Monitoring and Critical Care

General Veterinary Monitoring Questions

How long is battery life? 
About four to five hours depending on use (100 readings at one reading per minute). Then it can be recharged just by plugging it in to a 110 or 220 watt outlet. Charge time is about four hours.

Can I try one for a week to see if it really gets blood pressure readings? 
Demo models are available, and you can check with your local distributor to see if they have one. What you really have to decide is, can blood pressure measurement be helpful in your practice. The monitor will obtain blood pressures. It's been proven already in over 2,500 practices and is used by almost every university veterinary teaching hospital. Ask your colleagues or check out the message boards on the VIN network. If it does not function properly, it will be replaced with one that does. Depending on the model you choose, there is a 2 or 3-year warranty on parts and labor, one year on the battery.

Blood Pressure

Why monitor blood pressure? 
Clinically, blood pressure values provide a tremendous amount of useful information to the practitioner. Because of the difficulty in measuring blood pressure by direct means, non-invasive monitoring has become a practical method of estimating arterial blood pressures and pulse rate. During anesthesia and surgery, automated NIBP monitoring is a very effective means of detecting hypotension, diagnosing internal bleeding, titrating IV fluid administration, monitoring anesthetic depth and evaluating the patient's overall health status. In the exam room, it can be used to diagnose hypertension and is recognized as being an important component of a thorough wellness exam, providing useful baseline data and offering an important early warning sign of more serious medical conditions. During anesthesia, changes in blood pressure are the best first alert warning of impending problems in both cats and dogs.

How is automated NIBP useful in surgery, specifically? 
To make sure the animal is well oxygenated, that the blood pressure stays adequate, and to monitor the depth of anesthesia. Dr. John Ludders, anesthesia professor at Cornell U. says if a patient goes out of range too high, it could mean that patient is too light, that pain medications have become ineffective or that a patient is getting into trouble. Carbon dioxide can also build up when epinephrine is used, causing increased blood pressure and increased heart rate. If the patient goes out of range too low, it could mean the patient is too deep, hemorrhaging, has inadequate fluid volume or may be hypothermic.

What is a typical problem in surgery that can be avoided by using an automated NIBP monitor?
A classic problem in the dog occurs when a high dose of acepromazine has been given preanesthesia. The patient appears outwardly to be doing okay, respiratory rate is as expected, mucous membranes are pink but systolic pressure is too low----68 mmHg. Another common cause of hypotension with inhalation anesthesia is that the animal is too deep. Decreasing vaporizer settings and administration of IV fluids should bring systolic blood pressure back to acceptable limits----above 80 mmHg in a reasonably short time.

Is it more difficult to get pressures in cats? 
Yes, because of cats' physiology. Cats have greater control of their peripheral vasculature than dogs. Their response is to stress is peripheral vasoconstriction. Coupled with small vessels to begin with, this makes blood pressure measurements in cats more difficult. As a result, in checking awake cats for hypertension, it should be done in a relaxed atmosphere - soft lights, and no white coats. Put the cats in the owner's or assistant's lap and stroke the pet to relax it. 

In surgery, inhalation anesthetics, isoflurane and sevoflurane cause peripheral vasodilation but if pain management protocols are inadequate, release of vasoactive mediators will cause vasoconstriction making measurement of blood pressure very difficult if not impossible. Drugs used for anesthesia can also be part of the problem. Cats are often anesthetized with ketamine or Telazol combined with xylazine. The reduced peripheral blood flow subsequent to drug-induced hypotension, combined with reflex bradycardia, and either sinus or ventricular dysrhythmia, can complicate matters further.

Which is more important, a blood pressure monitor or a pulse oximeter? 
They are both very useful measurements of patient well-being. Blood pressure measurements provide a first alert to potential problems, especially hypotension. By the time a pulse oximeter sounds the alarm, oxygen levels are already too low.

