Abg interpretation

Abg interpretation

1. ABG INTERPRETATION SUBJECT: PHYSIOTHERAPY IN CARDIOPULMONARY CONDITIONS (BPT 402) SUBMITTED TO: DR. JAMAL MOIZ SUBMITTED BY: MEHPARA KHAN BPT 4 TH YEAR JAMIA MILLIA ISLAMIA Centre for Physiotherapy and Rehabilitation Sciences 1

2. Arterial blood gases (ABG's) is a blood test which is used to give an indication of ventilation, gas exchange and acid-base status and is taken from an arterial blood supply . It should be noted that it is not to be confused with venous blood gases which are used when arterial supply is not available or unreliable due to disease. The line in is usually inserted in the radial artery located at the wrist but is also sometimes used in the femoral artery in the groin It can be argued that one of the most important clinical uses of ABG analysis is to assess if a patient is in Type 1 (Hypoxemia) or Type 2 (hypercapnia) respiratory failure and it is important that as physiotherapists we able to quickly and correctly interpret this.   ABGs give us information about the activity in both the respiratory system and the 'metabolic' system. If one system is disturbed, the other will try to restore the balance or compensate. Both systems work together in an attempt to keep pH in the normal range. They are commonly used to; identify acid/base disorders, identify gas exchange problems, monitor the effects of oxygen therapy .

3. Acid-Base Balance pH Reflects acid-base balance and responds to metabolic and respiratory changes. Body cells and chemical reactions are acutely sensitive to the pH of their environment. Lower pH = Acidic Higher pH= Alkaline Regulation Acid-base balance is disturbed if; CO2 removal by the lungs is abnormal, production of acid from tissues is abnormal, and removal of acid is abnormal. [2] Deviation from normal pH is resisted by 3 mechanisms; The Buffering system Acts like a chemical sponge and neutralises acids and bases. It is an acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO3), and carbon dioxide (CO2) that attempts to maintain the bloods pH. It also plays a role in the duodenum among other tissues, to support proper metabolic function . The Lungs The respiratory component t hat reacts if the buffering system is not enough and the lungs hel p s i n r egulating CO2. The Kidneys The Metabolic component and is the last mechanism to work and begins to eliminate acid.

4. Why is it Necessary to Order an ABG Analysis? The utilization of an ABG analysis becomes necessary in view of the following advantages: Aids in establishing diagnosis. Guides treatment plan. Aids in ventilator management. Improvement in acid/base management; allows for optimal function of medications. Acid/base status may alter electrolyte levels critical to a patient’s status.

5. Respiratory Acidosis Respiratory acidosis is caused by inadequate alveolar ventilation leading to the retention of carbon dioxide and an increase in free hydrogen ions. It occurs when decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and results in a decrease in the blood's  pH.   Decreased Ph, Increased PaCO2 Causes Hypoventilation Acute Lunge Injury Upper airway obstruction Lower airway obstruction Impaired alveolar filling Chronic Lung Disease Neuromuscular disorders Obesity CNS Depression Symptoms- Headache, Anxiety, Blurred vision, Restlessness, Drowsiness,Tremors,Delirium , Coma .

6. Metabolic Acidosis Metabolic acidosis involves excess fixed acid production, i.e. lactate or loss of HCO 3 .It occurs when the body produces excess quantities of acid or the kidneys are not removing sufficient acid from the body. If left untreated, metabolic acidosis can lead to acidemia . Acidemia occurs when the bloods pH is low (<7.35) due to an increased production of hydrogen ions by the body or its inability to form bicarbonate (HCO3) in the kidneys.  Decreased pH, Decreased HCO3 Causes Renal disease Liver disease Lactic acidosis Prolonged lack of oxygen Shock Posioning Medications Dehydration Diarrhoea Symptoms- Rapid breathing, Confusion, Lethargy, Cold , clammy skin, Tachycardia and arrhythmia .

7. Respiratory Alkalosis Respiratory alkalosis is caused by over excretion of carbon dioxide (hyperventilation) resulting in more CO2 than normal being exhaled. Thus, leading to a reduction in free hydrogen ions and an alkalotic state . Increased pH, Decreased PaCO2 Causes Hyperventilation Acute asthma CNS disturbance High altitude Pneumonia Drugs Fever Sepsis Symptoms- Diziness , Peripheral paraesthesia , Confusion, Dry mouth.

8. Metabolic Alkalosis Metabolic alkalosis occurs as a result of decreased hydrogen ion concentration which leads to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations . Increased pH Increased HCO3 Causes Excess alkali administration Hyperkalaemia IV penicillin Re-feeding syndrome Massive blood transfusion Diuretic therapy Vomitting Symptoms- Weakness,Myalgia , Polyuria , Cardiac arrhythmias, Hypoventilation .

9. Interpretation of ABGs ABG Definitions PH: The measure of hydrogen ions in the blood PaC02: Partial pressure of Carbon Dioxide in the blood, the acidic element of the balance Acidic component Indicator of respiratory function Changes rapidly to compensate Pa02: Partial pressure of oxygen in the blood. HCO3-: Bicarbonate ion concentration in the blood, the basic element of the balance Basic/Alkaline component Indicator of metabolic function Compensation is slower BE: Base Excess = quantity of strong acid or base that is required to restore pH to normal .

10. When you are analyzing ABG results there are three things to look for when trying to find out if your patient is in respiratory or metabolic acidosis or alkalosis. Here they are and their normal numeric values: -pH: 7.35-7.45 -CO2: 35-45 (CO2 lab value ALWAYS indicates a RESPIRATORY issue) - HCO3: 22-26 (HCO3 lab value ALWAYS indicates a METABOLIC issue) Now to determine when these values are considered an acid or base -For pH anything less than 7.35 is an acid and anything greater than 7.45 is a base. -For CO2 (NOTE: it is the opposite) anything less than 35 is a base and anything greater than 45 is an acid. - For HCO3 anything less than 22 is an acid and anything greater than 26 is a base. Look at the pH Increased = Alkalosis Decreased = Acidosis Look at the PaCO2 Increased = Respiratory Acidosis Decreased = Respiratory Alkalosis Look at the HCO3 Increased = Metabolic Alkalosis Decreased = Metabolic Acidosis

11. Compensation The bodies pH is closely controlled and this is done through various mechanisms to maintain it at a constant value. It is important to note that the body will never overcompensate as the drivers for compensation cease as the pH returns to normal. In practice, compensation for an acidosis will not cause an alkalosis or visa versa. If pH is NORMAL despite an abnormal PCO2 and HCO3 it must be compensated. Look at the pH - Which side of 7.4 is it? Look for the cause PCO2 goes in the opposite direction to pH HCO3 travels in the same direction as pH The other value is the compensator Finding compensated, partially compensated, or uncompensated ABG problems: When PaCO2 is high, but pH is normal instead of being acidic, and if HCO3 levels are also increased, then it means that the compensatory mechanism has retained more HCO3 to maintain the pH. When PaCO2 and HCO3 values are high but pH is acidic, then it indicates partial compensation. It means that the compensatory mechanism tried but failed to bring the pH to normal. If pH is abnormal and if the value of either PaCO2 or HCO3 is abnormal, it indicates that the system is uncompensated. This is probably because of either respiratory or metabolic acidosis .

12. References Sood , P., Paul, G., & Puri , S. (2010). Interpretation of arterial blood gas. Indian journal of critical care medicine : peer-reviewed, official publication of Indian Society of Critical Care Medicine, 14(2), 57–64. https:// doi.org/10.4103/0972-5229.68215