A new patient arrives by private vehicle to the ER. The nurse runs over from triage and says to you: “Doctor, this patient doesn’t look so good.”
You bring him back to the trauma bay and check his vital signs: his blood pressure is 60/— and his heart rate is 140.
1. Is this patient in shock?
2. What is the first thing you would do to treat his hypotension?
Given the information in the case, we can’t actually tell. Remember, “shock” is not just “looking bad” and is not just a low blood pressure. And shock is not just decreased peripheral perfusion. And shock is not just reduced systemic oxygen delivery. Ultimately, shock is decreased end-organ tissue respiration. Stated differently, “shock” is suboptimal oxygen consumption and carbon dioxide excretion at the cellular level.
The most practical method of diagnosing shock is to look at end-organ function. The organs most sensitive to hypoperfusion are the brain and the kidneys. A confused or anxious patient should be a source of concern, just as oliguria should trigger you to investigate further. Perfusion of the skin and extremities can also be sensitive indicators of shock, as the body preferentially shunts blood to the core when cardiac output is compromised. This is why surgeons will often feel the big toe as a quick and dirty measure of cardiac output. Other organ systems can of course also be hypoperfused, but evidence of, for example, cardiac or hepatic dysfunction is usually a late sign.
Another method of diagnosing shock is to look for systemic signs of decreased end-organ tissue respiration. This is most easily done by measuring the pH of the blood. While arterial blood gases are traditionally used, venous blood gases can also be of huge practical clinical value when a patient is really sick. Venous gases reflect arterial acid/base status with useful precision. Just add 0.05 to the venous pH and you will get the arterial pH. Subtract 5 from the arterial Pco2 and you get arterial Pco2. So you don’t need to repeatedly stick the artery (see Table 7-1).
A little bit like sorting your socks, some surgeons are more comfortable “classifying” shock—all the while acknowledging that it is the cardiovascular response to a stressor (blood loss/myocardial ischemia) that dictates the danger. Class I (fully compensated) shock is how a young healthy patient presents following a 2-U (750 mL) bleed. This young person can vasoconstrict, diverting blood flow away from his extremities in a manner that preserves completely normal coronary and carotid flow. The problem, of course, is that the same 2-U bleed in a Supreme Court justice may prove lethal.
On the other end of the clinical spectrum, class IV shock represents a near-death state that is seen with severe blood loss ...