acid base balance [Recovered]

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“If one advances confidently in the direction of his dreams, he will meet with a success unexpected in common hours --Henry David Thoreau "Shoot for the moon.  Even if you miss it, you will land among the stars….!" - Les Brown

Acid-Base Balance :

Acid-Base Balance DR.M.RAVICHANDRA,M.S ASST. PROFESSOR OF SURGERY RIMS ,SRIKAKULAM

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Strong and Weak Acids and Bases A strong acid ..rapidly dissociates and releases large amounts of H+ in solution….HCl Weak acids ..less tendency to dissociate their ions … is H2CO3 A strong base … reacts rapidly and strongly with H+ and quickly removes these from a solution…OH- A typical weak base is HCO3- Most of the acids and bases in the extracellular fluid that involved in normal acid-base regulation are weak acids and bases

Types of Acids in the body:

Types of Acids in the body Volatile acids: Can leave solution and enter the atmosphere. H 2 C0 3 (carbonic acid). Pco 2 is most important factor in pH of body tissues . Pco2 is a measurement of tension or partial pressure of carbon dioxide in the blood. The normal arterial pCO2 is 4.1- 5.6 k Pa (31- 42 mmHg)

Types of Acids in the body:

Types of Acids in the body Fixed Acids: Acids that do not leave solution. Sulfuric and phosphoric acids.(H2SO4&H3PO4) Catabolism of amino acids, nucleic acids, and phospholipids.

Types of Acids in the body (CONTD):

Types of Acids in the body (CONTD) Organic Acids: Byproducts of aerobic metabolism, during anaerobic metabolism and during starvation, diabetes. LACTIC ACID, KETONES ,PYRUVIC ACID

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Normal Hydrogen Ion Concentration and pH of Body Fluids the blood H+ concentration is normally maintained within tight limits around a normal value of about 0.00004 mEq/L (40 nEq/L) Ph= log 1/H= -log [H] Ph=7.4

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pH = pK + log HCO 3 CO 2

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DEFENCE MECHANISMS AGAINST pHCHANGES

2.PHYSIOLOGICAL BUFFER SYSTEMS:

2.PHYSIOLOGICAL BUFFER SYSTEMS 1.CHEMICAL BUFFER SYSTEMS

Defenses Against Changes in Hydrogen Ion Concentration:

Defenses Against Changes in Hydrogen Ion Concentration There are three primary systems that regulate the H+ concentration the chemical acid-base buffer systems of the body fluids (2) the respiratory center (3) the kidneys

Buffer Systems:

Buffer Systems a buffer system is a combination of two compounds that minimizes pH changes when acid or base is added to a solution A pair of substance is involved: one substance yield H+ ion when PH is increased the other binds with H+ ion when pH is decreased.

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Chemical buffer system Combination of weak acid and weak base Binds to H + as H + concentration rises Releases H + as H + concentration falls Can restore normal pH almost immediately Three major chemical buffer systems Bicarbonate system Phosphate system Protein system

buffers:

buffers Accomplished by converting: Strong acid  Weak acid Strong base  Weak base

BODY BUFFER SYSTEMS:

BODY BUFFER SYSTEMS bicarbonate/carbonic acid major plasma buffer phosphate: H2PO4- / HPO42- major urine buffer ammonium: NH3 / NH4+ also used to buffer the urine proteins: important in ICF Hb: is the main buffer against CO2 changes

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BICARBONATE BUFFER SYSTEM Carbonic acid (H 2 CO 3 ) Weak acid Bicarbonate ion (HCO 3 - ) Weak base CO 2 + H 2 0  H 2 CO 3  H + + HCO 3 - Works along with respiratory and urinary system These systems remove CO 2 or HCO 3 - THE RATIO OF BICARBONATE TO CARBONIC ACID IS NORMALLY 20:1 Alterations in the ratio alters Ph irrespective of absolute concetrations

