Breathing

Respiratory failure occurs when there is inadequate pulmonary gas exchange such that blood and carbon dioxide cannot be maintained at normal levels.

PaO2 < 8kPa is the point on the oxygen-haemoglobin dissociation curve below which rapid desaturation occurs
Type 1 RF: hypoxia with normal or reduced carbon dioxide
Type 2 RF: hypoxia with hypercarbia (may have a chronic element - check if bicarbonate is high)
Commonest cause of decreased LoC in the surgical patient

Classify causes of respiratory failure:

Acute fall in functional residual capacity without pulmonary vascular dysfunction
- Failure of chest mechanics after trauma or other processes that render the lungs stiff and non-compliant
- Acute post-op atelectasis, sputum retention, pneumonia or depression of respiration caused by analgaesic, sedative or neuromuscular blocking drugs
- Frailty and malnutrition contribute
Acute fall in FRC, with pulmonary vascular dysfunction
- Left ventricular failure
- Fluid overload
- Pulmonary hypertension
- PE
- Neurogenic pulmonary oedema
- ARDS
Airflow obstruction
- COPD
- Asthma
- Others

High flow oxygen
- Don't worry about depressing hypoxic drive to breathe
Apply pulse oximeter
- Delay of around 20seconds between actual and displayed values
- Sats >94% is equivalent to 8kPa oxygen
- Impeded by:
  - Factors blocking skin
  - Arrhythmias
  - Profound anaemia
  - SaO2 < 70%
  - Movement
  - Peripheral vasoconstriction
  - Diathermy
  - Bright lights
Chart review
Hx and systematic examination
- Look, listen, feel - as per 'ABCD' section
Available results
- ABG
- ECG
- Bloods
- CXR
- Pre-op RFTs
  - Peak expiratory flow
  - Vital capacity
  - FEV1

Chest PT
Incentive spirometry
Nebulised saline, and change inhalers to nebs
Adequate analgaesia
Bring CPAP
HDU vs ICU
Art line etc
Humidified oxygen
- Whenever oxygen by mask for >24 hours is required
- High sputum load

High-flow oxygen supplied through a tight-fitting mask, incorporating expiratory valves, which maintains a set airway pressure from 2.5 to 10cmH20.
Airway pressure is prevented from dropping below the set value, leading to recruitment of underventilated alveolae, increased FRC, decreased intrapulmonary shunt and work of breathing, and may improve oxygenation
Most useful in type 1 resp failure
Can be used after major surgery to reduce the risk of respiratory complications
Must be co-operative and in control of airway
Be careful after upper GI surgery due to risk of involuntary air swallowing and gastric distension
Can be connected to tracheostomy
Failing to tolerate CPAP:
- Refractory hypoxaemia
- Increased respiratory rate
- Progressively smaller tidal volumes
- CO2 retention
- Agitation -> obtundation

Useful in type 2 resp failure to prevent or treat CO2 retention
High pressure during inspiration (about 20cm H2O), lower pressure during expiration (5cm H2O)
The pressure difference generates gas flow into the lungs during inspiration
Not appropriate if CV unstable, decreased GCS, severe metabolic acidosis, low RR, unco-operative
NGT usually required to reduce gastric distension
If CO2 doesn't improve within 30 mins, it probably won't work
Generally requires critical care support
Failing to tolerate:
- Refractory hypoxaemia
- Increased RR
- Progressively smaller tidal volumes with worsening CO2 retention

Allows control of all factors to suit patient's needs, including oxygen 100% and adjustment of RR, TV and frequency
SIMV - synchronised intermittent mandatory ventilation
- Preserves some of the patient's respiratory muscle activity by synchronising ventilation around the patient's own respiratory effort
PEEP
- High PEEP causes decreased venous return and a fall in CO, which may be very severe if the patient is hypovolaemic
- High PEEP can cause barotrauma
- High PEEP plus high oxygen can promote the toxic effects of oxygen - generally don't go above 80% with high PEEP
Highest level of respiratory support is basically PCIRV (pressure-controlled inverse ratio ventilation), FiO2 > 0.8, PEEP>10cm H2O, and permissive hypercarbia. The only other things to do from here are to increase FiO2 to 100% and pronate the patient. After that you will need to put them on cardiopulmonary bypass.
Weaning
- Requires:
  - Original cause of resp failure has been treated
  - Sedative drugs low enough not to depress respiration
  - FiO2<0.4 is sufficient maintain PaO2
  - No hypercarbia
  - Minimal sputum
  - Nutritional status is normal and electrolytes
  - Diaphragm and intercostals are working
  - The patient is reasonably co-operative

Absence of gas from all or part of a lung
Reduced breathing -> retention of secretions -> distal collapse
Risk factors:
- Elderly
- Obese
- Smokers
- Lung disease
Prevent:
- Pre-op breathing exercises
- Intra-op humidification
- Ensuring good tidal volumes
- Avoid unnecessarily high FiO2
Presentation
- Cough
- SOB
- CP
- Pleural effusion
- Can develop into cyanosis/tachycardia
- Inflammatory markers will generally be normal - if raised, suspect transformation into pneumonia
Treat
- Deep breathing
- Coughing
- Analgaesia
- Incentive spirometer
- Mobilisation
- High-flow nasal oxygen