Clinical Application of

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Clinical Application of Dead Space Fraction
Measurements
presented by Mark Siobal BS RRT RCP Clinical
Specialist Respiratory Care Services San
Francisco General Hospital UCSF Department of
Anesthesia
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Clinical Application of Dead Space Fraction
Measurements

• Review of pulmonary physiology, ventilation
  perfusion matching, and physiologic dead space
• Define mechanical, anatomical, and alveolar dead
  space
• III. Clinical usefulness of serial dead space
  measurements
• IV. Review of methods used to determine dead
  space fraction
• V. Implications for the Respiratory Care Provider

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Physiologic Dead Space is the Percent of Wasted
Ventilation
Calculated by the Bohr Enghoff equation (1938)
VDphys PaCO2 - PeCO2 VT PaCO2
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Multiple Inert Gas Elimination Technique (MIGET)

• More accurate measurement of Dead Space
• Eliminates the use of CO2 as a single tracer gas
• Eliminates the overestimation of dead space

Complicated and Clinically Impractical
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Ventilation to Perfusion Matching
Pure Shunt Perfusion with NO Ventilation
Pure Dead Space Ventilation with NO Perfusion
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Ventilation to Perfusion Mismatch
Pure Shunt Perfusion with No Ventilation
Pure Dead Space Ventilation with No Perfusion
Shunt Like Units
Dead Space Like Units
gt
lt
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Increase in Physiologic Dead Space caused
by Ventilation to Perfusion Mismatch
Low Perfusion
No Perfusion
Hyperinflation

• Airway Obstruction
• Dynamic Hyperinflation
• Tidal Volume
• PEEP

• Low Cardiac Output
• Pulmonary Vascular
• Injury
• Extravascular
• Compression

• Pulmonary Embolus
• Vascular Obliteration

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Components of Physiologic Dead Space
Anatomic Alveolar
20 40
Anatomic Vd
15 25
Alveolar Vd
5 15
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How is Dead Space Measured ?
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Douglas Bag Exhaled Gas Collection
VCO2
PeCO2
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Douglas Bag Exhaled Gas Collection
PeCO2
VDphys PaCO2 - PeCO2 VT PaCO2
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Douglas Bag Exhaled Gas Collection
Eliminate mechanical dead space and correct for
compression volume.
PeCO2
VDphys PaCO2 - PeCO2 VT PaCO2
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Metabolic Analyzer
Inspired Gas Sampling
Expired Gas Collection
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Metabolic Analyzer
Inspired Gas Sampling
Expired Gas Collection
VCO2 VO2
R Q
REE
FiCO2 FeCO2
FiO2 FeO2

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Metabolic Analyzer
VDphys PaCO2 - PeCO2 VT PaCO2
FeCO2 x (760 47) PeCO2
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Metabolic Analyzer
Eliminate mechanical dead space and correct for
compression volume.
VDphys PaCO2 - PeCO2 VT PaCO2
FeCO2 x (760 47) PeCO2
x correction factor
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Volumetric Capnography (NICO2) Single Breath CO2
Analysis
Validated against a metabolic analyzer by Kallet
et al, Resp Care 2005 and used in many studies
for dead space fraction measurements
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Volumetric Capnography Single Breath CO2 Analysis
CO2 and Volume instead of CO2 and Time Capnogram
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Volumetric Capnography Single Breath CO2 Analysis
III
II
I
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Fowler Dead Space (1948) Single Breath CO2
Analysis
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Fletcher Dead Space (1981) Single Breath CO2
Analysis
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Fletcher Dead Space (1981) Single Breath CO2
Analysis
Y
Z
X
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Fletcher Dead Space (1981) Single Breath CO2
Analysis
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Fletcher Dead Space (1981) Single Breath CO2
Analysis
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Fletcher Dead Space (1981) Single Breath CO2
Analysis
Increase in physiologic dead space secondary to a
increase in alveolar dead space.
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Yang Equal Area Dead Space (2006) Single Breath
CO2 Analysis
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Yang Equal Area Dead Space (2006) Single Breath
CO2 Analysis
Allows partitioning of physiologic dead space
into anatomic and alveolar components directly
from the volume axis of the capnogram.
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Yang Equal Area Dead Space (2006) Single Breath
CO2 Analysis
225 / 565 40
225 ml
160 ml
65 ml
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Why is it Important to Measure Dead Space
Fraction in the Clinical Setting ?
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Indicator of the Severity of Lung Injury and a
Predictor of Mortality

