Acid base balance + fluid balance

Acid Base and Fluid Balance Dr.Nasim Ullah Siddiqui

Homeostasis A delicate balance of fluids, electrolytes, and acids and bases is required to maintain good health. This balance is called Homeostasis: The bicarbonate buffering system is an important buffer system in the acid-base homeostasis of living things, including humans. As a buffer, it tends to maintain a relatively constant plasma pH and counteract any force that would alter it. In this system, carbon dioxide (CO 2 ) combines with water to form carbonic acid (H 2 CO 3 ), which in turn rapidly dissociates to form hydrogen ion and bicarbonate (HCO 3 - ).The reaction is catalyzed by the enzyme carbonic anhydrase . When carbon dioxide dissolves in water, it can do so as a gas dissolved in water or by reacting with water to produce carbonic acid.

Any disturbance of the system will be compensated by a shift in the chemical equilibrium according to Le Chatelier's principle . For example, if the blood gained excess hydrogen ions (a process called acidosis ), some of those hydrogen ions would shift to carbon dioxide, minimizing the increased acidity. This buffering system becomes an even more powerful regulator of acid-base homeostasis when it is coupled with the body's capacity for respiratory compensation , in which breathing is altered to modify the amount of CO 2 in circulation. In the above example, the body could increase breathing ( respiratory alkalosis ) to expel the excess CO 2 , pulling still more hydrogen ions toward the production of carbon dioxide. The process could continue until the excess acid is all exhaled .

When carbon dioxide dissolves in water, it can do so as a gas dissolved in water or by reacting with water to produce carbonic acid. In the cells of your body, the rate of carbonic acid production is accelerated by the enzyme carbonic anhydrase when excess hydrogen ions are added to the system the equilibrium is shifted to the left. This means that some of the added hydrogen ions will react with the bicarbonate ions to produce carbonic acid and the carbonic acid will dissociate into carbon dioxide and water as shown below. Carbonic acid is known as a weak acid because it partially dissociates into the positive Hydrogen ions and negative bicarbonate ions. When hydrogen ions are removed from the reaction, the equilibrium will shift to the right. More carbon dioxide will combine with water and more carbonic acid will be produced and more hydrogen ions and bicarbonate ions will be produced.

Regulation of Acid-Base Balance Lower concentration of H+, more alkaline, higher pH The pH is also a reflection of the balance between CO2 (regulated by lungs) and bicarb (regulated by kidneys) Normal H+ level is necessary to Maintain cell membrane integrity Maintain speed of cellular enzymatic actions

Chemical Regulation Carbonic acid-bicarbonate buffer system is the first to react to change in the pH of ECF H+ and CO2 concentrations are directly related ECF becomes more acidic, the pH decreases, producing acidosis ECF receives more base substances, the pH rises, producing alkalosis Lungs primarily control excretion of CO2 resulting from metabolism Kidneys control excretion of hydrogen and bicarb

Acid-Base Balance Acid-Base balance is: the regulation of HYDROGEN ions.

pH The acidity or alkalinity of a solution is measured as pH . The more acidic a solution, the lower the pH. The more alkaline a solution , the higher the pH. Water has a pH of 7 and is neutral. The pH of arterial blood is normally between 7.35 and 7.45

Hydrogen ions The more Hydrogen ions, the more acidic the solution and the LOWER the pH. The lower Hydrogen concentration, the more alkaline the solution and the HIGHER the pH.

Buffer Systems Regulate pH by binding or releasing Hydrogen Most important buffer system: Bicarbonate-Carbonic Acid Buffer System (Blood Buffer systems act instantaneously and thus constitute the body’s first line of defense against acid-base imbalance)

Respiratory Regulation Lungs help regulated acid-base balance by eliminating or retaining carbon dioxide pH may be regulated by altering the rate and depth of respirations changes in pH are rapid, occurring within minutes normal CO 2 level 35 to 45 mm Hg

Renal Regulation Kidneys the long-term regulator of acid-base balance slower to respond may take hours or days to correct pH kidneys maintain balance by excreting or conserving bicarbonate and hydrogen ions normal bicarbonate level 22 to 26 mEq/L.

