Approach to the undifferentiated shock patient

The undifferentiated shock state is a colloquialism which describes a haemodynamically unstable patient who is peri-arrest and you don't know why.

The ED trainees have to deal with this problem in their fellowship exam much more frequently than the CICM candidates, judging by the rate of its appearance in the papers. Past incarnations of this topic have included the following SAQs:

  • Question 18 from the first paper of 2016 (58 y.o. with pneumonia, with high PEEP)
  • Question 17 from the second paper of 2013 (septic patient with pancreatitis)
  • Question 4 from the first paper of 2011 (febrile 75 y.o. with history of cardiac disease)
  • Question 1a and Question 1b from the second paper of 2002 (hypotensive post-op patient)

The questions each give a brief sentence of history, which is usually irrelevant when one looks at the way the college worded their answer. Clearly, they were looking for an answer to the question "how do you assess a patient in a non-specific shock state, and maintain their organ perfusion while looking for a cause?"

Probably the best single resource for a rapid revision of this topic would be the UpToDate article. If one is unwilling to pay them, ACEP have an excellent resource by Goldberg and Liu (2015).

Differential diagnosis of shock

This is explored in greater detail in the primary exam chapter on the definition and classification of shock, but the table of causes is sufficiently important to be repeated in these notes several times.

Differential Diagnosis of Shock

Artifactual or spurious

  • Inaccurately measured blood pressure
  • Noradrenaline line is not connected

Mechanical support failure

  • IABP augmentation failure
  • VA ECMO malfunction


  • Inadequate fluid intake
  • Loss of fluid
    • Vomiting
    • Diarrhoea
    • Ileostomy losses
    • Sweating
    • Polyuria
    • Burns
    • Pancreatitis
    • Ascites
    • Post-operative "third spacing"
  • Loss of blood
    • Traumatic or surgical
    • Gastrointestinal
    • Uterine (postpartum)
    • Retroperitoneal or abdominal
    • Fractures
    • Pulmonary / intrathoracic

Non-mechanical failure of the circulation

  • Extreme anaemia
  • Extreme hypoxia
  • Mitochondrial toxicity (eg. cyanide poisoning)
  • Inappropriately high metabolic demand (eg. malignant hyperthermia)


  • Ischaemia
  • Sudden "valve failure", eg. infective endocarditis
  • Septal or ventricular rupture
  • Myocarditis
  • Cardiac contusion (contusio cordis)
  • Drug overdose (of negative inotropes)
  • Rate problem: too fast or too slow
  • AF (loss of atrial kick)
  • Severe acidosis (myocardial depression)


  • Septic shock
  • Toxic shock syndrome
  • Anaphylaxis
  • Angioedema
  • Neurogenic (i.e. loss of sympathetic tone)
  • Adrenal insufficiency
  • Thyroid insufficiency (myxoedema)
  • Drug overdose (of vasodilators)
  • CO2 excess
  • Reperfusion "post arrest" syndrome


  • Intracardiac obstruction:
    • Pulmonary embolism
    • Valve obstruction (thrombosis, myxoma)
    • LVOT or RVOT obstruction
    • Amniotic fluid embolism
  • Extracardiac obstruction
    • Cardiac tamponade
    • Tension pneumothorax
    • Dynamic hyperinflation
    • Excessive positive pressure ventilation
    • Restrictive pericarditis
    • Chest compression (traumatic asphyxia)

Assessment of undifferentiated shock

This vaguely follows the algorithms offered by the UpToDate article. The investigation algorithm ends up with the pulmonary artery catheter as the final common pathway for shock investigation. The immediate management remedies problems as they are found. In italicised text are the immediate goals of assessment and resuscitation. The algorithm should be applicable to both totally undifferentiated ED patients whom you have never met and to the long-stay ICU patient with all their lines and tubes in.

The most important factor for the candidates to remember is the great value being placed on bedside ultrasonography, particularly on transthoracic echo. These techniques are now the standard for core ICU training, and the literature is strongly supportive  (eg. Corl et al, 2015 ). That literature? It's written by the examiners, and their friends. The key mark-scoring phrases to manipulate these people would include the following nuggets:

  • "goal-directed echocardiography"
  • "focussed point-of-care bedside ultrasound",
  • "rapid ultrasound for shock and hypotension (RUSH)"
  • "rapid assessment by cardiac echo (RACE)"
  • "abdominal and cardiac evaluation with sonography in shock (ACES)"

Immediate management: a primary survey

  • Assess airway patency
    • Exclude airway obstruction and asphyxia
  • Assess breathing:
    • Oxygenation (saturation probe)
    • Ventilation (end tidal CO2, chest auscultation)
    • Exclude tension pneumothorax and massive haemothorax
  • Assess circulation
    • Peripheral and central temperature/capillary refill
    • Vital signs (heart rate, blood pressure)
    • Equipment check
      • Exclude artifactual shock and equipment failure as the cause of shock, eg. IABP malfunction, ECMO circuit problems, vasopressor infusion drug error.
    • Head-to-toe exposure
      • Exclude externally obvious haemorrhage
      • Exclude anaphylaxis/angioedema
    • Point of care TTE: rapid assessment with cardiac echo
      • Exclude cardiac tamponade
      • Exclude massive PE
  • Establish venous access
  • Collect a series of generic laboratory investigations, most importantly an ABG
  • Assess neurology (i.e. spinal injury)
    • Exclude neurogenic ("spinal") shock

Ongoing empirical resuscitation

  • Ventilate the intubated patient with low-moderate PEEP (0.1cmH2O/kg)
  • Commence fluid bolus: 10ml/kg.
  • Commence/escalate vasopressor infusion: no evidence to decide which is best (Metaraminol? Peripheral noradrenaline?).

Secondary survey: history, examination, investigations

  • Rapid focused history
    • Immediate events preceding the collapse
    • Drug administration history
    • Recent interventions
    • Relevant background history
    • Collateral from recently attending staff/family
  • Repeat focused examination and investigations
    • ECG
    • CXR
    • ABG with special attention to lactate
    • Head to toe examination
      • Fluid status
      • Sources of sepsis
      • Toxidromes
      • Abdominal examination, looking for AAA, retroperitoneal haematoma and pancreatitis
    • Bedside abdominal and chest ultrasound, looking for collections
    • Formal (skilled) TTE, looking for valvular dysfunction, LVOT obstruction, regional wall motion abnormalities and septal defects
  • Laboratory investigations
    • Full blood count
    • Electrolytes and urea
    • Inflammatory markers
    • Cardiac injury biomarkers


Vincent, Jean-Louis, and Daniel De Backer. "Circulatory shock." New England Journal of Medicine 369.18 (2013): 1726-1734.

Goldberg S, Liu P, "Undifferentiated Shock" Critical Decisions in Emergency Medicine March 2015 • Volume 29 • Number 3

Corl, Keith, Sameer Shah, and Eric Gartman. "Ultrasound Evaluation of Shock and Volume Status in the Intensive Care Unit." Ultrasound in the Intensive Care Unit. Springer New York, 2015. 65-76.