Dealing with dyspneic cats (Proceedings)

Dyspneic cats are frequently presented to clinicians as emergencies. Because they are fragile and very easily stressed, it is a good idea to have a planned, rational and quickly implementable strategy for their management. With careful handling and therapy, these dynamic patients can be satisfying to treat.

Initial stabilization

At their initial presentation, most dyspneic cats are easy to recognize and are extremely stressed. Cats often "hide" their illnesses and their owners may not recognize that there is a problem until it has progressed to a severe state. Furthermore, as a species, cats are not used to being handled by strangers or being transported by their owners to a strange place. Therefore, the patient is often presented with advanced or even fulminant disease, and may struggle or panic if stressed by handling. Thus, in addition to decreased oxygen availability due to disease, these patients may experience increased oxygen demands because of muscle activity.

Therefore, optimal initial management of dyspneic cats should involve an initial short period (10-15 minutes) of stabilization in oxygen, ideally with minimal handling in a quiet place. For most cats, this brief opportunity to rest allows them to improve their tissue oxygen delivery and decrease their oxygen consumption, optimizing their condition so that the clinician can then perform a brief physical examination and determine the optimal therapy. While the cat is resting in oxygen, the clinician has an opportunity to have a brief conversation with the owner to determine the pertinent history, including signalment, pre-existing diseases and medications, exposure to other cats and toxins, and the duration and progression of the dyspnea.

Methods of oxygen administration for cats

Several possible methods of oxygen administration are commonly used. Each method has specific advantages and disadvantages, and the clinician should attempt to familiarize himself with as many different methods as possible.

Masks, bags, hoods

In each case, oxygen is pumped into a contained area over the head or muzzle of the animal. Most oxygen masks are made of transparent plastic, through which the animal can be observed. Several methods have been advocated by which increased concentrations of oxygen can be achieved, including canopy O2, placement of a plastic bag over the head into which oxygen is pumped, and the use of an Elizabethan collar with plastic wrap covering the front.

Advantages

• Easy to use

• Quickly placed in position in emergency situations

• Depending on flow rates and tightness of fit, very high oxygen concentrations can be achieved

• Because only the head is covered, the clinician can still work with the animal for diagnostic tests or therapeutics

Disadvantages:

• May not be well tolerated by dyspneic animals, and involves handling and restraint which may not be tolerated by dyspneic cats

• Not effective in animals that are moving around

• Animals can overheat extremely quickly, especially if they are large and rapidly breathing. The clinician must observe carefully for evidence of excessive panting and increases in body temperature, which could be very detrimental in the dyspneic animal.

• Carbon dioxide may build up to high concentrations, especially if there is no avenue for outflow from the hood or mask. Hypercarbia can lead to significant respiratory acidosis.

Oxygen cages

Oxygen cages are now supplied by a number of manufacturers. As well as providing a higher concentration of inspired oxygen, a good oxygen cage should also allow control of internal cage temperature and humidity. A good oxygen cage (Intensive Care Systems, Plas Labs, Lansing, Michigan) should be capable of reaching oxygen concentrations in excess of 80%, for use with severely dyspneic animals.

Advantages

• Non-invasive and very well tolerated, especially by cats

• High oxygen concentrations can be achieved

Disadvantages

• The animal is hidden behind glass walls, and cannot be manipulated, examined, or treated by the clinician

• Large dogs may become overheated

• Oxygen cages are expensive to obtain

• Oxygen cages can be wasteful of oxygen, since each time the door is opened the oxygen inside is lost and must be replaced

Intubation and positive pressure ventilation

Ventilatory support may be required If respiratory failure is already present or is predictable based on the condition of the patient. Anesthesia, intubation and positive pressure ventilation may be required to allow vital diagnostic tests such as radiographs to be performed, especially in animals that are in extreme distress and are not responding to non-specific therapy. Dyspneic patients should only be anesthetized and ventilated as a last resort, to support respiratory function while diagnostic tests are performed and definitive therapy is pursued.

Initial examination of the dyspneic cat

Once the cat has had a few minutes to stabilize with minimal handling and oxygen supplementation, the next step is for the clinician to perform a brief physical examination. This examination should be brief and should concentrate on the cardiopulmonary systems; a further and more detailed physical examination should be delayed until the patient is more stable. The physical examination should include evaluation of the mucous membranes, palpation of the chest wall, cervical area, and cranial thorax, and auscultation of the heart and lungs.

Palpation

A brief palpation of the neck and chest wall can provide helpful information. Cervical masses can be found that might be contributing to an airway obstruction, and the compressibility of the cranial thorax can be decreased in animals with cranial mediastinal masses.

Mucous membrane color

Evaluation of the mucous membranes can provide useful information about the respiratory system. The mucous membranes may vary from brick red, normal pale pink, white, through grey, to purple or blue. The color depends on the amount of blood flow through the tissues, the concentration of hemoglobin in the blood, and whether or not the hemoglobin is saturated with oxygen. Clinicians attempt to use mucous membrane color as a crude estimate of the degree of hypoxemia, but it is important to recognize that it is in fact a very insensitive tool, as cyanosis does not occur until the PaO2 is less than about 55 mmHg. In addition, if the mucous membranes are pale (as occurs often in cats because of either anemia or vasoconstriction) then cyanosis may not be visible because there is not enough hemoglobin circulating through the capillary beds in the mucosae.

