1 / 40

Arterial versus Venous Blood Gas Analysis

Arterial versus Venous Blood Gas Analysis. Rama B Rao, MD Bellevue Hospital Center/NYUMC 2005. Case 1. A 78 year old woman with a history of HTN,

omer
Download Presentation

Arterial versus Venous Blood Gas Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Arterial versus Venous Blood Gas Analysis Rama B Rao, MD Bellevue Hospital Center/NYUMC 2005

  2. Case 1 • A 78 year old woman with a history of HTN, A fib, DM, and COPD presents with severe abdominal pain. On examination she has diffuse severe tenderness throughout the abdomen, and mild wheezes with the following vital signs: • HR 110 bpm, RR 22/min, T37°C, BP 105/70 mmHg Oxygen Saturation of 93% on RA • A blood gas is obtained with a lactate • VBG 7.20/29/33 HCO3 12 Lactate 9

  3. Case 2 • A 30 year old male with a CD4 of 8 presents with dyspnea on exertion. Oxygen saturation is 88% and rises to 95% on 100% NRB. • An ABG is attempted, but the sample obtained is not pulsating and is likely to be venous. • VBG on room air results are 7.38/35/40 HCO3 23

  4. Arterial Blood Gas Sampling • A-a gradient • Ventilation • Acid-base status • Lactate • Electrolytes • Co-oximetry

  5. A-a Gradient • Difference between what is measured in the artery on an ABG, and what exists in the alveoli • Alveolar gas =Ambient gas minus what displaces it from the internal environment • pAO2= Inspired O2 - (CO2/0.8) • A-a gradient is • calculated pAO2 - measured paO2

  6. A-a Gradient and paO2 • When is it useful to calculate a gradient? • When will it affect your interventions in the emergency department?

  7. A-a Gradient Indications • Assessment of PaO2 for subsequent interventions • A-a gradient > 35 mmHg or paO2 < 70 mmHg • Anonymous. Consensus statement on the use of corticosteroids as adjunctive therapy for pneumocystis pneumonia in the acquired immunodeficiency syndrome. The National Institutes of Health-University of California Expert Panel for Corticosteroids as Adjunctive Therapy for Pneumocystis Pneumonia New England Journal of Medicine. 323(21):1500-4, 1990 Nov 22. • Venous sampling inadequate

  8. Co-oximetry • Oxyhemoglobin • De-oxyhemoglobin • Methemoglobin • Carboxyhemoglobin • Venous co-oximetry is acceptable for MetHgb and COHgb Touger M et al. Ann Emerg Med 1995;25:481-3

  9. Lactate Indications • Unidentified anion gap metabolic acidosis • Management/Prognosticator • Early goal directed therapy in sepsis1: • SIRS hypotension despite fluid resuscitation or lactate ≥ 4 mmol/L • Blunt trauma2 1. Rivers E, et al. New Engl J Med 2001;345:368-377; 2. Lavery RF. J Am Coll Surg 2000;190:656-664

  10. Lactate: ABG vs VBG • Not affected by tourniquet1 • Venous lactate closely approximates arterial lactate, esp in blunt trauma2 • Elevated venous lactate 100% sensitive for arterial lactic acidemia3 • Venous lactate adequate 1.Tortella BJ Acad Emerg Med 1996;3:415, 2.Lavery RF. J Am Coll Surg 2000;190:656-664 3. Younger JG. Acad Emerg Med 1996;3:730-734

  11. Acid-base Status • Attempt to correlate arterial and venous gases • Specific vs Nonspecific conditions • Attempt at generating an equation

  12. Diabetic Ketoacidosis • Prospective convenience sample • Prior to treatment • Mean difference between arterial and venous pH 0.03 (0-0.11) • Not validated for mixed acid-base disorders, hypotensive pts, or ventilatory insufficency • VBG good correlation, useful to follow Brandenburg MA, Ann Emerg Med 1998;31:459-465

  13. Acute Respiratory Failure • Excluded unstable hemodynamics or pressor requiring pts • 46 intubated patients in ICU • Compared ABG vs VBG • Created equation • Validated? predictions Chu Y. J Formosan Med Assoc 2003;102:539-43

  14. Acute Respiratory Failure • % Change pH 0.5  0.45 • % Change pCO2 17.09  9.60 • % Change HCO3 9.72  7.73 • Authors conclude VBG predictive of ABG in stable ventilated patients • Limited applicability in ED patients Chu Y. J Formosan Med Assoc 2003;102:539-43

  15. ED Patients • Prospective • 171 non-arrest, and 12 arrest pts • Unable to predict arterial from venous samples • Change in pH 0.056 (SD) • Change in pCO2 7.51 (SD) Gennis PR Ann Emerg Med 1985;14:845-9

  16. ED Patients • Venous pH  7.25 98% predictive of an arterial pH  7.20 • Venous pH  7.00 98% predictive of an arterial pH  7.05 • Venous pCO2  40 98% predictive of an arterial pCO2  48 Gennis PR Ann Emerg Med 1985;14:845-9

  17. ED Patients • Prospective, observational • Physician questionairre • Mean change in pH 0.036 ; in pCO2 6 • Differences too large by questionairre • 40% eligible patients captured • Not many acidemic patients (pH 7.39) • Limited utility, but good correlation Rang LCF Can J Emerg Med 2002;4:7-15

  18. Pediatric Patients • ICU patients • Good correlation VBG, ABG, CBG for all parameters except for paO2 in hypotension • Change in pH difficult to assess from data • Potential utility in this subgroup Yldzdas D. Arch Dis Childhood 2004;89;176-180

