12. anesthetic problems and emergencies

1Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.

Every anesthetic procedure has the potential to cause the death of the animal

Anesthetic Problems and Emergencies

Chapter 12


Anesthetic Problems and Emergencies: Human Error

Failure to get an adequate history and do a physical examination

Lack of attention to the anesthetic machine and patient

Inability to recognize early signs of trouble Incorrect administration of drugs or

administration of incorrect drugs Lack of knowledge of pharmacology and

improper calculations Fatigue and inattentiveness


Anesthetic Problems and Emergencies: Equipment Issues

Equipment failure Carbon dioxide absorbent exhaustion

(rebreathing system) Empty oxygen tank Incorrect assembly of the anesthetic machine Endotracheal tube (ET) blockage


Anesthetic Problems and Emergencies: Equipment Issues (Cont’d)

Vaporizer problems Using the wrong anesthetic agent Tipping the vaporizer Vaporizer dial becomes stuck or jammed Vaporizer is overfilled Two vaporizers used at the same time

Pop-off valve problems Failure to open the pop-off valve


Reduce the Adverse Effects of Anesthetic Agents

Choose a protocol suitable for the condition or needs of the patient

Be familiar with side effects and contraindications for preanesthetic and general anesthesia agents

Multidrug protocols are safer than single drug protocols


Anesthetic Problems and Emergencies: Patient Factors

Geriatric animals Have reached 75% of life expectancy Decreased heart, lung, and liver function Presence of degenerative disorders Poor response to stress Reduced anesthetic requirements Prolonged recovery Tendency for hypothermia


Anesthetic Problems and Emergencies: Patient Factors (Cont’d)

Neonates and pediatric animals are less than 3 months old Preoperative fasting IV 5% dextrose in lactated Ringers during

anesthesia Use pediatric microdrip administration set Use pediatric or gram scale to weigh animals <5 kg Injectable agents may require dilution



Neonates and pediatric animals Have reduced anesthetic requirements Neonates have reduced liver and kidney function Induction with inhalant agents Intubation and catheterization are difficult Prone to hypothermia



Brachycephalic animals Anatomic characteristics Avoid agents that depress respiration or relax

muscles of the pharynx/larynx Prone to bradycardia Difficult induction period

• Preoxygenate if possible Difficult to intubate

• Use laryngoscope and smaller diameter tube



Brachycephalic animals (Cont’d) Use agents that allow rapid recovery Monitor closely during recovery for dyspnea Recover in an excitement-free or stress-free

environment Postoperative tranquilizers may be needed



Sighthounds Increased sensitivity to some anesthetic agents

Obese animals Require lower doses of drugs on a per-kilogram

basis Anesthetic agents are poorly distributed to fat Possible respiratory difficulty; preoxygenate Shallow, rapid respirations during anesthesia



Cesarean delivery Most often an emergency surgical procedure Patient is in compromised condition due to

advanced pregnancy Patient is not properly prepared for surgery (e.g.,

not fasted) Most anesthetic agents will cross the placenta and

affect fetuses Patient is at risk for going into shock during

surgery


Cesarean Anesthetic Protocols

Epidural with tranquilizers or neuroleptanalgesic IV fluids and oxygen also administered Monitor blood pressure

General anesthesia with injectable or inhalant agents Preoxygenation is helpful Propofol or ketamine

Opioid agents Reversible in both mother and neonate


Anesthetic Concerns for Cesarean Patients

Hypoxemia Hypercarbia Hypotension Physiological anemia Acid/base imbalance Tissue trauma Cardiac arrhythmias


Care of Puppies and Kittens Delivered by Cesarean Section

Respiratory function Deliver oxygen by facemask Intubate with 16- or 18-gauge IV catheter and

gently bag every 5 seconds Aspirate fluid from the mouth and nose with

eyedropper or bulb syringe Administer reversal agents, doxapram, and/or

dilute atropine as needed


Care of Puppies and Kittens Delivered by Cesarean Section (Cont’d)

Cardiac function Gentle cardiac massage Deliver oxygen by facemask

Allow to nurse as soon as mother is recovered Watch neonates if mother is still groggy Anesthetic agents secreted in milk don’t affect

neonates



Recent trauma that requires emergency attention Trauma ailments increase anesthetic risk

