What is Acute Hypoxemic Respiratory Failure (AHRF)?

Acute Hypoxemic Respiratory Failure (AHRF): Definition and Management

Acute hypoxemic respiratory failure (AHRF) is caused by a wide range of etiologies including pulmonary infection, inflammation, or exacerbation of chronic heart or lung disease, resulting in insufficient oxygen delivery to tissues that does not meet their metabolic needs. 1

Definition and Clinical Presentation

• AHRF is characterized by hypoxemia (low blood oxygen levels) with the clinical spectrum ranging from mild hypoxemia to full-blown acute respiratory distress syndrome (ARDS) 1
• Unlike acute hypercapnic respiratory failure (which involves elevated CO2 levels), AHRF primarily involves oxygenation problems, though both can coexist 1
• The condition represents an inability to maintain adequate oxygen delivery to tissues despite supplemental oxygen therapy 2

Pathophysiology

• AHRF results from inflammatory processes that disrupt the capillary-epithelial interface in the lungs 3
• This disruption leads to:
  • Pulmonary edema causing intrapulmonary shunting 4
  • Decreased lung compliance 3
  • Ventilation-perfusion mismatch 2
  • Increased work of breathing 1

Causes

• Pulmonary infection (pneumonia) 1
• Pulmonary inflammation 1
• Exacerbation of chronic heart or lung diseases 1
• Acute respiratory distress syndrome (ARDS) 3
• Acute lung injury (ALI) 3

Clinical Management

Oxygen Therapy

• The primary goal is to ensure normal oxygenation of the body 2
• Target oxygen saturation (SaO2) of 88-92% is recommended in all causes of AHRF 1
• Conventional oxygen therapy (COT) options include:
  • Nasal prongs 1
  • Facemask with reservoirs 1
  • Venturi mask 1

Advanced Respiratory Support

• High-flow nasal cannula (HFNC) is suggested over conventional oxygen therapy in adults with AHRF 1

• Benefits of HFNC include:

  • Providing airflows up to 50-60 L/min that match inspiratory demands 1
  • Reliable achievement of FiO2 up to 100% 1
  • Low level of positive end-expiratory pressure (PEEP) in upper airways 1
  • Decreased risk of patient self-inflicted lung injury (P-SILI) 1
  • Carbon dioxide washout of upper airways 1
  • Reliable humidification 1
  • Enhanced patient comfort 1

• Noninvasive ventilation (NIV) may be considered in selected cases 5

• Invasive mechanical ventilation (IMV) is required when noninvasive strategies fail 1, 5

Monitoring

• Continuous oxygen saturation monitoring 1
• Intermittent measurement of pCO2 and pH 1
• ECG monitoring if pulse rate >120 bpm or if there is dysrhythmia 1
• Close monitoring for signs of clinical deterioration to avoid delayed intubation when using noninvasive strategies 5

Prognosis and Outcomes

• HFNC may reduce the need for intubation (risk ratio 0.89) and escalation to NIV (risk ratio 0.76) compared to conventional oxygen therapy 1
• HFNC reduces patient discomfort and dyspnea, and slightly lowers respiratory rate 1
• Mortality remains similar whether using HFNC or conventional oxygen therapy in the short term (hospital, ICU, or 28 days) and at 90 days 1

Important Considerations and Pitfalls

• Avoid delayed intubation when using noninvasive strategies by predefining specific criteria for escalation 5
• Avoid hyperoxygenation as it can be harmful in patients with AHRF 1
• When providing NIV, oxygen enrichment should be administered as close to the patient as possible 1
• Optimize ventilator settings before increasing FiO2 1
• High oxygen flow rates (>4 L/min) may cause mask leak and delayed triggering, potentially worsening patient-ventilator asynchrony 1