Anaesthetic emergencies and their management

 

 

ANAESTHETIC EMERGENCIES AND THEIR MANAGEMENT

Objectives

This module deals with

• Bradycardia
• Tachycardia
• Shock
• Signs of CPA
• Treatment for CPA
• Drugs used in CPR

REASONS FOR ANAESTHETIC EMERGENCIES

·  Human error

o No knowledge of  equipment and anaesthetic drug and its action, miscalculation of dose, incorrect route of administration and wrong medications.

·  Equipment problems

o Failure to deliver oxygen, empty cylinders, misconnected gas lines and kinked or plugged endotracheal tubes.

·  Ventilatory problems

o Hypoventilation due to anaesthetic over dose, hyperventilation due to inadequate anaesthesia.

·  Circulatory problems

o Hypotension, bradycardia, tachycardia and shock.

BRADYCARDIA

·  Bradycardia may arise due to

o Excessive depth of anaesthesia

o Excessive vagal tone (often increased by intubation vasovagal reflex and traction of abdominal organs)

o Terminal hypoxia

o Endogenous and exogenous toxaemias

o Conduction disturbances in myocardium

o Hyperkalaemia

o Hypothyroidism

Treatment

o Administration of atropine or glycopyrrolate.

o Dopamine 2.5 to 20ug/kg/min I.V.

o Isoproterenol 5 to 10 ug/kg/min I.V.

 

 

TACHYCARDIA Tachycardia may arise due to Light level of anaesthesia Hypovolaemia Hypoxia Hypercarbia (More CO2) Hyperthyroidism Normally pulse rate may either be equal or slightly deficit of heart rate Heart rate above 180 per minute in dogs and above 200 per minute in cats are considered as tachycardia.

 

SHOCK

·  Shock is defined as inadequate blood flow to the vital organs or the inability of the body cells to metabolize nutrients normally.

·  The tissue perfusion depends on the cardiac function, circulatory volume and integrity of vascular function.

·  Shock can be classified as

o Hypovolemic shock

o Cardiogenic shock

o Vasculogenic shock

o Hyperdynamic shock

o Hypodynamic shock

HYPOVOLEMIC SHOCK

Causes

·  Due to inadequate volume of fluids or blood due to the loss of whole blood, plasma or loss of water and electrolytes

·  Loss of blood in accident

·  Loss of plasma protein into inflamed body cavities

·  Loss of fluid and electrolytes in diarrhoea

Symptoms

·  Depressed, dull and lack luster/lusterless eyes

·  Pale or white or blue mucous membrane

·  Reduced capillary refill time

·  Cold extremities

·  Tachycardia

·  Fast and weak pulse

·  Elevated respiratory rate

·  Reduced body temperature

CARDIOGENIC SHOCK

Causes

·  Occurs when the heart fails to pump adequate blood to maintain perfusion. Failure could be due to reduced venous filling and reduced cardiac output. This condition is common in small animals.

·  Cardiac tamponade

·  Rupture of chordae tendinae

·  Toxic myocardial depression

·  Cardiac arrhythmia

·  Severe prolonged systemic vascular resistance

Symptoms

·  Depressed, dull and lack luster/lusterless eyes

·  Pale or white or blue mucous membrane

·  Reduced capillary refill time

·  Cold extremities

·  Tachycardia

·  Fast and weak pulse

·  Elevated respiratory rate

·  Reduced body temperature

·  Distended pulsating peripheral veins

·  Hepatomagaly

·  Peripheral oedema

·  Cardiac dysrhythmia

·  Heart murmurs

VASCULOGENIC SHOCK

Causes

·  The vessels supplying the blood to the tissues are affected and the perfusion is reduced

·  Arteriolar constriction

·  Prolonged sympathetic stimulation

·  Vasomotor paralysis due to head injuries

·  Endotoxic and septic shock can also be categorized under vasculogenic shock as the toxins produce vasodilation due to the release of histamine, bradykinin and prostoglandins.

HYPERDYNAMIC SHOCK

Causes

·  An early stage of septic shock is an example of hyperdynamic shock.

Signs

Stage I

·  Increase in cardiac output

·  Decrease in arteriovenous oxygen difference

·  Decrease in systemic vascular resistance

·  Blood pressure may be normal or reduced

·  Oxygen utilization at cellular level is reduced

Stage 2

·  Cardiac output may be normal

·  Hypotension

·  Respiratory acidosis with metabolic alkalosis

·  Elevated heart rate

Stage 3

·  Reduction in cardiac out put

·  Elevated heart rate

·  Increased difference in arteriovenous oxygen level

·  Increase in systemic vascular resistance

·  Hypotension

·  Brick red mucous membrane due to peripheral vasodilation

·  Pyrexia due to toxins and damaged leukocytes

HYPODYNAMIC SHOCK

·  It occurs at the terminal stage of sepsis or during the absorption of toxins. This can be otherwise called as fourth stage of septic shock.

