This chapter builds on the ABCDE Approach chapter, which explains how to assess breathing (B - Breathing), the expected common interventions, and the objectives in a critical patient's initial approach and management. You can return to that chapter here:

Below, you will find a summary of the chapter's content. The topic is discussed in detail in the Oxford Handbook of Critical Care (see Suggested Reading).

Respiration and respiratory failure

The primary function of the lungs—breathing—is the exchange of gases between the atmosphere and the circulatory system. This gas exchange can be simplified into:

Oxygenation of the body through inhalation of oxygen (O2)

Ventilation through the exhalation of carbon dioxide (CO2)

Respiratory failure/insufficiency (RI)

RI is a syndrome in which the body is unable to ensure adequate gas exchange (O2, CO2), leading to hypoxemia and/or hypercapnia.

* During ongoing oxygen therapy, a hypoxemic disturbance can be masked, revealing only the hypercapnic component. 

Another possible classification from a time perspective includes:

Acute RI (e.g. Bronchopneumonia, ARDS, ...)

Chronic RI (e.g. COPD, Cystic Fibrosis, ...)

Clinical presentation of RI

• increased work of breathing, shortness of breath
• tachypnea: increased respiratory rate
• dyspnea: subjective feeling of breathlessness
• orthopneic position
• use of accessory respiratory muscles, nasal flaring
• sweating
• communication is limited to short sentences, words, or gestures

Hypoxaemia

• cyanosis
• restlessness, anxiety
• in severe cases, it can lead to quantitative disturbances of consciousness, bradycardia, and cardiac arrest

Hypercapnia

• headache
• confusion
• in severe cases: convulsions, quantitative disturbances of consciousness, respiratory arrest, cardiac arrest

Diagnostics

• Pulse oximetry: peripheral oxygen saturation (SpO2)
  
• Capnometry: detection of exhaled CO2 (etCO2)
• Blood gas analysis: preferably arterial blood sample
• Chest X-ray/heart and lung imaging
• Chest CT scan
  
• Lung ultrasound (LUS)

Oxygen Therapy

Adequate saturation: SpO2 94-98 % (pO2 10-13.3 kPa)

(Warning: even hyperoxemia has its side effects, including higher mortality)

Special cases

Patients with COPD usually have lower oxygen saturation

• The target SpO2 is 88-92% if their chronic value is unknown.
• Higher levels can disrupt hypoxic pulmonary vasoconstriction, worsen ventilation-perfusion mismatch, and cause other adverse effects.

Conversely, the highest possible inspiratory oxygen fraction is used during CPR or certain intoxications (e.g., carbon monoxide, cyanides).

Types of oxygen therapy

Conventional (O2 delivery 0-15 l/min)

High-flow (O2 delivery 60 to 100 l/min)

Nasal High Flow

Diagram and description of the parts of the most commonly used system: nasal high-flow oxygen therapy

Initial NHF setting

according to the WHO

Failure of oxygen therapy

Conventional and high-flow oxygen therapy has its limitations.
If the therapy used is without effect or fails, rapid escalation in the order is necessary:

Both conventional and high-flow oxygen therapy have their limitations. If the therapy being used is ineffective or fails, rapid escalation is necessary in the following order:

1. Conventional methods with increased O2 flow
   
2. High-flow Oxygen Therapy
3. IPPV -  Intermittent Positive Pressure Ventilation
4. As rescue therapy, ECMO (Extracorporeal Membrane Oxygenation), if indication criteria are met

Suggested Reading for this chapter: