NMED 3850 A Advanced Online Design January 26, 2010 V. Mahadevan.
CXR and ABG interpretation for RT Pattabhi raman, Mahadevan & Arjun Srinivasan Pulmonology...
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Transcript of CXR and ABG interpretation for RT Pattabhi raman, Mahadevan & Arjun Srinivasan Pulmonology...
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CXR and ABG interpretation for RT
Pattabhi raman, Mahadevan & Arjun Srinivasan
Pulmonology AssociatesKMCH
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Introduction
• Basic ideas about situations that RT would be facing with regards to CXR and ABG.
• Not going to be a comprehensive account of both.
• Might be too basic.• Speaker does not consider himself to be an
authority in both these topics .
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CXR
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Different tissues in our body absorb X-rays at different extents:
•Bone- high absorption (white)
•Tissue- somewhere in the middle absorption (grey)
•Air- low absorption (black)
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Film Quality
• First determine is the film a PA or AP view.
PA- the x-rays penetrate through the back of the patient on to the film
AP-the x-rays penetrate through the front of the patient on to the film.
All x-rays in the ICU are portable and are AP view
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Quality
• Is the film over or under penetrated if under penetrated you will not be able to see the thoracic vertebrae.
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Quality (cont)
• Check for rotation
– Does the thoracic spine align in the center of the sternum and between the clavicles?
– Are the clavicles level?
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NORMAL CHEST P/A
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Abnormalities that RTs encounter
• White stuff on CXR-Collapse of lung / lobes and Consolidation
• The black stuff-Pneumothorax, Pneumomediastinum
• Displaced lines,tubes,Ryles Tubes.
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White stuff - edema
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Air bronchogram sign
• In a normal chest x-ray, the tracheobronchial tree is not visible beyond 4th order
• It becomes recognizable if the surrounding alveoli is filled, providing a contrast or if the bronchi get thickened
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CAUSES
• Normal expiratory radiograph• Consolidation• Pulmonary edema• Nonobstructive pulmonary atelectasis-
RDS,compression atelectasis,Fibrotic scarring(radiation fibrosis,bronchiectatic lobe)
• Interstial disease-sarcoid,CFA• Neoplasms-BAC,lymphoma
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White stuff - Collapse
• Important to recognise• May be lobar or segmental• Lower lobe collapse are more important to
recognise as they carry more volume• Usually positioning would help in a ventilated
patients and Bronchoscopy is done only if patient is hypoxemic ,suspected foreign body or failure of positioning.
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Collapse LLL
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LLL collapse
• Common in ICU• Slightly difficult to pick up clinically.• Look for the diaphragm.
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RLL – LL PA
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Upper lobes
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Air beyond lungs
• Faulty ventilation strategy
• Iatrogenic
• Trauma patients
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Air around lungs
• Pneumo mediastinum• Subcutaneous emphysema• Pneumothorax
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Black stuff-Pneumomediastinum
• Continuous diaphragm sign• Ring around the artery sign
• Important to realise barotrauma during ventilation
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Pneumomediastinum
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Pneumomediastinumcontinuous diaphragm sign
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Ring around the artery sign
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Continuos diaphragm sign
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Pneumothorax
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Hyperlucent hemithorax sign
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Deep sulcus sign
• Air collects in the most superior portion.• In ventilated patient, it occupies anterior and
lateral portion of chest which is the most non dependant in supine lying.
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Deep sulcus
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Tubes and lines
• Important reason for taking an X-Ray• After ET /Trach or central lines, xrays give an
idea of the position of tubes and lines.• Need to rule out complications.
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Importance of penetrated film
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Hose goes where the nose goes
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High ET
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RMB intubation
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ICD position
Very low Too high
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NG tube
Twisted NG tube in airway
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Central line
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ABG
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The Body and pH
• Homeostasis of pH is tightly controlled• Extracellular fluid = 7.4• Blood = 7.35 – 7.45• < 6.8 or > 8.0 death occurs• Acidosis (acidemia) below 7.35• Alkalosis (alkalemia) above 7.45
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43
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44
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As required for ECG interpretation,
a systematic approach to ABGs enhances accuracy.
There are NO short-cuts!
A Systematic Approach
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The Anatomy of a Blood Gas Report
----- XXXX Diagnostics ------
Blood Gas Report248 05:36 Jul 22 2000Pt ID 2570 / 00
Measured37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected38.6o
CpH 7.439pCO2 47.6 mm HgpO2 123.5 mm Hg
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %ct CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Measured Values
Temperature Correction:Is there any value to it?
Calculated Data:Which are the useful ones?
