Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 155

Two randomized trials of resuscitated post-cardiac arrest patients have shown that mild therapeutic hypothermia drastically improves sur- vival with appropriate neurological recovery (49% vs. 26% in one trial, 55% vs. 39% in the other trial).^187,188 Based on the inclusion criteria of these trials, patients with the following features have a class I recommendation for hypothermia:

 Patients with VF/VT arrest who had return of spontaneous circulation within 60 minutes of cardiac arrest. Hypothermia may be used in patients with asystole or PEA (less evidence and generally poorer outcomes in comparison to VT/VF).

 Persistent coma with Glasgow Coma scale <8.

 Cardiac arrest is not due to trauma or drug overdose.

Exclusion criteria:

 Persistent hypotension (mean pressure <60 mmHg) despite the use of one vasopressor. The requirement for IABP is not a contraindication.

 Uncontrolled active bleeding or intracranial hemorrhage ± severely abnormal coagulation studies or platelets <50 × 109/l.

Patients in the hypothermia protocol should have hypothermia induced as soon as possible after arrival to the emergency department, with a temperature goal of 32–36 °C within 6 hours after return of spontaneous circulation. The temperature is reduced by 0.5–1 °C per hour. In one of the trials, hypothermia was initiated as late as several hours after restoration of circulation, and the goal temperature was achieved at a mean of 8 hours (interquartile range, 4–16 hours).¹⁸⁸ However, hypothermia should not be initiated later than 6 hours, as there is probably no benefit beyond this point.

In the control group of the two major hypothermia trials, the post-arrest temperature was close to 38 °C. A later study suggested that the mere prevention of this post-arrest hyperthermia with a low normal temperature of 36 °C is as effective as a temperature goal of 33 °C, which was used in the two early trials.¹⁸⁹

Hypothermia is achieved using ice packs, cold intravenous saline, or a cooling blanket with adjustable settings. The patient may be given paralytic agents to prevent the counterproductive shivering during induction of hypothermia. Paralytic agents are not usually necessary once the goal temperature is reached. Sedation is also administered. Hypothermia is maintained for 24 hours, then the patient is rewarmed very slowly, at a rate no faster than 0.5 °C per hour. Since the patient is sedated, the neurologic prognosis of patients undergoing hypothermia may not be properly assessed until 72 hours after rewarming.

During hypothermia, the patient is monitored for the following side effects:¹⁹⁰

 Metabolic: hypokalemia (resulting from intracellular K shift), hyperglycemia, mild reduction of GFR, cold-induced diuresis. Hypokalemia should not be aggressively replaced, as severe hyperkalemia may occur during rewarming.

 Bradyarrhythmia, VT.

 Bleeding (coagulation factors are less effective during hypothermia).

 Increased infectious risk; seizures.

 Hypotension is multifactorial in these patients but may be worsened by hypothermia. Hypothermia reduces cardiac output and increases systemic vascular resistance.

The early initiation of hypothermia does not preclude the early performance of coronary angiography and PCI. The induction of hypothermia prior to or on arrival to the catheterization laboratory has been shown to be safe in several studies.¹⁷⁶ In fact, PCI should be performed urgently, and hypothermia started as soon as possible, preferably before the initiation of PCI (international consensus recommendation).¹⁹¹ Antithrombotic therapies may also be used and have not significantly increased bleeding risk in hypothermic patients, but the patient should still be carefully monitored for bleeding.¹⁹⁰