Acid and Base Balance and Imbalance酸碱平衡与不平衡

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

2、dissociate only partially 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 mo

3、st enzymes function only with 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

4、 h+ + hco3-8control of acids1. buffer 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 :

5、 hco3- : h2co3hcl + nahco3 h2co3 + naclnaoh + h2co3 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

6、 present on 27 amino acids.122. respiratory mechanisms exhalation of 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 la

7、rge amounts of acid can also excrete base can conserve and produce bicarb 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

8、 days151617acid-base imbalances ph 7.45 alkalosis the body response to acid-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 hypoventi

9、lation can help : respiratory compensation. if problem is respiratory, renal mechanisms 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 acid

10、osis causes disorientationcoma death20alkalosis alkalosis causes over excitability 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

11、 blood levels of co2 above 45 mm hg. hypercapnia high levels of co2 in blood chronic 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 di

12、stress syndrome pulmonary edema pneumothorax24compensation for respiratory acidosis kidneys eliminate hydrogen ion and retain bicarbonate ion25signs and symptoms of respiratory acidosis breathlessness restlessness lethargy and disorientation tremors, convulsions, coma respiratory rate rapid, then gr

13、adually depressed skin warm and flushed due to vasodilation caused by excess co226treatment 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

14、imbalance primary cause is hyperventilation28respiratory alkalosis conditions that stimulate 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 seps

15、is29compensation of respiratory alkalosis kidneys conserve hydrogen ion excrete bicarbonate ion30treatment 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 c

16、oncentrations of bicarb drop below 22meq/l causes: loss of bicarbonate through diarrhea or renal 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 meta

17、bolic acidosis increased ventilation renal excretion of hydrogen ions if possible k+ exchanges with excess 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 cause

18、s: excess vomiting = loss of stomach acid excessive use of alkaline drugs certain diuretics endocrine disorders heavy ingestion of antacids severe dehydration36compensation for metabolic alkalosis alkalosis most commonly occurs with renal dysfunction, so cant count on kidneys respiratory compensatio

19、n difficult hypoventilation limited by hypoxia37symptoms of metabolic alkalosis respiration slow and shallow hyperactive reflexes ; tetany often related to depletion of electrolytes atrial tachycardia dysrhythmias38treatment of metabolic alkalosis electrolytes to replace those lost iv chloride conta

20、ining solution treat underlying disorder39diagnosis of acid-base imbalances1. note whether the ph is low (acidosis) or high (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 respirator

21、y. 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 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 i

22、s in intensive care because he suffered a severe myocardial infarction 3 days ago. the lab reports the following values from an arterial 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.

23、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 mgldlarterial blood gas analysisph 7.35-7.45pcoz35 -45 mm hgpoz 90-100 mm hg (declines with age)4445disordermetabolic acidosismetabolic alkalosisrespiratory acid

24、osis acute chronicrespiratory alkalosis acute chronicexpected compensationpco2 = 1.5 hco3- + 8 2pco2 increases by 7mmhg for each 10meq/l increase in the serum hco3-hco3- increases by 1 for each 10mmhg increase in the pco2hco3- increases by 3.5 for each 10mmhg increase in the pco2hco3- falls by 2 for

25、 each 10mmhg decrease in the pco2hco3- falls by 4 for each 10mmhg decrease in the pco246formulaswomen: total body water (tbw) = .5 x body weight (kg)men: total body water (tbw) = .6 x body weight (kg)osmolal gap = osm,measured) - osm,caculatcd)anion gap (ag) = ua - uc = na - (ci- + hco,-) osm gap =

26、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 acidosisincreased anion gapdiabetic ketoacidosisl-lactic acidosisd-lactic acidosisalcoholic ketoacidosisuremic acidosis (

27、advanced renal failure)salicylate intoxicationethylene glycol intoxicationmethanol intoxicationparaldehyde intoxicationnormal anion gapmild to moderate renal failuregastrointestinal loss of hco3- (acute diarrhea)type i (distal) renal tubular acidosistype i1 (proximal) renal tubular acidosisqpe iv re

28、nal tubular acidosisdilutional acidosistreatment of diabetic ketoacidosis (ketones lost in urine)increased anion gap la mud pie (mnemonic)lactate (sepsis, ischemia, etc.)aspirinmethanoluremiadiabetic ketoacidosis paraldehyde, propylene glycolisopropyl alcohol, inhethylene glycol (antifreeze, low cal

29、cium)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 meq/l, high ag acidosis is almost certainly present.59a patient presents with: ph 7.15, calcu

30、lated 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, 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 patien