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Med Surg - Acid-Base Balance

Terms in this set (33)

Acid pH
0-6
Alkaline pH
8-14
Acid-Base Regulation Regulatory Mechanisms
- buffers
- respiratory system
- renal system
(Regulatory Mechanisms) Buffers
- fastest-acting system
- chemical/protein buffers that bind or release hydrogen ions to adjust blood's pH
- act chemically to change strong acids to weak acids or bind acids
- primary regulator of acid-base balance
- cells have a lot of potassium in them - potassium and hydrogen are both positives, too much for the cells to handle
- have to decide whether they should take on hydrogen ions
- if they do, they exchange the hydrogen for the potassium, and dump potassium into the blood
(Regulatory Mechanisms) Respiratory System
- CO2 binds with water to create carbonic acid
- carbonic acid dissociates into hydrogen ions and bicarbonate
- respiratory center in medulla controls breathing
- increased respirations lead to increased CO2 elimination and decreased CO2 in blood
- decreased respirations lead to CO2 retention
- second-line of defense
(Regulatory Mechanisms) Renal System
- takes the longest
- works long-term
- conserves bicarbonate and excretes acid
(Regulatory Mechanisms) What are the 3 mechanisms for acid elimination in the renal system?
1.) secrete free hydrogen
2.) combine H+ with ammonia (NH3)
3.) excrete weak acids
A patient with an acid-base imbalance has an altered potassium level. The nurse recognizes that the potassium level is altered because:

A. Potassium is returned to extracellular fluid when metabolic acidosis is corrected.
B. Hyperkalemia causes an alkalosis that results in potassium being shifted into the cells.
C. Acidosis causes hydrogen ions in the blood to be exchanged for potassium from the cells.
D. In alkalosis, potassium is shifted into extracellular fluid to bind excessive bicarbonate.
C
When do acid-base imbalances occur?
when compensatory mechanisms fail
Classification of Imbalances
- respiratory (CO2) or metabolic (HCO3)
- acidosis or alkalosis
- acute or chronic
Why do ABG values show?
- acid-base status
- underlying cause of imbalance
- body's ability to regulate pH
- overall oxygen status
Interpretation of ABGs
ACIDIC BASIC
- pH: 7.35-7.45
- paCO2: 45-35 (respiratory)
- HCO3: 22-26 (metabolic)
- paO2: 80-100
ROME
Respiratory
Opposite
Metabolic
Equal
(Respiratory Acidosis) ABG
pH low
CO2 high
HCO3 normal
(Respiratory Acidosis) Respiratory Rate
low (increase in CO2 levels)
(Respiratory Acidosis) Causes
• Depression of the respiratory center.
(1) Head injuries.
(2) Oversedation with sedatives and/or narcotics.
- drug overdose

• Conditions affecting pulmonary function.

(1) COPD
(2) Pneumonia.
(3) Atelectasis.

• Conditions that interfere with chest wall excursion.
(1) Thoracic trauma: flail chest.
(2) Diseases affecting innervation of thoracic muscle (Guillain-Barré syndrome, myasthenia gravis, polio).
(3) Mechanical hypoventilation.

- any condition that causes hypoventilation
(Respiratory Acidosis) Treatment
treat the underlying cause
(Respiratory Alkalosis) ABG
pH high
CO2 low
HCO3 normal
(Respiratory Alkalosis) Carbonic Acid
deficit
(Respiratory Alkalosis) Causes
hyperventilation
- anxiety
• Primary stimulation of CNS: hyperventilation. Can be due to emotional origin (anxiety, fear, apprehension), CNS infection (encephalitis), or salicylate poisoning.
• Reflex stimulation of CNS. Hypoxia stimulates hyperventilation (heart failure, pneumonia, pulmonary emboli).
Can also be stimulated by fever.
• Mechanical hyperventilation, resulting in "over breathing."
(Respiratory Alkalosis) Treatment
- treat the underlying cause
- deep breaths
(Metabolic Acidosis) ABGs
low pH
normal PaCO2 low HCO3
(Metabolic Acidosis) Deficit
bicarbonate
(Metabolic Acidosis) What causes it?
- when acid (other than carbonic acid) accumulates in the body
- when bicarb is lost in body fluids
(Metabolic Acidosis) Causes
- diarrhea
- calculate the anion gap to determine cause
(Metabolic Acidosis) Treatment
know cause to treat; insulin in diabetics, antidiarrheals
(Anion Gap) Normal
8-12 mmol/L
(Anion Gap) Cations
- sodium
- potassium (sometimes)
(Anion Gap) Anions
- chlorine
- HCO3-
(Anion Gap) What does it mean if the gap is big?
- albumin, PO4, SO4, and organic acids are high in the body
- organic acids; causing it
- causes: DKA, lactic acidosis
(Metabolic Alkalosis) ABGs
high pH
normal PaCO2 high HCO3
(Metabolic Alkalosis) Causes
- vomiting
- tums/baking soda
(Metabolic Alkalosis) Treatment
Fix the problem, replace the potassium
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