ACID BASE BALANCE

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ACID BASE BALANCE
Presented by Martin Ponciano, LVN, MS
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Arterial Blood Gases

• Indicator of respiratory and renal function in
  maintaining acid base balance
• Indicator of adequacy of oxygenation

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ACID-BASE BALANCE

• LUNGS AND KIDNEYS CONTROL ACID-BASE BALANCE
• INDICATES VENTILATION / OXYGENATION PROBLEMS
• VENTILATION MOVEMENT OF AIR INTO AND OUT OF
  LUNGS
• OXYGENATION OXYGEN TO TISSUES

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• OXYGEN IS TRANSPORTED TO TISSUES BY CIRCULATORY
  SYSTEM
• EXCHANGE CARBON DIOXIDE WHICH IS PRODUCED BY
  METABOLISM IN BODY CELLS

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• CARBON DIOXIDE SOLUBLE AND DISSOLVES INTO THE
  BLOOD
• IN THE BLOOD CARBON DIOXIDE FORMS BICARBONATE
  (BASE) OR CARBON ACID (ACID)

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• THE LUNGS CONTROL BICARBONATE LEVELS
• CONVERTS BICARBONATE TO CARBON DIOXIDE FOR
  EXCRETION
• CONTROL RATE AND DEPTH OF BREATHING TO ADJUST
  AMOUNT OF CARBON DIOXIDE (BICARBONATE) LOST
  quick fix

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INCREASE IN PaCO2 VENTILATION PROBLEM

• BLOW OFF CO2
• DROP IN PaCO2 BELOW 35
• ALKALOSIS (INCREASE pH)
• HYPERVENTILATION
• RETAIN CO2
• INCREASE IN PaCO2 ABOVE 45
• ACIDOSIS (DECREASE IN pH)
• HYPOVENTILATION

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CAUSE FOR

• Respiratory acidosis
• Hypoventilation, acute upper airway obstruction,
  massive pulmonary edema, drug overdose,
  neuromuscular disease, head trauma
• Respiratory alkalosis
• Hyperventilation, anxiety, fever, stimulant
  drugs, mechanical ventilation

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Respiratory alkalosis

• Respiratory rate increases above need to maintain
  normal CO2 levels increased amount CO2 exhale
• Increase in pH above 7.45
• Hypocapnia occurs abnormal low arterial carbon
  dioxide level

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• Hypocapnia causes cerebral vasoconstriction,
  overexcites autonomic nervous system
• You will see
• Increased heart rate
• Fall in K levels
• Angina
• Tingle in fingers and toes
• Diaphoresis
• Restlessness
• Anxiety
• Decreased LOC

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• Prolonged hypocapnia
• Hyperreflexia
• Tetany
• Seizure
• Arrhythmias
• Coma
• Death

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Respiratory acidosis

• Respirations decrease retain CO2 in larger than
  normal amounts
• Drop in pH below 7.35
• CO2 builds in tissues and fluids
• Hypercapnia occurs greater than normal amounts
  of CO2 in blood

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• Hypercapnia causes cerebral blood vessels to
  dilate, change in hemoglobin where it releases
  O2, CO2 builds up in all tissues and fluids
• You will see
• Decreased arterial oxygen saturation
• Increase respiratory rate shallow, rapid
• Headache
• Confusion
• Nausea / vomiting

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• Prolonged hypercapnia
• Increase acid urine
• Shallow, depressed respirations
• Hyperkalemia
• Arrhythmias
• Decreased LOC
• Coma
• Death

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CAUSES FOR

• Metabolic acidosis
• Decreased ability to excrete acid, diarrhea,
  renal disease, ketoacidosis, lactic acidosis,
  ingestion of certain toxins
• Metabolic alkalosis
• Elevation of serum bicarbonate, hypokalemia,
  nasogastric suctioning, vomiting, diuretic
  therapy, excessive administration of sodium
  bicarbonate

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Arterial Blood Gases

• Indicator of respiratory and renal function in
  maintaining acid base balance
• Indicator of adequacy of oxygenation

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Normal values

• pH reflection of acidity or alkalinity of blood
• 7.35 to 7.45
• PaO2 oxygen in arterial blood
• 80 to 100 mm Hg
• PaCO2 adequacy of alveolar ventilation
• 35 to 45 mm Hg
• HCO3 primary base in arterial blood
• 22 to 26 mEq/L
• O2 sat hemoglobin combined with oxygen
• Greater than 95 percent

