Abg interpretation
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Transcript of Abg interpretation
ABGs
What is an ABG
o Arterial Blood Gas --- Drawn from artery
o It is an invasive procedure.
o Caution must be taken with patient on anticoagulants.
o Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.
What are components of ABG?
The Components pH / PaCO2 / PaO2 / HCO3 / O2sat / BE
Desired Ranges pH - 7.35 - 7.45 PaCO2 - 35-45 mmHg PaO2 - 80-100 mmHg HCO3 - 21-27 O2sat - 95-100% Base Excess - +/-2 mEq/L
Why Order an ABG?
Aids in establishing a diagnosis Helps guide 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 patient status/care
Logistics
When to order an arterial line -- Need for continuous BP monitoring Need for multiple ABGs
Where to place -- the options Radial Femoral Brachial Dorsalis Pedis Axillary
Acid Base Balance
The body produces acids daily 15,000 mmol CO2
50-100 mEq Nonvolatile acids
The lungs and kidneys attempt to maintain balance
Acid Base Balance
Assessment of status via bicarbonate-carbon dioxide buffer system
CO2 + H2O <--> H2CO3 <--> HCO3- + H+
ph = 6.10 + log ([HCO3] / [0.03 x PCO2])
pH
Normal pH is 7.35-7.45 Value <7.35 is acidotic Value >7.45 is alkalotic Acidosis & Alkalosis can be caused
by a problem with the respiratory system or a metabolic cause
Can also have combined respiratory/metabolic states
The Terms & Types
ACIDS Acidemia Acidosis
Respiratory CO2
Metabolic HCO3
BASES Alkalemia Alkalosis
Respiratory CO2
Metabolic HCO3
Is it Respiratory or Metabolic?
1. Respiratory Acidosis
2. Respiratory Alkalosis
3. Metabolic Acidosis
4. Metabolic Alkalosis
Increased pCO2 >50
Decreased pCO2<30
Decreased HCO3 <18
Increased HCO3 >30
Respiratory Acidosis
ph, CO2, Ventilation Causes
CNS depression Pleural disease COPD/ARDS Musculoskeletal disorders Compensation for metabolic alkalosis
Respiratory Acidosis
Acute vs Chronic Acute - little kidney involvement.
Buffering via titration via Hb for example
pH by 0.08 for 10mmHg in CO2
Chronic - Renal compensation via synthesis and retention of HCO3 (Cl to balance charges hypochloremia)
pH by 0.03 for 10mmHg in CO2
Assessing Oxygenation
Normal value for arterial blood gas 80-100mmHg
Normal value for venous blood gas 40mmHg
Normal SaO2 Arterial: 97% Venous: 75%
Important points for assessing tissue oxygenation
This is the O2 that’s really available at the tissue level.
Is the THb normal? Low THb means the ability of the blood
to carry the O2 to the tissues is decreased
Is perfusion normal? Low perfusion means the blood isn’t
even getting to the tissues
Signs & symptoms of Respiratory Acidosis
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
Management Increase the ventilation. Causes can be treated rapidly
include pneumothorax, pain and CNS depression r/t medication.
If the cause can not be readily resolved, mechanical ventilation.
Caution for given O2 in chronic respiratory failure
Respiratory Alkalosis
pH, CO2, Ventilation CO2 HCO3 (Cl to balance charges
hyperchloremia) Causes
Intracerebral hemorrhage Salicylate and Progesterone drug usage Anxiety lung compliance Cirrhosis of the liver Sepsis
Respiratory Alkalosis
Acute vs. Chronic Acute - HCO3 by 2 mEq/L for every
10mmHg in PCO2
Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg in PCO2
Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH
Signs & symptoms CNS: Light Headedness, numbness,
tingling, confusion, inability to concentrate and blurred vision.
Dysrhythmias and palpitations Dry mouth, diaphoresis and tetanic
spasms of the arms and legs.
