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Let’s review. Regulation of Acid-Base Balance. Buffering systems neutralize acids & bases & include lungs & renals Buffer— substance or a group of substances that can absorb or release H+ to correct an acid-base imbalance Arterial pH indirect measurement of H+ ion.

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Let s review

Let’s review


Regulation of acid base balance

Regulation of Acid-Base Balance

  • Buffering systems neutralize acids & bases & include lungs & renals

  • Buffer—substance or a group of substances that can absorb or release H+ to correct an acid-base imbalance

  • Arterial pH indirect measurement of H+ ion


Regulation of acid base balance1

Regulation of Acid-Base Balance

  • pH reflection of balance between CO2 (lungs) & HCO3- (renal)

  • Acidosis

    • Increased amount of H+ ions

    • Normal pH 7.35-7.45

    • pH = 7 is neutral

    • pH < 7 is acid

    • pH > 7 is alkaline


Regulation of acid base balance2

Regulation of Acid-Base Balance

  • AB balance exists when the rate at which the body produces acid or bases = the rate at which the acids or bases are excreted

  • Normal hydrogen ion level is necessary to maintain cell membrane integrity & speed of cellular enzymatic actions


Acid base regulators

Acid-Base Regulators

  • Chemical regulation

    • Largest chemical buffer in ECF is carbonic acid/bicarb buffer system

    • First buffer system to react

    • Reacts in seconds

    • Lungs control excretion of carbon dioxide


Acid base regulators1

Acid-Base Regulators

  • Kidneys control excretion of hydrogen & bicarbonate ions

  • ECF becomes more acidic pH decreases

  • ECF receives more base substances, pH rises


Acid base regulators2

Acid-Base Regulators

  • Biological Regulation

    • Occurs after chemical buffering

    • Occurs hydrogen ions are absorbed or released by cells

    • Hydrogen ion + charged & must be exchanged with another + charged ion—frequently K+

  • Conditions that produce excess acidH+ ion enter cellpotassium ion leaves cellenters ECFelevated K+ levels


Acid base regulators3

Acid-Base Regulators

  • Biological buffer

    • Hemoglobin-oxyhemoglobin system

    • CO2 diffuses to RBCforms carbonic aciddissociates to H+ & HCO3+ ionsH+ ions attach to hemoglobinHCO3+ available for buffering

  • Chloride shift in RBCs

    • Bld oxygenated in lungs, bicarb diffuses into cellchloride travels from hemoglobin to plasma to maintain electrical neutrality


Acid base regulators4

Acid-Base Regulators

Metabolic acidosisresp increasegreater amt CO2 exhaleddecreased acidic level

  • Physiological regulation

    • Lungs & kidneys

    • If diseased is no longer effective for regulation

    • Lungs adapt rapidly to imbalance

    • Increased H+ & CO2 ions stimulate respiration


Acid base regulators5

Acid-Base Regulators

  • Physiological Regulation

    • Kidneys take a few hrs to several days to regulate acid-base balance

    • Inc or dec HCO3+ production

    • Certain amino acids in renal tubules change to ammonia NH3- & excreted by kidneys


Acidosis

Acidosis


Acid base balance

Acid-Base Balance

  • Acid-base balance is regulated by the body’s ability to maintain arterial pH 7.35-7.45

  • Checked by ABGs

  • Deviation from normal value indicates experiencing an acid-base imbalance


Breakdown of abgs

Breakdown of ABGs

  • pH

    • Measures H+ ions concentration in body fluids

    • Slight change can be life threatening

    • Acidic—increase in H+ ions

    • Alkaline—decrease in H+ ions


Let s review

ABGs

  • PaCO2

    • Partial pressure of carbon dioxide in arterial bld

    • Reflection of depth of pulmonary ventilation

    • Normal 35-45 mm Hg

    • **Hyperventilation PaCO2 < 35 mm Hg

    • Carbon dioxide is exhaled & amt dec


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ABGs

  • **hypoventilation

    • PaCO2 is > 45 mm Hg

    • Less carbon dioxide is exhaled

    • Increasing concentration of carbon dioxide


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ABGs

  • PaO2

    • Parital pressure of O2 in arterial bld

    • Normal 80-100 mm Hg

    • N0 primary role in A-B regulation when normall

    • PaO2 < 60 causes anaerobic metabolism—produces lactic acid—metabolic acidosis


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ABGs

  • Oxygen Saturation

    • When hemoglobin is saturated with O2

    • Normall 95-99%

    • Changes in temp,PaCO2 & pH affect oxygen


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ABGs

  • Base Excess

    • Amt of blood buffer

    • Normal +/- 2 mEq/L

    • High value—alkalosis

      • Citrate excess from rapid blood transfusions

      • IV HCO3 infusion DKA\

      • Ingestion large amt bicarb solutions (antacids)


