Respiratory Work-up in horses
Dr. C.J. (Kate) Savage BVSc(hons), MS, PhD, Diplomate ACVIM
Specialist in Equine Medicine
Head of Equine Clinical Services,
Equine Centre, University of Melbourne, Werribee, AUSTRALIA.
Performing a thorough physical examination, including (1) rebreathing auscultation of
the trachea and left and right hemithoraces and (2) percussion of the sinuses is essential
in the sick horse. Endoscopic examination of the upper and lower respiratory system
is also critical for definitively diagnosing certain conditions. The veterinarian also is
assisted in diagnosing respiratory disease in the horse by ultrasonographic evaluation,
tracheal lavage (TL) techniques and broncho-alveolar lavage (BAL) and more rarely
radiographs (more in foals). Thoracocentesis and thoracic drainage may be used
diagnostically and therapeutically. Lung biopsy is used rarely but can be a useful tool.
EVALUATION OF THE PATIENT FROM A DISTANCE
-The first thing to notice is the condition score of the horse, as this may help determine
whether there is underlying chronicity to the disease state.
-Then note the respiratory effort that the horse is making by watching the movement of
the nares and the abdomen. Flaring nares are indicators of either upper or lower
respiratory distress, as is abdominal effort in breathing. It is very important to attempt
to discern whether or not the horse is in predominantly expiratory or inspiratory
distress
-In general, horses with upper respiratory (i.e. extrathoracic) compromise/partial
obstruction have greater difficulty during inspiration, whereas horses with intrathoracic
non-fixed obstruction usually demonstrate greater effort during expiration. However,
if horses have fixed intra- or extra-thoracic obstructions, then dyspnoea may occur
during both inspiration and expiration.
WHY do we care ?
-Assessment of the external abdominal oblique musculature is important. If it is
hypertrophied (“heave line”), then the effort of breathing presumably has been greater
than normal (hyperpnoea). This is often particularly noticeable in cases of Recurrent
Airway Obstruction [RAO, Inflammatory airway disease (IAD), Chronic obstructive
Airway Disease, COPD].
-Horses with pleural pain or effusion often have shallow breathing and abducted
elbows. Sometimes there may be a plaque of sternal oedema (the badge of
pleuropneumonia” !). You have to try to discern this from ventral oedema due to
hypoalbuminaemia (eg. colotyphlitis (diarrhoea loss!) etc.) and rarely local trauma.
-If the horse has either puncture wounds, lacerations (especially of the thorax, axillary
(elbow), pectoral or cervical regions), then these should be observed, but also warrant
closer inspection, palpation and ultrasonographic and/or radiological evaluation.
Smaller puncture wounds penetrating air-filled thoracic or tracheal structures may only
show up as emphysema (crackly feeling in skin).
PHYSICAL EXAMINATION OF THE HORSE
A thorough physical examination is essential. Horses with apparent respiratory
distress may suffer from respiratory disease, however, in a large number of cases
tachypnoea may occur secondary to involvement of other systems and manifest
because of pain or acid-base complications. Common causes for tachypnoea of nonpulmonary origin in equine neonates are fever, septicaemia, shock and neurological
abnormalities.
-the resting respiratory rate in horses with a history or obvious clinical signs of
respiratory distress should be performed before exciting the horse in any way. To best
perform this measurement on foals, the foal should not be restrained in any manner, as
this can substantially change the resting values for the respiratory and heart rates.
-The normal respiratory rate:
1) adult horses = (8)12 to 24 breaths per minute (bpm) – usually < 16 bpm
2) foals during the first weeks of life the respiratory rate = 20 to 40 BPM.
3) foals (new born - first few hours after parturition), the respiratory rate is
often elevated to approximately 60 to 80 bpm.
-Respiratory depth and effort should also be ascertained.
-In horses with thoracic pain of pleural origin (pleurodynia) their breathing pattern is
often shallow, so that expansion and tension of inflamed tissues is not exacerbated (i.e.
minimise the pain !). Palpation of the pectoral, axillary and thoracic regions is
important in cases of trauma, as emphysema [feels crackly (crepitus) and sometimes
looks bumpy and “blown up” may be better recognized via palpation rather than
visually].
