Evaluation of the Effects of Hospital Visit Stress on Physiologic Parameters in the Cat

Abstract

Physiologic parameters such as blood pressure, rectal temperature, heart rate, and respiratory rate are an important part of the medical assessment of a patient. However, these factors can potentially be affected by stress. The purpose of this study was to compare physiologic parameter data gathered from cats in the home environment with those gathered in a veterinary hospital. Thirty healthy cats were evaluated both at home and at Colorado State University's Veterinary Medical Center. Doppler systolic blood pressure, temperature, heart rate, and respiratory rate were recorded, and the differences between the values obtained in the home and veterinary clinic environments were evaluated using the Wilcoxon sign rank test. A significant difference was found in blood pressure, heart rate, and respiratory rate between the home and veterinary hospital environments. This information may help practitioners recognize that physiologic abnormalities can sometimes be due to transportation or environmental stress rather than medical illness.

An important part of veterinary patient assessment is obtaining physiologic parameters such as blood pressure, temperature, heart rate, and respiratory rate. Measurement of body temperature and determination of hyperthermia (temperature > 102.5°F) are important in the assessment of sick animals. Classification of body temperature as euthermic, hyperthermic or febrile is critical to the diagnostic process. ¹ Although a clinical history of heat exposure and subsequent resolution may differentiate hyperthermia from fever, on initial assessment it can be challenging to do so. Determination of respiratory rate and heart rate are also important for assessing the health status of a patient. Increased respiratory rate could indicate respiratory disease, cardiac disease, pleural space disease, or pain; while tachycardia may suggest cardiac or metabolic disease, pain, or hypovolemia. Measurement of blood pressure is critical in sick animals and those at risk for hypotension and hypertension as both can be associated with organ damage and should be addressed promptly.^2–4 The measurement of blood pressure is also an important part of the clinical staging of chronic kidney disease (CKD), which is a relatively common problem in the cat. ⁵

Changes in any of these physiological parameters due to stress could confound the clinical assessment of the patient, with the detection of hypertension in cats providing particular challenges for veterinarians in this regard. The existing standard of care is to conduct multiple blood pressure measurements over a period of time before diagnosing hypertension and prescribing medications, unless the blood pressure is elevated (>160 mm Hg) in conjunction with signs of organ damage, or a concurrent illness associated with hypertension is present.^3,6 Even with multiple assessments, it is unclear how much the hospital visit itself and the act of measuring the blood pressure affects cats.

In humans, elevation in blood pressure due to the stress of the clinical setting is referred to as the ‘white coat syndrome’ and has been recognized for decades. ⁷ This phenomenon is thought to be mediated by the sympathetic system, but the precise mechanism is unknown. In cats the existence of the ‘white coat syndrome’ was explored in a study in which research cats with radiotelemetry implants underwent a simulated veterinary office visit. ⁸ Based on the findings, it was concluded that cats do experience a ‘white coat effect’. As the actual act of measuring blood pressure may also affect the reading, the results of this study are difficult to extrapolate to client-owned cats for which readings are obtained using a non-invasive method of measuring blood pressure.

Belew et al ⁸ also assessed heart rate by radiotelemetry in cats in the home environment and clinic environment, and found that there was a significant increase in heart rate in the clinic. To the best of the authors' knowledge, no previous studies exist to document the extent to which a cat's respiratory rate can become elevated as a result of the stress of a hospital visit. Similarly, no previous studies have explored the degree of elevation that may occur in a cat's temperature purely as a result of the hospital visit, or as a result of resistance or struggling while the reading is obtained. The objectives of the present study were, therefore, to determine whether the stress associated with a hospital visit has an effect on the feline physiologic parameters of blood pressure, rectal temperature, heart rate and respiratory rate. Our hypothesis was that the value of all of these parameters is increased in the hospital environment, compared to values obtained at home.

Materials and methods

Animals

The study population consisted of 30 apparently healthy cats (based on a normal clinical history and physical examination) owned by veterinary students and faculty at Colorado State University (CSU). The Institutional Animal Care and Use Committee at CSU approved the study, and all owners reviewed and signed consent forms prior to participation in the study.

