Arterial blood gas analysis PPT for the cardio student. Very important topic and concepts that should be clear to those who are dealing with ICU patients

1. ABG ( ARTERIAL BLOOD GAS
)
HIMANSHUARORA

2. ABG ( Arterial blood gass)
◦ ABG – Arterial blood gases, which are present in the blood is called arterial blood gases for eg
CO2, O2, SPo2. PH etc.
◦ An arterial-blood gas (ABG) test measures the amounts of arterial gases, such as Oxygen,
carbondioxide, PH, bicarbonate and saturated oxygen .
◦ An ABG test requires that a small volume of blood be drawn from the radial artery because it is
easily accessible, can be compressed to control bleeding . The selection of which radial artery
to draw from is based on the outcome of an Allen's test.
◦ Other arteries for withdrawIng of blood are – Dorsalis pedis, Femoral and brachial artery.

3. Procedure
◦ Required equipment
◦ Gloves
◦ Apron
◦ Pre-heparinised arterial blood gas syringe .
◦ Arterial blood gas needle (23 G)
◦ Alcohol wipe (70% isopropyl)
◦ Gauze or cotton wool
◦ Tape
◦ Lidocaine 1% (1 mL)
◦ Subcutaneous needle .

4. ◦ Check for any contraindications to arterial blood gas sampling:
◦ Absolute contraindications: peripheral vascular disease in the limb, cellulitis surrounding the
site or arteriovenous fistula.
◦ Relative contraindications: impaired coagulation (e.g. anticoagulation therapy, liver disease,
low platelets <50).
◦ Check if the patient has an allergy to local anaesthetic (e.g. lidocaine).

5. ◦ Position the patient so that they are sitting comfortably, ideally with their wrist supported by a
pillow. If a bed is available, the patient can lay down for the procedure (this is sometimes
preferable, particularly if the patient is prone to vasovagal syncope).
◦ Ask the patient if they have any pain before continuing with the clinical procedure.
◦ Then choose the appropriate artery, if radial artery will be choosen then need to perform a
simple test for better outcome.

6. ◦ Allen test is a medical sign used in physical examination of arterial blood flow to the
hands.
◦ The original test proposed by Allen is performed as follows:
◦ The patient is asked to clench both fists tightly for 1 minute at the same time.
◦ Pressure is applied over both radial arteries simultaneously so as to occlude them.
◦ The patient then opens the fingers of both hands rapidly, and the examiner compares
the colour of both. The initial pallor should be replaced quickly by rubor.

8. Indication
◦ 1) Respiratory failure. And assess its severity.
◦ 2) To monitor the patient on ventilator and assist weaning.
◦ 3) To Measure the acid-base level in the blood of people who are have heart
failure, kidney failure, uncontrolled diabetes, sleep disorders, severe infections, or
after a drug overdose.
◦ 4) Severe metabolic disturbance e.g. diabetic ketoacidosis
◦ 5) All critically ill patients.

9. Parameters for ABG test
◦ 1) PH 7.35 to 7.45 in which from 7.35 to 7.39 is acidic and from 7.40 to 7.45 basic.
◦ 2) PCO2 35 to 45 mmhg
◦ 3) PO2 80 to 100 mmhg
◦ 4) SPO2 >90%
◦ 5) Bicarbonates 22 to 28 mEq/l

10. ◦ Main 3 functions which are checked during ABG test
◦ - Respiratory function PCO2
◦ - metabolic function HCO3
◦ - Acid base balance PH.

11. Main 4 disorders which will be found
during ABG analysis
◦ 1 Respiratory Acidosis
◦ 2 Respiratory Alklosis
◦ 3 Metabolic Acidosis
◦ 4 Metabolic Alklosis

12. Interpretation.
◦ Rules
◦ If PH HCO3 PCO2
◦ Compensated Abnormal Abnormal / normal Abnormal /
Normal
◦ Partly compensated Abnormal Abnormal Abnormal
◦ Fully compensated Normal Abnormal Abnormal.

13. Henderson Hasselbach Equation
◦ PH ~ HCO3/ PCO2.
◦ HCO3 is metabolic component
◦ PCO2 is Respiratory component
◦ Acc. To this equation always consider abnormal values for eg. If the Hco3 is abnoraml and
the pco2 is normal then we will say that the Metabolic acidosis or alkalosis.