-Evaluate mucous membranes (mm colour, crt) before taking the rectal temperature as that could promote contamination of the veterinarian’s hands with faecal material
and potentiate other disease, like Salmonellosis!
-Normal mucous membranes should be pink and moist with a capillary refill time less
than 2.0-2.5 seconds.
-If mucous membranes are cyanotic, injected or pale, or have petechial
haemorrhages further testing should be considered to enhance
documentation of these abnormalities.
-As well as inspecting the mucous membranes in horses, an oral examination may also
be performed at this time. This is especially relevant in foals with a history of nasal
reflux of milk, compounded by respiratory disease. Although there are a number of
reasons for this syndrome, these foals always should be examined for cleft palate.
Sometimes owners do not recognize that there is a problem in horses with minor soft
palate clefts, although if questioned specifically owners usually relate that there is a
prolonged history of nasal reflux of fluid (eg. milk, water). Secondary aspiration
pneumonia is a relatively common complication in these animals, especially where the
cleft deformity is severe.
-The heart rate provides valuable information about the horse’s demeanour, stimuli to
sympathetic innervation and the state of the cardiac system. If the horse is in pain for
any reason (eg. pleuropneumonia, colic, laceration) tachycardia is frequently present.
It is important to judge: (1) the severity of the tachycardia and (2) whether the
tachycardia is significant and related to other clinical signs, consistent with either
primary respiratory disease or other system involvement (eg. mucopurulent nasal
discharge, fever and coughing in cases of pneumonia versus pulse deficits, abnormal
jugular pulsation and weight loss in cardiac failure versus abdominal pain and absence
of borborygmi in horse with colic). Arrhythmias are important to document in horses
in which one suspects respiratory disease or where tachypnoea or respiratory distress
exist. When arrhythmias occur there may be an underlying cardiac problem, electrolyte
or acid-base abnormalities or they may be idiosyncratic. If an arrhythmia is detected,
yet the remainder of clinical signs shown by the horse could fit with either respiratory
or cardiac disease, then cardiac disease must be considered. If cardiac murmurs are
detected alone or in combination with an arrhythmia, or the jugular pulse is visible
more than a third of the way up the cervical region, when the horse’s head is in an
upright position, primary cardiac disease is more likely than primary respiratory
disease. However, this does not mean that respiratory distress cannot occur in cases of
cardiac failure. Horses that develop left-sided heart failure with increases in left atrial
pressure can acquire pulmonary oedema and severe respiratory signs.
-Horses with transient severe airway obstruction or increased pulmonary artery
pressure may also generate pulmonary oedema.
The degree of radiation of cardiac sounds (this is not talking about a murmur, just
about how far you can hear normal heart sounds from the heart) provides information
on whether excessive pleural fluid exists. Cardiac sounds radiate over a greater area if
there is pleural fluid present because the sound travels in it better. . In cases in which
this feature is detected the practitioner should follow cardiac auscultation with thoracic
auscultation (with and without a rebreathing bag), percussion and ultrasonography (if a
portable unit with a 3.5 to 5 MHz sector transducer is available that is fantastic. It is
also possible to examine the thorax to a lesser degree with a linear 5 MHz transducer –
i.e. the rectal probe).
-Normal equine lung and tracheal sounds usually cannot be discerned above the normal
noise of a stable, however, in a quiet area, normal sounds may be heard in horses that
are not fat. However, in general rebreathing auscultation is more effective and only
takes three to five minutes. The aims of auscultation are to: (1) recognize abnormal
versus normal sounds and (2) recognize the boundaries of normal lung sounds.
DON’T DO IT IF ALREADY DYSPNOEIC
-Lung sounds are referred to as crackles or wheezes.
-Crackles are short-duration (< 20 msec) discontinuous sounds that are -classified as
intermittent or explosive. These are generated by either equalization of pressures after
a collapsed region reopens or by air passage through fluid, hence they often occur at
the end of inspiration (as transpulmonary pressure is high) and may sound like
bubbling. Crackles may occur in a number of disease situations: those with fluid
(secretions or edema) in the airways or alveoli, or those with intermittent expansion
after collapse. The most common clinical scenarios that may produce crackles in the
horse are: (1) pneumonia, (2) RAO/COPD, (3) pulmonary oedema in congestive heart
failure or smoke inhalation and (4) pulmonary fibrosis.
