Transcript AICU-C-7_McVent2 - Thomas Jefferson University

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Mechanical Ventilation #2
Alain Broccard, MD
John Marini, MD
University of Minnesota
Regions Hospital
St Paul, MN
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Slide 2
Objectives
• To understand:
– Pressure Control ventilation
• Inverse Ratio
– Bi-Level pressure ventilation
– Auto PEEP
• How to measure and correct
– Venilator weaning
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Slide 3
Pressure Controlled Ventilation
• Key set variables:
– Pressure, TI, and frequency
– PEEP and FIO2
• Mandatory breaths
– Ventilator generates a predetermined pressure for a
preset time
• Spontaneous breaths
– PCV-AC mode: same as mandatory breaths
– PCV-SIMV mode: unsupported or PS
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Slide 4
Key Parameter to Monitor is VT
What Causes a Decreased
VT During PCV?
• Change in mechanics
  airway resistance: e.g.,
bronchospasm
  respiratory system
compliance .e.g, pulmonary
edema, pneumothorax
•
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Slide 5
AutoPEEP 
Auto-PEEP
(Intrinsic PEEP, PEEPi)
-The pressure applied to the alveoli due to trapped volume
Marini, Wheeler. Crit Care Med. The Essentials. 1997.
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Slide 6
Suspecting and Measuring
AutoPEEP
Suspect AutoPEEP if flow at the
end of expiration does not
return to the zero baseline.
Total PEEP
PEEPe
Pressure
End expiratory pause
PEEPi
Time
AutoPEEP is commonly measured by performing a pause at the end of expiration. In a
passive patient, flow interruption is associated with pressure equilibration through the entire
system. In such conditions, proximal airway pressure tracks the mean alveolar pressure
caused by dynamic hyperinflation.
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Slide 7
Bi-Pap & Airway Pressure
Release Characteristics
• Allow spontaneous breaths superimposed on a set
number of “pressure controlled” ventilator cycles
• Reduce peak airway pressures
• “Open” circuit / enhanced synchrony between patient
effort and machine response
• Settings:
Pinsp and Pexp (Phigh and Plow)
Thigh and Tlow
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Slide 8
Inverse Ratio Airway Pressure Release
(APRV), and Bi-Level (Bi-PAP)
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Slide 9
Unlike PCV, BiPAP Allows Spontaneous Breathing
During Both Phases of Machine’s Cycle
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Slide 10
Bi-Level Ventilation
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Slide 11
Bi-Level Ventilation
With Pressure Support
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Slide 12
Automatic Tube Compensation
• The endotracheal tube offers resistance to ventilation both on
inspiration and on expiration.
• A low level of pressure support can help overcome this pressure
cost, but its effect varies with flow rate.
• Automatic tube compensation (ATC) adjusts its pressure output in
accordance with flow, theoretically giving an appropriate amount of
pressure support as needed as the cycle proceeds and flow
demands vary within and between subsequent breaths.
• Some variants of ATC drop airway pressure in the early portion of
expiration to help speed expiration.
• Supplemental pressure support can be provided to assist in tidal
breath delivery.
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Slide 13
External and Tracheal Pressures Differ
Because of Tube Resistance
ATC offsets a fraction of tube resistance
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Slide 14
Discontinuation of Mechanical
Ventilation
• To discontinue mechanical ventilation requires:
– Patient preparation
– Assessment of readiness
• For independent breathing
• For extubation
– A brief trial of minimally assisted breathing
• An assessment of probable upper airway patency after
extubation
– Either abrupt or gradual withdrawal of positive
pressure, depending on the patient’s readiness
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Slide 15
Preparation: Factors Affecting
Ventilatory Demand
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Slide 16
Other Factors
• Secretions
– How frequent is suctioning occuring?
– Consistancy
• Base line
– Chronic COPD
– CO2 retention
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Slide 17
Measures to Enhance
the Weaning Process
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Slide 18
Extubation Parameters
• Respiratory Rate <40/min
• Tidal Volume 5 ml/kg
• Minute Ventilation < 10L/min
• Vital Capacity 10 ml/kg
• PaO2/FiO2 ratio >200
• NIF -25cmH2O
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Slide 19
Rapid Shallow Breathing Index
Resp Rate
-------------Tidal Vol
If RSBI > 105: 95% extubations failed
If RSIB < 105: 80% extubations successful
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Slide 20
Three Methods for Gradually
Withdrawing Ventilator Support
• Although the majority of patients do not require gradual
withdrawal of ventilation, those that do tend to do better
with graded pressure supported weaning than with
abrupt transitions from Assist/Control to CPAP or with
SIMV used with only minimal pressure support.
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Slide 21
Extubation Criteria
• Ability to protect upper airway
– Effective cough
– Alertness
• Improving clinical condition
• Adequate lumen of trachea and larynx
– “Leak test” during airway pressurization with the cuff
deflated
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Slide 22
Extubated
• Add supplemental oxygen
• Watch for signs of decompensation
• Avoid over sedation
• Encourage coughing
• Incentive spirometer
• Out of bed
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Slide 23
Self Assessment
The following case study provide you with the opportunity
to review the current and previous modules on mechanical
ventilation.
Review
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References and Suggested
Readings
• Hubmayr RD, Abel MD, Rehder K. Physiologic approach
to mechanical ventilation. Crit Care Med. 1990;18:10313.
• Tobin MJ. Mechanical ventilation. N Engl J Med.
1994;330;1056-61.
• Marini JJ. Monitoring during mechanical ventilation. Clin
Chest Med. 1988;9:73-100.
• Brochard L. Noninvasive ventilation for acute respiratory
failure. JAMA. 2002;288:932-935.
• Calfee CS, Matthay MA. Recent advances in mechanical
ventilation. Am J Med. 2005;118:584-91.
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Slide 26