<unk>  index (SI) has been defined as ; SI≥0.6 is a clinical<unk> . Such ratio value is clinically employed to determine the scope or emergence of<unk> . The SI correlates with the extent of<unk>  and thus may facilitate the early identification of severely injured patients threatened by complications due to blood loss and therefore need urgent treatment, i.e. blood transfusion. + Patients classified by<unk>  Index: traditional vital signs presented at the emergency department (ED) admission and at first scene. Group I (SI <0.6, no<unk>  Group II (SI ≥0.6 to <1.0, mild<unk>  Group III (SI ≥1.0 to <1.4, moderate<unk>  Group IV (SI ≥1.4, severe<unk>  SBP at scene (mmHg) Mean ± standard deviation 136.8 (32.8) 121.9 (29.4) 105.2 (33.1) 92.9 (34.4) Median (IQR) 138 (120 to 160) 120 (105 to 140) 100 (90 to 120) 90 (70 to 110) SBP at ED (mmHg) Mean ± standard deviation 148.4 (25.6) 124.1 (20.2) 96.9 (16.8) 70.6 (15.7) Median (IQR) 147 (130 to 160) 120 (110 to 138) 98 (86 to 108) 70 (60 to 80) HR at scene (beats/minute) Mean ± standard deviation 83.0 (19.2) 94.0 (20.6) 103.7 (26.6) 110.5 (31.3) Median (IQR) 80 (70 to 95) 94 (80 to 105) 105 (90 to 120) 115 (100 to 130) HR at ED (beats/minute) Mean ± standard deviation 73.7 (13.6) 91.3 (15.1) 109.1 (17.9) 122.7 (19.5) Median (IQR) 74 (65 to 80) 90 (80 to 100) 110 (100 to 120) 120 (110 to 135) SI at scene (beats/minute) Mean ± standard deviation 0.6 (0.2) 0.8 (0.3) 1.1 (0.4) 1.3 (0.5) Median (IQR) 0.6 (0.5 to 0.7) 0.8 (0.6 to 0.9) 1.0 (1.0 to 1.0) 1.2 (0.9 to 1.6) Data presented as n (%), mean ± standard deviation or median (interquartile range (IQR)). n = 21,853; P <0.001 for all parameters. ED Emergency department, GCS Glasgow coma scale, HR Heart rate, SBP Systolic blood pressure, SI =<unk>  index. Bleeding Recognizing the degree of blood loss via vital sign and mental status abnormalities is important. The American College of Surgeons Advanced Trauma Life Support (ATLS) hemorrhagic<unk>  classification links the amount of blood loss to expected physiologic responses in a healthy 70 kg patient. As total circulating blood volume accounts for approximately 7% of total body weight, this equals approximately five liters in the average 70 kg male patient. *Class 1: Volume loss up to 15% of total blood volume, approximately 750 mL. Heart rate is minimally elevated or normal. Typically, there is no change in blood pressure, pulse pressure, or respiratory rate. *Class 2: Volume loss from 15% to 30% of total blood volume, from 750 mL to 1500 mL. Heart rate and respiratory rate become elevated (100 BPM to 120 BPM, 20 RR to 24 RR). Pulse pressure begins to narrow, but systolic blood pressure may be unchanged to slightly decreased. *Class 3: Volume loss from 30% to 40% of total blood volume, from 1500 mL to 2000 mL. A significant drop in blood pressure and changes in mental status occur. Heart rate and respiratory rate are significantly elevated (more than 120 BPM). Urine output declines. Capillary refill is delayed. *Class 4: Volume loss over 40% of total blood volume. Hypotension with narrow pulse pressure (less than 25 mmHg). Tachycardia becomes more pronounced (more than 120 BPM), and mental status becomes increasingly altered. Urine output is minimal or absent. Capillary refill is delayed. Again, the above is outlined for a healthy 70 kg individual. Clinical factors must be taken into account when assessing patients. For example, elderly patients taking beta blockers can alter the patient's physiologic response to decreased blood volume by inhibiting mechanism to increase heart rate. As another, patients with baseline hypertension may be functionally hypotensive with a systolic blood pressure of 110 mmHg. Non-bleeding Various laboratory values can be abnormal in<unk> . Patients can have increased BUN and serum creatinine as a result of pre-renal kidney failure. Hypernatremia or hyponatremia can result, as can hyperkalemia or hypokalemia. Lactic acidosis can result from increased anaerobic metabolism. However, the effect of acid–base balance can be variable as patients with large GI losses can become alkalotic. In cases of hemorrhagic<unk> , hematocrit and hemoglobin can be severely decreased. However, with a reduction in plasma volume, hematocrit and hemoglobin can be increased due to hemoconcentration. Low urinary sodium is commonly found in<unk>  patients as the kidneys attempt to conserve sodium and water to expand the extracellular volume. However, sodium urine can be low in a euvolemic patient with heart failure, cirrhosis, or nephrotic syndrome. Fractional excretion of sodium under 1% is also suggestive of volume depletion. Elevated urine osmolality can also suggest<unk> . However, this number also can be elevated in the setting of impaired concentrating ability by the kidneys. Central venous pressure (CVP) is often used to assess volume status. However, its usefulness in determining volume responsiveness has recently come into question. Ventilator settings, chest wall compliance, and right-sided heart failure can compromise CVPs accuracy as a measure of volume status. Measurements of pulse pressure variation via various commercial devices has also been postulated as a measure of volume responsiveness. However, pulse pressure variation as a measure of fluid responsiveness is only valid in patients without spontaneous breaths or arrhythmias. The accuracy of pulse pressure variation also can be compromised in right heart failure, decreased lung or chest wall compliance, and high respiratory rates. Similar to examining pulse pressure variation, measuring respiratory variation in inferior vena cava diameter as a measure of volume responsiveness has only been validated in patients without spontaneous breaths or arrhythmias. Measuring the effect of passive leg raises on cardiac contractility by echo appears to be the most accurate measurement of volume responsiveness, although it is also subject to limitations. History and physical can often make the diagnosis of<unk> . For patients with hemorrhagic<unk> , a history of trauma or recent surgery is present. For<unk>  due to fluid losses, history and physical should attempt to identify possible GI, renal, skin, or third-spacing as a cause of extracellular fluid loss. Although relatively nonsensitive and nonspecific, physical exam can be helpful in determining the presence of<unk> . Physical findings suggestive of volume depletion include dry mucous membranes, decreased skin turgor, and low jugular venous distention. Tachycardia and hypotension can be seen along with decreased urinary output. Differential diagnosis While hemorrhage is the most common cause of<unk>  in the trauma patient, other causes of<unk>  are to remain on the differential. Obstructive<unk>  can occur in the setting of tension pneumothorax and cardiac tamponade. These etiologies should be uncovered in the primary survey. In the setting of head or neck trauma, an inadequate sympathetic response, or neurogenic<unk> , is a type of distributive<unk>  that is caused by a decrease in peripheral vascular resistance. This is suggested by an inappropriately low heart rate in the setting of hypotension. Cardiac contusion and infarctions can result in cardiogenic<unk> . Finally, other causes should be considered that are not related to trauma or blood loss. In the undifferentiated patient with<unk> , septic<unk>  and toxic causes are also on the differential.
Hypovolemic shock
Obstructive shock
Distributive shock
Neurogenic shock
Cryptic shock
Septic shock
Spinal shock
Vasodilatory shock