Focused Assessment with Sonography in Trauma (FAST): An Overview

Traumatic injuries are one of the leading causes of death, and intraperitoneal bleeds occur in approximately 12% of blunt traumas [1]. A quick assessment of trauma and detection of intraperitoneal fluid is increasingly essential in trauma patients’ assessment. The implementation of point-of-care ultrasound (POCUS) has had a significant impact on patient management, especially in a trauma setting. POCUS is easy to use at the bedside, non-invasive and inexpensive.

The Focused Assessment with Sonography in Trauma (FAST) is an ultrasound protocol used to assess hemoperitoneum and hemopericardium [2]. The FAST protocol is sensitive and specific for detecting intraperitoneal free fluid. According to previous studies, sensitivity ranges from 75-100%, and specificity ranges from 88-100% [3]. The FAST exam is rapid and can be completed in less than 5 minutes. It also has multiple advantages, including decreased time to interventions like surgery and length of stay at the hospital [4]. The Extended FAST (eFAST) protocol, which involves examinations of each hemithorax for hemothorax and pneumothoraces, has recently been introduced by several institutions [2].

Regions Examined

The FAST exam assesses the pericardium and multiple potential spaces within the peritoneal cavity for free fluid. The patient is often assessed in the supine position.

The right flank or right upper quadrant (RUQ) view assesses the hepatorenal recess (also known as Morrison’s pouch), as well as the right paracolic gutter, the hepato-diaphragmatic area, and the caudal edge of the left liver lobe [2]. The pericardial view, also known as the subcostal or the subxiphoid, is usually assessed next. The liver is commonly used as a sonographic window of the heart to evaluate pericardium. Ultrasound can detect little pericardial fluid with sensitivity and specificity approaching 100% [5]. The pericardial view also helps to differentiate between pleural and pericardial effusions and visualize right ventricular collapse during diastole [2]. Next, the left upper quadrant (LUQ) is used to visualize the splenorenal recess, the subphrenic space and the left paracolic gutter. If the eFAST protocol is being conducted, the RUQ and LUQ views are also used to examine the left and right hemithorax. Lastly, the pelvic or the suprapubic view is used to assess for free fluid in the rectovesical pouch in males and rectouterine and vesicouterine pouches in women [2]. The bladder acts as a sonographic window for this view.


While there are no complications related to the FAST exam itself, the use of ultrasound does have some limitations, one of which is the requirement for at least 150-200 cc of intraperitoneal fluid for an ultrasound to be able to detect. This can lead to false negatives when free fluid is in fact present [6]. False positives in the FAST exam may also occur and can be due to the presence of ascites, pre-existing pleural or pericardial effusions unrelated to the trauma, ruptured ovarian cysts or ruptured ectopic pregnancies [2]. Healthcare workers should be aware that POCUS and the FAST protocol have limitations dependent on the provider’s experience and the patient’s body habitus.   

Further Reading and Free Online Course


  1. Poletti, P. A., Mirvis, S. E., Shanmuganathan, K., Takada, T., Killeen, K. L., Perlmutter, D., Hahn, J., & Mermillod, B. (2004). Blunt abdominal trauma patients: can organ injury be excluded without performing computed tomography?. The Journal of Trauma57(5), 1072–1081.
  2. Bloom, B. A., & Gibbons, R. C. (2020). Focused Assessment with Sonography for Trauma.
  3. Brenchley, J., Walker, A., Sloan, J. P., Hassan, T. B., & Venables, H. (2006). Evaluation of focussed assessment with sonography in trauma (FAST) by UK emergency physicians. Emergency Medicine Journal23(6), 446–448.
  4. Melniker, L. A., Leibner, E., McKenney, M. G., Lopez, P., Briggs, W. M., & Mancuso, C. A. (2006). Randomized controlled clinical trial of point-of-care, limited ultrasonography for trauma in the emergency department: the first sonography outcomes assessment program trial. Annals of Emergency Medicine48(3), 227–235.
  5. Mandavia, D. P., Hoffner, R. J., Mahaney, K., & Henderson, S. O. (2001). Bedside echocardiography by emergency physicians. Annals of emergency medicine38(4), 377–382.
  6. Von Kuenssberg Jehle, D., Stiller, G., & Wagner, D. (2003). Sensitivity in detecting free intraperitoneal fluid with the pelvic views of the FAST exam. The American journal of emergency medicine21(6), 476–478.
Cite this article as: Maryam Bagherzadeh, Canada, "Focused Assessment with Sonography in Trauma (FAST): An Overview," in International Emergency Medicine Education Project, September 20, 2021,, date accessed: September 21, 2023

The Case of the Perplexing Crepitations

perplexing crepitations

Occam’s Razor – the simplest explanation is most likely to be correct.

