Acute Respiratory Failure

• Type 1: Hypoxaemia with normal (or low) Pa$\mathrm{CO}{}_2$
  • Primarily a failure of oxygenation
  • Usually responds to oxygen therapy
• Type 2: Hypoxaemia with an increased Pa$\mathrm{CO}{}_2$
  • Failure of ventilation and oxygenation
  • Requires ventilatory assistance as well as supplemental oxygen
• ABG results of P$\mathrm{O}{}_2$ <60mmHg or P$\mathrm{CO}{}_2$ >50mmHg with an associated pH <7.30 is suggestive of acute respiratory failure

Causes

• Acute obstruction
• Pulmonary
  • Bronchosapsm with wheeze (e.g. Asthma Exacerbation, COPD, anaphylaxis)
  • Pneumothorax
  • Massive pleural effusion
  • Interstitial lung disease
  • Pulmonary Hypertension
• Cardiovascular
  • Acute Pulmonary Oedema
  • Pulmonary Embolism
• Neuromuscular
  • Depressed level of consciousness
  • Muscular weakness (Guillain-Barré syndrome, myaesthenia gravis, muscular dystrophy)
  • Drug intoxication (opioid, sedative)
  • Poisoning (carbon monoxide, opioid)
• Most common aetiologies for acute dyspnoea in hospitalised patients:
  • Alveolar problem
    • Flash Pulmonary oedema (e.g. due to tachyarrhythmia, ischaemica/ACS, hypertensive emergency, TACO)
    • Aspiration pneumonitis
    • TRALI
  • Airway problem
    • Anaphylaxis
    • Angioedema
    • Mucous plug
    • Endotracheal tube dislodgement
  • Pulmonary embolism
  • Pneumothorax (post-procedure)
  • Tamponade (post-procedure, post-MI)

Overview of Assessment and Management

1. Always call for help
2. Give oxygen
3. Assess the patient
4. CXR/ABG/VBG
5. Consider adjuncts
6. Escalation of care

Assessment

• Can remember as RATES (respiratory rate, auscultate, trachea position, effort of breathing and saturation)
• Airway Patency

  • Assess airway function
    • Signs of partial airway obstruction:
      • Hoarse voice, inability to speak or cough
      • Stridor, snoring or gurgling secretions
      • Soft-tissue retraction-tracheal tug, rib or abdominal recession
      • Loss, or an uncoordinated rise and fall, of the chest and/or abdomen
        • ‘See-saw’ pattern of chest and abdominal movement: the chest is drawn in and the abdomen expands on inspiration and the opposite occurs on expiration
      • Altered level of consciousness or mental status or agitation
      • GCS ≤8
    • Features of partial airway obstruction
      • Tripod position
      • Reluctance to speak or cough
      • Increased work of breathing with nasal flaring accessory muscle use
    • Inspect
      • Upper airway for foreign material if possible or using laryngoscopy
      • Erythema or urticaria with lip, tongue or palatal swelling
        • Listen for bronchospasm and examine for circulatory features that suggest Anaphylaxis
      • Localised trauma, burns infection or tumour
    • Palpate the anterior neck, including the thyroid cartilage for pain, inflammation, crepitus, swelling or masses
    • Investigate for any cause of depressed consciousness (e.g. hypoglycaemia or opioid intoxication)
    • Signs and features of complete airway obstruction
      • No stridor, airway sounds or breath sounds on lung auscultation
      • Inability to ventilate the patient with a bag-mask
      • Rapid development of cyanosis and unconsciousness

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• Work of breathing
  • Signs include: ↑ RR, use of accessory muscles, soft-tissue recession, ↑ HR, sweaty/clammy skin
• Effectiveness of respiratory function (saturation probe)
  • Hypoxia
    • Cyanosis (oxygen saturation <88%)
    • Cardiac ischaemia or arrhythmias
    • Acidosis from tissue hypoxia (lactic acidosis)
    • Anxiety, agitation or depressed consciousness
    • ↑ A-a gradient on ABG
  • Hypoventilation
    • Vasodilation
    • Headache, drowsiness and lethargy
    • Asterixis
    • Acidosis - respiratory acidosis (inadequate removal of $\mathrm{CO}{}_2$)
• Respiratory decompensation
  • Decompensation is when severe or prolonged respiratory insult causes exhaustion or a reduction in the patient’s physiological reserves
  • Signs of decompensation
    • Gasping
    • ↓ respiratory effort
    • Sweating, lethargy, apathy, drowsiness and coma
    • Tachycardia → bradycardia (preterminal sign)
    • Respiratory arrest followed by cardiac arrest
  • If a patient has any features of decompensation, call senior staff or a MET call immediately
• Diagnose the cause
  • Common conditions which can progress to respiratory failure:
    • Pneumonia
    • Exacerbation of COPD
    • Acute Pulmonary Oedema
    • Asthma Exacerbation (Pa$\mathrm{CO}{}_2$ rises very late)
    • Pulmonary Embolism
    • Pneumothorax

