Small Animal Nursing II Exam 3 - The Hypothermic Patient, Cardiovascular System, and Respiratory Diseases

Hypothermia

Drop in body temperature below standard references ranges

Lack of monitoring

Hypothermia is routinely experienced in anesthesia and surgery, generally due to

> 98°F

Mild stage hypothermia would mean a temperature of

96-98°F

Moderate stage hypothermia would mean a temperature of

92-95°F

Severe hypothermia would mean a temperature of

< 92°F

Critical stage hypothermia would mean a temperature of

• Metabolism

• Blood viscosity

• Decreased cardiovascular function

• Increases amount of anesthetic drugs needed

• Risk for infection due to lack of perfusion

• Decreased immune function

Hypothermia creates abnormal reactions in the body including

• Metabolic rate slows

• Reduced drug metabolism and drug elimination (prolonged recovery)

• Electrolyte and pH imbalances (hyperkalemia and acidosis)

How does hypothermia affect metabolism?

Life-threatening bradycardia

Hyperkalemia in cats with urinary obstruction can lead to

Metabolism decreases 10% for each 1.8°F loss of body temperature

At what rate does the metabolism slow in a hypothermic patient?

Increases blood viscosity or thickness

How does hypothermia affect blood viscosity?

• Increased PCV from splenic contraction

• Increased amount of work of myocardium

• Increased PT/PTT

• Hypocoagulability leading to excessive bleeding

What affects does increased blood viscosity have on the body of a hypothermic patient?

Hypocoagulability

Reduced blood coagulation which can occur as a result of hypothermia

• Hypotension due to reduced response from baroceptors

• Reduced cardiac output

• Bradycardia from hyperkalemia

How does hypothermia affect the body's cardiovascular response?

Hypotension

At 95°F, active vasodilation occurs, leading to

Thermoregulation

At < 94°F, ______ is impaired, and peripheral vasoconstriction is replaced with vasodilation

• Depression of CNS

• Deeper plane of anesthesia causes hypoventilation which leads to hypercapnia

A hypothermic patient requires a higher amount of anesthetic drug. How does this need affect the body?

Minimum alveolar concentration (MAC)

Amount of anesthetic gas vapor in lungs needed for anesthesia

• Cold environment (most common)

• Altered thermoregulation of the body (second most common)

• Heat-loss mechanisms

Identify causes of hypothermia

Altered thermoregulatory response

The most common cause of hypothermia is a cold environment. Identify the second most common cause.

• May be caused by agents used in anesthesia

• Loss of body heat during surgery

• Physical factors (lack of body fat, large body surfaces, vasodilation, hypothalamus function)

Identify factors that can alter the body's thermoregulatory response

Tail and legs

The patient's _____ release or absorb heat to maintain normothermia when awake

Normothermia

Normal body temperature

Radiation, convection, conduction, and evaporation

Identify the four heat-loss mechanisms

Radiation (heat away from body)

Exchange of heat between the body and environmental objects via infrared rays

Convection (⇧ surface area → ⇧ convection)

Occurs as body heat is transferred to air moving over the skin surface

Conduction

Occurs when the body touches a cooler surface

Insulate patient

How can you prevent the loss of body heat through conduction?

Evaporation

When moisture on the skin or in respiratory tract dissolves into air, pulling body heat with it

Surgical prep solutions or O2 administration

What can cause hypothermia in a patient through evaporation?

• Pediatric patients

• Geriatric patients

• Thin patients

• Patients undergoing open body cavity procedures

Which patients are at high risk for hypothermia?

Due to their immature ability to thermoregulate (i.e high metabolic rate, limited SQ fat, limited shivering)

Why are pediatric patients susceptible to hypothermia?

Due to their loss of thermoregulation abilities (i.e decreased muscle mass, metabolic rate, redistribution of fat slows transfer of body heat)

Why are geriatric patients susceptible to hypothermia?

15-40% (inhibits muscular activity and decreases heat production)

Anesthesia decreases basal metabolic rate by

Oxygen is cold and can promote hypothermia, especially when using a non-rebreathing system

How can oxygen promote hypothermia?

