1. Pathopharmacology of
Acid Base Imbalances
Wanda Lovitz, APRN

2. After this lecture (& for the exam) you should be able to:
Understand the underlying pathophysiology of acid-base imbalances
Identify who is at risk for acid-base disorders and why
Analyze ABG’s given to you *or* select a set of ABG’s that would be consistent with a patient scenario
Explain what someone looks like who is experiencing an acid-base disorder
Discuss what you the nurse can do to treat acid- base disorders

3. Overview: Definition of Acid-Base
Regulators of Acid-Base
Types of Imbalances
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis
Blood buffer system
Lungs
Kidneys
Uncompensated, Partially Compensated
Or Fully compensated

4. Definitions: Acids - Contain H+
Alkali(Base) -Contain NO H+, but accept them from acids
pH = Measure of concentration of H+ in body fluid

5. Acid Base Normal body fluid pH 7.35 - 7.45 pH Scale 1-14
7 Neutral (water)
< 7 Acid
> 7 Alkali
Normal body fluid pH

6. PH of various liquids PH = measurement of acidity or alkalinity of the blood

7. Three Major Homeostatic Regulators of Acid-Base
BLOOD BUFFER SYSTEMS
Lungs
Kidneys

8. Blood Buffer System as a regulator of PH
“Buffer” - acts as a chemical sponge, by either soaking up or releasing H+ so pH remains stable
BUFFERS JOB  to combine with acid/base added to the system to prevent marked CHANGE in pH
acts within 1 second!!

9. Blood buffer system with exercise

10. Blood Buffer System Acidic Blood Alkalotic Blood
Decrease in force of cardiac contractions
Decrease in vascular response to catecholamines
Decrease in the effect of some medications
Alkalotic Blood
Interferes with tissue oxygenation
Intereferes with normal NEUROLOLGICAL and MUSCULAR function

11. Three Main Buffer Systems Body’s Self Regulator System
CARBONIC ACID - BICARBONATE SYSTEM
(H²CO³) ( HCO³)
Phosphate System (need not know for now)
Protein System (need not know for now)

12. Dissociates into H²O and CO²
H2CO3 - HCO3 System (carbonic acid/bicarbonate system= most important buffer system in the ECF)
If strong acid is introduced into body:
HCl + NaHCO³ H²CO³ + NaCl
(hydrochloric acid) + (sodium bicarb) (carbonic acid) + (sodium chloride)
“Weak acid”
Dissociates into H²O and CO²
& is excreted by lungs
H+ =  PH (blood is more acidic)
H2CO3 (Carbonic acid) really is all about the LUNGS
CO2 and H2O released with EXHALATION

13. If strong base is introduced into body: NaOH + H²CO³  NaHCO3 + H²O
H2CO3 - HCO3 System
If strong base is introduced into body:
NaOH + H²CO³  NaHCO3 + H²O
(hydroxide/soda) (carbonic acid) (sodium bicarbonate) (water)
“buffer”
“weak base”
excreted by kidneys
H+ = PH (blood is more alkalotic)
HCO3 (Bicarbonate) is really all about the KIDNEYS
Hydrogen EXCRETED by the kidney

14. The ability to maintain a stable pH relies on a STEADY RATIO:
(base) HCO³
(acid) H²CO³
Exact quantities not important as long as ratio remains 20 : 1

15. Simple Scale Explanation Of HCO³/CO² Ratio
So... Too much acid, need to ADD BASE or (take away acid) to balance the scale
AND ....Too much base, need to ADD ACID (H+) or (take away base)
to BALANCE the scale

16. Respiratory Control of pH
Responds in MINUTES to hours
Remember the ‘blood buffer system responds in SECONDS!
Lungs are the primary controller of H²CO³ ( H+/acid) supply
CO2 is carried in the blood to the LUNGS. In the lungs, excess CO2 combines with H2O to form carbonic acid (H2CO3)
This triggers the lungs to increase or decrease the rate and depth of ventilation

17. H²CO³  CO² + H²O excreted in exhalation
Rate
> of respirations
Depth released
control amount of CO² <
retained

18. Respiratory Control of pH
When pH is ___ then there is an __ in the respiratory rate/depth
Result: greater excretion of CO² via lungs
“CO2 is blown off”
When pH is ___ then there is a ___ in the respiratory rate/depth
Result: “CO² retained”

19. Renal Control of pH Responds in HOURS TO DAYS
Remember the blood buffer responds in SECONDS and the lungs respond in MINUTES TO HOURS
Kidneys are the primary controller of HCO³ (base/alkalosis) supply

20. Renal Control of pH
When pH is __ , kidneys excrete H+ ( H+) and HCO³ (bicarb) is formed and retained.
When pH is ___ , kidneys retain
H+ (acid or H+) and HCO³ is excreted.

