Farm Animal Anesthesia by unknow

Author:unknow
Language: eng
Format: epub
ISBN: 9781119672531
Published: 2022-01-22T00:00:00+00:00

7.5.11 Cardiovascular Collapse

During anesthesia, significant and prolonged decrease in pulse pressure, hypotension, increased capillary refill time, pale mucous membranes, bradycardia, and/or tachycardia can lead to cardiovascular collapse. Causes of perioperative collapse include significant endotoxin‐induced peripheral vasodilation, severe systemic disease, extreme hypovolemia due to dehydration and/or blood loss, and excessive deep anesthesia resulting in profound myocardial depression. Treatment of impending cardiovascular failure should begin with correction of the causative disease status, rapid administration of supportive fluid (90 ml/kg), and reduction or even cessation of anesthesia. Additional symptomatic treatments include vasoactive drugs (e.g. dopamine, phenylephrine, ephedrine) for hypotension, inotropic drugs (e.g. dobutamine) for myocardial depression, chronotropic drugs (e.g. atropine, glycopyrrolate) for bradycardia, and antiarrhythmic drugs (e.g. lidocaine) for ventricular arrhythmias such as ventricular tachycardia or premature ventricular contractions [43].

Prolonged untreated cardiovascular collapse may result in cardiac arrest and death. Cardiopulmonary resuscitation (CPR) should follow the general ABC technique. A is opening of the airway by endotracheal intubation, B is the initiation of controlled breathing by squeezing an Ambu bag or using the rebreathing bag of an anesthesia machine (12–20 breaths/minute), and C is the establishment of artificial circulation by cardiac compression (80–100 compressions/minute). After CPR has been instituted, an IV catheter should be placed if one is not already in place. If the attempts at IV catheterization are unsuccessful, emergency drugs may be administered intratracheally through the endotracheal tube at 2–2.5 times the IV dose after dilution with sterile water or saline to a volume of 5–10 ml. Absorption of the drugs from the lung is sometimes significant enough to be more effective than IV administration through a peripheral vein [43]. Emergency drugs and products frequently used during CPR include 100% O2, balanced electrolyte solutions, atropine, lidocaine, and epinephrine. Depending on the animal's condition, the vasoactive drugs mentioned previously can be administered in conjunction with emergency drugs. Electrical defibrillation is the most effective treatment for conversion of ventricular fibrillation, but it is not practical in field situations or effective in large animals. Epinephrine (10 μg/kg IV) is usually the drug of choice for treatment of ventricular fibrillation. Epinephrine induces peripheral vasoconstriction and increases arterial diastolic blood pressure, intracranial and coronary blood flow, coarseness of ventricular fibrillation, and positive inotropic effect by stimulating α and β adrenoceptors. Potential side effects of epinephrine include increased myocardial and cerebral O2 demand, postresuscitation arrhythmia, and tachycardia. A bolus injection of lidocaine (0.5–2 mg/kg IV) may be used to treat postresuscitation ventricular arrhythmia. Chemical defibrillation with IV potassium chloride (1 mg/kg) and acetylcholine (6 mg/kg) followed by administration of 10% calcium chloride (1 ml/10 kg [22 lb]) has been recommended for treatment of ventricular fibrillation. Although it is ineffective in defibrillation, this technique usually converts fibrillation to asystole [43]. A normal sinus rhythm is actually easier to initiate from asystole than from fibrillation.

In general, the best treatment for perioperative complications is prevention, which requires a devoted and vigilant anesthetist. Careful preanesthetic evaluation and preparation, proper use of anesthetic regimens, and adjustment of the dosages of the anesthetics used can prevent most anesthetic‐related complications. Close monitoring and attention

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