Big Shock…..Do we ❤ POCUS?

‘Red Standby 4 mins’ tannoys the nurse in charge.

‘It’s a 70yr old male BP 68/49, pulse 120, GCS 14/15, O2 sats 98% on 15L NRB, temperature 37.5°C’ you are reliably informed by a colleague.

What goes through your mind in the minutes before similar patients arrive in your department? It almost makes me as nervous as watching England taking penalties in Euro 2020 😥! The potential differential diagnoses are multiple but it’s down to you to find the cause quickly and more importantly to try to fix things before the patient deteriorates further.

I think we’d all agree that one of the most challenging presentations in emergency medicine is the undifferentiated shocked patient. It’s commonly seen and is associated with high mortality and poor outcomes for patients. In a paper by Jones et al with over 4700 patients they showed that hypotension had a threefold higher risk of in hospital death and a tenfold higher risk of sudden unexplained death than those without hypotension. Also the lower the blood pressure and the longer a patient stays in shock the higher the mortality.1

Shock is not a diagnosis in itself but a clinical state that if not corrected rapidly can spiral into death and so speed is of the essence as patients arrive critically unwell, often with limited information about their condition. It is defined as the ‘life-threatening failure of adequate oxygen delivery to the tissues and may be due to decreased blood perfusion of tissues, inadequate blood oxygen saturation, or increased oxygen demand from the tissues that results in decreased end-organ oxygenation and dysfunction.’ One of the main features of shock is hypotension. The 2016 Consensus definitions for Sepsis and Septic Shock defined hypotension as a systolic blood pressure below 90 mmHg or a mean arterial pressure less than 65 mmHg. 2

Shock is classified into different types based on the pathophysiology

• Cardiogenic- when cardiac function impaired secondary to acute myocardial infarction, arrhythmia, myocarditis, endocarditis or acute on chronic heart failure

• Obstructive- where the heart is prevented from pumping effectively by compression or a physical blockage such as in a tension pneumothorax, cardiac tamponade or pulmonary embolism.

• Distributive- systemic vasodilation leads to decreased blood flow to the vital organs. This is seen in anaphylaxis, sepsis or the rarely seen neurogenic shock where spinal cord damage leads to loss of sympathetic vasomotor tone.

• Hypovolemic-This is commonly seen with acute blood loss after trauma but also fluid loss from diarrhoea and vomiting or diabetic ketoacidosis. (Standl et al 2018) 3

These causes are not exclusive and with increasing comorbidities it is possible to see mixed causes of shock. This is where point of care ultrasound (POCUS) can help us with our decision making in shocked patients to try to improve the speed of diagnosis and management. But what does the evidence say? Is it really that helpful? There are many shock protocol algorithms so which is best? What are the patient orientated outcomes?

We’ll try to answer those questions in the following sections.

Evolution of shock Protocols

Ultrasound in medicine has been used for over five decades. It has the benefits of being safe as no radiation is emitted and now that modern ultrasound machines are becoming smaller and more portable can be used in the Emergency Department at the bedside with patients who are critically unwell or injured and undergoing active resuscitation. 4 Studies of POCUS have shown that diagnoses and management of patients have been changed in between 30-80% of cases where it has been used but most of these studies looked at one target organ only. 4

As patients are complex and often have multiple comorbidities it makes sense to consider the patient as a whole and assess multiple body areas with ultrasound. Standardized clinical algorithms have been developed for patients presenting in shock to assess the main organs and critical body zones where pathology could cause shock. In 2001 Rose et al were the first to publish an ultrasound algorithm for shocked patients that they called the Undifferentiated Hypotensive Patient (UHP) protocol. The protocol looked at the three areas they believed would give a rapid diagnosis of reversible causes of shock. The three areas they described were the subxiphoid view of the heart for cardiac evaluation, midline abdomen (sliding inferiorly) views for abdominal aorta assessment and scanning Morison’s pouch in the right upper quadrant looking for free fluid. 5 UHP was built upon in 2009 with the Rapid Ultrasound in Shock (RUSH) 6 and Abdominal and Cardiac Evaluation with Sonography (ACES) examinations 7.

