General approach to respiratory distress

image of General approach to respiratory distress
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It is essential that patients in respiratory distress are recognized immediately. Respiratory distress is caused by hypoxaemia, hypercapnia, or a significant increase in the work of breathing. This chapter covers diagnosis, emergency stabilization, approach to undiagnosed respiratory distress, pulmonary function testing in the dyspnoeic patient and intubation and positive pressure ventilation.

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7.1 A terrier presented in severe respiratory distress. Note the open mouth, extended neck and abducted elbows.
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7.2 The oxyhaemoglobin dissociation curve demonstrates the relationship between partial pressure of oxygen dissolved in the blood ( O) and the saturation of haemoglobin with oxygen ( O). The sigmoid shape of the curve occurs as a result of a conformational change in the haemoglobin molecule following binding of the first molecule, allowing binding of the remaining three molecules to occur more rapidly. This facilitates both oxygen intake in the lungs and oxygen release to the tissues. The plateau of >90% haemoglobin saturation also provides a wide margin of safety – lung disease may result in significant decreases in Owithout a concurrent decrease in saturation. Desaturation can occur rapidly, however, once the O decreases to a value of <60 mmHg.
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7.3 A Field Spaniel in congestive heart failure was placed in an oxygen cage to provide oxygen supplementation. He was in severe respiratory distress and would not tolerate an oxygen mask or nasal prongs. Temperature, inspired oxygen concentration and humidity can be controlled in these units.
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7.4 Nasal oxygen prongs that are manufactured for human patients can be used in many canine patients to provide oxygen supplementation.
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7.5 Nasal oxygen can also be provided by suturing a red rubber catheter into one nostril and inserting it a premeasured length equal to the distance from the nostril to the medial canthus of the eye.
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7.7 Oxygen can be humidified by bubbling it through a chamber filled with distilled water. This reduces airway irritation by preventing desiccation.
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7.11 A tracheostomy was created in this mixed breed dog for recovery from anaesthesia after surgery to correct laryngeal scarring. A 50% circumferential incision was made into the trachea between rings to place the tracheostomy tube. Stay sutures placed around the tracheal rings cranial and caudal to the incision can be seen.
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7.12 Right lateral cervical radiograph of a 9-year-old male neutered Domestic Shorthair cat that presented with a 2–3-week history of decreased appetite, 3-day history of anorexia and increased upper airway noise with respiratory distress. Note the large laryngeal mass.
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7.16 Trans-tracheal wash. (a) The ventral neck of the dog is clipped and aseptically prepared. (b) An 18 G through-the-needle catheter is pushed through the skin and ‘popped’ into the trachea between two tracheal rings. (c) The catheter is angled downward and fed all the way into the trachea. The sterile sheath is removed, the needle is withdrawn and the needle guard replaced, and the stylet is removed. (d) Sterile saline is flushed into the catheter and the catheter is then aspirated to obtain the sample.
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7.18 (a) Right lateral and (b) ventrodorsal radiographs of a 4-year-old female Domestic Shorthair cat presented with a 2-day history of increased respiratory rate and effort and a 1-day history of anorexia. Note the bronchial pattern, often described as ‘doughnuts’ and ‘tramlines’, and hyperinflation of the lungs.
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7.19 A post-mortem examination of this 4-year-old cat revealed aspirated plant material in a bronchus. (Reproduced with permission of Veterinary Learning Systems, Trenton, NJ)
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7.23 (a) Right lateral, (b) left lateral and (c) ventrodorsal radiographs of a 4-year-old male German Shepherd Dog with chronic rhinitis. The dog presented following an acute episode of gagging and retching and in respiratory distress. Note the alveolar pattern and air bronchograms (predominantly in the right middle lung lobe and caudal portion of the left cranial lung lobe), which are typical of aspiration pneumonia.
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7.24 (a) Right lateral and (b) ventrodorsal radiographs of a 2-month-old male Cane Corso that presented with increased respiratory rate and effort after being choked when its lead became entangled with that of another dog. The dog was briefly unconscious after the incident. Note the bilateral alveolar pattern localized to both caudal lung lobes; this is the classic pattern and distribution seen with non-cardiogenic oedema.
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7.25 (a) Left lateral and (b) ventrodorsal radiographs of a 4-year-old Bichon Frise that presented in severe respiratory distress after a road traffic accident. Significant right-sided pulmonary contusions are present (alveolar pattern) in addition to a pneumothorax, pneumomediastinum and subcutaneous emphysema.
