Airway examination
A patient may require an examination of their laryngeal movement immediately before intubation , for diagnostic purposes before airway surgery , such as those with laryngeal paralysis or BOAS . Deep sedation or a light anaesthesia plane needs to be achieved , so the patient ' s mouth can be safely opened to allow sight of the vocal cords abducting .
If the patient has been premedicated before the examination , it is important to note that opioids will reduce the cough reflex , but this should not impact the normal movement of the vocal cords . Acepromazine and medetomidine will cause dose-dependent relaxation of pharyngeal tone , which may be undesirable as it can give ‘ false positives ’ of laryngeal abnormalities .
If sedative drugs are not used for premedication , they can be given after the examination , for their minimum alveolar concentration-sparing and balanced anaesthesia properties . There is no difference between alfaxalone and propofol in terms of effect on laryngeal movement [ 11 ] .
During light sedation or anaesthesia to facilitate an airway examination , a patient may lose the compensation strategies they usually rely on to support their breathing ( e . g . an extended neck or an orthopnoeic stance ). These patients may suddenly decompensate , losing the ability to ventilate effectively , requiring immediate induction and rapid control of their airway . All intubation equipment and breathing systems should be prepared beforehand in case this occurs .
It is important to note that during laryngeal manipulation , vagally mediated bradycardia may occur , especially when displacing the epiglottis . A pre-calculated dose of an anticholinergic drug , such as atropine , can be drawn up and ready to administer in patients with high vagal tone , such as brachycephalic breeds . Administering an anticholinergic drug pre-emptively is controversial , as the tachycardia associated with the use of these drugs will increase myocardial oxygen consumption and make watery airway secretions thicker .
Intubation
If a patient ' s cough reflex needs to be suppressed before intubation ( e . g . patients with increased intracranial pressure ( ICP ) or intraocular pressure ), intravenous ( IV ) lidocaine or fentanyl can be administered before the induction agent . Topical lidocaine at 0.4 mg / kg does not abolish the cough response in dogs , but it is abolished with 1.5 mg / kg lidocaine IV [ 12 , 13 ] .
Prior to induction , a 7 µ g / kg fentanyl bolus has been found to be superior to a 2 mg / kg lidocaine bolus in suppressing the cough reflex in dogs , as it also blunts the increase in the heart rate associated with stimulation during intubation [ 14 ] . However , using fentanyl to decrease the cough reflex may be undesirable in patients with raised ICP , as there are reports in human medicine that it increases the ICP due to vasodilation [ 15 ] .
After induction , once the patient is at an appropriate depth of anaesthesia , the airway should be secured with an airway device . The correct technique for using a laryngoscope and intubating a patient in sternal recumbency is described below .
1 . An assistant holds the patient ' s head up so the lower jaw is relaxed . Use the laryngoscope blade to flick the patient ' s tongue out to the side .
2 . Using the non-dominant hand , grasp the tongue and pull it forward over the incisors .
3 . Adjust the grip to hold the tongue in a ‘ scissor clip ’ between the second and third fingers , leaving the thumb free .
4 . With the other hand , slide the tip of the laryngoscope blade down the tongue and under the epiglottis .
5 . Once the tip of the blade is in position , hold both the tongue and the laryngoscope in the nondominant hand .
6 . With the same hand , apply pressure to the back of the laryngoscope with the thumb , which will depress the base of the tongue and release the epiglottis from the soft palate . This enables visualisation of the larynx and entry into the trachea . Apply lidocaine spray to the larynx in cats .
7 . With the dominant hand , select an appropriate ETT to advance into the laryngeal opening , then remove the laryngoscope from the oral cavity .
8 . If the patient is at high risk of GOR ( e . g . pregnant bitches and brachycephalic dogs ), the ETT should be secured and the cuff inflated while the head is raised .
Once intubation has been achieved , confirmation of correct placement is achieved by direct sight , with capnography , or by observing condensation on the ETT or movement in the reservoir bag . The thorax can also be bilaterally auscultated for lung sounds during a PPV breath . Pushing on the patient ' s thorax is not advised by the author , as this reduces the patient ' s functional residual capacity ( FRC ).
The ETT should be secured after placement with a tie , before inflation of the cuff . The gold standard in airway protection is to use an ETT with an inflated cuff [ 2 ] . The cuff must be checked with only oxygen being delivered to the patient before the volatile agent is administered .
50 Veterinary Nursing Journal