Acid base balance + fluid balance
-
Upload
zahra-al-haj-issa -
Category
Health & Medicine
-
view
5.717 -
download
8
description
Transcript of 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 (CO2) combines with water to form carbonic acid (H2CO3), which in turn rapidly dissociates to form hydrogen ion and bicarbonate (HCO3
- ).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 CO2 in circulation. In the above example, the body could increase breathing (respiratory alkalosis) to expel the excess CO2, 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 anhydrasewhen 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 integrityMaintain 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 dioxidepH may be regulated by altering the rate and depth
of respirationschanges in pH are rapid,
occurring within minutes
normal CO2 level 35 to 45 mm Hg
Renal Regulation
Kidneysthe long-term regulator of acid-base balanceslower 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
Ageespecially infants and the elderly
Gender and Body Sizeamount of fat
Environmental TemperatureLifestyle
stress
Acid-Base Imbalances
Respiratory AcidosisRespiratory AlkalosisMetabolic AcidosisMetabolic Alkalosis
Respiratory acidosis pH ↓
PaCO2 ↑
HCO3 ↓
Respiratory alkalosis pH ↑
PaCO2 ↓
HCO3 ↑
Metabolic acidosis pH ↓
PaCO2
HCO3 ↓
Metabolic alkalosis pH ↑
PaCO2
HCO3 ↑
Respiratory AcidosisMechanism
Hypoventilation or Excess CO2 Production
EtiologyCOPDNeuromuscular DiseaseRespiratory Center Depression Late ARDSInadequate mechanical ventilationSepsis or BurnsExcess carbohydrate intake
Respiratory Acidosis (cont)Symptoms
Dyspnea, Disorientation or comaDysrhythmiaspH < 7.35, PaCO2 > 45mm HgHyperkalemia or Hypoxemia
TreatmentTreat underlying causeSupport ventilationCorrect electrolyte imbalanceIV Sodium Bicarbonate
Respiratory Alkalosis
Risk Factors and etiologyHyperventilation due to
extreme anxiety, stress, or painelevated body temperatureoverventilation with ventilatorhypoxiasalicylate overdosehypoxemia (emphysema or pneumonia)CNS trauma or tumor
Respiratory Alkalosis (cont)
SymptomsTachypnea or HyperpneaChest painLight-headedness, syncope, coma, seizuresNumbness and tingling of extremitiesDifficult concentrating, tremors, blurred visionWeakness, paresthesias, tetanyLab findings
pH above 7.45CO2 less than 35
Respiratory Alkalosis (cont)
TreatmentMonitor VS and ABGsTreat underlying diseaseAssist client to breathe more slowlyHelp client breathe in a paper bag or apply rebreather maskSedation
Metabolic Acidosis
Risk Factors/EtiologyConditions that increase acids in the blood
Renal FailureDKAStarvationLactic acidosis
Prolonged diarrheaToxins (antifreeze or aspirin)Carbonic anhydrase inhibitors - Diamox
Metabolic Acidosis (cont)
SymptomsKussmaul’s respirationLethargy, confusion, headache, weaknessNausea and VomitingLab:
pH below 7.35Bicarb less than 22
Treatmenttreat underlying causemonitor ABG, I&O, VS
Metabolic AlkalosisRisk Factors/Etiology
Acid loss due tovomitinggastric suction
Loss of potassium due tosteroidsdiuresis
Antacids (overuse of)
Metabolic Alkalosis (cont)Symptoms
Hypoventilation (compensatory)Dysrhythmias, dizzinessParesthesia, numbness, tingling of extremitiesHypertonic muscles, tetanyLab: pH above 7.45, Bicarb above 26
CO2 normal or increased w/comp Hypokalmia, Hypocalcemia
TreatmentI&O, VSgive potassiumtreat 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.
CompensationThe Respiratory system and Renal systems
compensate each other attempt to return the pH to normal
ABG’s show that compensation is present whenthe 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.