Will a blood pressure monitor pay for itself? 
Yes, in a matter of months. Many veterinarians will admit privately that they have lost a patient that they attribute to be an anesthetic death. It is very difficult to put a cost on the untimely death of a patient? Those who are using a blood pressure monitor feel it not only offers better patient care, but may even help grow their practice as their clients are aware of a sophisticated piece of equipment being used and understand the reasons. These clients often indirectly stimulate their friends to visit their veterinarian for blood pressure evaluation of their pet. According to AAHA, most veterinarians charge between $15 and $35 as a monitoring fee or between $5 and $15 for hypertension screening during the annual or bi-annual physical. At this rate, the monitor can be paid for in less than a year, becoming a profit center thereafter. 

Download a brochure on the Cardell BP Screening Program and learn how to incorporate routine blood pressure checks into your practice.

What sets the Cardell® technology apart from other non-invasive blood pressure monitors? 
Cardell technology is specifically designed for animals. Sharn Veterinary pioneered automated blood pressure monitoring for the veterinary market. In 1991, we worked with Johnson & Johnson's Critikon Company to bring veterinarians the gold standard and top selling human blood pressure monitor, the Dinamap. In the early years, we expanded the heart rate range beyond human protocols to 250 bpm, and expanded the selection of cuff sizes to accommodate the smaller limbs on animals. In 1999, the Dinamap was discontinued for veterinary use. With the experience and knowledge of the limitations that oscillometric technology had in veterinary medicine, we found a new manufacturer and worked with them to re-engineer the algorithms so that the monitor would detect oscillations even in the small vessels of cats and kittens, and expanded the heart rate range to 300 bpm. The result has been a reputation as the best non-invasive blood pressure technology in veterinary medicine.

Does the Cardell work on cats and dogs? Awake cats? Horses? 
Yes. Studies have shown that the oscillometric technology in Cardell monitors give reliable and accurate readings in anesthetized dogs and cats. It has also been shown to be clinically accurate and reliable in awake cats. Veterinary speakers and lecturers have endorsed the Cardell as being "the only one that works" in small animals with a very low failure rate. A recent study also validated the Cardell for use on foals and there are equine practices across the country that use the Cardell on adult horses. Overall, the Cardell is designed for use on animals with a pulse rate range of 20-300 beats per minute with appendage size big enough to accommodate the smallest cuff. This includes dogs, cats, pigs, cows, horses and others. It has also been used to establish baseline values on swans. It has not been found useful in rodents and smaller birds because of small limb size limits of pulse rate.

Where should the cuff be placed? 
For dogs, the best site for cuff placement is on the front leg over the metacarpal area, and alternately, either the area over the anterior tibial artery just below the hock or metatarsal area. In the cat, the cuff should be placed over the median artery of the forelimb between the elbow and carpus. In dogs and cats less than 5 lbs., it is best to place the cuff above the elbow which would be over the brachial artery. In awake cats, the tail is also an acceptable site to measure BP. Cuff placement on the horse should be as close to the base of the tail as possible over the Coccygeal Artery.

How many cuffs come with the monitor, how long do they last and what about replacement cuffs? 
Each new monitor comes with 13 cuffs in 7 different sizes - widths of 2.0cm (1), 2.5cm (2), 3cm (3), 4cm (3), 5cm (2), 8cm (1), and 10cm (1). When choosing cuff size, remember that the width of the cuff should represent 40-60% of the circumference of the limb on which you will place it, rounding up to the next size cuff if in between. The cuffs are reusable, but like a toothbrush, eventually wear out. They should be cleaned if they become soiled, but never submerged in liquid. The small animal cuffs (2.5-5cm) are $5.85 each to replace.

What size cuff should be used? 
The cuff size is determined by the circumference of the limb on which it will be placed. For cats and dogs, the ratio of cuff width to limb circumference should be about 40%. If in between cuff sizes, round up. After placement, the cuff should not be so loose that it can be rotated over the site or so tight of obstruct venous return. If it does not stay connected when inflated, select the next larger size cuff. A perfect fit will be with the self attached loops just over the felt but not beyond.

