Acid Base Review All Systems

Normal Values

• HCO3: 24
• pH: <7.35 & > 7.45
• pCO2: 40
• Renal Compensation begins after 72 hours (3 days)

  Respiratory System

Hypoxemia – Low PaO2 in the setting of also low PAO2 –> Normal A-a gradient?

• High Altitutde, FiO2 is low
• Alveolar Hypoventilation (due to Chemoreceptor Trig –> respiratory drive)
• High A-a gradient?
• V/Q mismatch
• Diffusion impairement
• Right to left shunt

Emphysema: Chronic Respiratory Acidosis w/ Metabolic Compensation

• Inc CO2 retention –> Inc Acidosis
• High HCO3 to compensate –> slightly acidic pH
• often with Hypoxemia (PaO2 < 75 mmHg onroomair)

Pulmonary Embolism -> Respiratory Alkalosis

• High V/Q ratio
• P.Emboli –> ischemia –> infl mediators, dyspnea –> stimulation of respiratory drive –> Hyperventilation –> CO2 removal (Hypocapnea) –> Respiratory Alkalosis
• CO2 removal is directly dependent on Ventilation
• O2 diffusion is limited by Hb Oxgcarrying capacity and it is maxed out already

Hypercapnea and Hypoxemia in Obstructive Sleep Apnea

• reflex Vasoconstriction –> Pulmonary hypertension

Altitute Sickness

1. First: PiO2 is reduced (parttial pressure of inspiored oxygen) –> Hypoxemia –> Chemoreceptors trigger change and respond with Hyperventilation –> Excessive C02 removal (Hypocapnea) –> Respiratory Alkalosis
2. Within ours to several days: Kidneys respond –> Decrease HCO3 reabsorption in PCT & Decrease H+ secretion –> Compensatory Metabolic Acidosis
3. Chronic Hypoxemia –> Inc EPO –> Inc RBC count
   • Alkalosis causes LEFT SHIFT –> Reduced O2 delivery to tissues –> Eventually RBCs increase 2,3 BPG to increase O2 delivery`

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Renal System

Diuretics Overuse –> Increase pH, Increase HCO3 retention –> METABOLIC ALKALOSIS

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GastroIntestinal System

Excessive Vomitting –> Loss of HCL –> H+ loss, High pH, High HCO3 –> __Metabolic Alkalosis –> Compensated: Hypoventilation –> pCO2 retention.

• Vomiting –> Reduced Renal Perfusion –> RAAS –> Inc Na/H20 retension and Excretion of K+ and H+ –> Metabolic Alkalosis
• RAAS –> Inc HCO3 reabsorption
• Hypokalemia –> K+/H+ exchanger –> Loss of H+

Acute Ischemic Colitis

• Ischemia –> Bowel undergoes anerobic metabolism –> Lactate accumulation –> Anion Gap Metabolic Acidosis
• Acidosis -+-> Renal Amniogenesis –> Renal epithelial cells [[ Glutamine –> NH3 + HCO3 ]]
• Glutamine –> Glutamate –> alphaketoglutamate –> glucose + CO2

Toxicology

Opioid Overdose: respiratory arrest –> Hypoventilation, Hypoxemia –> retention of CO2 –> Acute Respiratory Acidosis