7. Difficult to Ventilate (High Airway Pressures)

Question 1

What factors may cause you to experience difficulty ventilating an anaesthetised patient intra-operatively?

Patient factors

Answer 1

This can be classified into patient factors and non-patient factors.
Patient factors:

1
> Reduced chest wall compliance:

• Chest wall rigidity, malignant hyperthermia or opioids
• Prone position
• Obesity
• Kyphoscoliosis
• Raised abdominal pressures, e.g. pneumoperitoneum
• Inadequate paralysis or patient ‘fighting’ ventilator.

2
> Reduced lung compliance:

• Pneumothorax
• Bronchospasm
• Lobar collapse or atelectasis
• Pulmonary oedema
• Pulmonary fibrosis
• Aspiration
• ARDS

Question 2

What factors may cause you to experience difficulty ventilating an anaesthetised patient intra-operatively?

Non-patient factors:

Answer 2

1
> Anaesthetic circuit:

• Blockage, compression, kinking of tubing
• Incorrect connection of circuit, scavenging, reservoir bag, filter, humidifier, APL valve or PEEP valve.

2
> Ventilator:

• Excessive tidal volumes.

3
> Endotracheal tube:

• Kinked
• Misplaced, e.g. oesophageal or endobronchial
• Obstructed, e.g. sputum, blood or foreign body

Treat the identified cause, clearly document the sequence of events on the anaesthetic chart and complete a critical incident form.

Question 3

How would you identify such a case?

Answer 3

Presentation:

> Difficult to ventilate

> Decreased compliance in reservoir bag, poor chest expansion, low minute volume

> High airway pressure and alarm limits reached

> Abnormal CO2 trace

> Hypoxia

> Circulatory collapse

Question 4

Describe your management

Answer 4

. State that this is an anaesthetic emergency,
and that you would call for
senior anaesthetic assistance.

> ABC approach:
assess and resuscitate simultaneously.

> Check the basic parameters: 
heart rate, 
ECG, 
blood pressure, 
oxygen saturation, 
ETCO2 trace.

> Hand-ventilate with 100% oxygen.

> Ask the surgeon to stop operating until it is safe to continue.

> Exclude obvious causes:
start at the patient
(check tube position and auscultate chest)
and
sequentially examine from the airway back to
the anaesthetic machine.
Treat the cause as you discover it.

Consider switching to an alternative circuit, e.g. Ambu bag.

Consider the context:

> Patient position: prone, Trendelenburg

> Pre-existing disease: asthma, obesity, ARDS

> Timing of event: e.g. following central venous line insertion

> Risk factors: allergy, bronchospasm

> Surgery: e.g. laparoscopy with pneumoperitoneum.