·  Hypodynamic shock is common in large animal practice. E.g. terminal stage of horses with colic and cow with coliform mastitis.

Signs

·  Myocardial depression

·  Maldistribution of blood volume

·  High peripheral resistance

·  Endothelial damage

·  Infarcts in vital organs

·  Acute respiratory failure and hypoxaemia

SIGNS OF CPA No ausculatatable heart sound No palpable pulse Cyanotic mucous membrane Dilated pupil No ventilatory attempts or agonal gasps Unconsciousness It is really a true emergency condition, which is to be treated immediately within a period of 2 to 3 minutes. The basic life support in cardio pulmonary resuscitation(CPR) is the optimal management of airway(A), Breathing(B) and circulation(C). Otherwise called as ABC of CPR.

TREATMENT OF CPA by CPR

Airway

·  The head must be immediately extended

·  If not intubated intubate the animal immediately.

·  Examine for the possible obstruction of the airway with food materials or kinked endotracheal tube

·  In emergency perform tracheostomy to maintain airway patent

·  In case of bronchospasm treat the animal with aminophylline 5 mg/kg I.V.

Breathing

·  Institute artificial respiration using rebreathing bag or mechanical ventilators at the rate of 12 to 20 breaths per minute.

·  Supply 100% oxygen

·  Or use AMBU type resuscitation bag (using room air 21% oxygen) or mouth to endotracheal or mouth to muzzle procedures to maintain breathing

·  Analeptic agents(Respiratory stimulant) like doxapram can be administered at the rate of 1 mg/kg I.V.

·  The other agents are specific alpha 2 antagonist (yohimbine) and opioid pure antagonists (naloxone).

Circulation

·  External cardiac massage by chest compression at the rate of 90 to 120 per minute. In dogs the chest compression can be attempted by placing the hands on either side of the chest. In cats the forefinger and the thumb is used.

·  Open cardiac massage is done at the rare of 60 to 100 per minute. If surgery is performed in the thorax its easy to provide open chest massage. During abdominal procedures if emergency occurs the thoracic cavity can be entered through the diaphragm.

·  Defibrillation –To restore the normal contractions and pulse rate in ventricular arrythemias. The defibrillation is done using external or internal paddles of cardiac defibrillators. The power setting depends on the weight of the animals. In small animals the heart is defibrillated at the rate of 1 to 10 J/kg using external paddles and 0.1 to 1 J/kg using internal paddles.

DRUGS USED IN CPR

Calcium solutions

·  Administered as inotropic agent(change the force of contraction) or in hypocalemic agent.

·  It strengthens the myocardial contraction.

·  Dose : Calcium gluconate 10% solution at the rate of 0.5 mg/kg I.V.

Dobutamine

·  It is a sympathomimetic amine, which stimulates beta 1 and beta 2 adrenergic receptors.

·  It decreases peripheral vascular resistance and increases cardiac output, blood pressure and tissue perfusion.

·  Rapid intravenous administration may cause cardiac dysrhythmias.

·  Dose 0.25 to 20 µg/kg/min in small animals and 0.5 to 2.0 µg/kg/min in large animals.

Ephedrine

·  It stimulates beta 1, beta 2 and alpha 1 receptors.

·  The cardiac output and blood pressure are increased.

·  It is indicated in mild to moderate hypotension.

·  Dose 0.05 to 0.5 mg/kg I.V in small animals and 0.022 to 0.66 mg/kg I.V.

Isoproternol

·  It is a sympathomimetic amine, which stimulates beta 1, beta 2 and adrenergic receptors located in the heart, bronchial smooth muscles, skeletal muscle and alimentary tract.

·  It decreases peripheral vascular resistance, diastolic blood pressure and mean arterial pressure and increases cardiac output and systolic blood pressure.

Epinephrine or Adrenaline

·  It is a sympathomimetic amine that stimulates alpha 1, 2 and beta 2 adrenergic receptors.

·  It dilates the vasculature of muscles and constricts cutaneous, mucosal and renal vasculature.

Doxapram (Dopram)

·  It is a nonspecific analeptic agent used to act on the peripheral chemoreceptors.

·   Dose. 1.0 mg/kg I.V.

Sodium bicarbonate

·  It is a buffer aids in reversing metabolic acidosis.

·  Dose  = 0.3 x base deficit (mEq/L) x Body weight.

Coricosteroids

·  These group of agents increases the glucose production, induce hypokalemia by sodium retention.

·  They have inotropic effect on the heart and maintain vasomotor response and suppress the adrenal gland.

·  Indicated in shock and malignant hyperthermia.

Lignocaine

·  Indicated in premature ventricular contraction.

·  Dose 0.5 to 2 mg/kg in large animals and 1 to 5 mg/kg in small animals.