fluids and electrolytes, acids and bases chapter 4
TRANSCRIPT
Fluids and Fluids and Electrolytes,Electrolytes,
Acids and BasesAcids and BasesChapter 4
Distribution of Body FluidsTotal body water – all fluids – 60% weight
(kg)Intracellular fluid (ICF) 40% TBW
Extracellular fluid (ECF) 20% TBWInterstitial fluid – between cellsIntravascular fluid – blood plasmaLymph, synovial, intestinal, CSF, sweat,
urine, pleural, peritoneal, pericardial and intraocular fluid
“cells live in a fluid environment with electrolytes and acid base concentrations maintained within a
narrow range”
changes or shifts → radically alter
metabolism → life threatening
Distribution of Body FluidsPediatrics
◦75% to 80% body weight◦Susceptible to significant changes in body fluids - dehydration
Aging◦↓ % of total body water◦ adipose and muscle mass ◦↓ renal function◦↓ thirst perception
Water Movement Between ICF and ECF“water, nutrients and waste products”capillary interstitial space
• 1.Capillary hydrostatic pressure – blood pressure “fluid out”
• • 2.Capillary oncotic pressure – water
attraction “fluid in”(Plasma Proteins)
• Interstitial hydrostatic pressure – fluid towards capillary
• Interstitial oncotic pressure – water attraction “fluid in”
water movement
Edema: 4 Major Causes“excessive accumulation of fluids within the
interstitial space”1.↑ hydrostatic pressure
◦Venous obstruction – DVT, hepatic obstruction◦Salt and water retention – heart, renal failure
2.↓ plasma oncotic pressure◦↓ albumin – liver disease, malnutrition, kidney
disease, burns, hemorrhage
Edema↑ capillary permeability – trauma,
burns, neoplastic and allergic reactions
Lymph obstruction – removal nodes (surgery) inflammation or tumors
Sodium, Chloride & Water Balance
“kidneys and hormones” – central role
Water : ADH – hypothalamus – posterior pituitary
Na+ and Cl- ◦aldosterone – adrenal gland◦Natriuretic hormones– atrial muscle
Sodium, Chloride BalanceSodium (Na+)
◦Primary ECF cation◦Regulates osmotic forces◦Role
Neuromuscular irritability, acid-base balance, cellular reactions, and membrane transport
Chloride (Cl-)◦Primary ECF anion◦Provides electroneutrality
Sodium and Water BalanceBalance between Na+ and H2O - ↑ or ↓ of salt↑ or ↓ water
Tonicity – change in concentration of solutes (salt) with relation to solvent (water)
Tonicity (280 – 294m Osm)Isotonic – 0.9% NaCl – iso osmolar
imbalance no cells
Hypertonic – ECF > 0.9% NaCl – (↓ H2O or ↑ salt) cells shrink
Hypotonic – ECF < 0.9% NaCl (↑ H2O or ↓ salt) cells swell
“Extracellular Fluid”- interstitial space
Sodium (Na+)
90% ECF cations135 – 145 mEq/L
Hypernatremia - > 145 mEq/L
Hyponatremia - < 135 mEq/L
Hypernatremia-causes• ↑ Na or ↓ H2O• IV therapy – acidosis (NaHCO3)
Cushing's Syndrome - ↑ ACTH → aldosteronefever, respiratory infection - ↓ H2Odiabetes, diarrhea - ↓ H2O ↓ H2O intake - coma
• H2O movement ICF → ECF(interstitial)• Manifestations–Intracellular dehydration: convulsions, thirst, fever, muscle twitching, hyperreflexia
Hyponatremia↓ Na or ↑ H2O Vomiting, diarrhea, GI suction, burns,
diuretics, D5W replacement (isotonic sol’n)
Manifestations◦Lethargy, confusion, depressed reflexes, seizures, coma, hypotension, tachycardia, ↓ urine output
HypochloremiaResult of hyponatremia or ↑ HCO3
Vomiting – loss HCl
Cystic fibrosis
Potassium (resting potential)Major intracellular electrolyte98% intracellular – Na – K – ATP Pump3.5 – 5.0 mEq/L
Transmission and conduction of nerve impulses, normal cardiac rhythm, skeletal and smooth muscle contractions: “action potentials”
“BAD BOY of ELECTROLYTES”
Potassium LevelsChange in pH affects K+ balance –
acidosis – ↑ ICF H+ → K+ moves out to ECF maintains + ion balance