Fluid & Electrolyte Balance
Where’s the water?
Water content varies with age & tissue type
1. Infants – 73%
2. Adult male – 60%
3. Adult female – 50%
4. 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 plasmaSolvent for nutrients and waste productsNecessary for hydrolysis of nutrientsEssential for metabolismLubricant in joints and GI tractCools the body through perspirationProvides some mineral elements
Composition of Body Fluids
Body fluids contain ElectrolytesAnions – negative charge
Cl, HCO3, SO4
Cations – positive charge Na, K, Ca
Electrolytes are measured in mEqMinerals are ingested as compounds and are
constituents of all body tissues and fluidsMinerals act as catalysts
Electrolytes in Body Fluids
Normal ValuesSodium (Na+) 35 – 145 mEq/LPotassium (K+) 3.5 – 5.0 mEq/LIonized Calcium (Ca++) 4.5 – 5.5 mg/dLCalcium (Ca++) 8.5 – 10.5 mg/dLBicarbonate (HCO3) 24 – 30 mEq/L
Chloride (Cl--) 95 – 105 mEq/LMagnesium (Mg++) 1.5 – 2.5 mEq/LPhosphate (PO4
---) 2.8 – 4.5 mg/dL
Body FluidsIntracellular fluid (ICF)
found within the cells of the bodyconstitutes 2/3 of total body fluid in adultsmajor cation is potassium
Extracellular fluid (ECF)found outside the cellsaccounts of 1/3 of total body fluidmajor 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
UrineInsensible fluid lossFeces
Electrolytes
SodiumPotassiumChloridePhosphate
MagnesiumCalciumBicarbonate
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/LNa+ 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
Sources of intake & output
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:
ThirstAntidiuretic 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.
DehydrationChronic 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 hydrationA severe drop in osmolalityCaused by:
Excessive water intakeRenal dysfunction
Major consequence is hyponatremia.Hyponatremia results in:
Cerebral edema (brain swelling)Sluggish neural activityConvulsions, muscle spasms, deranged behavior.
Treated with I.V. hypertonic mannitol or something similar.
A rather lame
illustrationYou do remember
how osmosis works, don’t you?
Sodium regulation
Blood pressure, sodium, and water
Atrial Naturetic Peptide:The heart’s
own compensatory mechanism.
Reabsorption of
bicarbonate
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 itselfOsmotic 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 SolutionThe same concentration as blood plasma; expand fluid
volume without causing fluid shift
Hypotonic SolutionLower concentration than blood plasma; moves fluid into the
cells causing them to enlarge
Hypertonic solutionHigher concentration than blood plasma; pulls fluid from cells
causing them to shrink
Movement of Body Fluids
Diffusion = Molecules move from higher concentration to lowerConcentration 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 membranesEnables larger substances to move into cellsMolecules can also move to an area of higher concentration
(Uphill)Sodium-Potassium Pump
Potassium pumped in – higher concentration in ICFSodium pumped out – higher concentration in ECF
Regulation of Body Fluids
Homeostasis is maintained throughFluid intakeHormonal regulationFluid output regulation
Fluid Intake
Thirst control center located in the hypothalamusOsmoreceptors monitor the serum osmotic pressureWhen osmolarity increases (blood becomes more
concentrated), the hypothalamus is stimulated resulting in thirst sensationSalt 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 daySolid foods about 800 – 1000 mL per dayOxidative metabolism – 300 mL per day
Those unable to respond to the thirst mechanism are at risk for dehydrationInfants, 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 osmolarityPain, stress, circulating blood volume effect the release of
ADHIncrease in ADH = Decrease in urine output = Body
saves waterMakes renal tubules and ducts more permeable to water
Hormonal Regulation
Renin-angiotensin-aldosterone mechanismChanges in renal perfusion initiates this mechanismRenin responds to decrease in renal perfusion secondary to
