Boxers seem to be sensitive to acepromazine (boxer-ace syndrome) (Hall et al. 2001). Its administration might cause hypotension and fainting in that breed. The presence of a higher vagal tone and slower heart rate in the breed is believed to be the cause of this syndrome. The drug has to be used with caution in boxers, and its administration must be followed by a very close monitoring of the blood pressure. Anticholinergics such as atropine and intravenous fluids need to be available.
Miniature Schnauzers may develop sick sinus syndrome. The abnormal cardiac rhythm may worsen with anesthesia, leading to decreased cardiac output potentially severe enough to cause a cardiovascular collapse. A preanesthetic electrocardiogram (ECG) may be indicated if the patient has a questionable history (Seymour and Duke-Novakovski 2007).
Doberman Pinschers can develop von Willebrand’s disease, a coagulation disorder. Any carrier of the disease should ideally be identified prior to any surgical procedure with a bleeding potential. Preferably, von Willebrand’s factor can be checked or a buccal mucosal bleeding time (BMBT) can be assessed before surgery (Seymour and Duke-Novakovski 2007).
Different genders bring different considerations. A female patient might be pregnant, and physiological as well as pharmacological characteristics in both the mother and fetus will have to be considered.
Immature (neonate or pediatric) patients have undeveloped organ function and have specialized needs. For instance, their small body mass will make them very prone to hypothermia, and temperature support should be maintained throughout the anesthesia and into the postoperative period. Hypoglycemia is another complication observed in neonates because they have a higher metabolic rate than do adult patients. A mature (geriatric) patient is more prone to age-related changes in organ function. These changes are progressive and unalterable.
The behavior of the animal can impact the choice of drugs dramatically. This is a subjective evaluation. The animal should be observed with and without the owner. Some owners might make their animal more nervous; others might be very useful in helping to keep the patient calm during the initial exam as well as answering any questions related to patient history.
The choice of drug and dose for anesthesia sedation, tranquilization, or immobilization is largely dependent on the temperament of the species/breed. Catecholamines (hormones from the adrenal glands) are increased in stressed patients. This can cause arrhythmias, hypotension, and even cardiac arrest.
The existence of a preexisting condition may require additional diagnostics. A patient with a history of increased thirst and urination may indicate a renal or endocrine disorder, and organ function will have to be investigated because behavioral problems could also cause similar symptoms. Excessive fatigue might be the sign of a cardiopulmonary disease or might result from arthritis or other conditions and should be checked. In ferrets, a loss of fur may indicate a change in hormones, which could be due to a recent ovariohysterectomy or could indicate adrenal associated endocrinopathy (AAE).
It is important in all cases that pertinent information is obtained. The following questions can be asked routinely of all clients (Alef et al. 2007):
Good knowledge of the patient’s current medication and the possible interaction with commonly used anesthesia drugs will help influence decisions made when planning the anesthetic protocol. This includes choice of drugs as well as route of administration (oral versus injectable).
Minimize oral intake of medication during the fasting period and change to injectable, if possible. If there is concurrent drug use, take precaution. Organ system function should be evaluated via diagnostic testing.
The aminoglycocides (gentamycin) can be nephrotoxic and might also interfere with normal neuromuscular function. Check renal function before using such ABs and ensure good kidney perfusion through fluid therapy and arterial blood pressure monitoring during the procedure. Avoid using aminoglycocides if neuromuscular blockade is necessary.
Nonsteroidal antiinflammatory drugs (NSAIDs). NSAIDs (meloxicam, carprofen, deracoxib) are analgesics that inhibit prostaglandin formation in the inflammatory pathway. Side effects from the use of NSAIDs come from the fact that some prostaglandins are also important in renal, clotting, GI, and liver function. Monitor blood pressure closely, provide fluids, and evaluate chemistry serum profiling prior to anesthesia.
Adjunctive analgesic drugs (AADs). These drugs have varying pharmocodynamic interactions when used with traditional analgesics (opioids, NSAIDs, local anesthetics). The effects will involve some of the same receptors and could potentiate or enhance analgesic action, whether a patient is in acute or chronic pain. Choose the anesthetic regime carefully if a patient is currently on one of the AADs (oral, injectable, or topical) because organ function may already be compromised (liver, kidney, heart, and so forth).
