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ACID-BASE DISORDERS. NITIN BHATT, M.D. DIRECTOR, I.C.U. VAMC, RENO . ACID_BASE DISORDERS. 12000 to 15000 mEq of volatile acids are produced daily by body and excreted as CO2 by lungs

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acid base disorders
ACID-BASE DISORDERS

NITIN BHATT, M.D.

DIRECTOR, I.C.U.

VAMC, RENO

acid base disorders2
ACID_BASE DISORDERS
  • 12000 to 15000 mEq of volatile acids are produced daily by body and excreted as CO2 by lungs
  • 1 mEq / kg / day of non-volatile acids (sulfuric and phosphoric acids) are produced daily by body and excreted by the kidneys
  • The pH of body fluids is determined by the amount of acid produced, the buffering capacity and the acid excretion by lungs and the kidneys
  • The most important buffers in the body are, hemoglobin, plasma proteins and bicarbonate
addition of acid
Addition of acid
  • First the acid binds to extracellar buffers, then intracelluar buffers and finally to alkaline salts in bones.
  • PCO2 is lowered by stimulation of respiratoty center
  • Finally, the kidneys increase the excretion of acids.
  • If all these mechanisms fail, patient develops acidemia
acid base disorders4
ACID-BASE DISORDERS
  • ACIDEMIA: lower than normal arterial blood pH
  • ALKALEMIA: higher than normal arterial blood pH
  • ACIDOSIS: a process that tends to acidify body fluids and may lead to acidemia. Could result from metabolic or respiratory dysfunction or compensatory response.
  • ALKALOSIS: a process that tends to alkalinize body fluids and may lead to alkalemia. Could result from metabolic or respiratory dysfunction or compensatory response.
  • Acidosis and alkalosis may or may not be associated with abnormal pH in the same direction..
acid base disorders5
ACID_BASE DISORDERS
  • SIMPLE ACID BASE DISORDER: when there is only one primary disorder
  • MIXED ACID BASE DISORDER: when there are two or more primary disorders present at the same time
acid base disorders6
ACID-BASE DISORDERS
  • NORMAL ANION GAP = 12
  • NORMAL PH = 7.40
  • NORMAL PCO2 = 40
  • NORMAL HCO3 = 24
acid base disorders7
ACID-BASE DISORDERS

DEFINITIONS

METABOLIC ACIDOSIS = HCO3 <24 OR Anion Gap >12

METABOLIC ALKALOSIS = HCO3 >24

RESPIRATORY ALKALOSIS = PCO2 <40 or PCO2 less than expected for primary metabolic abnormality.

RESPIRATORY ACIDOSIS = PCO2 >40 or PCO2 higher than expected for primary metabolic abnormality.

HIGH ANION GAP (>12-20) always indicates primary metabolic acidosis.

We do not compensate for abnormality of one system with compensation by the same system( MET OR RESP).

acid base disorders8
ACID BASE DISORDERS
  • PRIMARY PRIMARYCOMPENSATORY

DISORDERABNORMALITYCHANGE

MET. ACIDOSIS LOWER HCO3 LOWER PCO2

MET. ALKALOSIS HIGHER HCO3 HIGHER PCO2

RESP. ACIDOSIS HIGHER PCO2 HIGHER HCO3

RESP. ALKALOSIS LOWER PCO2 LOWER HCO3

REMEMBER: compensatory response never brings the pH back to normal, therefore, if the pH is in acidic direction, it tells you that the process or processes in acidic direction are the primary disorders.

acid base disorders9
ACID_BASE DISORDERS

Compensatory Process

  • Tends to return ratio of HCO3 to PCO2 back toward normal and therefore normalize the arterial pH
  • Does not return pH to normal except in primary respiratory alkalosis of chronic duration.
  • Require normal function of kidneys and lungs
  • Lack of appropriate compensation suggests second primary disorder
  • Compensatory response creates second lab abnormality
  • Appropriate degree of compensation can be predicted.
acid base disorders10
ACID_BASE DISORDERS

