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1 : Arterial Blood Gas DR DIPESH
2 : What is an ABG Arterial Blood Gas Analysis Drawn from artery- radial, brachial, femoral It is an invasive procedure. Caution must be taken with patient on anticoagulants.
3 : What Is An ABG? pH [H+] PCO2 Partial pressure CO2 PO2 Partial pressure O2 HCO3 Bicarbonate BE Base excess SaO2 Oxygen Saturation
4 : COMPONENTS OF THE ABG pH : 7.35 – 7.45 Pao2 : 80-100 mm Hg PCO2 : 35– 45 mmHg HCO3 : 22 – 26 mmol/L B.E : -2 to +2mEq/L SaO2 : >95%
5 : H2O + CO2 ? H2CO3 ? HCO3 + H+ Acid/Base Relationship
6 : There are two buffers that work in pairs H2CO3 NaHCO3 Carbonic acid base bicarbonate These buffers are linked to the respiratory and renal compensatory system Buffers
7 : The Respiratory buffer response The blood pH will change the level of H2CO3 present. This triggers the lungs to either increase or decrease the rate and depth of ventilation Activation of the lungs to compensate for an imbalance starts to occur within 1-3 minutes
8 : The Renal Buffer Response The kidneys excrete or retain bicarbonate(HCO3-). If blood pH decreases, the kidneys will compensate by retaining HCO3 Renal system may take from hours to days to correct the imbalance.
9 : ACID BASE DISORDER Res. Acidosis Is defined as a pH less than 7.35 with a paco2 greater than 45 mmHg. Acidosis –accumulation of co2, combines with water in the body to produce carbonic acid, thus lowering the pH of the blood. Any condition that results in hypoventilation can cause respiratory acidosis.
10 : Causes CNS:- Depression d/t medications such as narcotics, sedatives, or anesthesia. NEURO MUSCULAR:- Spinal cord injury, Neuromuscular diseases, or Neuromuscular blocking drugs. RESPIRATORY:- Atelectasis, Pneumonia, Pneumothorax, Pulmonary edema, Bronchial obstruction or Massive pulmonary embolus.
11 : Signs & symptoms Respiratory : Dyspnoea, respiratory distress and/or shallow respiration. Nervous: Headache, restlessness and confusion. If co2 level extremely high drowsiness and unresponsiveness may be noted. CVS: Tacycardia and dysrhythmias
12 : Management Treat the cause if reversible condition present. Stop depressive medications, If the cause can not be readily resolved, mechanical ventilation.
13 : Respiratory alkalosis Psychological responses, anxiety, fear and pain leading to hyperventilation. Increased metabolic demands such as fever, sepsis, pregnancy or thyrotoxicosis. CAUSES
14 : Signs & symptoms CNS: Light Headedness, numbness, tingling, confusion, inability to concentrate and blurred vision. Dysrhythmias and palpitations Dry mouth, diaphoresis Tetanic spasms of the arms and legs.
15 : Management Resolve the underlying problem Monitor for respiratory muscle fatigue When the respiratory muscle become exhausted, acute respiratory failure may ensue, which may require mechanical ventilation
16 : Metabolic Acidosis Bicarbonate less than 22mEq/L with a pH of less than 7.35. CAUSES:- Renal failure Diabetic ketoacidosis Anaerobic metabolism Starvation Salicylate intoxication
17 : Sign & symptoms CNS: Headache, confusion and restlessness progressing to lethargy, then stupor or coma. CVS: Dysarrhythmias Warm, flushed skin Nausea and vomiting Kussmaul’s respirations
18 : Management Treat the cause Hypoxia of any tissue bed will produce metabolic acids as a result of anaerobic metabolism even if the pao2 is normal Restore tissue perfusion to the hypoxic tissues The use of bicarbonate is indicated for known bicarbonate - responsive acidosis such as seen with renal failure
19 : Metabolic alkalosis Bicarbonate more than 26m Eq /L with a pH more than 7.45 CAUSES:- Ingestion of excess antacids, excess use of bicarbonate, or use of lactate in dialysis. Protracted vomiting, gastric suction, excess use of diuretics, or high levels of aldesterone.