In the Emergency Room, we are faced with a multitude of cases, and Occam’s Razor serves best when we need to narrow down on the differential diagnoses.

Sometimes, a few cases may evade this category and continue to baffle us even after a thorough history is obtained or a detailed clinical examination is performed. If we are lucky enough to get the point-of-care (POC) lab tests in time (or the mere availability of POC), they aid in the diagnosis and decision-making. At times, these POC lab tests also may not provide much help.

I have described one such case – a 21-year-old male with fever, dyspnea, desaturation, and multiple petechiae of 3 days duration.

Case Presentation

A 21-year-old male came at 9.30 pm to the ER with fever and breathlessness for three days. Being a healthcare worker himself, he had suspected pneumonia and started oral Amoxiclav, oral Clarithromycin, and Paracetamol. Despite this, there was no improvement in clinical status. He had progressively worsening breathlessness and continuous low-grade fever. On day 3, he developed a few petechial spots over his arms and minimal subconjunctival hemorrhage.

He recalls having myalgia in the lead up to these symptoms, for which he had received several injections of intramuscular Diclofenac. The injection sites now had developed small hematomas. There were no other visible bleeding manifestations. He clearly said that he had had no contact with any infectious patients and had self-isolated after developing these symptoms. His workplace had sent blood and sputum cultures – which came back negative. Their only concern was a continuous rise in the WBC count and sent to our hospital for further management.


The patient was very ill-looking and extremely dyspneic with obvious usage of accessory respiratory muscles. He was profusely diaphoretic, had bilateral subconjunctival hemorrhage, multiple petechiae, anasarca, dyspnea, and 99.6⁰F. His Vitals were heart rate – 134/min, blood pressure – 110/70mmHg, respiratory rate – 34/min, SpO2 – 72% in room air; 98% with NIV. There were bilateral crepitations in all lung fields + no obvious abnormalities on CVS, CNS, and abdominal examination. POC ultrasound revealed multiple B-lines in all lung areas. Dilated IVC. The remaining cardiac, abdomen, and limb USGs were normal. ABG revealed Type 1 respiratory failure with elevated lactates. Bedside CXR and chest CT revealed diffuse bilateral lung infiltrates – not typical of pulmonary edema or pneumonia. Probable ARDS was mentioned. Blood samples had been sent for necessary investigations, including cultures and peripheral blood smear.


Meanwhile, opinions were obtained from critical care consultants and pulmonologists regarding further management. Based on the clinical findings, it was decided to start the patient on broad-spectrum antibiotics (BSA), albumin transfusion, diuretics for the fluid overload status, and NIV for respiratory failure [all in suspicion of sepsis with MODS]. The patient was started on BSA before shifting to the ICU. Meanwhile, the blood reports arrived, suggestive of possible Myelodysplastic Syndrome (WBC – 95,000, Hb – 7g/dl. Peripheral Blood Smear report was Acute Myeloid Leukemia – possible M2 or M3.

The patient was immediately started on IV fluids, and oncology consultation was immediately obtained for chemotherapy initiation. Albumin and diuretics were withheld in suspicion of blast crisis and leukostasis / leukemic infiltration of the lungs. The patient was started on Cisplatin and other chemotherapeutic agents; bicarbonate infusion for urine alkalinization; allopurinol to treat hyperuricemia due to cytolysis; aggressive IV fluids for prevention of AKI due to chemotherapy and hyperuricemia [Tumour Lysis Syndrome]. Bone marrow biopsy was done during his hospital stay, which confirmed blast crisis AML-M3. His clinical condition improved considerably, and he was discharged from the hospital on Day 7.

