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Acid-Base Balance Interactive Tutorial

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Acid-Base Balance Interactive Tutorial

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    1. Acid-Base Balance Interactive Tutorial Emily Phillips MSN 621 Spring 2009 E-mail: All images imported from Microsoft Clipart & Yahoo Image gallery

    2. How to navigate this tutorial: To advance to the next slide click on the box To return to the previous slide click on the box To return to the Main Menu: click the box Hover over underlined text for a definition/explanation To return to the last slide viewed click on the button Click the for additional information

    3. Objectives: Define acid base balance/imbalance Explain the pathophysiology of organs involved in acid base balance/imbalance Identify normal/abnormal and compensated/uncompensated lab values Explain symptoms related to acid base imbalances and compensated vs. uncompensated Appropriate interventions and expected outcomes

    4. Main Menu:

    5. Acid-Base Pretest: What is the normal range for arterial blood pH?

    6. Incorrect Close but not quite try again.

    7. Incorrect Close, but no cigar 7.52 would indicate alkalosis.

    8. Correct! This is the correct parameters for arterial blood pH with the extracellular fluid in the middle at 7.40 well done!

    9. Acid-Base Pretest: What 2 extracellular substances work together to regulate pH?

    10. Incorrect Sorry, but not exactly although sodium bicarbonate plays a role as a buffer in acid-base balance it isnt 1 of the extracellular substances that works to regulate pH

    11. Correct! Right on! Carbonic acid and bicarbonate are the two primary extracellular regulators of pH. pH is also further regulated by electrolyte composition within the intra & extracellular compartments.

    12. Incorrect Although carbonic acid is 1 of 2 extracellular substances that work to regulate pH, acetic acid is not; its simply a weak acid.

    13. Acid-Base Pretest: Characterize an acid & a base based on the choices below.

    14. Correct! Acids are molecules that have the ability to release H+ ions & bases are molecules that have the ability to accept or bind with H+ ions.

    15. Incorrect Think this through and try again. Acids increase the concentration of H+ ions & bases decrease the concentration. Think of an acid like a wet sponge & a base as a dry sponge. What happens when you squeeze a wet sponge? Likewise, what happens to a dry sponge when placed in a bucket of water?

    16. Incorrect If you think of an acid as wet sponge & a base as a dry sponge; what happens when a wet sponge gets squeezed & a dry sponge gets wet?

    17. Acid-Base Pretest: Buffering is a normal body mechanism that occurs rapidly in response to acid-base disturbances in order to prevent changes in what?

    18. Incorrect HCO3- is its own buffer system which is very important because HCO3- can be regulated by the kidneys & CO2 by the lungs. Nice try, but think again

    19. Incorrect The bicarbonate buffer system utilizes carbonic acid & sodium bicarbonate to buffer, but carbonic acid is NOT the major ion involved in acid-base balance.

    20. Correct! Excellent! H+ ion concentration is most important to regulate in order to prevent acid-base balance disturbances.

    21. Acid-Base Pretest: What are the two systems in the body that work to regulate pH in acid-base balance & which one works fastest?

    22. Incorrect These two systems do work together to regulate pH in acid-base imbalance, however, the renal system works over a matter of days as opposed to hours think it over & try again.

    23. Correct! Great work! Both the respiratory & renal systems work to regulate pH in acid-base imbalance; the respiratory system works in a matter of minutes & is maximal within 12-24 hours while the renal (kidneys) system continues to function for days to restore pH within normal limits (WNL).

    24. Incorrect The renal system does work to regulate pH in acid-base imbalance, but the GI system does not try again.

    25. Acid-Base Balance: Homeostasis of bodily fluids at a normal arterial blood pH pH is regulated by extracellular carbonic acid (H2CO3) and bicarbonate (HCO3-) Acids are molecules that release hydrogen ions (H+) A base is a molecule that accepts or combines with H+ ions

    27. Acids and Bases can be strong or weak: A strong acid or base is one that dissociates completely in a solution - HCl, NaOH, and H2SO4 A weak acid or base is one that dissociates partially in a solution -H2CO3, C3H6O3, and CH2O

    29. The Body and pH: Homeostasis of pH is controlled through extracellular & intracellular buffering systems Respiratory: eliminate CO2 Renal: conserve HCO3- and eliminate H+ ions Electrolytes: composition of extracellular (ECF) & intracellular fluids (ICF) - ECF is maintained at 7.40

    30. Protein Buffer Systems: Largest buffer system in the body Amphoteric: can function as acids or bases Contain several ionizable groups able to bind or release H+ Largely located in cells; H+ & CO2 diffuse across cell membranes for buffering by Albumin & plasma globulins

