Ventilators, Modes and Flows
Bonjo Batoon, MS, CRNA
Objectives
• Discuss the differences between pressure and volume control modes of ventilation
• Discuss acute lung injury (ALI) and adult respiratory distress syndrome (ARDS)
• Describe and discuss airway pressure release ventilation (APRV)
How do you know the patient is breathing?
Common Modes of Ventilation
Mode Trigger Limit Cycle off Spont resp Flow of gas
VCV Time Volume Time ? Constant
PVC Time Pressure Time ? Decelerating
SIMC Time or pt Pressure or volume
Time Yes Constant or decelerating
PSV Patient Pressure Flow of gas Yes Decelerating
PCVG/PRVC Time or pt Volume Time ? Decelerating
Volume ControlPressure
Scalar
FlowScalar
Pressure Control
FlowScalar
Pressure Scalar
Constant flow
Constant Pressure
Pressure control
Volume control
Red= pressureVolume control
Pressure control
Elevated Peak Airway Pressures
• Why?• Pt getting light• Kinking• Obstructions• Secretions• ARDS• Bronchospasm• TRALI• Aspiration• Alveolar derecruitment
Why Change I:E Ratio?
• More important in VC modes
Flow scalar
Vt= 600RR= 10I:E= 1:1I+E= 6 secI= 3 secE= 3 secFlow velocity= 200 ml/sec
Vt= 600RR= 10I:E= 1:2I+E= 6 secI= 2 secE= 4 secFlow velocity= 300 ml/sec
PAP 30PAP 27
I:E ratio
Auto PEEP
No return to baseline in flow scalar
VC
PC
Management Auto PEEP
↓ Minute ventilation• ↓ Vt• ↓ RR
↑ I:E ratio• Allow ↑ exhalation
Cardiovascular compromise• Disconnect circuit• Reconnect• Lower setting• Volume resuscitate
Auto PEEP
VC 14 BPM
VC 10 BMP
Flow Scalar Auto PEEP
Spontaneous Ventilation
Pressure Scalar
FlowScalar
Negative inspiratory pressure
Negative inspiratory flow
Negative inspiratory pressure
Turbulent flow Suctioned Spontaneous effort Vec 10mg
Positive End Expiratory Pressure
PEEP
PEEP
PEEP 15 No PEEP
Collateral Channels of Ventilation
Acute Lung Injury & Adult Respiratory Distress Syndrome
ALI• Acute onset P/F ratio < 300
mmHg• Bilateral pulmonary infiltrates
on xray• Not r/t cardiogenic pulmonary
edema
ARDS• ALI +
• P/F ratio < 200 mmHg• Severe ARDS
• P/F ratio < 150 mmHg
The ARDS Definition Task Force*. Acute Respiratory Distress SyndromeThe Berlin Definition. JAMA. 2012;307(23):25262533.
doi:10.1001/jama.2012.5669
ARDS severity Pa02/FiO2 Mortality %Mild 200300 27
Moderate 100200 32
Severe <100 45
ALI/ARDS risk factors
Primary Secondary
Aspiration TRALI
Contusion Pacreatitis
Pneumonia Sepsis
Inhalational injury TBI
Ventilator induced lung injury
Bakowitz et al. Acute lung injury and the Acute respiratoryDistress syndrome in the injured patient. Scandinavian Journal
of Trauma, Resuscitation and Emergency Medicine. 2012. 20:54.
6 ml/kg 12 ml/kg
Mortality (%) 31.0 39.8
Vent free days 12 ± 11 10 ± 11
• 22% ↓ mortality• Possible ↓ lung injury
• r/t excessive stretch• Excessive opening/closing
• Suggests beneficial effects↑ PEEP/↓ Vt
Airway Pressure Release Ventilation(APRV)
T1 T1
T2 T2
P1
P2P2
Pressure scalarPressure
Time
Advantages of APRV
• Lower PAPs• ↓ dead space ventilation• ↑ alveolar recruitment• Allows pts to spontaneously breath at any point• ↓ sedation and need for paralysis
Inflection Points
Volume
Pressure
HIP
LIPP2
P1
Atelectrauma
VolutraumaOverdistension
Lesion NPV APRV
Mortality 60% 0%
Atelectasis 0.03 ± 0.02 0.0 ± 0.02
Fibrinous deposits 1.75 ± 0.16 0.4 ± 0.19
Airspace space hemorrhage 1.88 ± 0.16 0.33 ± 0.19
Capillary congestion 2.15 ± 0.15 0.83 ± 0.17
Thickened alveolar walls 1.95 ± 0.14 0.33 ± 0.17
Cellular infiltration 2.93 ± 0.09 1.97 ± 0.11
ARDS risk factors• ↑ ISS• Chest injury• Femur fractures• Resuscitative care
• RBCs/FFP• + fluid balance
• STC fluid 11.5 L + blood products
Management of APRV Patient
• Know the initial settings• P1:P2; T1:T2; Fio2• Do they need APRV?• Suctioning requirements?
• RT will be present for transport• Avoid disconnects at all cost!!
• Have a clamp available
Management of APRV Patient
Know they will need higher support levels intraoperative• Case dependent• Additional transfusions• Positioning
TIVA
Paralysis as needed
What happens if APRV is not working?
ECMO and Lung Rescue Unit
• Risks of hypoxemia outweighs risk of invasive procedure
• Rests the lungs
Bibro et al. Crit Care Nurse. October 2011 31:e8e24
Summary
Know and pay attention to ALL ventilator parameters
Consider flow and pressure waveforms as vital signs
Be vigilant
Prevention and anticipation are essential