Acid-Base Balance Interactive TutorialEmily PhillipsMSN 621Spring 2009E-mail: emmalemmaRN@hotmail.comAll images imported from Microsoft Clipart & Yahoo Image gallery

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

Objectives:Define acid base balance/imbalanceExplain the pathophysiology of organs involved in acid base balance/imbalanceIdentify normal/abnormal and compensated/uncompensated lab valuesExplain symptoms related to acid base imbalances and compensated vs. uncompensatedAppropriate interventions and expected outcomes

Main Menu:Acid-Base PretestThe Buffer SystemsABG Interpretation& Case StudiesAcid-Base Review testDiagnostic Lab ValuesMetabolic DistubancesRespiratory DisturbancesAcid-Base Compensation

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

7.38 7.467.40 7.527.35 7.45

Incorrect

Close but not quite try again.Next QuestionPrevious Question

Incorrect

Close, but no cigar 7.52 would indicate alkalosis.Next QuestionPrevious Question

Correct!

This is the correct parameters for arterial blood pH with the extracellular fluid in the middle at 7.40 well done!Next QuestionPrevious Question

Acid-Base Pretest:What 2 extracellular substances work together to regulate pH?Sodium bicarbonate& carbonic acidCarbonic acid& bicarbonateAcetic acid & carbonic acid

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 pHNext QuestionPrevious Question

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.Next QuestionPrevious Question

Incorrect

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

Acid-Base Pretest:Characterize an acid & a base based on the choices below.Acids release hydrogen (H+) ions& bases accept H+ ions.Acids accept H+ ions & bases release H+ ionsBoth acids & bases can release& accept H+ ions

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.Next QuestionPrevious Question

IncorrectThink 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?Next QuestionPrevious Question

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?Next QuestionPrevious Question

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? HCO3-H2CO3H+

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 againNext QuestionPrevious Question

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.Next QuestionPrevious Question

Correct!

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

Acid-Base Pretest:What are the two systems in the body that work to regulate pH in acid-base balance & which one works fastest?The Respiratory & Renal systemsRenalThe Respiratory & Renal systemsRespiratoryThe Renal & GI systemsRenal

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.End PretestPrevious Question

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).End PretestPrevious Question

Incorrect

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

Acid-Base Balance:Homeostasis of bodily fluids at a normal arterial blood pHpH 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

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

The Body and pH:Homeostasis of pH is controlled through extracellular & intracellular buffering systemsRespiratory: eliminate CO2Renal: conserve HCO3- and eliminate H+ ionsElectrolytes: composition of extracellular (ECF) & intracellular fluids (ICF)- ECF is maintained at 7.40

Protein Buffer systemHCO3-BuffersystemK+ - H+Exchange

Protein Buffer Systems:Largest buffer system in the bodyAmphoteric: can function as acids or basesContain several ionizable groups able to bind or release H+Largely located in cells; H+ & CO2 diffuse across cell membranes for buffering by Albumin & plasma globulinsPrevious Slide

Bicarbonate Buffer System:Uses NaHCO3 as its weak base & H2CO3 as its weak acidThe HCO3-/CO2 buffer system can readily add or remove components from the bodyAn ample supply of CO2 provided via metabolism, replaces H2CO3 lost when excess base is addedIn turn, the kidneys conserve or form new HCO3- in the presence of excess acid & excrete HCO3- in the presence of excess basePrevious Slide

Plasma Potassium-Hydrogen Exchange:Both positively charged ions move freely between IC & EC compartmentsDecreases in plasma K+ cause movement of K+ from ICF to ECF & movement of H+ from ECF to ICFWith 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

Previous Slide

Quick Review: Click the BoxesA donator of H+ ionsAn acceptor of H+ w/ pH 7.0

Regulated by EC Controlled by ECH2CO3 & HCO3-& IC buffer systems

Eliminates CO2Conserves HCO3-Eliminates H+ ions

An Acid is:A Base is:pH is:Respiratory System: pH is:Renal System:

Respiratory Control Mechanisms:Works within minutes to control pH; maximal in 12-24 hoursOnly about 50-75% effective in returning pH to normalExcess CO2 & H+ in the blood act directly on respiratory centers in the brainCO2 readily crosses blood-brain barrier reacting w/ H2O to form H2CO3H2CO3 splits into H+ & HCO3- & the H+ stimulates an increase or decrease in respirations

Renal Control Mechanisms:Dont work as fast as the respiratory system; function for days to restore pH to, or close to, normalRegulate 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

H+ elimination & HCO3-conservation

H+ Elimination & HCO3- Conservation:

Begins with Na+/H+ transport systemH+ secreted in tubular fluid & Na+ reabsorbed in tubular cellSecreted H+ couples w/ filtered HCO3- & CO2 & H2O resultH2O secreted in urine & CO2 diffuses into tubular cell combining w/ H2O to form HCO3- via a carbonic anhydrase-mediated reactionHCO3- is reabsorbed into the blood along w/ Na+, & newly generated H+ is secreted into tubular fluid beginning a new cycle Previous Slide

Mechanisms of Acid-Base Balance:The ratio of HCO3- base to the volatile H2CO3 determines pHConcentrations of volatile H2CO3 are regulated by changing the rate & depth of respirationPlasma 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 4.5Phosphate Buffer systemAmmoniaBuffer system

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

The Ammonia Buffer System:This buffer system is the more complex of the twoThe 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 tubules2) recycling & reabsorption of NH3 in the kidneys medulla, &3) buffering of H+ ions by NH3 in the collecting tubules.Previous Slide

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

Incorrect

Actually the kidneys work to regulate pH through the regeneration or reabsorption of HCO3- & excretion of H+Next QuestionPrevious Question

Correct!