20 : Signs/symptoms CNS: Dizziness, lethargy disorientation, seizures & coma. M/S: weakness, muscle twitching, muscle cramps and tetany. GIT:- Nausea, vomiting Respiratory depression.
21 : TREATMENT Treat the underlying cause. Supportive treatment. Isolyte G infusion. Stoping of ofending medications.
22 : MIXED METABOLIC AND RESPIRATORY METABOLIC ACIDOSIS – RESPIRATORY ALKALOSIS  Key: High- or normal-AG metabolic acidosis; prevailing PaCO2 below predicted value.  Example: Na+, 140; K+, 4.0; Cl–, 106; HCO3–, 14; AG, 20; PaCO2, 24; pH, 7.39 (lactic acidosis, sepsis in ICU)
23 : METABOLIC ACIDOSIS – RESPIRATORY ACIDOSIS Key: High- or normal-AG metabolic acidosis; prevailing PaCO2 above predicted value. Example: Na+, 140; K+, 4.0; Cl–, 102; HCO3–, 18; AG, 20; PaCO2, 38; pH, 7.30 (severe pneumonia, pulmonary edema)
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31 : Step 1: Acidemic or Alkalemic? Assess the pH –acidotic / alkalotic If above 7.5 – alkalotic If below 7.35 – acidotic
32 : Step 2: Is the primary disturbance respiratory or metabolic? If pH and paCO2 moves in opposite direction – primary respiratory problem. pH decreases below 7.35, the paCO2 should rise. If pH rises above 7.45, the paCO2 should fall.
33 : Step 2: Is the primary disturbance respiratory or metabolic? If pH ands HCO3 are moving in the same direction--primary problem is metabolic If pH increases the HCO3 should also increase If pH decreases HCO3 should also decrease
35 : Step 3. For a respiratory disturbance, determine whether it is acute or chronic. If the change in paCO2 is associated with the change in pH, the disorder is acute. In chronic process the compensatory process brings the pH to within the clinically acceptable range ( 7.30 – 7.50). A change in the pH of 0.08 for each 10 mm Hg indicates an ACUTE condition. A change in the pH of 0.03 for each 10 mm Hg indicates a CHRONIC condition.
36 : Step 4. For a metabolic acidosis, determine whether an anion gap is present. AG = (Na+ + K+) – (cl- + Hco3-) Normal value 12 ± 2 mEq/litre Most useful to diagnose etiology of metabolic acidosis. Anion gap will be normal in diarrhoea, while it will be increased in lactic acidosis, keto acidosis and renal failure.
37 : BASE EXCESS It is an estimate of the amount of strong acid or base needed to correct the metabolic component of an acid base disorder Formula With the base excess10 in a 50kg person with metabolic acidosis Hco3 needed for correction is: = 0.3 X body weight X BE = 0.3 X 50 X10 = 150 mMole.
38 : Step 5. Assess the normal compensation by the respiratory system for a metabolic disturbance Determine if there is a compensatory mechanism working to correct the pH. E.g. In primary respiratory acidosis with increased PaCO2 and decreased pH, compensation occurs when the kidneys retain HCO3.
39 : Assess the PaCO2 In an uncompensated state – when the pH and paCO2 moves in the same direction: the primary problem is metabolic. The decreasing paco2 indicates that the lungs acting as a buffer response (blowing of the excess CO2) If evidence of compensation is present but the pH has not been corrected to within the normal range, this would be described as metabolic disorder with the partial respiratory compensation.
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41 : Assess the HCO3 The pH and the HCO3 moving in the opposite directions, we would conclude that the primary disorder is respiratory and the kidneys acting as a buffer response: are compensating by retaining HCO3 to return the pH to normal range.
43 : Partially compensated
44 : ~ PaCO2 – pH Relationship 80 7.20 60 7.30 40 7.40 30 7.50 20 7.60


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