Distúrbios Ácidos-Básicos

Distúrbios Ácidos-Básicos

1. Alcalóticos

   • Metabólicos
     • pH> 7,40
       • H2CO3 > 28
         • PCO 2--------------------------0,7 mmHg H2CO3-----------------------------1 mEq/L platô 55 mmHg.
       • PaCO2>40
         • PaCO2 = HCO3- + 10
     • Geração
       • ↑ Upper GI losses of H+
       • ↑ Renal losses of H+
       • Hypokalemia intracellular shift of H+
       • ↑ HCO3- intake
       • Contraction alkalosis
       • Manutenção
         • ↓ HCO3- excretion
           • ↓ Effective arterial blood volume (prerenal states)
           • Hypochloremia
         • ↑ H+ secretion/HCO3- reabsorption/regeneration
           • Stimulated by hypokalemia (H+/K+-ATPase)
           • Stimulated by ↑ distal tubular Na+ delivery in the setting of high aldosterone
   • Respiratório
     • pH > 7,40
       • PaCO2 < 30-35
         • Crônica HCO3–------4 mEq/L PaCO2 --------10-mm Hg
         • Aguda s/ tempo
     • ↑ FR
       • ↑ Drive from the CNS (pathologic or physiologic) Hypoxemia-induced causes → body attempts to correct the hypoxia at the expense of CO2 loss

2. Acidóticos

   • Respiratória
     • pH< 7,35
       • pCO2> 45 (Hipercapnia)
         • Aguda
           • H2CO3 -----1 mmol PCO2------10 mmHg
         • Crônica
           • H2CO3 -----1 mmol PCO2------40 mmHg
         • CAUSAS
           • ↓ Alveolar ventilation (VA):
             • ↓ Respiratory rate
               • Medications: Opiates Benzodiazepines Primary brain disorders: Stroke, encephalitis, brainstem d. ---Obstructive sleep apnea
             • ↓ Volume total = Incapacidade de expandir completamente o pulmão
               • Respiratory muscle weakness,
                 • Guillain–Barré syndrome Myasthenia gravis ALS Muscular dystrophy Cervical&nbsp;spine&nbsp;injury above C3 Metabolic disorders:&nbsp;hypophosphatemia,&nbsp;hypomagnesemia,&nbsp;hypokalemia
               • Diminuição da complacência da parede torácica
                 • Decreased&nbsp;chest wall compliance : Obesity Kyphoscoliosis Ankylosing spondylitis Pectus excavatum
             • ↑ Dead space
               • ↑ Alveolar dead space: impaired ability for gas exchange
                 • Pulmonary fibrosis: Scar tissue prevents gas exchange. Pulmonary edema: Fluid in alveoli prevents gas exchange. Pulmonary embolus: Blood clot prevents perfusion of alveoli. Chronic obstructive pulmonary disease (COPD): alveoli destruction Asthma: airway obstruction preventing effective alveolar ventilation
             • Quanto de ar chega p/ ser oxigenado?
           • SEVERA redução da capacidade de difusão pulmonae
           • Severa disfunção de missmatch e perfusão?
           • Podem ser por alterações que dificultam a eliminação de CO2
             • Abnormal gas exchange: “can’t breathe enough”
               • Pulmão
             • “Can’t breathe”
               • Peripheral nervous system Respiratory muscles and chest wall Upper airways
             • “Won’t breathe”
               • SNC
   • Metabólica
     • pH< 7,4
       • H2CO3 < 24 pCO2 < 40
         • PCO2 = serum HCO3 + 15
           • PCO2&nbsp;= decimal portion of&nbsp; pH&nbsp; (e.g.,&nbsp; pH&nbsp; 7.3 would predict a&nbsp; PCO2 of 30)
           • OBS: The lowest possible PCO2 from respiratory compensation is 8–12 mm Hg
           • Formula de winter (PCO 2 arterial = 1,5 x HCO 3 sérico + 8 ± 2).
             • Estreitar ddx: ANION GAP
               • c/ potássio: AG 8–16 mEq/L AG = (Na + K) - (HCO3 + Cl)
                 • Hipercloremica
                   • Ácidose não AG, o cloro aumenta de forma compensatória&nbsp;
               • s/ potássio: 4–12 mEq/L AG= Na -(HCO3+Cl)
                 • Normocloremica
                   • Acidose AG o cloro não aumenta de forma compensatória&nbsp;
                   • Plasma osmolality = 2 (Na+) + (BUN / 2.8) + (glucose / 18) + (ethanol / 4.6) osmolal gap is ≤ 10.
                     • Determinar se é por alcols tóxicos&nbsp; &gt; 25 específico p/ toxidade por alcool&nbsp;
     • 3 causas primárias
       • ↑ Acid production:
         • Acidose láctica
         • Cetoacidose
         • Alcols tóxicos
         • Medicação
       • Impaired H+ excretion
       • Loss of HCO3-
       • Acidose dilucional

3. RESPIRATÓRIO

   • Efeitos da respiração superficial VS Profunda : -espaço morto fisiológico e volume total
     • Espaço morto fisiológico = espaço morto anatomico + espaço morto alveolar
       • Alveolar ventilado mas não perfundido&nbsp;
     • RESPIRAÇÃO PROFUNDA: ↑ TV + fixed volume of dead space Dead space is a smaller fraction of total ventilation. Better gas exchange → no hypercapnia
     • RESPIRAÇÃO SUPERFICIAL = ↓ TV + fixed volume of dead space Dead space is a higher fraction of total ventilation. Worse gas exchange → risk for hypercapnia
   • Minute ventilation = tidal volume × respiratory rate
   • Alveolar ventilation (VA): The fraction of the minute ventilation that participates in gas exchange
     • VA = (tidal volume – dead space) × respiratory rate