Respiratory difficulties May result from pneumothorax, pulmonary

contusions, hemorrhage, or diaphragmatic hernia Decreases the VT of the patient leading to

decreased oxygenation Increased CO2 levels leading to acid/base

imbalance and cardiac arrhythmias Loss of blood or fluid sequestration changes blood

pressure



Change in blood pressure Resulting from a change in cardiac output or

vascular tone Anesthetic depth will affect both parameters Hypotension → decreased tissue perfusion →

tissue hypoxia/anoxia → anaerobic glycolysis → lactic acid production → acid/base imbalance

Monitor blood pressure closely• Doppler or oscillometric methods • Digital pulse palpation • Capillary refill time


Fluid Therapy for Hypotension

Crystalloid fluid administration May have to deliver small boluses for rapid

therapy Crystalloid fluids stay in intravascular space

<2 hours Watch for fluid overload, especially in cats Monitor heart rate, blood pressure, mucous

membrane color, and capillary refill time


Fluid Therapy for Hypotension (Cont’d)

Colloid fluid administration Helpful if blood pressure can’t be maintained Remain in the intravascular space longer than

crystalloids Will increase colloidal osmotic pressure and help

stabilize blood pressure Given in smaller volume in conjunction with

crystalloids



Respiratory problems in the trauma patient Direct trauma to the chest leading to lung collapse

or failure of alveolar gas exchange Must remove air/fluid from chest cavity prior to

anesthesia Deliver supplemental oxygen

Oxygen delivery methods Flow-by-oxygen Nasal catheters Oxygen collars


Oxygen Delivery Methods


Thoracocentesis (Chest Tap)

To relieve pneumothorax or pleural effusion from chest cavity

Performed by veterinarian Prepped by veterinary technician Temporary bandage over chest wound Place animal in sternal recumbency or standing

position Shave lateral chest wall between the 7th and 9th

intercostal spaces caudal to point of the elbow Aseptically prepare 4 cm × 4 cm area Prepare a 20- to 22-gauge, 1- to 1½-inch catheter

with a three-way stopcock and large syringe


Other Considerations for the Trauma Patient

Cardiac arrhythmias Common 12-72 hours after trauma Electrocardiograms

Shock: especially where hemorrhage is significant Internal injuries: fractures or ruptured organs Anesthesia

Best to delay it until the animal is stabilized Delay allows more thorough patient workup

including thoracic radiographs



Preexisting cardiovascular disease Anemia Shock Cardiomyopathy (primary or secondary) Congestive heart disease (mitral valve

insufficiency) Heartworm disease Coexisting imbalances (e.g., hypoxia,

hypercapnia, electrolyte imbalances)



Bradycardia Most common cardiac anesthetic problem Caused by preanesthetic or anesthetic drugs Force of cardiac contraction may also be

decreased Blood return to the heart may be decreased

(preload) Treat with drugs or adjustment of anesthetic depth



Cardiac arrhythmias Caused by anoxia/hypercarbia, poor tissue

perfusion, acid/base imbalance, myocardial damage

Difficult to detect on physical examination; may find dropped beats

Diagnose with ECG and report immediately to veterinarian who will determine the treatment required

Concurrent pulmonary disease is sometimes seen



Anesthetic considerations Stabilize patient as per veterinarian’s instructions Preoxygenate with facemask 5 minutes prior to

induction Increased risk of overhydration with IV fluid

• Monitor for pulmonary edema



Respiratory disease Caused by:

Pleural effusion Diaphragmatic herniaPneumothorax PneumoniaTracheal collapse Pulmonary edema

Clinical signs • Tachypnea• Dyspnea• Cyanosis


Anesthetic considerations VT is reduced and respiratory rate is decreased in

most anesthetized animals A decrease in VT will result in a decreased alveolar

gas exchange Lighten anesthesia as much as possible in a

patient with respiratory disease Provide intermittent ventilation Evaluate oxygen-carrying capacity with PCV or

pulse oximeter Preoxygenation is necessary prior to induction



Respiratory Problems During Anesthesia

Clinical signs: dyspnea or cyanosis Assessment

Respiratory character and volume Depth of anesthesia Associated with pain Proper ET tube placement ET tube blockage Oxygen saturation Arterial or end-tidal CO2


Respiratory Problems During Anesthesia (Cont’d)

Actions Intermittent positive-pressure ventilation Reintubate if necessary Radiographs and thoracocentesis



Diaphragmatic hernia Preoxygenate for 5-10 minutes prior to induction Avoid head-down patient positions before and

during anesthesia Rapid intubation Ventilatory assistance or ventilator if necessary Postoperative observation for signs of respiratory

distress


Anesthetic Problems and Emergencies: Patient Factors (Cont’d) Hepatic disease

Liver necessary for drug metabolism, blood clotting factors, plasma proteins, carbohydrate metabolism