Metabolic Acidosis

  • Caused by excess acid production which overwhelms renal capacity to excrete acids ( DKA ) , loss of alkali (diarrhea) or renal failure
  • Tissues and RBCs act to increase the serum HCO3 by exchanging intracellular Na & K for extracellular H , resulting in increased serum K and HCO3
  • Increased pulmonary ventilation leads to decreased PaCO2 and change in pH toward normal
  • HCO3 <10 OR Anion Gap > 12 always suggest primary metabolic acidosis
acid base disorders11
ACID_BASE DISORDERS

Urinary Anion-Gap

  • Useful in differential diagnosis of hyperchloremic acidosis
  • Calculated as U. Na + U. K – U. Cl
  • A negative U. Anion Gap ie Cl >> Na + K suggests appropriate urinary NH4 excretion and G.I. loss of HCO3
  • A positive U. Anion Gap ie. Cl << Na + K suggests RTA with distal acidification defect and inadequate NH4 excretion in urine
acid base disorders13
ACID-BASE DISORDERS
  • RESPIRATORY ACIDOSIS

ACUTE: 10 INCR. IN PCO2 LEADS TO 1 INCR. IN HCO3

CHRONIC: 10 INCR. IN PCO2 LEADS TO 3-3.5 INCR. IN HCO3

  • RESPIRATORY ALKALOSIS

ACUTE; 10 DECR. IN PCO2 LEADS TO 2 DECR. IN HCO3

CHRONIC 10 DECR. IN PCO2 LEADS TO 4-5 DECR. IN HCO3

  • METABOLIC ACIDOSIS

PCO2 = LAST 2 DIGITS OF pH

  • METABOLIC ALKALOSIS

1 MEQ INCR. IN HCO3 LEADS TO 0.6-0.7 INNCR. IN PCO2

pco2 hco3 buffer system
PCO2-HCO3 buffer system
  • CO2 gas  CO2 dissolved + H2O
  • CO2 + H2O  H2CO3  H + HCO3
  • H= K x H2CO3÷ HCO3
  • H2CO3 or PCO2 represents respiratory system function
  • HCO3 represents kidney or metabolic system
acid base disorders15
ACID-BASE DISORDERS

HENDERSON HASSELBALCH EQUATION

Ph = Pk + log HCO3/ H2CO3

Rearranging the above per Kassier and Bliech

H = 24 X PCO2/HCO3 ( H= Hydrogen ion conc.)

H at normal pH of 7.40 is 40 Nanamol/Liter

therefore, 40 = 24 X 40 (PCO2)/24(HCO3)

acid base disorders17
ACID_BASE DISORDERS
  • SIMPLE ACID BASE DISORDER: when there is only one primary disorder
  • MIXED ACID BASE DISORDER: when there are two or more primary disorders present at the same time
acid base disorders18
ACID-BASE DISORDERS

SYSTEMATIC ANALYSIS OF ACID-BASE DISORDER

  • 1, Find out which one is the primary process or processes. If the pH is abnormal, there has to be a minimum of one primary process ( Acidosis or Alkalosis ). We can not identify more than three primary processes at one time with our current knowledge of acid-base analysis.
  • 2, Do not apply equations for primary respiratory disorders, if there is also a concurrent primary metabolic disorder present.
  • 3, Do not try to calculate expected PCO2 for primary metabolic acidosis, if there is also a concurrent primary respiratory disorder or if HCO3 >24.
  • Use as many equations of acid-base disorders that can be applied in the case, to get the maximum information.
causes of hyperchloremic metabolic acidosis
CAUSES OF HYPERCHLOREMIC METABOLIC ACIDOSIS

HYPOKALEMIC

Proximal RTA, acetazolamide,coumarin/ Distal RTA

Post-hypocapnea

Diarrhea, Pancreatic fistula, Biliary drainage

Ureterosigmoidostomy, Ileal bladder

HYPERKALEMIC OR NORMOKALEMIC

Type-4 RTA

HCl infusion/ingestion

Dilutional acidosis

urinary chloride in metabolic alkalosis
Less than 20 mEq/l

( saline responsive )

Vomiting/NG_Tube suction

Chloride wasting diarhhea

Colonic villous adenoma

Remote diuretic therapy

Post hypercapnea

Poorly reabsorbed anions

Glucose refeeding

Greater than 20 mEq/l

( saline unresponsive )

Primary Hyperaldosteronism

Cushing`s syndrome

Exogenous steroids/ Licorice

Adrenal 11 or 17 hydroxylase defects

Liddle`s /Barter`s syndromes

K and Mg deficiency

Milk alkali syndrome

Urinary chloride in metabolic alkalosis
acid base disorders30
Acid-base Disorders

An acutely ill 50 yr. old woman with a history of vomiting x 4 days is brought to E.R. P/E shows profound lethargy, P= 120, RR=12, BP 80/50. Lab: Na=140, K=3.3, Cl=85, HCO3=25, PCO2=41 and pH=7.40.