The anesthetist should be familiar with the physiological effect, as well as the pharmacology, of each of these drugs (positive inotropes, vasodilators, beta-2 blockers) because they will alter the CV function, such as the heart rate, blood pressure, stroke volume, and overall cardiac output.
A sympathomimetic agent, which releases norepinephrine by stimulation of both the alpha and beta-adrenergic receptors, phenylpropanolamine HCL is used primarily to treat incontinence. Patients treated with this drug are prone to vasoconstriction, increased heart rate and blood flow, increased blood pressure, and mild CNS stimulation. Be cautious when adding drugs in the anesthesia regime that may potentiate these effects (α2 agonists, anticholinergics, positive inotropes, and so forth).
It is important to evaluate the possible pharmacokinetic/pharmacodynamics (PK/PD) interaction of each drug individually with commonly used anesthesia agents as well as the pharmacologic effects on each patient. Cancer patients might have various systemic disorders, and caution is necessary when designing an anesthetic protocol.
Phenobarbital is a barbiturate drug used to control seizures. This drug might potentiate the effect of some anesthetic agents, and dosage needs to be modified accordingly. Any drugs that might potentiate seizure activity will have to be avoided. Attempt to eliminate any factor that might trigger a seizure (stress, pain, and so forth).
These are insecticides used to treat endo/ectoparasites. They inhibit plasma cholinesterases and might prolong activity of certain local anesthetics and potentiate neuromuscular blocking drugs (atricurium, pancuronium).
Diabetic patients have special needs during anesthesia. A modified fasting protocol, as well as frequent monitoring of blood glucose, should be part of the anesthesia plan for these patients.
A preanesthetic physical exam is required for every patient. Be consistent in the approach. This may be a head-to-tail or a body systems approach. All the systems are interesting to the anesthetist, but the cardiovascular, respiratory, renal, and hepatic are most important. Recognizing abnormal changes of the body systems during a physical exam will be difficult unless you are familiar with normal physiological vital signs of individual species and breeds (Ettinger and Feldman 2006).
When evaluating the cardiovascular system during physical examination, look for signs of adequate tissue perfusion (Perkowski 2000). The capillary refill time (CRT) indicates adequacy of perfusion but is not the most accurate method because many things can affect it. Blood pressure monitoring is more ideal. By looking and touching the mucous membranes, a patient is assessed for hydration; normal is moist and pink.
Auscultate heart sounds while trying to identify abnormal sounds (murmurs) and palpate peripheral pulses. The heart rate should be auscultated while palpating the pulse and these should match, one heart beat for every pulse. Below are common pulse locations on the dog and cat:
- DOG Femoral, tibial, dorsopedal, palmar digital, lingual, caudal arteries
- CAT Femoral, tibial, dorsopedal, caudal
Pulse pressure (PP) is the difference between systolic arterial pressure (SAP) and diastolic arterial pressure (DAP). A strong pulse equals a large PP; a weak pulse equals a small PP. Pulse quality may be similar for two different blood pressure measurements. The pulse will feel the same; however, the tonicity of the artery will be different (vasoconstricted, vasodilated, and so forth).
Cardiovascular disease should be controlled prior to anesthesia. A diagnosis should be made and a further workup may be indicated to assess the risk associated with anesthesia. Tools used to diagnose cardiovascular disturbances include auscultation (murmurs and arrhythmias), complete blood count (anemia and thrombocytopenia), diagnostic imaging (ultrasound and radiography). ECG is a measurement of electrical function of the heart. This test should be performed if there is a notion of an arrhythmia or a disease potentially causing electrical changes in the heart. Situations that might trigger arrhythmias would be trauma, pain, electrolyte alterations, catecholamine release, hypoxemia, hypercapnia, certain anesthetics, and myocardial disease.
Cardiac murmurs are classified on a scale of 1–6. A murmur intensity greater than 3/6 may warrant a workup, which would involve measurement of the valve function through cardiac ultrasound, echocardiogram, or possibly radiography (if ultrasound or echo is not available).
Any patient with cardiovascular disease should be identified, treated if necessary, and monitored constantly. Intravenous fluid therapy will be unique to each patient dependent on the type and severity of disease. The heart is the “fluid pump.” If the pump does not function well, it will not pump fluid around the body as it should, and it may not be able to process additional fluid efficiently. Fluid volume as well as type should be carefully administered.
