One approach to circulation and blood flow in the critical care unit

Table 1 Types of shock and relationship with blood pressure and cardiac output

	Blood pressure	Cardiac output
Hypovolemic	?	↓
Cardiogenic	?	↓
Obstructive	?	↓
Distributive	↓ (Most of the time)	?

?: May be high, normal, or low.

Table 2 Hypovolemic shock categories

	I	II	III	IV
Blood loss (mL)	Up to 750	750-1500	1500-2000	> 2000
% of blood loss	Up to 15	15-30	30-40	> 40
Blood pressure	Normal	Normal	Decreased	Decreased
Mentation	Preserved	Anxious	Confused	Lethargic

Summary as described by the American College of Surgeons in The Advanced Trauma Life Support training program.

Table 3 Conditions that affect the venous oxygen saturation measurement

Condition	SvO2 change
Anemia (Hemoglobin < 8)	↓
Low cardiac output	↓
Agitation	↓
Sepsis	↑
States of hypoxia	↓
Anesthesia (↓ O2 utilization)	↑

Normal SvO₂: 60%-80%.

Table 4 Correlates of low cardiac output

	Low CO	High CO
Blood pressure	↓	↓
Heart rate	↑	↑
Systemic vascular resistance	↑	↓
CO	↓	↑
Pulse pressure	↓	↑

CO: Cardiac output.

Table 5 Crystalloid vs colloid solutions

Crystalloid	Colloid
Lower price	Expensive
Believed to be safer	Some toxic (hydroxyethyl starch)
Higher amount needed for resuscitation	Less required
Slower action	Faster action
Moves out the intravascular space faster	Remains in circulation longer