Special Sub-Topic: "Chilling Out" After Cardiac Arrest
|When the heart stops beating, the brain is affected in many ways. Which of these listed is NOT one of them?|
Brain cells work extra hard to keep blood circulating.. Brain cells, like other body cells, need a source of oxygen and nutrients in order to work hence. Circulation of blood is a function of the heart hence, the option about the brain working harder maintain blood circulation is incorrect.
Once blood flow to the brain stops, oxygen stores are depleted in about 20 seconds and glucose is used up in about 5 minutes.
The interruption of blood flow to the brain during a cardiac arrest sets off a cascade of chemical reactions resulting in death of brain cells.One would expect this damage to stop as soon as spontaneous circulation returns, however, the return of circulation causes further release of chemicals and more damage takes place. This is known as "reperfusion injury" and it continues for about 24 to 48 hours post arrest.
Induced hypothermia reduces reperfusion injury and in turn fosters a better post cardiac arrest outcome.
|What is induced hypothermia?|
Therapeutic lowering of the body temperature to reduce tissue damage after a period of ischemia.. In the latter part of the 1900s, studies regarding the benefits of therapeutic hypothermia were done on animals such as dogs. These studies yielded positive results prompting studies on humans as well. On the basis of studies done on humans published in 2002, induced hypothermia was considered best practice for victims of cardiac arrest.
Lowering the body temperature reduces metabolic activity and hence the need for oxygen. For each degree Celsius the body temperature drops, the metabolic rate drops 6 - 7 percent. Making the body temperature lower than 30 degrees Celsius however, can result in lethal arrhythmia such as ventricular fibrillation. The target range is between 32 - 34 degrees Celsius.
|Unfortunately, not all survivors of cardiac arrests are suitable candidates for induced hypothermia.
Which of these listed below would be a suitable candidate for induced hypothermia?|
Patient 'Y' for whom CPR was initiated soon after a witnessed arrest.. The best candidates are the ones for whom the arrest was cardiac in origin, the down time is known, CPR was started promptly and there was return on spontaneous circulation (ROSC)within 60 minutes.
|Hypothermia inducing modes may be invasive or non invasive.
t. Several methods are available for inducing hypothermia - both invasive and non invasive. Non invasive devices include wraps, gel pads, blankets and packs, while invasive methods involve the use of intravascular catheters and infusion of iced intravascular fluids.
Invasive catheters are usually connected to a cooling device which helps to maintain body temperature within set limits. Whatever, the method used, careful monitoring of the body temperature is crucial.
|When inducing hypothermia, a primary goal of management is to PREVENT SHIVERING.
Why should shivering be prevented?|
Shivering increases metabolic activity resulting in increased oxygen demands.. The body's natural response to coldness is to shiver. This increases metabolic activity and produces warmth. Apart from increasing oxygen consumption, shivering makes it difficult to achieve and maintain target temperature. Temperature is not monitored externally in these subjects.
|Which of the follow categories of drugs may be used to prevent shivering and provide comfort during induced hypothermia?|
Sedatives and analgesics. A variety of sedatives and analgesics have been used during induced hypothermia. Some of these drugs include fentanyl, midazolam and propofol. Some patients require a paralytic agent such as vecuronium.
|When assessing a patient during hypothermia therapy, which of the following clinical features will you NOT expect to find?|
Flushed skin. Hypothermia is associated with constriction of the blood vessels. The hypothermic individual is therefore likely to manifest with weak pulse and appears pale. Sedatives and analgesia coupled with decreased metabolism can result in slow pulse/bradycardia. Flushed skin is associated with increased blood flow and perfusion of the skin (which does not occur in these clients).
Because of the decreased skin perfusion, among other things, the risk for skin breakdown is also increased.
|During hypothermia, there's a decrease in the release of insulin from the pancreas. Consequently, which of these features should one expect?|
Hyperglycemia. The decrease in insulin release from the pancreas, coupled with increased resistance to insulin by the body cells, results in high circulating levels of glucose. Some patients my require insulin therapy during the hypothermic phase of management.
|Induced hypothermia is not without its problems. Hypothermia causes potassium to be shifted into the cells resulting in low serum levels of potassium. Some patients also experience 'cold diuresis' causing them to urinate excessively.
During hypothermia the patient may manifest with all of the following features EXCEPT|
pyrexia. Although the incidence of infection is increased in these clients, pyrexia, for obvious reasons, is not a feature. The excess fluid loss in urine may cause dehydration and a drop in blood pressure. There's also loss of potassium in the urine. More importantly, intracellular shifts in potassium lead to hypokalemia. One needs to be careful with potassium replacement particularly at the end of the hypothermic phase of therapy because as the body is rewarmed, potassium is shifted out of the cells and hyperkalemia becomes a problem.
|Once the hypothermia therapy is completed, the patient has to be rewarmed.
Which of the following measures is NOT implemented during the rewarming phase?
Systematic increase in the amount of sedation. Although some amount of sedation and analgesia should be continued during the rewarming phase, the focus should be to wean off instead of increase sedation. As the blood vessels dilate during rewarming, the blood pressure is likely to drop. Potassium also shifts out of the cells causing hyperkalemia. Fluid and electrolyte balance should be monitored.
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