1、1Acid and Base Balance and Imbalance2pH Review pH=-log H+H+is really a proton Range is from 0-14 If H+is high,the solution is acidic;pH 73 Acids are H+donors.Bases are H+acceptors,or give up OH-in solution.Acids and bases can be:Strong dissociate completely in solution HCl,NaOHWeak dissociate only p
2、artially in solution Lactic acid,carbonic acid4The Body and pH Homeostasis of pH is tightly controlled Extracellular fluid=7.4 Blood=7.35 7.45 8.0 death occurs Acidosis(acidemia)below 7.35 Alkalosis(alkalemia)above 7.4556Small changes in pH can produce major disturbances Most enzymes function only w
3、ith narrow pH ranges Acid-base balance can also affect electrolytes(Na+,K+,Cl-)Can also affect hormones7The body produces more acids than bases Acids take in with foods Acids produced by metabolism of lipids and proteins Cellular metabolism produces CO2.CO2 +H20 H2CO3 H+HCO3-8Control of Acids1.Buffe
4、r systemsTake up H+or release H+as conditions changeBuffer pairs weak acid and a baseExchange a strong acid or base for a weak oneResults in a much smaller pH change9Bicarbonate buffer Sodium Bicarbonate(NaHCO3)and carbonic acid(H2CO3)Maintain a 20:1 ratio:HCO3-:H2CO3HCl+NaHCO3 H2CO3 +NaClNaOH+H2CO3
5、 NaHCO3 +H2O10Phosphate buffer Major intracellular buffer H+HPO42-H2PO4-OH-+H2PO4-H2O+H2PO42-11Protein Buffers Includes hemoglobin,work in blood and ISF Carboxyl group gives up H+Amino Group accepts H+Side chains that can buffer H+are present on 27 amino acids.122.Respiratory mechanisms Exhalation o
6、f carbon dioxide Powerful,but only works with volatile acids Doesnt affect fixed acids like lactic acid CO2 +H20 H2CO3 H+HCO3-Body pH can be adjusted by changing rate and depth of breathing133.Kidney excretion Can eliminate large amounts of acid Can also excrete base Can conserve and produce bicarb
7、ions Most effective regulator of pH If kidneys fail,pH balance fails14Rates of correction Buffers function almost instantaneously Respiratory mechanisms take several minutes to hours Renal mechanisms may take several hours to days151617Acid-Base Imbalances pH 7.45 alkalosis The body response to acid
8、-base imbalance is called compensation May be complete if brought back within normal limits Partial compensation if range is still outside norms.18Compensation If underlying problem is metabolic,hyperventilation or hypoventilation can help:respiratory compensation.If problem is respiratory,renal mec
9、hanisms can bring about metabolic compensation.19Acidosis Principal effect of acidosis is depression of the CNS through in synaptic transmission.Generalized weakness Deranged CNS function the greatest threat Severe acidosis causes Disorientationcoma death20Alkalosis Alkalosis causes over excitabilit
10、y of the central and peripheral nervous systems.Numbness Lightheadedness It can cause:Nervousness muscle spasms or tetany Convulsions Loss of consciousness Death2122Respiratory Acidosis Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg.Hypercapnia high levels of CO2 in blood Chronic
11、conditions:Depression of respiratory center in brain that controls breathing rate drugs or head trauma Paralysis of respiratory or chest muscles Emphysema23Respiratory Acidosis Acute conditons:Adult Respiratory Distress Syndrome Pulmonary edema Pneumothorax24Compensation for Respiratory Acidosis Kid
12、neys eliminate hydrogen ion and retain bicarbonate ion25Signs and Symptoms of Respiratory Acidosis Breathlessness Restlessness Lethargy and disorientation Tremors,convulsions,coma Respiratory rate rapid,then gradually depressed Skin warm and flushed due to vasodilation caused by excess CO226Treatmen
13、t of Respiratory Acidosis Restore ventilation IV lactate solution Treat underlying dysfunction or disease27Respiratory Alkalosis Carbonic acid deficit pCO2 less than 35 mm Hg(hypocapnea)Most common acid-base imbalance Primary cause is hyperventilation28Respiratory Alkalosis Conditions that stimulate
14、 respiratory center:Oxygen deficiency at high altitudes Pulmonary disease and Congestive heart failure caused by hypoxia Acute anxiety Fever,anemia Early salicylate intoxication Cirrhosis Gram-negative sepsis29Compensation of Respiratory Alkalosis Kidneys conserve hydrogen ion Excrete bicarbonate io
15、n30Treatment of Respiratory Alkalosis Treat underlying cause Breathe into a paper bag IV Chloride containing solution Cl-ions replace lost bicarbonate ions31Metabolic Acidosis Bicarbonate deficit -blood concentrations of bicarb drop below 22mEq/L Causes:Loss of bicarbonate through diarrhea or renal
16、dysfunction Accumulation of acids(lactic acid or ketones)Failure of kidneys to excrete H+32Symptoms of Metabolic Acidosis Headache,lethargy Nausea,vomiting,diarrhea Coma Death33Compensation for Metabolic Acidosis Increased ventilation Renal excretion of hydrogen ions if possible K+exchanges with exc
17、ess H+in ECF(H+into cells,K+out of cells)34Treatment of Metabolic Acidosis IV lactate solution 35Metabolic Alkalosis Bicarbonate excess-concentration in blood is greater than 26 mEq/L Causes:Excess vomiting=loss of stomach acid Excessive use of alkaline drugs Certain diuretics Endocrine disorders He