Dehydration and hypovolemia should ideally be treated prior to anesthesia. Both might reduce tissue perfusion and ultimately reduce drug clearance. REHYDRATE anesthesia patients prior to anesthesia.
The main function of the respiratory system is to allow gas exchange (oxygenation and CO2 elimination). The respiratory system is composed of an upper and lower tract. The upper part of the tract consists of the nasal cavity, pharynx, larynx, and trachea. Symptoms of diseases associated with the upper respiratory tract may include sneezing or snorting. There may be facial swelling or rubbing, nasal discharge, and/or dyspnea (difficulty breathing). Parts of the lower tract include bronchi, bronchioles, and alveoli. Open mouth breathing, tachypnea, dyspnea, or orthopnea (difficulty breathing unless sitting or standing up), as well as cyanosis, tachycardia, and collapse, can be symptoms of lower respiratory tract disease. If these symptoms are found on exam, there is potential for a decreased ability for the lungs to exchange CO2 for oxygen at the level of the alveoli. If patients are severely dyspneic during physical examination, oxygen therapy can be beneficial as long as it does not stress the patient.
Normal function of the respiratory system is examined through auscultation of all lung fields as well as observing the quality (depth and rhythm) and rate of ventilation. Wheezes, crackles, and stridor sounds heard with or without a stethoscope are problematic and can reveal respiratory tract disease. Moist, pink mucous membranes (MM) with a CRT of <2 seconds indicate adequate oxygenation/perfusion. Pale MM can be an indication of hypotension, hypothermia, hypoxemia, vasoconstriction (from α2 agonists), and low packed cell volume. A red brick coloring can point to venodilation, blood sludging, hypercarbia, or endotoxemia.
Arterial blood gases, which include oxygen arterial tension (PaO2) and carbon dioxide arterial tension (PaCO2), can be beneficial in determining the oxygen CO2 exchange. Radiography and/or ultrasound can also be helpful in recognizing abnormalities within the thorax. It is important to remember that pain, stress, discomfort, and central nervous system depression (CNS) can alter the function of the respiratory system and should be considered if there are abnormalities noted. Almost all anesthetics are respiratory depressants; therefore, a patient with a respiratory disorder may need ventilation support during the anesthetic period.
Palpation of the kidneys should be performed for size and symmetry. Record history and clinical findings such as polyuria/polydipsia (PU/PD) or vomiting and lethargy. Owners may recognize a strange smell to either the patient’s breath or urine. Renal serum chemistry, urine specific gravity (USG), and full urinalysis will help diagnose renal disorders. An azotemic or uremic (retaining nitrogenous wastes in blood can indicate poor kidney function) patient is more sensitive to anesthetics and must be stabilized prior to anesthesia. A postrenal azotemia is severe in nature and usually associated with a urethral obstruction (blocked cat). Decreased renal perfusion under anesthesia may worsen preexisting disease. In chronic renal failure, there is a multisystemic compromise (anemia, hypertension) on top of renal dysfunction. Maintenance of adequate perfusion is essential.
Fluids may be required to stabilize the patient prior to anesthetic drug administration. Also, metabolism and excretion of anesthetics may be prolonged; therefore, use drugs that are eliminated quickly (e.g., Propofol) as well as lower dosages.
A thorough evaluation of the hepatic system is essential because it determines how well the patient can metabolize and excrete anesthetic drugs. On physical exam, record history of lethargy, jaundice (hyperbilirubinemia), increased thirst, or dark-colored urine. In certain patients, the abdomen may appear enlarged. Hepatic diseases that may affect function include infection, toxicity, portosystemic shunts (PSS), overdose of medication, cancer, and hereditary disease. Progressed disease may lead to seizure, coma, and death.
Plasma proteins, alkaline phosphatase (ALK Phos), and alanine aminotransferase (ALT) are diagnostic tests that will help identify the severity of disease. Animals with PSS will often have increased bilirubin, bile acids, white blood cell count, and clotting times as well. It is common with the PSS or patients with hepatic disease to see decreased blood glucose, albumin, total plasma proteins, and packed cell volume as well. Diagnostic imaging (DI) can be useful to diagnose obvious abnormalities. Anesthesia may be required to take fine needle aspirates (FNAs) of the liver for tissue sampling during ultrasound examination.