Vasodilation

How can anesthetic drugs promote hypothermia?

Fully dilated vessels lose heat 8x faster than constricted vessels

Some anesthetic drugs cause vasodilation. How quickly do fully dilated vessels lose heat compared to constricted vessels?

Decrease minimum alveolar concentration (MAC)

Body temperature can be controlled by using multimodal anesthesia protocol which then allows you to

Passive (i.e flannel blanket, bubble wrap, plastic wrap)

Prevention of hypothermia by preventing heat loss

Normothermic or mildly hypothermic patient

Passive prevention of hypothermia would be used for which type of patient?

Active external (i.e warm air or water blankets, IV warmer, conductive fabric)

Prevention of hypothermia by providing heat to the body surface

Anesthetized patient with moderate, severe, or critical hypothermia

Active external prevention of hypothermia would be used for which type of patient?

Active internal (i.e sterile warm lavage, warm IV fluids)

Prevention of hypothermia by heating the body core

Open chest or abdomen surgeries or severe hypothermia

Active internal prevention of hypothermia would be used for which type of patient?

Esophageal thermometer

Provides a real-time constant core temperature

• Pre-warm with blankets or water bottles

• Insulate patient from cold surfaces

• Do not oversaturate patient with surgical prep solutions

How can you prevent heat loss in a preoperative patient?

2 °F

A patient can lose up to ____ during the first hour of anesthesia

• Inline fluid warmers

• Forced warm air systems (bair hugger)

• Conductive fabrics (hot dog warming system)

• Circulating warm water blankets

How can you use active warmers to prevent heat loss in a patient intra-op?

• Bubble wrap or plastic wrap

• Flannel blankets or space blankets

• Low oxygen flow

How can you use passive warmers to prevent heat loss in a patient intra-op?

20-22 mL/kg/minute

Risk of heat loss can be reduced if the oxygen flow rate is calculated for the patient instead of being set arbitrarily high. Identify the appropriate O2 flow rate.

• Shivering increases O2 demand and prolongs recovery

• In humans, hypothermia delays wound healing

What affect does heat loss have on the post-operative patient?

98.5 °F

In a post-op patient, active body warming should be discontinued after rectal temperature reaches

Afterdrop (patient monitored for 1-2 hours after heat is discontinued)

Cold peripheral blood circulating back to core during the initial stages of rewarming from hypothermia

Myocardium

Cardiac muscle

Pericardium

Sheath covering the heart

Myocardial disease

80% of heart cases in cats are related to

Valvular disease

75% of heart cases in dogs are related to

Tachycardia, abnormal femoral pulses, murmurs, and arrhythmias

Identify common symptoms of heart disease

∙ Heart murmur and/or arrhythmia

∙ Weak, bounding or asynchronous femoral pulse

∙ Hypoxemia (cyanosis)

Identify early signs of heart disease found on physical exam

> 40 breath per minute

A patient with heart disease might be tachypneic with a resting respiratory rate of

Congestive heart failure (CHF)

Decreased cardiac output and tissue hypoxia cause poor venous return and fluid overload

Left-sided congestive heart failure

Decreased cardiac output results in pulmonary edema

∙ Dyspnea

∙ Tachypnea

∙ Cyanosis

∙ Crackles, wheezes, and decreased lung sounds on auscultation

Identify clinical signs of left-sided congestive heart failure

Right-sided congestive heart failure

Decreased cardiac output results in venous congestion in abdominal and thoracic cavities

∙ Edema

∙ Jugular distention

∙ Abdominal distention due to ascites

∙ Hepatomegaly

∙ Pleural and pericardial effusions

Identify clinical signs of right-sided congestive heart failure

∙ Reduce afterload using ACE inhibitors (Enalapril, Benazepril)

∙ Improve contractility using positive inotropes (Pimobendan)

∙ Treat volume overload using diuretics (Furosemide, Spironolactone)

• +/- Prevent blood clots

• Low Na diets, stress reduction, and exercise restriction

How is congestive heart failure treated?