decrease in extracellular volumeRenin 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
AldosteroneReleased 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 retainedVolume 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 lossKidneysLungsSkinGI 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 LossContinuous and occurs through the skin and lungs Can significantly increase with fever or burns
Sensible Water Loss occurs through excess perspirationCan be sensible or insensible via diffusion or perspiration
500 – 600 mL of insensible and sensible fluid lost through skin each day
Fluid Output Regulation
LungsExpire approx 500 mL of water dailyInsensible water loss increases in response to changes in
resp rate and depth and oxygen administration
GI Tract3 – 6 liters of isotonic fluid moves into the GI tract and then
returns to the ECF200 mL of fluid is lost in the feces each day
Diarrhea can increase this loss significantly
Regulation of Electrolytes
Major Cations in body fluidsSodium (Na+)Potassium (K+)Calcium (Ca++)Magnesium (Mg++)
Sodium Regulation
Most abundant cation in the extracellular fluidMajor contributor to maintaining water balance
Nerve transmissionRegulation of acid-base balanceContributes 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 fluidRegulates metabolic activitiesRequired for glycogen deposits in the liver and skeletal
muscleRequired 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 cells99% of calcium is in the bones and teeth1% is in ECF50% of calcium in the ECF is bound to protein (albumin)40% is free ionized calcium Is necessary for
Bone and teeth formationBlood clottingHormone secretionCell membrane integrityCardiac conductionTransmission of nerve impulsesMuscle contraction
Magnesium Regulation
Essential for enzyme activitiesNeurochemical activitiesCardiac and skeletal muscle excitabilityRegulation
DietaryRenal mechanismsParathyroid hormone action
50 – 60% of magnesium contained in bones1% in ECFMinimal amount in cell
Anions
Chloride (Cl-) Major anion in ECFFollows sodium
Bicarbonate (HCO3-)
Is the major chemical base bufferIs found in ECF and ICFRegulated by kidneys
Anions
Phosphate (PO4---)
Buffer ion found in ICFAssists in acid-base regulationHelps to develop and maintain bones and teethCalcium and phosphate are inversely proportionalPromotes normal neuromuscular action and participates in
carbohydrate metabolismAbsorbed through GI tractRegulated by diet, renal excretion, intestinal absorption and PTH
Causes of Electrolyte Imbalances
Excessive sweatingFluid loss leading to dehydrationExcessive vomitingDiuretics like Lasix (K+ depletion)Massive blood lossDehydration may go unnoticed in hot, dry climatesRenal failure
Sodium
Most abundant in extracellular spaceMoves among three fluid compartmentsFound in most body secretions
Hyponatremia – Low Sodium
SeizuresPersonality changesNausea/vomitingTachycardiaConvulsionNormal Na (135-145)
Hypernatremia
Excessive Na in ECFLoss of water
DiarrheaInsensible water lossWater deprivation
Gain of SodiumDiabetes insipidusHeat stroke
Hypokalemia – Low Potassium
Severe leg crampsFlaccid musclesFatigueIrregular pulseChest discomfortEKG changes
T wave flattens
Normal Potassium-3.5-5
Hyperkalemia
CNSNausea and vomiting
Peripheral Nervous SystemTremors, twitching
Heart Bradycardia, peaked T wave
Hypocalcemia – Low Calcium
Tingling of fingersTetanyMuscle crampsPositive Trousseau’s
Carpal spasmPositive Chvostek’s
Contraction of facial muscle when facial nerve tapped
Hypercalcemia
CausesProlonged immobilityOsteoporosisThiazide diureticsAcidosis
Signs/symptomsN/V, weaknessHypoactive reflexesCardiac arrest
Hypomagnesemia
CausesMalnutritionAlcoholismPolyuriaPre-ecclampsia
Signs/symptomsMuscle tremorHyperactive deep reflexesChvostek’s/Trousseau’sDifficulty breathing
Hypermagnesemia
CausesRenal failureExcessive intake
Signs/symptomsLow BPMuscle weaknessAbsent reflexesBradycardia
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