As aspiration in veterinary patients is often unobserved , diagnosis is based on a combination of clinical signs and radiographic evaluation , which can be supported by ultrasonography [ 3 ] . Aspiration pneumonia can be life-threatening , but early recognition and treatment can prevent additional damage and reduce morbidity and mortality [ 4 , 6 ] .
In humans , pneumonia is a common complication of seizure activity ; it occurs because the gag reflex , which protects against aspiration , is inhibited during a seizure [ 7 ] . Studies have found an association between the level of consciousness and the risk of aspiration . Moreover , in veterinary patients , risk factors for aspiration pneumonia include decreased mentation [ 8 ] . Kogan et al . [ 5 ] reported that neurological diseases such as seizures are the third most common cause of canine aspiration pneumonia . Brachycephalic breeds are also at a higher risk , due to their particular anatomy and physiology [ 9 ] .
Respiratory support
This patient displayed upper respiratory noise on admission , which is common in brachycephalic dogs . Discussion with the owner revealed that the upper respiratory noise was present before the onset of seizure activity [ 10 ] . On presentation , the patient demonstrated a respiratory alkalosis , as shown by the hypocapnia . The later development of aspiration pneumonia led to tachypnoea and increased respiratory effort .
Hypocapnia and respiratory alkalosis are common in aspiration pneumonia patients and can be caused by hyperventilation [ 2 ] . Acute alkalaemia can cause seizures due to vasoconstriction and decreased cerebral perfusion [ 11 ] . Furthermore , a study demonstrated that 56 % of dogs with aspiration pneumonia are hypoxic ; this is often caused by a ventilation – perfusion mismatch [ 3 , 12 ] . Additionally , brachycephalic breeds may be prone to hypoxia , and oxygen support is also recommended for seizuring patients to ensure tissue perfusion [ 13 , 14 ] .
Oxygen therapy is imperative in these cases . There are a number of methods of providing oxygen to the patient . The most common methods used by the VN are flow-by ( where anaesthetic tubing connected to an oxygen supply is held near the patient ' s nares ) or an oxygen mask [ 10 ] . However , these are labour intensive , so suitable only for short-term use . An oxygen cage , oxygen hood , nasal prongs , nasal catheter or a transtracheal catheter are better suited to longer-term oxygen supplementation .
Oxygen cages are considered the most effective method of oxygen supplementation ; they are less stressful for the patient and allow continuous monitoring by the VN . Certain commercial units or incubators can provide a predetermined oxygen concentration and allow control of temperature and humidity [ 15 ] . However , these are expensive , so are not commonly found in practice .
Many first opinion practices will have an oxygen kennel ; this is a perspex-fronted kennel connected to an oxygen supply . Although less effective due to the gaps at the kennel sides , this is a cheaper and more accessible option . Alternatively , an oxygen kennel can be fashioned by covering a standard kennel with cling film . The disadvantage of the latter options is the risk of overheating and over-humidifying the kennel . Furthermore , it must be noted that when using any oxygen kennel , the oxygen concentration decreases rapidly whenever the door is opened , and it takes time to build up again .
Alternatively , an oxygen hood can be created by placing cling film over an Elizabethan collar , leaving a space at the top to allow carbon dioxide and water vapour to escape , with oxygen tubing fed through the back . However , a hood would be unsuitable for this patient , as the temperature within the collar can rapidly rise , and the patient had a history of hyperthermia . Brachycephalic patients are also at greater risk of overheating [ 16 ] . Nasal prongs and catheters may also be unsuitable , as sneezing during placement can increase intracranial pressure ( ICP ), which was a concern for this patient ; additionally , the prongs can be easily dislodged in brachycephalic breeds . A transtracheal catheter can be considered if patients are intolerant of other methods or have an upper airway obstruction . Although its placement is technically challenging , higher oxygen concentrations can be provided by this method [ 15 ] .
A summary of recommended oxygen flow rates and approximate inspired oxygen concentrations for each
[ 12 , 17 ]
supplementation method is provided in Table 1 ( page 35 ). A commercial oxygen cage or oxygen kennel would be the most appropriate for the patient in this case , due to the risk of hyperthermia or increased ICP posed by the other methods .
The patient ' s oxygenation status should be monitored to assess its response to supplementation . Kogan et al . [ 5 ] found that dogs with aspiration pneumonia responded poorly to supplemental oxygen , confirming that severe lung damage can occur . If oxygenation continues to fall , more intensive support should be considered , such as endotracheal intubation and positive-pressure ventilation . Additional measures such as high-flow oxygen and mechanical ventilation are not commonly available in first opinion veterinary practice , which may necessitate referral . However , this may not be feasible , due to patient stability , finances or availability . It should be noted that patients with aspiration pneumonia can decompensate quickly [ 2 ] .
The VN can assess oxygenation using a pulse oximeter , which is available in most veterinary practices . This non-invasive method measures arterial haemoglobin saturation with oxygen ( SpO 2
). However , small changes in SpO 2 correlate with large changes in PaO 2
( arterial partial pressure of oxygen ), as the relationship is not linear [ 18 ] ; this means that the sensitivity of SpO 2 to
34 Veterinary Nursing Journal