14. 4 Step method
◦ Step 1 – Use PH to determine the Acidosis and Akalosis
◦ Normal value of PH id 7.35 to 7.45 If ph is > 7.45 is alkalosis
◦ If ph value <7.35 Acidosis.
◦ Step 2 Interpretation of Equation and analysis Is either uncompensated, partly or fully compensated.
◦ Step 3 Determine respiratory effect
◦ Normal value 35 to 45 mmhg if > 45 acidosis ( low ph) , <35 alkalosis high ph)
◦ Or
◦ Determine Metabolic effect
◦ Normal value 22 to 28 mEq/l If > 28 Alkalosis , <22 acidosis.
◦ Step 4 If both the metabolic and respiratory factors are abnormal then minus the abnormal value
from the normal value and considered greater one .

15. Solve Example
◦ PH = 7.46 Ab.
◦ Pco2 = 44.4 normal
◦ HCO3 = 31.1 Ab.
◦ Pco2 113.2 Ab.
◦ Step 1 Alkalosis
◦ Step 2 Interpretation of formula PH~HCO3/PCO2
◦ Uncompensated.
◦ Step 3 Metabolic
◦ Conclusion = Uncompensated metabolic alkalosis Hyperoxemia. ( 1)

16. ◦ PH = 7.47
◦ PCO2 = 48 mmhg
◦ HCO3 = 32 mmol/ l
◦ PO2 = 110 mmhg

17. Causes of respiratory Acidosis
◦ Airway obstruction disease like
◦ COPD
◦ asthma
◦ CNS depression
◦ Neuromuscular impairment
◦ Ventilatory restriction
◦ Increased CO2 production: Due to increase intake of carbohydrates
◦ Incorrect mechanical ventilation settings

18. Causes of respiratory alkalosis
◦ fever, pain, fear, anxiety, CVA, cerebral edema, brain trauma, brain tumor, CNS
infection
◦ Hypoxemia or hypoxia: , low FiO2
◦ pleural effusion, pneumonia, pneumothorax, pulmonary embolus
◦ Drugs, hormones: salicylates, catecholamines, progestins
◦ Pregnancy, liver disease, sepsis, hyperthyroidism
◦ Incorrect mechanical ventilation settings

19. Causes of metabolic alkalosis
◦ Hypovolemia
◦ GI loss of H+
◦ Vomiting, gastric suction, diarrhea .
◦ Renal loss H+
◦ Loop and thiazide diuretics, post-hypercapnia
◦ Hypervolemia,
◦ Renal loss of H+: edematous states (heart failure, cirrhosis, nephrotic syndrome),
excess ACTH, renal artery stenosis, bicarbonate administration

20. Causes of metabolic acidosis
◦ Diarrhea, ileostomy, proximal colostomy .
◦ proximal RTA
◦ carbonic anhydrase inhibitor (acetazolamide)
◦ Renal tubular disease
Chronic renal disease
Distal RTA
Aldosterone inhibitors or absence

21. ◦ Arterial blood gas (ABG) values alone don't provide enough information to diagnose a
problem. For example, they can't tell whether low levels are caused by lung or heart
problems. Arterial blood gas values are most helpful when they are reviewed with
other examinations and tests.
◦ An ABG test is often done for a person who is in the hospital because of severe injury
or illness. The test can measure how well the person's lungs and kidneys are working
and how well the body is using energy.
◦ An ABG test may be most useful when a person's breathing rate is increased or
decreased or when the person has very high blood sugar (glucose) levels, a severe
infection, or heart failure.

23. Extubation
◦ Removal of tracheal tube or tracheotomy tube from the trachea is termed as
Extubation.

24. Creteria for extubation
◦ Approach
◦ Determine disease resolution and consider other factors
◦ Identify candidates for spontaneous breathing trial
◦ Perform spontaneous breathing trial
◦ Identify candidates for extubation
◦ Extubation and post-extubation care.

25. DETERMINE DISEASE
RESOLUTION
◦ Begins with the resolution of respiratory failure and/or the disease that prompted initiation of
mechanical ventilation
◦ Criteria to define disease resolution are not defined
◦ A systemic approach emphasising objective surrogate markers of recovery
◦ Adequate oxygenation and gas exchange
◦ PaO2 >60mmHg on FiO2 <40%
◦ PEEP 5–8cmH2O
◦ CXR stable or improving

26. ◦ absent or only low dose vasopressors/inotropes
◦ SBP>90mmHg.
◦ Stable cardiac rhythm
◦ No tacycardia
◦ No evidence of myocardial ischemia
◦ GCS>8 equivalent, some able to follow commands, some neither.
◦ No continuous sedative infusion or neuromuscular blockade
◦ no significant weakness (e.g. can lift head off pillow, raise arms in air for 15 seconds, clap
hands)
◦ pain controlled

27. No significant acidosis
◦ No electrolytes disturbance .
◦ adequate fluid status (not overloaded)
◦ abdominal pain/ distention controlled
◦ tolerating feeds
◦ Adequate hemoglobin
◦ Sepsis control.