    31. Bicarbonate Buffer System: Uses NaHCO3 as its weak base & H2CO3 as its weak acid The HCO3-/CO2 buffer system can readily add or remove components from the body An ample supply of CO2 provided via metabolism, replaces H2CO3 lost when excess base is added In turn, the kidneys conserve or form new HCO3- in the presence of excess acid & excrete HCO3- in the presence of excess base

    33. Plasma Potassium-Hydrogen Exchange: Both positively charged ions move freely between IC & EC compartments Decreases in plasma K+ cause movement of K+ from ICF to ECF & movement of H+ from ECF to ICF With an EC decrease in K+, K+ moves out & is replaced by H+ As a result, changes in EC K+ levels affect acid-base balance & vice versa

    34. Quick Review: Click the Boxes A donator of H+ ions An acceptor of H+ w/ pH <7.0 ions w/ pH >7.0 Regulated by EC Controlled by EC H2CO3 & HCO3- & IC buffer systems Eliminates CO2 Conserves HCO3- Eliminates H+ ions

    35. Respiratory Control Mechanisms: Works within minutes to control pH; maximal in 12-24 hours Only about 50-75% effective in returning pH to normal Excess CO2 & H+ in the blood act directly on respiratory centers in the brain CO2 readily crosses blood-brain barrier reacting w/ H2O to form H2CO3 H2CO3 splits into H+ & HCO3- & the H+ stimulates an increase or decrease in respirations

    36. Renal Control Mechanisms: Dont work as fast as the respiratory system; function for days to restore pH to, or close to, normal Regulate pH through excreting acidic or alkaline urine; excreting excess H+ & regenerating or reabsorbing HCO3- Excreting acidic urine decreases acid in the EC fluid & excreting alkaline urine removes base

    38. H+ Elimination & HCO3- Conservation: Begins with Na+/H+ transport system H+ secreted in tubular fluid & Na+ reabsorbed in tubular cell Secreted H+ couples w/ filtered HCO3- & CO2 & H2O result H2O secreted in urine & CO2 diffuses into tubular cell combining w/ H2O to form HCO3- via a carbonic anhydrase-mediated reaction HCO3- is reabsorbed into the blood along w/ Na+, & newly generated H+ is secreted into tubular fluid beginning a new cycle

    39. Mechanisms of Acid-Base Balance: The ratio of HCO3- base to the volatile H2CO3 determines pH Concentrations of volatile H2CO3 are regulated by changing the rate & depth of respiration Plasma concentration of HCO3- is regulated by the kidneys via 2 processes: reabsorption of filtered HCO3- & generation of new HCO3-, or elimination of H+ buffered by tubular systems to maintain a luminal pH of at least 4.5

    40. The Phosphate Buffer system: Uses HPO42- and H2PO4- present in tubular filtrate Both become concentrated in the fluid due to relatively poor absorption & reabsorption of H2O from tubular fluid H+ combines w/ HPO42- to form H2PO4- giving the kidneys the ability to increase secretion of H+ ions When H+ ions in the bloodstream decrease, pH increases & vice versa Subsequently hydrogen phosphate either accepts or releases H+ ions to maintain pH within the bloodstream

    41. The Ammonia Buffer System: This buffer system is the more complex of the two The generation of HCO3- & excretion of H+ by this system occurs in 3 steps: 1) synthesis of NH4+ from glutamine, an amino acid in the proximal tubule, thick ascending loop of Henle & distal tubules 2) recycling & reabsorption of NH3 in the kidneys medulla, & 3) buffering of H+ ions by NH3 in the collecting tubules.

    42. Acid-Base Balance Review test: The kidneys regulate pH by excreting HCO3- and retaining or regenerating H+

    43. Incorrect Actually the kidneys work to regulate pH through the regeneration or reabsorption of HCO3- & excretion of H+

    44. Correct! Youre absolutely right! The kidneys actually do the opposite in order to regulate pH. Nicely done.

    45. Acid-Base Review test: H2CO3 splits into HCO3- & H+ & it is the H+ that stimulates either an increase or decrease in the rate & depth of respirations.

    46. Correct! You got it! This is because H+, along with CO2 in the blood stream, act directly on respiratory centers in the brain.

    47. Incorrect The correct answer is TRUE. Please review the Respiratory Control Mechanisms slide as needed.

    48. Acid-Base Review test: Plasma concentration of HCO3- is controlled by the kidneys through reabsorption/regeneration of HCO3-, or elimination of buffered H+ via the tubular systems.