Lessons Learnt

  1. Recognising leukostasis and hyperviscosity in the ED in an undiagnosed AML patient is extremely difficult.
  2. While considering different diagnoses based on clinical findings, always keep an open eye. Rare diseases present to the ED just like all others.
  3. Aggressive fluid management is needed in hyperviscosity syndrome. If we had started this patient on diuretics as planned, the blood would have become more viscous and lead to multisystem thrombosis.
  4. Increased metabolism in AML can present as pyrexia. With the other features of anemia, leucocytosis, petechiae, and anasarca, we are likely to diagnose this as sepsis. When in doubt, look through other causes of pyrexia (PUO).
  5. Anasarca in leukemia does not warrant albumin transfusion as this may worsen fluid status. They may actually be in need of steroid therapy.
  6. Point of Care Lab testing is essential to reduce the number of diagnostic errors in the ED.
Cite this article as: Gayatri Lekshmi Madhavan, India, "The Case of the Perplexing Crepitations," in International Emergency Medicine Education Project, June 14, 2021,, date accessed: September 21, 2023

Recent Blog Posts By Gayatri L. Madhavan

Approach to Jaundice in the Emergency Department

A 50-year-old male presents to the emergency department (ED) with nausea and vomiting, diminished appetite, and recent changes in his skin color, which he describes as turning “yellow.” This seemed to have worsened over the past few weeks, after which he began to worry and presented to the ED.

The patient’s vital signs are normal. His physical exam is positive for icteric sclerae, jaundice in the face and chest, and hepatomegaly. He is not tender to palpation on the abdomen. The rest of his exam is otherwise normal.


Jaundice is not a diagnosis, but a clinical manifestation of an underlying problem, specifically elevated serum bilirubin. Patients with Jaundice present with yellow discoloration of the skin, mucous membranes, and sclera. They can present to the ED with Jaundice in isolation or along with other symptoms. It is the Emergency Physician’s task to evaluate the patient, find the underlying cause, order the appropriate investigation and decide whether the patient requires admission to the hospital and consultation with other physicians.

Normal physiology of bilirubin metabolism

Bilirubin is the end product of heme metabolism. This occurs in three phases: pre-hepatic, hepatic, and post-hepatic phases. Approximately 75-80% of bilirubin comes from the catabolism of red blood cells. Initially, this bilirubin is unconjugated, which is insoluble in water and soluble in fat. Therefore, unconjugated bilirubin can easily cross the blood-brain barrier and the placenta [1].

Unconjugated bilirubin is actively transported to the liver by albumin and is conjugated by the enzyme glucuronosyltransferase. Subsequently, conjugated bilirubin is either stored in bile in the gallbladder or excreted through the biliary tract, where it eventually reaches the intestines and is excreted from the body [1,2].

Pathophysiology and differential diagnosis

The classic definition of jaundice is a serum bilirubin level greater than 2.5 to 3 mg per dL (42.8 to 51.3 µmol per L), with a clinical presentation of yellow skin and sclera [1]. As described in the above section, bilirubin metabolism occurs in three phases, and dysfunction of any of these steps can lead to jaundice.

Pre-hepatic causes

Unconjugated hyperbilirubinemia or elevated levels of unconjugated bilirubin before it reaches the liver can lead to jaundice. This can occur due to excessive heme metabolism from increased red blood cell breakdown (hemolysis) and the saturation of enzymes that conjugate it. A few underlying etiology for this include hemolytic anemia, sickle cell anemia, spherocytosis, glucose-6-PD deficiency, hemolytic uraemic syndrome, and transfusion reaction [1,3].

Hepatic causes

Any process that impacts liver functioning can lead to jaundice. Some of the hepatic causes of jaundice in adults include viral hepatitis, chronic alcohol consumption, autoimmune diseases such as primary biliary cirrhosis, genetic disorders such as Gilbert syndrome, hereditary metabolic defects such as Dubin-Johnson syndrome, and some drugs that can lead to drug-induced liver disease such as acetaminophen, oral contraceptives, estrogenic and anabolic steroids [4-6].

Post-hepatic causes

Any process that instigates post-hepatic obstruction can lead to jaundice due to elevated levels of conjugated bilirubin. Some of these include cholelithiasis leading to obstruction of the biliary duct system, biliary tract tumors, biliary duct strictures, and jaundice secondary to pancreatitis [1, 7].

