC-RA
junction
Can be used as a surrogate for
adequate cardiac index
Early warning indicator
Used to guide therapy in sepsis &
congenital cardiac surgery
ScvO2
Oxygen Delivery
Hemoglobin Cardiac
output
Heart
rate
Preload
Oxygen Consumption
Oxygenation
/ventilation
Stroke
volume
Afterload
FiO2
Contractility
Metabolic demands
SvO2 or ScvO2: What’s the difference?
• PA catheter or central line
• Global or regional
– SvO2 represents mixed venous blood from:
• SVC ≅ 70%
• CS ≅ 37%
• IVC ≅ 80%
– ScvO2 represents blood returning from upper or
lower body (depending on site)
• Normal values:
– SvO2 (60-80%)
– ScvO2 (70-75%)
• ScvO2 usually runs ~7% higher than SvO2
• Difference can widen in shock states when
perfusion redistribution occurs
Regional oxygen saturation from upper body
ScvO2 ……
SvO2
Trends with SvO2 values, nearly interchangeable
ScvO2 ……
SvO2
Reinhart et al Intensive Care Med. 2004
Has been considered a surrogate for cardiac
output / index in pediatrics
Tibby et al Arch Dis Child 2003
“Adequate” oxygenation can only be defined when
tissue O2 supply matches tissue O2 demand
Usually consumption (VO2) independent of delivery (DO2)
DO2I= CO x SaO2 x Hgb x 1.34 x 10 = 650 + 50 ml/min/m2
VO2I= CO x (SaO2-SvO2) x Hgb x 1.34 x 10 = 120-200 ml/min/m2
If VO2 increases or DO2 decreases, tissue oxygenation is
maintained by increasing oxygen extraction
O2ER = VO2/DO2 x 100 = 25 + 2%
If DO2 drops below a critical level, oxygen extraction
becomes exhausted resulting in VO2 dependent on DO2 or
oxygen debt
Tissue hypoxia occurs!
Note: O2ER increases well before lactate begins to accumulate
ScvO2 / SvO2
Physiology
70-75%
Normal extraction
(non-cyanotic cardiac)
< 70% and > 50%
Compensatory extraction
( demand or supply)
< 50% and > 30%
Limits of extraction
(beginning of lactic
acidosis)
< 30% and > 25%
Severe lactic acidosis
< 25%
Cellular death
Bloos & Reinhart; Intensive Care Med (2005) 31:911–913
Factors to be considered in Oxygenation
Alveolar-pulmonary capillary O2 transport
• Gas exchange in terminal portion of lungs
O2 transport in the blood
• Hemoglobin & oxyhemoglobin
− Arterial O2 content (CaO2)
− Oxyhemoglobin dissociation curve
− O2 delivery (DO2)
DO2
Cellular respiration
•
•
Oxygen consumption
Oxygen extraction ratio (O2ER)
− Tissue oxygenation dependent on
microcirculation
− Microcirculation adjusts to enhance O2
extraction
VO2
Critical O2
Tissues extract
what’s needed. If
DO2 decreases or
VO2 increases,
O2ER increases
to meet demands
Once O2 extraction
has been maximized,
VO2 becomes
dependent on DO2
Pathologic
VO2
Tissue hypoxia
occurs when VO2
exceeds DO2
DO2
O2ER may increase to
meet O2 demands, when
DO2 is decreased or
VO2 is increased.
Normal
Normal O2ER 25-30%
O2 ER
Pathologic
DO2
O2 debt: Why is it important?
It needs to be paid back with interest
Interest
VO2
O2 debt
DO2 needs to meet current
O2 needs and satisfy the
needs that were previously
unmet
Time
Oxygen Saturation Values
Site
Acyanotic
Cyanotic
Superior vena cava
70-75%
35-55%
Right atrium / ventricle
75%
67% / 80%
Pulmonary vein
95%
88%
Aorta
95%
80%
Left atrium / ventricle
95%
90%
Inferior vena cava
78%
Pulmonary Hypertension in Post-op Cardiac
Critical Heart Disease in Infants & Children 2nd Ed
Stimulant: Pain, agitation, hypoxia, hypothermia, suctioning,
acidosis, hypercarbia
PVR
R L shunt
Qp Qs
ScvO2/SvO2
DO2
PaO2
PaCO2
Cardiac arrest
Hypoxic vasoconstriction
When is Change Significant?
• Change from baseline ≥ 5-10%
sustained > 5 minutes
• Values may fluctuate ± 5%, with
activities or interventions (i.e.
suctioning)
• Slow recovery may indicate
cardiopulmonary system’s inability to
respond to increases in O2 demand
ScvO2 < 70%
Causative Factors
Clinical Conditions
(Decreased O2delivery)
↓Cardiac Output (CO)
↓O2 Saturation (SaO2)
↓ Hgb concentration
Left ventricular dysfunction
Shock
Hypovolemia
Hypoxemia
Lung Disease
Respiratory failure
Anemia
Hemorrhage
Hemodilution
Dyshemoglobinemias
ScvO2 < 70%
Causative Factors
Clinical Conditions
Increased O2 consumption
Traumatic brain injury (138%)
Burns (100%)
Sepsis (50-100%)
Shivering (50-100%)
MODS (20-80%)
Increased WOB (40%)
Position change (31%)
Suctioning (27%)
Bath (23%)
Dressing change (10%)
Fever each °C (10%)
ScvO2 > 70%
Causative Factors
Increased O2 delivery
(DO2)
Decreased O2 consumption
(VO2)
Clinical Conditions
PaO2
Hemoglobin
Cardiac output
Anesthesia
Hypothermia
Dyshemoglobinemias
Venous hyperoxia
Understanding the clinical significance of
SvO2 (ScvO2) measurements….can help
guide clinical decision-making to assure
adequate oxygenation to meet tissue
needs.
(Sanders, 1997 Applied Pathophysiology)
“Useful in
patient types”
• Congenital cardiac surgery
• Pediatric sepsis
“Useful in patient
management”
• Fluid administration &
boluses
• High risk surgery
• Vasoactive infusions
• Respiratory failure
• Blood transfusions
• Trauma
• Ventilatory management
• Burns
• Arrest resuscitation
• Jugular bulb
• End-organ perfusion
Thank You!
“Hypoxia not only stops the machine, it wrecks
the machinery”
John Scott Haldane, 1880
[email protected]
www.Edwards.com/pediasat