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Interpreting ABGs

• Step 1
• Check pH value
• Normal 7.35 to 7.45
• Less than 7.35 / acidotic
• Greater than 7.45 / alkalotic
• Step 2
• Check PaCO2
• Normal 35 to 45 mm Hg
• Less than 35 / alkalosis
• Greater than 45 / acidosis

• ACIDOTIC lt7.35
• ALKALOTIC gt7.45
• PaCO2 lt35 ALKALOSIS
• PaCO2 gt 45
• ACIDOSIS

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• If number moves opposite pH indicates respiratory
  imbalance
• If number moves with pH indicates respiratory
  system is compensating for metabolic imbalance

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• Step 3
• Check HCO3
• Normal 22 26
• Less THAN 22 / ACIDOSIS
• Greater THAN 26 / ALKALOSIS
• Moves with pH indicates metabolic imbalance
• Moves away from pH indicates metabolic
  compensation for respiratory imbalance

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• Step 4
• Check PaO2
• Normal 80 100
• Mild hypoxemia less than 80
• Moderate hypoxemia - less than 60
• Severe hypoxemia less than 40
• For every year over 60, subtract 1 from limits on
  mild and moderate hypoxemia

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• pH 7.35 to 7.45
• Acid lt7.35 Alkaline gt7.45
• PaCO2 35 to 45
• Alkaline lt35 Acid gt45
• HCO3 22 to 26
• Acid lt22 Alkaline
  gt6

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Respiratory acidosis

• pH 7.20
• PaCO2 50
• HCO3 24

• Acid
• Acid
• Normal

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Respiratory alkalosis

• pH 7.59
• PaCO2 22
• HCO3 24

• Alkaline
• Alkaline
• Normal

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• View arterial blood gas interpretation in lab

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• Normal Levels of Substances in the Arterial
  Blood
• pH 7.40 0.05
• pCO2 (partial pressure of carbon dioxide) 40 mm
  Hg
• pO2 (partial pressure of oxygen) 90 - 100 mm Hg
• Hemoglobin O2 saturation 94 - 100
• HCO3- 24 meq / liter

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• Vignette 1
• A 14-year-old girl with cystic fibrosis has
  complained of an increased cough productive of
  green sputum over the last week. She also
  complained of being increasingly short of breath,
  and she is noticeably wheezing on physical
  examination. Arterial blood was drawn and
  sampled, revealing the following values
• pH 7.30 pCO2 50 mm Hg
• pO2 55 mm Hg
• Hemoglobin - O2 saturation 45
• HCO3- 24 meq / liter

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Discussions

• How would you classify this girl's acid-base
  status?
• How would the kidneys try to compensate for the
  girl's acid-base imbalance?
• List some other causes of this type of acid-base
  disturbance.

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• Vignette 2
• A 76-year-old man complained to his wife of
  severe sub-sternal chest pains that radiated down
  the inside of his left arm. Shortly afterward, he
  collapsed on the living room floor. Paramedics
  arriving at his house just minutes later found
  him unresponsive, not breathing, and without a
  pulse. CPR and electroconvulsive shock were
  required to start his heart beating again. Upon
  arrival at the Emergency Room, the man started to
  regain consciousness, complaining of severe
  shortness of breath (dyspnea) and continued chest
  pain. On physical examination, his vital signs
  were as follows
• Systemic blood pressure 85 mm Hg / 50 mm Hg Heart
  rate 175 beats / minute Respiratory rate 32
  breaths / minute Temperature 99.2oF His breathing
  was labored, his pulses were rapid and weak
  everywhere, and his skin was cold and clammy. An
  ECG was done, revealing significant "Q" waves in
  most of the leads. Blood testing revealed
  markedly elevated creatine phosphokinase (CPK)
  levels of cardiac muscle origin. Arterial blood
  was sampled and revealed the following
• pH 7.22 pCO2 30 mm Hg pO2 70 mm Hg Hemoglobin -
  O2 saturation      88 HCO3- 2 meq / liter

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Discussions

• What is the diagnosis? What evidence supports
  your diagnosis?
• How would you classify his acid-base status? What
  specifically caused this acid-base disturbance?
• How has his body started to compensate for this
  acid-base disturbance?
• What would his blood pH be if his body had not
  started compensating for the acid-base
  disturbance? Show your work.

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References

• Christensen, B., Kockrow, E. (2006).
  Foundations of Nursing, 5th Ed. St. Louis
  Mosby/Elsevier.
• McGraw-Hill Publications. (2000). Case History
  14 Acid-Base Physiology. Retrieved June 30,
  2010, from Case Studies Anatomy and Physiology
  http//www.mhhe.com/biosci/ap/a p_casestudies/cas
  es/ap_case14.html
•