    49. Correct! Yes! Reabsorption of filtered HCO3- or generation of new HCO3- & or H+ ion elimination via phosphate & ammonia buffer systems help the kidneys regulate plasma concentrations of HCO3-.

    50. Incorrect Please review Mechanisms of Acid-Base balance if needed.

    51. Acid-Base Review test: The ratio of H+ to HCO3- determines pH.

    52. Incorrect The answer is false. Its the ratio of HCO3- to volatile H2CO3 that determines pH.

    53. Correct! Youre right, the answer is false. REMEMBER: concentrations of volatile H2CO3 are regulated by changing the rate & depth of respirations.

    54. Acid-Base Review test: Secreted H+ couples with filtered HCO3- & CO2 & H2O result.

    55. Correct! Well done! If you look back at the H+ Elimination & HCO3- Conservation slide, this is part of the Na+/H+ transport system.

    56. Incorrect Sorry, but the correct answer is true.

    57. Metabolic Disturbances: Alkalosis: elevated HCO3- (>26 mEq/L) Causes include: Cl- depletion (vomiting, prolonged nasogastric suctioning), Cushings syndrome, K+ deficiency, massive blood transfusions, ingestion of antacids, etc. Acidosis: decreased HCO3- (<22 mEq/L) Causes include: DKA, shock, sepsis, renal failure, diarrhea, salicylates (aspirin), etc. Compensation is respiratory-related

    58. Metabolic Alkalosis: Caused by an increase in pH (>7.45) related to an excess in plasma HCO3- Caused by a loss of H+ ions, net gain in HCO3- , or loss of Cl- ions in excess of HCO3- Most HCO3- comes from CO2 produced during metabolic processes, reabsorption of filtered HCO3-, or generation of new HCO3- by the kidneys Proximal tubule reabsorbs 99.9% of filtered HCO3-; excess is excreted in urine

    59. Metabolic Alkalosis Manifestations: Signs & symptoms (s/sx) of volume depletion or hypokalemia Compensatory hypoventilation, hypoxemia & respiratory acidosis Neurological s/sx may include mental confusion, hyperactive reflexes, tetany and carpopedal spasm Severe alkalosis (>7.55) causes respiratory failure, dysrhthmias, seizures & coma

    60. Treatment of Metabolic Alkalosis: Correct the cause of the imbalance May include KCl supplementation for K+/Cl- deficits Fluid replacement with 0.9 normal saline or 0.45 normal saline for s/sx of volume depletion Intubation & mechanical ventilation may be required in the presence of respiratory failure

    61. Metabolic Acidosis: Primary deficit in base HCO3- (<22 mEq/L) and pH (<7.35) Caused by 1 of 4 mechanisms Increase in nonvolatile metabolic acids, decreased acid secretion by kidneys, excessive loss of HCO3-, or an increase in Cl- Metabolic acids increase w/ an accumulation of lactic acid, overproduction of ketoacids, or drug/chemical anion ingestion

    63. Metabolic Acidosis Manifestations: Hyperventialtion (to reduce CO2 levels), & dyspnea Complaints of weakness, fatigue, general malaise, or a dull headache Pts may also have anorexia, N/V, & abdominal pain If the acidosis progresses, stupor, coma & LOC may decline Skin is often warm & flush related to sympathetic stimulation

    64. Treatment of Metabolic Acidosis: Treat the condition that first caused the imbalance NaHCO3 infusion for HCO3- <22mEq/L Restoration of fluids and treatment of electrolyte imbalances Administration of supplemental O2 or mechanical ventilation should the respiratory system begin to fail

    65. Quick Metabolic Review: Metabolic disturbances indicate an excess/deficit in HCO3- (<22mEq/L or >26mEq/L Reabsorption of filtered HCO3- & generation of new HCO3- occurs in the kidneys Respiratory system is the compensatory mechanism ALWAYS treat the primary disturbance

    66. Respiratory Disturbances: Alkalosis: low PaCO2 (<35 mmHg) Caused by HYPERventilation of any etiology (hypoxemia, anxiety, PE, pulmonary edema, pregnancy, excessive ventilation w/ mechanical ventilator, etc.) Acidosis: elevated PaCO2 (>45 mmHg) Caused by HYPOventilation of any etiology (sleep apnea, oversedation, head trauma, drug overdose, pneumothorax, etc.) Compensation is metabolic-related

    67. Respiratory Alkalosis: Characterized by an initial decrease in plasma PaCO2 (<35 mmHg) or hypocapnia Produces elevation of pH (>7.45) w/ a subsequent decrease in HCO3- (<22 mEq/L) Caused by hyperventilation or RR in excess of what is necessary to maintain normal PaCO2 levels

    69. Respiratory Alkalosis Manifestations: S/sx are associated w/ hyperexcitiability of the nervous system & decreases in cerebral blood flow Increases protein binding of EC Ca+, reducing ionized Ca+ levels causing neuromuscular excitability Lightheadedness, dizziness, tingling, numbness of fingers & toes, dyspnea, air hunger, palpitations & panic may result

    70. Treatment of Respiratory Alkalosis: Always treat the underlying/initial cause Supplemental O2 or mechanical ventilation may be required Pts may require reassurance, rebreathing into a paper bag (for hyperventilation) during symptomatic attacks, & attention/treatment of psychological stresses.