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NaOH + H2CO3 H2O + Na HCO3 HCl + Na HCO3 NaCl + H2CO3

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*Image via Bing BICACARBONATE BUFFER

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pK 6.1 the concentrations of CO2 and HCO3 not great . the most powerful extracellular buffer in the body the two elements of the buffer system are regulated by the kidneys and the lungs

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PHOSPHATE BUFFER SYSTEM Dihydrogen phosphate ion (H 2 PO 4 - ) Weak acid Monohydrogen phosphate ion (HPO 4 2- ) Weak base H 2 PO 4 -  H + + HPO 4 2- More important in buffering kidney filtrate than in tissue

Phosphate Buffer System :

Phosphate Buffer System The main elements of the phosphate buffer system are H2PO4- and HPO4 NaOH + NaH2PO4 H2O+ Na2HPO4 HCl + Na2HPO4 NaCl + NaH2PO4

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pK 6.8 8 % of the concentration of the bicarbonate buffer the total buffering power less than that of the bicarbonate buffering system .

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the phosphate buffer is important in the tubular fluids of the kidney for two reasons (1) phosphate concentrated in the tubules (2) the tubular fluid has lower pH than the extracellular fluid does - bringing the operating range of the buffer closer to the pK (6.8) of the system important in buffering intracellular fluid because the concentration of phosphate in this fluid is many times that in the extracellular fluid

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PROTEIN BUFFER SYSTEM Proteins are more concentrated than bicarbonate and phosphate buffers Accounts for ~75% of all chemical buffering of body fluids Buffering ability due to certain functional groups of amino acid residues

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except for the red blood cells, the slowness with which H + and HCO3 move through the cell membranes often delays the maximum ability of the intracellular proteins to buffer extracellular acid-base abnormalities . the pKs of many of these protein systems close to 7.4 .

Isohydric buffer system:

Isohydric buffer system The buffer system buffers each other by shifting hydrogen from buffer to other

2. Respiratory mechanisms:

2. Respiratory mechanisms Exhalation of carbon dioxide Powerful, but only works with volatile acids Doesn’t affect fixed acids like lactic acid CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - Body pH can be adjusted by changing rate and depth of breathing

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the overall buffering power of the respiratory system is one to two times as great as the buffering power of all other chemical buffers in the ECF combined

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Renal Control of Acid-Base Balance:

Renal Control of Acid-Base Balance Alkalosis →↑urinary HCO3- (base) Acidosis →↓urinary HCO3- new HCO3- production

Acid-Base Imbalances:

Acid-Base Imbalances pH< 7.35 acidosis pH > 7.45 alkalosis

Respiratory acidosis:

Respiratory acidosis A CONDITION WHERE THE PCO2 IS ABOVE THE NORMAL RANGE MORE THAN 5.6 kilopascals (or) more than 42mmof hg

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*Image via Bing compensatory mechanisms in respiratory acidosis

Respiratory acidosis in clinical setting:

Respiratory acidosis in clinical setting Inadequate ventilation of anaesthetized patient When the effects of muscle relaxants have not worn off or been fully reversed at the end of anaesthesia Risk increases when the patient has pre existing pulmonary disease like ch. Bronchitis or emphysema Thoracic & upper abdominal incisions

Respiratory alkalosis:

Respiratory alkalosis A CONDITION WHERE THE ARTERIAL PCO2 IS BELOW THE NORMAL RANGE LESS THAN 31 MM OF HG (OR) LESS THAN 5.6 KILO PASCALS

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Respiratory alkalosis clinical conditions:

Respiratory alkalosis clinical conditions Excessive pulmonary ventilation during ANAESTHAESIA ( H yperventilation) H igh altitudes H yperpyrexia H ypothalamic lesions H ysteria

Metabolic acidosis:

Metabolic acidosis A condition where there is a deficit of base or excess of acid other than carbonic acid(H2CO3)

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Ulcerative colitis Gastro colic fistula High intestinal fistula Prolonged intestinal aspiration