Entered Data:Derived from other sources
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----- XXXX Diagnostics ------
Blood Gas Report
Measured37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected38.6o
C
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Oxygenation Parameters:O2 Content of blood:Hb x O2 Sat x Const. + Dissolved O2
Oxygen Saturation:
Alveolar / arterial gradient:
Arterial / alveolar ratio:
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Oxygen Saturation
pO2
Satu
ratio
n
0 60 120
100% Most blood gasmachines estimate saturation from an idealized dissociation curve
Gold standard is co-oximetry
Errors may occur with abnormal haemoglobins.
Oxygen content is calculated from this.
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Alveolar-arterial DifferenceInspired O2 = 21%= piO2 = (760-45) x .21=150 mmHg
O2
CO2
palvO2 = piO2 - pCO2 / RQ= 150 - 40/0.8= 150 – 50 = 100 mm Hg
partO2 = 90 mmHg
palvO2- partO2 = 10 mmHg
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Alveolar-arterial Difference
O2
CO2
Oxygenation FailurepiO2 = 150
pCO2 = 40
palvO2= 150 – 40/.8=150-50 =100
pO2 = 45
D = 100-45 = 55
Ventilation FailurepiO2 = 150
pCO2 = 80
palvO2= 150-80/.8 =150-100
= 50
pO2 = 45
D = 50-45 = 5
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----- XXXX Diagnostics ------
Blood Gas Report
Measured37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Calculated DataHCO3 act 31.1 mmol / L
O2 Sat 98.3 %pO2 (A - a) 32.2 mm Hg
Entered DataFiO2 30.0 %
The Blood Gas Report:The essentials
pH 7.40 + 0.05PCO2 40 + 5mm HgPO2 80 - 100mm Hg
HCO3 24 + 4mmol/L
O2 Sat >95A-a D 2.5+(0.21 x Age) mm Hg
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Technical Errors Glass vs. plastic syringe: Changes in pO2 are not clinically importantNo effect on pH or pCO2
Heparin (1000 u / ml):Need <0.1 ml / ml of bloodpH of heparin is 7.0; pCO2 trends downAvoided by heparin flushing & drawing 2-4 cc blood
Delay in measurement:Rate of changes in pH, pCO2 and pO2 can be reduced to 1/10 by cooling in ice slush(4o C)No major drifts up to 1 hour
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Step 1Look at the pH
Is the patient acidemic pH < 7.35or alkalemic pH > 7.45
Step 2Is it a metabolic or respiratory disturbance ?
Acidemia: With HCO3 < 20 mmol/L = metabolicWith PCO2 >45 mm hg = respiratory
Alkalemia: With HCO3 >28 mmol/L = metabolicWith PCO2 <35 mm Hg = respiratory
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Step 3If there is a primary respiratory disturbance, is it acute?
Expect D pH = 0.08 x D PCO2 / 10 (acute)Expect D pH = 0.03 x D PCO2 / 10 (chronic)
Step 4For a respiratory disorder is renal compensation OK?
Respiratory acidosis: <24 hrs: D [HCO3] = 1/10 D PCO2
>24 hrs: D [HCO3] = 4/10 D PCO2
Respiratory alkalosis: 1- 2 hrs: D [HCO3] = 2/10 D PCO2
>2 days: D [HCO3] = 5/10 D PCO2
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Step 5If the disturbance is metabolic is the respiratorycompensation appropriate?
For metabolic acidosis:Expect PCO2 = (1.5 x [HCO3]) + 8 + 2(Winter’s equation)
For metabolic alkalosis:Expect PCO2 = (0.7 x [HCO3]) + 21 + 1.5
If not: actual PCO2 > expected : hidden respiratory acidosisactual PCO2 < expected : hidden respiratory alkalosis
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Step 6If there is metabolic acidosis, is there an anion gap?
Na - (Cl-+ HCO3-) = Anion Gap usually <12
If >12, Anion Gap Acidosis : MethanolUremiaDiabetic KetoacidosisParaldehydeInfection (lactic acid)Ethylene GlycolSalicylate
Question: Should I calculate an anion gap when there is no acidemia?
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Step 7Does the anion gap explain the change in bicarbonate?
D anion gap (Anion gap -12) ~ D [HCO3]
If D anion gap is greater; consider additional metabolic alkalosis
If D anion gap is less; consider a nonanion gap metabolic acidosis
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To conclude
• Spend time with the patient and try and make sense of CXR and ABG .
• Continuous effort is required to master them.• Interpretation of both xrays and ABG have to
take the clinical context.
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THANK YOU