    71. Respiratory Acidosis: Occurs w/ impairment in alveolar ventilation causing increased PaCO2 (>45 mmHg), or hypercapnia, along w/ decreased pH (<7.35) Associated w/ rapid rise in arterial PaCO2 w/ minimal increase in HCO3- & large decreases in pH Causes include decreased respiratory drive, lung disease, or disorders of CW/respiratory muscles

    73. Respiratory Acidosis Manifestations: Elevated CO2 levels cause cerebral vasodilation resulting in HA, blurred vision, irritability, muscle twitching & psychological disturbances If acidosis is prolonged & severe, increased CSF pressure & papilledema may result Impaired LOC, lethargy/coma, paralysis of extremities, warm/flushed skin, weakness & tachycardia may also result

    74. Treatment of Respiratory Acidosis: Treatment is directed toward improving ventilation; mechanical ventilation may be necessary Treat the underlying cause Drug OD, lung disease, chest trauma/injury, weakness of respiratory muscles, airway obstruction, etc. Eliminate excess CO2

    75. Quick Respiratory Review: Caused by either low or elevated PaCO2 levels (<35 or >45mmHg) Watch for HYPOventilation or HYPERventilation; mechanical ventilation may be required Kidneys will compensate by conserving HCO3- & H+ REMEMBER to treat the primary disturbance/underlying cause of the imbalance

    76. Compensatory Mechanisms: Adjust the pH toward a more normal level w/ out correcting the underlying cause Respiratory compensation by increasing/decreasing ventilation is rapid, but the stimulus is lost as pH returns toward normal Kidney compensation by conservation of HCO3- & H+ is more efficient, but takes longer to recruit

    77. Metabolic Compensation: Results in pulmonary compensation beginning rapidly but taking time to become maximal Compensation for Metabolic Alkalosis: HYPOventilation (limited by degree of rise in PaCO2) Compensation for Metabolic Acidosis: HYPERventilation to decrease PaCO2 Begins in 1-2hrs, maximal in 12-24 hrs

    79. Respiratory Compensation: Results in renal compensation which takes days to become maximal Compensation for Respiratory Alkalosis: Kidneys excrete HCO3- Compensation for Respiratory Acidosis: Kidneys excrete more acid Kidneys increase HCO3- reabsorption


    82. Normal Arterial Blood Gas (ABG) Lab Values: Arterial pH: 7.35 7.45 HCO3-: 22 26 mEq/L PaCO2: 35 45 mmHg TCO2: 23 27 mmol/L PaO2: 80 100 mmHg SaO2: 95% or greater (pulse ox) Base Excess: -2 to +2 Anion Gap: 7 14

    83. Acid-Base pH and HCO3- Arterial pH of ECF is 7.40 Acidemia: blood pH < 7.35 (increase in H+) Alkalemia: blood pH >7.45 (decrease in H+) If HCO3- levels are the primary disturbance, the problem is metabolic Acidosis: loss of nonvolatile acid & gain of HCO3- Alkalosis: excess H+ (kidneys unable to excrete) & HCO3- loss exceeds capacity of kidneys to regenerate

    84. Acid-Base PCO2, TCO2 & PO2 If PCO2 is the primary disturbance, the problem is respiratory; its a reflection of alveolar ventilation (lungs) PCO2 increase: hypoventilation present PCO2 decrease: hyperventilation present TCO2 refers to total CO2 content in the blood, including CO2 present in HCO3- >70% of CO2 in the blood is in the form of HCO3- PO2 also important in assessing respiratory function

    85. Base Excess or Deficit: Measures the level of all buffering systems in the body hemoglobin, protein, phosphate & HCO3- The amount of fixed acid or base that must be added to a blood sample to reach a pH of 7.40 Its a measurement of HCO3- excess or deficit

    86. Anion Gap: The difference between plasma concentration of Na+ & the sum of measured anions (Cl- & HCO3-) Representative of the concentration of unmeasured anions (phosphates, sulfates, organic acids & proteins) Anion gap of urine can also be measured via the cations Na+ & K+, & the anion Cl- to give an estimate of NH4+ excretion

