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50 Cards in this Set
- Front
- Back
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Introduction
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Maintaining an acid-base balance is vital to our body's cellular function and homeostasis
We need a balance between acids & bases to survive We have regulatory mechanisms in us that help us achieve this balance (20 bases: 1 acid) |
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pH
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The negative logarithm of the H+ concentation. The H+ concentration of a solution is responsible for its' acidity. (norm: 7.35-7.45)
A decreased pH signifies an elevated H+ (acidosis) An increased pH signifies less H+ (alkalosis) |
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Acid
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A compound that gives up H+ or donates protons, e.g. H2CO3
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Base
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A H+ ion acceptor or proton acceptor, e.g. HCO3
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pCO2 or PaCO2
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Refers to the partial pressure of CO2 gas within an ABG sample (norm: 35-45)
Regulation is carried out by the lungs and is referred to as the respiratory component in acid-base terminology Increased respiratory rate (increased alveolar ventilation) = elimination of CO2 = decreased pCO2 Decreased respiratory rate (alveolar hypoventilation) = accumulation of CO2 = increased pCO2 |
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HCO3
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Bicarbonate is the major blood base (norm: 22-26 meq/L)
Regulation is carried out by the kidneys and is referred to as the renal or metabolic component in acid-base terminology An increased HCO3 = increased pH (decreased H+) A decreased HCO3 = decresed pH (increased H+) |
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pO2 or PaO2
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Refers to the partial pressure of O2
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Acid-Base Balance
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Many disease processes can alter the acid-base balance of our bodies, the result may be acidosis or alkalosis
If this occurs, our regulatory systems will have to work harder to balance out our acids & bases All of this has to do with interpreting ABGs |
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ABG interpretation
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Purpose of ABG interpretation is to determine the acid-base status and OXYGENATION of our clients
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Basic Concepts
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Acid-base balance is achieved by regulating H+ ion concentration in the body fluids
H+ concentration is presented as pH Increase H+ = solution more acid Decrease H+ = solution more alkaline |
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Relationship between ph and H+ ion concentration
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There is an inverse relationship between pH and H+ concentration
Increase H+ = decrease pH/visa versa |
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Ratio of base to acid
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pH determined by the ratio of base to acid = 20 to 1
The balance between acids and bases must be kept within a narrow range of 7.35-7.45, in ECF (blood which is slightly alkaline 7=neutral) |
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Acidosis
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a pH < 7.35
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Alkalosis
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a pH > 7.45
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Acid-Base Balance
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The acidity or alkalinity of a solution depends on its' H+ concentration
An increase H+ = acidity (Decrease pH) A decrease H+ = alkalinity (increase pH) |
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Regulatory Mechanisms: First Responder
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Chemical Buffers: react immediately, fastest and primary regulator
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Respiratory System: Second Respondeer
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Responds within minutes
Reaches maximum effectiveness within hours |
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Renal System: Third Responder
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Slow to respond
Takes 2-3 days to respond maximally |
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Buffer Systems
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The function of buffers is to react with strong acids & bases & replace them with weak ones that change the normal pH only slightly
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Buffer Systems
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Chemical buffers include: bicarbonate (HCO3), PO4, and protein buffers
The most important buffer sys. is carbonic acid (H2CO3) bicarb (HCO3) system |
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H2CO3-HCO3 Buffer System
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Consists of a pair of compounds
One is a weak acid (H2CO3) carbonic acid One is a weak base (HCO3) bicarb In solution, this pair dissociates as follows: acidic component=H2CO3>/<H+ +HCO3 base component= NaHCO3>/<Na+ +HCO3 Each member has a specific role in helping the body maintain constant pH |
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H2CO3-HCO3 Buffer System
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If body's pH is threatened by presence of a strong acid, the weak base of the buffer attacks: e.g. HCL+NaHCO3</> NaCL+H2CO3
(strong acid+weak base)</>salt+weak acid |
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H2CO3-HCO3 Buffer System
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Summary: due to the action of the weak base/NaHCO3 (of buffer syst.), the strong acid (HCL) has been replaced by a weak acid and salt therefore pH remains relatively constant. THIS IS THE KEY pH REMAINS CONSTANT
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REVIEW-Buffer System
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H+ acid
Ratio of base to acid 20 bases: 1 acid First body system to respond |
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REVIEW-Buffer System
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THEN we must remember that in order to keep a normal pH the body must have a 20:1 ratio of base to acid
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REVIEW-Buffer System
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Therefore the buffered substances (HCO3 & H2CO3) that are produced from buffering regulatory sys. have to be removed from the body to maintain the 20:11 ratio.
HOW DO WE DO THIS? |
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REVIEW-Buffer System
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This is done by the kidneys or by the lungs
Second body response=Respiratory system -H2CO3(carbonic acid)>H2O+CO2(lungs) -CO2 is excreted by the lungs |
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The Respiratory System
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Lungs serve to regulate only the H2CO3 portion of the HCO3-H2CO3 buffer system
Lungs excrete CO2 and H2O Amount of CO2 in blood is directly r/t H2CO3 concentration CO2+H2O=H2CO3 With increased RR less CO2 remains in blood With decreased RR=increased CO2 in blood |
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Respiratory System
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If the etiological factor of an acid-base imbalance is resp. failure then the resp. system looses its' ability to correct a pH alteration
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Third body response=Renal System
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Increase CO2(because our lungs hold on to it) our body will combine the CO2 with H2O to make H2CO3. This will dissociate into H+ + HCO3 and our kidneys will reabsorb or excrete the HCO3 and excrete or reabsorb H+ ions.
