23 Respiratory distress
Dogs and cats with respiratory distress are a relatively common presentation to emergency clinics. These patients are often extremely unstable and a rational approach to their management can make the difference between life and death in the initial period following presentation. This is especially true of cats and the bulk of this chapter will therefore focus on this species. However, many of the principles discussed are equally applicable to dogs, about which some information is provided at the end.
Respiratory distress can occur as a result of an abnormality affecting any one or more of the following areas:
Being able to identify the area affected is extremely important with respect to patient management.
It is often possible to make sensible judgements as to the most likely causes of a cat’s respiratory distress on the basis of its signalment and a very brief history. For example:
Clinical Tip
The author’s initial approach to a cat that presents with moderate or severe respiratory distress is as follows.
The cat is first briefly observed in its carrier as much information can often be obtained from this approach (see Table 23.1).
Table 23.1 Observations and their interpretation in cats with respiratory distress
An extremely brief examination is then performed. This is done with the cat in its carrier, if that is the cat’s preferred option and the carrier design allows. Otherwise, it is done in close proximity to a prepared oxygen cage and only if the cat has not been distressed in any noticeable way by removal from its carrier. Attention is paid to the following:
Table 23.2 presents some of the more common causes of respiratory distress in cats and possible associated findings on auscultation. The reader is reminded that normal lung sounds are quieter caudodorsally and louder cranioventrally.
Table 23.2 Some causes of respiratory distress in cats and possible associated findings on auscultation
| Cause of respiratory distress | Possible findings on auscultation |
|---|---|
| URT obstruction | Increased URT noise with possible stridor/stertor |
| Feline bronchial disease | Harsh lung sounds, wheezes, (crackles) |
| Pulmonary oedema | Harsh lung sounds, crackles |
| Pulmonary contusions | Loud/harsh lung sounds (crackles) |
| Pleural effusion | Lung sounds quieter ventrally (harsh dorsally); heart sounds may be muffled |
| Pneumothorax | Lung sounds quieter dorsally (or diffusely) |
| Intrathoracic mass | Lung sounds dull (heart sounds displaced) |
| Diaphragmatic rupture | Lung sounds dull, gut sounds in thorax |
URT, upper respiratory tract.
Following brief examination, the cat is placed in an oxygen cage and kept under close observation. The author uses this time to have a discussion with the owner. The combination of the cat’s signalment, history, observation and brief examination may well have identified the anatomical location and possibly the specific cause of the cat’s respiratory distress. It may therefore be possible at this stage to discuss the treatment plan, prognosis and costs with the owner before the cat is subjected to further management. For example:
Clinical Tip
Given the often unstable and precarious status of dyspnoeic cats, it is more important than ever to subject each proposed intervention to a risk–benefit analysis.
The clinician should not be afraid to leave a cat in oxygen for an extended period of stabilization without performing any interventions (other than possibly drug therapy).
The next step in the patient’s management is dependent on the suspected diagnosis, on the cat’s response to oxygen therapy and on the owner’s position with respect to the costs involved. It is not therefore possible to be too prescriptive here and what follows is a general discussion of the interventions that may be indicated.
A more comprehensive physical examination is required but this is often delayed until intravenous access has been established.
There are a number of benefits of establishing intravenous access as soon as possible, including more rapid drug administration in a subsequent crisis. Nevertheless, there is no rational justification for excessive manual restraint of a cat with respiratory distress and an intravenous catheter should only be placed if the patient is sufficiently compliant. If a catheter is placed, blood should be obtained for an emergency database (see Ch. 3).
The results of standard haematology and biochemistry screening are extremely unlikely to affect the management of a cat with respiratory distress in the initial period. If blood sampling is deemed to be important in the patient’s management, the reader is encouraged to delay venepuncture until the cat is much more stable and to make use of topical local anaesthesia (EMLA® cream 5%, AstraZeneca – see Ch. 5).
A number of different drugs may be indicated in the early management of a cat with respiratory distress and these are summarized in Table 23.3. If a diagnosis is not immediately forthcoming when presented with a cat in severe respiratory distress, and the cat is in extremis or response to oxygen therapy alone is poor, it is reasonable to administer an empirical combination of agents via the intramuscular route. The author administers furosemide, dexamethasone and terbutaline by intramuscular injection in such cases and this is usually accompanied by morphine at a dose rate of 0.1 mg/kg (estimated body weight).