-Wheezes are longer, continuous sounds (> 250 msec) that are often high pitched.
These sounds are generated mostly by vibration of the tissue or secretions of the larger
airways (i.e. caudal trachea, main, lobar and segmental bronchi), after constriction
during expiration or opening during inspiration. Some horses may have severe
involvement of the smaller, respiratory bronchioles without correspondingly severe
wheezes, because the smaller airways cannot generate the velocity required for these
sounds. However, horses with RAO/COPD and inflammatory airway disease (IAD)
often have expiratory wheezes, as the intrathoracic airways are involved.
-There are a number of methods for rebreathing a horse, and one can improvise with
whatever materials are available in the truck (eg. soft plastic bag, obstetrical sleeve). If
none of these items are available, then the simplest method to ensure deep breathing by
the horse is to have the person holding the horse gently place their hand over both
nares, occluding them totally. The horse, depending on its temperament will tolerate
this for a variable time (eg. 10 to 90 seconds). It is best to have the person holding the
nares release as soon as the horse becomes restless, so movement does not interfere
with auscultation. Repeat approximately four to seven times in order to evaluate both
hemithoraces and the trachea. The horse will take a number of deep breaths after
releasing the nares. Alternatively, a holder may gently place a plastic bag (or
disposable plastic bootie or obstetrical sleeve) over the muzzle of the horse. The
crackling of the plastic frightens some horses, so softer plastic items are preferred.
Once the plastic bag is in place over the muzzle the holder(s) should ensure that the
plastic is not sucked into the nares during inspiration, so hold it from the top and even
hold onto and extend the bottom of the bag. The horse should be ausculted while the
bag is in place if good movement of the bag is occurring, but it is best to auscult after
the bag has been removed so that the horse breaths deeply. If coughing occurs while
the rebreathing bag is in place, then it should be noted if it is severe, paroxysmal or
continuous, and whether it appears productive or dry. The easiest way to determine if
a cough is productive in a horse is to watch carefully just after coughing - if the horse
swallows immediately after the coughing it is likely that the cough is productive and
endoscopic examination may reveal significant tracheal discharge. If coughing is
severe or the horse seems distressed by the examination it should be terminated.
-Horses with pleuropneumonia or traumatic pleuritis often exhibit signs of pleural pain
(pleurodynia) on palpation of the intercostal spaces. Horses may grunt, tense their
intercostal muscles as a guarding mechanism or display evasive behaviour. In further
attempts to decrease the pain, the horse may have abducted elbows, prefer to stand
rather than lie and avoid coughing if possible. If coughing occurs it is usually soft and
shallow as is breathing. If the ventrum of the thorax is palpated then not only may it
induce pleurodynia, but one may also discern that there is a plaque of oedema along
the sternal region. This is commonly seen in horses with pleural effusion.
-PERCUSSION CAN BE USED TO TRY TO DETERMINE IF A FLUID LINE
IS PRESENT (i.e. abnormal pleural fluid in chest)
The nares should be examined at close range for the degree of movement and flaring
during inspiration and expiration, and also for any scalding or depigmentation, caused
by chronic nasal discharge. A hand should always be placed a few centimetres in front
of the left and right nares to check for symmetrical and sufficient airflow, especially in
horses with inspiratory stridor suggestive of upper respiratory tract involvement or in
those with facial deformation. Then the SUBMANDIBULAR, LATERAL
RETROPHARYNGEAL, PAROTID AND PRESCAPULAR LYMPH NODES
should be palpated to ascertain their consistency (i.e. firm versus soft) and whether
they are enlarged. Don’t forget that the medial retropharyngeal lymph nodes really
need to be visualised (in the guttural pouches via endoscopy) to see if they are
enlarged. Mediastinal lymph nodes may obstruct anterior vena cava and give rise to an
abnormal jugular pulse or head swelling (use your ultrasound machine or refer it for
ultrasonography with a 2-3.5 MHz probe).
Conditions of viborg’s triangle include cellulitis and guttural pouch tympany, guttural
pouch empyema and guttural pouch mycosis. Whilst guttural pouch tympany is usually
obvious in affected foals and younger horses, it may be difficult to accurately define
guttural pouch empyema using palpation alone.
