CURRENT Essentials of Critical Care.pdf

68 Current Essentials of Critical Care■■■Respiratory AcidosisEssentials of Diagnosis• Arterial pH 7.35; elevated PaCO 2 and, if chronic, compensatoryretention of serum HCO 3 ; due to ineffective alveolar ventilationor increased CO 2 production• Symptoms depend on absolute increase and rate of rise in PaCO 2• Tremor, asterixis, incoordination, confusion, somnolence, coma• Headache, papilledema, retinal hemorrhages• Dyspnea, respiratory fatigue and failure• Hypoxemia common unless receiving supplemental oxygenDifferential Diagnosis• Central nervous system depressants• Obesity hypoventilation syndrome• Chronic obstructive lung disease• Acute airway obstruction: acute aspiration, laryngospasm, bronchospasm• Restrictive defects: large pleural effusion, hemothorax, pneumothorax,fibrothorax, pulmonary fibrosis, flail chest• Pulmonary edema: cardiogenic or pulmonary permeability(ARDS)• Neurologic and neuromuscular disorders: Guillain-Barré syndrome,botulism, tetanus, phrenic nerve injury, cervical spinelesion, multiple sclerosis, poliomyelitis, myasthenia gravis• Organophosphate toxicity• Muscular weakness: electrolytes, muscular dystrophyTreatment• Correct underlying etiology• Avoid central suppressing agents• Mechanical ventilation or noninvasive positive-pressure ventilation• Aim to normalize pH and not PaCO 2 ; overcorrection of chronichypercapnia leads to alkalemia• Mild degree of respiratory acidosis well tolerated; may be beneficialin management of ARDS (“permissive hypercapnia”)■ PearlThe acute worsening of respiratory acidosis seen in chronic CO 2 -retaining patients with COPD receiving high-flow oxygen supplementationis more likely due to worsening of V /Q mismatch and notnecessarily due to suppression of hypoxic drive.ReferenceEpstein SK et al: Respiratory acidosis. Respir Care 2001;46:366. [PMID:11262556]