Human patients’ blood pressure is routinely measured during medical exams and surgical procedures. In the veterinary world, however, blood pressure is monitored in fewer than half of all patients under anesthesia and less often during clinical exams, according to estimates.
The disparity traditionally has been linked to the equipment and its cost.
“The veterinary profession has been plagued by inconsistent veterinary-specific monitoring equipment, which has made many practitioners gun-shy about incurring substantial equipment related expense,” says Robert Stein, DVM, Dipl. AAPM, executive director of the Veterinary Anesthesia and Analgesia Support Group.
“Many veterinarians are frustrated by a piece of equipment purchased at a great price, often at a convention after hearing an energetic rep sing the monitor’s praises, only to have it become the most expensive door stop in the building.”
Those days are changing. Manufacturers report that veterinarians are showing an elevated interest in veterinary blood pressure devices as the technology advances and the supporting evidence comes to light.
Dr. Stein was an early believer in monitoring the blood pressure of every anesthetized patient. He started using the Dinamap 1846SX, a human monitor available on the secondary market, in 1995.
“You learn the feel of the equipment, its nuances, how to obtain the best, most consistent and believable values,” Stein says. “When we added Doppler, we were initially frustrated by the time spent trying to place the probe. Doppler wasn’t consistently used until I spent time on the University of Florida’s anesthesia and analgesia service in 2006. It was a ‘duh’ moment when I realized that it really wasn’t all that hard, it was just that we were making it hard.”
Gerald F. Maass, president and chief operating officer of CardioCommand Inc. in Tampa, Fla., acknowledges some veterinarians’ reluctance to use BP equipment, saying pets don’t sit calmly and extend their arm. The idea of checking blood pressure in veterinary medicine seemed unnecessary until hypertension became a growing concern, he says.
“Hypertension is diagnosed as a primary disease in human medicine, but in the veterinary world, it is argued that the disease is secondary to other diseases,” Maass notes. “Whether hypertension is a symptom or a cause of illness in animals, something needs to be done to detect and treat it in dogs and cats.”
Knowing how to obtain an accurate BP measurement and using reliable equipment is essential to treating hypertension, says Larry Tilley, DVM, Dipl. ACVIM (cardiology).
“When BP is greater than 180 on repeated measurements in senior animals or an animal with chronic kidney, adrenal or thyroid disease, an animal should be treated for hypertension,” says Dr. Tilley, who has written numerous veterinary references and textbook chapters on hypertension. “If BP is greater than 160 with evidence of ocular or neurologic signs, hypertension treatment is necessary. Most hypertensive emergencies have a BP of 180 to 200.”
Manufacturers are aware of practitioner frustrations and say they are working to improve their offerings.
“The white-coat theory affects pets,” says Paul Ulbrich, CEO of Vmed Technology in Mill Creek, Wash. “Owners holding them helps, but with some animals the whole veterinary office experience can alter their BP. The sheer difficulty in acquiring an accurate reading is a deterrent to vets. BP monitoring today is more accurate than ever before.”
Vmed sponsors veterinary conference wet labs to teach techniques for obtaining the most accurate readings.
Advances in diagnostic BP measurement include the automatic averaging of readings, says Andrew Schultz Jr., director of monitoring and critical care at Midmark Animal Health in Versailles, Ohio.
“Unlike the single spot-check reading we get with our doctors, research suggests that the most accurate diagnostic readings with indirect devices are achieved by taking five to seven sequential readings,” Schultz says. “Discard outliers and use the average of the others as the diagnostic measurement.”
While collecting a BP reading on a conscious animal is a preventive tool, monitoring BP during surgery may mean preventing an emergency.
“About 20 to 50 percent of veterinarians have BP monitors available in the anesthetic arena, but only a portion of those practices are likely using their monitor consistently enough to know how believable the BP readings are,” Stein says.
“The real eye opener is the number of practices that I see who have no willingness to manage hypotension. It isn’t hard or expensive to add additional analgesic to allow for a reduction in anesthetic gas levels, or add an inotrope or colloid to increase cardiac output or vascular volume.
“Many practitioners are starting to talk the talk about BP monitoring, but some are unwilling or undereducated about how to walk the BP management walk.”
Stein says too many veterinarians are intimidated by the equipment and the difficulty associated with BP interpretation.
“Some simply have their heads in the sand on this issue,” Stein says. “In the outpatient arena, effective BP management can reduce retinal hemorrhage, excessive renal protein loss and the adverse effect of hypertension at the glomerular level.”
Hypotension can’t be ignored, either.
“It can contribute to undetected renal functional loss that may not be evident to the practitioner or client for many years and may only manifest as a shortened life span,” Stein says.