21. Acid Base imbalances can be assessed in the clinical setting by using
serum lab plasma findings….
Find out the”story” behind WHY the ABGs were ordered

22. Arterial Blood Gases “ABG’s”
Purpose: To ASSESS acid-base status and to determine adequacy of oxygenation and ventilation

23. Arterial Blood Gases Consist of:pH
indicates balance or impeding acidosis/alkalosis
pCO2 (chemoreceptors in the brain)
respiratory parameter (Lungs can only remove carbonic acid)
35-45 mm Hg
HCO3
metabolic (kidney) parameter (kidneys can remove other acids, ie. Lactic acid (but NOT carbonic acid)
22-26 mEq/L

24. Arterial Blood Gases vs Pulse Oximetry reading
PaO2 Saturation = partial pressure of oxygen in the plasma of ARTERIAL blood
Measured via ABG (INVASIVE BLOOD TEST)
Free/unbound oxygen molecules
Is an indication of TISSUE PERFUSION
Determined by ALVEOLAR PO2 and NOT related to hgb
Normal mm Hg
Start supplemental oxygen if below 60 mm Hg
SpO2 = measured by PULSE OXIMETRY
NONINVASIVE
Indicates the percent of oxygen bound to hemoglobin.
Measures blood saturation
NOT ABLE TO DETECT TISSUE HYPOXIA
Expressed in percentage
Normal is %
Take action if below 90%

25. Key Definitions Primary EVENT Primary DISORDER Compensatory mechanisms
Is the PROBLEM that initiates the acid-base imbalance
Hypoventilation, hyperventilation, diarrhea, vomiting, pain
Primary DISORDER
Is WHAT RESULTS from the primary event
Respiratory acidosis/alkalosis, metabolic acidosis/alkalosis
Compensatory mechanisms
Physiologic activities that ADJUST THE PH TOWARD A MORE NORMAL LEVEL without correcting the underlying cause of the disorder
If lungs are the source of the problem... Kidneys compensate
If kidneys are the source of the problem .... Lungs compensate

26. Primary Acid Base Disorders

27. Acidosis Occurs:too much carbonic acid OR not enough bicarb
H+ in blood (acid)…too much acid
Examples of PRIMARY EVENTS:
RESPIRATORY acidosis  problem or cause: HYPOVENTILATION (CO2 retained = EXCESS CARBONIC ACID)
HCO³in blood (bicarbonate) ….not enough bicarbonate
→ METABOLIC acidosis  problem or cause: EXCESS PRODUCTION OF LACTIC ACID
Metformin/Glucophage
ketone production as with DKA
kidney dysfunction resulting in kidneys unable to secrete acid(phosphorus,uric acid)
persistent diarrhea = losing base

28. Diarrhea vs Vomiting: acid/base
Secretions BELOW the stomach (including pancreatic and biliary secretions) are relatively ALKALINE
So prolonged diarrhea could cause metabolic acidosis
The body is losing HCO3 (bicarb) – so balance of 20:1 is shifted towards acid.
Secretions ABOVE the pyloric sphincter are relatively ACIDIC
So…prolonged vomiting could cause metabolic alkalosis
The body is losing acid H+ - so the balance of 20:1 is shifted towards alkaline.

29. Drawing by nursing student showing effect of vomiting & diarrhea on ABGs

30. Alkalosis Occurs: too much Bicarb OR not enough CARBONIC ACID
in blood HCO³ (bicarbonate)…too much BICARBONATE
Examples of primary events:
Metabolic ALKALOSIS
 taking excess baking soda, alka-seltzer
problem or cause: hypokalemia causing hydrogen to shift into the intracelllular space,
prolonged vomiting (loss of HCL from vomiting causes hydrogen ions to be lost)
 in blood excretion of hydrogen (H+)…not enough CARBONIC ACID
Respiratory ALKALOSIS
 problem or cause: hyperventilation

31. General Cause of Imbalance is termed:
“Metabolic”
HCO3 (bicarbonate) level changes secondary to metabolic alterations (kidneys)
“Respiratory”
H²CO³(carbonic acid) level changes secondary to respiratory alterations (lungs)

32. Respiratory Acidosis: Acute & Chronic
H²CO³ excess in ECF (too much acid/H+)
Cause:
Hypoventilation  “primary event”  CO2 retained (H+)
Acute vs chronic causes (resp arrest vs COPD)
ABGs:
pH <  A
pCO2 > 45 A (more H+) retaining CO2 and H2)
HCO *↔
* HCO3 WNL with acute respiratory acidosis; no time for kidneys to compensate

