Acid base imbalances
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Acid Base Imbalances. Acid-Base Regulation. Body produces significant amounts of carbon dioxide & nonvolatile acids daily Regulated by: Renal excretion of acid (H+ combines with phosphate or ammonia, which are excreted) Respiratory excretion of CO2

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Acid base regulation
Acid-Base Regulation

  • Body produces significant amounts of carbon dioxide & nonvolatile acids daily

  • Regulated by:

    • Renal excretion of acid (H+ combines with phosphate or ammonia, which are excreted)

    • Respiratory excretion of CO2

    • Buffer systems (hemoglobin, phosphate, bicarbonate, proteins)


Measurement
Measurement

  • Arterial:

    • Normal pH 7.36-7.44; normal HCO3 25; normal pCO2 40

  • Peripheral venous:

    • pH is 0.02-0.04 lower than arterial

    • HCO3 is 1-2 mEq/L higher than arterial

    • pCO2 is 3-8 mmHg higher, depending on peripheral extraction and use of O2



Definition
Definition

  • Decreased pH due to pulmonary CO2 retention (hypoventilation causes hypercapnea)

  • CO2 retention causes increased H2CO3 production – causes acidemia

  • Serum HCO3 is normal acutely, and increases as compensation occurs


Causes
Causes

  • Increase in PaCO2

  • Anything which causes a decrease in minute ventilation has the potential to cause respiratory acidosis

    • Airway

    • CNS depression

    • Pulmonary disease

    • Hypoventilation of neuromuscular conditions


Symptoms
Symptoms

  • CO2 narcosis:

    • Headache, blurred vision

    • Asterixis, tremors, weakness

    • Confusion, somnolence

  • If prolonged:

    • Signs of increased ICP

    • Papilledema


Compensation
Compensation

  • Acutely:

    • intracellular proteins buffer

    • HCO3 is formed by the intracellular buffers

    • Compensation is insignificant

  • Chronically

    • Renal retention of HCO3 is the primary buffering system

    • Onset: 6-12 hrs, takes days to complete


Compensation1
Compensation

  • Acute:

    • HCO3 increases 1 mEq/L for every 10 mmHg rise in PCO2

    • Insignificant effect on pH

  • Chronic:

    • HCO3 increases 3.5-5 mEq/L for every 10mmHg rise in PCO2

    • Can almost normalize pH

    • Usually results in hypochloremia


Management
Management

  • Must increase minute ventilation

  • Must also improve ventilation

    • Bronchodilators, postural drainage, antibiotics (i.e. treat underlying cause)

  • Role of hypoxic drive???



Causes1
Causes

  • Increased minute ventilation

    • Leads to low pCO2, high pH

    • If acute, HCO3 is normal

    • If chronic, HCO3 will drop due to renal comp.

  • Causes:

    • CNS diseases, hypoxemia, anxiety, hypermetabolic states, toxic states, hepatic insufficiency, assisted ventilation


Symptoms1
Symptoms

  • Mimic hypocalcemia

  • Depend on degree, acuity & cause

  • Due to irritability of CNS & PNS, and increased cerebral vascular resistance

    • Paresthesias of lips, extremities; lightheadedness, dizziness, muscle cramps, carpopedal spasms


Management1
Management

  • Treat underlying cause

    • i.e. remove stimulus

  • Treat symptoms

    • E.g. benzos, pain medication, rebreathing mask (allows CO2 retention)



Definition1
Definition

  • Low pH due to increased HCO3 or decreased H+

  • Requires loss of H+ or retention of HCO3

  • Must know PCO2… elevation of HCO3 could be due to renal compensation for chronic respiratory acidosis


Causes2
Causes

  • Increased HCO3 reabsorption due to volume, K+ or Cl- loss

  • Loss of H+ and Cl- from vomiting and NG suctioning can lead to HCO3 retention

  • Renal impairment of HCO3 excretion


Causes3
Causes

  • Hypovolemic

    • Vomiting/suction, diuretics, adenomas

  • Euvolemic/Hypervolemic

    • Exogenous mineralocorticoids, ectopic ACTH, Cushing’s, severe hypoK, adenoCA

  • Unclassified

    • Milk-alkali syndrome, IV PCN rx, metabolism of organic acid anions, massive transfusion, nonparathyroidhypercalcemia


Treatment
Treatment

  • Treat underlying causes

  • Replace losses

  • May be saline-responsive or saline resistant



Mechanism
Mechanism

  • Increased production of acids

  • Decreased renal excretion of acids

  • Loss of alkali


Alcoholic ketoacidosis
Alcoholic Ketoacidosis

  • Normal glucose

  • High ketones

  • Drinking binge; starvation


Lactic acidosis
Lactic Acidosis

  • 2 different forms; l- and d-

  • Increased production vs. decreased elimination

  • Systemic

    • Sepsis, hypovolemia, hypoxia

  • Localized

    • E.g. bowel ischemia, metformin, HIV meds


Treatment1
Treatment

  • Correct underlying cause

  • Reduce O2 demand

  • Ensure adequate O2 delivery to tissues

  • HCO3

    • Given to improve hemodynamic consequences of acidosis


Summary
Summary

  • Look at pH

  • Look at pCO2 and HCO3

  • Look at patient!!

  • Treat the patient, not the numbers