The RUSH exam determined to diagnose more causes of shock and divided causes of shock into those affecting the ‘pump’, the ‘tank’ and the ‘pipes’. A helpful mnemonic is HI MAP (and also because we want a higher MAP!) and recalls the order of structures scanned: heart, inferior vena cava, Morison’s pouch, aorta and pneumothorax scanning. This is a video by Scott Weingart one of the early developers of the RUSH exam.

Part of the RUSH exam is the measurement of the IVC and is a controversial topic. Good evidence for where to actually measure the IVC, whether to measure in M-mode or B-mode, what ‘normal’ measurements are and how the IVC diameter changes in ventilated versus spontaneously breathing patients is currently lacking. 8 Bowel gas and unfavourable body habitus can make measurements difficult and measurements can vary between scanners particularly between the beginner and expert scanners.9 The utility of IVC diameter measurements may be best at the extremes i.e very full or completely collapsed but further research into the unknowns should be conducted before we can use IVC measurement with confidence. 8 A recent metanalysis of the evidence for IVC measurement concluded that ultrasound ‘does not seem to be a reliable method to predict fluid responsiveness’ with pooled sensitivities and specificities of 71% (95% CI: 0.62-0.80) and 75% (95% CI: 0.64-0.85%). 10

The ‘tank’ is also assessed by looking at the lungs for a pneumothorax as demonstrated by absence of lung sliding and the ‘barcode sign’ in M-mode. The lungs can be assessed for B-lines which would indicate the possibility of pulmonary oedema and cardiogenic shock and evidence of free fluid at the lung bases which could represent a haemothorax or pleural effusion depending on the clinical context. A Focused Assessment with Sonography in Trauma (FAST) scan would then assess for free fluid in the right and left upper quadrants and pelvis. Recent metanalyses showed sensitivities of 0.74 and 0.68 for intrabdominal free fluid detection in FAST scanning which demonstrates significant limitations for abdominal trauma. 11,12 The final part of the RUSH exam is an ultrasound scan of the ‘pipes’ namely assessing the large blood vessels of the body for rupture or a thrombus such as a abdominal aortic aneurysm, dissection or deep vein thrombus.

A potential addition to the conventional RUSH exam is assessing for a potential ectopic pregnancy too. An ectopic pregnancy could potentially be discovered by visualising free fluid in the abdomen in the clinical context of a woman of child bearing age and confirmed with a positive serum β-HCG. Also visualising an intrauterine pregnancy is a good rule out test for an ectopic pregnancy which has a sensitivity of 99.3%.

ACES is another multisite scan of a patient in shock. Six areas are scanned. Firstly the heart is visualised from a subxiphoid view to assess the size of the ventricles, overall contractility and to look for a cardiac tamponade. Next the IVC is assessed for collapsibility then the abdominal aorta looking for an AAA. Finally right and left upper quadrants and pelvis are visualised to look for free fluid. 7

In 2017 the Sonography in Hypotension and Cardiac arrest (SHoC) consensus guidelines were developed to further improve POCUS shock scanning 13. The guidelines use a hierarchical approach of Core, Supplementary and Additional views to scan based on the most common POCUS findings in shock. 14 The Core views should be completed in all shocked patients and include

  1. Cardiac- Supxiphoid and Parastenal long axis views looking for pericardial fluid, right heart strain, ventricular sizes and global contractility.
  2. Lung- Looking for multiple (three or more per intercostal space) B-lines, consolidation, pleural fluid and pneumothorax.
  3. Inferior vena cava– changes in diameter with respiration.

Supplementary views include parasternal and apical cardiac and additional views (where clinically indicated) include assessing for free fluid in the abdomen, aortic views and looking for a DVT.