Management Resolve the underlying problem Monitor for respiratory muscle
fatigue When the respiratory muscle
become exhausted, acute respiratory failure may ensue
Metabolic Acidosis
pH, HCO3
12-24 hours for complete activation of respiratory compensation
PCO2 by 1.2mmHg for every 1 mEq/L HCO3
The degree of compensation is assessed via the Winter’s Formula
PCO2 = 1.5(HCO3) +8 2
Anion GAP
Calculation of AG is useful approach to analyse metabolic acidosis
AG = (Na+ + K+) – (cl- + Hco3-) * 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.
The Causes
Metabolic Gap Acidosis M - Methanol U - Uremia D - DKA P - Paraldehyde I - INH L - Lactic Acidosis E - Ehylene Glycol S - Salicylate
Non Gap Metabolic Acidosis Hyperalimentation Acetazolamide RTA (Calculate
urine anion gap) Diarrhea Pancreatic Fistula
Sign & symptoms
CNS: Headache, confusion and restlessness progressing to lethargy, then stupor or coma.
CVS: Dysrhythmias Kussmaul’s respirations Warm, flushed skin as well as
nausea and vomiting
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
Metabolic Alkalosis
pH, HCO3
PCO2 by 0.7 for every 1mEq/L in HCO3
Causes Vomiting Diuretics Chronic diarrhea Hypokalemia Renal Failure
Signs/symptoms
CNS: Dizziness, lethargy disorientation, siezures & coma.
M/S: weakness, muscle twitching, muscle cramps and tetany.
Nausea, vomiting and respiratory depression.
It is difficult to treat.
Stepwise approach to ABG
Step 1: Acidemic or Alkalemic? Step 2: Is the primary disturbance
respiratory or metabolic? Step 3. Asses to Pa O2. A value below 80mm
Hg indicates Hypoxemia. For a respiratory disturbance, determine whether it is acute or chronic.
Step 4. For a metabolic acidosis, determine whether an anion gap is present.
Step 5. Assess the normal compensation by the respiratory system for a metabolic disturbance
Compensated or Uncompensated—what does this mean?
1. Evaluate pH—is it normal? Yes
2. Next evaluate pCO2 & HCO3
• pH normal + increased pCO2 + increased HCO3 = compensated respiratory acidosis
• pH normal + decreased HCO3 + decreased pCO2 = compensated metabolic acidosis
Compensated vs. Uncompensated
1. Is pH normal? No2. Acidotic vs. Alkalotic3. Respiratory vs. Metabolic
• pH<7.30 + pCO2>50 + normal HCO3 = uncompensated respiratory acidosis
• pH<7.30 + HCO3<18 + normal pCO2 = uncompensated metabolic acidosis
• pH>7.50 + pCO2<30 + normal HCO3 = uncompensated respiratory alkalosis
• pH>7.50 + HCO3>30 + normal pCO2 = uncompensated metabolic alkalosis
Practice
12 year old diabetic presents with Kussmaul breathing
pH : 7.05 pCO2: 12 mmHg pO2: 108 mmHg HCO3: 5 mEq/L BE: -30 mEq/L
Severe partly compensated metabolic acidosis without hypoxemia due to ketoacidosis
17 year old w/severe kyphoscoliosis, admitted for pneumonia
pH: 7.37 pCO2: 25 mmHg pO2: 60 mmHg HCO3: 14 mEq/L BE : -7 mEq/L
Compensated respiratory alkalosis due to chronic hyperventilation secondary to hypoxia
9 year old w/hx of asthma, audibly wheezing x 1 week, has not slept in 2 nights; presents sitting up and using accessory muscles to breath w/audible wheezes
pH: 7.51 pCO2: 25 mmHg pO2 35 mmHg HCO3: 22 mEq/L BE: -2 mEq/L
Uncompensated respiratory alkalosis with severe hypoxia due to asthma exacerbation
7 year old post op presenting with chills, fever and hypotension
pH: 7.25 pCO2: 32 mmHg pO2: 55 mmHg HCO3: 10 mEq/L BE: -15 mEq/L
Uncompensated metabolic acidosis due to low perfusion state and hypoxia causing increased lactic acid