Most likely acid-base disorder is

A) metabolic acidosis

B) metabolic alkalosis

C) respiratory acidosis and metabolic alkalosis

D) respiratory alkalosis

E) metabolic acidosis and metabolic alkalosis

acid base q 2
ACID-BASE Q-2
  • pH=7.5
  • PCO2=27
  • HCO3=23
acid base q 3
ACID-BASE Q-3
  • pH=7.25
  • PCO2=60
  • HCO3=26
acid base q 4
ACID-BASE Q-4
  • pH=7.20
  • PCO2=21
  • HCO3=8
acid base q 5
ACID BASE Q-5
  • Na=145
  • Cl=99
  • HCO3=24
  • pH=7.4
  • PCO2=40
acid base q 6
ACID BASE Q-6
  • pH=7.10
  • PCO2=50
  • Na=145
  • Cl=100
  • HCO3=15
slide37

A 65 yr old homeless woman who collapsed in a pub is brought to E.R. P/E: comatose,P=120,BP=58/40.IV N.S. started 10 min.earlier,Pt. Now intubated. I.V. bicarbonate was given with fluids, and Dopamine was started but hypotension persists

questions related to previous pt
Questions related to previous pt.
  • A) what is the acid base abnormality before intubation? 1, met. Acid. 2, resp acid. 3, met and resp acidosis 4, met acid and met alk 5, met acid, resp acid and met alkalosis.
  • B) what is the cause of acid-base abnormality 30 min after intubation ? 1, uremia 2, distal RTA 3,resp acidosis 4, lactic acidosis, 5 DKA
acid base disorders39
ACID-BASE DISORDERS
  • A 45 yr old man with progressive renal failure x 1 yr., comes to your office because of N/V/ pruritus and weakness. P/E shows P=84,RR=20,BP=180/110
  • Lab: Glu=98,Na=138,K=5.5,Cl=100,HCO3=16,BUN=155,Cr= 12.6, PCO2=29,pH=7.30,urine pH=5.0. Most likely DX is
  • A) metabolic alkalosis
  • B) respiratory alkalosis
  • C)metabolic alkalosis and respiratory acidosis
  • D)metabolic acidosis
  • E) metabolic acidosis and respiratory alkalosis
acid base disorders40
ACID-BASE DISORDERS
  • A 42 YR old alcoholic man presents with hematemesis, anemia and mild orthostatic hypotension. Lab as follows

Hct=36%, Glu=85, Na=138, K=3.3, Cl=97, HCO3=35, BUN=25, Cr.=1.2,

Urine pH=6.8, Urine Cl=8 meq/L and Urine K=42 meq/L

  • Most appropriate therapy for this patient is
  • A, Furosemide or Ethacrynic acid
  • B, Sodium Chloride
  • C, Potassium Chloride and Sodium Chloride
  • D, Potassium Chloride
  • E, I.V. D5W
acid base disorders41
ACID-BASE DISORDERS
  • A patient with DKA has following lab values,
  • HCO3=12 and PCO2=33
  • What is the acid base disorder?
  • Remember: it takes 12-24 hrs to get optimum response from respiratory system in case of acute metabolic acidosis. And in about 5% of cases,the patient may not fall within the values obtained by applying the rule for expected PCO2 in primary metabolic acidosis
acid base disorders42
ACID –BASE DISORDERS
  • A child with a 3-4 hour history of asthma exacerbation has ABG values as follows: pH=7.24, PCO2=65, HCO3=26
  • What is the acid base disorder?
  • A 65 years old man with long standing history of COPD presents with diarrhea x 24 hours. ABG values are: pH=7.24, PCO2=65, HCO3=26
  • What is the acid-base disorder?