Factors Affecting Balance Age especially infants and the elderly Gender and Body Size amount of fat Environmental Temperature Lifestyle stress

Acid-Base Imbalances Respiratory Acidosis Respiratory Alkalosis Metabolic Acidosis Metabolic Alkalosis

Respiratory acidosis pH ↓ PaCO2 ↑ HCO3 ↓ Respiratory alkalosis pH ↑ PaCO2 ↓ HCO3 ↑ Metabolic acidosis pH ↓ PaCO2 HCO3 ↓ Metabolic alkalosis pH ↑ PaCO2 HCO3 ↑

Respiratory Acidosis Mechanism Hypoventilation or Excess CO 2 Production Etiology COPD Neuromuscular Disease Respiratory Center Depression Late ARDS Inadequate mechanical ventilation Sepsis or Burns Excess carbohydrate intake

Respiratory Acidosis (cont) Symptoms Dyspnea, Disorientation or coma Dysrhythmias pH < 7.35, PaCO 2 > 45mm Hg Hyperkalemia or Hypoxemia Treatment Treat underlying cause Support ventilation Correct electrolyte imbalance IV Sodium Bicarbonate

Respiratory Alkalosis Risk Factors and etiology Hyperventilation due to extreme anxiety, stress, or pain elevated body temperature overventilation with ventilator hypoxia salicylate overdose hypoxemia (emphysema or pneumonia) CNS trauma or tumor

Respiratory Alkalosis (cont) Symptoms Tachypnea or Hyperpnea Chest pain Light-headedness, syncope, coma, seizures Numbness and tingling of extremities Difficult concentrating, tremors, blurred vision Weakness, paresthesias, tetany Lab findings pH above 7.45 CO2 less than 35

Respiratory Alkalosis (cont) Treatment Monitor VS and ABGs Treat underlying disease Assist client to breathe more slowly Help client breathe in a paper bag or apply rebreather mask Sedation

Metabolic Acidosis Risk Factors/Etiology Conditions that increase acids in the blood Renal Failure DKA Starvation Lactic acidosis Prolonged diarrhea Toxins (antifreeze or aspirin) Carbonic anhydrase inhibitors - Diamox

Metabolic Acidosis (cont) Symptoms Kussmaul’s respiration Lethargy, confusion, headache, weakness Nausea and Vomiting Lab: pH below 7.35 Bicarb less than 22 Treatment treat underlying cause monitor ABG, I&O, VS

Metabolic Alkalosis Risk Factors/Etiology Acid loss due to vomiting gastric suction Loss of potassium due to steroids diuresis Antacids (overuse of)

Metabolic Alkalosis (cont) Symptoms Hypoventilation (compensatory) Dysrhythmias, dizziness Paresthesia, numbness, tingling of extremities Hypertonic muscles, tetany Lab: pH above 7.45, Bicarb above 26 CO2 normal or increased w/comp Hypokalmia, Hypocalcemia Treatment I&O, VS give potassium treat underlying cause

Interpreting ABGs 1. Look at the pH is the primary problem acidosis (low) or alkalosis (high) 2. Check the CO2 ( respiratory indicator) is it less than 35 (alkalosis) or more than 45 (acidosis) 3. Check the HCO3 ( metabolic indicator) is it less than 22 (acidosis) or more than 26 (alkalosis) 4. Which is primary disorder (Resp. or Metabolic)? If the pH is low (acidosis), then look to see if CO2 or HCO3 is acidosis (which ever is acidosis will be primary). If the pH is high (alkalosis), then look to see if CO2 or HCO3 is alkalosis (which ever is alkalosis is the primary). The one that matches the pH (acidosis or alkalosis), is the primary disorder.

Compensation The Respiratory system and Renal systems compensate each other attempt to return the pH to normal ABG’s show that compensation is present when the pH returns to normal or near normal If the non primary system is in the normal range (CO2 35 to 45) (HCO3 22-26), then that system is not compensating for the primary. For example: In respiratory acidosis (pH<7.35, CO2>45), if the HCO3 is >26, then the kidneys are compensating by retaining bicarbonate. If HCO3 is normal, then not compensating.

Water content varies with age & tissue type Infants – 73% Adult male – 60% Adult female – 50% Elderly – 45% Fat has the lowest water content (~20%). Bone is close behind (~22 – 25%). Skeletal muscle is highest at ~65%.