Data collection

Systolic blood pressure, rectal temperature, heart rate, and respiratory rate were measured in the home environment and at the veterinary clinic on the same day by a single student researcher. Physiologic parameters were first measured in the home environment in the following order; blood pressure, heart rate, respiratory rate and temperature. The owners then drove the cats to the veterinary clinic, where physiologic parameters were again obtained, in the same order, after a 10 min acclimatization period. Systolic blood pressure was measured as an average of five readings obtained using a Parks Doppler unit (Parks Medical Electronics, Las Vegas, NV) on the right or left forelimb and sized to 40% of the circumference of the forelimb. Temperature was measured with a 10 s digital thermometer (Vicks V900F/V901F, Kaz, Hudson, NY) following blood pressure assessment. Heart rate was determined by auscultation and respiratory rate by visual observation. The cats' attitude during manipulation was scored on a scale of 0–3 using the following parameters: calm (0) or agitated (1); compliant (0) or struggling (1); quiet (0) or vocalizing/hissing (1).

Statistical analysis

The physiologic parameter data for cats in their home environment and at the veterinary hospital were compared using a non-parametric Wilcoxon sign rank test. Statistical significance was set at P < 0.05.

Quality control

Calibration of the Parks Doppler unit was performed at the beginning of the study, after every five readings during the study, and at the end of the study using a pressure manometer. The student researcher conducted these calibrations.

Results

Animals

Thirty cats participated in the study. Three additional cats were disqualified after becoming intractably fractious in the home environment. Sixteen cats were neutered males and 14 cats were spayed females. Breeds included 20 domestic shorthairs, two domestic longhairs, three Siamese mixes, and one each of Ragdoll, Persian, Russian Blue, Himalayan, and Burmese. Median age of participating cats was 4 years (range 0.6–11 years). Five cats were reported to have an indoor/outdoor lifestyle and the remaining 25 were indoor only. Median transportation time to the veterinary hospital was 12 min with a range of 5–40 min.

Physiologic parameters

Median and range of physiologic parameters obtained from cats in the home environment and the veterinary hospital environment are reported in Table 1. A statistically significant difference was found between the home environment and the veterinary hospital environment for blood pressure (P = 0.04), heart rate (P < 0.0001), and respiratory rate (P = 0.01).

Table 1.

Recorded differences in physiologic parameters measured in cats in the home environment followed by the hospital environment. A statistically significant difference was detected between the home environment and the veterinary hospital environment for the parameters blood pressure (P = 0.04), heart rate (P < 0.0001), and respiratory rate (P = 0.01).

	Home environment		Hospital environment
	Median	Range	Median	Range
Blood pressure (mmHg)	131	96–167	138	106–164
Rectal temperature (°F)	101.2	98.6–102.7	101.5	100.4–103.0
Heart rate (beats/min)	153	110–250	190	128–256
Respiratory rate (breaths/min)	50	24–84	58	18–192

Measured physiological parameters in the home and hospital environments are depicted in Fig 1A—D as Bland—Altman plots to allow the variability between environments to be appreciated for each subject. Two cats were disqualified from respiratory rate analysis, one due to constant sniffing in the home environment and one due to panting in the hospital environment. The mean difference between blood pressure in the home environment and the hospital environment was a 6 mmHg increase, with a range of 26 mmHg decrease to a 31 mmHg increase. The mean difference between temperature in the home environment and the hospital environment was a 0.3°F increase, with a range of a 1.3°F decrease to a 2.1°F increase. The mean difference between heart rate in the home environment and the hospital environment was 33 beats/min increase, with a range of a 20 beats/min decrease to a 76 beats/min increase. The mean difference between respiratory rate in the home environment and the hospital environment was 12 breath/min increase, with a range of a 30 breath/ min decrease to a 108 breath/min increase.

Fig 1.

Bland—Altman plots illustrating the difference between the home and clinic environment for (A) blood pressure, (B) rectal temperature, (C) heart rate and (D) respiratory rate. The horizontal line represents no difference. Cats below the line experienced an increase in the measured parameter in the clinic environment. Using a Wilcoxon sign rank test, a statistically significant difference was found between the home environment and the veterinary hospital environment for blood pressure (P = 0.04), heart rate (P < 0.0001), and respiratory rate (P = 0.01).

When attitude scores were compared between the two environments, 50% of cats experienced a decrease in their score in the hospital environment compared to home, 20% of cats experienced an increase in their score, and 30% of cats experienced no change in their attitude score.

Discussion

This study examined the physiologic parameters of blood pressure, temperature, heart rate, and respiratory rate in cats in the home environment in comparison to the veterinary hospital. A statistically significant difference was seen between the home environment and the veterinary hospital environment for the parameters blood pressure, heart rate, and respiratory rate.

