Pathophiso 2-5 Acid-Base Balance

Acid

Formed as end product of proteins, carbs, or fat metabolism - acids donate [H+]

Base

Accept [H+] and balance acids to help maintain the body's normal pH

Alkaline/ [ OH-]

Organs involved in acid-base regulation

Bones - buffer reserve, lungs- [COz] control, kidneys- [H+]/[HCO3-] control

When [H+] is higher

PH is lower

When [h+] is low

pH is high/alkaline

Neutral pH for biological fluids

pH 7.4

Acidosis

pH <7.35 with elevated [H+] I decrease in bicarbonate/ base

Alkalosis

pH >7.45 with reduced [H+] increased bicarbonate

Volatile acid form

Can be eliminated as [C02] gas ex. Carbonic acid [H2CO3]

Nonvolatile acid form

Can be eliminated by kidneys, ex. Lactic, sulfuric, phosphoric, and other organic acids

Mechanisms to maintain normal pH

1. physiologic chemical barriers (immediate), 2. Respiratory - acid-base control (minutes), 3. renal acid-base control ( hours to days)

Buffer systems

Bind excess [H+] or [OH-] w/o major change in pH respond quickly before lungs + kidneys can fully compensate

Bicarbonate-carbonic acid buffer system

Lungs adjust [C02], kidneys reabsorb/regenerate [HCO3 - ] and excrete [H+]

Protein buffers

Plasma + intracellular buffers

Proteins have negative charge + bind [H+], hemoglobin is great

Renal buffers

Renal tubules, phosphate + ammonia buffers are active in tubules

Carbonic acid - bicarbonate system

CO2 + H2O = H2C03 = [HCO3-] +[H+]

Lungs adjust CO2 production

Kidneys reabsorb or regenerate [HC03-] and excrete [H+] in urine

Carbonic anhydrase

Enzyme in erythrocytes that help CO2 combine with water to form carbonic acid [H2C03]

Normal blood pH

7.35 -7.45

Normal ABG value for PaCO2

35 - 45 mm Hg

Normal ABG value for PaO2

90 - 100 mm Hg

Normal ABG value for [HCO3-]

22 - 26 mEq/L

Normal ABG value for SaO2

95-100%

Respiratory acidosis

Low pH + high PaCO2 of > 45 mm Hg

Ventilation problems lead to CO2 retention → carbonic acid increases

Ex. of respiratory acidosis due to alveolar hypoventilation

Decreased ventilation vs CO2 production

Ex. Of respiratory acidosis due to CNS depression

Drugs, head injury

Respiratory muscle paralysis / chest wall disorders

Kyphoscoliosis. obesity

Ex of respiratory acidosis due to lung disease

COPD, asthma, pneumonia, pulmonary edema

Common causes of respiratory acidosis

Sleep apnea, pulmonary embolism •alveolar hypoventilation, CNS depression, respiratory muscle paralysis, chest wall disorders, lung disease

Common causes of respiratory alkalosis

Hypoxemia, hypermetabolic States, toxins, mixed personality disorder secondary to metabolic acidosis, hysteria anxiety, ventilator overuse

Ex of respiratory alkalosis due to hypoxemia

Pulmonary disease, CHF, high altitude

Ex of respiratory alkalosis due to hypermetabolic states

Fever, anemia, thyrotoxicosis (excess thyroid hormones in blood)

Ex of respiratory alkalosis ove to toxins/illness

Early salicylate intoxication, cirrhosis, sepsis

Metabolic acidosis

Low pH + low/normal PaCO2, often decreased [HCO3-]

Diabetic ketoacidosis

Causes of metabolic acidosis

Ketoacidosis (diabetes mellitus, starvation)

Lactic acidosis (shock, hypoxemia)

ingestions (ammonium chloride, ethylene glycol, methanol, salicylates, paraldehyde)

advanced renal failure (distal renal tubular acidosis)

diarrhea / bicarbonate

Respiratory Alkalosis

High pH + low PaCO2 of < 35 mm Hg

Hyperventilation → cO2 loss → carbonic aid falls

Anion gap formula

([Na+] + [K+]) - ([Cl-] + [HCO3-]) = - 10-12 meg/l mEq/L

Metabolic alkalosis

High pH + high [HCO3-]

PCO2 high or normal bc not primary cause

*compensation clue shallow/low respirations

Elevated anion gap in metabolic acidosis

Excess acids consume [HCO3-], ex. Ketoacidosis, lactic acidosis, renal failure, toxins/ingestions

Normal gap/hyperchloremic metabolic acidosis

[HCO3-] loss replaced by increased [Ci-], ex. Diarrhea, early renal failure, proximal/distal tubular acidosis, ureterosigmoidoscopy I surgery to connect ureters to colon so urine leaves via rectum

clinical signs of metabolic acidosis

respiratory distress

headache, drowsiness,

seizures, coma

GI: nausea, vomiting

CV: dysrhythmias, decreased contractility, hypotension

treatment for metabolic acidosis

treat underlying cause

fluids/electrolytes

dialysis if severe

IV sodium bicarbonate in select cases

causes of metabolic alkalosis

acid loss via vomiting or diuretics

bicarbonate gain through bicarbonate intake and its precursors (in baking soda, leavening agent, etc in food and water)

endocrine: hyperaldosteronism (sodium retention, H+/K+ loss

consequences/signs of metabolic alkalosis

electrolyte shifts —> hypokalemia, hypocalcemia

hypochloremia worsens alkalosis

weakeness, muscle cramps, paresthesias

hyperactive reflexes, tetany, seizures

confusion, convulsions, atrial tachycardia

treatment of metabolic alkalosis

correct underlying cause

NaCl replacement for hypochloremic states

K+ supplementation

restore volume status

role of lungs in pH compensation

adjust ventilation to change CO2 and H+

short term compensation in minutes; cannot be maintained indefinitely

role of Kidneys in pH compensation

adjusts H+ excretion and HCO3- retention/excretion

hours to days , can be maintained longer

respiratory compensation for acidosis

low pH stimulates chemoreceptors —> increased ventilation —> decreased CO2 levels —> decreased H+ —> raises pH

renal compensation for acidosis

excrete H+ and retain bicarbonate

respiratory compensation for alkalosis

elevated pH triggers decreased ventilation —> increased CO2 levels —> increased H+ which lowers pH

renal compensation for alkalosis

retain H+ and excrete bicarbonate

acid-base pattern caused by diarrhea

metabolic acidosis

losing intestinal contents = losing alkaline/base

acid base pattern caused by vomiting

metabolic alkalosis

losing stomach contents = losing acids

acid-base pattern caused by asthma

respiratory acidosis

difficulty releasing or retaining CO2

potassium blood test serum levels

normal: 3.5-5.0 mEq/L

hyperkalemia: 5.0-5.5mEq/L (above 6 needs immeadiate attention bc it causes dangerous heart rhythms)

hypokalemia: 3.0-3.5 (under 2.5 is life threatening)

sodium blood test serum levels

normal: 135-145 mEq/L

hyponatremia: below 135 indicates overhydration, kidney diseasse, or heart failure

hypernatremia: above 145 indicates dehydration, excessive intake, kdiney dysfunction

total calcium blood test levels

normal: 8.5 - 10.5 mg/dL

hypercalcemia: over 10.6, over 14.0 is an emergency

hypocalcemia: 8.5mg/dL