How does the oscillometric method compare with doppler? 
This question is mostly asked in reference to accuracy. In this respect, there is no clinical difference. As for ease-of- use, simplicity, versatility and robustness, the Cardell monitor far exceeds the doppler in practice. More important is that it is automated and displays systolic, diastolic, and mean arterial pressure plus pulse rate and will retain values in memory. Download a chart comparing the two here. The gold standard for blood pressure is direct arterial pressure, and studies have shown the Cardell to be accurate at low and normal pressures and to underestimate direct values at high pressures. There is also a recent study that has shown no clinical difference between the Cardell and doppler in awake cats. Note that there is one study that concludes that doppler is preferred to oscillometric in awake cats (Brown et al, UGA, JAVMA 2004). Note, however, that the study was performed using the Dinamap, a monitor tha t was designed to measure oscillations in human blood vessels and was discontinued for veterinary use in 1999. These studies can be found on our "In The News" page. 

Technically, the oscillometric method is based on the principle that pulsatile blood flow through an artery creates oscillations of the arterial wall. These are transmitted to the cuff which passes them through the pressure hose to a transducer within the monitor. A microprocessor analyzes them and determines systolic, mean and diastolic pressure values and pulse rate.

Can the Cardell be used to diagnose hypertension in cats? 
Yes it can. Its portability and reliability allow the monitor to be moved from surgery into an exam room for wellness exams and feline hypertension checks. Besides cuff selection and placement, special attention should be paid to the environment. Since the feline patient is highly sensitive to its environment, care should be taken to provide a quiet, calm location to perform the exam. Four to five relatively consistent measurements should be taken and averaged. This average should be used to determine pressure and pulse rate values. Before making a final diagnosis, this process should be repeated on a second visit. If any disruption occurs during or between measurements, an extra 5-10 minutes should be given to calm the animal before resuming. Measurements should be taken prior to taking a rectal temperature or performing any other tests.

Is it necessary to shave, use gel, find the artery and listen for the blood flow? 
No. There is no need for gel or shaving the site. If very badly matted hair is found over the carpal or tarsal areas, hair should be clipped over the ventral site but not completely around the foot. For most animals, just wrap the cuff and press "start."

Are there any other tips for obtaining accurate and reliable blood pressure readings? 
The cuff should be maintained as close to the level of the right atrium as possible. Because of gravity, placing it higher than this will produce a lower reading, and placing it lower will produce a higher reading. Thus, lateral recumbency is the ideal position, although a cuff on the base of the tail on a cat can be maintained at heart level while in your lap (or the owners'). When wrapping the cuff, use the "Goldilocks" approach: not too tight, not too loose. If it's too tight, the cuff itself will occlude venous return , rather than the inflation of the cuff and it will result in a false low reading. A cuff that is too loose will give a false high reading or will it will come apart at the Velcro as it is inflated. Although the blood pressure technology is designed to operate with some artifact, take care to keep the animal warm and calm to prevent shivering (shudder and movement will stop the determination cycle). Finally, consistency is very important so be sure to record not only the BP values that are derived (four or five and their average), but keep records of who took the reading, cuff placement and size, coinciding health factors of the animal and the animal's temperament. At subsequent exams, try to replicate these factors (at least the ones you have control over).

Does the monitor provide history and trends? Can this be printed or saved to a PC? 
Yes. In models 9401 & 9402, 24 hours of event and trend history is saved in the monitor's memory, up to 480 individual entries. With the RS-232 serial port (optional in the basic models, standard in the multiparameter monitors), data can be printed directly by the optional Citizen's printer or downloaded as a text file on a PC. There are instructions in the users manual that explain how to do this. Further, an anesthesia report has been developed so that users can create an AAHA-compliant anesthesia report and download tabular data directly into it.

What are normal pressures? At what point is hypertension suspected? 
It is essential to know the reference range of blood pressure in a given species in order to properly evaluate the animal’s blood pressure and detect hypertension or hypotension. When using different measurement techniques (oscillometry or direct blood pressure measurements), one must also remember that methodological factors influence results. Therefore, technique-specific reference values should be known. Species-specific, breed-specific, and individual differences in normal blood pressure ranges can be observed. 