Youre absolutely right! The kidneys actually do the opposite in order to regulate pH. Nicely done.Next QuestionPrevious Question

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.

TRUEFALSE

Correct!

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

Incorrect

The correct answer is TRUE. Please review the Respiratory Control Mechanisms slide as needed.Next QuestionPrevious Question

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. TRUEFALSE

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-.

Next QuestionPrevious Question

Incorrect

Please review Mechanisms of Acid-Base balance if needed. Next QuestionPrevious Question

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

Incorrect

The answer is false. Its the ratio of HCO3- to volatile H2CO3 that determines pH.Next QuestionPrevious Question

Correct!

Youre right, the answer is false. REMEMBER: concentrations of volatile H2CO3 are regulated by changing the rate & depth of respirations.Next QuestionPrevious Question

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

Correct!

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

Incorrect

Sorry, but the correct answer is true.End Post testPrevious Question

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- (

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 kidneysProximal tubule reabsorbs 99.9% of filtered HCO3-; excess is excreted in urine

Metabolic Alkalosis Manifestations:Signs & symptoms (s/sx) of volume depletion or hypokalemiaCompensatory hypoventilation, hypoxemia & respiratory acidosisNeurological s/sx may include mental confusion, hyperactive reflexes, tetany and carpopedal spasmSevere alkalosis (>7.55) causes respiratory failure, dysrhthmias, seizures & coma

Treatment of Metabolic Alkalosis:Correct the cause of the imbalanceMay include KCl supplementation for K+/Cl- deficitsFluid replacement with 0.9 normal saline or 0.45 normal saline for s/sx of volume depletionIntubation & mechanical ventilation may be required in the presence of respiratory failure

Metabolic Acidosis:Primary deficit in base HCO3- (

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

Treatment of Metabolic Acidosis:Treat the condition that first caused the imbalanceNaHCO3 infusion for HCO3-

Quick Metabolic Review: Metabolic disturbances indicate an excess/deficit in HCO3- (26mEq/LReabsorption of filtered HCO3- & generation of new HCO3- occurs in the kidneysRespiratory system is the compensatory mechanismALWAYS treat the primary disturbance

Respiratory Disturbances:Alkalosis: low PaCO2 (45 mmHg)Caused by HYPOventilation of any etiology (sleep apnea, oversedation, head trauma, drug overdose, pneumothorax, etc.)Compensation is metabolic-related

Respiratory Alkalosis:Characterized by an initial decrease in plasma PaCO2 (7.45) w/ a subsequent decrease in HCO3- (

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

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

Respiratory Acidosis:Occurs w/ impairment in alveolar ventilation causing increased PaCO2 (>45 mmHg), or hypercapnia, along w/ decreased pH (

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

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

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

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

Metabolic Compensation:Results in pulmonary compensation beginning rapidly but taking time to become maximalCompensation 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

Respiratory Compensation:Results in renal compensation which takes days to become maximalCompensation for Respiratory Alkalosis:Kidneys excrete HCO3-Compensation for Respiratory Acidosis:Kidneys excrete more acidKidneys increase HCO3- reabsorption

DIAGNOSTIC LAB VALUES & INTERPRETATION

Normal Arterial Blood Gas (ABG)Lab Values:Arterial pH: 7.35 7.45HCO3-: 22 26 mEq/LPaCO2: 35 45 mmHgTCO2: 23 27 mmol/LPaO2: 80 100 mmHgSaO2: 95% or greater (pulse ox)Base Excess: -2 to +2Anion Gap: 7 14

Acid-Base pH and HCO3-Arterial pH of ECF is 7.40Acidemia: 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 metabolicAcidosis: loss of nonvolatile acid & gain of HCO3- Alkalosis: excess H+ (kidneys unable to excrete) & HCO3- loss exceeds capacity of kidneys to regenerate

Acid-Base PCO2, TCO2 & PO2If PCO2 is the primary disturbance, the problem is respiratory; its a reflection of alveolar ventilation (lungs)PCO2 increase: hypoventilation presentPCO2 decrease: hyperventilation presentTCO2 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

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 7.40Its a measurement of HCO3- excess or deficit

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

Anion GapThe 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 cationsA rise in unmeasured cations is seen in hyperkalemia, hypercalcemia, hyper-magnesemia, lithium intoxication or multiple myeloma

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 necessaryCl- is the most abundant in the ECF & can substitute for HCO3- when such a shift is needed.