The larynx and cranial tracheal region should also be palpated in an attempt to induce a
cough. The character of the induced cough [(i.e. dry, productive, harsh, frequent,
paroxysmal (i.e. bouts)] and the ease with which it was elicited provide information
about the respiratory condition. Other reasons for palpation of the trachea are to
ascertain whether it is flattened or whether chondroma formation exists. Both
conditions could cause respiratory difficulty during both inspiration and expiration, but
the latter is indicative of the existence of a prior respiratory problem of sufficient
severity that warranted percutaneous transtracheal lavage. For this reason many
veterinarians palpate the trachea of horses as part of a pre-purchase examination.
Percussion of the frontal and maxillary sinuses should be part of every physical
examination in which the respiratory system is thought to be involved. There are six
paranasal sinuses in the equine skull: (1) frontal sinus, (2) rostral maxillary sinus, (3)
caudal maxillary sinus, (4) ventral conchal sinus, (5) dorsal conchal sinus and (6)
sphenopalatine sinus, all of which communicate with the nasal cavity by some direct or
indirect route and are lined with respiratory epithelium.
-The best method for percussion of the sinuses is to open the mouth and grab the
tongue (this increases resonance so it’s easier to hear), then identify the specific
regions and then, using two fingers, tap the sinus region on the right and then the left
side at the same level. This allows comparison of the left and right sides, one of which
can act as a control side, except in cases of bilateral involvement or deviation of the
septum. .
ENDOSCOPY OF THE RESPIRATORY SYSTEM FOR THE AMBULATORY
CLINICIAN
Rhinoscopy, pharyngoscopy and laryngoscopy and tracheoscopy are important aids to
the diagnosis of conditions affecting these areas.
-The endoscope usually travels from the nostril to the pharynx by the ventral meatus,
however, the middle and dorsal meati also can be evaluated.
-It is imperative to ensure that the endoscope is positioned in the ventral meatus if the
pharynx is to be reached, otherwise the ethmoid turbinates may be traumatized with
subsequent profuse bleeding (unhappy client !).
To avoid this iartrogenic haemorrhage (yes, your fault !!) with your scope or stomach
tube, make sure that you are positioned in the ventral meatus, but also as you retract
the tube or scope from oesophagus, trachea or larynx (and are pulling out) ensure that
the holder of the horse has the head restrained so it can’t toss it, as a head toss often
“tosses” the scope or tube into the ethmoids.
-Provided the endoscope is moved relatively quickly from the point of the external
nares to approximately 10 cm into the nasal passage, the horse usually does not object
strenuously to endoscopy. However, after this point, in order to evaluate all of the
structures of the nasal passages, one should move the endoscope very slowly and
manipulate the endoscope into the middle meatus to evaluate discharge that may
emanate from the sinuses and the dorsal meatus. THIS IS A USEFUL METHOD IF
YOU REALLY NEED TO LOOK AT THE NASAL PASSAGES (and you don’t
want the scope to traumatise them first). OTHERWISE the best method of effective
rhinoscopy is to pass the endoscope into the pharynx via the ventral meatus (i.e. to a
level of approximately 25 to 40 cm ), examine the pharynx, larynx and trachea and then
slowly retract the endoscope in order to evaluate the nasal passage. For complete
examination the endoscope should be passed into both the left and right nares.
-Tracheoscopy: The trachea should be evaluated to ascertain: (1) the presence and
character of discharge, (2) the presence of anatomical defects or abnormalities. If
examination of the corina and bronchi is necessary, then the endoscope length will
need to exceed the commonly used one (1) meter endoscope.
TRACHEAL LAVAGE – great for culture, and best for cytology if you need it from
both left and right lungs (think about the difference with a BAL – see later--I usually
sedate the horse eg. for a 500 kg that is not dyspnoeic: 150 mg xylazine + 2mg
butorphanol. Often they just need to be twitched.
Tracheal lavage can be percutaneous using a catheter or can be endoscopic, as long as
one has an immersible (sterilisable endoscope – don’t forget to sterilise the water
bottle too and use sterile water to fill it !!).
