ARTERIAL BLOOD GAS INTERPRETATION Merlin Ann Mathew INTRODUCTION

ARTERIAL BLOOD GAS INTERPRETATION. . . Merlin Ann Mathew

INTRODUCTION �The arterial blood gas test measures: Ø Ø Ø Arterial partial pressure of oxygen Arterial partial pressure of carbon dioxide Blood ph Arterial o 2 saturation Bicarbonate value Electrolyte values

�The blood is commonly drawn from: Ø Ø Ø Radial artery Brachial artery Femoral artery(less common) �The selection of which radial artery to draw blood from is based on the outcomes of ALLENS test.

ABG PARAMETERs. . . �Ph �Pco 2 �Po 2 �Base excess � 02 saturation �Bicarbonate �Hemoglobin �Temperature �Sodium �Potassium �Calcium �Chlorin � 7. 35 – 7. 45 � 35 – 45 mmhg � 100 – 150 mmhg �-2 - +2 mmol/l �>95% � 22 – 26 mmol/l � 11. 5 – 16. 5 g/dl � 37 � 135 – 145 meq/l � 3. 6 – 5. 2 mmol/l � 1. 1 – 1. 3 meq/l � 96 – 106 meq/l

VBG PARAMETERS �Ph � 7. 38+/-. 02 �Pco 2 � 45+/- 5 �Po 2 � 40+/- 5 �Base excess � 0+/-2 �spo 2 � 70%

How to read an ABG �Look for the ph to determine whether it is alkalosis or acidosis. �Determine respiratory involvement by looking pco 2 � Determine metabolic involvement by looking bicarbonate value.

�Decrease in blood ph --- acidosis �Increase in blood ph--- alkalosis �Pco 2 > 45 mmhg ---respiratory acidosis �Pco 2<35 mmhg---respiratory alkalosis �Hco 3<22 ---metabolic acidosis �Hco 3>26 ---metabolic alkalosis

Respiratory acidosis �There is fall in ph due to increase in pc 02. �There is increased bicarbonate level in blood. �Causes: Ø COPD Ø Pneumonia Ø Respiratory under ventilation Ø Patient with pulmonary disease. • On pump causes: Ø Decrease o 2 delivery Ø Decrease sweep gas flow Ø Decrease Hb value

�Symptoms: Ø Headache Ø Blurred vision Ø Confusion �Restlessness �Treatment: Ø Adjust the sweep gas flow(on pump) Ø Treat the underlying cause. Ø Non invasive positive pressure ventilation(CPAP) Ø Bronchodilators to reverse airway obstruction.

RESPIRATORY ALKALOSIS �There is rise in ph due to fall in pco 2 �There is decreased bicarbonate level �Causes: Ø CNS disorders Ø Administration of certain drugs Ø hypoxia Ø Pulmonary receptor stimulation • On pump causes: Ø Increase sweep gas flow Ø Decrese 02 requiremnt of tissue with hypothermia.

�Symptoms: Ø Dyspnea Ø Numbness Ø Chestpain Ø Dizziness Ø Confusion �Treatment: Ø Change ventilator setting Ø Decrease the breathing rate

METABOLIC ACIDOSIS �There is decrease in bicarbonate concentration. �There is fall in ph due to metabolic cause. �Causes: Ø Poisoning Ø Kidney failure Ø Diarrhoea Ø Diabetes • On pump causes: Ø Hypotension Ø Hypoperfusion Ø Increase o 2 extraction

�Symptoms: Ø Nausea Ø Vomiting Ø Lethargy Ø Hyperapnea �Treatment: Ø Addition of sodium bicarbonate

�Half correction: BASE EXCESS X PATIENT WEIGHT 6 �Full correction: BASE EXCESS X 3 PATIENT WEIGHT

METABOLIC ALKALOSIS �A increase in ph due to metabolic causes �A increase in bicarbonate conc �Causes: Ø Hyperchloremia Ø Hypokalemia Ø Administration of corticosteroids. • On pump causes: Ø Incresed bicarbonate value.

�Symptoms: Ø Confusion Ø Muscle twitching Ø Nausea Ø Vomiting Ø Numbness �Treatment: Ø Decrease diuretic therapy Ø Decrease fluid intake.

ELECTROLYTE MANAGEMENT �Potassium: Ø Ø Normal range: 3. 5 – 5. 5 meq/l Increased potassium--- hyperkalemia Ø Corrected by : v v v Diuretics GI infusions Hemofiltration replacement therapy with 0. 9% saline.

�Calcium: Ø Maintain calcium level at 0. 8 mmol/l for 15 -20 mn after myocardial reperfusion. �Glucose: Ø Ø Normal range --- 72 – 137 mg/dl. Increased glucose --- hyperglycemia.

�Causes include: Ø Ø Surgical stress. Cpb Hypothermia Cardioplegia solution. �Glucose level should be maintained <300 mg/dl.

�ABG is mainly analysed by 2 techniques: Ø Ø alpha stat method Ph stat method

ALPHA STAT METHOD �Corrected by not adding co 2 to bypass circuit. �Offers protection from micro emboli. �Correction: Ø Ø Ø Total co 2 remains constant Cerebral blood flow is unaltered MAP increases. �Paco 2 in maintained at 35 -45 mmhg �Ph is maintained at 7. 4. �Measured at patients actual temp (37 deg celcius)

PH STAT METHOD �Corrects the arterial blood gas to the patients temp but adds co 2 to bypass circuit. �Results in cerebral vasodilation �Correction: Ø Ø Total body co 2 increases Cerebral blood flow and MAP increases. �Paco 2 is maintained at 40 mmhg �Ph maintained at 7. 4. �Measured at hypothermia( to what temp we cool the pt).

�Ph = 7. 38 �Pco 2 = 76 �Hco 3 = 42 �BE = +14 �Identify the condition?