The examination time must also be carefully planned, and ET intubation performed immediately if respiratory compromise occurs [ 2 ]. Having a selection of small ET tubes, a bougie, a stylet and a laryngoscope ready will facilitate ET intubation [ 8 ]( Figure 3, page 27). Positioning the patient in sternal recumbency with the head elevated optimises lung expansion and avoids aspiration of oral contents. Suction equipment can remove secretions obstructing the airway and help lavage the oesophagus if necessary [ 8, 9 ]. The use of a capnograph is considered best practice to confirm the correct placement of the ET tube [ 10 ].
In this case, the ET intubation was achieved quickly. However, when intubation is not successful, the human anaesthesia literature recommends prioritising oxygenation and limiting the number of orotracheal intubation attempts to three, with a fourth attempt being performed only by an experienced anaesthetist [ 11 ]. Provision of oxygen using a face mask, nasal cannulae, a supraglottic airway device or through a transtracheal catheter is suggested [ 11 ], although in patients with an upper airway obstruction these techniques might not be effective.
A bougie or a rigid urinary catheter inserted into the airway can be used as an ET tube introducer; the tube can be threaded over it, facilitating intubation [ 8 ]. The urinary catheter has the advantage of allowing the attachment of a 2.5 ml syringe, without the plunger, which can be connected to a 7 mm ET tube connector and a breathing system to provide oxygen supplementation and IPPV [ 8 ]. Argano et al. [ 12 ] reported the use of a urinary catheter with handmade holes to optimise oxygen delivery to a dog undergoing intratracheal stent placement, a device modification similar to some airway exchange catheters used in human anaesthesia [ 13 ].
In some cases, it is safer to abort the procedure and let the patient recover [ 8 ]. However, residual anaesthesia and pre-existing airway disease can increase the risk of airway obstruction [ 11 ].
If all methods of securing the airway fail, the patient is at risk of cardiorespiratory arrest due to hypoxia. Emergency front-neck-access techniques such as cricothyroidotomy and tracheostomy might be necessary to rescue the airway [ 14 ].
Anaesthesia maintenance with TIVA
During upper airway surgery, the intermittent stopping of a volatile anaesthetic agent can cause fluctuations in the patient ' s depth of anaesthesia; therefore, TIVA is suggested in these cases to provide a more stable plane of anaesthesia [ 15 ]. In this case, boluses of propofol were used to maintain anaesthesia following the removal of the ET tube, rather than a CRI. This approach was chosen due to the anticipated short duration of the surgical procedure and the concurrent administration of a dexmedetomidine CRI, which reduces the required dose of propofol while also providing muscle relaxation, sedation and analgesia [ 15 ]. Although the administration of intermittent boluses of propofol can result in variations in the plasma concentration of the drug, and consequent less predictable hypnosis and side effects [ 16 ] compared with a CRI, propofol accumulates in the adipose tissue due to its high lipid affinity, which extends its metabolism and elimination, prolonging the recovery period.
Suboptimal anaesthesia can increase the risk of GOR and regurgitation, and may result in aspiration pneumonia, oesophagitis and oesophageal stricture [ 6 ]. Shorter starvation times and the administration of gastroprotectants such as omeprazole( ideally starting the day before anaesthesia) and metoclopramide( as soon as the signs of regurgitation develop or in a patient with a history of regurgitation, immediately after admission) are associated with a decrease in the incidence of regurgitation [ 1 ]. In this case, both drugs were administered approximately 4 hours before premedication.
If regurgitation is observed during anaesthesia while the patient is still intubated, the patient ' s head must be placed in a slightly elevated position and the oral cavity cleaned. It is important to ensure that the ET tube is cuffed and in place. Oesophageal suction and lavage with tap water is advised to increase the oesophageal pH, as this will prevent oesophagitis and the risk of oesophageal stricture [ 6 ]. Oesophageal lavage with sodium bicarbonate and water is also suggested in the literature as an effective method to increase the oesophageal pH to > 4 after GOR [ 17 ]. To the authors ' knowledge, in cases of regurgitation without an ET tube in place it would be better to lower the patient ' s head to allow the fluid to drain away from the larynx, and suction the gastric contents, as described by Scales and Clancy [ 18 ] for managing regurgitation during the recovery period. Although the use of alpha-2 adrenergic agonists may induce vomiting, Petruccione et al. [ 19 ] reported no significant differences in the incidence of regurgitation in brachycephalic breeds receiving acepromazine or dexmedetomidine as premedication.
In this case, the flow-by technique was elected to provide oxygen supplementation to the patient. However, based on the findings of McNally et al. [ 4 ] in a study of the relationship between preoxygenation and oxygen desaturation times, it is understood that the SpO 2 was maintained above 97 % in the first 5 minutes, due to the prior oxygenation provided by IPPV before ceasing volatile anaesthesia and withdrawing the ET tube. The oxygen saturation started to decrease gradually, most likely related to respiratory depressive effects caused by propofol and the dexmedetomidine CRI( secondary to muscle relaxation). Hypoxaemia is defined as a partial pressure of oxygen( PaO 2
) < 80 mmHg, which correlates with an SpO 2 of < 95 % [ 20 ]. Although the patient ' s SpO 2
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