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ACID BASE NOTES •

An Arterial Blood gas (ABG) testing has become the gold standard in sick patients who are at risk for sudden decompensation or those with a respiratory component. ABG is a blood test that measures the acidity, or pH, and the levels of oxygen (O2) and carbon dioxide (CO2) from an artery. The test is used to check the function of the patient's lungs and how well they can move oxygen and remove carbon dioxide.

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How Is an ABG Drawn? o An Arterial Blood Gas requires the collection of a small sample of blood generally a minimum of 0.5 ml, but a full 1 ml is preferred. Blood can be drawn via an arterial stick from the wrist, groin, or forearm. o The radial artery is most commonly used to obtain the sample. However, the femoral artery and brachial artery can be used if necessary. If the patient already has a pre-existing arterial line, this can be used to obtain the sample.

The Allen test is a first line standard test used to assess the arterial blood supply of the hand. Two arteries supply blood to your hand. One is the radial artery, and the other is the ulnar artery. A healthy hand needs both arteries open and working. Otherwise, you could get permanent hand damage. A positive Allen test means that the patient does not have an adequate dual blood supply to the hand which would be a negative indication for catheterization, removal of the radial artery or any procedure which may result in occlusion of the vessel.

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CAUSES OF ACID-BASE DISORDERS o Is it lung scenario – respiratory problem? o Is the client over-ventilating (gas exchange, look at SAO2) – respiratory alkalosis ▪ hyperventilating ▪ Ventilator setting too high ▪ Anxiety attack ▪ Aspirin overdose (early)

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o Is the client under-ventilating – respiratory acidosis ▪ COPD (Emphysema, bronchitis) ▪ Drowning ▪ Drug Overdose ▪ Pneumonia ▪ Ventilator setting too low ▪ Pulmonary emboli ▪ Asthma If not lung(ventilation) it is a Metabolic problem o Metabolic Alkalosis: ▪ CAUSES • Prolonged vomiting (loss of hydrogen ions) • Ingestion of too much bicarbonate/antacids (base) – overdose on Tums) • hyperemesis • prolonged suctioning -NGT • loop and thiazide diuretic therapy (causes increase in chloride) • hypokalemia o Metabolic Acidosis: ▪ CAUSES • acute renal failure • diarrhea • 3rd degree burn over 60% of body • DKA • excessive laxative use • aspirin toxicity (late) • ileostomy/colostomy drainage • hyperkalemia

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SIGNS AND SYMPTOMS 1.When pH goes down the client shuts down (except for Potassium, because it will try to compensate– increased hydrogen ions (CO2) levels •

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Signs and symptoms of acidosis: hyporeflexia , bradycardia, bradypnea, lethargy, urinary retention, obtunded, Paralytic ileus, Adynamic ileus (need ambu bag), hyperkalemia (K+ greater than 5) MACKussmaul )(Kussmaul respiration is a compensatory respiratory disorder characterized by deep and labored breathing pattern often associated with severe metabolic acidosis, particularly diabetic ketoacidosis (DKA) but also kidney failure.– Metabolic Acidosis (high anion gap, which means higher than normal levels of acid in the blood.)

2.When pH goes up the client goes up (systems get hyper-excitable (alkalosis) – increased bicarbonate level •

Signs and symptoms of alkalosis: irritability, tremors, agitation, hyperreflexia (3, 4)….. 2 normal, 1-0 is hypo-reflexia; tachypnea, tachycardia, borborygmi (increase bowel sounds), seizure (suction at the bedside - aspirate), hypokalemia (K+ less than 3.5)

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INTERPRETING ABG RESULTS

pH Acidosis 7.35

7.36 7.37

alkalosis 7.38

7.39 STOP 7.40 7.41 7.42

7.43

7.44

7.45

PRINCIPLES

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Normal pH =7.35 – 7.45 Normal HCO3 = 22 – 26 Normal CO2 = 35 – 45 Normal PaO2 = 80 – 100% Normal SaO2 = 95 – 100%

UNCOMPENSATED • •

Ultimately, the body is yet to fix the problem or has been unable to fix the problem. If pH is abnormal and if the value of either PaCO2 or HCO3 is abnormal, it indicates that the system is uncompensated. o o o o

Determine if pH is acidosis or alkalosis (place arrow) Is either the CO2 or HCO3 normal? = Uncompensated Look at the arrows. Use ROME (Respiratory Opposite; Metabolic Equal) If the abnormal value arrow is going in the same direction as the pH it is a Metabolic problem; If abnormal value arrow is going in opposite direction of pH = respiratory problem

Egs. Metabolic acidosis uncompensated………. pH 7.23 paCO2 37 HCO3 18 Metabolic alkalosis uncompensated……… pH 7.46 paCO2 36 HCO3 32 Respiratory Alkalosis uncompensated …… pH: 7.56, CO2: 23, HCO3: 23 Respiratory acidosis uncompensated……... pH 7.20 paCO2 49 HCO3 25

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COMPENSATION

Compensation can be thought of as the body’s attempt at correcting an imbalance. Is one system in the body trying to compensate for an abnormality in another system? We can examine this by looking at the opposing system (the opposite component of the problem). For example, in an acidosis, we’d look at what the HCO3- is doing. Whereas in an alkalosis, to determine if the body is compensating, we’d look at what the CO2 is doing.

****CO2 and HCO3 arrows in the same direction as pH = metabolic problem **** CO2 and HCO3 arrows in the opposite direction of pH = respiratory problem Identify if alkalosis or acidosis by looking at the pH (put arrow and write answer) 2. Look at CO2 and HCO3 (Are both out of range?) (put arrow) 3. Is the CO2 and HCO3 arrows going in the opposite direction as the pH? Respiratory problem. If the CO2 and HCO3 arrows going in the same direction as the pH? Metabolic problem. (Write beside number 1 answer) ROME 4. Lastly, look at the pH. If the pH is out of range - Partial compensation; If pH is within range - Full compensation. 1.

PARTIALLY COMPENSATED •

It means that the compensatory mechanism tried but failed to bring the pH to normal

• pH is abnormal and both HCO3 and CO2 are abnormal a. For example: i. ii.

Partially compensated Respiratory Acidosis…. pH 7.26 C02 50 HC03 46 Partially Compensated Metabolic Alkalosis pH: 7.84, CO2: 46, HCO3: 28

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FULLY COMPENSATED

• If the pH is back within normal range but CO2 and HCO3 are still abnormal, then a full-compensation has occurred For example: i.

Fully compensated Respiratory Alkalosis …pH 7.41 paCO2 26 HCO3 17

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Fully Compensated Metabolic Acidosis pH: 7.37, CO2: 34, HCO3: 20

PRACTICE QUESTIONS a. pH 7.20 paCO2 49 HCO3 25 _________________________________________ b. pH 7.52

C02 49

HC03 50 __________________________________________

c. pH 7.36

C02 50

HC03 28 __________________________________________

d. pH 7.44

C02 50

HC03 36

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e. pH 7.25 paCO2 60 HCO3 27 ____________________________________________ f. pH 7.39 paCO2 33 HCO3 15 __________________________________________ g. pH 7.39 paCO2 48 HCO3 28 ___________________________________________ h. pH 7.50 paCO2 26 HCO3 24

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i. pH 7.41 paCO2 26 HCO3 17 ___________________________________________ j. pH 7.31 paCO2 34

HCO3 21 _________________________________________

k. pH 7.52 paCO2 48

HCO3 28 _________________________________________

l. pH 7.42 paCO2 50 HCO3 37 __________________________________________ m. pH 7.56 paCO2 20

HCO3 15 _________________________________________...