This core approach has been validated in finding the causes of shock in a further study of 138 patients. 15

POCUS in Paediatric Shock

POCUS has been used less in children than adults but a protocol has been developed based on ACES and RUSH. It starts with Lung then cardiac, IVC and then abdominal views. Further details are found here. 16

One interesting difference to be aware of is cranial POCUS via open fontanelle as this is a potential source of haemorrhage particularly in trauma and children with coagulopathies. Recent international consensus guidelines have advocated the use of POCUS in critically ill neonates and children 17 and recommend POCUS in intracranial haemorrhage, cardiac views, IVC compressibility and lung views for pneumothorax and pneumonia.

Criticisms

Over the years numerous multiorgan POCUS protocols have been described which on review are essentially very similar looking at the heart, lungs, IVC, FAST scan areas and the aorta. 18 A criticism of the POCUS worldwide community is that they have been more focused on developing new protocols rather than asking clinically relevant questions such as does using POCUS in shocked patients improve important patient outcomes? 19 Another criticism is the ‘one size fits all’ approach of the POCUS shock protocol whereby all patients are recommended to get all the ultrasound views regardless of their presentation and low diagnostic yield of certain scans.

Outcomes for clinicians and patients

Two studies have demonstrated that a POCUS protocol in undifferentiated hypotensive patients can aid diagnoses, reduce diagnostic uncertainty and help with the management of patients. 21,22 Both studies were single centre, prospective observational trials with 108 and 118 patients from Italy and America respectively. Despite the limitations the conclusions appear valid and show the diagnostic benefits of using POCUS. An additional benefit of faster diagnoses should be reduced Emergency Department length of stay and avoidance of overcrowding.

The best evidence supporting the use of the RUSH exam comes from two meta-analyses and systematic reviews by Keikha et al 22 and Stickles et al 19. Keikha et al found the sensitivity of RUSH was 0.87 CI (0.80-0.92) and specifities 0.98 (0.96-0.99). Hypovolemic shock had a higher sensitivity of 1.0 (CI 0.91-1.0) and specificity of 0.94 (0.87-0.98). Keikha et al found sensitivities of 0.81 (CI 0.73-0.88) for hypovolemic shock, 0.83 ( CI 0.71-0.92) for cardiogenic shock and 0.93 (CI 0.68-1.0) for obstructive shock. Both papers found that the RUSH exam was useful for diagnosing between the main causes of shock but was better as a rule in test as the specificities were superior to the sensitivities.

So, if we can make better diagnoses then you would hope and expect that patient outcomes would be better too. Unfortunately, studies looking at patient outcomes are lacking and the two that have been published are on the same cohort of patients. In 2018 Atkinson et al looked at whether POCUS in shock improves mortality of patients. It was a well-designed international, randomised control trial in six centres of 273 patients that compared POCUS and usual care with usual care only in patients with hypotension (systolic blood pressure >100 mmHg or shock index >1.) The primary outcome was 30-day mortality or hospital discharge and the POCUS protocol was a combination of the ACES and RUSH exams.

The trial showed no benefits in ‘survival (76.5% survival in the POCUS group vs 76.1% in the non-POCUS group), length of stay, rates of CT scanning, inotrope use, or fluid administration’. The study concluded that POCUS may not provide survival benefit in hypotensive patients. There were significant limitations with the study however. The study was underpowered and had a sample size intended to detect a 10% reduction in mortality which would be hard to achieve. (Crager, Hofman 2018) The study had to be ended early because of difficulty recruiting patients, excluded potentially helpful views such as gallbladder and lung consolidation and had low rates of diagnoses where POCUS would be helpful such as tamponade or AAA (Brunet, M. and Chaplin, T., 2019) In the study 52% of patients were diagnosed with septic shock but the POCUS protocol wasn’t designed to look for common causes of sepsis such as cholecystitis or lung consolidation which we know POCUS is good for 24, 25. Looking for causes of sepsis in shocked patients would be a useful addition to protocols and should be the source of future research.