Blood pressure monitoring is by far the most useful clinical tool to assess tissue perfusion in anesthetized animals, says Jeff Ko, DVM, MS, Dipl. ACVA, a professor of anesthesia at Purdue University in West Lafayette, Ind.
“Without a reliable blood pressure monitor, it is difficult to [check] tissue perfusion and cardiovascular function in the anesthetized patient,” Dr. Ko says.
As the standard of care increases for pets, the use of blood pressure monitors as part of anesthesia becomes essential, he notes.
“Blood pressure should be checked when a patient is under sedation or general anesthesia,” Ko says. “Awake patients also need to be checked routinely during the regular physical exam. However, very few blood pressure monitors are reliable for measuring awake patients. This is mainly due to motion and artifacts that affect the monitoring ability.”
Daniel Kozisek, customer service director at Bionet America Inc. in Tustin, Calif., says BP monitoring is a staple in equine practice, especially when operating on high-risk patients.
“An anesthetized patient’s BP will change before other parameters,” Kozisek says. “A change in BP allows vets to detect a problem earlier.”
The most important development in BP technology, Schultz says, is that oscillometric monitoring is being offered in multiparameter formats for use in areas f the hospital that require monitoring of vital signs like ecg, SPO2, CO2 and temperature.
“Though the same monitors used successfully on unconscious and sedated patients are used successfully in practice to obtain readings on awake patients, studies validating and supporting use on awake patients are nearly impossible,” Schultz says. “To do so would mean comparing the readings simultaneously to direct arterial measurement via catheterized artery.”
Board-certified practitioners like Stein have their preferred brands but recognize the accuracy improvement in many BP devices.
Indirect BP monitors are not perfect, Stein says, but “They help establish a feel for where the patient is and help you see trends as they unfold.
“It is becoming more common to perform direct BP monitoring in the primary care setting.”
Experts suggest assigning one technician to do blood pressure monitoring.
“This technician will become an expert in positioning the animal and reading results because he or she will be performing so many readings,” Tilley says. “One technician performing the BPs also means more accurate results.”
Manufacturers of BP machines say some practicing veterinarians haven’t learned to perform a proper BP check and haven’t discovered its preventive benefits.
“We’re hoping for a shift in the way veterinarians view BP measuring,” Kozisek says. “If they don’t know the value in monitoring BP, they’re not going to use it.”
Cuff size and patient positioning need to be correct to get an accurate reading, experts say. Uncooperative patients help prove the need for greater veterinary-specific BP technology.
“Companies are starting to cater more to the veterinary industry,” Kozisek says. “SunTech makes monitoring devices that underwent independent university testing for accuracy. Part of an accurate reading is the technology and part is the skill behind the person performing the reading. A quiet room is vital for an accurate cat measurement, even more than what’s needed for a dog.”
Veterinarians often want to know when they will see a return on their investment.
“Veterinarians can charge as a line-item for exam room BPs or list it on a bill as one of the services provided during a visit,” Kozisek says. “Monitoring charges are part of any anesthesia protocol. Veterinarians can charge for BP measuring separate or adjust fees accordingly to cover the service. A $3,000 piece of equipment could pay for itself in a matter of months.”
The difficulty in acquiring an animal BP measurement lends itself to a service charge, CardioCommand’s Maass says.
“Most veterinarians using BP monitoring during surgery or in the clinic charge,” Maass says. “It could be that some veterinarians didn’t consider BP monitoring as a revenue source, considering the service is included in human exam fees.
Types of Monitoring
With Doppler BP, meters detect blood flow as a change in the frequency of reflected sound (Doppler shift) due to the motion of underlying red blood cells. Blood pressure is read by the operator using an aneroid manometer connected to the occluding cuff placed proximal to the Doppler transducer
- Often a faster method of detecting BP.
- A reliable systolic measurement in small animals with high heart rates like cats.
- More labor intensive because the patient’s hair must be clipped on the inside of the elbow.
- Diastolic values are difficult to obtain.
- Operator dependent
Oscillometric BP detects fluctuations produced in the occluding cuff. Machines using this technique generally determine systolic, diastolic and mean arterial pressures as well as pulse rate.
- Good for use in surgery and on dogs.
- Automated measurement of systolic, diastolic and mean BP.
- Requires less restraint.
- No shaving necessary.
- Not good for use in awake cats.
- Accurate measurements may take longer if the animal moves.
Photoplethysmograph measures arterial volume by attenuation of infrared radiation and is designed for use on the human finger.
- Can be used on cats and small dogs weighing less than 10 kilograms.
Intra-arterial uses an arterial catheter to measure pre- and post-heart BP.
- Provides real-time BP.
- Provides real-time BP.
- Is invasive.