Functions of Body Fluid Major component of blood plasma Solvent for nutrients and waste products Necessary for hydrolysis of nutrients Essential for metabolism Lubricant in joints and GI tract Cools the body through perspiration Provides some mineral elements

Composition of Body Fluids Body fluids contain Electrolytes Anions – negative charge Cl, HCO3, SO4 Cations – positive charge Na, K, Ca Electrolytes are measured in mEq Minerals are ingested as compounds and are constituents of all body tissues and fluids Minerals act as catalysts

Electrolytes in Body Fluids Normal Values Sodium (Na+) 35 – 145 mEq/L Potassium (K+) 3.5 – 5.0 mEq/L Ionized Calcium (Ca++) 4.5 – 5.5 mg/dL Calcium (Ca++) 8.5 – 10.5 mg/dL Bicarbonate (HCO 3 ) 24 – 30 mEq/L Chloride (Cl -- ) 95 – 105 mEq/L Magnesium (Mg++) 1.5 – 2.5 mEq/L Phosphate (PO 4 --- ) 2.8 – 4.5 mg/dL

Body Fluids Intracellular fluid (ICF) found within the cells of the body constitutes 2/3 of total body fluid in adults major cation is potassium Extracellular fluid (ECF) found outside the cells accounts of 1/3 of total body fluid major cation is sodium

Terms Osmosis: movement of water across cell membranes from less concentrated to more concentrated Solutes: substances dissolved in a liquid Osmolality: the concentration within a fluid Diffusion: movement of molecules in liquids from an area of higher concentration to lower concentration Filtration: fluid and solutes move together across a membrane from area of higher pressure to one of lower pressure Active Transport: substance moves across cell membranes from less concentrated solution to more concentrated - requires a carrier

Routes of Fluid Loss Urine Insensible fluid loss Feces

Electrolytes Sodium Potassium Chloride Phosphate Magnesium Calcium Bicarbonate Electrolytes are important for: Maintaining fluid balance Contributing to acid-base regulation Facilitating enzyme reactions Transmitting neuromuscular reactions

Electrolyte concentrations are calculated in milliequivalents mEq/L = ion concentration (mg/L) x number of charges on one ion atomic weight Na + concentration in the body is 3300 mg/L Na + carries a single positive charge. Its atomic weight is approximately 23. Therefore, in a human the normal value for Na + is: 3300 mg/L = 143 mEq/L 23 Note: One mEq of a univalent is equal to one mOsm whereas one mEq of a bivalent ion is equal to ½ mOsm. However, the reactivity of 1 mEq is equal to 1 mEq.

Relative electrolyte concentrations: Plasma, Interstitial Fluid & ICF

Regulation of water balance It is not so much water that is regulated, but solutes. osmolality is maintained at between 285 – 300 mOsm. An increase above 300 mOsm triggers: Thirst Antidiuretic Hormone release

The Thirst Mechanism An increase of 2 – 3% in plasma osmolality triggers the thirst center of the hypothalamus. Secondarily, a 10 – 15% drop in blood volume also triggers thirst. This is a significantly weaker stimulus.

Dehydration Chronic dehydration leads to oliguria . Severe dehydration can result in hypovolemic shock . Causes include: Hemorrhage Burns Vomiting Diarrhea Sweating Diuresis, which can be caused by diabetes insipidus, diabetes mellitus and hypertension (pressure diuresis).

Hypotonic hydration A severe drop in osmolality Caused by: Excessive water intake Renal dysfunction Major consequence is hyponatremia. Hyponatremia results in: Cerebral edema (brain swelling) Sluggish neural activity Convulsions, muscle spasms, deranged behavior. Treated with I.V. hypertonic mannitol or something similar.

A rather lame illustration You do remember how osmosis works, don’t you?

Blood pressure, sodium, and water

Atrial Naturetic Peptide: The heart’s own compensatory mechanism.

