SonoPath LLC. Enhancing Diagnostic Efficiency in Veterinary Medicine.
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Getting The Most Out Of Your Sonogram
Compiled in the spirit of diagnostic efficiency, the following suggestions are intended to be mutually beneficial
for clinical practitioners, staff, and patients.
Light Sedation:
Many patients, in addition to being unwell and suffering from various symptoms, feel nervous and irritable
when they are at a veterinary hospital. As clinical sonographers, we certainly do not want to aggravate their
experience further during an imaging session. Thus, in order to minimize stress and maximize diagnostic value,
it can be useful to administer light sedation, such as opioids (butorphanol or something similar), or another
preferred medication, so that practitioners can conduct detailed sonograms under more compliant and relaxed
circumstances. Below is a list of various protocols; some indicate light sedation and are applicable for cardiac
patients, and others suggest more significant sedation. A well-timed injection before the expected ultrasound is
ideal for “taking the edge off” and will not compromise the patient’s clinical status or the sonographer’s ability
to perceive localized pain on imaging, which itself can be a significant finding during a scan. This procedure
may also allow for the procurement of minor samples without requiring further sedation and will usually avoid
the need for additional personnel to help with restraining more difficult patients. Ultimately, light sedation can
make the visit more efficient and pleasurable for all. Moreover, if a patient is routinely difficult, the sedation
may have the added benefit of allowing one to perform procedures that are otherwise difficult to complete, such
as oral exams, ear exams, nail trims, and detailed physical examinations.
Certain sedatives are not appropriate prior to an echocardiogram or for patients with a comprised cardiovascular
status. Avoid Dexdomitor in dogs that are about to undergo an echocardiogram, as it will cause a depression in
contractility and heart rate, which will affect the interpretation of the exam. Ketamine should also be avoided in
cardiac patients. Inhalant anesthesia, such as isoflurane or sevoflurane, can be utilized in fractious cats if
butorphanol alone is not effective. Propofol should not be used in cases of suspected pericardial effusion or
hypovolemic patients.
Feline Sedation Protocols:
1. Butorphanol (0.1-0.4 mg/kg PO IV) usually provides adequate sedation for an abdominal or cardiac exam.
The typical dose is 0.1-0.2 mg/kg IV, which on its own provides mild sedation and is often sufficient in
compromised patients. Intramuscular dosing can be performed, but provides a lesser degree of sedation and
needs to be given 15-20 minutes before the exam.
2. Acepromazine (0.01-0.03 mg/kg IV or IM) and butorphanol (0.1-0.4 mg/kg IV or IM) or buprenorphine (20
ug/kg IM).
3. Midazolam (0.2-0.4 mg/kg) and buprenorphine (20 ug/kg IM).
4. Midazolam (0.2 mg/kg IV) and butorphanol (0.1-0.2 mg/kg IV).
5. Ketamine (2-4 mg/kg IV) and diazepam (0.2-0.3 mg/kg IV) or midazolam (0.3 mg/kg IV). This will result in
a more profound sedation than the other protocols. Do not use in cats with preexisting or suspected cardiac
disease or hypertrophic cardiomyopathy.
6. “Kitty Magic”: For a 5 kg cat, administer 0.2 ml Dexdomitor, 0.2 ml ketamine, and 0.2 ml buprenorphine IM
to achieve deep sedation; use 0.1 ml IM of each medication for light sedation. Do not use in cases of suspected
cardiac disease or when an echocardiography is required.
7. Propofol is given by IV injection. It will provide complete anesthesia, but is short-acting and can be followed
by a CRI, if needed, to maintain anesthesia. Alternatively, one can insert an endotracheal tube and administer
inhalant anesthesia. One typically resorts to the latter when trying to obtain an ultrasound-guided biopsy. If a
premedication is given, such as butorphanol or butorphanol/diazepam, then the induction dose is 4 mg/kg IV by
slow bolus. If used alone without premedication, the dose is increased to 6 mg/kg IV. The CRI dose is 0.6
mg/kg/min. Propofol is contraindicated in pericardial effusion or hypovolemic patients.
Canine Sedation Protocols:
1. Butorphanol is typically administered at 0.1-0.4 mg/kg IV; however, it can also be given at 0.4 mg/kg IM, but
will take longer to take effect. Used alone, it is often effective in compromised patients or those who require
minimal sedation. For more pronounced sedation, combine butorphanol with acepromazine, diazepam, or
midazolam.
