Respiratory Acidosis
Although four types of respiratory failure have been described, it is usual to classify respiratory failure into Type-1 and Type-2: the latter is associated with hypoventilation and respiratory acidosis (see next section).
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Respiratory Acidosis
Contents 7.1 7.2 7.3 7.4
Respiratory Failure ........................................................................................................ The Causes of Respiratory Acidosis ............................................................................. Acute Respiratory Acidosis: Clinical Effects................................................................ Effect of Acute Respiratory Acidosis on the Oxy-hemoglobin Dissociation Curve ........................................................................................................ 7.5 Buffers in Acute Respiratory Acidosis.......................................................................... 7.6 Respiratory Acidosis: Mechanisms for Compensation ................................................. 7.7 Compensation for Respiratory Acidosis ....................................................................... 7.8 Post-hypercapnic Metabolic Alkalosis.......................................................................... 7.9 Acute on Chronic Respiratory Acidosis........................................................................ 7.10 Respiratory Acidosis: Acute or Chronic? .....................................................................
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A. Hasan, Handbook of Blood Gas/Acid-Base Interpretation, DOI 10.1007/978-1-4471-4315-4_7, © Springer-Verlag London 2013
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7.1
7
Respiratory Acidosis
Respiratory Failure
Although four types of respiratory failure have been described, it is usual to classify respiratory failure into Type-1 and Type-2: the latter is associated with hypoventilation and respiratory acidosis (see Sect. 7.2).
Respiratory failure
Type 1 (Hypoxemic respiratory failure)
Type 2 (Hypercapnic respiratory failure)
PaO2 is low (PaO2 < 50 mmHg)
PaO2 is low (PaO2 < 50 mmHg)
CO2 is not elevated (PaCO2 < 60 mmHg)
CO2 is elevated (PaCO2 > 60 mmHg)
See Sect. 1.25
See Sect. 1.26
Type 3 (Per-operative respiratory failure) FRC falls below closing volume as a result of atelectasis. Contributing factors: Supine posture General anesthesia
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Depressed cough reflex Splinting due to pain
Type 4 (Shock with hypo perfusion) The proportion of the cardiac output to the respiratory muscles rises by as much as ten-fold when the work of breathing is high; this can seriously impair coronary perfusion during shock.
7.2
7.2
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The Causes of Respiratory Acidosis
The Causes of Respiratory Acidosis
In terms of CO2 production and excretion, alveolar hypoventilation is the major mechanism for hypercarbia (See Sects. 1.34 and 1.35). Quite often however, increase in dead space is an important mechanism (Sect. 1.30). Causes of acute hypercapnia
Central depression of respiratory drive Drugs Sedatives, opiates, anaesthetic agents CNS lesions CNS trauma, strokes, encephalitis Neuromuscular Spinal cord lesions or trauma (at or above level of C4) High central neural blockade Tetanus Poliomyelitis Amyotrophic lateral sclerosis Myasthenia gravis Organophosphate poisoning B
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