Abg analysis Notes

ARTERIAL BLOOD GAS ANALYSIS

of 32

ARTERIAL BLOOD - GAS - ANALYSIS

of 32

Definition

Purpose

Indication

Information provided by ABG

Normal values

When ABG is ordered

Acidosis and alkalosis

Extraction

Factors affecting ABG

of 32

ABG

Blood gas analysis, also called arterial blood gas (ABG) analysis, is a test which measures the amount of oxygen (O2) and carbon dioxide (CO2) in the blood, as well as the acidity (PH) of the blood.

of 32

PURPOSE An ABG is typically requested to determine the PH

of the blood and the partial pressure of the oxygen (PaO2) and partial pressure of the carbon dioxide ( Pa Co2) within it.

An ABG analysis evaluate how effectively the lung are delivering the oxygen to the blood and how efficiently they are eliminating carbon dioxide from it.

The test also indicate how well the lungs and kidneys are interacting to maintain normal blood PH ( acid –base balance).

of 32

If the PH become deranged, normal cell mechanism is affected.

In addition, the acid – base component of the test provides information on kidney function too.

of 32

Blood gas studies are usually done to assess respiratory disease and other condition that may affect the lungs, and to manage patients receiving oxygen therapy ( respiratory therapy).

It is used to assess the effectiveness of the gaseous exchange and ventilation, be it spontaneous or mechanical.

of 32

ABG allows patient’s metabolic status to be assessed too, giving an indication of how they are copying with their illness.

It would therefore seem logical to request an ABG on any patient who is or has the potential to become critically ill.

This includes patients in critical care areas and those on wards who ‘trigger’ early – warning scoring systems.

of 32

Indications for ABG;

(1) Severe respiratory or metabolic disorders

(2) Clinical features of hypoxia or hypercapnia

(3) Shock

(4) Sepsis

(5) Decreased cardiac output

(6) Renal failure

(7) Ideally any baby on oxygen therapy

(8) Inborn errors of metabolism

of 32

Information provided by an ABG;

PaO2;

This is the partial pressure of the oxygen dissolved within the arterial blood and will determine oxygen binding to haemoglobin (SaO2).

Normally low reading indicate hypoxia.

Normal values; 9.3 – 13.3 kpa or 80 – 100 mmHg.

of 32

PaCo2;

this is the partial pressure of carbon dioxide dissolved with in the arterial blood. It is used to assess the effectiveness of ventilation. A high PaCo2 (respiratory acidosis) indicates under ventilation, a low PaCo2 ( respiratory alkalosis) indicate hyper or over ventilation.

Normal values; 4.7 to 6.0 kpa or 35 – 45 mmhg, although in chronic pulmonary diseases it may be considerably higher and still normal for that patient.

of 32

SaO2

Oxygen saturation measures how much of the haemoglobin in the red cells is carrying oxygen. Although similar to SpO2 ( measured by pulse oximeter), it is more accurate.

Normal values; 97% and above, although levels above 90% are often acceptable in critically ill patients.

of 32

PH

The PH measures hydrogen ions (H+) in blood.

Normal values; 7.35 – 7.45

A PH less than 7.35 is called acid and PH greater than 7.45 is called basic alkaline).

of 32

HCO3- ( bicarbonate)

Bicarbonate is a chemical (buffer) that keeps the PH of blood from becoming too acidic or too basic and indicate whether a metabolic problem is present (such as ketoacidosis).

A low HCO3- indicate metabolic acidosis and a high value indicate metabolic alkalosis.

HCO3 levels can also become abnormal when the kidneys are working to cobensate for a respiratory issues to normalize the blood PH.

Normal value; 22 – 26 mmol/l

of 32

BASE EXCESS

Base excess is used for the assessment of the metabolic component of acid – base disorders, and indicate whether the patient has metabolic acidosis or metabolic alkalosis.

of 32

A negative base excess indicate that the patient has metabolic acidosis (primary or secondary to respiratory alkalosis).

A positive base excess indicate that the patient has metabolic alkalosis (primary or secondary to respiratory acidosis).