  19. Pediatric Patients • PICU patients: ABG, VBG, CBG • pCO2 correlates best with capillary sampling • Venous sampling limited utility • Capillary BG, and Pulse oximetry useful • Mean change pH 0.04 • Potentially useful in this subgroup Kirubakaran C. Indian J Pediatr 2003;70:781-5

  20. COPD* • Patients recovering from acute exacerbation • Compared pCO2 in venous and arterial samples • N= 48 • pCO2 similar in each sample • Limited utility Elborn JS. Ulster Med J 1991;60:164-7 in Hinder K. Center for Clinical Effectiveness. www.med.monsh.edu/au/publichealthcare/cce

  21. mean pH • Gennis 0.056 • Kirubakaran 0.04 • Yldzdas 0.0397? • Rang 0.036 • Chu 0.037 (0.5%) • Brandenburg 0.03

  22. mean pCO2 • Gennis 7.38 • Kirubakaran - • Yldzdas 3.1 • Rang 6 • Chu 6.75 (17.09%) • Brandenburg -

  23. mean HCO3 • Gennis 1.21  2.55 SD • Kirubakaran - • Yldzdas 1.67? • Rang 1.5 (1.3-1.7) • Chu 2.56 (9.72%) • Brandenburg very close

  24. Case 1 • A 78 year old woman with a history of HTN, A fib, DM, and COPD presents with severe abdominal pain. On examination she has diffuse severe tenderness throughout the abdomen, mild wheezes and the following vital signs: • HR 110 bpm, RR 22/min, T37°C, BP 105/70 mmHg • A blood gas is obtained with a lactate

  25. Case 1 • VBG 7.20/29/33 HCO3 12 Lactate 9 • What should you do? • A. Repeat the lactate as an arterial sample • B. Empirically start a bicarbonate drip • C. Intubate for respiratory failure • D. Repeat the sample as arterial, presume a severe lactic acidemia is present

  26. Case 1 • VBG 7.20/29/33 HCO3 12 Lactate 9 • What should you do? • A. Repeat the lactate as an arterial sample • B. Empirically start a bicarbonate drip • C. Intubate for respiratory failure • D. Presume a severe lactic acidemia is present

  27. Case 2 • A 30 year old male with a CD4 of 8 presents with dyspnea on exertion. An ABG is attempted, but the sample obtained is not pulsating and is likely to be venous.

  28. Case 2 • VBG results are 7.38/35/40 HCO3 23 • What should you do? • A. Start empiric corticosteroid therapy • B. Repeat the gas as an arterial sample • C. Send a lactate, urine for ketones, and a repeat chemistry • D. Correct pCO2 by adding a correction factor of 7 mmHg

  29. Case 2 • VBG results are 7.38/35/40 HCO3 23 • What should you do? • A. Start empiric corticosteroid therapy • B. Repeat the gas as an arterial sample • C. Send a lactate, urine for ketones, and a repeat chemistry • D. Correct pCO2 by adding a correction factor of 7 mmHg

  30. Case 3 • A 29 year old female is struck by a car while crossing the street. She is awake and alert with normal vital signs and oxygen saturation and a large bruise across her right flank. • An IV line is placed. Should she get a complete gas or just a lactate? If so, venous or arterial?

  31. Case 3 • A 29 year old female is struck by a car while crossing the street. She is awake and alert with normal vital signs and oxygen saturation and a large bruise across her right flank. • An IV line is placed. Should she get a complete gas or just a lactate? If so, venous or arterial?

  32. Case 4 • A 26 year old male with a history of insulin requiring diabetes presents with abdominal pain, vomiting once, and polydipsia. He has missed one day of medication. His glucose is 487 mg/dL • He is mildly tachycardic, RR 24, afebrile, with clear lungs and a soft abdomen

  33. Case 4 • What should you do? • A. Send an ABG and lactate as he may have a triple acid-base disorder • B. Obtain a urine for ketones, VBG with electrolytes, and repeat as ABG if necessary • C. Obtain an ABG as he is tachypneic and may have an A-a gradient • D. Correct a venous pH by 0.05 upwards to obtain arterial value

  34. Case 4 • What should you do? • A. Send an ABG and lactate as he may have a triple acid-base disorder • B. Obtain a urine for ketones, VBG with electrolytes, and repeat as VBG after care and ABG only if necessary • C. Obtain an ABG as he is tachypneic and may have an A-a gradient • D. Correct a venous pH by 0.05 upwards to obtain arterial value

  35. Case 5 • An 8 week old male presents in respiratory distress after 2 days of cough and nasal congestion with poor feeding. His oxygen saturation is 88% on room air. His lungs sound clear.

  36. Case 5 • What should you do? • A. Presume methemoglobinemia and empirically treat • B. Obtain an arterial sample for MetHgb • C. Consider congenital right to left shunt, sepsis, pneumonia, or methemoglobinemia and send capillary blood gas • D. Consider broad differential, administer oxygen, obtain cultures, venous metHgb if no response to oxygen, and ABG

  37. Case 5 • What should you do? • A. Presume methemoglobinemia and empirically treat • B. Obtain an arterial sample for MetHgb • C. Consider congenital right to left shunt, sepsis, pneumonia, or methemoglobinemia and send capillary blood gas • D. Consider broad differential, administer oxygen, obtain cultures, venous metHgb if no response to oxygen, and an ABG to assess paO2

  38. Conclusions • Venous lactate and co-oximetry are clinically valuable alternatives to arterial samples • paO2 is inadequately assessed with venous sampling

  39. Conclusions • Extremely acidemic venous pH will likely predict severe arterial acidemia • A normal venous pH is likely to exclude severe arterial pH abnormalities • No single equation has been validated to predict arterial from venous sampling

  40. Conclusions • All decisions must be made with regards to the clinical context of the patient and whether management would be potentially affected.

More Related