Atkinson et al produced a further paper using the same cohort of patients and method but published data on secondary outcomes of shock index, early warning scores, lactate, bicarbonate and mean fluid bolus volume which again showed no significant differences between the POCUS and control groups. 26

So while the best available evidence shows no benefits in clinically important patient outcomes we need to ask ourselves why this is and should we abandon using POCUS in shock? If it isn’t useful is it potentially harmful? We know POCUS can delay chest compressions in cardiac arrest and potentially cause harm 27 so is it possible that doing POCUS in a shocked patient that has a high chance of having sepsis as a cause may delay giving prompt antibiotics that we think improves survival 28 at the expense of looking for a cardiac tamponade or AAA that the pre-test probability of them having is already low. Further studies need to be carried out to answer these vital questions but until we get a definitive answer I think the evidence does support using POCUS in shocked patients.

My personal approach in clinical situations is to gather as much information as I can using the ambulance pre-alert (as the prehospital observations alone may make you think of sepsis), history taking and bedside tests such as venous blood gases and electrocardiograms alongside POCUS to inform my clinical decision making. We’re big fans of Bayes therorum at St. Emlyns and so whichever conditions have the highest pre-test probability that’s what I’ll be looking for. I believe a focused ultrasound examination would be the best way to investigate a shocked patient based on your pre-test probability of history, observations and bedside findings as this is true to how we practice emergency medicine in real life situations as per the figure I have designed below.

Figure 13. Targeted Shock protocol

Conclusion

Although the evidence for POCUS in shocked patients doesn’t show a survival benefit it does support the view that it is a useful adjunct for clinicians in diagnosing and treating patients. A focused scan based on the pre-test probability of the cause of shock may be a better way of using POCUS rather than the one size fits all approach and would be a good topic for future research. As sepsis is a common cause of shock, clinicians should consider looking for sources of sepsis in their protocols.

Thanks for reading and I’d love to hear any comments.