Help relax veins and arteries to lower blood pressure

How do ACE inhibitors such as enalapril and benazepril help reduce afterload in CHF patients?

Sodium retains water so a low Na diet can help decrease volume overload

Why is a low sodium diet recommended for CHF patients?

Venous congestion

Right-sided heart failure leads to

Pulmonary edema

Left-sided heart failure leads to

Heart failure

Inadequate tissue perfusion in prolonged heart disease

∙ Tachypnea

∙ Syncope

∙ Weakness

∙ Prolonged CRT and pale MM

∙ Exercise intolerance in dogs

∙ Anorexia, depression, weight loss, or sudden death in cats

Identify clinical signs of heart failure

Exercise intolerance

Which signs of heart failure are specific to dogs?

Anorexia, depression, weight loss, or sudden death

Which signs of heart failure are specific to cats?

Cardiomyopathy

Disease of the heart muscle

Hypertrophic cardiomyopathy (HCM)

The most common cardiomyopathy in cats

∙ Thickened L ventricular wall → small ventricular lumen

∙ Decreased cardiac output

Hypertrophic cardiomyopathy (HCM) results in

Radiographs or echocardiogram

How is hypertrophic cardiomyopathy diagnosed?

∙ Diuretics

∙ ACE Inhibitors

∙ Beta blockers (anti-arrhythmic drug)

∙ +/- Anticoagulants to prevent saddle thrombus

How is hypertrophic cardiomyopathy treated?

Saddle thrombus

Painful, incurable condition where a clot is present in the bifurcation of the distal aorta

Extreme atrial and ventricular dilation leading to decreased contractility

Dilated cardiomyopathy (DCM) results in

Left side (especially seen in Boxers)

Which side of the heart is most often affected by dilated cardiomyopathy?

Radiographs, echocardiogram, and ECG

How is dilated cardiomyopathy diagnosed?

∙ Diuretics

∙ ACE Inhibitors

∙ Positive inotropes to help the heart contract better

How is dilated cardiomyopathy treated?

Feline hyperthyroidism

Ventricular hypertrophy in hypertrophic cardiomyopathy can be seen secondary to

Canine parvovirus infection

Dilated cardiomyopathy may be seen secondary to

Degenerative atrioventricular valve disease (primarily in dogs)

Thickening of tissue of the atrioventricular valve's leaflets or cusps

Mitral valve (left side of the heart)

60% of degenerative atrioventricular valve disease cases involve only the

Mitral and tricuspid valves

30% of degenerative atrioventricular valve disease cases affect

Tricuspid valve (right side of the heart)

10% of degenerative atrioventricular valve disease cases affect

Heart murmurs

Degenerative atrioventricular valve disease is associated with _____ on physical examination

Electrocardiagram

How is degenerative atrioventricular valve disease diagnosed?

∙ Diuretics

∙ ACE inhibitors

∙ Positive inotropes

∙ Antihypertensives

∙ Anti-arrhythmics

How is degenerative atrioventricular valve disease treated?

Antigen testing with 4Dx +/- enlarged pulmonary vessels

How is heartworm disease diagnosed in dogs?

∙ Positive heartworm antibody titer

∙ Basophilia and eosinophilia on CBC

∙ Enlarged pulmonary vessels on radiographs

∙ Echocardiography

How is heartworm disease diagnosed in cats?

∙ Adulticide therapy followed by 3-4 weeks of activity restriction + steroids

∙ Microfilaricide therapy

∙ Surgery in emergencies

How is heartworm disease treated in dogs?

Inflammatory response caused by heartworm increases risk of pulmonary thromboembolisms

Why is activity restriction necessary for a patient following heartworm disease treatment?

Treatment is dangerous and a HW+ cat has a poor prognosis

How is heartworm disease treated in cats?

Anaphylactic shock

The death of just one heartworm could trigger

Prevention

The key to treated heartworm disease is