A 72-year-old man undergoes resection of an abdominal aneurysm. He arrives in the ICU with a core temperature of 33degC (91.4degF) and shivering. Which of the following is a physiologic consequence of the shivering?
## **Core Concept**
The patient's condition describes hypothermia, a lower than normal body temperature, which can occur after surgery, especially during lengthy procedures like an abdominal aneurysm resection. Shivering is a common response to hypothermia as the body attempts to generate heat. This response is mediated by the hypothalamus, which acts to increase the body's temperature set point.
## **Why the Correct Answer is Right**
Shivering in response to hypothermia increases the body's metabolic rate, which in turn generates heat. This process consumes oxygen and produces carbon dioxide. One of the physiological consequences of shivering is an increase in **myocardial oxygen demand**. This occurs because shivering increases the workload on the heart, similar to exercise, by increasing heart rate, contractility, and systemic vascular resistance. This increase in myocardial oxygen demand can be problematic, especially for patients with pre-existing heart disease, as it may lead to myocardial ischemia.
## **Why Each Wrong Option is Incorrect**
- **Option A:** While hypothermia and shivering can lead to various metabolic and cardiovascular changes, a decrease in myocardial oxygen demand is the opposite of what actually occurs. Shivering increases, rather than decreases, myocardial oxygen demand due to the increased metabolic rate and workload on the heart.
- **Option B:** A decrease in systemic vascular resistance is not a direct consequence of shivering. In fact, shivering typically increases systemic vascular resistance as part of the body's response to cold stress, which helps to generate heat.
- **Option C:** While shivering does increase carbon dioxide production as a byproduct of increased metabolism, stating it as a standalone consequence without context of the question (which seems to focus on cardiovascular or immediate physiological impacts) might not directly address the question's apparent focus.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **shivering in hypothermic patients increases myocardial oxygen demand**, which can be particularly concerning for patients with cardiovascular disease. This is why managing hypothermia and preventing shivering are important aspects of perioperative care.
## **Correct Answer:** . Increased myocardial oxygen demand.