2. Butorphanol (0.1-0.4 mg/kg IV) with acepromazine (0.01 mg/kg IV) or butorphanol (0.1-0.4 mg/kg IM) and
acepromazine (0.02 mg/kg IM).
3. Butorphanol (0.1-0.4 mg/kg IV) and diazepam (0.3 mg/kg IV) or butorphanol (01-0.4 mg/kg IV) and
midazolam (0.15 mg/kg IV).
4. Dexmedetomidine (Dexdomitor) (10 ug/kg IM). After the procedure has been completed, a reversal agent—
Antecedin (atipamezole) at an equal volume to injection—can be utilized to awaken the patient. Do not use
Dexdomitor when echocardiography is required or in compromised patients or when sampling the liver given
the venous congestion that occurs in the liver with this sedative. Doses of Dexdomitor depend on the degree of
sedation required, from mild to moderate to anesthetic plane. Heavy sedation is dosed based on body surface
area (per m2) at 125 ug/m2 and can be combined with an opioid, such as butorphanol (0.2-0.4 mg/kg), and
ketamine (2.5-4 mg/kg), and given IM or IV. Dexdomitor is administered at 375 ug/m2 to achieve a surgical
plane, but unless it is being used to conduct guided biopsies, one does not typically require that level of
anesthesia during ultrasonography.
5. Propofol by IV injection will provide anesthesia for a limited time. It can be administered as a CRI, if needed,
to maintain anesthesia, or an endotracheal tube can be placed and an inhalant anesthesia administered. The latter
is preferable when one is trying to obtain an ultrasound-guided biopsy. If a premedication is given, such as
butorphanol or butorphanol/diazepam, then the induction dose should be 4 mg/kg IV by slow bolus. If used
alone without premedication, the dose should be increased to 6 mg/kg IV. The CRI rate is 0.6 mg/kg/min.
Propofol is contraindicated in pericardial effusion or hypovolemic patients.
Clinical Cardiac Management:
The case management of chronic cardiac disease in dogs and cats will likely entail administering a combination
of cardiac medications (e.g. diuretics, ACE inhibitors, pimobendan, and others). Thus, it is necessary to submit
an initial chemistry panel and urinalysis to assess the safest drug protocol based on the patient’s current renal
function status. If the patient has been taking enalapril or benazepril with furosemide, rechecking BUN,
creatinine, and electrolytes is imperative for monitoring renal function. If the patient has concurrent renal
disease, monitoring the urine protein content is also important in managing concurrent cardiac and renal
disease. Both furosemide and enalapril/benazepril can result in prerenal azotemia; thus, BUN and creatinine
may not necessarily be elevated because of renal toxicity. The correlation of BUN and creatinine with urine
specific gravity is essential for differentiating prerenal from renal azotemia. It also important to note that the
concurrent administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is contraindicated for patients
who are already on ACE inhibitors and furosemide, as all of these classes of medication can lead to decreased
renal perfusion and therefore result in elevated BUN and creatinine and even azotemia.
Other Considerations:
Coughing: Coughing patients should have thoracic radiographs (including three views of the thorax to assess for
metastasis as well as soft tissue neck films when appropriate) before one performs an echocardiogram. An
echocardiogram will evaluate the left atrial size and indicate whether congestive heart failure may be present;
however, it will not fully identify pulmonary edema, a collapsing trachea, a bronchial pattern, or other
significant respiratory abnormalities, all of which may exist in coughing animals and require radiographic
assessment for detection. Although one will be able to visualize lung tumors in the immediate
echocardiographic window, tumors and other lesions in the periphery of the lung field will not likely be noted in
the echocardiogram, particularly in large animals. Lung lesions located adjacent to or within a few millimeters
of the thoracic wall may be evaluated by ultrasound if the sonographer knows where to concentrate efforts
outside the normal cardiac window; however, avoiding the ubiquitous lung air artifact can be challenging when
there is no direct target provided by the chest radiographs. If a typical “goose honk” cough is present in the
patient’s history, then inspiratory/expiratory radiographs of the cranial thorax will help rule in tracheal collapse.
Echocardiography is also beneficial for ruling in or out concurrent pulmonary hypertension.
