Program Information. Mechanical Ventilation #2. Alain Broccard, MD John Marini, MD University of Minnesota Regions Hospital St Paul, MN. Objectives. To understand: Pressure Control ventilation Inverse Ratio Bi-Level pressure ventilation Auto PEEP How to measure and correct
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Alain Broccard, MD
John Marini, MD
University of Minnesota
St Paul, MN
Pressure Control ventilation
Bi-Level pressure ventilation
How to measure and correct
Key set variables:
Pressure, TI, and frequency
PEEP and FIO2
Ventilator generates a predetermined pressure for a preset time
PCV-AC mode: same as mandatory breaths
PCV-SIMV mode: unsupported or PS
Change in mechanics
airway resistance: e.g., bronchospasm
respiratory system compliance .e.g, pulmonary edema, pneumothorax
What Causes a Decreased
VT During PCV?
-The pressure applied to the alveoli due to trapped volume
Marini, Wheeler. Crit Care Med. The Essentials. 1997.
TimeSuspecting and Measuring AutoPEEP
Suspect AutoPEEP if flow at the end of expiration does not return to the zero baseline.
End expiratory pause
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.
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.
ATC offsets a fraction of tube resistance
To discontinue mechanical ventilation requires:
Assessment of readiness
For independent breathing
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
How frequent is suctioning occuring?
Respiratory Rate <40/min
Tidal Volume 5 ml/kg
Minute Ventilation < 10L/min
Vital Capacity 10 ml/kg
PaO2/FiO2 ratio >200
If RSBI > 105: 95% extubations failed
If RSIB < 105: 80% extubations successful
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.
Ability to protect upper airway
Improving clinical condition
Adequate lumen of trachea and larynx
“Leak test” during airway pressurization with the cuff deflated
Add supplemental oxygen
Watch for signs of decompensation
Avoid over sedation
Out of bed
The following case study provide you with the opportunity to review the current and previous modules on mechanical ventilation.
Hubmayr RD, Abel MD, Rehder K. Physiologic approach to mechanical ventilation. Crit Care Med. 1990;18:103-13.
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.