Although the changes in systolic blood pressure, heart rate and respiratory rate were all found to be statistically significant, the clinical relevance of these changes is not uniformly apparent. An increase in blood pressure of 6 mmHg would usually not be considered to be highly clinically significant, given the inherent variability of blood pressure measurement via Doppler, which has been previously documented. 9 However, the mean increases in heart rate (33 beats/min) and respiratory rate (12 breaths/min) could have more clinical relevance. In addition, examination of the largest observed increases in each of the physiologic parameters suggests that the effects of stress should be considered when assessing individual patients. Specifically, the highest documented increase in blood pressure between the home and veterinary hospital environment was 31 mmHg, the greatest change in temperature was an increase of 2.1°F, the largest increase in heart rate was 76 beats/min, and the greatest increase in respiratory rate was 108 breaths/min. Each of these changes would be considered to be clinically important in a feline patient. For example, in the classification of feline CKD, a difference in blood pressure of >10 mmHg is sufficient to move a cat from a ‘low risk’ to a ‘moderate risk’ arterial pressure substage. ⁵

In this study, the mean increase in rectal temperature of 0.3°F between the home and hospital environments was not statistically significant, and would also not be regarded as clinically significant. However, it is noteworthy that three cats that had temperatures <102.5°F in the home environment subsequently developed an elevation in temperature in the hospital environment that potentially could be considered to be medically significant. Rectal thermometry is regarded as an acceptable method for estimating core body temperature, ¹⁰ although stress or physical exertion may potentially increase this parameter. ¹¹ Based on the results of this study, the stress of transport and the hospital environment should be considered a differential for hyperthermia in felines. Conversely, one cat that had a temperature over 102.5°F in the home environment subsequently had a normal temperature in the hospital environment, implying that the stress of temperature measurement alone is sufficient to elevate rectal temperature.

The results of this study support the concept that a ‘white coat effect’ exists for some cats in the hospital environment. Past studies have noted that blood pressure in dogs is affected by stress^12–14 and a previous study in which telemetry was used to assess blood pressure and heart rate in cats came to a similar conclusion. ⁸ It appears that this effect is also found in cats in which the non-invasive Doppler measurement of blood pressure is used, a technique used commonly in practice, but one that may also induce stress due to manipulation. The cats utilized in this study were healthy adults, and potentially these effects may be magnified in sick animals, particularly those with renal compromise. ⁸

Interestingly, measurement of physiologic parameters in the home environment was not as straightforward as anticipated. Cats in this environment were more likely to object to manipulation by apparent agitation, struggling, and vocalizing, and thus many cats experienced a decrease in their attitude score in the hospital environment compared to the home. This serves as a reminder that the act of obtaining physiologic measurements in cats contributes to stress that may affect the readings. Struggling and vocalization are behaviors that are likely associated with a sympathetic response, as indicated by a study showing an increase in epinephrine, norepinephrine, cortisol and glucose in cats stressed by a spray bath. ¹⁵ Anecdotally, measurement of blood pressure in the home environment has been recommended to circumvent the sympathetic ‘white coat effect’ in the clinic environment, but the results of the present study imply that obtaining measurements in the home environment may also provide a significant source of stress, as cats may be less tolerant of manipulations in their own territory. Three cats that were previously considered by their owners to be generally malleable in the clinic environment were fractious when physiologic parameter measurement was attempted in the home environment, and subsequently were disqualified from the study for the safety of the handlers.

Factors that could have affected the outcome of this study include a potential bias due to the volunteer based selection of participants, and disqualification of fractious cats, both of which may have inadvertently predisposed the study population towards less stress-prone individuals. It should also be noted that the order in which physiologic parameters were measured may have affected the results of the subsequent measurements. For instance, measured parameters such as respiratory rate may not be representative of the normal feline population as they occurred after restraint and manipulation, and not at rest.

In conclusion, a statistically significant difference was detected between the home environment and the veterinary hospital environment for the parameters blood pressure, heart rate, and respiratory rate. Although mean differences in parameters may not be uniformly clinically relevant, the observed range of increase for all the parameters could be very significant in individual animals. Thus the results of this study support the idea that stress may result in elevated physiologic parameters for cats in the hospital environment, and clinicians should bear this in mind when assessing feline patients upon presentation. In addition, medical assessment in the home environment does not necessarily preclude stress-related changes in physiologic parameters.