Plus-Hex REFERRAL NURSING the oxygen dissociation curve ( Waddel & King , 2018 ). Haemoglobin is expected to be fully saturated at a PaO 2 between 60 and 70 mmHg ( Waddel & King , 2018 ). Animals with a normal lung function breathing room air typically have a PaO 2 five times greater than the inspired percentage concentration of oxygen ( Angel & Seymour , 2015 ). Therefore , a patient breathing room air (~ 21 % oxygen ) should have a PaO 2 of 100 mmHg , whereas a patient breathing 100 % oxygen when anaesthetised and intubated should have a PaO 2 of 500 mmHg ( Angel
& Seymour , 2015 ). A PaO 2 of less than 55 mmHg is immediately life threatening ( Farrell et al ., 2019 ).
Animals in severe respiratory distress are expected to have an increased respiratory rate and effort with hypoxaemia and hypocapnia with PaCO 2 values < 35 mmHg . However , in this patient there was a marked hypoxaemia ( PaO 2
34.3 mmHg ) and a relative hypercapnia ( PaCO 2 39.0 mmHg ).
PaCO 2 is the primary indicator for the ventilatory function of a patient . Elevations in PaCO 2 typically develop due to hypoventilation as the patient is breathing inefficiently with a reduced alveolar minute ventilation ( respiratory rate ( RR ) × tidal volume ( TV )) ( Hopper & Powell , 2013 ). It is important , however , to consider that in haemodynamically unstable patients ,
CO 2 will accumulate within the venous system due to low flow states and does not indicate an issue with ventilation ( Hopper & Powell , 2013 ). Hypoventilation may be due to multiple issues , either neurological , metabolic or respiratory in origin , and can indicate respiratory fatigue .
In this patient , it was determined the relatively high
PaCO 2 was a product of a reduced TV , as it has been shown that those with lung parenchymal disease have reduced compliance , which results in a lower TV ( Rozanski , 2015 ). In addition , due to the poor compliance of the lungs , the work of breathing is greatly elevated and consequently respiratory fatigue may develop , resulting in orthopnoea and appearance of fatigue , like that of the patient ( Hopper & Powell , 2013 ). To prevent this , mechanical ventilation was chosen as an intervention .
Further diagnostics
Diagnosis was based on history and clinical examination . Thoracic radiographs were taken at the referring veterinary practice and were not repeated on arrival . On reflection , thoracic ultrasound could have been used as it allows repeated assessment and is a noninvasive imaging method . Continuous ECG monitoring is necessary to monitor heart rate and the presence of dysrhythmias . However , in this case , the puppy was stressed and unwilling to allow ECG pads or clips to be placed .
Part 1 summary
There are numerous causes of non-cardiogenic pulmonary oedema , therefore it is vital to gain a detailed history to guide differential diagnoses . Having an understanding of the pathophysiology can help to guide diagnostic tests such as radiography and blood gas analysis , which will further allow specific treatments to be instigated . Often these patients present dyspnoeic and , to prevent further deterioration , the team must work efficiently and quickly to triage the patient . A whole-team approach proved useful in Buddy ’ s case , where the veterinary nurses and interns assessed the patient while the veterinary clinician gained history and consent . The case study in Part 2 discusses the management of Buddy ’ s airway , including ventilation , oxygen therapy and the medications prescribed .
REFERENCES
Agudelo , C . F . & Schanilec , P . ( 2015 ) Pulmonary oedema in a hunting dog : a case report . Veterinarni Medicina . 60 ( 8 ), 446 – 449 .
Angell , L . & Seymour , C . ( 2015 ) A simple approach to blood gas analysis : the essentials . Veterinary Nursing Journal . 30 ( 5 ), 135 – 139 .
Bouyssou , S ., Specchi , S ., Desquilbet , L . & Pey , P . ( 2017 ) Radiographic appearance of presumed noncardiogenic pulmonary oedema and correlation with the underlying cause in dogs and cats . Veterinary Radiology & Ultrasound . 58 ( 3 ), 259 – 265 .
Farrell , K ., Hopper , K ., Cagle , L . & Epstein , S . ( 2019 ) Evaluation of pulse oximetry as a surrogate for PaO2 in awake dogs breathing room air and anesthetized dogs on mechanical ventilation . Journal of Veterinary Emergency and Critical Care . 29 ( 6 ), 622 – 629 .
Glaus , T . M . ( 2012 ) Non-cardiogenic pulmonary oedema . BSAVA World Congress 2012 . Available from : https :// www . vin . com / apputil / content / defaultadv1 . aspx ? pId = 11349 & catId = 34760 & id = 5328316 [ Accessed 3 March 2021 ].
Glaus , T . M ., Schellenberg , S . & Lang , J . ( 2010 ) Kardiales und nicht kardiales Lungenödem : Pathomechanisem and Ursachen . Schweizer Archiv für Tierheilkunde . 152 ( 7 ), 311 – 317 .
Hopper , K . & Powell , L . ( 2013 ) Basics of mechanical ventilation for dogs and cats . Veterinary Clinics of North America : Small Animal Practice . 43 ( 4 ), 955 – 969 .
Latimer-Jones , K . ( 2020 ) How to detect the subtle changes of early deterioration . The Veterinary Nurse . 11 ( 7 ), 325 – 330 .
Louro , L . F ., Raszplewicz , J ., Hodgkiss-Geere , H . & Pappa , E . ( 2019 ) Postobstructive negative pressure pulmonary oedema in a dog . Veterinary Record Case Reports . 7 ( 3 ), e000892 .
Powell , L . L . ( 2002 ) Causes of respiratory failure . Veterinary Clinics of North America : Small Animal Practice , 32 ( 5 ), 1049 – 1058 .
Rozanski , E . ( 2015 ) Oxygenation and ventilation . Veterinary Clinics of North America : Small Animal Practice . 45 ( 5 ), 931 – 940 .
Sumner , C . & Rozanski , E . ( 2013 ) Management of respiratory emergencies in small animals . Veterinary Clinics of North America : Small Animal Practice . 43 ( 4 ), 799 – 815 .
Tong , W . and Gonzalez , A . ( 2020 ) Respiratory Emergencies . Veterinary Clinics of North America – Small Animal Practice . 50 ( 6 ), pp1237-1259 .
Waddell , L . and King , L . ( 2018 ) General approach to dyspnoea . In : BSAVA Manual of Emergency and Critical Care . Eds : King , L . and Boag , A .
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