History and physical examination

A good history and physical examination of patients presenting with jaundice to the ED is key in their diagnosis.

On history, the patient should be asked about alcohol and drug use, recent travel, sexual contact with a person with known or suspected hepatitis, recent tattoos or body piercings, and previous biliary surgery. A focused review of systems should also be conducted. For example, a history of fever and viral symptoms can point towards viral hepatitis, while the presence of constitutional symptoms such as weight loss and night sweat may point towards a malignancy [8].

The physical examination should comprise vital signs and a complete abdominal examination, assessing for right upper quadrant tenderness, ascites, hepatomegaly, splenomegaly, and ascites [9]. Additionally, the physical examination should focus on evaluating encephalopathy by looking for asterixis and changes in mental status and underlying liver disease by assessing for bruising, spider angiomas, gynecomastia, and palmar erythema [1, 8-9]. Lastly, it is important to remember that the presence of painless jaundice and an abdominal mass may point towards obstruction from a malignancy.


Laboratory assessment

First line serum testing should include a complete blood count (CBC) to check for hemolysis, bilirubin level with fractionation, aminotransferases (AST and ALT) to assess for hepatocellular injury (although these may be normal in chronic liver disease), alkaline phosphatase, prothrombin time and/or international normalized ratio, albumin, and protein to assess for liver synthetic function. If these tests come back normal, further tests may be needed to identify the underlying cause of the patient’s jaundice, such as hepatitis serology, autoimmune markers, and investigation for acetaminophen levels [1,8].


The majority of diagnostic imaging will be done outside of the ED. However, emergency physicians can conduct initial ultrasound screening to assess for bile duct dilation, biliary obstruction, and the presence of cholelithiasis. A CT scan can also be ordered to assess for intraparenchymal liver and pancreas disease [1,8]. Outside of the ED, investigation with Endoscopic Retrograde Cholangio-Pancreatography (ERCP), Magnetic Resonance Cholangio-Pancreatography (MRCP), and a liver biopsy may be warranted.


In the ED, emergency physicians are often involved in the initial investigation of a patient with jaundice in ruling out life-threatening conditions and to decide whether a patient should be discharged or admitted for further management. For example, physicians should first assess medical emergencies that can present with jaundice, such as ascending cholangitis, acute hepatic failure, and massive hemolysis. Timely diagnosis, resuscitation, treatment initiation, and emergent consultation of these conditions are critical in the ED. Additionally, patients with elevated AST/ALT levels should be admitted if there are any signs of sepsis, coagulopathy, altered mental status, and intractable pain and vomiting. The presence of hepatocellular injury, coagulopathy, and altered mental status may point towards fulminant liver failure and may require acute fluid resuscitation and hemodynamic monitoring in an acute care setting [10]. Otherwise, depending on the underlying cause of a patient’s jaundice, surgical, gastroenterological or interventional radiological consultation may be required in an outpatient setting.

References and Further Reading

  1. Roche, S. P., & Kobos, R. (2004). Jaundice in the adult patient. American family physician69(2), 299-304.
  2. Wolfson, A. B., Hendey, G. W., Ling, L. J., Rosen, C. L., Schaider, J. J., & Sharieff, G. Q. (2012). Harwood-Nuss’ clinical practice of emergency medicine. Lippincott Williams & Wilkins.
  3. Sackey K. (1999). Hemolytic anemia: part 1. Pediatr Rev, 20,152-8.
  4. Pasha, T. M., & Lindor, K. D. (1996). Diagnosis and therapy of cholestatic liver disease. Medical Clinics of North America80(5), 995-1019.
  5. Schramm, C., Kanzler, S., Zum Büschenfelde, K. H. M., Galle, P. R., & Lohse, A. W. (2001). Autoimmune hepatitis in the elderly. The American journal of gastroenterology96(5), 1587-1591.
  6. Lewis, J. H. (2000). Drug-induced liver disease. Medical Clinics84(5), 1275-1311.
  7. Custis, K., Brown, C., & El Younis, C. M. (2000). Common biliary tract disorders. Clinics in Family Practice2(1), 141-154.
  8. Fargo, M. V., Grogan, S. P., & Saguil, A. (2017). Evaluation of jaundice in adults. American family physician95(3), 164-168.
  9. Winger, J., & Michelfelder, A. (2011). Diagnostic approach to the patient with jaundice. Primary Care: Clinics in Office Practice38(3), 469-482.
  10. Vaquero, J., & Blei, A. T. (2003). Etiology and management of fulminant hepatic failure. Current gastroenterology reports5(1), 39-47.
Cite this article as: Maryam Bagherzadeh, Canada, "Approach to Jaundice in the Emergency Department," in International Emergency Medicine Education Project, May 17, 2021,, date accessed: September 21, 2023

