Download Acid-Base Imbalance

Acid-Base Imbalance
NRS 440
2010
What is pH?
• pH is the concentration of hydrogen (H+)
ions
• The pH of blood indicates the net result of
normal acid-base regulation, any acidbase imbalance, and the body’s
compensatory mechanisms
• The human body must maintain a very
narrow pH range
– 7.35-7.45
What is pH?
• In terms of the human body:
• acidosis<------7.4------>alkalosis
– Carbon dioxide is the “acid” (CO2)
• Normal: 35-45 mmHg
– Bicarbonate is the “base” (HCO3)
• Normal: 22-26 mEq/L
•
How does the body maintain
pH?
Buffer systems
– Prevent major changes in pH by removing or
releasing a hydrogen (H+) ion
– Act chemically to change strong acids into
weaker acids or to bind acids to neutralize
their effects
1. Carbonic acid (H2C03) buffer system
neutralized hydrochloric acid
2. Phosphate buffer system neutralizes strong
acids
•
How does the body maintain
pH?
Buffer systems
3. Intracellular and extracellular proteins act as
buffer systems
4. The cell can act as a buffer by shifting
hydrogen in and out of the cell
How does the body maintain
pH?
• Kidneys
– Regulate bicarbonate in the ECF
– The kidneys will retain or excrete H+ ions or HCO3
ions as needed
– Normally acidic urine
• Lungs
– Control CO2
– Adjust rate and depth of ventilation in response to
amount of CO2 in the blood
• A rise in arterial blood CO2 stimulates respiration
• Oxygen content of arterial blood will also stimulate
respiration
Acidosis and Alkalosis
• Metabolic acidosis
– Decreased HCO3 or increase in other acids
• Metabolic alkalosis
– Increased HCO3 and excess loss of acids
• Respiratory acidosis
– Increased PaCO2 due to hypoventilation
• Respiratory alkalosis
– Decreased PaC02 due to hyperventilation
Imbalances
• Imbalances in PaCO2 are influenced by
respiratory causes
• Imbalances in HCO3 are influenced by
metabolic processes
Metabolic Acidosis
• Low pH (<7.35)
• Low HCO3 (<22 mEq/L)
• Body may attempt to compensate by
increasing respirations to decrease CO2
High anion gap acidosis
– Results from excessive accumulation of fixed
acid
Normal anion gap acidosis
– Results from direct loss of bicarbonate
Metabolic acidosis
• Primary feature is decrease in serum HCO3
• Hyperkalemia may also occur due to shift of
potassium out of the cells
– Hypokalemia may occur once the acidosis is
corrected
• Treatment is aimed at correcting the
metabolic defect
– IV bicarbonate
– Potassium management
– Dialysis
Metabolic Alkalosis
• High pH (>7.45)
• High serum HCO3 (>26)
• Body may attempt to compensate by decreasing
respirations to increase CO2
• Treatment is aimed at treating the underlying
disorder
–
–
–
–
Chloride supplementation
Restore normal fluid volume
Maintain potassium
Carbonic anhydrase inhibitor if unable to tolerate
volume resuscitation
Respiratory Acidosis
• Low pH (<7.35)
• High serum CO2 (>42)
• Body may attempt to compensate through
renal retention of HCO3 (does not happen
quickly - hours to days)
– Chronic respiratory acidosis occurs with chronic
pulmonary disease (eg, emphysema, OSA)
• Pt. will often be asymptomatic, as the body has time to
compensate
– Acute respiratory acidosis may be severe and will
produce symptoms
Respiratory Acidosis
• Treatment is directed at improving
ventilation --> treat the underlying cause
– Pulmonary hygiene to clear respiratory
tract
– Adequate hydration to help clear
secretions
– Supplemental oxygen
– Adjustment of mechanical ventilation as
appropriate
Respiratory Alkalosis
•
•
•
•
High pH (>7.45)
Low PaCO2 (<35)
Always due to hyperventilation
Body may compensate through increased
kidney excretion of bicarbonate (does not
happen quickly - hours to days)
• Treatment is aimed at correcting the cause
of hyperventilation
– If anxiety-related, may breathe into a closed
system (rebreathe CO2)
Interpreting Arterial Blood
Gases
•
•
•
•
•
•
pH (7.35-7.45)
PaO2 (80-100 mmHg on room air)
O2 saturation (95-100%)
PaCO2 (35-45 mmHg)
HCO3 (22-26 mEq/L)
Base excess (or deficit) (+2 to -2 mEq/L)
– Sum of bases (alkalis)
Interpreting Arterial Blood
Gases
• 1. Determine if acidosis or alkalosis
– *use 7.40 as normal in this step
• 2. Determine the component that caused
the abnormality in step 1
• 3. Determine if the gas is compensated
– If the pH is 7.35-7.45, it is compensated
– If the pH is <7.35 or >7.45, it is
uncompensated
Case Study
• Alan
– 17 years old
– History of:
•
•
•
•
Feeling “bad”
Fatigue
Constant thirst
Frequent urination
Case Study
• Alan
– Blood glucose is 484 mg/dL
– Respirations are 28, lungs are clear to
auscultation
– Breath has a fruity odor
Case Study
• Alan
– What acid-base disorder would you
expect?
– What is the treatment for the disorder?
Practice
Low <---- Neutral ----> High
pH
7.46
CO2
30
HCO3
22
Practice
Low <---- Neutral ----> High
pH
7.38
CO2
51
HCO3
29
Practice
Low <---- Neutral ----> High
pH
7.28
CO2
HCO3
35
18
Case Study
• Susan’s ABG results are:
–
–
–
–
pH 7.20
PaCO2 58 mm Hg
PaO2 59 mm Hg
HCO3- 24 mEq/L
1. Describe a patient who would have these
ABGs, including history and assessment.
2. What is the treatment?