LAM II: Equine Respiratory

Describe a normal equine breathing effort and pattern.

- Breathing effort: Minimal movement of nares, thorax and abdomen is normal

- Breathing pattern: Synchronic chest and abdomen movement is normal

What are signs indicative of an upper airway obstruction?

- Audible respiratory noise

- Increased inspiratory effort

- Decreased nostril airflow

What are signs indicative of lower airway disease?

- Increased expiratory effort (abdominal push)

- +/- adventitious lung sounds

What are signs of respiratory disease observed in the equine head?

- Nasal discharge (consider character, amount, unilateral/bilateral)

- Nostril flaring

- Reduce nostril airflow

- Lymphadenopathy

- Facial swelling

- Dull sinus percussion

Cause of nostril flaring?

- Increased respiratory effort

Cause of reduced nostril airflow?

- Upper airway obstruction

Broad Ddx for lymphadenopathy?

- Inflammation

- Infection

- Neoplasia

Ddx for equine facial swelling?

- Tooth root abscess

- Suture line periositits

- Neoplasia

Ddx for dull equine sinus percussion?

- Fluid (sinusitis)

- Mass

- Cyst

What areas should be ausculted during an equine respiratory examination?

- Trachea

- Lungs (at rest, with rebreathing bag, after exercise)

What are abnormal sounds which can be heard on equine lung auscultation? What do these sounds indicate?

- Crackles: Airways opening on inspiration (due to fluid or atelectasis)

- Wheezes: Vibration of airway walls (bronchoconstriction)

- Pleural friction rubs: Parietal and visceral pleura rubbing together

- Decreased bronchovesicular sounds: Pleural effusion (severe consolidation as with fibrosis)

How is a rebreathing examination performed? What is the purpose of this examination?

- Using a large garbage bag filled with air

- Leads to an increase in inspired CO2 to encourage deep breathing

What are normal changes expected in equine respiration during a rebreathing examination?

- No cough

- Increased bronchivesicular sounds

- No adventitious lung sounds

- No tracheal rattling

- Recovery within a few breaths after bag removal (4-6)

How is equine thoracic percussion performed?

- Tap a spoon in the ICS during auscultation

- Aerated tissues like the lungs should result in a resonant sound

What does a dull sound on equine thoracic percussion indicate?

- Fluid-filled structures (lung abscesses vs. consolidated lung vs. pleural effusion)

- Can be used to compare dorsal vs. ventral lung and identify the line of pleural effusion

Indications for equine thoracic US?

- Suspicion of lower airway disease (pleural effusion, pneumonia, thoracic neoplasia, pneumothorax)

- Rib fractures

What are some limitations of thoracic US?

- Does not penetrate air

- Only detects superficial lung lesions (Deeper parenchymal lesion may be missed)

- May lead to underestimation of disease severity

What are some advantages of thoracic US?

- Readily available to most practitioners

- Portable

- Allow for examination of lungs even when there is pleural effusion

What do "comet tails" indicate on thoracic US?

- Pleural roughening

Consolidation on thoracic US can indicate what?

- Non-aerate lung (edema vs. discharge vs. mass (neoplasia or fibrosis) vs. atelectasis)

Pnuemonia/aspiration pneumonia in horses most commonly affects which lung fields?

- Caudoventral

DDx for respiratory disease in a horse with unremarkable thoracic radiographs?

- Equine asthma

- Upper airway disease

- Diaphragmatic paralysis (rare)

DDx for diffusely increased lung opacity in the caudodorsal equine lungs on thoracic radiographs?

- EIPH

- Focal pneumonia (FB, embolus, thromboembolus)

- Iatrogenic (BAL)

DDx for diffusely increased lung opacity in the caudoventral equine lungs on thoracic radiographs?

- Aspiration pneumonia

- Broncho-/pleuropneumonia

DDx for generalize/diffuse increased opacity of equine lungs on thoracic radiographs?

- Interstitial pneumonia

- Pulmonary fibrosis

- Pulmonary edema

DDx for one/multiple discrete tissue opacities in the equine lungs on thoracic radiographs?

- Neoplasia

- Abscess

- Bacterial or fungal granuloma

- FB (single)

- Pulmonary edema (Patchy opacities possible)

- EMPF (multiple)

- Eosinophilic interstitial pneumonia (multiple)

- Idiopathic granulomatous interstitial pneumonia (multiple)

Indications for equine upper airway endoscopy?

