Tests
1st tests to order
lactate (arterial blood gas)
Test
High lactate is less sensitive and also less specific for shock than commonly appreciated. Lactate levels are determined by production rate (hypoxia, glycolysis) and clearance. High lactate indicates more severe hypoperfusion and shock. Cut-offs for hyperlactacidemia vary: >18 mg/dL (>2 mmol/L) is the most commonly used.[41] A low or normal venous lactate eliminates concern for an elevated arterial lactate.
Result
>18 mg/dL (>2 mmol/L) is suggestive of tissue hypoperfusion
blood gases
Test
Acidemia is a common finding, at least in severe shock. It may be metabolic, due to high lactate levels and acute kidney injury, and/or respiratory, due to hypercapnia.
Hypoxia indicates inadequate oxygen delivery, and supplemental oxygen is required especially if <60 mmHg (<8 kPa). It is helpful to compare with a previous result if available.
The base deficit indicates the degree of volume deficit and is particularly useful in acute hemorrhage.
Venous blood gas is increasingly being used as it is less invasive and less painful than arterial blood gas.[34]
Result
arterial: pH <7.35 indicates acidosis; PaO₂ normal or low (normal range is 80-100 mmHg/9.3 to 13.3 kPa); base deficit 2 to -2 mEq/L is baseline normal; venous: pH <7.31 indicates acidosis; base deficit of 6 to 8 mEq/L is baseline normal
CBC
Test
Hemoglobin commonly underestimates the blood volume lost and a trend is more significant than an absolute figure, unless very low.
Result
Hb <100 g/L is suggestive of hemorrhage as the cause; however, may be normal in the early stages due to vasoconstriction; WBC may be <4 or >12 x 10³/microliter if sepsis is present
BUN and creatinine
serum electrolytes
Test
Serum electrolytes should be measured at baseline and regularly until the patient improves.[32][43]
Result
serum electrolytes frequently deranged (e.g., hyperkalemia in trauma, acute kidney injury, and diabetic ketoacidosis; hypokalemia with diarrhea or vomiting; hypernatremia in burns and diarrhea or vomiting; hyponatremia in trauma and sometimes in diarrhea and vomiting)
coagulation studies (INR, activated PTT)
Test
Baseline test, especially before central line placement.
Result
may be prolonged (e.g., disseminated intravascular coagulation associated with septic shock)
blood glucose
Test
May show hypoglycemia or hyperglycemia.[35]
Result
may be low or high
anion gap
Test
Assessment of the anion gap for elevated glucose to assess for diabetic ketoacidosis. Also found with some forms of alcohol toxicities.[44]
Anion gap is calculated by subtracting the sum of serum chloride and bicarbonate from measured sodium concentration.[45][46]
Result
anion gap may be elevated (to >10-12 mEq/L)
CRP
Test
High CRP levels (>200 mg/L) indicate severe inflammation. The higher the level, the greater the degree of inflammation. Lower concentrations (<200 mg/L) may be found in septic states but also after myocardial infarction or surgery.
Result
high values suggest infection and inflammation; sepsis should be considered as a cause
ECG
Test
Very useful in helping to determine the etiology of shock, in particular cardiogenic causes.[1][3][15][31]
In pulmonary embolism the classic S1Q3T3 pattern of right heart strain may be seen, but its absence does not exclude pulmonary embolism as a cause; often only sinus tachycardia will be present.
In cardiac tamponade, low or varying QRS amplitudes may be seen.
Result
may reveal cause of shock: arrhythmia (ventricular or supraventricular tachycardia, heart block) or coronary ischemia (ST segment elevation, new bundle branch block, inverted T waves); may reveal evidence of underlying electrolyte abnormalities (e.g., hypokalemia or hyperkalemia)
Tests to consider
chest x-ray
Test
Often helpful in determining the cause of shock (e.g., pneumonia, aortic widening, globular heart in cardiac tamponade).[1][3]
A chest x-ray is usually not required if a tension pneumothorax is suspected; decompression is the first-line intervention.
Result
can identify hemothorax, widened mediastinum with aortic disruption; appearance of cardiac shadow may suggest tamponade but is not diagnostic; can identify pneumonia as cause of or associated with septic shock
focused assessment with sonography for trauma scan
Test
Can be performed rapidly at the bedside to look for free fluid (usually blood) around the heart (pericardial effusions) or in the abdomen (suggestive of intra-abdominal injury). The sensitivity is operator-dependent.
Result
identifies free fluid in the abdomen or pericardial effusion
echocardiography
Test
Useful to identify pericardial tamponade (where focused assessment with sonography for trauma scan is not available), myocardial depression (infarction, myocarditis), right ventricular failure (infarction, pulmonary embolism), critical acute valve disease (endocarditis, chordal rupture), and hypovolemia (small diameters of ventricles and vena cava).[1][15][47][48][49][50]
Result
cardiac output and stroke volume, pericardial effusion, low left ventricular ejection fraction, regional akinesia, dilatation and contractility of ventricles, valve dysfunction
procalcitonin
Test
Elevated procalcitonin (PCT) levels have been associated with sepsis and may help differentiate sepsis from causes of the systemic inflammatory response syndrome.[51][52] High PCT levels are associated with mortality from sepsis in 90-day follow-up. Other pro-inflammatory states, such as acute pancreatitis, trauma, major surgery, and burns, can also increase procalcitonin.[53] Changes in procalcitonin levels may occur later than that of lactate, although changes in both markers combined are highly predictive of outcome from 24 hours to 48 hours.[54] For adults with an initial diagnosis of sepsis or septic shock and adequate source control where optimal duration of therapy is unclear, a combination of procalcitonin and clinical evaluation is recommended to decide when to discontinue antimicrobials.[2] Do not perform PCT testing without an established, evidence-based protocol.[55]
Result
high values suggest sepsis
end tidal carbon-dioxide (capnography)
Test
Side stream or direct capnography (when endotracheal airway is in place) can be helpful in assessing pulmonary perfusion matched to ventilation. In the critical care setting, below expected (or decreasing) end tidal carbon dioxide measured by capnography is associated with impaired matching of pulmonary perfusion and ventilation. This may assist in determining presence of shock.[36]
Result
can assess impaired matching of pulmonary perfusion and ventilation
ultrasound of thorax
Test
Useful to identify fluid in the pleural spaces and consolidation, as well as possible aortic root aneurysms.
A dissection flap may also be seen but ultrasound has limited sensitivity for aortic dissection and retroperitoneal bleeding. If either of these are suspected, CT would be the investigation of choice.
Result
may detect pleural effusions or an aortic root aneurysm; can identify lung consolidation consistent with heart failure or pneumonia
ultrasound of abdomen
Test
Useful for identifying blood in the peritoneum and abdominal aortic aneurysms. Ultrasound can also detect the inferior vena cava (IVC) diameter, pulsation, and collapsibility, which can be used to estimate the overall intravascular volume; in hypovolemia the IVC diameter and pulsation are reduced and collapsibility is increased.
A dissection flap may also be seen but ultrasound has limited sensitivity for aortic dissection and retroperitoneal bleeding. If either of these are suspected, CT would be the investigation of choice.
Result
may detect abdominal aortic aneurysm and peritoneal blood
CT thorax, abdomen, and pelvis
Test
CT can very efficiently identify or exclude many potential shock etiologies, but is potentially unsafe in a hemodynamically unstable patient. Patients must be stabilized before transfer to the imaging suite. Very useful in trauma patients with multiple injuries.[56][57]
Result
may detect site of hemorrhage, foci of infection or infarction, pulmonary embolism, aortic dissection, or aneurysm
computed tomographic pulmonary angiography
Test
Computed tomographic pulmonary angiography (CPTA) may identify pulmonary embolism (PE), alongside other appropriate assessment tools. CTPA is the preferred investigation tool for definitive confirmation of PE, and is appropriate to use in most (but not all) patients.[58][59]
Result
PE is confirmed by direct visualization of the thrombus in a pulmonary artery; it appears as a partial or complete intraluminal filling defect
urinalysis and urine pregnancy test
Test
Useful to detect signs of infection in suspected sepsis. Rapid urine pregnancy test for women of childbearing age.
Result
positive beta human chorionic gonadotropin in ectopic pregnancy; signs of infection include blood, nitrites, and leukocytes; ketones may be present in diabetic ketoacidosis or vomiting and diarrhea
pelvic ultrasound
Test
Useful in evaluation of possible ectopic pregnancy if urine pregnancy test is positive.
Result
may show ectopic or empty uterus suggestive of ectopic pregnancy
x-ray long bones
Test
Fractures of the femur can cause shock due to blood loss, especially in the elderly.
Result
fractures of long bones
x-ray spine
Test
Useful if there is suspicion of spinal injury in cases of neurogenic shock.
Result
fracture of spine
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