1、A Practical Approach to Acid-Base Disorders Bin DU,MD Medical Intensive Care Unit Peking Union Medical College Hospital Primary Acid-Base Disorders Variable Primary Disorder Normal Range,Arterial Gas Primary Disorder pH Acidemia 7.35 7.45 Alkalemia PCO2,mmHg Respiratory alkalosis 35 45 Respiratory a
2、cidosis HCO3,mmol/L Metabolic acidosis 22 26 Metabolic alkalosis Rules of Thumb for Recognizing Primary Acid-Base Disorders Without Using a Nomogram Rule 1 Look at the pH.Whichever side of 7.40 the pH is on,the process that caused it to shift to that side is the primary abnormality.Principle:The bod
3、y does not fully compensate for primary acid-base disorders Simple Acid-Base Disorders Acute Respiratory Alkalosis Arterial Gas Value Interpretation pH PCO2*HCO3 7.50 29 mmHg 22 mmol/L Alkalemia Respiratory alkalosis Normal HCO3 Causes Anxiety Hypoxia Lung disease with or without hypoxia Central ner
4、vous system disease Drug use salicylates,catecholamins,progesterone Pregnancy Sepsis Hepatic encephalopathy Mechanical ventilation*This is the primary abnormality Acute Respiratory Acidosis Arterial Gas Value Interpretation pH PCO2*HCO3 7.25 60 mmHg 26 mmol/L Acidemia Respiratory acidosis Normal HCO
5、3 Causes Central nervous system(CNS)depression drugs,CNS event Neuromuscular disorders myopathies,neuropathies Acute airway obstruction upper airway,laryngospasm,bronchospasm Severe pneumonia or pulmonary edema Impaired lung motion hemothorax,pneumothorax Thoracic cage injury flail chest Ventilator
6、dysfunction*This is the primary abnormality Chronic Respiratory Acidosis With Metabolic Compensation Arterial Gas Value Interpretation pH PCO2*HCO3 7.34 60 mmHg 31 mmol/L Respiratory acidosis Metabolic compensation Causes Chronic lung disease obstructive or restrictive Chronic neuromuscular disorder
7、s Chronic respiratory center depression central hypoventilation*This is the primary abnormality The Importance of Differentiating Acute From Chronic Respiratory Acidosis Acute respiratory acidosis Medical emergency requiring emergent intubation and mechanical ventilation Chronic respiratory acidosis
8、 Often a clinically stable condition Metabolic Acidosis With Respiratory Compensation Arterial Gas Value Interpretation pH PCO2 HCO3*7.50 48 mmHg 36 mmol/L Alkalemia Respiratory compensation Metabolic alkalosis Causes Urinary Chloride Level Low Urinary Chloride Level Normal or High Vomiting,nasogast
9、ric suction Diuretic use in past Posthypercapnia Excess mineralocorticoid activity Cushings syndrome,Conns syndrome,exogenous steroids,licorice ingestion,increased renin states,Bartters syndrome Current or recent diuretic use Excess alkali administration Refeeding alkalosis*This is the primary abnor
10、mality Metabolic Acidosis With Respiratory Compensation Arterial Gas Value Interpretation pH PCO2 HCO3*7.20 21 mmHg 8 mmol/L Acidemia Respiratory compensation Metabolic acidosis Anion gap=sodium chloride bicarbonate Normal=12 2(SD)mmol/L Causes Nonanion Gap Anion Gap GI bicarbonate loss Diarrhea Ure
11、teral diversions Hydrochloric administration Posthypocapnia GI=gastrointestinal Renal bicarbonate loss Renal tubular acidosis Early renal failure Carbonic anhydrase inhibitors Aldosterone inhibitors Ketoacidosis Diabetic Alcoholic Renal failure Lactic acidosis Rhabdomyolysis Toxins Methanol Ethylene
12、 glycol Paraldehyde Salicylates*This is the primary abnormality Mixed Acid-Base Disorders ABG Interpretation ABG pH 7.49,PCO2 47 mmHg,HCO3 35 mmol/L,Na 139 mmol/L,K 3 mmol/L,Cl 89 mmol/L Interpretation Simple metabolic alkalosis with compensatory respiratory acidosis?or Mixed metabolic alkalosis and
13、 respiratory acidosis?Summary of Expected Compensation for Simple Acid-Base Disorders Primary disorder Initial chemical change Compensatory response Expected range of compensation Metabolic acidosis HCO3 decrease PCO2 decrease PCO2=1.5(HCO3)+8 2 PCO2=last two digits of pH PCO2=1 1.3(HCO3)Metabolic a
14、lkalosis HCO3 increase PCO2 increase PCO2:variable increase PCO2=0.9(HCO3)+9 PCO2=0.6(HCO3)Summary of Expected Compensation for Simple Acid-Base Disorders Primary disorder Initial chemical change Compensatory response Expected range of compensation Respiratory acidosis PCO2 increase HCO3 increase Ac
15、ute(H+)=0.8(PCO2)HCO3=PCO2/10 Chronic(H+)=0.3(PCO2)HCO3=3.5 x PCO2/10 Respiratory alkalosis PCO2 decrease HCO3 decrease Acute(H+)=0.8(PCO2)HCO3=2 x PCO2/10 Chronic(H+)=0.17(PCO2)HCO3=5 x PCO2/10 ABG Interpretation ABG pH 7.40,PCO2 40 mmHg,HCO3 24 mmol/L,Na 139 mmol/L,K 4 mmol/L,Cl 105 mmol/L Calcula
16、tion AG=139 105 24=10 Interpretation normal ABG Interpretation ABG pH 7.49,PCO2 47 mmHg,HCO3 35 mmol/L,Na 139 mmol/L,K 3 mmol/L,Cl 89 mmol/L Calculation AG=139 89 35=15 PCO2=0.6(HCO3)=0.6 x 11=6.6 mmHg Interpretation Simple metabolic alkalosis ABG Interpretation ABG pH 7.65,PCO2 30 mmHg,HCO3 32 mmol/L,Na 139 mmol/L,K 2.8 mmol/L,Cl 92 mmol/L Calculation AG=139 92 32=15 HCO3=2(PCO2/10)=2 x 10/10=2 mmHg Interpretation Mixed metabolic and respiratory alkalosis ABG Interpretation ABG pH 7.61,PCO2 30