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ABGs

  • Base excess

    • Low value—acidosis

      • Lg amts of bicarb ion excretion

      • ie: diarrhea


Let s review

ABGs

  • Bicarbonate

    • Major renal component

    • Kidneys excrete & retain to maintain normal balance

    • Principal buffer ECF

    • Normal 22-26 mEq/L

    • Metabolic acidosis < 22 mEq/L

    • Metabolic alkalosis > 26 mEq/L


Acid base imbalances

Acid-Base Imbalances

  • Either respiratory or metabolic, depend on their underlying cause

  • Corrects AB imbalances through process known as compensation


Respiratory acidosis

Respiratory Acidosis

  • pH < 7.35

  • PaCO2 >45 mm Hg

  • PaO2 < 80 mm Hg

  • Bicarb level normal if uncompensated

  • Bicarb level > 26 mEq/L if compensated

  • HypoventilationCSF & brain cells become acidicneurological changes hypoxemiafurther neurological impairment

  • Hyperkalemia & hypercalcemia can occur

  • Kidneys hold to bicarb & release hydrogen ions UA—may take 24 hrs


Respiratory acidosis causes

Respiratory Acidosis Causes

  • Hypoventilation resulting primary respiratory problems

    • Chest wall injury

    • Respiratory failure

    • Cystic fibrosis

    • Pneumonia

    • Atelectasis (obstruction of small airways often caused by mucus)

  • Hypoventilation resulting from factors other than resp system

    • Obesity

    • Head injury

    • Drug overdose (OD) with resp depressant

    • Paralysis of resp muscles caused by neurological alterations


Respiratory acidosis1

Respiratory Acidosis

  • S/S

    • Convulsion

    • Coma

    • Muscular twitching

    • Confusion

    • Dizziness

    • Lethargy

    • HA

    • Warm flushed skin

    • Ventricular dysrhythmia


Respiratory alkalosis

Respiratory Alkalosis

  • pH >7.45

  • PaCO2 <35 mm Hg

  • PaO2 normal

  • HCO3 nl if short-lived or uncompensated

  • HCO3 <22 mm Hg if compensated

  • Begins outside resp system ie: anxiety, panic attack OR within resp system ie: initial phase of asthma attack

  • Body does not usually compensate because pH returns to nl before kidneys can respond


Respiratory alkalosis1

Respiratory Alkalosis

  • Causes

    • Salicylate overdoes

    • Anxiety

    • Hypermetabolic states ie: fever, exercise

    • CNS disorders ie: head injury, infections

    • Asthma

    • Pneumonia

    • Inappropriate vent settings

  • S/S

    • Confusion

    • Dizziness

    • Convulsions

    • Coma

    • Tachypnea

    • Numbness/tingling of extremities

    • dysrhythmias


Metabolic acidosis

Metabolic Acidosis

  • High acid content of bld

  • Loss of HCO3

  • pH <7.35

  • PaCO2 normal if uncompensated

  • <35 mm Hg if compensated

  • PaO2 normal or increased

  • HCO3 < 22 mEq/L

  • O2 Sat normal


Metabolic alkalosis

Metabolic Alkalosis

  • pH >7.45

  • PaCO2 normal if uncompensated

  • PaCO2 >45 mm Hg if compensated (occurs by decreasing RR & no renal disease)

  • PaO2 normal

  • HCO3 > 26 mEq/L

  • Causes

    • Excessive vomiting

    • Prolong gastric sx

    • Excess aldosterone

    • Hypokalemia

    • Hypercalcemia

    • Use of drugs ie: steriods, diuretics, sodium bicarb


Question

Question

  • Interpret the following ABGs:

    • pH?

    • PCO2 ? mm Hg

    • PO2 ? mm Hg

    • HCO3 ? mEq/L

    • O2 Sat ? %


Let s review

Normal blood gas in an artery for humans:

pH 7.35–7.45

PaCO2 35–45 mmHg

PaO2 80–100 mmHg

HCO3− 22–26 mmol/L


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