Recent Blog Posts By Maryam Bagherzadeh

FOAMed Resources for ECG Interpretation

You often hear that learning how to read an electrocardiogram (ECG or EKG) is like learning a new language. Interpreting ECGs is an essential skill for emergency physicians who frequently treat patients with acute cardiac conditions. As a medical student, it is crucial to practice as much as possible because it takes time to develop this skill and become comfortable with it. The International Federation of Emergency Medicine (IFEM) lists basic electrocardiographic analysis as an essential component of undergraduate education for medical students including recognition of acute myocardial infarction and life-threatening arrhythmias.

As I went through my emergency medicine rotation during my clerkship, I found that this skill took a lot of practice to learn. Along the way, I discovered some excellent resources that helped me get better at it. I wanted to share these Free Open Access to Medical Education (FOAMed) resources to help other medical students looking to strengthen their ECG skills and apply their knowledge on a shift in the emergency department.

Analysis and Interpretation of the Electrocardiogram from Queen’s University

This self-directed online module was where I started. Reading ECGs requires a systematic approach and I really liked how this module presents a step-by-step breakdown. It includes clearly labeled overview diagrams of the different intervals and segments as well as expected values for a normal ECG. The “Approach to the ECG” section is very helpful with examples provided to help you master each step. Check out the ECG index section for examples of different ECG rhythms including some details about each arrhythmia, ECG criteria and associated clinical presentations.

Practical Clinical Skills

This is a very comprehensive website that is useful for anyone from beginners to more advanced medical learners. The ECG basics was a great introduction to the different parts of tracing and how each part relates to cardiac physiology. There’s a concise reference guide of arrhythmias for quick review. What I liked most about this resource was the opportunity to check your knowledge with the ECG Quiz. There’s also an excellent ECG Tutor section, which allows you to customize the quiz and practice the types of rhythms you are having most difficulty with. This website also features ECG content in Spanish!

Life in the FAST Lane

Life in the Fast Lane is a great all-around resource for students interested in emergency medicine. Even beyond ECGs, they have excellent clinical cases for practicing chest x-ray and ultrasound interpretation as well as other common clinical presentations (see the Top 100 tab). They also have a toxicology section that features illustrated flashcards. Check it out!

For ECGs, I found Life in the Fast Lane to be a very comprehensive resource. From a review of the basics to a comprehensive library of examples by an arrhythmia – this FOAMed resource has a lot to offer anyone looking to brush up on their ECG skills. I used this resource later in my studies when I already had some basic knowledge. I found the Top 100 ECG Clinical Cases section very useful. This section allows you to practice ECG interpretation, check your answers, and many are contextualized with a clinical scenario. The clinical outcome section of these ECG cases was great in helping to link an arrhythmia to clinical management. It was a great review of what you are going to do for the patient once you interpret their ECG. There were also often additional commentary and resources provided for more in-depth reading about the arrhythmia if desired. I found it very useful in my EM rotation.

Free ECG Simulator

This is a well-designed, sleek resource that I discovered only after my EM rotation. Some of my colleagues have found it very helpful and highly recommend it. The “learn” mode is great for review, and you can check your knowledge afterward with the game mode. Pro tip: you can change the settings from ‘dynamic’ to ‘static’ mode when you are still learning. The ‘dynamic’ mode can be a little stressful, but it makes for a great added challenge when you are more comfortable with ECG interpretation!

These are some of the resources I found useful when learning how to read ECGs. Everyone has their own learning style. Hopefully, one of these resources works well for you too. I am sure there are many other excellent resources out there. If you have enjoyed any other great FOAMed resources on ECG interpretation, please share them with us in the comments.