-Percutaneous tracheal lavage:
•palpate the tracheal rings in mid-ventral neck
•clip and prepare skin with surgical prep
•3-5 ml local anaesthetic – 25 g needle – subcutaneous bleb and then infuse on midline
down to tracheal rings
•1 cm stab incision (no 15 blade) – I have the blade facing up, so if the horse lifts its
head unexpectedly it doesn’t make a large laceration
•sterile nested trochar or catheter (special ones are made for tracheal lavages) passes
through the incision and then (holding the trachea firmly) move down to the trachea,
and seat your trochar /catheter between the tracheal rings (don’t go through the
cartilage !!). Point slightly down towards the corina as you go through - you don’t
want to perforate the other side !!
•Remove stylet
•place the sterile tubing down the trochar/catheter
• pass 10 of 30 ml (adult) or 3-12 ml of 5-15 ml (foal, yearling, pony) of sterile
lactated ringers (kinder to cells than saline !). Then try to retrieve and inject more
lactated ringers if necessary. TRY NOT TO INDUCE COUGHING AND KEEP
THE HEAD STILL!
•Remove the sterile tubing
•If the sample is very viscous, just aspirate for as long as is practical and then if you
can’t get it to the syringe, just remove the polyethylene tubing and cut it with sterile
technique and push the lactated ringers through the tube so some goes into a plain tube
for culture (aerobic and anaerobic) and into an EDTA tube for cytology. If you have
to send it away, transfer the culture to an aerobic/anaerobic swab and make some
slides from the secretions in the EDTA tube
•Remove the trochar/catheter – place sterile swabs on the incision and press to control
local haemorrhage.
•BEFORE PERFORMING A PERCUTANEOUS TL/TW – warn the client that
rarely you may see emphysema, local infection and chondroma formation. Owners of
Thoroughbreds love the endoscopic TL because there is no evidence of a TL having
taken place – whereas one always runs ones fingers down the trachea in weanlings and
yearlings to check for a chondroma !
-Endoscopic tracheal lavage:
•the guarded Darien® catheter is great, but hard to get
•so polyethylene tubing (non-guarded) is usually sufficient.
•It helps if you pass the scope straight to the nasopharynx and without touching the
sides of the nasal passages too much, lift the chin of the horse (to facilitate laryngeal
opening) and slip the endoscope into the trachea. Then pass (whilst looking for
secretions) and then push the polyethylene tubing out and pass 15 of 30 ml (adult) or
3-12 ml of 5-15 ml (foal, yearling, pony) of sterile lactated ringers (kinder to cells than
saline !). Then advance 5-15 cm and without getting the tip of your scope in the fluid,
use the polyethylene tubing to aspirate the fluid (with secretions !).
•If it is very viscous, just aspirate for as long as is practical and then if you can’t get it
to the syringe, just remove the polyethylene tubing and cut it with sterile technique and
push the lactated ringers through the tube so some goes into a plain tube for culture
(aerobic and anaerobic) and into an EDTA tube for cytology. If you have to send it
away, transfer the culture to an aerobic/anaerobic swab and make some slides from the
secretions in the EDTA tube.
I use TL for culture and sensitivity usually, as it gets bacteria from both right and left
hemithoraces and both ventral and dorsal portions of the lungs. It is also useful for
cytology if you believe you have a localised disease process, because it gathers the
cells from all parts of the lung. If you have generalised disease, then BAL cytology is
fantastic, because although it gathers cells from a very small part of the lung (usually
we think right dorsal if BAL is performed “blindly” with a BAL tube and a long sterile
endoscope is not used), it doesn’t matter that your sample is from a small area if all the
lung has similar cells, but of course in a pulmonary abscess that is localised in the left
ventral lung, then BAL is not a good choice, as you might get a normal sample !
BROCHOALVEOLAR LAVAGE (BAL) – A client will often refer to this
procedure as a “lung wash”
Bronchoalveolar lavage is a really important part of the respiratory examination. It is
the best test for cytology as long as the disease process is 1) diffuse [especially when
using a blind technique] or 2) localised and known (eg. through the sterilised 2.5-3m
endoscope, so you are directing the endoscope to a certain portion of the lung). Note:
I sometimes use this technique to lavage a pulmonary abscess too. Adequate sedation
and calm help is essential to making BAL an enjoyable part of the respiratory
examination.
