When Traditional Modes of Ventilation Fail
Rosalio Rubio MD; Sharon DeCruz, MD
University of California, Davis Medical Center, Sacramento, CA
Learning Objective
CXR on Admission
CXR on APRV
CXR on AC/PC
• 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
• 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
Case Information
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 endexpiratory 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
• APRV is a mode of ventilation that applies
continuous high airway pressure, followed by a
time cycled release phase to a lower set pressure
Trend in PaO2 and FiO2
• APRV allows for continuous recruitment by
spending 80-95% of the cycle at Phigh
PaO2 mmHg and FiO2 %
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)
Discussion
• APRV allows spontaneous breathing throughout
the ventilatory cycle leading to ventilationperfusion matching by preferentially aerating wellperfused dependent lung regions
• Improved alveolar recruitment and alveolar
ventilation can lead to increased oxygenation in
patients with severe ARDS
Ventilator Days
Pressure vs. Time and Flow vs. Time in APRV
Initial Setting for APRV
Thigh
Tlow
Phigh
Plow
FiO2
4-6 seconds
0.6-0.8 seconds based on T-PEFR
Plateau pressure of 25 – 35 cmH2O
0
4-6 seconds
• 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
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
Definitions
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
References
1.
Rasanen J, Cane RD, Downs JB, et al. Airway pressure release ventilation during
acute lung injury: a prospective multicenter trial. Crit Care Med. Oct 1991;19(10):1234-1241.
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.