Happy scanning

P

References

  1. Jones, A.E., Yiannibas, V., Johnson, C. and Kline, J.A., 2006. Emergency department hypotension predicts sudden unexpected in-hospital mortality: a prospective cohort study. Chest, 130(4), pp.941-946.
  2. Synger, M., Deutschman, C.S., Seymour, C.W., Shankar-Hari, M., Annane, D. and Bauer, M., 2016. The Third International Consensus Definitions for Sepsis and Septic Shock. JAMA, 315(8), pp.801-810.
  3. Standl, T., Annecke, T., Cascorbi, I., Heller, A.R., Sabashnikov, A. and Teske, W.,The nomenclature, definition and distinction of types of shock. Deutsches Ärzteblatt International, 115(45), p.757.
  4. Cid, X., Canty, D., Royse, A., Maier, A.B., Johnson, D., El-Ansary, D., Clarke-Errey, S., Fazio, T. and inpatients with cardiopulmonary diagnosis at admission: study protocol of a randomized controlled trial—the IMFCU-1 (Internal Medicine Focused Clinical Ultrasound) study. Trials, 21(1), pp.1-15.
  5. Rose, J.S., Bair, A.E., Mandavia, D. and Kinser, D.J., 2001. The UHP ultrasound protocol: a novel ultrasound approach to the empiric evaluation of the undifferentiated hypotensive patient. The American journal of emergency medicine19(4), pp.299-302.
  6. Perera, P., Mailhot, T., Riley, D. and Mandavia, D., 2010. The RUSH Exam: Rapid Ultrasound in Shock in the Evaluation of the Critically lll. Emerg Med Clin North Am, 28, pp.29-56.
  7. Atkinson, P.R.T., McAuley, D.J., Kendall, R.J., Abeyakoon, O., Reid, C.G., Connolly, J. and Lewis, D., 2009. Abdominal and Cardiac Evaluation with Sonography in Shock (ACES): an approach by emergency physicians for the use of ultrasound in patients with undifferentiated hypotension. Emergency Medicine Journal, 26(2), pp.87-91.
  8. Nickson, C., 2020 The Dark Art of IVC Ultrasound. https://litfl.com/the-dark-art-of-ivcultrasound/ accessed 12/7/21
  9. Pourmand, A., Pyle, M., Yamane, D., Sumon, K. and Frasure, S.E., 2019. The utility of point-of-care ultrasound in the assessment of volume status in acute and critically ill patients. World journal of emergency medicine, 10(4), p.232.
  10. Orso, D., Paoli, I., Piani, T., Cilenti, F.L., Cristiani, L. and Guglielmo, N., 2020. Accuracy of ultrasonographic measurements of inferior vena cava to determine fluid responsiveness: a systematic review and meta-analysis. Journal of intensive care medicine, 35(4), pp.354-363.
  11. Netherton, S., Milenkovic, V., Taylor, M. and Davis, P.J., 2019. Diagnostic accuracy of eFAST in the trauma patient: a systematic review and meta-analysis. Canadian Journal of Emergency Medicine, 21(6), pp.727-738.
  12. Stengel, D., Leisterer, J., Ferrada, P., Ekkernkamp, A., Mutze, S. and Hoenning, A., Point‐of‐care ultrasonography for diagnosing thoracoabdominal injuries in patients with blunt trauma. Cochrane Database of Systematic Reviews, (12).
  13. Atkinson, P., Bowra, J., Milne, J., Lewis, D., Lambert, M., Jarman, B., Noble, V.E., Lamprecht, H., Harris, T., Connolly, J. and Kessler, R., 2017. International Federationfor Emergency Medicine Consensus Statement: sonography in hypotension and cardiac arrest (SHoC): an international consensus on the use of point of care ultrasound for undifferentiated hypotension and during cardiac arrest. Canadian Journal of Emergency Medicine, 19(6), pp.459-470
  14. Milne, J., Atkinson, P., Lewis, D., Fraser, J., Diegelmann, L., Olszynski, P., Stander, M. and Lamprecht, H., 2016. Sonography in Hypotension and Cardiac Arrest (SHoC): Rates of abnormal findings in undifferentiated hypotension and during cardiac arrest as a basis for consensus on a hierarchical point of care ultrasound protocol. Cureus, 8(4).
  15. Lussier, D., Pham, C., Milne, J., Lewis, D., Diegelmann, L., Lamprecht, H., Henneberry, R., Fraser, J., Stander, M., van Hoving, D.J. and Fredericks, D., 2017. LO44: Initial validation of the core components in the SHoC-Hypotension Protocol. What rates of ultrasound findings are reported in emergency department patients with undifferentiated hypotension? Results from the first Sonography in Hypotension and Cardiac Arrest in the Emergency Department (SHOC-ED1) Study; an international randomized controlled trial. Canadian Journal of Emergency Medicine, 19(S1), pp.S42-S43
  16. Hardwick, J.A. and Griksaitis, M.J., 2020. Fifteen-minute consultation: Point of care ultrasound in the management of paediatric shock. Archives of Disease in ChildhoodEducation and Practice.
  17. Singh, Y., Tissot, C., Fraga, M.V., Yousef, N., Cortes, R.G., Lopez, J., Sanchez-deToledo, J., Brierley, J., Colunga, J.M., Raffaj, D. and Da Cruz, E., 2020. International evidence-based guidelines on Point of Care Ultrasound (POCUS) for critically ill neonates and children issued by the POCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC). Critical Care, 24(1), pp.1-16.
  18. Seif, D., Perera, P., Mailhot, T., Riley, D. and Mandavia, D., 2012. Bedside ultrasound in resuscitation and the rapid ultrasound in shock protocol. Critical Care Research and Practice2012.
  19. Stickles, S.P., Carpenter, C.R., Gekle, R., Kraus, C.K., Scoville, C., Theodoro, D., Tran, V.H., Ubiñas, G. and Raio, C., 2019. The diagnostic accuracy of a point-of-care ultrasound protocol for shock etiology: a systematic review and meta-analysis. Canadian Journal of Emergency Medicine21(3), pp.406-417.
  20. Volpicelli, G., Lamorte, A., Tullio, M., Cardinale, L., Giraudo, M., Stefanone, V., Boero, E., Nazerian, P., Pozzi, R. and Frascisco, M.F., 2013. Point-of-care multiorgan ultrasonography for the evaluation of undifferentiated hypotension in the emergency department. Intensive care medicine, 39(7), pp.1290-1298.
  21. Shokoohi, H., Boniface, K.S., Pourmand, A., Liu, Y.T., Davison, D.L., Hawkins, K.D., Buhumaid, R.E., Salimian, M. and Yadav, K., 2015. Bedside ultrasound reduces diagnostic uncertainty and guides resuscitation in patients with undifferentiated hypotension. Critical care medicine, 43(12), pp.2562-2569.
  22. Keikha, M., Salehi-Marzijarani, M., Nejat, R.S., Vahedi, H.S.M. and Mirrezaie, S.M., 2018. Diagnostic Accuracy of Rapid Ultrasound in Shock (RUSH) Exam; A systematic review and meta-analysis. Bulletin of emergency & trauma6(4), p.271.
  23. Atkinson, P.R., Milne, J., Diegelmann, L., Lamprecht, H., Stander, M., Lussier, D.,Pham, C., Henneberry, R., Fraser, J.M., Howlett, M.K. and Mekwan, J., 2018. Doespoint-of-care ultrasonography improve clinical outcomes in emergency department patients with undifferentiated hypotension? An international randomized controlledtrial from the SHoC-ED investigators. Annals of emergency medicine, 72(4), pp.478-489.
  24. Alzahrani, S.A., Al-Salamah, M.A., Al-Madani, W.H. and Elbarbary, M.A., 2017. Systematic review and meta-analysis for the use of ultrasound versus radiology in diagnosing of pneumonia. Critical ultrasound journal, 9(1), pp.1-11.
  25. Hilsden, R., Leeper, R., Koichopolos, J., Vandelinde, J.D., Parry, N., Thompson, D. and Myslik, F., 2018. Point-of-care biliary ultrasound in the emergency department (BUSED): implications for surgical referral and emergency department wait times. Trauma surgery & acute care open, 3(1), p.e000164.
  26. Atkinson, P.R., Beckett, N., French, J., Banerjee, A., Fraser, J. and Lewis, D., 2019. Does point-of-care ultrasound use impact resuscitation length, rates of intervention, and clinical outcomes during cardiac arrest? A study from the sonography in hypotension and cardiac arrest in the emergency department (SHoC-ED) investigators. Cureus, 11(4).
  27. In’t Veld, M.A.H., Allison, M.G., Bostick, D.S., Fisher, K.R., Goloubeva, O.G., Witting, M.D. and Winters, M.E., 2017. Ultrasound use during cardiopulmonary resuscitation is associated with delays in chest compressions. Resuscitation, 119, pp.95-98.
  28. https://litfl.com/antibiotic-timing/

