Use The Ventilation-Perfusion to Manage Shock

Shock is often defined clinically by a low blood pressure. However, it is not the measure of the blood pressure that is the problem; it is what that low measurement does to tissue perfusion. Therefore, shock is decreased tissue perfusion. More precisely, shock is decreased tissue oxygenation. The goal of treatment should be to balance oxygen delivery with oxygen consumption to maintain tissue oxygenation.

It may be difficult to remember all of the components of oxygen delivery and consumption when a patient is in distress. The concept of the Ventilation-Perfusion train might be helpful. The Ventilation-Perfusion train uses the analogy of a train carrying passengers from one station to another. The station on the left side (station “A”) is where the passengers board. If they cannot get there they cannot board. The same concept is true of oxygen in the body. If oxygen can’t get in the lungs, then it can’t be transported to the tissues.

Next, people go from station “A” to the car on the train. If this train pulls up with just one small car, then very few people can be transported. The concept holds true for hemoglobin in the blood. If the hemoglobin level is low, then very little oxygen will be transported. Next, there must be a locomotive to pull the cars. This is like the cardiac output in the body. Lastly, if the train brought 100 people to station “B” and the need was for 200, it still didn’t meet the need. In the body, delivered oxygen must meet oxygen consumption or tissue ischemia results.

In order to manage shock, all of these variables will need to be optimized. The lungs can be optimized by providing good pulmonary hygiene before the patient decompensates. During the acute crisis, appropriate oxygen therapy should be initiated to “start” the ventilation-perfusion train.

Hemoglobin levels need to be monitored and maintained. Pay attention to how much of the patient’s blood is lost to venopuncture. Critically-ill patients can lose as much as 850cc of blood to venopuncture during their ICU stay.

Decreased cardiac output can adversely affect oxygen delivery. Many patients have previous cardiac disease that can limit cardiovascular response to shock. Hemodynamics may have to be optimized to maintain an acceptable cardiac output.

Oxygen consumption must be decreased as much as possible in order to achieve a balance. Two factors that nurses can manage at the bedside are: 1) the patient’s activity level, and 2) fever. Activity can be decreased with reassurance, pain control, or sedation. Antipyretics and cooling blankets can be used to restore normal body temperature and decrease oxygen consumption.

Treatments that increased blood pressure (vasopressors), and oxygen saturation (high-flow oxygen) can cause adverse effects that actually contribute to further decompensation. By manipulating all of the variables of oxygen delivery and balancing them with oxygen consumption the patient will experience fewer adverse effects of treatment and maintain tissue oxygenation.