Cite this article as: David Wiercigrach, Canada, "FOAMed Resources for ECG Interpretation," in International Emergency Medicine Education Project, May 22, 2020,, date accessed: September 21, 2023

Cranial CT Anatomy: A simple image guide for medical students

cranial ct anatomy

Computed tomography (CT) is the most useful brain imaging tool in emergency medical practice. It is also the first imaging modality in patients presenting to the emergency department with headache, stroke and head trauma.

Many cranial lesions can easily be recognized in CT. One of the key points of diagnosing cranial lesions is knowing the anatomical structures. This gives us the advantage to evaluate CT by combining clinical findings with the image.

We created an image series for the most essential eight anatomical structures.

cranial CT slices

Centrum Semiovale

centrum semiovale

Lateral Ventricles

lateral ventricles

3rd Ventricle, Basal Ganglia, Superior Cerebellar Cistern

3rd Ventricle, Basal Ganglia, Superior Cerebellar Cistern​

3rd Ventricle, Basal Ganglia, Quadrigeminal Plate

3rd Ventricle, Basal Ganglia, Quadrigeminal Plate

Midbrain, Interpeduncular Cistern​

interventricular cistern

Suprasellar Cistern, 4th Ventricle

Suprasellar cistern, 4th ventricle

Sella Turcica

sella turcica

Pons, Medullary Junction

pons medullary junction

Further Reading

Bonus Infographic

Cite this article as: Murat Yazici, Turkey, "Cranial CT Anatomy: A simple image guide for medical students," in International Emergency Medicine Education Project, September 4, 2019,, date accessed: September 21, 2023

Venous blood gas analysis: Less arterial punctures!


Blood gas analysis is probably one of the most used tests for diagnosis and therapeutic guidance in the emergency departments (EDs) and intensive care units (ICUs).

The evaluation of arterial blood gas (ABG) analysis is commonly used to estimate acid-base status, oxygenation and concentration of carbon dioxide (CO2) in critically ill patients. However, arterial blood (AB) may be difficult to obtain due to weak pulses or movement of the patient. Furthermore, because the thick walls and their innervation, it is more painful for the patient.

Therefore, venous blood gas (VBG) analysis is an alternative to estimate pH and other values in a quicker and easier way.

Venous blood gas analysis

Venous blood (VB) can be obtained from different places. You should always consider the location and the sampling method to interpret the results.

Figure 1 - Types of samples and locations for extraction

VBG analysis is an alternative for ABG in situations of low peripheral perfusion such as shock states of any etiology.

VBG has been studied in critically ill patients as an alternative in patients who do not have a central venous catheter (CVC) (Tavakol, 2013; Byrne, 2014). If a tourniquet is used to facilitate venous puncture, it should be released approximately a minute before the extraction in order to avoid changes induced by ischemia. (Cengiz, 2009). However, VB is preferred from a CVC given its higher correlation with AB. The values obtained from a VBG and an ABG are interchangeable in clinical practice, in both central VB (Malinoski, 2005; Walkey, 2010; Mallat, 2015) and peripheral VB (Malatesha, 2007; Chu, 2003; Kelly, 2001), except for the values of oxygen saturation (SaO2) and partial pressure of oxygen (PaO2).

VB Central VB Peripheral


0.03 – 0.05 below arterial values
0.02 – 0.04 below arterial values


4 – 5 mmHg above arterial values
3 – 8 mmHg above arterial values


Minimal variation
1 – 2 mEq/L above arterial values

PaO2 / SaO2

No correlation
No correlation

Table 1 – Correlation between venous blood gases and arterial blood gases

Mixed VB (obtained from a pulmonary artery catheter) gives similar results to the values obtained from a CVC. (Ladakis, 2001; Tsaousi, 2010). One should be cautious when interpreting VBG, it has to be always correlated to the clinical state of the patient and if it is necessary, it should be confirmed with an ABG.

Central venous gas analysis

Central VBG analysis allows us to assess the metabolic state of a patient with a good correlation with ABG. Even though central VB is not adequate to assess oxygenation efficacy, this can be estimated by pulse oximetry. Likewise, central VBG analysis gives us central venous oxygen saturation (SatvO2), which is a very sensitive marker of the respiratory, hemodynamic and metabolic homeostatic variations. (Gattinoni, 2017).