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Renal System
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If the renal system is the cause of an acid-base imbalance (e.g. renal failure) then it looses its' ability to correct a pH alteration
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Summary of Buffer Systems
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Our buffer systems work in conjunction with the kidneys and the lungs
CO2 & H2O=regulated by the lungs HCO3 & H+=regulated by the kidneys(they excrete or reabsorb these) |
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REMEMBER....
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An acid-base disturbance is produced when ratio of 20:1 between base (HCO3) and acid (H2CO3) is altered.
Compensation: ability of the body to correct an acid-base imbalance by controlling CO2 concentration and by retaining or eliminating both H+ and HCO3- ions When the compensatory mechanism fails an acid-base disturbance results. |
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TYPES OF ACID-BASE IMBALANCES
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Metabolic Acidosis(decreased HCO3)
Metabolic Alkalosis(increased HCO3) Respiratory Acidosis(increased CO2) Respiratory Alkalosis(decreased CO2) |
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Metabolic Alkalosis (remember lk in alkalosis=low K+ (potassium))
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Severe Vomiting=Low K+
Excess gastric suction=Low K+ Diuretic Excess NaHCO3 intake, or L/R IV Hypokalemia Excess Mineralcorticoids hypernatremia hyperglycemia hypokalemia |
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Metabolic Acidosis
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Diabetic Ketoacidosis
Starvation, crash diets Severe Diarrhea, (ileostomy) Renal Failure, increased K+ Shock GI Fistulas ASA overdose |
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Respiratory Acidosis (retain CO2)
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COPD
Barbiturate overdose, hypoventilation Severe pneumonia Guillain-Barre syndrome, other muscle weakness-depressed respirations Under ventilation or Atelectasis |
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Respiratory Alkalosis (blow-off CO2)
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Hyperventilation
-hypoxia -Pulmonary embolism -Anxiety, fear, pain, stress fever Mechanical over-ventilation Stimulated respiratory center -Septicemia -Brain injury |
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ROME
Respiratory Opposite Metabolic Equal |
Respiratory Acidosis=pH Low, pCO2 High
Respiratory Alkalosis=pH High, pCO2 Low Metabolic Acidosis=pH Low, HCO3- Low Metabolic Alkalosis=pH High, HCO3- High |
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KEY POINTS TO REMEMBER
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1. In respiratory acid-base imbalances, the pH and PaCO2 values are inversely abnormal
Ventilation determines respiratory acid-base balance: Hypoventilation produces acidosis; hyperventilation produces alkalosis. For respiratory acidosis, be sure patient's airway is clear, administer oxygen as ordered, and closely monitor his cardiac function and clinical status. For respiratory alkalosis, try to calm the patient and slow his breathing. |
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KEY POINTS TO REMEMBER
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In metabolic acid-base imbalances, the pH and HCO3 values are both high or both low.
A large gain of a strong acid or a loss of bicarbonate produces metabolic acidosis; a loss of acid or a gain of bicarbonate produces metabolic alkalosis. For metabolic acidosis or alkalosis, monitor the patient's vital signs, cardiac status, intake and output, level of consciousness, and ABG levels; administer replacement fluids and electrolytes; and protect the patient from injury. |
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Assessment Metabolic Acidosis
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Early restless, drowsy, coma
Disoriented, dizzy Decreased B/P Headache Metabolic, N/V, diarrhea and Abd. Pain Metabolic=deep rapid, Kussmaul's Resp Respiratory=rapid shallow hypoventilation (lungs unable to compensate)trying to blow off CO2 |
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Assessment: Alkalosis
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Confusion, dizzy
N/V Tachycardia and arrhythmias Hypokalemia Respiratory=deep rapid breathing, tingling of extremities (lungs unable to compensate) Metabolic=slow respirations (compensate Hypoventilation) |
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Nursing Process
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Multitude of nursing diagnoses are applicable for clients experiencing any of the acid-base imbalances depends on cause
Ineffective Breathing Pattern Altered Tissue Perfusion Risk for Injury |
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Oxygenation
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Both PO2 and SaO2 are used to determine the adequacy of Oxygenation
PO2 measures the O2 dissolved in Blood norm=80-100 (direct measurement) SaO2 measured by Oximetry measures the Oxyhemoglobin Saturation (% of Hgb combined with O2) norm = 94-98 |
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Oxyhemoglobin dissociation curve
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Normally the SaO2 drops incrementally when PaO2 drops slightly BUT when PaO2 is below 60 this does not hold true.
30-60-90 rule -If SaO2 is 60, PaO2 maybe 30 -If SaO2 is 90 the PaO2 maybe 60 While PaO2 of 90 usually indicates SaO2 of 95% BELOW 93% SaO2 INDICATES WHAT PaO2??? |
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Hypoxia
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PaO2 or SaO2 fall below normal
Manifestations: Disorientation Decreased AP, Decreased RR Diaphoresis Cyanosis Coma, death Longstanding (COPD)=fatigue, drowsiness, apathy |
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Drawing ABG's
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Obtained by MD, resp therapy, ?IV Nurse
Arterial therefore pressure for 5 minutes or 15 if anticoagulated Sent on ice unless immediate transport Lab slip Temperature, LOC Supplemental O2 Time,date,initials |
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Acid Base/ABG's: NORMALS
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pH=7.35-7.45
pCO2=35-45 HCO3=22-26 |
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VERY IMPORTANT!!!!
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Remember anytime you have a normal pH you have complete or full compensation
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