Managing patients with shock

A beautiful review about circulatory shock in the NewEngland Journal of Medicine gives us practical advice for dealing with patients in shock. I summarise here three important learning points from that article. 

1. Diagnosing circulatory shock

Do not define shock only by the presence of arterial hypotension even though a blood pressure lower than 90mm Hg systolic and a mean blood pressure less than 70mm Hg are often present. This is because in those with chronic hypertension, the fall in blood pressure may not reflect the degree of shock. Also, the blood pressure alone may be misleading as it can be low in people who have chronic hypotension or have just suffered a transient episode of vasovagal syncope. The diagnosis of shock needs signs of poor perfusion to tissues and organs. The article tells us to consider the diagnosis of shock when there is tachycardia and signs of poor tissue perfusion as seen through three windows in the body:

                a. The skin: Cold and clammy

                b. The brain: Confusion, disorientation or other signs of altered mental status

                c. The kidney: A urine output of less than 0.5ml per kg per hour.

2. The VIP rule for resuscitation

This is the Ventilate, Infuse and Pump rule.  Ventilate (when needed) to ensure adequate oxygen intake. In this context we must remember that pulse oximetry is unreliable as a measure of adequate oxygen in the blood when there is peripheral vasoconstriction. So blood gases must be measured for this purpose. 

Fluids must always be infused in patients with shock since even those with cardiogenic shock can benefit from fluid resuscitation. However infusion of fluids must be carefully monitored. A fluid challenge refers to the infusion of 300 to 500ml of fluids (usually crystalloids) over a period of 20 to 30 minutes in order to see whether there is any improvement in one or more of the parameters of circulatory shock. The results of such a fluid challenge can then guide decisions for further infusion of fluids. 

Inotropic agents need to be used when the hypotension is severe or when the response to fluid resuscitation is slow or insufficient.

3. Using inotropic agents in circulatory shock

The authors consider norepinephrine to be the agent of first choice in those with shock whose cardiac output is not decreased. This will be seen in conditions like the early stages of septic shock (distributive shock). In the dose range of 0.5 to 2ug per kg per minute, norepinephrine elevates mean blood pressure without increasing the heart rate. Dobutamine is considered the agent of first choice in those with shock who need an increase in cardiac output. Both dobutamine and norepinephrine can be used together when needed. The authors do not recommend either dopamine or epinephrine as agents of first choice. Dopamine increases the risk of arrhythmias and increases mortality in the acute stage when given to patients with cardiogenic shock. Epinephrine increases the risk of arrhythmias and reduces splanchnic blood flow. These agents can be used as second line agents if necessary. Low dose vasopressin is an agent that can be added to norepinephrine for those with septic shock who have an adequate cardiac output.