Respiratory acidosis resident survival guide

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Qasim Khurshid.M.B.B.S

Causes

Life Threatening Causes

Life-threatening causes include conditions that may result in death or permanent disability within 24 hours if left untreated.

• Sedative overdose (eg, narcotic or benzodiazepine, some anesthetics, tricyclic antidepressants)
• Epiglottitis
• Foreign body aspiration
• Angioedema
• Pulmonary embolism (usually severe)
• Respiratory muscle fatigue
• Periodic paralysis
• Phrenic nerve injury
• Organophosphates poisoning
• Procainamide toxicity

Common Causes

• Sedative overdose (eg, narcotic or benzodiazepine, some anesthetics, tricyclic antidepressants)
• Encephalitis
• Brainstem disease
• Central and obstructive sleep apnea
• Amyotrophic lateral sclerosis
• Dynamic hyperinflation (eg, upper and lower airway disorders including chronic obstructive pulmonary disease, severe asthma)
• Endstage interstitial lung disease
• Pulmonary embolism (usually severe)
• Thyrotoxicosis
• Foreign body aspiration
• Retropharyngeal disorders
• Obstructive goiter
• Vocal cord paralysis
• Hypophosphatemia
• Hypomagnesemia
• Hyperthyroidism
• Tetanus
• Botulism
• Succinylcholine and neuromuscular blockade

Diagnosis

Shown below is an algorithm summarizing the diagnosis of respiratory acidosis.

Suspected acid base disorder

Acidemia pH<7.35

Normal pH

Alkalemia pH>7.45

Metabolic acidosis HCO3<24mmol/L CO2:HCO3 12:10

Respiratory acidosis pCO2>40mmHg

Metabolic alkalosis HCO3>28mmol/L CO2:HCO3 7:10

Respiratory alkalosis pCO2<35mmHg

Anion gap

Non anion gap

Acute CO2:HCO3 10:1

Chronic CO2:HCO3 10:3

Acute CO2:HCO3 10:2

Chronic CO2:HCO3 10:4

Appropriate compensation Ratio(CO2:HCO3) Metabolic acidosis 12:10 Metabolic alkalosis 7:10 Acute respiratory acidosis 10:1 Chronic respiratory acidosis 10:3 Acute respiratory alkalosis 10:2 Chronic Respiratory alkalosis 10:4

Treatment

Shown below is an algorithm summarizing the treatment of acute respiratory acidosis.

Apnea or Respiratory distress(of recent onset)

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Airway patency scured

Yes

NO

Oxygen-rich mixture delivered

Airway patent

Remove dentures,foreign bodies, or food particles Consider tracheal intubation

Mental status and blood gas evaluated

Patient alert, Blood pH>7.10 or PaCO2<80mmHg

Patient obtunded,Blood pH<7.10 or PaCO2>80mmHg

Administer O2 via nasal mask or prongs to maintain pO2>60mmHg Correct reversible causes of pulmonary dysfunction with antibiotics,bronchodilators,and corticosteriods as needed Monitor patient with abnormal arterial blood gases at 20-30 minutes of interval initially and less frequently thereafter If PaO2 does not increase to >60mmHg or PaCO2 rises to >80mmHg,proceed to therapy for obtunded

Consider use of non invasive ventilation through a nasal or full face mask Consider intubation or initiation of mechanical ventilation if non invasive ventilation fails or contraindicated If arterial pH<7.10 on ventilatory support, administer sodium bicarbonate to maintain blood pH between 7.10 to 7.20 Correct reversible causes of pulmonary dysfunction with antibiotics,bronchodilators,and corticosteriods as needed

Do's

• Respiratory acidosis should be considered in patients with limited respiratory reserve (COPD exacerbation) and present with increasing shortness of breath, new hypoxemia ,change in mental status or hypersomnolence.
• When patients present with suspected acute respiratory acidosis, the physician should simultaneously assess and stabilize the airway, breathing, and circulation, perform a brief clinical bedside assessment with telemetry and oxygen monitoring, draw an arterial blood gas (ABG), and administer initial empiric bedside therapies.
• A brief history and examination should be performed at the bedside so that therapies targeted at a specific underlying cause can be administered quickly
• In addition to ABGs, a complete blood count, serum chemistries including bicarbonate and electrolytes, and a chest radiograph should be performed
• Always treat the underlying cause of respiratory acidosis.

Don'ts

• Do not use non-invasive ventilation if patient is unable to protect the airway.
• Do not use non-invasive ventilation if patient have cardiac or pulmonary arrest or impending respiratory muscle fatigue

References

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