Normal values; -3 to +3mmol/l

of 32

NORMAL RESULTS

PaO2 ; 80 – 100 mm Hg

PaCo2 ; 35 – 45 mm Hg

Oxygen content ; 15 – 23 %

SaO2 ; 94 – 100%

HCO3- ; 22 – 26mmhg

PH ; 7.35 – 7.45

of 32

WHEN ABG IS ORDERED...?

When you have symptoms of O2 / CO2 or PH imbalance such as shortness of breath.

Patient who are ‘on oxygen” may have their blood gases measured at intervals to moniter effectivness of treatment.

Head or neck trauma, injury that may affect breathing. Checking the blood gases from the umbilical cord of

newborns may uncover respiratory problems as well as determine the baby’s acid / base status.

Testing is usually done if a newborn’s condition indicates that he / she may be having difficulty in breathing.

of 32

RESPIRATORY ACIDOSIS

Respiratory acidosis is characterised by a lower PH and an increased PCO2, and is due to respiratory depression (not enough O2 and CO2 out).

Causes; CNS depression Pleural disease COPD/ARDS Musculoskeletal disorders Compensation for metabolic alkalosis

ph, CO2, Ventilation

of 32

RESPIRATORY ALKALOSIS

Respiratory alkalosis, characterised bye a raised PH and decreased PCO2, is due to over ventilation.

pH CO2 Ventilation

CAUSES; Intracerebral hemorrhage Salicylate and Progesterone drug usage Anxiety lung compliance Cirrhosis of the liver Sepsis

of 32

METABOLIC ACIDOSIS

It is characterised by a lower PH and decreased HCO3- , the blood is too acidic on a metabolic / kidney level.

Causes include diabetes, shock, and renal failure.

pH, HCO3

of 32

CAUSES

Metabolic Gap Acidosis Acetazolamide RTA (Calculate urine anion gap) Diarrhea Pancreatic Fistula

Non Gap Metabolic Acidosis M - Methanol U - Uremia D - DKA P - Paraldehyde I - INH L - Lactic Acidosis E - Ehylene Glycol S - Salicylate

of 32

METABOLIC ALKALOSIS

It is characterised by an elevated PH and increased HCO3- and is seen in hypokalemia, chronic vomiting (losing acid from stomach), and sodium bicarbonate overdose.

Causes Vomiting Diuretics Chronic diarrhea Hypokalemia Renal Failure

pH HCO3

of 32

Extraction;

Arterial blood for blood gas analysis is usually extracted by a phlebotomist, nurse, respiratory therapist or Dr.

Blood is most commonly drawn from the radial artery, because it is easily accessible, can be compressed to control bleeding and has less risk for occlusion.

of 32

The femoral artery (or less often), the brachial artery is also used, especially during emergency situations or with children.

Blood can also taken from an arterial catheter placed in one of these arteries.

of 32

FACTORS AFFECTING ABG VALUE

Extreme of age; neonatal to geriatrics

Exercise

Pregnancy

Sleep

Change in the body temperature

High altitude

of 32

Extreme of age;

Neonatal; neonates have many changes going on in the initial life progress – foetal circulation changes traumatically in the 1st

hours and days of life.

Geriatrics; decreased cardiac out put, residual volume of lung, breathing capacity affects ABG.

of 32

Exercise ;

Increasing activity from rest resulting in increased O2 consumption in patient with cardiopulmonary dysfunction. In the normal population the human body compensate by increasing O2 consumption to meet the work load.

of 32

Pregnancy;

Hormonal and mechanical factors have an negative affect on cardiopulmonary function.

During last trimester women often observe shorting of breath and difficulty in taking a deep breath secondary to diaphragm encroachment.

of 32

During sleep;

There is decrease in minute ventilation.

High altitude;

Low barometric pressure associated with high altitude signifies decreased in the amount of O2 available to the individual.

of 32

Change in body temperature;

Increased temperature can increase metabolism. Therefore increase O2 consumption.

of 32

Abg analysis Notes

Documents

Transcript of Abg analysis Notes