acid-base_fars - revisi.pdf
TRANSCRIPT
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Acid-Base Balance
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Normal Acid-Base Balance
Normal pH 7.35-7.45
Narrow normal range
Compatible with life 6.8 - 8.0 (7.0
6.8)
___/______/___/______/___
6.8 7.35 7.45 8.0
Acid Alkaline
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pH & H+ Concentration
of Body Fluid Body Fluid H+ concentration
mEq/L
pH
Extracellular Fluids
Artery Vein Interstitial
4,0 x 10-5
4,5 x 10-5
4,5 x 10-5
7.40
7.35
7.35
Intracellular Fluid 1 x 10-3 s.d 4 x 10-5 6.0 7.4
Urine 3 x 10-2 s.d 1 x 10-5 4.5 8.0
Gastric Acid (HCl) 160 0.8
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Handerson-Hasselbalch Equation
pH = - log10[H+]
pH = pK + log HCO3-
(0.03 x PCO2)
pH = pK + log HCO3-
(0.03 x PCO2)
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Maintenance of Balance
Balance maintained by:
Buffering systems
Lungs
Kidneys
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Buffer Systems
Prevent major changes in pH
Act as sponges
3 main systems 1. Bicarbonate-carbonic acid buffer
2. Phosphate buffer
3. Protein buffer
H+
H+ H+
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Buffer Systems
1. Bicarbonate buffer - most important
Active in ECF and ICF
2. Phosphate buffer
Active in intracelluar (ICF) fluid
3. Protein buffer - Largest buffer store
Albumins and globulins (ECF)
Hemoglobin (ICF)
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Bicarbonate-Carbonic Acid
Bodys major buffer (90%)
Also called as : Base Spare
Carbonic acid - H2CO3 (Acid)
Bicarbonate - HCO3 (Base)
1 20
pH = 7.4
H2CO3 HCO3
24 mEq/L 1.2 mEq/L
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Bicarbonate-Carbonic Acid
Ratio important
Not absolute values
Person with COPD (CAL)
1 20
7.4
H2CO3 HCO3
48 mEq/L 2.4 mEq/L
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Regulation
Key concept
Carbonic anhydrase equation
CO2 +H2O H2CO3 H+ + HCO3
Carbon Carbonic Bicarbonate
Dioxide Acid
(ACID) (BASE)
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Acid
Substance that contains H+ ions
that can be released (H2CO3)
Carbonic acid releases H+ ions
Base
Substance that can accept H+ ions
(HCO3)
Bicarbonate accepts H+ ions
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As CO2 increases, carbonic acid increases, H+ ions increase
pH drops.. becomes more acidic
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Acidic
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As HCO3 increases, H+ decreases
pH rises, becomes more alkaline
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Basic >7.45)
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Respiratory & Renal
Regulation
Lungs control CO2
Kidneys control HCO3
pH = kidneys (bicarbonate)
lungs (carbon dioxide)
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Respiratory Regulation Mechanisms of control
Hyperventilation -- blow off CO2
Hypoventilation -- retain CO2
Regulation rapid...
Seconds to minutes
Measured by PaCO2 - Normal
35-45 mm Hg
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Renal Regulation
Mechanism of control
Excretion or retention of
H+ or HCO3
Regulation.. Slow
Hours to days to change pH
Normal serum HCO3
22-26 mEq/L
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Renal Regulation of Acid-Base
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Acid Base Imbalance
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Four Basic Types of Imbalance
Respiratory Acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis
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Acid-Base Imbalances
Primary cause or origin:
Metabolic
Changes brought about by systemic
alterations (cellular level)
Respiratory
Changes brought about by
respiratory alterations
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Acid-Base Imbalances
Compensation
Corrective response of kidneys and/or lungs
Compensated
Restoration of pH and 20 : 1 ratio
Uncompensated
Inability to adjust pH or 20 : 1 ratio
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Compensation
When a primary acid-base disorder exists, the body
attempts to return the pH to normal via the other
half of acid base metabolism.
Primary metabolic disorder Respiratory compensation
Primary respiratory disorder Metabolic compensation
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Compensation (continued)
Primary Disorder Compensatory Mechanism
Metabolic acidosis Increased ventilation
Metabolic alkalosis Decreased ventilation
Respiratory acidosis Increased renal reabsorption of HCO3-
in the proximal tubule
Increased renal excretion of H in the
distal tubule
Respiratory alkalosis Decreased renal reabsorption of HCO3-
in the proximal tubule
Decreased renal excretion of H+ in the
distal tubule
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Acid-Base Imbalances
Ratio of 20 to 1 out of balance
Acidosis (acidemia)
pH falls below 7.35
Increase in blood carbonic acid or
Decrease in bicarbonate
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Respiratory Acidosis
Carbonic acid excess
Exhaling of CO2
inhibited
Carbonic acid builds up
pH falls below 7.35
Cause = Hypoventilation (see chart)
H2CO3
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Acid-Base Imbalances
Normal
1 20
7.4
H2CO3 HCO3
24 mEq/L 1.2 mEq/L
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Respiratory Acidosis
1 13
7.21
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Respiratory Acidosis
Compensation: How?