Any change in the pulmonary, hemodynamic, metabolic or oxygen transport functions will affect SatvO2. In other words, when we assess SatvO2 value, we are analyzing the result of the interaction between all its determinants:

1) Oxygen input (respiratory system)
2) Oxygen transport (hemoglobin)
3) Oxygen availability DO2 (cardiac output)
4) Oxygen consumption VO2 (tissues).

Gasometric assessment of a central VB sample and its relation with the pulse oximetry will provide us with more information than an ABG analysis.

Global tissue perfusion

In recent year it has been shown that the difference between the value of CO2 obtained from mixed venous blood or central venous blood sample and the value of CO2 obtained from an arterial blood sample is correlated with an increased anaerobic cellular metabolism when the result shows values above 6mmHg. This increase in the veno-arterial CO2 difference is given by an increase of hydrogen in plasma coming from the intracellular environment because of anaerobic metabolism; these hydrogen molecules are buffered in plasma and metabolized to CO2. The causes of the increase in the veno-arterial CO2 difference are mainly due to hypoperfusion secondary to the inadequate cardiac output of mitochondrial dysfunction. (Ospina-Tascón, 2016). Likewise, the quotient of the veno-arterial CO2 difference and the arterio-venous O2 difference has been related with higher accuracy of the tissue perfusion status.


During the assessment of critically ill patients, the analysis of blood gases stands up as a fundamental step in the process of attention. A VBG analysis and SpO2 can give us enough information to make decisions even if there is no ABG analysis available, besides being easy to obtain a sample, implies less pain and less punctures in general. An indication of taking an AB sample is to assess tissue perfusion in severely ill patients.


Byrne AL, Bennett M, Chatterji R, Symons R, Pace NL, Thomas PS. Peripheral venous and arterial blood gas analysis in adults: are they comparable? A systematic review and meta analysis. Respirology. 2014 Feb;19(2):168-175. doi: 10.1111/resp.12225. Epub 2014 Jan 3. Review. PubMed PMID: 24383789.

Cengiz M, Ulker P, Meiselman HJ, Baskurt OK. Influence of tourniquet application on venous blood sampling for serum chemistry, hematological parameters, leukocyte activation and erythrocyte mechanical properties. Clin Chem Lab Med. 2009;47(6):769-76. doi: 10.1515/CCLM.2009.157. PubMed PMID: 19426141.

Gattinoni L, Pesenti A, Matthay M. Understanding blood gas analysis. Intensive Care Med. 2018 Jan;44(1):91-93. doi: 10.1007/s00134-017-4824-y. Epub 2017 May 11. PubMed PMID: 28497267.

Ladakis C, Myrianthefs P, Karabinis A, Karatzas G, Dosios T, Fildissis G, Gogas J, Baltopoulos G. Central venous and mixed venous oxygen saturation in critically ill patients. Respiration. 2001;68(3):279-85. PubMed PMID: 11416249.

Malatesha G, Singh NK, Bharija A, Rehani B, Goel A. Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial emergency department assessment.  Emerg Med J. 2007 Aug;24(8):569-71. PubMed PMID: 17652681; PubMed Central PMCID:  PMC2660085.

Malinoski DJ, Todd SR, Slone S, Mullins RJ, Schreiber MA. Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients. Arch Surg. 2005 Nov;140(11):1122-5. PubMed PMID: 16342377.

Mallat J, Lazkani A, Lemyze M, Pepy F, Meddour M, Gasan G, Temime J, Vangrunderbeeck N, Tronchon L, Thevenin D. Repeatability of blood gas parameters, PCO2 gap, and PCO2 gap to arterial-to-venous oxygen content difference in critically ill adult patients. Medicine (Baltimore). 2015 Jan;94(3):e415. doi: 10.1097/MD.0000000000000415. PubMed PMID: 25621691; PubMed Central PMCID: PMC4602629.

Ospina-Tascón GA, Hernández G, Cecconi M. Understanding the venous-arterial CO(2) to arterial-venous O(2) content difference ratio. Intensive Care Med. 2016  Nov;42(11):1801-1804. Epub 2016 Feb 12. Review. PubMed PMID: 26873834.