Generation of new bicarbonate from phosphate

Generation of bicarbonate from glutamine deamination

Movement of Body Fluids Osmosis = movement across a semi-permeable membrane from area of lesser concentration to are of higher concentration; high solute concentration has a high osmotic pressure and draws water toward itself Osmotic pressure = drawing power of water (Osmolality) Osmolarity = concentration of solution

Movement of Body Fluids Colloid or Oncotic pressure = keeps fluid in the intravascular compartment by pulling water from the interstitial space back into the capillaries

Solutions Isotonic Solution The same concentration as blood plasma; expand fluid volume without causing fluid shift Hypotonic Solution Lower concentration than blood plasma; moves fluid into the cells causing them to enlarge Hypertonic solution Higher concentration than blood plasma; pulls fluid from cells causing them to shrink

Movement of Body Fluids Diffusion = Molecules move from higher concentration to lower Concentration gradient Filtration = water and diffusible substances move together across a membrane; moving from higher pressure to lower pressure Edema results from accumulation of excess fluid in the interstitial space Hydrostatic pressure causes the movement of fluids from an area of higher pressure to area of lower pressure

Active Transport Requires metabolic activity and uses energy to move substances across cell membranes Enables larger substances to move into cells Molecules can also move to an area of higher concentration (Uphill) Sodium-Potassium Pump Potassium pumped in – higher concentration in ICF Sodium pumped out – higher concentration in ECF

Regulation of Body Fluids Homeostasis is maintained through Fluid intake Hormonal regulation Fluid output regulation

Fluid Intake Thirst control center located in the hypothalamus Osmoreceptors monitor the serum osmotic pressure When osmolarity increases (blood becomes more concentrated), the hypothalamus is stimulated resulting in thirst sensation Salt increases serum osmolarity Hypovolemia occurs when excess fluid is lost

Fluid Intake Average adult intake 2200 – 2700 mL per day Oral intake accounts for 1100 – 1400 mL per day Solid foods about 800 – 1000 mL per day Oxidative metabolism – 300 mL per day Those unable to respond to the thirst mechanism are at risk for dehydration Infants, patients with neuro or psych problems, and older adults

Hormonal Regulation ADH (Antidiuretic hormone) Stored in the posterior pituitary and released in response to serum osmolarity Pain, stress, circulating blood volume effect the release of ADH Increase in ADH = Decrease in urine output = Body saves water Makes renal tubules and ducts more permeable to water

Hormonal Regulation Renin-angiotensin-aldosterone mechanism Changes in renal perfusion initiates this mechanism Renin responds to decrease in renal perfusion secondary to decrease in extracellular volume Renin acts to produce angiotensin I which converts to angiotensin II which causes vasoconstriction, increasing renal perfusion Angiotensin II stimulates the release of aldosterone when sodium concentration is low

Hormonal Regulation Aldosterone Released in response to increased plasma potassium levels or as part of the renin-angiotensin-aldosterone mechanism to counteract hypovolemia Acts on the distal portion of the renal tubules to increase the reabsorption of sodium and the secretion and excretion of potassium and hydrogen Water is retained because sodium is retained Volume regulator resulting in restoration of blood volume

Hormonal Regulation Atrial Natriuretic Peptide (ANP) ANP is a hormone secreted from atrial cells of the heart in response to atrial stretching and an increase in circulating blood volume ANP acts like a diuretic that causes sodium loss and inhibits the thirst mechanism Monitored in CHF

Fluid Output Regulation Organs of water loss Kidneys Lungs Skin GI tract

Fluid Output Regulation Kidneys are major regulatory organ of fluid balance Receive about 180 liters of plasma to filter daily 1200 – 1500 mL of urine produced daily Urine volume changes related to variation in the amount and type of fluid ingested Skin Insensible Water Loss Continuous and occurs through the skin and lungs Can significantly increase with fever or burns Sensible Water Loss occurs through excess perspiration Can be sensible or insensible via diffusion or perspiration 500 – 600 mL of insensible and sensible fluid lost through skin each day

Fluid Output Regulation Lungs Expire approx 500 mL of water daily Insensible water loss increases in response to changes in resp rate and depth and oxygen administration GI Tract 3 – 6 liters of isotonic fluid moves into the GI tract and then returns to the ECF 200 mL of fluid is lost in the feces each day Diarrhea can increase this loss significantly

Regulation of Electrolytes Major Cations in body fluids Sodium (Na+) Potassium (K+) Calcium (Ca++) Magnesium (Mg++)

Sodium Regulation Most abundant cation in the extracellular fluid Major contributor to maintaining water balance Nerve transmission Regulation of acid-base balance Contributes to cellular chemical reactions Sodium is taken in via food and balance is maintained through aldosterone

