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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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Mechanical ventilation 2

Mechanical Ventilation #2

Alain Broccard, MD

John Marini, MD

University of Minnesota

Regions Hospital

St Paul, MN


To understand:

Pressure Control ventilation

Inverse Ratio

Bi-Level pressure ventilation


How to measure and correct

Venilator weaning

Pressure controlled ventilation
Pressure Controlled Ventilation

Key set variables:

Pressure, TI, and frequency


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

Key parameter to monitor is vt
Key Parameter to Monitor is VT

Change in mechanics

 airway resistance: e.g., bronchospasm

 respiratory system compliance .e.g, pulmonary edema, pneumothorax

AutoPEEP 

What Causes a Decreased

VT During PCV?

Auto peep intrinsic peep peepi
Auto-PEEP (Intrinsic PEEP, PEEPi)

-The pressure applied to the alveoli due to trapped volume

Marini, Wheeler. Crit Care Med. The Essentials. 1997.

Suspecting and measuring autopeep

Total PEEP





Suspecting 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.

Bi pap airway pressure release characteristics
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

Bi level ventilation
Bi-Level Ventilation Phases of Machine’s Cycle

Bi level ventilation with pressure support
Bi-Level Ventilation Phases of Machine’s CycleWith Pressure Support

Automatic tube compensation
Automatic Tube Compensation Phases of Machine’s Cycle

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.

External and tracheal pressures differ because of tube resistance
External and Tracheal Pressures Differ Because of Tube Resistance

ATC offsets a fraction of tube resistance

Discontinuation of mechanical ventilation
Discontinuation of Mechanical Ventilation Resistance

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

Other factors
Other Factors Resistance


How frequent is suctioning occuring?


Base line

Chronic COPD

CO2 retention

Measures to enhance the weaning process
Measures to Enhance Resistancethe Weaning Process

Extubation parameters
Extubation Parameters Resistance

Respiratory Rate <40/min

Tidal Volume 5 ml/kg

Minute Ventilation < 10L/min

Vital Capacity 10 ml/kg

PaO2/FiO2 ratio >200

NIF -25cmH2O

Rapid shallow breathing index
Rapid Shallow Breathing Index Resistance

Resp Rate


Tidal Vol

If RSBI > 105: 95% extubations failed

If RSIB < 105: 80% extubations successful

Three methods for gradually withdrawing ventilator support
Three Methods for Gradually Withdrawing Ventilator Support Resistance

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.

Extubation criteria
Extubation Criteria Resistance

Ability to protect upper airway

Effective cough


Improving clinical condition

Adequate lumen of trachea and larynx

“Leak test” during airway pressurization with the cuff deflated

Extubated Resistance

Add supplemental oxygen

Watch for signs of decompensation

Avoid over sedation

Encourage coughing

Incentive spirometer

Out of bed

Self assessment
Self Assessment Resistance

The following case study provide you with the opportunity to review the current and previous modules on mechanical ventilation.



Mv case
MV Case Resistance

References and suggested readings
References and Suggested Readings Resistance

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.