BASIC VENTILATION

Dr David Maritz

Mechanical ventilation. Emergency Med Clin N Am. 26 (2008) 849 - 862

Introduction

• Emergency room-vs-ICU-vs-operating room

• Trouble shooting in ICU

• Terminology!

• Specific scenarios

Introduction

• Why is the patient on the ventilator?

• Is the patient breathing spontaneously?

• Who is doing the greater work of breathing?

• Volume or pressure targeted strategy?

• Dual controlled mode?

• What is the set respiratory rate?

• What is the total respiratory rate?

• What is the set extrinsic / applied PEEP?

• Is there intrinsic / auto PEEP?

• What is the I:E ratio, flow rate, trigger mode?

• What do the respiratory graphics indicate?

Introduction

• Volume targeted ( volume cycled , volume assist / control)

• Pressure targeted

• Dual

Introduction

• RR x Vt = MV

• Intubated for airway protection• Septic / severe acidosis• ALI / ARDS• Other scanarios

Introduction

• Adjust FiO2

• Extrinsic PEEP – offset loss of FRC

• Caution in:– Elevated ICP– Unilateral lung process– Hypotension– Hypovolaemia– Pulmonary embolism

Introduction

• Flow waveform – decelerate– Optimise recruitment

• Trigger mode – detects pressure or flow gradient– Patient triggers ventilator– Too high – increased work– Too low – auto trigger– 1 – 3 cmH2O

Spontaneous breathing

• Supported by pressure support ventilation (PSV)

• Clinician sets FiO2 / PEEP

• Patient sets RR / flow rate

• VT dictated by PS / patient effort / lung compliance

• Back up apnea rate

Volume targeted mode

• Ventilator will generate necessary driving pressure to reach the targeted volume

• Beware auto / intrinsic PEEP ( breath stacking)• Therefore progressive air trapping

Pressure targeted mode

• Ventilator generates preset inspiratory pressure

• Vt function of respiratory mechanics

• Better pressure distribution

• Any change in system compliance / resistance will affect Vt

Asthma / COPD

• Volume depleted• Hyperinflation (auto-PEEP)• 8-10 breaths per minute• Decrease inspiratory time / increase expiratory time• Vt 6-7 ml/kg• Increase flow rate (80-100l/min)• Square wave form• Permissive hypercapnia• Sedation / paralyze• Sudden hypotension:

– Disconnect fom ventilator

– Tension pneumo

Acute lung injury / ARDS

• ARDS:– PaO2/FiO2 < 200

– Bilat pulmonary infiltrates

– Wedge presssure < 18mmHg

• ALI:– PaO2 / FiO2 < 300

• Lung protection ventilation:– Vt 4-6ml/kg

– Higher resp rates

– Plateau pressures < 30cmH2O

– Permissive hypercapnia

• Volume targeted• Sedation / temp paralysis

Troubleshooting

• Respiratory distress in ventilated patients:– Anxiety

– Pain

– Inadequate ventilator settings

– ETT malfunction

– Pulmonary parenchymal process

– Extrapulmonary process

– Tension pneumotghorax

– Severe auto-PEEP

• Stable – vs - unstable

Hemodynamically stable

• Systematic approach

• Focused history / exam

• Check ventilator / circuit

• Respiratory mechanics ( Peak and Plateau pressures)

• CXR

• Bedside ultrasound

Problem with airflow

Decreased lung compliance

Hemodynamically unstable

• Remove from ventilator / hand ventilated 100% O2 (beware if high PEEP)

• Severe auto-PEEP:– Do not hyperventilate– Disconnect from ventilator / compress chest

• Tension pneumothorax: – Both sides!

• Check settings / circuit / ETT etc

• Reintubation – DIFFICULT AIRWAY

Noninvasive positive pressure ventilation

Noninvasive positive pressure ventilation in the emergency department. Emerg Med Clin N Am. 26 (2008) 835 - 847

Terminology!!

Definition

• CPAP a separate entity!– Continuous positive pressure

– Tight fitting facemask

– Spontaneous breathing

• NPPV / NIPPV / Bilevel pressure– Inspiratory pressure (IPAP / inspiratory positive airway pressure)

– End expiratory positive pressure (EPAP / expiratory positive airway pressure)

– Breaths triggered by patient (back up rate)

Rationale

• Avoid complications of invasive ventilation

• Avoid ICU admissions

• Reduce costs

• Improve mortality

Advantages of NIV     Preservation of airway defence mechanism   Early ventilatory support   Intermittent ventilation   Patient can eat, drink and communicate   Ease of application and removal   Patient can cooperate with physiotherapy   Improved patient comfort   Reduced sedation requirements   Avoidance of complications of intubation   Ventilation outside hospital setting possibleDisadvantages     Mask is uncomfortable/claustrophobic   Time consuming for medical and nursing staff   Airway is not protected   No direct access to bronchial tree for suction

Pathophysiology

• CPAP – increases alveolar recruitement– = extrinsic PEEP and EPAP

– Negates intrinsic PEEP ( auto PEEP / dynamic hyperinflation)

– Increases intrathoracic pressure

• NPPV / bilevel– IPAP = pressure support

– Rest during inspiration

Indications

• Acute exacerbations COPD• Asthma• Acute pulmonary oedema• Hypoxemic respiratory failure• Immunosuppressed patients• Do not intubate patients• Facilitation of weaning and extubation

Exacerbation COPD

• Initiate early

• Alongside with medical therapy

Asthma

• Extrinsic PEEP offsets intrinsic PEEP

Acute cardiogenic pulmonary edema

• CPAP and NPPV improve symptoms

• Neither improves mortality

• May decrease intubation rates

Hypoxic respiratory failure

• Mixed data

• Further studies needed

Feasibility

• Very little data on safety

• Failure of NPPV associated with:– GCS < 13

– RR > 20 after 1 hour

– pH < 7.35 after hour

Initiation

• No standard approach• High-low approach:

– High IPAP (20-25cmH2O)

• Low-high approach:– Low IPAP (8-10cmH2O)

• EPAP 3-4cmH2O• Significant autopeep / PEEPi - EPAP 4-8cmH2O• Titrate FiO2• Adjust EPAP

Summary

• Reversible conditions

• Bridging therapy

• Close monitoring / follow up