VNJ Volume 40 (1) February 2025 | Page 37

Plus-Hex CLINICAL

The body has autoregulatory mechanisms to maintain the correct ICP . This process is called pressure autoregulation , and it is controlled via the systemic mean arterial pressure ( MAP ). If MAP increases , vasoconstriction will occur , whereas if MAP decreases , vasodilation will occur . These changes influence the volume of blood within the cerebral blood vessels and therefore the ICP [ 4 ] . For example , if vasoconstriction occurs , there will be a reduced cerebral blood volume , leading to decreased ICP ; if vasodilation occurs there will be an increased cerebral blood volume and a subsequent increase in ICP .

The second autoregulatory system the body uses to maintain ICP is the partial pressure of carbon dioxide ( PaCO 2

) in arterial blood . Carbon dioxide is a potent vasodilator in the central nervous system . Increased

PaCO 2 causes vasodilation of cerebral blood vessels , which increases the blood volume within the brain tissue and , as a result , increases ICP . However , low

PaCO 2 causes vasoconstriction , which decreases cerebral blood volume , consequently reducing ICP [ 4 ] .

If there is an increase in ICP , the body ' s first response is to reduce the volume of CSF by passively reabsorbing it elsewhere within the body ' s tissues [ 6 ] . However , conditions such as that of a growing brain tumour may lead to excessive compression of the brain tissue and blood vessels via mass effect , leading to reduced cerebral perfusion . This will result in secondary cerebral hypoxia , which , if it persists , may lead to irreversible damage to the tissue , brain herniation and eventual death [ 3 ] . Therefore , it is important to consider what veterinary nurses ( VNs ) can do to identify the physiological changes in a patient that may indicate increased ICP . In addition , VNs should be aware of the interventions required to reduce ICP .

Patient assessment

The findings of the patient ' s initial clinical examination are shown in Table 1 .

Table 1 . The findings of Misty ' s clinical examination .

Parameter Demeanour

Mucous membranes

Chest auscultation

Heart rate and auscultation

Blood pressure

Finding

Depressed and disorientated but responsive to certain stimuli ( see Neurological examination )

Pale pink with a capillary refill time of < 2 s

No abnormalities were detected

128 beats / min

No arrhythmias or murmurs were detected

MAP = 113 mmHg

Measurements were taken using a Suntech oscillometric blood pressure monitor . Three consecutive readings were taken using a size 2 cuff on the left forelimb and an average MAP was calculated

Mild hypertension on admission . Blood pressure readings were repeated in the hospital to determine whether this was a situational increase or if the patient was truly hypertensive

Patient signalment

Temperature ( rectal )

Pain

Neurological examination

Mild hypothermia , 37.8 ° C

Comfortable

Recent recurrence of right forebrain signs including compulsive circling to the right-hand side , inconsistent menace response bilaterally , and delayed tactile and visual placement of both limbs on the left-hand side

Presentation

Misty , a 15-year-old female neutered domestic shorthair cat , was referred for further investigations following the recurrence of neurological clinical signs she had shown 2 years before . These signs included compulsive circling to the right-hand side , an inconsistent bilateral menace response , and delayed tactile and visual placement of both limbs on the left-hand side . Misty had previously undergone craniotomy surgery to excise a meningioma in January 2020 .

MAP , mean arterial pressure .

Diagnostics

Following the neurological examination , under the clinician ' s direction , an intravenous ( IV ) catheter was placed in the left cephalic vein and a blood sample was obtained . In-house blood analysis was carried out , including biochemistry and haematology screenings ; the results are shown in Figures 1a and 1b ( page 38 ).

Volume 40 ( 1 ) • February 2025

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