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7.26 Lateral thoracic radiograph of a mixed-breed dog with severe autoagglutinating haemolytic anaemia that developed acute respiratory distress. A presumptive diagnosis of pulmonary thromboembolism was made based on the severity of the hypoxia and lack of radiographic abnormalities.
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7.29 Thoracocentesis is performed in this small dog using a butterfly catheter and a three-way stopcock.
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7.33 Chest tube placement. (a) Prior to placement of the chest tube, the thoracic skin is pulled cranially by an assistant; release of the skin will create a subcutaneous tunnel for the tube. (b) The trochar thoracostomy tube has been inserted through a skin incision (10th intercostal space) and is being directed subcutaneously in a cranial direction. (a, courtesy of Dr D Holt; b, courtesy of Dr R White)
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7.34 Lateral thoracic radiograph of a 5-year-old Domestic Longhair cat presented for progressive respiratory distress. The radiograph reveals a marked pleural effusion. Thoracocentesis was performed and 150 ml of a chylous effusion was removed.
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7.35 (a) Left lateral and (b) ventrodorsal radiographs of a 2-year-old female neutered Tibetan Terrier that presented with a 2-day history of lethargy, anorexia and vomiting several times. There is bilateral pleural effusion (worse on the right) and an alveolar pattern in the right middle lung lobe with a subtle vesicular appearance to the parenchyma. The main lobar artery appears narrowed on the lateral view and there are smaller air bronchograms in the lobe that are not oriented in the proper direction. There is also an alveolar pattern in the left cranial lung lobe. The dog was diagnosed with a lung lobe torsion and taken to surgery for a right middle lung lobectomy.
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7.36 Lateral thoracic radiograph of a 9-year-old Siamese cat presented for increased respiratory rate and effort. Decreased chest compressibility and dull ventral lung sounds were noted on physical examination. The radiograph reveals a marked pleural effusion, elevation of the carina and narrowing of the trachea caused by a large mediastinal mass.
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7.37 (a) Right lateral and (b) ventrodorsal radiographs of an 8-year-old male neutered Golden Retriever presented in acute respiratory distress. On auscultation there were very dull lung sounds, especially on the left side of the thorax. A spontaneous pneumothorax was diagnosed and at surgery a leaking bulla was found in the left cranial lung lobe. A partial lung lobectomy was performed.
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7.38 (a) Right lateral and (b) ventrodorsal radiographs of a 10-year-old male Labrador Retriever that had been hit by a truck. A diaphragmatic hernia with herniation of the liver, part of the stomach and several loops of small intestine can be seen.
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7.39 Ventrodorsal radiograph of a 2-month-old male Pit Bull Terrier puppy after a road traffic accident. Fractures of ribs 4–9 can be seen on the left-hand side of the chest, in addition to severe pulmonary contusions.
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7.40 Normal capnogram showing the various phases of respiration. A = baseline, representing the beginning of expiration (dead space gas), this should be zero; B = sharp upstroke, representing the mixing of dead space gas and alveolar gas; C = change to alveolar gas; C–D = the alveolar plateau, increasing towards the endpoint; D = end-tidal carbon dioxide value; E = end of inspiratory phase, showing a rapid decrease in carbon dioxide. (Courtesy of K Walsh and reproduced from )
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7.41 Cavalier King Charles Spaniel with severe pulmonary contusions and a pneumothorax following a road traffic accident. He was hypoxaemic and in significant respiratory distress in an oxygen cage, so he was anaesthetized, intubated and positive pressure ventilation was initiated.
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7.42 (a) A ventilator breath compared with a spontaneous patient breath. The spontaneous breath (dotted line) begins as a negative inspiratory effort, followed by a slightly positive airway pressure during exhalation. In contrast, the ventilator breath (solid line) generates exclusively positive airway pressure. (b) In assist/control ventilation, the ventilator delivers a set number of breaths, to a set pressure or tidal volume. The machine delivers these breaths when the patient creates a negative pressure in the airway; if the patient is not breathing, the machine will automatically deliver the set respiration rate. If the patient breathes faster than the set rate, the machine is also triggered, and it will deliver the desired tidal volume for each patient-initiated breath. (c) In synchronous intermittent mandatory ventilation (SIMV), the ventilator is set to deliver a desired number of breaths. The breaths are delivered when the machine senses a negative pressure effort by the patient (‘synchronous’). Between each breath, if the patient breathes spontaneously, the machine does not ‘kick in’ with a breath of its own, and these patient-induced breaths only reach the negative pressure and tidal volume determined by the patient. IPPV = intermittent positive ressure ventilation.
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