Aldosterone; insulin, epinephrine, alkolosis, K+ → into cell
Glucagon # entry into cellGlucocorticoids → K+ excretion
Hypokalemia K+ < 3.5 mEq/L
↓ intake, ↑ loss, ↑ entry into cells
Manifestations: membrane hyperpolorizations ↓ excitability – weakness, smooth muscle, atrophy, cardiac dysrhythmias (bradycardia…asystole)
HyperkalemiaK+ > 5.0 mEq/L – rare
↑ shift from ICF (acidosis), ↓ renal excretion, insulin deficiency or cell trauma
HyperkalemiaMild attacks
◦↑ neuromuscular irritability – tingling of lips & fingers, restlessness, intestinal cramps – diarrhea
Severe attacks◦No repolarization → muscle weakness, ↓ tone,
flaccid paralysis ◦Cardiac dysrhythmias:”funky chicken”
◦SeeTable 4-6 Clinical Manifestations
Calcium (threshold potential)99% located in bone – hydroxyapatiteBone, teeth, blood clotting, hormone
secretion, cell receptor function Hypo - ↓ block of Na into cell ↑
neuromuscular excitability (muscle cramps)
Hyper - ↑ block Na - ↓ neuromuscular excitability (muscle weakness, cardiac arrest, kidney stones, constipation)
Big Picture…
Low SERUM K...decreased excitability◦Nerves & muscles…bradycardia---asystole
High SERUM K …increased excitability◦Cardiac dysrhythmias
Low SERUM Ca… increased excitability◦“Chvostek & Trousseau’s Signs”
High SERUM Ca… decreased excitability
Acid-Base BalanceAcid-Base BalanceHydrogen ion and pH
pH (0 to 14)Inverse logarithm of the H+ concentration -
0.0000001 mg/L – 1x10 -7
so pH = 7pH = power of hydrogenpH changes by one unit (7 → 6)
[H+] 10 fold
Biological fluidspH < 7.4 = acidic > 7.4 = basic
( 7.35-7.45)
pHAcids are formed as end products of
protein, carbohydrate and fat metabolism
Narrow “life range” – 7.35 – 7.45
Bone – lung – kidneys – major regulatory organs
“Absolute Range of Life:6.8-7.8” see Table 4-8 pH of body fluids
pHBody acids exist in two forms
◦Volatile H2CO3 (maybe eliminated as CO2)
◦Nonvolatile – eliminated by kidneys sulfuric, phosphoric
Buffering SystemsBuffer is a chemical that binds XS H+ or
OH- without a significant change in pH
Consists of a PAIR of a weak acid and its conjugate base
Most important plasma buffering system 1. Carbonic acid – bicarbonate system2. Hemoglobin (intracellular)
Buffering SystemsH2O + CO2 H2CO3 H+ + HCO3
-
1 20 Lung
Kidney
Phosphate- HPO4Ammonia –
NH3
Compensation◦Respiratory - ↑ or ↓ CO2
◦Renal - ↑ or ↓ acid/alkaline urine
Correction – buffer pairs →
Other Buffering SystemsProteins: - charge, mostly intracellular
Hemoglobin –
H + Hb → HHb + CO2 → HHbCO2 (weak acid)
Buffer Systems Rate of ReactionBuffer Systems Rate of Reaction
Bicarbonate system: instantaneously
Lungs: minutes to hours
Kidneys: hours to days
Acidosis and AlkalosisFour categories
◦Respiratory acidosis - ↑ PaCO2
◦Respiratory alkalosis - ↓ PaCO2
◦Metabolic acidosis - ↓ HCO3- or↑
other acids
◦Metabolic alkalosis - ↑ HCO3- (XS loss
acids)
Normal Values
pH = 7.35 – 7.45pO2 = 80 to 100 mmHgpCO2 = 35 – 45 mmHgHCO3 = 22-26 mEq/LSaO2 = > 92% - here
PatientABG: pH = 7.3
pCO2 = 40 mmHg pO2 = 70 mmHgHCO3 = 20 mEq/L
1. pH = ? → acidosis 2. pCO2 = ? → normal3. HCO3 = ? → low 4. pO2 = ? → low
Must know this…Must know this…
PaCO2: basic <(35-45mmHg) >acidotic
HCO3: acidotic < (22-26mEq/L)
>basic
ABG’s - CompensationABG’s - Compensation
Patient◦pH = 7.30 1. pH = acidotic◦PCO2 = 30mm Hg 2. PCO2 = alkalotic◦PO2 = 68mm Hg 3. PO2 = hypoxic◦HCO3 = 14mEq/L 4. HCO3 = acidotic◦O2 sat. = 92% 5. O2 sat = low◦ ◦“same directions = compensation”
◦Metabolic acidosis with partial respiratory compensation
Big Picture
ACIDOSIS: CNS depression◦Stupor to confusion to coma
ALKYLOSIS: CNS irritability◦Restlessness to seizures
Brittany Murphy
Died : Community acquired pneumonia,Anemia,Drug Intoxication