Blood Pressure: A patient’s blood pressure (BP) should be taken prior to conducting all echocardiograms and
all abdominal ultrasounds in which hypertension may be a comorbid condition. Patients may become tense
during these procedures due to positioning, cystocentesis, fine needle aspiration (FNA), and other variables;
stress and nervousness may lead to spuriously high results. Thus, one should ideally take BP measurements in a
quiet area in the hospital, such as the surgical recovery area, in effort to avoid the “white coat” effect. The
identification of true hypertension may alter the medication recommendations one makes after an ultrasound
examination. Hypertension is a contraindication for renal biopsy and may also preclude conducting an FNA of
an adrenal tumor. Research has shown that the Doppler blood pressure method is the most accurate means of
measuring BP other than taking a direct arterial BP and should therefore be employed.
Platelet Count: Conducting a platelet count is necessary for invasive procedures, such as FNA and core
biopsy. Clotting profile machines measure prothrombin time (PT) and partial thromboplastin time (PTT) only.
In the absence of a platelet count, a manual estimation can be obtained from a well-prepared blood smear. The
latter should consist of a monolayer of red cells just touching each other and be counted using a high-power
field (100x) microscope. Platelets can be estimated as the average number seen per high-power field multiplied
by a factor of 15. For example, if over 10 fields one finds an average of 10 platelets per high-power field, the
estimate is 150,000 platelets/ul. A buccal mucosal bleeding time (BMBT) can be conducted, preferably without
sedation. The BMBT assesses platelet function only and will be abnormal in cases of severe thrombocytopenia,
platelet function disorders, and von Willebrand’s disease. It is best performed using a spring-loaded lancet that
standardizes the cut (i.e., a Surgicutt® bleeding time device). Normal values are those in which clotting occurs
in under 4 minutes. One disadvantage of this test is that the quality of the results is operator-dependent; thus, it
helps to have had experience executing this test in order to obtain accurate results. Platelet counts greater than
50-70,000/ul are essential for any sampling to be performed.
PT and PTT: A patient may have post-biopsy or post-FNA bleeding, even with normal clotting parameters and a
normal platelet count. Lack of tissue integrity may play a role in post-sampling hemorrhage, such as that found
with severe hepatic lipidosis, which can result in a friable consistency in the liver. In cases of presumed hepatic
lipidosis, it is safer to conduct an FNA than a core biopsy unless the latter is indicated because of a suspected
inflammatory change based on the pattern of liver enzyme elevations and CBC results, or if the cytology results
are inconclusive. Core biopsies are often necessary for making structural as opposed to cellular diagnoses.
Chemistry Panels: If increased bilirubin is reported in the blood work, one should confirm that the serum is
icteric. A hemolyzed sample may yield mildly elevated bilirubin levels in the absence of truly icteric serum.
Urine bilirubin levels will increase prior to serum bilirubin levels; therefore, the two should be correlated to
help distinguish between hemolysis and a true elevation in bilirubin. Note that 1+/2+ bilirubinuria can be a
normal finding in male dogs.
Barium: The presence of barium in the gastrointestinal tract may cause significant artifact. Thus, there should be
ample time—at least 24 hours, when practical and possible—between conducting barium studies and abdominal
ultrasounds. Barium studies are rarely recommended anymore, however, due to the fact that it has become quite
easy to rule in or out gastrointestinal obstruction based on sonographic criteria. There is still a role for barium in
certain cases that are not as straightforward, but we have found them to be few and far between.
Fasting: Ideally, all animals should have fasted for approximately 12 hours prior to an abdominal ultrasound,
with the exception of diabetic animals and young puppies or kittens. Water should not be omitted for
dehydrated animals and patients with renal disease or PU/PD. In fact, water in the stomach can actually provide
a better window into regional structures.
If the area of interest is the gastrointestinal tract (particularly the stomach and small intestine), fasting is
necessary since the presence of food in the stomach may hide gastric lesions, including tumors and foreign
bodies.
If the area of interest is the urinary bladder, the urinary bladder should contain some quantity of urine since a
very empty urinary bladder may mimic pathologic lesions. Wall thickness cannot be assessed with an empty or
nearly empty bladder. For example, some apparent thickening lesions or mass effects may disappear when the
bladder is distended with urine or saline. In male dogs, a urinary catheter may be placed easily in an awake,
non-sedated animal to fill the bladder with sterile saline. In female dogs and all cats, the placement of urinary
catheters generally requires sedation. Alternatively, in healthy animals, a low dose of Lasix may be employed to
cause diuresis and additional urinary bladder filling in animals that can tolerate it medically. Ideally, all patients
should have a full bladder at the time of the exam.