28. Identify candidates for spontaneous
breathing trial
◦ Spontaneous breathing trials (SBT) are used to identify patients who are likely to fail
liberation from mechanical ventilation.
◦ SBT is a test for determining readiness to breathe without a ventilator”
◦ Ideally, during an SBT we want to observe the patient under conditions of respiratory
load that would simulate those following extubation.
◦ IDENTIFICATION OF PATIENTS SUITABLE FOR SBT
◦ Patients that pass the following daily ‘wean screen’ should undergo SBT:
◦ lung disease is stable/ resolving
◦ low FiO2 (< 50%) and PEEP (< 5-8cmH2O) requirement
◦ haemodynamic stability .
◦ able to initiate spontaneous breaths (good neuromuscular function)
◦ This indicates patients suitable for a spontaneous breathing trial, those who pass also
to be assessed for extubation.

29. Method
◦ SBT involves the following steps:
◦ It be conducted while the patient is still connected to the ventilator circuit.
◦ When using the ventilator a PS of 5 – 7 cmH2O and 1-5 cmH20 PEEP (so called ‘minimal
ventilator settings’) will overcome increased work of breathing through the circuit (i.e. ETT)
◦ If still on the ventilator the patient should have ‘minimal ventilator settings”
◦ Initial trial should last 30 – 120 minutes
◦ If patient is not tolerate this, then Test will be negative (But)
◦ 80% of patients who tolerate this time can be permanently removed from the ventilator

30. PERFORM SPONTANEOUS
BREATHING TRIAL
◦ IDENTIFY PATIENTS READY FOR TRIAL OF EXTUBATION
◦ Key questions
◦ Awake or easily rousable?
◦ Able to follow commands?
◦ Minimal volume of respiratory secretions?
◦ Intact gag and cough reflex to prevent aspiration? (absent gag is normal in many
people)
◦ Consider a cuff leak test to check for laryngeal oedema:
◦ Laryngeal edema reported in as many as 40% of prolonged intubations
◦ 5% patients experience severe upper airway obstruction following extubation
◦ can be detected by ‘cuff leak’ test

31. Cuff leak test
◦ The cuff leak test is used to predict risk of post-extubation stridor in intubated patients
◦ Use and interpretation of the test needs to take into account the overall context of the patient’s condition and the
management implications.
◦ Procedure
◦ Suction endotracheal and oral secretions and set the ventilator in the assist control mode with the patient receiving
volume-cycled ventilation
◦ With the cuff inflated, record displayed inspiratory and expiratory tidal volumes to see whether these are similar
◦ Deflate the cuff
◦ Directly record the expiratory tidal volume over the next six breathing cycles as the expiratory tidal volume will
reach a plateau value after a few cycles
◦ Average the three lowest values
◦ The difference between the inspiratory tidal volume (measured before the cuff was deflated) and the averaged
expiratory tidal volume (after cuff deflation) is the cuff leak volume

32. ◦ failed cuff-leak test
◦ was defined as a leak volume of less than 110 mL, or 15.5%
◦ of exhaled volume before cuff deflation.
◦ EXTUBATION AND POST-EXTUBATION CARE
◦ Monitor closely for Laryngospasm and Post-extubation stridor — reintubation is not
always need
◦ Consider high flow nasal prongs or non-invasive ventilation to treat or prevent post-
extubation respiratory failure

33. Extubation failure
◦ primary types of failure.
“the inability to tolerate removal of the translaryngeal tube.
“ liberation failure is used to refer to the inability to tolerate spontaneous ventilation without
mechanical support.
Causes of failure
1) Laryngospasm
2) Postobstructive Pulmonary Edema
3) Laryngeal Edema
4) Airway injury.

34. Treatment of Extubation Failure
◦ The onset of respiratory distress following extubation
◦ should alert the clinician that the patient is failing extuba-
◦ tion. Hypercapnia, hypoxia, and abdominal breathing are
◦ all signs that re-intubation may be necessary. Severe post-
◦ extubation stridor and an inability to manage secretions
◦ are additional indications for re-intubation.
◦ Patients who fail extubation have an increased mortality
◦ rate compared with patients who are successfully extu-
◦ bated on the first attempt

35. or patients who fail their first
◦ breathing trial are not extubated. NIV has not been shown to reduce
◦ the rates of re-intubation, and it can increase mortality by
◦ delaying re-intubation.

36. ◦ Thank you