VN April 2023

Vetnuus | April 2023 12 https://vimeo.com/237423698 Respiration It is important to closely monitor the rate, pattern, and depth of respiration throughout the perianesthetic period. 6 First, record the patient’s respiratory rate before the anesthetic event. Ideally the animal should be calm and relaxed, however many birds and small mammals will display a rapid respiratory rate in a clinical setting. 6 During anesthesia, observe the frequency and range of sternal motion as well as movement of the reservoir bag. Substitute balloons for reservoir bags for easier scrutiny of bag movement in patients with small tidal volumes. 6 Respiration can also be monitored by placing a sensor near the nostrils or mounted on the anesthetic breathing system close to the endotracheal tube or face mask connector. Some monitors utilize a pressor sensor, which can be triggered by chest wall movements. A special concern in tiny patients is obstruction of the endotracheal tube. This can occur as a result of bending or kinking or through blockage of the tube with respiratory secretions. Tube blockage is often indicated by a sudden change in respiratory pattern with prominent whistling, wheezing, or harsh breath sounds produced. Expiration may appear difficult, slow, or nonexistent and the reservoir bag may no longer reflect movement. An end-tidal carbon dioxide monitor may show apnea or a change in waveform. 18 When blockage is suspected, quickly evaluate the endotracheal tube for a kink and correct. If the situation is not immediately improved or blockage is suspected, promptly remove the tube and replace as needed. 18 Although monitoring respiration has value, this vital sign does not adequately assess ventilation. 23 An end-tidal carbon dioxide monitor will provide valuable information in most intubated patients. 6 MAMMALS A change in respiration can be the first sign of a problem that requires intervention.Whenapneadevelops,therecanbea1-2-minutedelaybefore blood oxygen levels fall or carbon dioxide (CO2) levels rise inmammals. 6 BIRDS Birds are much less tolerant of apnea when compared to mammals and reptiles. If breathing stops for even 10-15 seconds this is often an indication to reduce anesthetic depth and assist ventilation. 19 REPTILES Most normal reptiles exhibit an intermittent breathing pattern characterized by exhalation and inspiration, followed by an apneic period of variable length. 2 All reptiles require intermittent positive pressure ventilation at a surgical plane of anesthesia. Standard guidelines recommend four to six breaths per minute; however this may need to be adjusted for each individual patient. 26 Based on blood gas analysis, five breaths per minute led to respiratory alkalosis in anesthetized rattlesnakes ( Crotalus durissus ) and one to two breaths per minute was deemed appropriate for this species. 26 A drop in arterial oxygen saturation stimulates the respiratory drive in most reptiles. This is the opposite to mammals, which respond to Figure 7: Doppler ultrasound probe placed directly over the heart of a snake. Photo credit: Katrina Lafferty, CVT, VTS. Figure 8The position of the heart varies among lizard species. The heart is located very close to the pectoral girdle in iguanids and agamids. In chameleons and varanid monitors (as shown here), the heart is located in a more caudal location. Photo credit: Katrina Lafferty, CVT, VTS. Leading Article