Potassium Regulation Major electrolyte and principle cation in the extracellular fluid Regulates metabolic activities Required for glycogen deposits in the liver and skeletal muscle Required for transmission of nerve impulses, normal cardiac conduction and normal smooth and skeletal muscle contraction Regulated by dietary intake and renal excretion

Calcium Regulation Stored in the bone, plasma and body cells 99% of calcium is in the bones and teeth 1% is in ECF 50% of calcium in the ECF is bound to protein (albumin) 40% is free ionized calcium Is necessary for Bone and teeth formation Blood clotting Hormone secretion Cell membrane integrity Cardiac conduction Transmission of nerve impulses Muscle contraction

Magnesium Regulation Essential for enzyme activities Neurochemical activities Cardiac and skeletal muscle excitability Regulation Dietary Renal mechanisms Parathyroid hormone action 50 – 60% of magnesium contained in bones 1% in ECF Minimal amount in cell

Anions Chloride (Cl - ) Major anion in ECF Follows sodium Bicarbonate (HCO 3 - ) Is the major chemical base buffer Is found in ECF and ICF Regulated by kidneys

Anions Phosphate (PO 4 --- ) Buffer ion found in ICF Assists in acid-base regulation Helps to develop and maintain bones and teeth Calcium and phosphate are inversely proportional Promotes normal neuromuscular action and participates in carbohydrate metabolism Absorbed through GI tract Regulated by diet, renal excretion, intestinal absorption and PTH

Causes of Electrolyte Imbalances Excessive sweating Fluid loss leading to dehydration Excessive vomiting Diuretics like Lasix (K+ depletion) Massive blood loss Dehydration may go unnoticed in hot, dry climates Renal failure

Sodium Most abundant in extracellular space Moves among three fluid compartments Found in most body secretions

Hyponatremia – Low Sodium Seizures Personality changes Nausea/vomiting Tachycardia Convulsion Normal Na (135-145)

Hypernatremia Excessive Na in ECF Loss of water Diarrhea Insensible water loss Water deprivation Gain of Sodium Diabetes insipidus Heat stroke

Hypokalemia – Low Potassium Severe leg cramps Flaccid muscles Fatigue Irregular pulse Chest discomfort EKG changes T wave flattens Normal Potassium-3.5-5

Hyperkalemia CNS Nausea and vomiting Peripheral Nervous System Tremors, twitching Heart Bradycardia, peaked T wave

Hypocalcemia – Low Calcium Tingling of fingers Tetany Muscle cramps Positive Trousseau’s Carpal spasm Positive Chvostek’s Contraction of facial muscle when facial nerve tapped

Hypercalcemia Causes Prolonged immobility Osteoporosis Thiazide diuretics Acidosis Signs/symptoms N/V, weakness Hypoactive reflexes Cardiac arrest

Hypomagnesemia Causes Malnutrition Alcoholism Polyuria Pre-ecclampsia Signs/symptoms Muscle tremor Hyperactive deep reflexes Chvostek’s/Trousseau’s Difficulty breathing

Hypermagnesemia Causes Renal failure Excessive intake Signs/symptoms Low BP Muscle weakness Absent reflexes Bradycardia

Cheat Sheet Increase pH – alkalosis Decrease pH – acidosis Respiratory – CO2 Metabolic (kidneys)– HCO3 CO2 has an inverse relationship with pH When pH goes down, CO2 goes up HCO3 follows pH. If pH goes up so does HCO3 CO2 increases, pH decreases – resp. acidosis CO2 decreases, pH increases – resp. alkalosis HCO3 increases, pH increases – metabolic alkalosis HCO3 decreases, pH decreases – metabolic acidosis

Question An older client comes to the emergency department experiencing chest pain and shortness of breath. An arterial blood gas is ordered. Which of the following ABG results indicates respiratory acidosis? 1. pH - 7.54, PaCO2 – 28, HCO3 – 22 2. pH – 7.32, PaCO2 – 46, HCO3 – 24 3. pH – 7.31, PaCO2 – 35, HCO3 – 20 4. pH – 7.5, PaCO2 – 37, HCO3 - 28

Acid base balance + fluid balance

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