Respiratory Acidosis

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Contents 1 Introduction 2 Etiology 3 Clinical-manifestations 4 Laboratory 5 Management 6 More General Terms 7 References

Introduction

• Inadequate pulmonary excretion of CO2.

Etiology

• CNS depression (inhibition of medullary respiratory center)

• drugs
• infection
• brain injury
• obesity

• neuromuscular disorder (disorders of repiratory muscles)

• myopathy
• Guillain-Barre syndrome
• myasthenic crisis
• hypokalemia

• pulmonary diseases (disorders of gas exchange across alveolar capillaries)

• chronic obstructive pulmonary disease
• sleep apnea
• asthma
• kyphoscoliosis
• pneumothorax

• increased carbon dioxide production
• mechanical ventilation

Clinical-manifestations

• agitation
• asterixis
• papilledema
• headache
• somnolence
• hypertension
• tachycardia
• heart failure
• cardiac arrhythmias

Laboratory

• arterial blood gas ( ABG)

• decreased pH
• increased pCO2

• serum bicarbonate:

• compensatory metabolic alkalosis generally does not result in HCO3- > 35 meq/L
• 3.0-3.5 meq/L increase in HCO3- for every 10 mm Hg increase in pCO2
• 3-5 days for compensatory metabolic alkalosis
  

• * Rules for predicting [[[Hco3- | HCO3-]]] compensation for pure respiratory acidosis

• acute: 1 meq increase in [[[Hco3- | HCO3-]]] for each 10 mm Hg increase in pCO2 ( PaCO2, arterial)
• chronic: 3.5 meq increase in [[[Hco3- | HCO3-]]] for each 10 mm Hg increase in pCO2
• failure of the [[[Hco3- | HCO3-]]] to increase by the expected value suggests complicating metabolic acidosis
• excessive increase in the [[[Hco3- | HCO3-]]] suggests complicating metabolic alkalosis [2] Complication:

• acute respiratory acid associated with risk of hypoxemia rather than acidemia or hypercapnia

Management

• therapy directed towards improving ventilation

• excessive oxygen may blunt respiratory drive & worsen hypoventilation in patients with chronic respiratory acidosis

• administration of bicarbonate

• may be harmful since low pH is a stimulus for respiration
• may be beneficial in patients with asthma on a ventilator

• may improve response to beta-adrenergic agonists
• may allow less vigorous ventilation reducing risk of barotrauma

• may be indicated to maintain plasma pH above 7.1

• post-hypercapneic metabolic alkalosis can usually be corrected with saline & discontinuation of loop diuretics [2]

More General Terms

• acidosis

References

1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 63
2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15 American College of Physicians, Philadelphia 1998, 2006, 2009

respiratory acidosis