CXR and ABG interpretation for RT Pattabhi raman, Mahadevan & Arjun Srinivasan Pulmonology Associates KMCH

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.

CXR

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)

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

Quality Is the film over or under penetrated if under penetrated you will not be able to see the thoracic vertebrae.

Quality (cont) Check for rotation – Does the thoracic spine align in the center of the sternum and between the clavicles? – Are the clavicles level?

NORMAL CHEST P/A

Abnormalities that RTs encounter White stuff on CXR-Collapse of lung / lobes and Consolidation The black stuff-Pneumothorax, Pneumomediastinum Displaced lines,tubes,Ryles Tubes.

White stuff - edema

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

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

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.

Collapse LLL

LLL collapse Common in ICU Slightly difficult to pick up clinically. Look for the diaphragm.

RLL – LL PA

Upper lobes

Air beyond lungs Faulty ventilation strategy Iatrogenic Trauma patients

Air around lungs Pneumo mediastinum Subcutaneous emphysema Pneumothorax

Black stuff-Pneumomediastinum Continuous diaphragm sign Ring around the artery sign Important to realise barotrauma during ventilation

Pneumomediastinum

Pneumomediastinum continuous diaphragm sign

Ring around the artery sign

Continuos diaphragm sign

Pneumopericardium

Pneumothorax

Hyperlucent hemithorax sign

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.

Deep sulcus

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.

Importance of penetrated film

Hose goes where the nose goes

High ET

RMB intubation

ICD position Very lowToo high

NG tube TwistedNG tube in airway

Central line

ABG

42 The Body and pH Homeostasis of pH is tightly controlled Extracellular fluid = 7.4 Blood = 7.35 – death occurs Acidosis (acidemia) below 7.35 Alkalosis (alkalemia) above 7.45

43

44

As required for ECG interpretation, a systematic approach to ABGs enhances accuracy. There are NO short-cuts! A Systematic Approach

The Anatomy of a Blood Gas Report XXXX Diagnostics Blood Gas Report 24805:36Jul Pt ID2570 / 00 Measured37.0 o C pH7.463 pCO mm Hg pO mm Hg Corrected38.6 o C pH7.439 pCO mm Hg pO mm Hg Calculated Data HCO 3 act31.1 mmol / L HCO 3 std30.5mmol / L BE6.6mmol / L O 2 CT14.7mL / dl O 2 Sat98.3% ct CO mmol / L pO 2 (A - a)32.2mm Hg pO 2 (a / A)0.79 Entered Data Temp38.6 o C ct Hb10.5 g/dl FiO % Measured ValuesTemperature Correction: Is there any value to it? Calculated Data: Which are the useful ones? Entered Data: Derived from other sources

----- XXXX Diagnostics Blood Gas Report Measured37.0 o C pH7.463 pCO mm Hg pO mm Hg Corrected38.6 o C Calculated Data HCO 3 act31.1 mmol / L HCO 3 std30.5mmol / L BE6.6mmol / L O 2 CT14.7mL / dl O 2 Sat98.3% t CO232.4mmol / L pO 2 (A - a)32.2mm Hg pO 2 (a / A)0.79 Entered Data Temp38.6 o C ct Hb10.5 g/dl FiO % Oxygenation Parameters: O 2 Content of blood: Hb x O 2 Sat x Const. + Dissolved O 2 Oxygen Saturation: Alveolar / arterial gradient: Arterial / alveolar ratio:

Oxygen Saturation pO 2 Saturation % Most blood gas machines estimate saturation from an idealized dissociation curve Gold standard is co-oximetry Errors may occur with abnormal haemoglobins. Oxygen content is calculated from this.

Alveolar-arterial Difference Inspired O 2 = 21%= p i O 2 = (760-45) x.21=150 mmHg O 2 CO 2 p alv O 2 = p i O 2 - pCO 2 / RQ = /0.8 = 150 – 50 = 100 mm Hg p art O 2 = 90 mmHg p alv O 2 - p art O 2 = 10 mmHg

Alveolar-arterial Difference O 2 CO 2 Oxygenation Failure p i O 2 = 150 pCO 2 = 40 p alv O 2 = 150 – 40/.8 = =100 pO 2 = 45 D = = 55 Ventilation Failure p i O 2 = 150 pCO 2 = 80 p alv O 2 = /.8 = = 50 pO 2 = 45 D = = 5

----- XXXX Diagnostics Blood Gas Report Measured37.0 o C pH7.463 pCO mm Hg pO mm Hg Calculated Data HCO 3 act31.1 mmol / L O 2 Sat98.3% pO 2 (A - a)32.2mm Hg Entered Data FiO % The Blood Gas Report: The essentials pH PCO mm Hg PO mm Hg HCO mmol/L O2 Sat>95 A-a D 2.5+(0.21 x Age)mm Hg

Technical Errors Glass vs. plastic syringe: Changes in pO 2 are not clinically important No effect on pH or pCO 2 Heparin (1000 u / ml): Need <0.1 ml / ml of blood pH of heparin is 7.0; pCO 2 trends down Avoided by heparin flushing & drawing 2-4 cc blood Delay in measurement: Rate of changes in pH, pCO 2 and pO 2 can be reduced to 1/10 by cooling in ice slush(4 o C) No major drifts up to 1 hour

Step 1 Look at the pH Is the patient acidemic pH < 7.35 oralkalemicpH > 7.45 Step 2 Is it a metabolic or respiratory disturbance ? Acidemia: With HCO 3 < 20 mmol/L = metabolic With PCO 2 >45 mm hg = respiratory Alkalemia:With HCO 3 >28 mmol/L = metabolic With PCO 2 <35 mm Hg = respiratory

Step 3 If there is a primary respiratory disturbance, is it acute? Expect  pH = 0.08 x  PCO 2 / 10 (acute) Expect  pH = 0.03 x  PCO 2 / 10 (chronic) Step 4 For a respiratory disorder is renal compensation OK? Respiratory acidosis:<24 hrs:  [HCO 3 ] = 1/10  PCO 2 >24 hrs:  [HCO 3 ] = 4/10  PCO 2 Respiratory alkalosis:1- 2 hrs:  [HCO 3 ] = 2/10  PCO 2 >2 days:  [HCO 3 ] = 5/10  PCO 2

Step 5 If the disturbance is metabolic is the respiratory compensation appropriate? For metabolic acidosis: Expect PCO 2 = (1.5 x [HCO 3 ]) (Winter ’ s equation) For metabolic alkalosis: Expect PCO 2 = (0.7 x [HCO 3 ]) If not: actual PCO 2 > expected : hidden respiratory acidosis actual PCO 2 < expected : hidden respiratory alkalosis

Step 6 If there is metabolic acidosis, is there an anion gap? Na - (Cl - + HCO 3 - ) = Anion Gap usually <12 If >12, Anion Gap Acidosis : Methanol Uremia Diabetic Ketoacidosis Paraldehyde Infection (lactic acid) Ethylene Glycol Salicylate Question: Should I calculate an anion gap when there is no acidemia?

Step 7 Does the anion gap explain the change in bicarbonate?  anion gap (Anion gap -12) ~  [HCO 3 ] If  anion gap is greater; consider additional metabolic alkalosis If  anion gap is less; consider a nonanion gap metabolic acidosis

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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