Acid and Base Balance and Imbalance

1Blood Gases, pH and Buffer SystemsBLOOD GASES2Oxygen and Gas Exchange3Oxygen and Gas Exchange (contd)4Oxygen and Gas Exchange (contd)5Oxygen and Gas Exchange (contd)6Oxygen and Gas Exchange (contd)7Measurement8Measurement (contd)9Measurement (contd)10Measurement (contd)11Measurement (contd)12Measurement (contd)Calculated ParametersHCO2-: based on Henderson-Hasselbalch equation; can be calculated when pH & PCO2 are knownCarbonic acid concentration: can be calculated using solubility coefficient of CO2 in plasma at 37CTotal carbon dioxide content: bicarbonate plus dissolved CO2 plus associated CO2 with proteinsCorrection for TemperatureBy convention, pH, PCO2, & PO2 are all measured at 37C.If patients body temperature differs from 37C, blood gas instrument can correct values; results at 37C should be reported, too, however, for reference.13Quality AssurancePreanalytic ConsiderationsProper patient identificationCorrect labeling of specimen & accurate info providedExperienced, knowledgeable personnelProper collection & handling of blood gas specimensTransport timeAnalytic Assessments: QC & Proficiency TestingSurrogate liquid control materials, tonometry, duplicate assays, non-surrogate QCInterpretation of Results14The use of arterial samples for pH and blood gas studies is recommended.However, peripheral venous samples can be used if pulmonary function or O2 transport is not being assessed.

Sources of error in the collection and handling of blood gas specimens include:the collection deviceform and concentration of heparin used for anticoagulationspeed of syringe fillingmaintenance of the anaerobic environmentmixing of the sample to ensure dissolution and distribution of the heparin, and transportstorage time before analysisACID AND BASES17pH ReviewpH = - log [H+]H+ is really a protonRange is from 0 - 14If [H+] is high, the solution is acidic; pH < 7If [H+] is low, the solution is basic or alkaline ; pH > 71819

20

2122The Body and pH232425

Small changes in pH can produce major disturbancesMost enzymes function only with narrow pH rangesAcid-base balance can also affect electrolytes (Na+, K+, Cl-)Can also affect hormones26The body produces more acids than basesAcids take in with foodsAcids produced by metabolism of lipids and proteinsCellular metabolism produces CO2.CO2 + H20 H2CO3 H+ + HCO3-27Regulation of AcidBase Balance: Lungs and Kidneys

Control of Acids-Base Balance29Control of Acids30Control of Acids31Bicarbonate-Carbonic AcidControl of Acids

33Control of Acids

34

Control of Acids

35Control of Acids36Rates of correction3738

39

Homeostatic Regulators of [H + ]

Factors Effecting BalanceACID-BASE IMBALANCE43Acid-Base Imbalances44Four Basic Types of ImbalanceCompensation46Acidosis47Alkalosis4849

Respiratory Acidosis50Respiratory Acidosis51Respiratory Acidosis52Compensation for Respiratory Acidosis53Signs and Symptoms of Respiratory Acidosis54Treatment of Respiratory Acidosis5556

Respiratory Alkalosis57Respiratory AlkalosisRespiratory Alkalosis59Signs and Symptoms of Respiratory Alkalosis60Tachypnea (or "tachypnoea") (Greek: "rapid breathing") is the condition of rapid breathing.60Compensation of Respiratory Alkalosis61Treatment of Respiratory Alkalosis6263

Metabolic Acidosis646566Symptoms of Metabolic Acidosis67Compensation for Metabolic Acidosis68Treatment of Metabolic Acidosis6970

Metabolic Alkalosis7172Compensation for Metabolic Alkalosis73Symptoms of Metabolic Alkalosis74Treatment of Metabolic Alkalosis7576

Diagnosis of Acid-Base Imbalances78INTERPRETATION OF BLOOD GASES

Step 1: Determine if the numbers fit. The right side of the equation should be within about 10% of the left side. If the numbers do not fit, you need to obtain another ABG

INTERPRETATION OF BLOOD GASESStep 2: determine if an acidemia (pH 7.44) is present.

Step 3: Identify the primary disturbance as metabolic or respiratory.83 In other words, identify which component, respiratory or metabolic, is altered in the same direction as the pH abnormality.

If both components act in the same direction (eg, both respiratory [pCO2 > 44 mm Hg] and metabolic [HCO3 - 12 mmol/L; caused by a decrease in [HCO3 -] balanced by an increase in an unmeasured acid ion from either endogenous production or exogenous ingestion (normochloremic acidosis).

Non anion Gap Acidosis:Anion gap = 8-12 mmol/L; caused by a decrease in [HCO3 -] balanced by an increase in chloride (hyperchloremic acidosis). Renal tubular acidosis is a type of non gap acidosis The anion gap is helpful in identifying metabolic gap acidosis, non gap acidosis, mixed metabolic gap and non gap acidosis. If an elevated anion gap is present, a closer look at the anion gap and the bicarbonate helps differentiate among(a) a pure metabolic gap acidosis(b) a metabolic non gap acidosis(c) mixed metabolic gap and non gap acidosis, and (d) a metabolic gap acidosis and metabolic alkalosis.

Compensations for Metabolic DisturbancesCompensations for Respiratory AcidosisCompensations for Respiratory AlkalosisClinical Example 172 y/o male, COPD with acute exacerbationUnder O2 2L/minpH 7.44 PCO2 54 PO2 60HCO3 36Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONMetabolic alkalosis with respiratory compensationMixed respiratory acidosis96Clinical Example 230 y/o male, sudden onset dyspneaRoom airpH 7.33 PCO2 24 PO2 111HCO3 12

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONMetabolic acidosisRespiratory compensationNormal A-a O2 gradientO2: hyperventilation

98Clinical Example 370 y/o male, acute hemoptysis and dyspneaRoom airpH 7.50 PCO2 31 PO2 88HCO3 24

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONRespiratory alkalosisNot been renal compensated yetNormal PO2, but A-a O2 gradient

100Clinical Example 418 y/o female, chest tightness and dyspnea for 4 hrsRR 28/min, distressed, widespread wheezingO2 mask 6L/minpH 7.31 PCO2 49 PO2 115HCO3 26

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONRespiratory acidosisNormal bicarbonate acuteMay have problems with oxygenation

102Clinical Example 537 y/o female, mild asthma historyWheezes for 3 weeks, increasing chest tightness and dyspnea for 24 hrs, call for ambulance with Oxygen useRR 18/min, anxious and distressedRoom airpH 7.37 PCO2 43 PO2 97HCO3 27

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONNormal?r/o CO2 retentionLow A-a O2: Oxygen use in the ambulance

104Clinical Example 619 y/o male, Duchenne muscular dystrophy on wheelchair for 7 yrsNo previous respiratory problems but frequent UTIRoom airpH 7.21 PCO2 81 PO2 44HCO3 36

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONRespiratory acidosisMetabolic compensationNormal A-a O2 pure ventilatory failure

106Clinical Example 757 y/o male, smoker, one week URI then 36 hrs productive cough, fever and dyspneaRR 36/min, distressed, CXR: RLL pneumoniapH 7.33 PCO2 27 PO2 51HCO3 222L/min

pH 7.34 PCO2 32 PO2 58HCO3 24 10L/min mask

Ref. rangepH7.35-7.45pCO235-45 mm HgpHCO32-26 mEq/LINTERPRETATIONEarly metabolic acidosisSevere hypoxemic respiratory failureIntra-pulmonary shunting

108