Vomiting and Regurgitation: Vomiting and regurgitating animals should have a lateral chest radiograph to
identify potential esophageal foreign bodies or megaesophagus. In some cases, it can be quite difficult to
distinguish regurgitation from vomiting, even when a veterinarian or veterinary staff member witnesses it
directly. An easy way to differentiate vomiting from regurgitation is to use a pH stick in the vomitus.
Hepatic Volume: The liver volume is best assessed on abdominal radiographs but experienced sonographers can
give subjective assessment on liver size based on the sonogram. The sonographer can subjectively assess
diaphragmatic angles and caudal hepatic contour as well as gastric and pyloric displacement, all of which are
supportive parameters for hepatomegaly or microhepatica; however, radiographs still provide the best global
assessment of hepatic size.
Owner Preparation for the Sonogram: It can be challenging when the sonographer finds a lesion that
necessitates sampling and the animal’s owner is unavailable for consultation at a crucial moment in the
diagnostic process. Diagnostic efficiency often depends on collecting samples early on during the workup and
minimizing excessive delay when making treatment decisions. Therefore, preparing the owner for the potential
need for sampling (FNA, biopsy, drainage, or other ancillary procedures) prior to conducting the sonogram and
obtaining preauthorization will not only save time, but also allow the sonographer to sample under timesensitive conditions and arrive at more accurate diagnoses.
In some cases, it is prudent to discuss the possible need for bicavity examination with the owner in advance. In
certain situations, the sonographer may discover a finding that would suggest the need for a bicavity
examination. For example, a dog with ascites may need an echocardiogram if there appears to be elevated
pressures on the right side due to the appearance of distended hepatic vasculature, or a cat with embolic disease
may need an abdominal scan if the heart is normal and one wants to evaluate the abdomen for other causative
conditions, such as neoplasia. Preemptive discussions will save time and possibly money if one has permission
to perform the necessary exams in one visit as opposed to needing to wait for a follow-up appointment, which
not only hampers diagnostic efficiency, but also may cause more inconvenience to the owner and increase his or
her expenses.
Value of a Negative Sonogram:
One of the chief values of an abdominal ultrasound is the opportunity it provides to evaluate multiple organ
systems simultaneously. When working up a case, a practitioner generates a problem list and crosschecks it with
a corresponding list of differential diagnoses. One can then rule in or out various disease processes, which helps
narrow down possible etiologies. The practitioner uses blood work, radiographs, and an abdominal ultrasound,
in conjunction with the results of a detailed patient history and physical exam, to systematically evaluate for
numerous diseases.
The abdominal ultrasound often plays a key role in the workup of an internal medicine case. It is crucial to note
that a negative sonogram provides equally important information as a positive one, as the ruling out of disease
is critical to the process of narrowing down differentials. As such, it is imperative that practitioners convey the
value of a negative sonogram to the owners prior to an exam.
The diagnostic workup of a patient will often be directed by test results, including the information gained from
a negative sonogram. If systemic disease and neoplasia is not found to be causal, for example, then other
systems can be assessed. For instance, in cases of severe weight loss in which the blood work is normal,
thoracic radiographs and abdominal ultrasound are unremarkable, and there is no evidence of protein-losing
nephropathy or enteropathy, then a neurological exam should be performed meticulously, especially in a
geriatric patient, as a primary central nervous system disease can result in significant weight loss. Therefore,
even in the absence of an obvious disease, the subsequent diagnostic steps can often be identified, allowing the
consultant or practioners to generate a diagnostic plan.
References:
Ko J. Dexmedetomidine and its injectable anesthetic-pain management combinations. Proceedings from
the Atlantic Coast Veterinary Conference, Atlantic City, NJ, October 12-15, 2009.
Murrell J. Sedation protocols in cats. Proceedings from the British Small Animal Veterinary Congress,
Birmingham, England, April 12-15, 2007.
Plumb DC. Veterinary Drug Handbook, 4th Ed. Ames, IA: Blackwell Publishing Professional; 2002.
Shaffran N. Sedation, anesthesia and pain management protocols for routine surgeries. Proceedings from
the World Small Animal Veterinary Association Congress, Auckland, NZ, March 6-9, 2013.