18、avy ingestion of antacids Severe dehydration36Compensation for Metabolic Alkalosis Alkalosis most commonly occurs with renal dysfunction,so cant count on kidneys Respiratory compensation difficult hypoventilation limited by hypoxia37Symptoms of Metabolic Alkalosis Respiration slow and shallow Hypera
19、ctive reflexes;tetany Often related to depletion of electrolytes Atrial tachycardia Dysrhythmias38Treatment of Metabolic Alkalosis Electrolytes to replace those lost IV chloride containing solution Treat underlying disorder39Diagnosis of Acid-Base Imbalances1.Note whether the pH is low(acidosis)or h
20、igh(alkalosis)2.Decide which value,pCO2 or HCO3-,is outside the normal range and could be the cause of the problem.If the cause is a change in pCO2,the problem is respiratory.If the cause is HCO3-the problem is metabolic.403.Look at the value that doesnt correspond to the observed pH change.If it is
21、 inside the normal range,there is no compensation occurring.If it is outside the normal range,the body is partially compensating for the problem.41Example A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago.The lab reports the following values from an arteria
22、l blood sample:pH 7.3 HCO3-=20 mEq/L(22-26)pCO2=32 mm Hg (35-45)42Diagnosis Metabolic acidosis With compensation43BloodSodium 135-145 mEq/LPotassium 3.5-5.0 mEqlLChloride 95-105 mEq/LBicarbonate 24-26 mEq/LOsmolality 280-295 mEqLOsmolal gap 10 mOsm/LAnion gap 9-16 mEqlLUrea nitrogen 10-20 mgldlArter
23、ial blood gas analysispH 7.35-7.45PCOZ35-45 mm HgPoz 90-100 mm Hg(declines with age)4445DisorderExpected CompensationMetabolic acidosisPCO2=1.5 HCO3-+8 2Metabolic alkalosisPCO2 increases by 7mmHg for each 10mEq/L increase in the serum HCO3-Respiratory acidosis AcuteHCO3-increases by 1 for each 10mmH
24、g increase in the PCO2 ChronicHCO3-increases by 3.5 for each 10mmHg increase in the PCO2Respiratory alkalosis AcuteHCO3-falls by 2 for each 10mmHg decrease in the PCO2 ChronicHCO3-falls by 4 for each 10mmHg decrease in the PCO246FormulasWomen:Total body water(TBW)=.5 X Body weight(kg)Men:Total body
25、water(TBW)=.6 X Body weight(kg)Osmolal gap=OSM,measured)-OSM,caculatcd)Anion gap(AG)=UA-UC=Na-(CI-+HCO,-)OSM GAP=OSM(measured)-OSM(cal)Values of greater than 10 mOsm/L are abnormal and suggest the presence of an exogenous substance AG is normally 9-16 mFq/L.4748Common Causes of Metabolic AcidosisInc
26、reased anion gapDiabetic ketoacidosisL-lactic acidosisD-lactic acidosisAlcoholic ketoacidosisUremic acidosis(advanced renal failure)Salicylate intoxicationEthylene glycol intoxicationMethanol intoxicationParaldehyde intoxicationNormal anion gapMild to moderate renal failureGastrointestinal loss of H
27、CO3-(acute diarrhea)Type I(distal)renal tubular acidosisType I1(proximal)renal tubular acidosisQpe IV renal tubular acidosisDilutional acidosisTreatment of diabetic ketoacidosis(ketones lost in urine)Increased Anion Gap LA MUD PIE(Mnemonic)Lactate(sepsis,ischemia,etc.)AspirinMethanolUremiaDiabetic k
28、etoacidosis Paraldehyde,Propylene glycolIsopropyl alcohol,INHEthylene glycol(antifreeze,low calcium)49Diabetic ketoacidosis(DKA)Patients with severe diabetic ketoacidosis typically present withHigh anion gap metabolic acidosisSevere acidemia(pH 20 mEqn,high AG acidosis is probably present.If AG 30 m
29、Eq/L,high AG acidosis is almost certainly present.59A patient presents with:pH 7.15,calculated HC03-6 mEq/L,PCOZ1 8 mmHg,sodium 135 mEq/L,chloride 114 mEq/L,potassium 4.5 mEqL,serumHC03-6 mEq/L.60A patient presents with:pH 7.49,HC03-35,PCO2-4 8,AG 16.61A patient presents with:pH 7.68,PCO2 35,HC03-40
30、,AG 18.62A previously well patient presents with 30 minutes of respiratory distress andpH 7.26,Pc02 60,HC03-26,AG 14.63Apatient presents with:pH 7.45,PCOZ65,HC03-44,AG 14.Short of breathfor 3 days.64A patient presents with diabetic ketoacidosis:pH 6.95,PCOZ 28,HC03-6,AG 32.65A patient with recurrent
31、 episodes of small bowel obstruction presents withsevere abdominal pain and vomiting:pH 7.33,PCO35,HC03-18,AG 33.Urine dipstick negative for ketones.The blood pressure is 82154 and the heartrate 116.66A 21-year-old diabetic patient presents with vomiting and pH 7.75,PCO24,HC03-32,AG 30.The urine is
32、strongly positive for ketones and serumketones are strongly positive.67A 50-year-old 70 kg alcoholic man presents with 4 days of nausea,vomiting,and mild abdominal pain following a week-long drinking binge.He is unableto take anything by mouth.His mucous membranes are dry,and his vital signsreveal a
33、n orthostatic blood pressure drop with a rise in pulse.The followinglaboratory data are obtained:Na 134 mEqn,K 3.1 mEq/L,HC03-20mEq/L,C1 80 mEq/L,glucose 86 mg/dl,BUN 52 mg/dl,Cr 1.4 mg/dl,amylasepending,serum ketones:high positive reading.ABG:pH 7.32,PCO40mm Hg,HC03-20 mEq/L.Urine sodium 7 mEqL(low).Urine ketones:high reading.What is your diagnosis,and what do you do?