Opposite regulating mechanism
Problem = depressed breathing,
build up of CO2 in blood
Response - Kidney retains HCO3
(Response .. Slow)
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Respiratory Alkalosis
Carbonic acid deficit
Increased exhaling
of CO2
Carbonic acid decreases
pH rises above 7.45
Cause = hyperventilation (see chart)
H2CO3
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Acid-Base Imbalances
Normal
1 20
7.4
H2CO3 HCO3
24 mEq/L 1.2 mEq/L
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Respiratory Alkalosis
1 40
7.70
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Respiratory Alkalosis
Compensation:
Problem = excess blowing off
of CO2
Result = decrease in carbonic
acid and increase in HCO3
Response: Kidney excretes excess
bicarbonate
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Metabolic Acidosis
Base-bicarbonate deficit
Low pH (< 7.35)
Low plasma bicarbonate (base)
Cause = relative gain in H+ (lactic acidosis, ketoacidosis)
or actual loss of HCO3
(renal failure, diarrhea)
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Acid-Base Imbalances
Normal
1 20
7.4
H2CO3 HCO3
24 mEq/L 1.2 mEq/L
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Metabolic Acidosis Kidney failure (decrease in bicarbonate)
1 10
7.10
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Metabolic Acidosis Lactic acidosis, keto acidosis (increase
acid no change in bicarbonate)
1 10
7.10
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Metabolic Acidosis
Compensation:
Problem = low HCO3 (base) or high H+ ion (acid)
Response: Lungs hyperventilate
Get rid of CO2
(decrease PaCO2 and therefore raise level of HCO3)
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Metabolic Alkalosis
Bicarbonate excess
High pH (> 7.45)
Loss of H+ ion or gain of HCO3
Most common causes vomiting,
gastric suctioning (NG tube)
Other: Abuse of antacids,
K+ wasting diuretics
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Acid-Base Imbalances
Normal
1 20
7.4
H2CO3 HCO3
24 mEq/L 1.2 mEq/L
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Metabolic Alkalosis
1 30
7.58
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Metabolic Alkalosis
Compensation:
Problem = too much base
Response: Lungs compensate by
hypoventilating
Retain CO2, increase PaCO2
Increase acid level in blood
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Assessing ABGs
pH 7.35 - 7.45
PaCO2 35 - 45 mmHg
HCO3 22 - 26 mEq/L
Base Excess -2 - +2 mEq/L
PaO2 80 - 100 mm Hg
O2 saturation 95 - 100 %
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Interpreting ABGs 1. Start with pH
Normal?
Acidosis?
Alkalosis?
___/______/___/______/___ 6.8 7.35 7.45 8.0
Acidosis Alkalosis
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Interpreting ABGs
2. Assess PaCO2
(respiratory value)
_____/________/______
35 45
Respiratory Respiratory
Alkalosis Acidosis (Note reversal)
(See Chart)
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Interpreting ABGs
3. Evaluate metabolic indicators
Bicarbonate (HCO3) 22-26
and
Base excess (-2 to +2)
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Interpreting ABGs HCO3
_______/_______/________
22 26
BE ______/_______/_________
-2 +2
Metabolic Metabolic
acidosis alkalosis
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Interpreting ABGs
4. Determine level of compensation
Has the body tried to readjust the pH?
Uncompensated
Partly compensated
Compensated
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Interpreting ABGs
Uncompensated
pH abnormal (high or low)
One component abnormal (high or low CO2 or HCO3)
The other component is normal
(The component not causing the acid-base imbalance is still normal)
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Partly compensated
pH not normal (but moving toward normal)
Both CO2 and HCO3 are outside normal range
The component that was normal is changing in order to compensate
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Interpreting ABGs
Compensated
pH normal
Other values abnormal in
opposite directions
One is acidotic the other alkaline
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Interpreting ABGs
Determine amount of hypoxemia present
Normal PaO2 (adults - room air)
< 70 years = 80-100 mm Hg
70-79 = 70-100 mm Hg
Drops 10 mm Hg for each decade
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Interpreting ABGs
Hypoxemia = < 70 mm Hg
(for adult < 70 years old)
Mild = 60-80 mm Hg
Moderate = 40-60 mm Hg
Severe = < 40 mm Hg
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Interpreting ABGs
Oxygen saturation (pulse
oximetry)
95-100%
< 91% confusion
< 70% life threatening
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Practice Problem
80 year old female with severe pneumonia, fever
pH = 7.25
PaCO2 = 55 mm Hg
HCO3 = 24 mEq/L
PaO2 = 65 mm Hg
O2 sat = 80%
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Practice Problems
What is the problem?
Acidosis or alkalosis?
Respiratory or metabolic?
Compensated or not?
Level of hypoxemia?
Diagnoses?
Interventions?