Preanesthetic agents must be chosen with care


Anesthetic Problems and Emergencies: Patient Factors (Cont’d) Renal disease

Kidneys maintain volume and electrolyte composition of body fluids

Renal excretion removes anesthetic agents and metabolites from the body

General anesthesia is associated with decreased blood flow to the kidneys

Diagnosis: urine specific gravity, BUN, creatinine Offer water up to 1 hour prior to premedication Correct dehydration prior to anesthesia



Urinary blockage Clinical signs

• Depression• Dehydration• Uremia• Acidosis• Hyperkalemia (can lead to cardiac arrest)

Inhalation agents are less hazardous for the patient


Anesthetic Problems and Emergencies

Animals won’t stay anesthetized Check vaporizer setting Check level of anesthetic in the vaporizer Proper ET tube placement or air leakage around it Patient apnea Shallow respirations Proper assembly of anesthetic machine with tight

connections Adequate oxygen flow Anesthetic machine/vaporizer is working properly Agonal breathing vs. light plane breathing


Anesthetic Problems and Emergencies (Cont’d)

Animals are too deeply anesthetized <6 bpm; shallow respirations, dyspnea Pale/cyanotic mucous membranes Capillary refill time >2 seconds Bradycardia Weak pulse; systolic blood pressure <80 mm Hg Cardiac arrhythmias; irregular QRS complexes or

VPCs Hypothermia Absent reflexes Flaccid muscle tone Dilated pupils



Pale mucous membranes Preexisting conditions Blood loss during surgery Anesthetic agent that causes vasodilation and

hypotension Hypothermia Pain



Prolonged capillary refill time (>2 seconds) Blood pressure cannot adequately perfuse

superficial tissues May result from conditions present prior to

induction May be secondary to blood loss during surgery May be seen in animals in deep anesthesia



Respiratory distress Dyspnea

• Patient is unable to obtain sufficient oxygen or remove adequate CO2

Cyanosis• Oxygenation is inadequate



Sources of respiratory distress during anesthesia Empty oxygen tank Flowmeter is turned off Anesthetic circuit or ET tube is blocked Airway obstruction or respiratory pathology Deep anesthesia



Tachypnea Rapid respirations as opposed to dyspnea Commonly seen with opioid use Associated with light anesthesia accompanied by

tachycardia and spontaneous movement May be seen in hyperthermic animals



Abnormalities in cardiac rate and rhythm seen in anesthetized animals Tachypnea

• May result from drugs, preexisting conditions, or surgical stimulation

• May not require treatment • Check vaporizer setting and anesthetic depth



Abnormalities in cardiac rate and rhythm are seen in anesthetized animals Bradycardia

• May be secondary to drug administration, vagal stimulation, deep anesthesia, or physiologic imbalances

• May not require treatment• Check vaporizer setting, bag with 100% oxygen, or

administer reversal drugs Cardiac arrhythmias

• May result from drugs and will have a short duration• May be a problem in geriatric patients or patients with

preexisting conditions• Common during induction and light anesthesia



Respiratory arrest Cessation of respiratory efforts Can lead to cardiac arrest Temporary arrest

• May follow injection of respiratory depressants or following a period of prolonged bagging

• Check other vital signs for abnormalities



Respiratory arrest (Cont’d) True arrest

• Requires immediate action• Can result from anesthetic overdose, cessation of

oxygen flow, or preexisting respiratory disease• May be preceded by dyspnea or cyanosis and abnormal

vital signs• May use Ambu bag, mouth-to-ET tube, or mouth-to-

muzzle resuscitation


Use of an Ambu Bag



Cardiac arrest No heartbeat is auscultated or palpated Normal QRS complexes are absent No arterial pulse and blood pressure <25 mm Hg Gray or cyanotic mucous membranes Widely dilated pupils, no corneal reflex Agonal breathing

Some prior warning is usually present Respiratory distress or arrest, cyanosis/dyspnea,

prolonged capillary refill time, arrhythmia



Cardiopulmonary cerebrovascular resuscitation (CPCR) started immediately after cardiac arrest Five people (ideal) involved

• 1 performs chest compressions• 2 bags the animal • 3 assesses the pulse during compressions and checks

the pulse or ECG when compressions are stopped• 4 draws up and administers drugs as per the

veterinarian’s instructions • 5 maintains a record of the patient’s status and

resuscitative treatment



Cardiac arrest with CPCR A = airway B = breathing C = circulation D = drugs E = ECG

