Shock Syndromes I

Shock is a heterogeneous group of syndromes best defined as “acute circulatory failure.” This arises

when the tissues receive an insufficient supply of oxygen to be able to perform vital metabolic functions.

distributive and vasodilatory, and (4) cardiogenic. In some clinical scenarios, multiple shock syndromes

can occur simultaneously.

The diagnosis of shock typically includes the interpretation of three variables: hemodynamic assessment,

clinical presentation, and biochemical signs.

In many cases, shock is first identified by the presence of hypotension. However, the blood pressure

limits used to define shock are arbitrary and may not be patient-specific (e.g., a patient with hypertension

before critical illness).

In shock states, the value typically used to describe hypotension is a systolic blood pressure (SBP)

less than 90 mm Hg or a mean arterial pressure (MAP) less than 70 mm Hg.

These values may vary within a range to permit autoregulation, allowing acceptable perfusion in

the setting of acute hypotension.

Clinical presentation of shock may be subtle and can manifest in many different ways. Usually, shock

is identified through an assessment of mentation, skin, and kidney function.

Assessment of mentation should include a careful examination for signs of confusion and

obtundation. These signs should be compared with those in the patient’s preexisting status. This

may be challenging in a patient who is a poor historian or in those with a diminished baseline

status.

Evidence of an existing shock syndrome can manifest with decreased capillary refill and cold,

clammy skin.

Altered kidney function in the setting of shock primarily presents with reduced urinary output

(e.g., less than 0.5 mL/kg/hour). Laboratory values such as serum creatinine (SCr) often lag behind

the immediate observation of urine volume and quality.

Biochemical assessment of patients with shock typically reveals hyperlactatemia (greater than 2

mmol/L) or reduced venous oxygen saturation (Svo2) (less than 70%), indicating abnormal cellular

oxygen metabolism.

Hemodynamic parameters can be either directly measured from a monitoring device or calculated

according to direct measurements (see Table 1).

Value

Equation (as applicable)

Normal Value

Systolic blood pressure (SBP)

90–140 mm Hg

Diastolic blood pressure (DBP)

60–90 mm Hg

Mean arterial blood pressure (MAP)a

[SBP + (2 × DBP)]/3

70–100 mm Hg

Heart rate (HR)

60–80 beats/min

Cardiac output (CO)b

HR•SV

4–7 L/min

Cardiac index (CI)

CO/BSA

2.5–4.2 L/min/m2

Stroke volume (SV)

CO/HR

60–130 mL/beat

Pulmonary artery systolic pressure (PASP)

20–30 mm Hg