/// QUARTERLY BEAT / OCTOBER 2021
QUARTERLY BEAT / OCTOBER 2021 ///
WEBINAR HIGHLIGHTS
JANE QUANDT , DVM, MS, DACVA, DACVECC Professor, University of Georgia VETgirl, Forum Consultant/Contributor Monitoring the Anesthetized Patient - Part 1
In this 2-part series webinar entitled “Monitoring: What monitors tell you & what is considered standard of care” Dr. Quandt reviews the physical exam parameters used for monitoring the anesthetized patient as well as endotracheal tube (ETT) mishaps and post-op emesis and regurgitation. Please check back in Q4 e-newsletter, where Dr. Quandt will review monitoring devices and parameters for monitoring the anesthetized patient.
Auscultation of the chest is a greatly underutilized method of assessing patients. Any patient that has a history of chest trauma, cardiac or pulmonary disease, or being mechanically ventilated should be ausculted both pre/post-operatively. Often, it is much easier to auscult an animal after intubation since upper respiratory sounds are minimized when a patient is correctly intubated. The best way to ensure correct intubation is direct visualization of the glottis and the presence of end-tidal CO2. Endotracheal tube mishaps: An over-inflated cuff on the ETT can cause tracheal irritation and possible necrosis and could lead to a tracheal tear. Tracheal tear is most commonly seen in cats following anesthesia for a dental. The cat presents with subcutaneous emphysema. Possible causes may include- overinflation of the ETT cuff, changes in body position without disconnections from the y-piece resulting in twisting of the tube within the trachea, traumatic intubation, and removal of the tube with the cuff still inflated. The overinflated cuff is the most important cause. Only inflate the cuff so there is no leak of air when the re-breathing bag is squeezed to a pressure of 15 to 20 cm H20. Endobronchial intubation is placement of the ETT down one bronchus and only ventilates one lung which can lead to hypoxemia. The ETT should be past the larynx and not further than the thoracic inlet. The ETT against the tracheal wall can impede ventilation, therefore it is preferred to have ETTs with a Murphy eye which is a second opening to prevent possible ventilation impairment. Post anesthetic blindness can occur in cats most commonly following dentals but can occur after endoscopy. The spring-held mouth gag seems to increase the risk. Hypotension may compound the risk. The blood supply to the feline brain is primarily via the maxillary artery. It is possible that the use of the mouth gag reduces blood flow to the brain through the maxillary artery by stretching of the vasculature and/or adjacent muscles with resulting vascular compromise. Some cats will regain vision but
The pulse pressure , or difference between the systolic and diastolic blood pressures, is responsible for the strength of the palpated pulse and is an estimate of stroke volume. A decrease in strength of the palpated pulse indicates a decrease in pulse pressure. • Weak pulses indicate decreased left ventricular stroke volume or poor ventricular filling, as seen with hypovolemia, ventricular failure, severe arrhythmias, pericardial disease and/or effusion, and subaortic stenosis (SAS). • Bounding pulses are seen with increased systolic pressure +/- decreased diastolic pressure such as with patent ductus arteriosus (PDA), aortic insufficiency, generalized or excessive vasodilation, and anemia (high output circulation). Heart rate should be counted when checking pulse quality. Normal heart rates vary with species. • Tachycardia can decrease the ventricular filling and coronary perfusion because the heart doesn’t have time to fill normally. It can occur with inadequate anesthetic depth and/ or pain, anesthetic drugs (thiobarbiturates, dissociatives, anticholinergics, catecholamines), hypotension, hypoxia, hypercarbia, anemia, and fever. • Bradycardia can cause decreased cardiac output and hypotension. It can be seen with increased vagal tone or vagal reflexes, excessive anesthetic depth, anesthetic drugs (opioids, alpha 2 agonists), hypertension (reflex bradycardia), hypoxia, hypothermia, increased intracranial pressure, and hyperkalemia. D. Respiratory System Ventilation is often decreased by anesthetic drugs via direct depression of CNS respiratory drive and relaxation of the respiratory muscles (intercostals and diaphragm). Ventilatory rate, effort and pattern (thoracic, abdominal or diaphragmatic) should be monitored and assisted if necessary. Assessment of ventilation may include, visualization of chest excursions under drapes, condensation inside the ETT at exhalation, monitoring the reservoir bag, listening for breath sounds via esophageal stethoscope and the presence of end- tidal CO2, but can be difficult in some patients.
Monitoring the anesthetized patient is the most important job during anesthesia. Thorough monitoring is the best way to assess the condition of your patient and avert disasters before they occur. Waiting for difficulties to arise not only delays solving the underlying problem(s) but also delays treatment of the obvious abnormalities. Monitoring basic parameters will draw attention to involved body systems. Although the sheet upon which we record information is divided into five-minute increments, monitoring should be constant from the time pre-medications are given until the patient returns to consciousness and is extubated. Trends, as well as absolute values, are important, and the periods before, during, and after anesthesia are included. A thorough preoperative physical exam and ASA status assignment are important in order to ascertain the beginning condition of the patient. Monitoring equipment is important for patient assessment, but NEVER lose sight of the patient. Physical monitoring is the easiest, cheapest, and best way to monitor your patient. A. Mucous Membranes Normal mucous membranes (mm) are pink, in most species. Pigmentation, especially in dark colored dogs and cats, can interfere with the interpretation of mm color. If the tongue and/or gums are dark, check the vulva/prepuce, toe webs or nail beds for a less pigmented area. Changes in mucous membrane color warrant attention. • Pink mm generally indicates acceptable oxygenation. Anemic or vasoconstricted animals may be difficult to assess. • Pale mm indicate hypotension and/or vasoconstriction as can be seen with blood loss, hypovolemia, hypothermia, decreased cardiac output (CO = HR x SV) related to anesthetic drugs, shock, patients with cardiac disease and bradycardic cases.
• Grey (ashen) mm indicates poor perfusion and are often seen with hypothermia or patients in shock. • Blue (cyanosis) mm indicates SEVERE hypoxemia and occurs when >5% of the hemoglobin (>5g Hgb/100 ml of blood) is desaturated. Severely anemic animals are difficult to assess because > 5g/dl of hemoglobin must be present in order to visualize cyanosis. Anemic patients with a PCV of 15% have a Hgb of 5 g/dl, which means all of the hemoglobin would need to be desaturated before cyanosis would be noticeable, and by this time the patient would be dead. B. Capillary Refill Time (CRT) Refill, return of color, after blanching the area with digital pressure, gives a subjective indication of tissue perfusion and vasomotor tone (e.g., vasoconstriction, vasodilation). • <1 second is normal in awake, healthy animals. • 1-2 seconds may be acceptable, but NOT necessarily normal, in anesthetized patients, especially if they are cold, hypotensive or vasodilated. • 2-3 seconds is prolonged, characteristic of increased sympathetic tone, vasoconstriction, hypotension, poor perfusion, or hypothermia. • >3 seconds is markedly prolonged, indicating severe decompensation. C. Heart Rate / Pulse Quality Rate, rhythm and strength of pulses give a subjective assessment of the cardiovascular system, contractility, blood volume and stroke volume; relative changes should be recorded and trends noted. Normal pulses are strong and regular, within the normal number of beats per minute (BPM) limits of the species. Pulses can be easily detected at the following arteries, lingual on the tongue of dogs, cats, metacarpal, brachial on the front leg of dogs, cats, horses, ruminants and wing of birds, metatarsal (dorsal pedal), femoral on the hind limb of most species and auricular in horses, ruminants, swine and floppy eared dogs, the artery runs down the middle of the ear.
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