    87. Anion Gap The anion gap is increased in conditions such as lactic acidosis, and DKA that result from elevated levels of metabolic acids (metabolic acidosis) A low anion gap occurs in conditions that cause a fall in unmeasured anions (primarily albumin) OR a rise in unmeasured cations A rise in unmeasured cations is seen in hyperkalemia, hypercalcemia, hyper-magnesemia, lithium intoxication or multiple myeloma

    89. Sodium Chloride-Bicarbonate Exchange System and pH: The reabsorption of Na+ by the kidneys requires an accompanying anion - 2 major anions in ECF are Cl- and HCO3- One way the kidneys regulate pH of ECF is by conserving or eliminating HCO3- ions in which a shuffle of anions is often necessary Cl- is the most abundant in the ECF & can substitute for HCO3- when such a shift is needed.

    90. Acid-Base Interpretation Practice: Please use the following key to interpret the following ABG readings. Click on the blue boxes to reveal the answers Use the button to return to the key at any time Or use the Back to Key button at the bottom left of the screen

    91. Acid-Base w/o Compensation:

    92. Interpretation Practice: pH: 7.31 Right! PaCO2: 48 Try Again HCO3-: 24 Try Again pH: 7.47 Try Again PaCO2 : 45 Right! HCO3- : 33 Try Again

    93. Interpretation Practice: pH: 7.20 Try Again PaCO2: 36 Try Again HCO3-: 14 Right! pH: 7.50 Try Again PaCO2 : 29 Right! HCO3- -: 22 Try Again

    94. Acid-Base Fully Compensated:

    95. Interpretation Practice: pH: 7.36 Try Again PaCO2: 56 Try Again HCO3-: 31.4 Right! pH: 7.43 Right! PaCO2 : 32 Try Again HCO3: 21 Try Again

    96. Acid-Base Partially Compensated:

    97. Interpretation Practice: pH: 7.47 Right! PaCO2: 49 Try Again HCO3-: 33.1 Try Again pH: 7.33 Try Again PaCO2 : 31 Try Again HCO3- : 16 Right!

    98. Case Study 1: Mrs. D is admitted to the ICU. She has missed her last 3 dialysis treatments. Her ABG reveals the following: pH: 7.32 Low, WNL = 7.35-7.45 PaCO2: 32 Low, WNL = 35-45mmHg HCO3-: 18 Low, WNL = 22-26mEq/L Assess the pH, PaCO2 & HCO3-. Are the values high, low or WNL?

    99. Case Study 1 Continued: What is Mrs. Ds acid-base imbalance? Right! Try Again Remember the difference between full & partial compensation. Go back & use the appropriate key if necessary.

    100. Case Study 2: Mr. M is a pt w/ chronic COPD. He is admitted to your unit pre-operatively. His admission lab work is as follows: pH: 7.35 WNL = 7.35-7.45 PaCO2: 52 High, WNL = 35-45mmHg HCO3-: 50 High, WNL = 22-26mEq/L Assess the above labs. Are they abnormal or WNL?

    101. Case Study 2 Continued: What is Mr. Ms acid-base disturbance? Try Again Right! Think about appropriate interventions- if the problem is metabolic, the respiratory system compensates & vice versa

    102. Case Study 3: Miss L is a 32 year old female admitted w/ decreased LOC after c/o the worst HA of her life. She is lethargic, but arouseable; diagnosed w/ a SAH. Her ABG reads: pH: 7.48 High; WNL = 7.35-7.45 PaCO2: 32 Low; WNL = 35-45mmHg HCO3-: 25 High; WNL = 22-26mEq/L What is the significance of her ABG values?

    103. Case Study 3 Continued: What is Miss Ls imbalance? Right! Try Again Great Job! Youve reached the end of the tutorial & I hope you found it helpful. Thank you!

    104. REFERENCES: Retrieved 3/5/09. Porth, C.M. (2005). Pathophysiology Concepts of Altered Health States (7th ed.). Philadelphia: Lippincott Williams & Wilkins. Retrieved 3/6/09. and Base.ppt#1. Retrieved 3/6/09. Retrieved 3/6/09. Retrieved 3/6/09.

    105. REFERENCES Retrieved 3/10/09. Alspach, J.G. (1998). American Association of Critical-Care Nurses Core Curriculum for Critical Care Nursing (5th ed.). Philadelphia: Saunders. Retrieved 4/14/09. Acid-Base Balance & Oxygenation Power Point. (2007). Milwaukee: Froedtert Lutheran Memorial Hospital Critical Care Class.