EQUINE VETERINARY EDUCATION / AE / MAY 2015


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around the head collar with zinc oxide tape (Strappal)9 and the cuff deflated. Ropes were attached to the head collar and tail to assist recovery. The horse stood successfully and smoothly on its first attempt. During this attempt the horse rubbed his nose along the wall causing the nasotracheal tube to flex. The most proximal end of the nasotracheal tube was then observed to break and the blue funnel-shaped extremity of the tube was seen hanging from the head collar. The horse made several attempts to swallow with increased respiratory rate and amplitude, attributed to the stress of the event and mechanical stimulation of the tube becoming lodged in the airways. There was no audible stertor or stridor, thus confirming the absence of a significant airway obstruction. The horse was monitored from outside the recovery box until it was standing calmly. When it was judged to be safe to enter the box, a physical examination was performed which detected no abnormalities apart from slightly increased respiratory effort. An endoscope was used to explore the upper airways and determine the location of the remainder of the tube. The nasotracheal tube could be seen inside the trachea, approximately 1.3m from the nostrils as measured on the endoscope. An alternative method had to be employed to retrieve the remaining length of tube as no grasping forceps of suitable strength, length and flexibility were available. A 12mm cuffed ETT6 was positioned over the endoscope.


The pilot balloon was attached to a minimum volume extension set (V-green i.v. extension set)10, which was connected to an air-filled 60 ml syringe (BD-Plastipak)11 (Fig 1a). The tube, pilot balloon and extension set were then secured to the endoscope with zinc oxide tape. This modified endoscopic device was introduced into the horse’s trachea and advanced until the endoscope was positioned within the broken nasotracheal tube. The 12mm ETT cuff was inflated until it pressed firmly against the inside wall of the nasotracheal tube. The combination of ET tubes and endoscope was then gently withdrawn as one unit. The 20mm tube became lodged in the nasopharynx


during removal. At this point the horse was observed to be swallowing repeatedly, but there was no evidence of airway


a)


obstruction as there was no indication of stridor or stertor in the horse’s respiratory pattern. The endoscope apparatus was removed and the 12mm ETT discarded. Oesophageal foreign body removal forceps were introduced through the right nostril alongside the endoscope. The broken nasotracheal tube was grasped and withdrawn. On examination, the remainder of the 20mm tube appeared intact, confirming the absence of remaining pieces within the trachea. The horse was given dexamethasone 0.01 mg/kg bwt i.v. (Dexadreson12 2 mg/ml) to limit the post operative swelling that may arise after such trauma.


Recovery continued uneventfully and repeat endoscopy 3


days later demonstrated mild erythema of the pharynx, trachea and nasal turbinates. The horse has had no further complications and returned to normal athletic activity and improved performance.


Discussion


Complications arising from endotracheal intubation have been previously reported in horses (Holland et al. 1986; Heath et al. 1989; Bednarski 2009). Rough placement of the tube or excessive intraoperative inflation of the cuff have both been shown to induce traumatic lesions of the upper airways of variable severity; however, often these are without any accompanying clinical signs (Holland


et al. 1986;


Touzot-Jourde et al. 2005; Saulez et al. 2009). Breakage and aspiration of an ETT is listed as a potential complication of leaving an ETT in place during recovery in horses (Bednarski 2009). However, to the authors’ knowledge, case reports of ETT breakage and aspiration have not previously been described in the veterinary literature. A number of factors could have contributed to the breakage. Firstly, mechanical stress was exerted on the tube during recovery, potentially exacerbated by the tape on the tube acting as a fulcrum. Secondly, the tube may be destabilised by pre-existing physical damage to its wall and, finally, integrity of the silicone may be damaged by repeated exposure to chemicals used for ETT maintenance. Mechanical stress leading to silicone endotracheal tube


b)


Fig 1: a) Endoscopic device: endoscope (1), 12mm cuffed ETT placed on the endoscope (2), extension set connected to the ETT pilot balloon (3) and air-filled syringe (4). b) Detail of the site of breakage on the 20mm ETT.


breakage has been reported in the human medical literature. One report (Takanami et al. 2007) found that the tube broke due to patient-inflicted trauma, another (Solomons 1987) due to positional kinking. In our case, the horse rubbed its head along the wall causing flexion of the tube. However, large animal ET tubes are significantly larger and more robust than those used in human medicine. Despite this, because of the increased wall thickness and rigidity of the large animal tubes, breakage due to flexion alone seems unlikely, leading many authors to recommend an ETT left in situ for recovery (Thomas et al. 1987; Southwood and Gaynor 2003; Taylor and Clarke 2007; Wagner 2008; Bednarski 2009). In human medicine, nasotracheal tubes are warmed prior to insertion to make them more flexible, but this may lead to tubes kinking more easily (Ayala and Coe 1997; Thong and Wong 2011). While it is possible that our tube had been warmed by the patient’s body heat, it is still unexpected that this would have a significant impact on its rigidity. It seems more likely that the location of the tape on the tube created a fulcrum where flexion stress was concentrated. Securing a nasotracheal tube in place during recovery using medical tape is a common practice in equine anaesthesia. In this case, zinc oxide tape was wrapped around the most rostral aspect of the tube (Fig 1b) and tied behind the ears. A fulcrum effect was thus


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