Patient assessment
On arrival at the referral hospital, Duke was immediately triaged by the intensive care unit( ICU) nursing team. Triage examinations aim to assess the three major body systems: cardiovascular, respiratory and neurological. A rapid, efficient assessment of the patient is performed to identify any life-threatening concerns that may require immediate intervention [ 3 ].
Duke was conscious, alert and responsive. His mentation was appropriate. He was able to ambulate appropriately, despite an injury to his left forelimb.
A‘ hands-off’ respiratory assessment was performed to avoid causing unnecessary stress: the respiratory rate was significantly higher than normal at over 100 breaths per minute [ 4 ]. The inspiratory respiratory effort was increased, and he was displaying a short, shallow respiratory pattern. Assessment of the respiratory pattern is essential and can aid in the localisation of respiratory issues [ 1 ]. Pleural space disease will often demonstrate a short, shallow respiratory pattern, termed a‘ restrictive pattern’, as the lungs are restricted in their ability to adequately expand, leading to reduced tidal volume and impaired oxygenation [ 1 ]. With pleural space disease, the lung sounds will often be reduced or absent due to the accumulation of fluid or air within the pleural space [ 1 ]. On auscultation, Duke ' s lung sounds were reduced bilaterally, both ventrally and dorsally, consistent with the presumed diagnosis of pleural space disease. Flow-by oxygen was provided and was well tolerated.
On reflection, the nursing team could have attempted to obtain a peripheral blood oxygen saturation( SpO 2
) measurement by pulse oximetry after his triage examination to evaluate his level of hypoxaemia. However, due to his unstable condition, this was not prioritised.
Duke ' s cardiovascular system was promptly assessed following the respiratory assessment. He was tachycardic with a heart rate of 140 – 160 beats per minute, with strong, synchronous pulses [ 3 ]. The tachycardia may have been caused by various factors, including stress, pain and hypoxaemia [ 4 ]. His mucous membranes were pink and his capillary refill time was 2 seconds.
The mucous membranes were examined to assess whether any cyanosis was present. The oxyhaemoglobin dissociation curve demonstrates that cyanosis could be present with severe hypoxaemia( SpO 2
< 80 %). Cyanosis becomes clinically detectable only when the concentration of deoxygenated haemoglobin in the blood reaches approximately 50 g / l. As severely anaemic patients have a reduced total haemoglobin concentration, they may not develop visible cyanosis despite marked hypoxaemia [ 1 ]. Therefore, the absence of cyanosis should not be used as a direct interpretation of a patient ' s ability to oxygenate. As demonstrated by the oxyhaemoglobin dissociation curve, a patient may have pink mucous membranes while being moderately hypoxaemic [ 1 ]. Oxygenation can be more accurately evaluated through the measurement of SpO 2 or, alternatively, the partial pressure of arterial oxygen( PaO 2
) can be measured via blood gas analysis.
Due to the findings during the triage examination, a continuous pneumothorax was suspected and immediate intervention was required. Duke ' s thoracostomy tube was used to evacuate his pleural space: a large volume of air( 2 litres) and a small volume of sanguineous fluid( 20 ml) were removed. An immediate improvement in his respiratory rate and effort was observed but was temporary, and he began to decompensate again rapidly.
The veterinary surgeon( VS) decided to proceed with basic diagnostic imaging and placement of a second thoracostomy tube on the left side of Duke ' s thorax under sedation. A further 250 ml of air was removed from the left thoracostomy tube upon placement; however, the pneumothorax persisted. Manual short-interval drainage was continued while options such as continuous thoracic drainage were discussed by the multidisciplinary team.
Diagnostic investigations
In most cases of pleural space disease, the patient is in acute distress; thoracocentesis can be performed as both a therapeutic and diagnostic intervention before further investigations [ 1 ]. Most patients will show an immediate improvement in their respiratory rate and effort after thoracocentesis, due to lung re-expansion allowing more effective ventilation. Thoracic focused ultrasonography can be a useful cage-side diagnostic tool for patients with respiratory distress [ 5 ]. It is non-invasive, quick and can be performed with minimal restraint. It does, however, require a skilled operator to perform and to interpret the findings. To identify pneumothorax, the sonographer should specifically aim to identify a glide sign, which denotes the normal movement of the lung gliding along the pleural surface of the chest wall [ 5 ]. In cases of pneumothorax, the glide sign will be absent [ 5 ].
Thoracic radiography can be another useful diagnostic tool [ 5 ]. In most cases, the patient should be stabilised before performing thoracic radiography. Radiography often requires restraint and / or sedation, which can be detrimental to a compromised respiratory patient and may lead to decompensation [ 5 ].
After his initial stabilisation, Duke was sedated with a combination of 0.002 mg / kg dexmedetomidine( Dexdomitor, Zoetis, 0.5 mg / ml) and 0.2 mg / kg methadone( Comfortan, Dechra, 10 mg / ml), both administered intravenously( IV), and thoracic radiographic images were taken. The radiographs revealed a large pneumothorax, despite recent drainage, and pulmonary contusions were also evident.
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