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Unit 3B - Acid­Base Balance Objectives Objectives Describe...

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Unformatted text preview: Acid­Base Balance Objectives Objectives Describe the physiologic mechanisms that maintain acid/base balance in the body Describe the basic acid/base imbalances that occur and the body’s compensation systems used to correct these imbalances Acid/Base Balance Acid/Base Balance Maintained within a narrow range for normal body function Changes in H+ ion concentration can have a significant impact on biologic processes in cells and tissues pH: represents the power of H+ pH of 7.0 = 10­7 One unit change in pH is 10­fold change in H+ Hydrogen Ion and pH Hydrogen Ion and pH More H+: acidic environment pH< 7.0 = acid Less H+: basis or alkaline environment pH> 7.4 = alkaline Body systems needed to regulate acid/base balance: Lungs Kidneys Bones Buffering Systems Buffering Systems Buffering occurs in response to changes in pH Three buffering systems 1)Carbonic acid­bicarbonate system: Lungs can ↓ carbonic acid by blowing off C02, kidneys can reabsorb bicarbonate or regenerate bicarbonate from C02 and H20; Normal ratio of bicarb to carbonic acid is 20:1 = pH 7.4 2) Protein buffering: i.e. Hgb intracellular buffer 3) Renal buffering: distal tubule secretes H+ into urine and reabsorbs bicarbonate Acid­Base Imbalances Acid­Base Imbalances Reflect changes in H+ ion concentration Acidemia: pH < 7.4 ( ↑ H+ ions)→ termed acidosis Alkalemia: pH > 7.4(↓ H+ ions)→ termed alkalosis Acid Base Imbalances Acid Base Imbalances Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis Mixed disturbances All can be compensated or partially compensated or no compensation. Arterial Blood Gases Arterial Blood Gases Determining Acid/Base Balance in the Body Normal values: pH: 7.35­7.45 pC02: 35­45 mm Hg HC03: 22­26 mEq/l pO2: 60­100 mm Hg Oxygen saturation: 96­100% Base excess + or – 2. Respiratory Acidosis Respiratory Acidosis Decrease in alveolar ventilation pH < 7.35 Increase in carbonic acid Pa Co2 > 45mmHg Causes: respiratory center depression (head trauma, medication), paralysis of respiratory muscles, chest wall disorders, pneumonia, bronchitis Symptoms: HA, visual changes, restlessness, rapid respiratory rate followed by ↓ respiratory rate followed by lethargy, disorientation, coma Kidneys compensate by retaining HC03 and eliminating H+ Respiratory Alkalosis Respiratory Alkalosis Alveolar hyperventilation Low Pa C02 levels (C02 < 35) hypocapnia Can be acute or chronic Causes: Hypoxemia (pulmonary disease, CHF, altitude); Hypermetabolic states (fever, hysteria, salicylate intoxication) Symptoms: dizziness, confusion, tingling of the extremities, convulsions, cerebral vasoconstriction, carpopedal spasm Compensation: kidneys, decrease H+ excretion and decreasing bicarbonate reabsorption Metabolic Acidosis Metabolic Acidosis Loss of bicarbonate, or increase in noncarbonic acids pH<7.35; HC03 < 22 Causes: Acute: lactic acidosis; Extended time period: renal failure, DKA Anion Gap: used to determine the type of acidosis. Represents the difference between the sum of Na+ and K+ and the sum of HC03­ and Cl­ (10­12mEq). Normal: metabolic acidosis due to HC03 loss; Elevated: due to anions or addition of acids (DKA, lactic acidosis) Symptoms: Neuro: HA, lethargy can progress to coma if severe, Respiratory:Kussmaul’s respirations (DKA);GI: nausea, vomiting, diarrhea, cramping; Severe: cardiac arrythmmias and death Compensation: Respiratory­­Kussmaul’s respirations to blow off excess acid Metabolic Alkalosis Metabolic Alkalosis Excessive loss of metabolic acids pH > 7.45; HC03< 22 Causes: hyperaldosteronism:HC03 retention with loss of K+ and H+, Diuretic therapy, vomiting (loss of Cl­ in HCl stimulates kidneys to retain HC03) Symptoms: weakness, muscle cramps, hyperactive reflexes, slow, shallow respirations, atrial tachycardia, confusion, tetany (increased binding of Ca++ to plasma proteins, thus ↓ionized Ca++ → hypopolarization of cells → A.P→ muscle contractions Compensation: Lungs: slow respirations to retain acid Arterial Blood Gas Arterial Blood Gas Clinical test used to determine the patient’s acid­base balance. Arterial blood used for determining the ABG. Steps to ABG interpretation Steps to ABG interpretation 1) Determine the pH 2) Look at the Pa CO2 3) Look at the HCO3 4) Determine if there is compensation ABG exercises ABG exercises pH: 7.42 PaC02: 40 HC03: 24 Normal values: pH: 7.35­7.45 pC02: 35­45 mm Hg HC03: 22­26 mEq/l pO2: 60­100 mm Hg Oxygen saturation: 96­100% Base excess + or – 2. Ask: pH: Acidosis or alkalosis C02: ↑ or ↓ HC03: ↑ or ↓ Compensated or Not compensated: (is pH normal?) Exercises Exercises pH: 7.25 PaC02: 50 HC03: 22 pH: 7.50 PaC02: 30 HC03: 26 Ask: pH: Acidosis or alkalosis C02: ↑ or ↓ HC03: ↑ or ↓ Compensated or Not compensated: (is pH Compensated normal?) normal?) More exercises More exercises pH: 7.50 PaC02: 42 HC03: 33 pH: 7.51 PaC02: 30 HC03: 24 pH: 7.36 PaC02: 50 HC03: 29 Ph 7.45 PaCO2: 33 HC03: 30 Ask: pH: Acidosis or alkalosis C02: ↑ or ↓ HC03: ↑ or ↓ Compensated or Not Compensated compensated: (is pH normal?) compensated: What More Practice? What More Practice? ABG interpretation http://www.ed4nurses.com/resources/1/pdf/AB http://www.vectors.cx/med/apps/abg.cgi http://respiratorytherapycave.blogspot.com/200 http://respiratorytherapycave.blogspot.com/20 ...
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