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