Table 23.3 Drugs that may be indicated in the early management of cats with respiratory distress
| Drug | Dose/route | Indications/comments |
|---|---|---|
| Furosemide | 1–4 mg/kg i.v., i.m. q 1–2 hr until clinical improvement; then q 12 hr | |
| Glyceryl trinitrate 2% ointment | Apply 6 mm q 6–8 hr topically | |
| Morphine | 0.1 mg/kg slow i.v., s.c., q 6 hr | |
| Butorphanol | 0.1 mg/kg i.v., s.c. | Indicated for anxiolysis or prior to thoracocentesis |
| Dexamethasone | 0.25 mg/kg i.v., i.m, s.c. q 24 hr | |
| Terbutaline | 0.01 mg/kg slow i.v., s.c. q 4 hr | |
| Midazolam | 0.1–0.2 mg/kg i.m. or i.v. | May be required for thoracocentesis |
| Ketamine | 1–2 mg/kg i.m. or i.v. | ntraindicated in hypertrophic cardiomyopathy |
i.m., intramuscular; i.v., intravenous; s.c., subcutaneous.
Although there are potential pitfalls with relying solely on pulse oximetry, it does provide an easy and non-invasive technique for monitoring compliant cats with respiratory distress. The probe may be fixed in place (e.g. on the pinna, paw or tail) and the monitor left in or out of the oxygen cage as appropriate.
Ultrasonography is extremely useful for respiratory distress in cats, where it is used to identify pleural effusion in particular. Even in the most novice hands, it may also be possible to detect gross abnormalities in cardiac morphology and fractional shortening, and diaphragmatic rupture can also be identified. Following an initial period of stabilization, it is the author’s experience that the vast majority of cats tolerate this procedure very well. If facilities allow, scanning can be done without removing the cat from the oxygen cage. Pleural fluid is identified as a predominantly anechoic or hypoechoic area between the hyperechoic lung margin and the chest wall. The edges of the lung lobes may be seen to be flapping about in the fluid.
Thoracocentesis is a relatively simple procedure to perform (see pp. 291–293). It readily allows pleural space disease to be identified, and can markedly improve a patient’s respiratory status by evacuating the pleural cavity and allowing the lungs to expand more fully. If pleural effusion is present, samples can also be collected for laboratory analysis. If pleural space disease is suspected, thoracocentesis should be performed before radiography to improve patient stability and to produce radiographs that are likely to yield more useful information.
In non-compliant cats with confirmed pleural space disease, it is preferable to use judicious cardiovascular-sparing sedation in order to allow the procedure to be performed successfully. This is likely to be safer for the patient than repeated attempts, with the extra potential for complications and greater stress to the cat. If circumstances allow, the author prefers to administer a low dose of an opioid (e.g. 0.1 mg/kg morphine slow i.v. or i.m.) to all cats prior to thoracocentesis. If this is inadequate alone, midazolam (0.1–0.2 mg/kg i.v. or i.m.) is administered in addition. If yet more sedation is required, ketamine (1–2 mg/kg i.v. or i.m.) is administered and topped up as necessary; however, ketamine must be used judiciously in cats with suspected heart disease as it is relatively contraindicated in hypertrophic cardiomyopathy.
It is neither possible nor indeed necessary to evacuate the pleural space entirely. That said, the removal of less than 15–20 ml/kg of pleural space-occupying material is unlikely to produce significant improvement in the patient’s respiratory status.
Clinical Tip
Thoracic radiography is usually indicated at some point in cats with respiratory distress that does not emanate from the upper respiratory tract. However, it is hopefully clear from this discussion that much information can be obtained through a combination of the patient’s history, signalment, observation, brief examination and response to medical therapy. Thoracic radiography straight after presentation is not typically necessary.
The approach advocated throughout this chapter of subjecting the patient to minimum stress is no more applicable than in the context of radiography. If radiography is performed, everything should be prepared before bringing the cat to the radiography room and minimal restraint should be used. If tolerated, oxygen supplementation is provided by mask or flow-by. The intention here is to produce an image that allows the anatomical area affected to be identified and not to produce the perfect thoracic radiograph. Even a rotated dorsoventral radiograph can provide more than enough information for the cat’s initial management. A dyspnoeic cat should never be restrained in dorsal recumbency and it is typically best to minimize the amount of time spent in lateral recumbency.
The approach to canine respiratory distress is very similar to that in cats as described above. In general, dogs are less precariously poised and less vulnerable to stress but nevertheless minimal stress, gentle handling and strict rest are paramount. In the author’s experience, dogs presenting with severe respiratory distress are most commonly suffering from: