blood gas analysis
DESCRIPTION
Blood Gas AnalysisTRANSCRIPT
![Page 1: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/1.jpg)
ABG analysis
“Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so
that we may fear less.”– Marie Curie
![Page 2: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/2.jpg)
ABG analysis
• Approach to blood gas analysis
• Examples
• Information overload
• Homework
![Page 3: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/3.jpg)
ABG analysis
![Page 4: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/4.jpg)
Stepwise approach
• Examine the pH and compare it to the normal range
• Identify the primary process that led to the change in pH
• Calculate the serum anion gap
• Identify the compensatory process (if one is present)
• Identify if any other disorders are present or there is a mixed acid-base process.
• Give a summary statement
![Page 5: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/5.jpg)
Normal Values
![Page 6: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/6.jpg)
Step 1:
• Examine the pH and compare it to the normal range
– pH low – acidaemia– pH high – alkalaemia
![Page 7: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/7.jpg)
Step 2:
• Determine the primary process that led to the change in the pH:– If acidaemia
• PCO2 is high – Resp Acidosis
• HCO3 is low – Metab Acidosis
– If Alkalaemia• PCO2 is low – Resp Alkalosis
• HCO3 is high – Metab Alkalosis
![Page 8: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/8.jpg)
![Page 9: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/9.jpg)
Identifing Primary Disorder
• Post-op on a PCA– ABG pH 7.25, PCO2 55, PO2 60, HCO3 25
• Cough fevers and dyspnoea– ABG pH 7.55, PCO2 30, PO2 63 HCO3 22
• Type 1 DM feels unwell– ABG pH 7.25, PCO2 28, PO2 95, HCO3 15
![Page 10: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/10.jpg)
Step 3: Calculate the serum anion gap (SAG)
(Na+ + K+) - (Cl- + HCO3-) = SAG
normal < 16
Na – Cl + HCO3 = SAG
normal < 12
• Should be done on all gases – why?• Affected by serum albumin
– Low albumin = lower upper limit of normal AG– For every 10g/L reduction in albumin – upper limit of normal AG
is reduced by 2.5
![Page 11: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/11.jpg)
? Mixed Disorder
• 30 F altered mental status. Tachypnoeic. Found with empty aspirin beside bed.
• ABG– pH 7.56 – PCO2 22 – PO2 110– HCO3 17 – Na 137 – Cl 99
![Page 12: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/12.jpg)
Step 4: Identify the compensatory process (if present)
– The body will attempt to bring the pH back towards the normal range
![Page 13: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/13.jpg)
Compensation
• The body never overcompensates for the primary process.
• The pace of compensation varies depending on whether it is respiratory or metabolic compensation.
• Despite the compensatory mechanisms, the pH may not return all the way to normal
• What may appear to be a compensatory process may not actually represent true compensation
• BASE EXCESS/BASE DEFICIT
![Page 14: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/14.jpg)
Compensatory Process
1. 40 M mountain researcher ascends to 15000 ft. After 3 weeks has an ABG
– ABG pH 7.44, PCO2 24, PO2 55, HCO3 16, AG 11
2. 65 M severe COPD workup for home O2– ABG pH 7.36, PCO2 60, PO2 60, HCO 34, AG 8
3. 40 F severe diarrhoea with multiple episodes over a 24 hour period
– ABG pH 7.37, PCO2 32, PO2 75, HCO3 18, AG 10
![Page 15: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/15.jpg)
Step 5: Determine if a Mixed Acid-Base Disorder is Present 1. Use compensation rules to see if expected response is present
– If not then there may be an additional process
2. Calculate Delta Gap
AG – 1224 – HCO3
Delta Ratio Suggests< 0.4 Hyperchloremic normal anion gap acidosis< 1 High AG & normal AG acidosis1 to 2 Pure Anion Gap Acidosis Lactic acidosis: average value 1.6 DKA more likely to
have a ratio closer to 1 due to urine ketone loss> 2 High AG acidosis and a concurrent metabolic alkalosis or a pre-
existing compensated respiratory acidosis
![Page 16: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/16.jpg)
Compensation RulesCompensation rules for
ExpectedPCO2
Metabolic acidosis Metabolic alkalosis
1.5 x [HCO3] + 8 (+/- 2) 0.7 x [HCO3] + 20 (+/- 5)0.9 x [HCO3] + 9 (+/- 5)
Expected
HCO3
Respiratory acidosis Respiratory alkalosis
Acute Chronic Acute Chronic
24 + pCO2 – 40 X 1
1024 + pCO2 – 40 X 4
1024 - 40- pCO2 X 2
10
24 – 40 – pCO2 X 5
10
For every 10mmHg change in pCO2 from normal (40mmHg), there is an expected change in HCO3 as follows
Acute Chronic
In Resp Acidosis, HCO3 goes up by
1 4
Resp Alkalosis, HCO3 goes down by
2 5
![Page 17: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/17.jpg)
Other Considerations
• Osmolar gap• Osmolar Gap = Measured Osm – Calculated Osm
(Calc Osm = 2 x Na + Urea + Glucose)
• Correction for Hyperglycaemia• Corrected Na+ = Measured Na+ + Glucose – 5
3
![Page 18: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/18.jpg)
Other Considerations
• Oxygenation– Hypoxia
• A-a Gradient
– Gas Exchange• P/F ratio
• A-a gradient
• Causes of hypoxaemia– Low inspired partial pressure
of oxygen (eg. high altitude)– Hypoventilation – Shunt – V/Q mismatch
– Diffusion limitation (rarely an
issue at sea-level)
![Page 19: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/19.jpg)
Differential Diagnosis
• High Anion Gap Metabolic Acidosis
• Normal Anion Gap Metabolic Acidosis (non-gap acidosis)
• Metabolic Alkalosis
• Respiratory Acidosis
• Respiratory Alkalosis
![Page 20: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/20.jpg)
Examples
1. 45 m, found drowsy, vomit on shirt. Hypotensive and tachycardic
– ABG: pH 7.22, PCO2 29, PO2 78, HCO3 11, Na 131, Cl 90
2. 60 m, recent hospitalisation for pneumonia. Presents 1 week later with severe diarrhoea, abdo pain and hypotension
– ABG: pH 7.29, PCO2 25, PO2 89, HCO3 10, Na 129, Cl 99
3. 56 F chronic renal failure presents with dyspnoea, tachypnoea. Normal lung exam and CXR
– ABG: pH 7.28, PCO2 29, PO2 85, HCO3 15, Na 131, Cl 105
![Page 21: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/21.jpg)
High Anion Gap Metabolic Acidosis
• CAT MUDPILES– Carbon monoxide/cyanide– Alcoholic Ketoacidosis– Toluene– Methanol/Metformin – Uremia – DKA/Alcoholic KA – Paraldehyde/propylene
glycol– Isoniazid/Iron– Lactic Acidosis – Ethanol/Ethylene Glycol – Salicylates
• Pathological Processes
• Ketoacids• Ingestions• Lactate• Renal Faliure/uraemia
• KILR• KILU
![Page 22: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/22.jpg)
Normal Anion Gap Metabolic Acidosis
• USED CARP– Ureteroenterostomy– Saline hydration– Endocrinopathies (hyperparathyroid, hyperthyroid, Addison's)– Diarrhea/ DKA/ Drugs– Carbonic anhydrase inhibitors– Ammonium chloride– Renal tubular acidosis– Parenteral nutrition/Pancreatic fistula
• Losing HCO3 (GI or Renal)• Gaining Cl-
![Page 23: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/23.jpg)
Metabolic Alkalosis
• Losing Acid (H+)– GI or renal
• Gain HCO3
• CLEVER– Contraction– Licorice – Endo: (Conn's, Cushings,
Bartter's) – Vomiting – Excess Alkali – Refeeding Alkalosis
• Chloride responsive– Vomiting– Nasogastric suction– Diurtetics
• Chloride unresponsive– Hyperaldosteroneism– Cushings– Bartters– Excess alkali– Licorice ingestion
![Page 24: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/24.jpg)
Respiratory Acidosis
• Acute Respiratory Acidosis – CNS Depression
(drugs/CVA) – Airway Obstruction – Pneumonia – Pulmonary Edema – Hemo/Pneumothorax – Myopathy
• Chronic Respiratory Acidosis – COPD– Restrictive lung – Any hypoventilation
state
![Page 25: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/25.jpg)
Respiratory Alkalosis
• Hyperventilation
• CNS disease
• Hypoxia
• Anxiety
• Mech Ventilators
• Progesterone
• Salicylates/Sepsis
![Page 26: Blood Gas Analysis](https://reader036.vdocument.in/reader036/viewer/2022081502/556e638ad8b42a6a248b4c80/html5/thumbnails/26.jpg)
Approach to ABG’s
• Examine the pH and compare it to the normal range
• Identify the primary process that led to the change in pH
• Calculate the serum anion gap
• Identify the compensatory process (if one is present)
• Identify if any other disorders are present or there is a mixed acid-base process.
• Give a summary statement