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

Acid-Base w/o Compensation:

Parameters: pH PaCO2 HCO3-Metabolic Alkalosis Normal MetabolicAcidosis NormalRespiratoryAlkalosis NormalRespiratoryAcidosis Normal

Interpretation Practice: pH: 7.31 Right!PaCO2: 48 Try AgainHCO3-: 24 Try Again

pH: 7.47 Try AgainPaCO2 : 45 Right!HCO3- : 33 Try Again

Back to KeyResp. AcidosisResp. AlkalosisMetabolic AcidosisResp. AlkalosisMetabolic AlkalosisMetabolic Acidosis

Interpretation Practice:pH: 7.20Try AgainPaCO2: 36Try AgainHCO3-: 14 Right!

pH: 7.50 Try AgainPaCO2 : 29 Right!HCO3- -: 22 Try AgainMetabolic AlkalosisResp. AcidosisMetabolic AcidosisMetabolic AlkalosisResp. AlkalosisResp. AcidosisBack to Key

Acid-Base Fully Compensated:

Parameters: pH PaCO2 HCO3-Metabolic AlkalosisNormal>7.40MetabolicAcidosisNormal7.40RespiratoryAcidosisNormal

Interpretation Practice:pH: 7.36Try AgainPaCO2: 56Try AgainHCO3-: 31.4 Right!

pH: 7.43 Right!PaCO2 : 32Try AgainHCO3: 21Try AgainCompensated Resp. AlkalosisCompensated Metabolic AcidosisCompensated Resp. AcidosisCompensated Resp. AlkalosisCompensated Metabolic AlkalosisCompensated Metabolic AcidosisBack to Key

Acid-Base Partially Compensated:

Parameters: pH PaCO2 HCO3-Metabolic AlkalosisMetabolicAcidosisRespiratoryAlkalosisRespiratoryAcidosis

Interpretation Practice:pH: 7.47 Right!PaCO2: 49Try AgainHCO3-: 33.1Try Again

pH: 7.33Try AgainPaCO2 : 31Try AgainHCO3- : 16 Right!Partially Compensated Metabolic AlkalosisPartially Compensated Resp. AlkalosisPartially Compensated Metabolic AcidosisPartially Compensated Metabolic AlkalosisPartially Compensated Resp. AcidosisPartially Compensated Metabolic AcidosisBack to Key

Case Study 1:Mrs. D is admitted to the ICU. She has missed her last 3 dialysis treatments. Her ABG reveals the following:pH: 7.32Low, WNL = 7.35-7.45PaCO2: 32Low, WNL = 35-45mmHgHCO3-: 18Low, WNL = 22-26mEq/L

Assess the pH, PaCO2 & HCO3-. Are the values high, low or WNL?The pH is:The PaCO2 is:The HCO3- is:

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.Partially Compensated Metabolic AcidosisFully Compensated Resp. Acidosis

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: 7.35WNL = 7.35-7.45PaCO2: 52High, WNL = 35-45mmHgHCO3-: 50High, WNL = 22-26mEq/L

Assess the above labs. Are they abnormal or WNL?The pH is:The PaCO2 is:The HCO3- is:

Case Study 2 Continued:What is Mr. Ms acid-base disturbance?

Try AgainRight!

Think about appropriate interventions- if the problem is metabolic, the respiratory system compensates & vice versa

Fully Compensated Metabolic AcidosisFully Compensated Resp. Acidosis

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: 7.48High; WNL = 7.35-7.45PaCO2: 32Low; WNL = 35-45mmHgHCO3-: 25High; WNL = 22-26mEq/LWhat is the significance of her ABG values?The pH is:The PaCO2 is:The HCO3- is:

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!Resp. AlkalosisMetabolic Alkalosis

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Porth, C.M. (2005). Pathophysiology Concepts of Altered Health States (7th ed.). Philadelphia: Lippincott Williams & Wilkins.

http://en.wikipedia.org/wiki/Dissociation_(chemistry). Retrieved 3/6/09.

http://www.clt.astate.edu/mgilmore/pathophysiology/Acid and Base.ppt#1. Retrieved 3/6/09.

http://www.uhmc.sunysb.edu/internalmed/nephro/webpages/Part_E.htm.Retrieved 3/6/09.

http://medical-dictionary.thefreedictionary.com/Volatile+acid. Retrieved 3/6/09.

REFERENCEShttp://wiki.answers.com/Q/How_does_the_phosphate_buffer_system_help_in_maintaining_the_ph_of_our_body. Retrieved 3/10/09.

Alspach, J.G. (1998). American Association of Critical-Care Nurses Core Curriculum for Critical Care Nursing (5th ed.). Philadelphia: Saunders.

http://medical-dictionary.thefreedictionary.com. Retrieved 4/14/09.

Acid-Base Balance & Oxygenation Power Point. (2007). Milwaukee: Froedtert Lutheran Memorial Hospital Critical Care Class.