Tavakol K, Ghahramanpoori B, Fararouei M. Prediction of Arterial Blood pH and Partial Pressure of Carbon dioxide from Venous Blood Samples in Patients Receiving Mechanical Ventilation. J Med Signals Sens. 2013 Jul;3(3):180-4. PubMed PMID: 24672766; PubMed Central PMCID: PMC3959008.

Walkey AJ, Farber HW, O’Donnell C, Cabral H, Eagan JS, Philippides GJ. The accuracy of the central venous blood gas for acid-base monitoring. J Intensive Care Med. 2010 Mar-Apr;25(2):104-10. doi: 10.1177/0885066609356164. Epub 2009 Dec 16. PubMed PMID: 20018607.

Further Reading

Cite this article as: Job Guillen, Mexico, "Venous blood gas analysis: Less arterial punctures!," in International Emergency Medicine Education Project, July 5, 2019,, date accessed: September 21, 2023

Interview – Vicky Noble – US training in medical schools

We interviewed with world renowned emergency and critical care US expert “Vicky Noble” about US training in medical schools.

Read US Chapters and Posts

Siedel Test

A 42 years old male, presents to the ED 1 hour after he was hammering a nail onto a wooden shelf, where the nail flew and strike his left open eye. In an attempt to help, his friend immediately removed the nail. After that, he has been having severe sharp pain and blurry vision in his left eye. On examination, the left eye had poor visual acuity, and he could only perceive light and movement. The pupil was fixed, dilated and non-reactive to light. Right eye examination was normal.

819.2 - eye penetran trauma 2 -siedel sign
819.1 - eye penetran trauma 1

How would you approach to this patient?

To learn more about it, read chapters below.

Read "Eye Trauma" Chapter

Read "Red Eye" Chapter

Quick Read

Globe rupture

It is an ophthalmologic emergency, consisting of a full-thickness injury in the cornea or sclera caused by penetrating or blunt trauma. Anterior rupture is usually observed, as this is the region where the sclera is the thinnest. Posterior rupture is rare and difficult to diagnose. It can be diagnosed through indirect findings such as contraction in the anterior chamber and decrease in intraocular pressure (IOP) in the affected eye. If there is a risk of globe rupture, a slit lamp test with 10% fluorescein must be conducted. Normal tissue is dark orange under a blue cobalt filter; a lighter color is observed in the damaged zone due to a lower dye concentration. Ultrasonography (USG) can be useful in making a diagnosis, especially with posterior ruptures. Computed tomography (CT) sensitivity ranges 56–75%. In cases of anterior globe injuries, USG use, and if there is a risk of a foreign metal body, magnetic resonance imaging, are contraindicated. Prompt ophthalmology consultation is required. While in the emergency department, tetanus prophylaxis, analgesics, bed rest, head elevation, and systemic antibiotic therapy are required. The most commonly preferred antibiotics are cefazolin and vancomycin. Age over 60 years; injury sustained by assault, on the street/highway, during a fall, or by gunshot; and posterior injuries are indications of a poor prognosis.

Siedel test

Seidel test is used to detect ocular leaks from the globe following injury. If there is penetration to the eye, aqueous leakage happens. However, the fluid is clear and hard to identify. Therefore, non-invasive test “Siedel” is used for better visualization of this leakage. Fluorescein 10% is applied to the injured eye, and the leakage becomes more prominent.

To learn more about it, read chapters below.

Read "Eye Trauma" Chapter

Read "Red Eye" Chapter

Action Plan

Creating Your Action Plan chapter written by Chew Keng Sheng from Malaysia is just uploaded to the Website!

Diagnostic Testing

Diagnostic Testing In Emergency Medicine chapter written by Yusuf Ali Altunci from Turkey is just uploaded to the Website!

Selected Diagnostic Tests

Selected Diagnostic Laboratory Tests are just uploaded to the website.

Cerebrospinal fluid analysis

by Arwa Alburaiki and Rouda Salem Alnuaimi Introduction CSF is a colorless fluid that is present within the subarachnoid space, central canal of the spinal cord

Read More »

Urine Analysis

by Jan Zajc Indications Urinalysis should be performed to evaluate the following Evaluation of renal & lower urinary tract abnormalities Assessment of some metabolic/endocrine disorders

Read More »

Do you need more?

From experts to our students! – eFAST