Many anesthetics will have prolonged action in patients with hepatic disease. Highly protein bound drugs with prolonged metabolism (thiobarbiturates, benzodiazepines) should be used cautiously in liver dysfunction patients. If there is profound CNS depression as well as lethargy, dosages can be decreased dramatically. Use short-acting/metabolizing anesthetic drugs for which recovery does not rely heavily on liver metabolism (e.g., propofol, inhalants).
The nervous system plays an essential role in anesthesia management. If there is an indication of a disorder, such as head trauma or paralysis, a full neurologic exam must be performed. Some diagnostic testing available for neurology may require general anesthesia (EEG, computed tomography or CAT Scan, MRI); therefore, plan the anesthesia regime accordingly.
Evaluate the mental status of each patient because all anesthetics will cause some degree of CNS depression; drug requirement may be decreased if there is evidence of such depression. Some nervous system disorders may require respiratory support (cervical spinal injuries interfering with the phrenic nerve will alter normal diaphragm movement). Intracranial trauma or lesions will require close monitoring of CO2, which, when elevated, can cause intracranial pressure to increase. Neuromuscular blocking drugs, dissociative agents, some antibiotics, and local anesthetic techniques may be contraindicated in certain neuropathies.
Gastrointestinal system (GI)
A thorough history from the owner is vital when evaluating the GI system. Diet, behavior, and duration and consistency of vomiting ± diarrhea should be noted. Electrolytes will be altered with any substantial losses—particularly a decrease in potassium. Evaluate hydration status on physical exam. Abnormalities, such as tumors and foreign bodies can be detected during abdominal palpation. A full CBC and chemistry profile including electrolytes should be evaluated. Diagnostic imaging can be beneficial for further assessment of the GI organs. Pain management is an important part of the protocol because many GI abnormalities that require anesthesia are likely to be painful. There may be the potential of a reduction in venous return due to the distension of abdominal organs. Measurement of arterial blood pressure is essential as well as ventilation; abdominal pressure may increase pressure to the thoracic cavity causing hypoventilation.
Common abnormalities found on the skin include ectoparasites, infection or abscess, masses or swelling, petechiation or bruising (can be an indication of a clotting problem), alopecia (may be endocrine dysfunction), and fungus. Skin scrapings/slides can be prepared to help identify certain fungi, parasites, and bacteria; histological examination of abnormal cells can indicate types of cancer (melanoma, sarcoma). It is important to identify the cause of the abnormality, although identification may not alter anesthetic protocol. The approach to disinfection may be altered. Sterile saline may be used in place of rubbing alcohol, intravenous catheters should be placed in nondiseased skin (if possible), and local anesthetic techniques may be contraindicated (epidural, infiltrative line block, and so forth). The use of gloves can be beneficial to both you and the patient.
Endocrine system (ES)
Suspicion of endocrine disease should be investigated with a full physical exam as well as CBC, chemistry (including BG and electrolytes), urinalysis, ECG, radiographs, and ultrasound. The endocrine system influences many of the body systems as a whole, and management of a patient with an ES disorder is multifactorial. Any metabolic disturbance should be corrected or stabilized prior to anesthesia. Diseases of this system may include one or more of the following: diabetes mellitus, insulinoma, Cushing’s disease, Addison’s disease, thyroid disorder (hypo/hyperthyroidism), hypo/hyperadrenocortism, adrenal-associated endocrinopathy (ferrets), and hypo/hyperglycemia.
Overall body condition
Evaluate overall body condition. This includes body weight, temperature, age, gender, and possibility of pregnancy. It also includes hydration status and pain assessment.
A dehydrated patient must be stabilized prior to anesthesia as this can increase drug uptake, metabolism, and clearance. Hypovolemia can affect cardiovascular function. Use skin turgor, eyeball position, moisture of mucous membranes, the simple lab tests, packed cell volume, total solids, and azo stick to determine hydration status. Body temperature can indicate disease and/or stress. Overall body condition can be altered by age. Although age is not a disease, the risk status increases as certain disease processes are expected in older patients.