Suggested Diagnosis

By History

• Cardiovascular risk factors (e.g. HTN, DM, smoking, prior MI) ⇒ APO
• Aspiration risk factors (e.g. post-stroke, sedating medications) ⇒ Aspiration
• Intrathoracic pressure within the last 24 hours:
  • Thoracocentesis, central line, PPM insertion ⇒ Pneumothorax
  • Pericardiocentesis, PPM lead extraction ⇒ tamponade
• New medication started recently
  • Anphylaxis (<6 hrs)
  • Angiodema (days)
• Transfusion within last 6 hours ⇒ TACO, TRALI

By Exam Finding

• Hypotension ⇒ PE, ACS, Pneumothorax, tamponade, Anaphylaxis
• Bilateral crackles ⇒ APO, Aspiration
• Wheezing ⇒ Non-specific
• Asymmetric lung findings ⇒ Aspiration, Pneumothorax, mucous plug, ET tube dislodgement
• Signs of DVT ⇒ PE

Investigations

• Investigations to consider and typical prioritisation in acute respiratory distress
  • Lung POCUS
  • Chest X-ray
  • ECG
  • ABG
  • Other labs including FBC, CMP, troponin, lactate, D-dimer
  • Echocardiogram
  • CTPA

Management

• Sit patient upright
• Do not neglect airway issues and place heavy importance of suctioning if relevant (e.g. aspiration, mucous plugging)
• Use supplemental oxygen in all hypoxic patients with high-flow oxygen at 15 L/min through a mask with a reservoir, (target oxygen saturation > 90-92%)
  • High inspired oxygen concentrations do not depress ventilation in patients who are in respiratory distress
  • In patients with COPD who chronically retain $\mathrm{CO}{}_2$ titrate use of a venturi mask
    • Giving too much oxygen to patients who chronically retain $\mathrm{CO}{}_2$ causes a rise in Pa$\mathrm{CO}{}_2$ because:
      • Changes in pulmonary vasoconstriction, dead space and shunting (V/Q mistmatch)
      • Haldane effect (haemoglobin molecules release $\mathrm{CO}{}_2$ in the presence of oxygen)
      • Blunting of the hypoxic drive; these patients depend on mild hypoxia to stimulate their respiratory centre
    • If unsure if they are a chronic retainer, check any previous blood gas results
    • Begin empirical $\mathrm{O}{}_2$ treatment under pulse oximetry monitoring
    • Increase/decrease oxygen delivery until $\mathrm{O}{}_2$ saturation is 88-92% by using different oxygen mixers in a venturi mask or changing the flow rate in a simple mask
    • Recheck blood gases and watch for a change in $P\mathrm{CO}{}_2$:
      • Continue with current therapy if $\mathrm{CO}{}_2$ is normalising
      • Decrease oxygen deliver if $\mathrm{CO}{}_2$ is increasing but maintain $\mathrm{O}{}_2$ saturation of 88-92%
        • If $\mathrm{CO}{}_2$ is increasing and you are unable to maintain oxygen saturation >88%, the patient requires assisted ventilation (BiPAP) see ventilation below
• Blood gases are necessary to determine the adequacy of ventilation (can use either venous or arterial as it will likely not influence immediate management) - see ABG Interpretation
• If wheezing, consider bronchodilators (see: COPD Exacerbation) perhaps nebulised
  • Rule out tachy-arrythmia or demand related ischaemia if you can prior
• If signs of APO consider nitrates if BP tolerates
  • Avoid jumping to diuretics in a euvolaemic patient with pulmonary oedema
• Consider reversing opiates
• Consider NIV

Ventilation

• Ensure the patient has not received respiratory depressants (e.g. opioids) in the past 24 hours (e.g. check pupils)
  • Give naloxone 0.2mg up to 2mg IV, SC or IM every 5 minutes repeated until alert
    • Be careful to avoid a withdrawal reaction: Start at 100 mcg IV in opiate-dependent patients
• Bag valve mask assisted manual ventilation may be required in a patient with ↓ LOC until definitive ventilation is available
  • Consider: CPAP, BiPAP ventilation or NIV machines
• If still no improvement contact ICU and make arrangements for ETT intubation
• Acute respiratory acidosis with a pH <7.2 usually requires mechanical ventilation until the precipitating cause can be reversed