33. Respiratory Acidosis Clinical S/S: Nursing actions:
CNS depression causing hypoventilation (head injury, narcotics, sedatives, anesthesia, pulmonary disorders, pain, abdominal distension,chest wall deformities, neuruomuscular problems)
Dyspnea, respiratory distress, shallow respirations
H/A, restlessness, confusion
Tachycardia, arrhythmias
 LOC, stupor, coma
Nursing actions:
aimed at INCREASING VENTILATION and improving O²- CO² exchange

36. Respiratory Alkalosis
H²CO³ (CARBONIC ACID) DEFICIT in ECF
Cause:
Hyperventilation  primary event CO2 blown off
Pain, increased metabolic demands such as with fever, sepsis, some medications (resp stimulants), acute anxiety, any lung disease that causes SOA, CNS lesions
ABGs:
pH > 7.45 ↑ B
pCO2 < 35 ↓ B (less H+) blowing off CO2 and H2O
HCO ↔

37. Respiratory Alkalosis
Clinical S/S:
CNS over-excitability
Light headedness, numbness, tingling
Confusion, blurred vison
Numbness of hands and feet
Hyperactive reflexes, seizures
Nursing Actions:
Treatment directed toward cause
Breathing into a paper bag will cause CO2 to be re-breathed

40. Metabolic Acidosis HCO³ (BICARBONATE) DEFICIT in ECF
excess acids are added OR bicarb is lost
PH less than 7.35
HCO3 less than 22
Causes (primary events):
Renal disease (kidney impairment affects acid secretion)
Diabetes (Type I DM) … DKA  ketones (acids)
Prolonged diarrhea (relative increased acid d/t loss of HCO3)
Starvation (body using fat for energy resulting in ketosis)

41. Metabolic Acidosis ABGs: HCO3 < 22 Acid (less base)
pH <  A
pCO ↔
HCO3 < 22 Acid (less base)

42. Metabolic Acidosis Clinical S/S: Nursing Actions: CNS depression
Kussmaul respirations (DKA)
Nursing Actions:
Treatment directed toward cause
IV NaHCO3 (sodium bicarbonate)

45. Metabolic Alkalosis HCO³ (BICARBONATE) EXCESS in ECF
excess H+(acid) are lost or HCO³(base) is added
Causes (primary events):
Increased intake of baking soda, Alka-Seltzer
Increased loss of HCl such as with prolonged vomiting or gastric suction

46. Metabolic Alkalosis HCO3 > 26 B ABGs: Clinical S/S:
pH > B
pCO2 – ↔
HCO3 > 26 B
Clinical S/S:
CNS overexcitability
Nursing actions:
directed toward cause

49. In all A/B imbalances the body attempts to take corrective action in order to maintain a normal pH
This is referred to as: COMPENSATION
and the compensatory mechanism will be opposite of the cause…

50. RESPIRATORY Acidosis/Alkalosis: Compensation
Are the results of respiratory alterations and the KIDNEY compensates by either:
conserving HCO3 (bicarbonate) ions (acidosis correction)
excreting HCO3 (bicarbonate)ions (alkalosis correction)
How fast for the kidneys to compensate? Hours to days

51. METABOLIC Acidosis/Alkalosis: Compensation
Are the results of metabolic alterations and the LUNGS compensates by either:
conserving CO2 ions (alkalosis correction)
excreting CO2 ions (acidosis correction)
(The kidney also attempts to “correct” imbalance by retaining/excreting HCO³)
How fast for the lungs to compensate? Minutes to hours

52. Expected Directional Changes in Blood Gases with Primary Acid-Base Disorders
Primary Disorder pH
PaCO²
HCO³
Respiratory acidosis (acute)
(uncompensated)
Respiratory alkalosis
Metabolic acidosis
Metabolic
alkalosis

53. Expected Directional Changes in Blood Gases with Primary Acid-Base Disorders
Primary Disorder pH
PaCO²
HCO³
Respiratory acidosis (acute)
(uncompensated)   ↔
Respiratory alkalosis
Metabolic acidosis ↓
Metabolic
alkalosis ↑

54. Summary Of Compensation Concepts
Respiratory Compensation
(the lungs are attempting to correct the problem)
Metabolic
Compensation
(the kidneys are attempting to correct
the problem)
Rate of compensation
Rapid
Slow
Major organ involved
Lungs
Kidneys
Compensatory activities of organ
Hyper/
hypoventilation
Retention/excretion of H+/HCO³
Acid-base problem triggering activation of compensation
Metabolic A-B abnormalities
Respiratory A-B abnormalities

55. Acid-Base Balance

56. Before the next lecture, complete the Acid-Base Prep Work before coming to class
Will not be collected; however, you will be
called upon to ‘present’
Your patient’ to the group