Part 2
Case Study : Nursing the canine patient with negative pressure pulmonary oedema
DOI 10.1080 / 17415349.2021.1931605
Lydia M . Barry , BSc ( Hons ), RVN , Cert VNECC
Paragon Referrals , Wakefield
Susannah Pothecary , BVSc , MRCVS
Paragon Referrals , Wakefield
Initial treatment
The patient , a 4-month-old border collie named Buddy , was initially placed into a paediatric incubator with oxygen piped in . This allowed us to observe the patient while setting up materials and equipment for intravenous catheter placement and blood sampling . This method was chosen over others , such as mask or flow-by , as the patient was easily stressed and did not tolerate handling . The aim of oxygen therapy was to correct hypoxaemia while providing supportive care to reduce stress . Oxygen should be delivered in the least stressful way , as movement and stress increase oxygen demand ( Haskey , 2015 ).
However , the incubator resulted in an inappropriately warm environment and each time the door was opened the fractional inspired oxygen concentration ( FiO 2
) dropped . Following the analysis of the blood gases and the clinical presentation , it was determined the patient had signs consistent with respiratory fatigue and consequently failure . The decision was made to anaesthetise , intubate and ventilate the patient .
Ventilation
One of the major advantages of ventilating is the decreased effort of breathing by the patient and the ability to control tidal volume , respiratory rate , inspired oxygen and pressure controls ( Rozanski , 2015 ). However , it is important to note that studies have shown patients with severe lung disease of non-infectious or cardiac causes that require ventilation tend to have a worse prognosis , with only 8 % of these dogs managing to be weaned from ventilation , compared with 50 % of dogs that required ventilation for aspiration pneumonia ( Hopper & Powell , 2013 ).
Anaesthesia was induced with alfaxalone ( Alfaxan , Jurox ) to effect , and maintained on oxygen and isoflurane 1 – 2 %.
Patients without neurological impairment require a light plane of anaesthesia to keep the patient comfortable while allowing sufficient pressures for adequate ventilation ( Drellich , 2002 ). On review of this case , total intravenous anaesthesia ( TIVA ) would have been a better option as using an inhalant anaesthetic requires the damaged organ to maintain the anaesthesia ( Drellich , 2002 ). In addition , it is important to consider the hypoxic pulmonary vasoconstriction ( HPV ) reflex , which results in the vascular smooth muscle of the pulmonary circulation constricting in response to regional hypoxia . This is an important mechanism to match regional ventilation and perfusion in the lungs , and all volatile agents , such as isoflurane , inhibit this beneficial mechanism ( Tarry & Powell , 2017 ).
The patient was manually ventilated before changing to an anaesthetic ventilator ( Wato Ex-35 , Mindray ) for more precise control of ventilation and use of several settings and measurements that can assist in the treatment of severe lung disease . These settings included pressurecontrolled ventilation ( PCV ), volume-controlled ventilation ( VCV ), peak inspiratory pressure ( PIP ), positive endexpiratory pressure ( PEEP ), and synchronised intermittent mandatory ventilation ( SIMV ).
VCV results in a chosen tidal volume ( TV ) being delivered during inspiration compared to PCV , which delivers a breath until a pre-set PIP is reached ( Hopper & Powell , 2013 ). PIP is the pressure generated in the anaesthetic breathing system that is required to push the gases into the lungs . In healthy lungs this should be relatively low , between 8 and 15 cmH 2
O , but in diseased lungs , which can be less compliant , higher pressures may be required to drive a sufficient TV into the lungs ( Drellich , 2002 ). PCV means that the volume delivered is limited to a specific pressure , which can reduce barotrauma to the lungs . However , when the lungs are less compliant , as they are when there is lung parenchymal disease , hypoventilation may occur as a smaller volume of fresh gas reaches the lungs and subsequent hypercapnia can develop ( Rozanski , 2015 ; Drellich , 2002 ).
PEEP is the maintenance of a certain chosen pressure in the airway during expiration . This results in the lung being held in a semi-inflated state , preventing full exhalation , and stops any alveoli from collapsing ( Hopper & Powell , 2013 ). PEEP can also prevent further injury to the damaged lung tissues as it reduces the shearing force that occurs when the alveoli snap open and closed ( Drellich , 2002 ). It is important to remember , however , that cardiac filling relies on normal negative inspiratory pressures and PEEP can reduce cardiac output via reduced venous return in hypovolaemic patients ( Barker , 2015 ).
40 Veterinary Nursing Journal