When Traditional Modes of Ventilation Fail

Rosalio Rubio MD; Sharon DeCruz, MD

University of California, Davis Medical Center, Sacramento, CA

Learning Objective

Case Information

Discussion

References

• To learn Airway Pressure Release Ventilation (APRV) in

Acute Respiratory Distress Syndrome (ARDS) with

refractory hypoxemia

• To review the initial settings of APRV and how to make

adjustments

History

• 31 yo morbidly obese man presented to the ED with a 5

day history of fevers, body aches, and shortness of

breath

• Initial evaluation demonstrated a patient in moderate

respiratory distress

• Patient was placed on non-invasive positive pressure

ventilation (NPPV)

Evaluation

• Patient desaturated to 70% while on NIPPV

• ABG showed a pH 7.40, PaCO2 48, PaO2 55, HCO3 29

• CXR showed diffuse bilateral pulmonary infiltrates

• Patient was intubated and ventilated using assist

control/pressure control (AC/PC) mode with fraction of

inspired oxygen (FiO2) of 100%

• Influenza A RT-PCR was positive

Hospital Course

• Patient remained hypoxemic and hypercarbic despite

increases in both pressure control (PC) and positive end-

expiratory pressures (PEEP)

• After 8 days of persistent hypoxia on AC/PC mode, the

patient was switched to APRV mode in an attempt to

improve oxygenation

• On day two of APRV, FiO2 was able to be weaned down

to 50%, and PaO2 increased to more than 90mmHg

• A Phigh of 39 cm H20 was required to achieve this level of

oxygenation given the patients low lung compliance

secondary to morbid obesity

• After 5 days on APRV, patient was transitioned back to a

traditional ventilation mode of AC/PC

• Patient was able to maintain his oxygenation and was

successfully extubated 8 days later

• Current guidelines advocate the use of low tidal

volume ventilation to decrease the risk of

ventilator-induced lung injury in ARDS

• In patients with ARDS, traditional modes of

ventilation may not achieve adequate oxygenation

due to impaired alveolar recruitment

• APRV is a mode of ventilation that applies

continuous high airway pressure, followed by a

time cycled release phase to a lower set pressure

• APRV allows for continuous recruitment by

spending 80-95% of the cycle at Phigh

• APRV allows spontaneous breathing throughout

the ventilatory cycle leading to ventilation-

perfusion matching by preferentially aerating well-

perfused dependent lung regions

• Improved alveolar recruitment and alveolar

ventilation can lead to increased oxygenation in

patients with severe ARDS

• Although low tidal volume strategies are proven to

decrease mortality, 1/3 of patients will still die from

ARDS. Such patients may benefit from APRV to

maintain oxygenation while providing time for the

underlying inflammatory process to resolve

CXR on Admission CXR on APRVCXR on AC/PC

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2. Frawley PM, Habashi NM. Airway pressure release ventilation: theory and practice.

AACN Clin Issues. May 2001;12(2):234-246; quiz 328-239.

3. Habashi NM. Other approaches to open-lung ventilation: airway pressure release

ventilation. Crit Care Med. Mar 2005;33(3 Suppl):S228-240.

4. Varpula T, Valta P, Niemi R, Takkunen O, Hynynen M, Pettila VV. Airway pressure

release ventilation as a primary ventilatory mode in acute respiratory distress syndrome. Acta

Anaesthesiol Scand. Jul 2004;48(6):722-731.

5. Stawicki SP, Goyal M, Sarani B. High-frequency oscillatory ventilation (HFOV) and

airway pressure release ventilation (APRV): a practical guide. J Intensive Care Med. Jul-Aug

2009;24(4):215-229.

Thigh 4-6 seconds

Tlow 0.6-0.8 seconds based on T-PEFR

Phigh Plateau pressure of 25 – 35 cmH2O

Plow 0

FiO2 4-6 seconds

Initial Setting for APRV

Ventilator Adjustments

Hypoxemia

• Increase FiO2

• Recruitment maneuver

• Increase Thigh

• Increase Phigh to max 40cmH2O

• Adjust Tlow to keep T-PEFR>50%

Hypercapnea/acidemia

• Increase Tlow

• Increase Phigh and Thigh to increase

minute ventilation

Trend in PaO2 and FiO2

Pressure high (Phigh): Baseline airway pressure level, higher of two airway pressures

Pressure low (Plow): Airway pressure resulting from pressure release, lower of two airway pressures

Time high (Thigh): Length of time for which P High is maintained

Time low (Tlow): Length of time for which P Low is maintained

Definitions

Pressure vs. Time and Flow vs. Time in APRV

Ventilator Days

PaO

2m

mH

g a

nd F

iO2

%