See also



Cite this article as: Pete Hulme, "Big Shock…..Do we ❤ POCUS?," in St.Emlyn's, July 22, 2021, https://www.stemlynsblog.org/big-shock-do-we-%e2%9d%a4-pocus/.

Posted by Pete Hulme

Dr Peter Hulme MB ChB, FRCEM, DTM&H, PGCert is a consultant in adult and paediatric emergency medicine in Central Manchester. His interests include tropical medicine, trauma, quality improvement, audit, POCUS, medical education and he is the developer of @majorincidentap. @Dr_Pete_EmMed

  1. I am a frequent user of POCUS mainly within the confines of a major referral service with the full suite of ICU, specialist, surgical, interventional and radiological services. I suspect that with that amount of high level support, it would be hard to show that a simple test I can perform at the bedside is the game changer when help is so readily at hand. However, what I do find is it can accelerate, treatment, disposition and referral decisions. This is still an important component to ED functioning when we are all so chronically overcrowded. As most big POCUS studies are done in busy centres, I do wonder if the mortality advantage would be seen in more remote areas where there are less bells and whistles and particularly where I live, a major centre may be several hours away.

    Reply

    1. Thanks for your comments Derek. I think it would be hard for any studies to show a mortality benefit as I very much doubt that a POCUS v no POCUS study would get ethical approval as it’s pretty much the standard of care for most EDs. I certainly agree that it helps speed up diagnosis and can help reduce ED length of stays.

      Reply

Thanks so much for following. Viva la #FOAMed