• For every 0.05 increase in dead space fraction,
  the odds of death increased by 45.
• Other observational studies suggest that a value
  of 0.60 or higher may be associated with more
  severe lung injury.

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Indicator of the Severity of Lung Injury and a
Predictor of Mortality
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Indicator of Lung Overdistension During PEEP
Titration
Optimum End Expiratory Airway Pressure in
Patients with Acute Pulmonary Failure Suter PM,
Fairley HB, Isenberg MD. NEJM 1975

• Best PEEP corresponds to the lowest dead space
  fraction and the highest compliance

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Indicator of Lung Overdistension During PEEP
Titration
Effects of PEEP on Dead Space and its Partitions
in ALI Beydon L, et al. Inten Care Med 2002

• Anatomic dead space increased slightly with PEEP
• Alveolar dead space did not vary systematically
  with PEEP
• In individual patients a decrease or increase of
  alveolar dead space paralleled a positive or
  negative response to PEEP in regards to
  oxygenation

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Indicator of Optimal PEEP Following Lung
Recruitment
Compliance and Dead Space Fraction Indicate an
Optimal Level of PEEP after Recruitment in
Anesthetized Patients Maisch S, et al. Anesth
Analg 2008

• Following a recruitment maneuver, optimal PEEP
  occurred at the highest compliance and the lowest
  dead space fraction.

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Dead space to tidal volume ratio predicts
successful extubation in infants and children.
Hubble CL, Gentile MA, Tripp DS, Craig DM,
Meliones JN, Cheifetz IM. Crit Care Med 2000
Dead Space Fraction 0.50 reliably predicts
successful extubation, whereas a VD/VT gt 0.65
identifies patients at risk for respiratory
failure following extubation.
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Dead Space Fraction Measurements on the Dräger
Ventilator
Uses Fowler Method to Calculate Anatomic Dead
Space Fraction and Volume Vds / Vt Vds (mL)
Integrated Mainstream CO2 Sensor
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Dead Space Fraction Measurements on the Dräger
Ventilator
VCO2 Minute Ventilation
VCO2 FeCO2 MV
FeCO2 x (760 47) PeCO2
VDphys PaCO2 - PeCO2 VT PaCO2
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Validation of Dead Space Fraction Measurements on
the Dräger Ventilator
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Validation of Dead Space Fraction Measurements on
the Dräger Ventilator
COMPARISON OF MEAN EXPIRED CO2 MEASUREMENTS
CALCULATED USING THE DRAGER XL VENTILATOR
VOLUMETRIC CAPNOGRAPHY VS THE RESPIRONICS NICO2
MONITOR Mark Siobal BS RRT, Julin Tang MD MS, San
Francisco General Hospital, UCSF Department of
Anesthesia. Hannah Ong SRT, Wesley Toy SRT,
Skyline College, San Bruno CA.
r 0.9874, r squared 0.9750
AARC Abstract 2008
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Dead Space Fraction Measurements on the Dräger
Ventilator

• Requires manually averaging VCO2 and MV over a 5
  10 minutes especially with large variations.
• Validation study is not complete.
• Requires commitment by Dräger to implement
  software revision.

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Dead Space Fraction Measurements Implications
for the Respiratory Care Practitioner

• Can be used to assess the severity of lung injury
  
• Predicts survival in ALI / ARDS
• Can be used as an indicator of lung recruitment
• vs overdistension
• May be helpful as a predictor of successful
  weaning from mechanical ventilation
• May be helpful in the diagnosis of pulmonary
  embolism