Veterinarians in all types of clinical practice see emergency patients. After initial airway, breathing, and circulation problems are addressed, more information is needed to help treat and diagnose the patient. A more detailed secondary examination and diagnostics such as blood analysis, urinalysis, and imaging studies should be performed after initial stabilization. A starting point for blood analysis includes blood glucose, packed cell volume, blood urea nitrogen, electrolytes, and blood gases. In addition, urine specific gravity and a blood smear will help determine an initial plan of treatment. Needless to say, in emergency situations the veterinarian and patient both benefit from quickly obtained blood analyses.
The use of an i-STAT (Heska, www.heska.com) handheld clinical analyzer allows the clinician to quickly and easily assess initial emergency blood analyses. This battery-operated analyzer uses self-contained disposable cartridges and requires only 0.05 ml of whole blood. Results are available in 2 minutes. Since the machine contains no electrodes, no maintenance is required and calibration is performed automatically at regular intervals.
Heska offers 11 separate cartridges for the analyzer-they vary from a single test (ie, glucose, creatinine, activated clotting time, cardiac troponin) to cartridges that yield 13 results (see Table). The results are both measured directly and calculated from measured results.
The i-STAT cartridges can be used 3 ways: for diagnosis/treatment, to determine prognosis, and for ongoing monitoring.
Diagnosis & Treatment
Results obtained provide information that permits the clinician to set up a treatment plan and give direction to owners about next steps. The cartridges that test glucose, electrolytes, blood urea nitrogen, creatinine, and acid-base status are most helpful. In addition, testing for activated clotting time will assist with the diagnosis of anticoagulant rodenticide poisoning.
The choice of which crystalloid fluids to administer is based on electrolyte and acid-base status. Blood gas analysis from an arterial sample will provide information about lung function and overall acid-base balance. Venous blood samples can indicate the acid-base status of the animal but will not provide much information about oxygenation.
The cartridges that test lactate, pH, and cardiac troponin I are the most valuable for determining prognosis.1,2 Lactate levels can provide information about oxygen delivery, oxygen demand of the tissues, and inadequate oxygen utilization within the tissues. Cardiac troponin I shows promise as a prognostic indicator for heart disease, but guidelines are not set.
These measures can be used to guide discussions with owners, but clinicians should be careful to avoid relying on single blood values to determine the whole picture. Trends of change are as important as an individual result. Frequent checking to see if the values are going in the right direction will provide more information about prognosis than a single individual test. Similarly, any blood result needs to be evaluated as part of the big picture clinically: if the results do not align with the clinical picture, repeat the test or reconsider the underlying assumptions about the disease and its treatment.
Frequent, ongoing monitoring is indicated in most hospitalized patients and patients that are not behaving as would be expected after starting treatment. Patients that benefit from frequent monitoring and adjustment of treatment based on results include those with metabolic disorders (diabetes, diabetic ketoacidosis, acute vomiting or diarrhea, Addison's disease, eclampsia, hypernatremia), those receiving anesthesia (and are hypopneic or hyperkalemic), and critical care patients. Using the same machine to monitor changes is important for consistency and better care of your patient.
The i-STAT has many advantages that can make practice easier. It is especially useful when results are needed rapidly and/or the ability to have blood analyzed by a standard laboratory is not readily available. For an initial diagnostic panel, the cost is reasonable, and the device can help the clinician direct treatment. The device also helps make ongoing monitoring of patients easier and more affordable.
The variety of cartridges allows clinicians to pick the tests they need. The small sample of blood required makes the device a good choice for puppies and kittens. In addition, blood gas analysis can be done immediately after the blood draw, without the need for icing the sample.
The i-STAT handheld analyzer has been tested against standard laboratory machines in both veterinary and human medicine studies and has correlated favorably.3,4
It can take some time for the staff to learn how to use the machine and cartridges. If the clinician is unsure of how the cartridges will be used, the cost of the cartridges can seem high. No cartridges are available for evaluating hepatic function, phosphorus, or proteins.
Depending on the i-STAT results, a complete blood panel may be needed, an additional step that increases the cost of blood analysis and means that the veterinarian will still need a laboratory that can do full blood panels, either in-house or off-site. In addition, knowledge of the value of lactate and cardiac troponin I levels is still evolving-what do these measures really tell us, and how should they be used to help patients and their owners?
The handheld analyzer costs $3500 to $5000. Cartridges cost from $5.50 to $20 each, and come in boxes of 5, 10, or 25 (depending on the type of cartridge). Newer cartridges are not compatible with older versions of the machine. Technician time to operate the machine is minimal once the proper technique is mastered. Cartridge errors increase cost because the cartridges cannot be reused. The cost to the client can be mitigated by improved patient care and quicker recovery time.
i-STAT HANDHELD CHEMICAL ANALYZER • Luke Rump
1. Plasma lactate concentration as a predictor of gastric necrosis and survival among dogs with gastric dilatation-volvulus: 102 cases (1995-1998). de Papp E, Drobatz KJ, Hughes D. JAVMA 215:49-52, 1999.
2. Serum concentrations of cardiac troponin I and cardiac troponin T in dogs with class IV congestive heart failure due to mitral valve disease. Linklater AKJ, Lichtenberger MK, Thamm DH, et al. J Vet Emerg Crit Care 17:243-249, 2007.
3. Use of a handheld device for analysis of blood electrolyte concentrations and blood gas partial pressures in dogs and horses. Looney AL, Ludders J, Erb HN, et al. JAVMA 213:526-530, 1998.
4. Evaluation of a portable clinical analyzer in a veterinary hospital setting. Grosenbaugh DA, Gadawski JE, Muir WW. JAVMA 213:691-694, 1998.
Evaluation of a portable clinical analyzer in a veterinary hospital setting. Grosenbaugh DA, Gadawski JE, Muir WW. JAVMA 213:691-694: 1998.