-see video in lecture
-If a horse has severe disease that you think involves some chronicity and a BAL
would be helpful, then sometimes it is advisable to have the horse on nasal oxygen and
to use a bronchodilator [eg. IV atropine and/or salbutamol/albuterol (Ventolin®)
and/or ipratropium bromide (Atrovent®)] in order to perform it with decreased
distress to the horse. In acute cases of severe disease such as pleuropneumonia or
pulmonary abscessation, it is used rarely (i.e. when diagnosis is obvious using less
invasive modalities and you can assume an infective process).
ULTRASONOGRAPHY
Try to scan the left and right hemithoraces without clipping in many cases. Use some
alcohol (or use just ultrasound gel in foals that are hypothermic). Clip the haircoat if
you have to, in order to decrease air/gas artefacts. Try to be systematic starting either
cranial and moving caudally and also scanning entire intercostals spaces from dorsal to
ventral, or start caudally and move dorsal to ventral.
Look for:
1) normal white line indicating normal aerated lung that moves with inspiration and
expiration and look for the typical reverberation air artefact.
2) Comet tails – these are little white lines of white that are perpendicular to the lung
surface – they look like a little “comet tail” hence the name. They indicate small
portions of lung that are not aerated (so can indicate pneumonia etc.) or sometimes
that even have bullous formation.
3) fluid (hypoechoic to anechoic – can be mixed, can be gas shadowing etc.) whenever
you are not sure of ventral lung sounds (think of pleuropneumonia; haemothorax if
there is swirling (sometimes traumatic, sometimes due to neoplasia and sometimes
idiopathic); look for consolidated lung; fibrin; and comet tails along the lung border
indicating small non-aerated areas of lung)
4) fractured ribs – in foals (especially large colts !) - with the disruption of the normal
linear regularity of the echogenic cortical bone (be especially vigilant if there is pain,
reluctance to lie on a particular side, emphysema/crepitus, focal oedema etc.)
5) more infrequently dorsal pneumothorax – with a break in the typical reverberation
air artefact.
6) pleural fluid and pneumothorax – It is easier to diagnose when there are both pleural
fluid and pneumothorax as you can get a “curtain sign”. The horse may have fluid and
air in the chest cavity when the horse has a pleuropneumonia and then ruptures some
diseased lung so that it is leaking air into the chest cavity as well OR when there is
trauma and the lung is punctured and there is haemothorax, as well as pneumothorax.
RADIOGRAPHY:
Standing horse or foal – if you want to do more than a weanling, you will need to refer
to a referral hospital for specialty radiographic equipment with the capability to
penetrate a chest
Lateral chest radiographs – we do 4-5 views – caudodorsal (very helpful – look for
normal end on vessels, as well as the parenchymal pattern), craniodorsal - -look for the
corina (bifurcation of the trachea), cardiophrenic angle – very important view behind
the heart (great to see pneumonias, including aspiration pneumonia even though not
completely ventral and it is caudal to heart), cardiac silhouette and then cranioventral
(which is cranial to heart with leg pulled forwards) – the latter is a difficult view.
Note: we can take good radiographs of the sinuses, pharynx, larynx and guttural
pouches. Laterals are most commonly taken and are easiest, but obliques and
dorsoventral views are also important for paranasal sinuses.
THORACOCENTESIS- a sterile technique
Standing horse – usually 6-7th intercostal space (ICS) – determined by
ultrasonography !
-For pleural fluid –usually a pleuropneumonia, but may be Neoplasia, haemothorax etc.
– cannula (eg. teat cannula) or argyle catheter (24 French for pleuropneumonia) is
placed VENTRALLY
-For air – usually a pneumothorax (can be bulla that have ruptured OR trauma –
penetrating wound) – the cannula or catheter is placed DORSALLY
-To prevent iatrogenic pneumothorax: Don’t forget your 3-way stopcock for a teat
cannula, or sterile haemostats followed by a Heimlich valve (one way valve) for an
argyle catheter (remember the poor man’s Heimlich valve is a sterile surgery glove
with a tiny hole in the tip attached to the catheter – for indwelling chest tubes, but a
Heimlich valve is superior).