Page 203 - WSAVA2018
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A. da Cunha1
1Louisiana State University, Veterinary Clinical Sciences, Baton Rouge- LA, USA
Anderson Favaro da Cunha, DVM, MS, Dipl.ACVAA Professor and Chief, Veterinary Anesthesia and Analgesia
Department of Veterinary Clinical Sciences
School of Veterinary Medicine, Louisiana State University
Baton Rouge, Louisiana, USA
When patients are anesthetized the veterinarian
needs to take responsibility for appropriate monitoring and supportive measures to avoid mortality and/or irreversible damage to important organs. Anesthetic crisis are unpredictable, and tend to be rapid in onset and devastating in nature. Close attention to vital signs allows us to judge the depth of anesthesia, avoiding overdoses and ensuring a positive outcome maximizing the safety of the anesthetic drugs and allowing us to treat any observed complication as soon as possible.
During anesthesia, monitoring the CNS is a simple
and reliable method used to determine the stage of anesthesia. This includes monitoring muscle tone, reflexes activity, and eye position. Basically, the swallowing reflex should be absent after induction of anesthesia and return during the recovery of anesthesia. It is usually considered safe to remove the endotracheal tube of a patient after the observation of the second swallowing reflex. The palpebral reflexes are also very useful. The palpebral reflexes can guide you during all phases of anesthesia. They are subdivided into lateral and medial palpebral reflexes. In dogs and cats the lateral palpebral reflex disappears with light anesthesia and heavy sedation. The medial palpebral reflex disappears during the induction of anesthesia and is usually associated with good muscle relaxation. Usually in dogs and cats, it is considered safe to intubate when medial palpebral reflex disappears. Palpebral reflexes should be absent when patient is well anesthetized. However, the swallowing and palpebral reflexes, can
be present when ketamine is used for induction. The corneal reflex should always be present unless your patient is too deep or dead. This reflex should not tested regularly due to high risk of corneal damage. Keep this test only for real emergencies, when you are testing if the patient is alive or not. The anal reflex
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is unpredictable. Jaw tone is an indicator of muscle relaxation and should be relaxed when patients are ready for surgery.
The eye positions in combination with the reflexes are very useful to grade the level of anesthesia in dogs and cats. Central eye position with strong palpebral reflex and strong jaw tone equals to light anesthesia. Ventromedial rotation of the eye with no palpebral reflexes and relaxed jaw tone equals to surgical anesthesia level. Central eye position with absente of palpebral reflex, relaxed jaw tone equals to too deep anesthesia level.
Ideally, we should monitor cardiac output of patients under anesthesia however, there is no cost effective, non invasive monitor currently available for veterinary patients that could be used during the day to day anesthesia. Since cardiac output is not an option, the veterinarian should focus the cardiovascular monitoring blood pressure (BP), heart rate (HR) and rhythm.
Peripheral Pulse Palpation is unreliable for the monitoring the BP but can help you to calculate the HR and identify arrhythmias. Pulse deficits occur when the pulse rate is higher than the auscultable HR, or some pulses feel weaker than others. If a pulse deficit is detected then an ECG is recommended. Peripheral pulse is only the difference between systolic and diastolic
BPs. The presence of a palpable pulse can give you an inaccurate indication of BP. Some authors believe that a systolic BP higher than 50 mmHg is necessary to ensure palpation of pulse. However, pulse palpation cannot substitute the real BP monitoring with non-invasive or invasive techniques.
Mucous Membranes Color may change with room light. To be precise, check both the gum and tongue color. Pink = good perfusion & oxygenation. Pale or gray = vasoconstriction, significant hypotension or cardiac arrest. Bright red = endotoxic or septic shock. Bright pink = hypercarbia.
Capillary Refill Time (CRT) should be <2 seconds. When prolonged a possible hypovolemia, low BP and/ or low cardiac output may be present. Also peripheral vasoconstriction due to used of alpha2 agonists or hypothermia can cause prolonged CRT.
Arterial blood pressure: The normal range that is associated with adequate tissue perfusion is: systolic arterial pressure (SAP)> 90 mmHg; mean arterial pressure (MAP)> 60 mmHg (small animals) and diastolic BP (DAP) > 40 mmHg. When values measured are less than these minimum values, we attempt to correct
the hypotension with fluids, anticholinergics and sympathomimetic agents

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