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Anion gap:

Anion gap This is a calculated estimation of the undetermined or unmeasured anions in the blood This is some times used to establish the cause of metabolic acidosis ANION GAP= (Na) _ (HCO3+Cl ) NORMAL ANION GAP IS 10-16 mmol / L

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ANION GAP MET ACIDOSIS:

ANION GAP MET ACIDOSIS KETOACIDOSIS LACTIC ACIDOSIS SALICYLATES POISONING SPIRITS –ETHANOL & METHANOL ALDEHYDES RENAL FAILURE

NON ANION GAP MET. ACIDOSIS:

NON ANION GAP MET. ACIDOSIS DIARRHOEA RENAL TUBULAR ACIDOSIS URETEROSIGMOIDOSTOMY TOTAL PARENTARAL NUTRITION ACETAZOLAMIDE INTESTINAL OBSTRUCTION INTESTINAL FISTULA

Compensation for Metabolic Acidosis:

Compensation for Metabolic Acidosis Increased ventilation Renal excretion of hydrogen ions if possible K + exchanges with excess H + in ECF ( H + into cells, K + out of cells)

MetabOlic alkalosis:

MetabOlic alkalosis A CONDITION WHERE THERE IS BASE EXCESS OR DEFICIT OF ANY ACID OTHER THAN CARBONIC ACID

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Cortisone excess Cushings syndrome

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*Image via Bing CHEYNE STOKES RESP TETANY

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COMPENSATION FOR MET. ALKALOSIS:

COMPENSATION FOR MET. ALKALOSIS RESPIRATORY - RETENTION OF CARBONDIOXIDE BY THE LUNGS RENAL – EXCRETION OF BICARBONATE BY THE KIDNEYS

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Changes in Arteial Concentrations of H + , HCO 3 - & CO 2 in Acid-Base Disorders Primary Disorder H + HCO 3 - CO 2 Cause of HCO 3 - Change Cause of CO 2 Change Respiratory Acidosis ↑ ↑ ↑ Renal Compensation Primary Abnormality Respiratory Alkalosis ↓ ↓ ↓ Metabolic Acidosis ↑ ↓ ↓ Primary Abnormality Reflex Ventilatory Compensations Metabolic Alkalosis ↓ ↑ ↑

Clinical Causes of Acid-Base Disorders:

Respiratory Acidosis ; ↑P CO2 & [H + ] Respiratory Alkalosis ; ↓P CO2 & [H + ] Metabolic Acidosis ; compensatory reflex hyperventilation ⇒ ↓P CO2 Tubular acidosis; ↓HCO 3 - reabsorption & H + secretion Diarrhea & Vomiting(intestinal); ↓HCO 3 - Diabetes Mellitus; ↑acetoacetic acid (ketone body) Ingestion of acids; aspirin, methyl alcohol Chronic renal failure; ↓acid excretion Hypoxia (severe exercise); ↑lactic acid Clinical Causes of Acid-Base Disorders

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Metabolic Alkalosis ; compensatory reflex hypoventilation ⇒ ↑P CO2 Diuretics; ↑distal tubule flow ⇒↑Na + reabsorption & H + secretion Excess Aldosterone; ↑H + secretion Vomiting; ↓H + (upper gastric content) Ingestion of alkaline drugs; sodium bicarbonate

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Summary of Acid-Base Disturbances Uncompensated Compensated pH [HCO 3 - ] P CO2 pH [HCO 3 - ] P CO2 Normal 7.4 24 mEq/L 40 mmHg Respiratory Acidosis ↓ - ↑ ↓ ↑ ↑ Respiratory Alkalosis ↑ - ↓ ↑ ↓ ↓ Metabolic Acidosis ↓ ↓↓ - ↓ ↓↓ ↓ Metabolic Alkalosis ↑ ↑↑ - ↑ ↑↑ ↑

Analysis of Acid-Base Disorders:

Analysis of Acid-Base Disorders

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