Auscultation

Careful auscultation of the heart, lungs and airways is a vital part of every physical examination. Auscultation should be performed in a quiet environment, and the cat should be breathing through a closed mouth. With practice, auscultation of the respiratory system is an extremely useful diagnostic tool that can be mastered by anyone. It is, however, yet another crude method of assessing the respiratory system. Falsely normal findings may occur in animals that are obese, or in very deep-chested animals. When a patient has a change in respiratory rate or pattern or a cough, pulmonary disease should be suspected even if auscultation appears normal. Normal respiration should be quiet and barely perceptible on auscultation. Several types of sound may be heard when the diseased respiratory system is ausculted:

Upper airway sounds: probably the most common findings. These are loud, harsh sounds that are particularly evident in animals with partial obstruction of the upper airway, but may also be heard in animals that are panting. These sounds are loudest at the thoracic inlet, and are particularly prominent when the bell of the stethoscope is placed over the trachea and larynx. It is important to always auscult the cervical trachea as well as the lungs, in order to determine what component of the ausculted sounds are coming from the airway.

Harsh rales: Rales are harsh noises that are coming from the lower airways, and may vary from a slight increase in respiratory noise, to profoundly harsh respiration. They are associated with various disorders of the lungs and/or airways, and are often caused by narrowing of airways and turbulent flow in the airways. Such narrowing might be caused by excess mucous, edema, neoplasia, or inflammation.

Wheezes: Wheezes are loud, slightly musical or squeaky sounds that come from the lower airways or bronchi. They represent air moving through airways that have been narrowed by mucous plugs or other pathology. Wheezes are commonly heard in patients with bronchial disease, for example in cats with feline asthma.

Crackles: Crackles sound like the rattle of plastic as it is crinkled. They are usually caused by the presence of fluid within the alveoli. The presence of crackles is usually an ominous sign of serious pulmonary disease. In some animals, crackles may be difficult to detect, and they may only be heard at the end of inspiration when the alveoli are most full of air. The can should be encouraged to take a deep breath by briefly holding the nostrils for a second or two. Crackles may vary in intensity from loud to very soft. Very loud harsh crackles are sometimes heard in dogs with severe bronchial disease, that do not have fluid in their alveoli. In such cases, the crackles are probably caused by the snapping open and closed of weakened bronchi.

Dull sounds: Sometimes it is difficult to hear air movement in all or part of the lung fields. If lung sounds cannot be heard in one localized area of the chest, this suggests absence of air movement through one particular lung lobe, such as might occur with a consolidated lung lobe, neoplastic masses, or lung lobe torsion. If the sounds are dull all over the chest, one might consider pleural disease such as pleural effusion, pneumothorax, or diaphragmatic hernia. In some cases, a fluid line may be ausculted above which air movement can be easily heard, but below which the sounds are dull.

Cardiac auscultation: Heart disease is an extremely important cause of dyspnea in cats, therefore the heart should be carefully ausculted in each case. Although some cats with congestive heart failure have normal cardiac auscultation, most will have evidence of a murmur or an arrhythmia. Discovery of an abnormal sound on cardiac auscultation elevates heart failure on the list of differentials and provides the clinician with an important therapeutic direction.

Management strategies

Once the physical exam has been completed, the clinician should be able to categorize the probable cause of dyspnea. The majority of dyspneic cats have one of the following:

• Congestive heart failure (dull lung sounds or crackles, heart murmur, arrhythmia)

• Feline bronchial disease/asthma (history of cough, harsh lung sounds or wheezes)

• Pleural effusion (dull lung sounds).

If possible without stressing the patient, a peripheral venous catheter should ideally be placed, which will facilitate management, especially if the cat decompensates and emergency intubation becomes necessary. If the patient is extremely fractious, catheter placement may be delayed until the patient is slightly more stable.

If a pleural effusion is suspected based on the finding of dull lung sounds on auscultation, the next step in management is to perform a thoracocentesis. This procedure should be performed prior to obtaining radiographs, as restraint and positioning for radiography can be very stressful and can precipitate desaturation in some cases. Thoracocentesis can be helpful because not only does it provide diagnostic information (analysis of the type of fluid obtained), but also if fluid can be completely evacuated from the chest then the procedure can be therapeutic as well.

If congestive heart failure causing pulmonary edema is suspected based on the findings of harsh lung sounds or crackles, then immediate therapy should include administration of furosemide, either intravenously if a catheter has been placed, or intramuscularly if not. Care should be taken to ensure that judicious doses of furosemide are used in this species, as most cats do not drink enough water to make up for excessive urinary water losses. Cats are more sensitive to furosemide than dogs, and therefore require about half of the dose that would be administered to a dog in a similar situation. Furosemide should be given to the dyspneic cat before congestive heart failure is confirmed by radiographs or echocardiography, as a single dose is unlikely to cause a problem even if the heart is not the cause of dyspnea.

If bronchial disease (feline asthma) is suspected based on the history and the auscultation of wheezes, harsh sounds with a normal cardiac auscultation, then immediate therapy should include the administration of corticosteroids and bronchodilators. Ideally, these drugs should be given intravenously, but if vascular access cannot be established, then they can be given intramuscularly, or by aerosol inhalation if the cat tolerates placement of a face mask.

Typically, thoracocentesis and/or the administration of these life-saving drugs can make a difference in even severely affected cats within a short period of time. Most cats will show improvement within 30-60 minutes. If the cat fails to improve after a reasonable time, then diagnostic tests including radiography should be pursued with great care. Oxygen should be provided by flow-by delivery during the procedure. If necessary, the cat may require sedation, but if the cat is sedated the clinician must be prepared to perform an immediate intubation if respiratory drive is decreased by the sedative drugs. Once intubated, the cat should receive positive pressure ventilation with 100% oxygen while diagnostics are pursued.

References Available On Request