Shock Syndromes II

Plasma loss (nonhemorrhagic): Loss of extracellular fluid (e.g., burns, pancreatitis, third spacing,

peritonitis, vomiting, diarrhea)

women). Hemorrhagic shock occurs when intravascular volume loss impairs Do2, generally greater

than 30% of total blood volume loss.

Clinical features of hypovolemic shock include hypotension, tachycardia, diaphoresis, altered

mentation, and decreased urinary output. If hypovolemic shock is secondary to blood loss from trauma,

physiologic variables may be used to estimate the extent of blood loss (Table 2).

Class I

Class II

(mild)

Class III

(moderate)

Class IV

(severe)

Blood volume loss (%)

< 15%

15%–30%

30%–40%

> 40%

Heart rate

↔

↔/↑

↑

↑/↑↑

Blood pressure

↔

↔

↔/↓

↓

Pulse pressure

↔

↓

↓

↓

Respiratory rate

↔

↔

↔/↑

↑

Urine output

↔

↔

↓

↓↓

Glasgow Coma Scale score

↔

↔

↓

↓

Base deficit

0 to -2 mEq/L

-2 to -6 mEq/L

-6 to -10 mEq/L

-10 mEq/L or less

aClassification system is only intended as a guide to initial therapy because the physiologic response to hemorrhage represents a continuum. Confounding factors

that influence the physiologic response to hemorrhage include patient age, severity of injury, time from injury, prehospital interventions, and medications for chronic

conditions. Therefore, it is not intended to wait for a patient to fit each precise physiologic classification before initiating volume resuscitation.

Information from: 10th Edition of the Advanced Trauma Life Support® (ATLS®) Student Course Manual. American College of Surgeons, 2018.

Physiologic response

Compensatory responses occur by different mechanisms ultimately aiming to maintain systemic

perfusion.

Neural response is immediate, occurring within minutes.

Sympathetic response: Activation of the low-pressure receptors within the right and left atria

and high-pressure receptors within the aortic arch and carotid sinus lead to increased secretion

of epinephrine and norepinephrine, resulting in increased heart rate, myocardial contractility,

and arteriolar/venous tone. Blood flow is preserved to critical organs.

ii.

Parasympathetic response: Reduced vagal tone leads to increased heart rate. Often, tachycardia

is the earliest sign of circulatory shock from acute blood loss.

Intrinsic response compensates for acute blood loss within hours.

Reduced capillary pressure leads to fluid redistribution from the interstitial space to the

vascular compartment as albumin shifts into the plasma.

ii.

The transcapillary refill can recruit up to 1 L into the intravascular compartment.

secretion of antidiuretic hormone, aldosterone, and renin increases sodium and intravascular

volume retention to restore the interstitial deficit from the transcapillary refill.