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exerted at the end of the tube, just behind funnel-shaped connector and may have increased the likelihood of tube breakage during flexion. Photographs taken after the incident demonstrated a
breakage of the body of the tube (Fig 1b). Examination of the fractured region identified holes in the material consistent with hypodermic needle punctures. Needles are sometimes inserted through the ETT wall to connect a side stream capnography sampling line during anaesthesia. This is a practical solution when the breathing system does not have a specially designed port or capnograph attachment. Repeated punctures of the same area may have created enough damage to weaken the tube in this case or to act as a stress riser and thus contribute to the breakage. Most modern machines now have a luer lock port on the Y-piece for capnography sampling, thus preventing ongoing damage to the ETT. The luer lock port also leads to less obstruction of the sampling line due to the larger diameter of the port compared to a needle. In the case reported here, the luer lock port was used for capnography sampling, but the ETT had been subject to needle insertions in the past. The reuse of silicone ETT in veterinary medicine is a standard
practice. After each use, the tubes are washed and disinfected, usually being soaked in chemical detergents then rinsed. In the case reported here, the tube was routinely disinfected with a diluted solution (1:10 in water) of Virkon S13, a balanced, stabilised blend of peroxygen compounds, surfactant, organic acids and inorganic buffers. The effects of this detergent on the ETT silicone are undocumented but it seems reasonable to consider that chronic exposure may, to some extent, alter its physical properties. Further research is needed in this area to provide clearer guidelines regarding ETT disinfection protocols and recommendations on maximum number of repeated uses of this equipment. Cases of ETT aspiration are also reported in human
medicine. Wong et al. (2002) described the aspiration of an ETT after disconnection from the T-connector during emergence delirium. The patient suffered rapid desaturation as a result of complete airway obstruction, leading the authors to hypothesise that the tube must have become lodged at the carina. This finding presumes the absence of a Murphy eye on the ETT although this was not clearly reported. In the case described here, the presence of a Murphy eye on the ETT along with the small diameter of the tube relative to the trachea and the deflation of the cuff prior to recovery ensured that significant airflow could be maintained both through and around the tube. This probably explains why no signs of severe airway obstruction were displayed. The increased respiratory efforts following the aspiration are likely to have arisen from mild airway irritation and the stress of the situation caused by the ETT. Although oxygen saturation had not been checked during the recovery of this horse, clinical status and normal physical examination was judged satisfactory for the foreign body to be endoscopically retrieved and no further chemical restraint was required. More invasive techniques such as tracheostomy had therefore been avoided. While leaving an ETT in situ during recovery can be recommended as a way of avoiding upper respiratory tract obstruction, the inherent risk of such practice must be acknowledged. Upper respiratory tract obstruction carries the risk of causing negative pressure pulmonary oedema (Kollias-Baker et al. 1993) and the tube itself may become
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obstructed. As a result, the benefit of leaving a tube in situ can be disputed, not only due to the risk of obstruction of the tube during recovery, for example through kinking, but also because of the risk of airway obstruction after the recovery period, for example, arytenoid cartilage paralysis may occur as late as 72 h after anaesthesia (Abrahamsen et al. 1990; Dixon et al. 1993; Southwood and Gaynor 2003). However, Taylor and Clarke (2007) report the possibility of the laryngeal lumen being reduced due to some procedures, such as a laryngeal tie-back and therefore leaving a tube in place for recovery is reasonable. It is obviously necessary to ensure a patent airway during recovery when the demand for oxygen will be elevated and the size of respiratory excursions increased with the effort of returning to standing. Clearly, at these moments there are often massive respiratory efforts seen and were there to be an obstruction, it is likely that the negative pressures generated would lead to pulmonary oedema. This provides reasonable grounds for trying to ensure a patent airway by leaving an ETT in situ. An alternative to leaving an ETT in situ for recovery is the
placement of a tracheostomy tube, either pre-emptively, or having the means to do so in the event of an emergency (Dixon 1988; Southwood et al. 2003; Wagner 2008; Bednarski 2009). However, this invasive technique is not without its own set of risks and complications (Pauwels 2006). Additionally, if the horse’s head is flexed excessively during recovery then the tracheostomy tube is also at risk of being obstructed. By comparison, leaving an ETT in place during recovery is often well tolerated by horses (Bednarski 2009), it is less invasive than performing a tracheostomy and associated with a reduced risk of upper airway obstruction (Thomas et al. 1987). As a result of the unforeseen complications noted in the case described here, it is advised that the horse be observed constantly during the recovery phase and that people are ready to intervene if required. As far as the authors are aware, there are no primary studies published detailing the risks and outcomes of leaving a nasotracheal tube in situ during recovery vs. placing a tracheostomy tube. However, it is recommended to place a tracheostomy tube if haemorrhage or swelling is suspected as a result of surgical trauma, or likely to be ongoing, for example after bilateral arytenoidectomy (Dixon 1988) and you are not merely trying to ensure a patent airway for the duration of the anaesthetic recovery. This case highlights a new risk that should be considered
when deciding whether to leave a nasotracheal tube in situ during recovery in horses. It is especially pertinent given the lack of robust evidence for the use of these tubes for such a purpose. There are currently no published prospective, multicentre, randomised clinical trials to support their use and while their use for recovery purposes seems logical for the avoidance of upper airway obstruction, the evidence for this is lacking. This case report also raises questions about the possible shelf life and number of times silicone nasotracheal tubes can be used and also the techniques and materials used to secure a tube in place. Further investigation may be warranted into the effects of cleaning agents on the integrity of the silicone as well as the amount of stress required to fracture these tubes. This case also supports the view that the insertion of hypodermic needles into silicone ETT for capnography sampling may weaken the tube and therefore such practice should be avoided.
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