Differentiating between these options is often done via a review of the clinical history , vaccination status and patient examination ( Sumner & Rozanski , 2013 ). This patient had no audible murmur or dysrhythmia and no radiographic changes to indicate a cardiac cause ( Tong & Gonzalez , 2020 ). In one paper , postobstructive pulmonary oedema appeared to show a more asymmetrical unilateral presentation compared to neurogenic pulmonary oedema . However , the paper also states that if the condition is severe , then changes appear to be more diffuse and bilateral ( Bouyssou et al ., 2017 ).
In this case , the patient had an acute onset of signs after the owners witnessed an incidence of upper airway obstruction and a period of collapse immediately prior to the onset of clinical signs . In addition , younger animals are at a higher risk of hypoxia due to their smaller functional capacity and thus more at risk of developing pulmonary oedema ( Louro et al ., 2019 ). Therefore , a presumptive diagnosis was made of negative pressure pulmonary oedema . In retrospect , an electrocardiogram ( ECG ) and echocardiography could have been indicated , to rule out any cardiac disease ( Agudelo & Schanilec , 2015 ).
Pathophysiology
Pulmonary oedema typically arises due to an increased intravascular hydrostatic pressure or a disturbed vascular permeability ( Glaus , 2012 ). It can also be caused by an altered oncotic pressure gradient or lymphatic drainage ( Glaus , 2012 ).
There are numerous events that may lead to the movement of fluid into the alveoli , including neurogenic oedema post brain-trauma or seizures , electrocution or re-expansion oedema following rapid removal of a pleural effusion or pneumothorax ( Bouyssou et al ., 2017 ). The described patient suffered negative pressure pulmonary oedema , secondary to airway obstruction ( Louro et al ., 2019 ). This can be caused by brachycephalic upper airway syndrome , laryngeal paralysis , tracheal collapse , endotracheal tube obstruction and strangulation .
During the obstruction , the patient struggled to breathe , resulting in an increased inspiratory effort . This can lead to mechanical ventilatory stress , which damages the pulmonary epithelium and endothelium ( Glaus , 2012 ). The patient became hypoxic , leading to a sympathetic capillary vasoconstriction ( Bouyssou et al ., 2017 ). Additionally , the increased inspiratory effort likely resulted in a large negative transpulmonary and interpleural pressure gradient ( Louro et al ., 2019 ).
When negative pressure in the thoracic cavity occurs , it can lead to a decrease in venous blood flow to the heart , allowing blood to pool in the pulmonary vessels ( Glaus , 2012 ). This increases the pulmonary intravascular volume which , when coupled with vasoconstriction , results in a significant increase in hydrostatic pressure ( Glaus , 2012 ).
There are limited reports in veterinary literature describing the treatment of such patients . The largest published research was a series of cases describing the radiographic appearance of 23 cases with pulmonary oedema ( Boiyssou et al ., 2017 ). Most recently , Louro et al . ( 2019 ) described the diagnosis and management of post-anaesthetic non-cardiogenic pulmonary oedema in a dog .
Arterial blood gas analysis
An arterial catheter was aseptically placed into the left dorsal pedal artery to allow for regular arterial blood gas analysis . A sample was taken on admission and then regularly throughout hospitalisation ( Figure 1 ).
PATIENT ’ S BLOOD GAS ANALYSIS RESULTS
pH – 7.4 ( 7.350 – 7.450 )
PCO 2
– 44.4 mmHg ( 35 – 38 mmHg )
pO 2
– 56.5 mmHg ( 85 – 100 mmHg )
cHCO 3
– 27.5 mmol / l ( 15 – 23 mmol / l ) BE ( ecf ) – 2.7 mmol / l (– 5 – 0.0 mmol / l )
cSO 2
– 88.8 % ( 90 – 100 %) Na + – 135 mmol / l ( 139 – 150 mmol / l ) K + – 3.4 mmol / l ( 3.4 – 4.9 mmol / l ) Ca ++ – 1.19 mmol / l ( 1.12 – 1.40 mmol / l ) Cl – – 100 mmol / l ( 106 – 127 mmol / l )
TCO 2
– 27.2 mmol / l ( 17 – 25 mmol / l ) Hct – 33 % ( 33 – 50 %) cHgb – 11.1 g / dl ( 12 – 17 g / dl ) BE – 2.3 mmol / l (– 5 – 0.0 mmol / l ) Glu – 7.6 mmol / l ( 3.3 – 6.4 mmol / l ) Lactate – 1.33 mmol / l ( 0.6 – 2.9 mmol / l ) BUN – 18 mmol / l ( 2.5 – 9.6 mmol / l ) Urea – 6.5 mmol / l ( 3.6 – 9.3 mmol / l ) Crea – 52 mmol / l ( 44 – 115 mmol / l ) BUN / Crea – 31.0 mg / μg ( 0.2 – 400 mg / μg ) Urea / Crea – 125.1 mmol / l ( 0.8 – 1615.4 mmol / l )
Figure 1 . Patient ’ s blood gas analysis results , including ( in brackets ) normal reference ranges for a canine arterial sample .
Arterial blood gas is considered the gold standard for monitoring oxygenation status ( Farrell et al ., 2019 ). The partial arterial pressure of oxygen ( PaO 2
) and carbon dioxide ( PaCO 2 ) can indicate lung function .
The PaO 2 represents the oxygen saturation of haemoglobin in a sigmoid relationship according to
38 Veterinary Nursing Journal