The most accurate assessments are made by comparing different blood pressure readings over time using serial measurements made at regular intervals (at least once yearly). This makes it possible to detect the initial signs of related disease (e.g. cardiovascular and renal disease) more sensitively and at an earlier stage. The normal values for dogs and cats are not identical.

FELINE NORMAL VALUES
The blood pressure values for cats are not breed-specific. However, the most sensitive way to detect changes in feline blood pressure is also by comparing individual blood pressure readings taken over time. Normal feline blood pressure: 124/84 Other investigators have reported comparable reference values: Cat 125 ± 11/89 ± 9 Brown et al, 1997 123 ± 14/88 ± 15 Curtet, 2001 125 ± 12/86 ± 15 Weber et al, 2002

CANINE NORMAL VALUES 
The normal values for dogs are breed-specific. Those for Golden Retrievers, Labradors and giant breeds tend to be lower than the overall average, and those for greyhounds and in general racing hounds tend to be higher. The table that follows lists the normal values for common dog breeds using oscillometric blood pressure monitors. Average canine blood pressure: 133/75 This figure was calculated as the mean of 1782 oscillometric measurement in clinically healthy dogs of different breeds. The overall average is therefore serves as a point of reference only. The individual, or at least breed-specific value must be known to most accurately determine whether a given patient’s blood pressure deviates from normal. Canine reference values (determined using an oscillometric system) 

GUIDELINES 
Mean arterial pressure (MAP) : Minimum to adequately perfuse all peripheral tissue beds: 60 – 70 mmHg Hypertension: Suspect with systolic pressure greater than 150 mmHg; affirmed when above 160-170 mmHg; also affirmed in cats when diastolic pressure is above 100 mmHg. 
Hypotension: During anesthesia, generally maintain systolic pressure above 80 mmHg.  

Capnography

Why monitor end-tidal CO2?
Decades of research and practical experience in medicine have demonstrated that monitoring end-tidal CO2 (“ETCO2”) can mean the difference between life and death. According to the ASA, it is mandatory for all intubated patients undergoing general anesthesia. Leading veterinary anesthesiologists advocate monitoring three things in terms of the physiological function of the patient under anesthesia: circulation, ventilation and oxygenation. Monitoring ETCO2 is the most thorough and comprehensive way to monitor ventilation.

In the early 1980s, the American Society of Anesthesiologists (ASA) did a study to determine why 1 in 5,000 of their patients died during routine surgery. They studied thousands of cases post-mortem, and determined that in over 80% of the time, they could have saved the patient had they been monitoring SpO2, ETCO2 or managing temperature better, and in 6 of 7 cases, it was ETCO2 that made the difference.

The ASA made it mandatory that every intubated patient under general anesthesia must be monitored for ETCO2 levels. As this has become standard practice, 20 years later, rather than a mortality rate of 1 in 5,000, it has been reduced to less than one in every 200-300,000. Studies published in veterinary medicine indicate that 1 in 1000 dogs die, 1 in 500 cats die, 1 in 100 horses die and if a cat is sick (Category 3 or worse) then 1 in 33 die from “anesthetic complications.” Thus, adding capnography to the routine presents us with an incredible opportunity to improve the practice of veterinary medicine.

A study published in 2006 reported that over 25% of veterinary patients hypoventilate during anesthesia, driving up CO2 levels that lead to hypercapnia, then acidosis, at the risk of cardiac failure. The only way to effectively detect this intraoperatively is through the use of a capnograph.

Dubbed by many as the “Anesthesia Disaster Early Warning System,” monitoring CO2 will help not only monitor your patient’s ventilation, but it will provide information about the anesthesia system that cannot be obtained elsewhere. The distinct waveform will change depending on things such as the performance of the CO2 absorber system, the vent valve, endotrachael tube seal, and will provide a clinical reminder of properly maintaining the anesthesia equipment. Failure to maintain the system or detect the resulting problems will increase the risk of death.