Circulation is the most important step so the correct order is CABDE


Cardiopulmonary Cerebrovascular Resuscitation (CPCR)

Circulation Most important factor is return of spontaneous

circulation (ROSC) Cardiac compressions

• Method depends on the size of the animal• Compress chest about 1/3 the diameter of the chest wall • 1-2 compressions/second generates 100 bpm heart rate • Compressions manually force blood through the heart

and into tissues• Each compression should produce a palpable femoral

pulse


Cardiopulmonary Cerebrovascular Resuscitation (CPCR) (Cont’d)

Circulation (Cont’d) Bag the patient every 10-12 seconds

• Simultaneously with compressions Some results should be seen within 2 minutes Internal compressions may be necessary Resuscitation is unlikely to be successful after

15 minutes Once spontaneous cardiac contractions are

established, continue bagging until spontaneous breathing is established (several hours)


Cardiac Compressions



Airway and breathing Intubate immediately if not already intubated Turn off vaporizer and nitrous oxide

• Animal should breathe 100% oxygen One breath every 10-12 seconds Chest should rise slightly during bagging



Drugs Veterinarian authorizes dosage, route, and nature

of drugs Catheterized animals

• Drugs administered IV followed by rapid fluid administration

• Be careful of overhydration Injections into the base of the tongue or by the

intratracheal route are the second choice Intracardiac injections should be avoided



Commonly used drugs Epinephrine

• Cardiac arrest Vasopressin

• In place of or alternated with epinephrine Atropine

• Anesthesia-related cardiac arrest Dopamine or dobutamine

• Increase force and rate of cardiac contractions



ECG Don’t use alcohol if a defibrillator is present Asystole

• No electrical activity Ventricular fibrillation

• Coarse vertical zig-zag lines resulting from disorganized muscular heart activity

Pulseless electrical activity (electromechanical dissociation, EMD)

• Normal or near-normal complexes


Pulseless Electrical Activity


ROSC Aftercare

Monitor cardiovascular and respiratory function Blood pressure, blood gases, pulse oximetry,

ECG, capnography Drug and fluid therapy varies Assess brain function Repeat arrest within 24 hours is common Following successful ROSC, other conditions

may arise Pulmonary or cerebral edema


Potential Problems During the Recovery Period

Regurgitation during anesthesia A passive process under anesthesia

• No retching, just fluid draining from animal’s mouth or nose

Stomach contents may be aspirated into respiratory tract

Most common occurrence in head-down surgical positions and in ruminants

Treatment• Immediate placement of cuffed ET tube• Clean out regurgitated material with suction


Potential Problems During the Recovery Period (Cont’d)

Vomiting during or after anesthesia Common in brachycephalic dogs or nonfasted

animals An active process usually accompanied by

retching Usually occurs as the animal is losing or regaining

consciousness Signs

• Airway obstruction leading to dyspnea/cyanosis, bronchospasm

Treatment• Intubation and suction if unconscious• Lower head and clean oral cavity if conscious


Potential Problems During the Recovery Period (Cont’d) Seizures

Seen with ketamine administration, after diagnostic procedures (myelography), or preexisting conditions

Signs• Spontaneous twitching; uncontrolled movements of

head, neck, and limbs; opisthotonus; triggered by a stimulus

Treatment• Reduce stimuli, postoperative analgesia, diazepam or

propofol, monitor for hyperthermia



Excitement Seen after barbiturate anesthesia or high opioid

doses, as spontaneous paddling and vocalization Treatment may not be necessary

• Sedatives may help• Naloxone can reverse opioids

Seizures should be differentiated from excitement



Dyspnea in cats Dyspnea is usually caused by laryngospasm

sometimes triggered by removal of the ET tube Laryngeal edema may result from repeated

intubation attempts May breathe with an audible stertor (wheeze)

during inspiration Differentiate from growling during expiration May resolve itself or may need oxygen

administration via facemask, intubation, or a tracheotomy

Is easier to prevent than treat



Dyspnea in dogs Breed-related

• Brachycephalic dogs Airway obstruction

• Anatomy, foreign objects, postsurgical tissue swelling Humidified oxygen can be delivered to an awake

animal• By facemask, nasal cannula, E-collar, or oxygen

cage/tent



Causes of prolonged recovery Impaired renal or hepatic function Hypothermia Patient susceptibility to anesthetic agent Breed variation Coexisting disorder Prolonged anesthesia or deep anesthesia

12. anesthetic problems and emergencies

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