- Suspicion of upper airways disease - decreased/asymmetric nostril air, upper airway noise, increased inspiratory effort, coughing when eating, dysphagia

- Localize source of nasal discharge/ epistaxis

- Perform tracheal wash

- Examine trachea and bronchus

Limitaitons of equine upper airway endoscopy?

- Unable to visualize sinus, entire ethmoids

- May exacerbate respiratory distress- providing supplement oxygen may help

Which cranial nerves are found in the medial compartment of the guttural pouch?

- 9, 10, and 12

Options for airway fluid sampling?

- Nasal swab

- Guttural pouch lavage

- Tracheal wash (TW/ TTW/ TTA)

- BAL

- Thoracentesis

Airway fluid samples can be submitted for what testing?

- Cytology

- C/S

- PCR

TTA collects a sample from where? BAL collects a sample from where?

- TTA collects a sample from entire lower respiratory tract (Gets fluids which have drained from the cranial 2/3 of the lungs to the thoracic inlet)

- BAL collects a sample from the distal terminal airways of one section of one lung (Blind); (Good for diffuse disease, i.e., asthma, but will bypass the entire cranial 2/3 of the lung)

Normal cell types in a tracheal wash?

- Predominance of macrophages, < 10% neutrophils, <1% eosinophil, occasional extracellular bacteria

What is the fluid sample of choice for diagnosis of pneumonia in horses? What findings are consistent with this?

- Tracheal wash

- Intracellular bacteria

Normal cell prevalence in BAL sample:

A. Alveolar macrophages

B. Lymphocytes

C. Neutrophils

D. Mast cells

E. Eosinophils

A. Alveolar macrophages 60-80%

B. Lymphocytes 20-35%

C. Neutrophils <5%

D. Mast cells <2%

E. Eosinophils <1%

- Note: Hemosiderophages common in racehorses

What fluid sample is preferred for the diagnosis of equine asthma? What findings are consistent?

- > 5% neutrophils or > 2% mast cells or > 1% eosinophils

When is a pleurocentesis performed?

- Only when there is pleural effusion (pleural fluid cannot be obtained in a normal patient)

What are normal cytology findings for pleural fluid?

- <5,000 cell/uL cells

- TP < 2.5 g/dL

- Mostly macrophages and neutrophils, low numbers of lymphocytes and mesothelial cells

What "blood" gas findings on pleural effusion can suggest sepsis?

- Elevated lactate

- Decreased glucose

What are large animal options for arterial blood collection?

- Transverse facial - ventral to zygomatic arch

- Dorsal metatarsal artery - between MT3 and MT4

- Brachial artery - medial aspect of elbow

- Femoral artery - external inguinal ring

- Carotid?

Air contamination of a blood sample will result in what findings?

- Increase in PO2 and decrease in PCO2 (Make it look better)

Plastic syringes with samples for blood gas should be analyzed how quickly after collection? What about for a glass syringe in an ice bath?

- Within 10 mins

- Within 2 hours

True or false: Venous samples for be used for blood gas analysis of the respiratory system.

- True; values are similar with the exception of PO2, so you cannot say a patient is hypoxemic while looking at a blood gas

Describe the prevalence of thoracic neoplasia in horses.

- Rare - Prevalence 0.15-0.6% of necropsied horses

Most common primary lung tumor of horses?

- Granular cell tumor

Most common thoracic neoplasia of horses?

- Lymphoma (multicentric); 54% and 74% of thoracic neoplasia in 2 studies

In what signalment of horses does thoracic neoplasia most commonly occur?

- Mature or aged horse, with exception of lymphoma which may also be observed in young animals.

Clinical signs of equine thoracic neoplasia?

- Cough

Increased expiratory effort

- Exercise intolerance

- Weight loss

- Abnormalities involving other body system such as diarrhea, cutaneous mass, ventral edema

- Paraneoplastic syndromes: hypercalcemia, hypertrophic osteopathy, hypoglycemia, unexplained fever

Methods for diagnosis of equine thoracic neoplasia?

- US: most often have pleural effusion, may see pulmonary nodules

- Radiographs: Usually nodular interstitial pattern

- Bronchoscopy

- Cytology of pleural fluid

- Cytology TTA and or/ BAL

- Aspirate or biopsy of thoracic mass - ultrasound-guided

- Biopsy of peripheral lymph node

What is HO?

- Symmetrical proliferation of connective tissue and subperiosteal bone along the diaphyses and metaphyses

Signs of HO?

- Usually lame

- Reluctance to move

- Effused joints

Etiology of HO?

- Associated with thoracic neoplasia, and other inflammatory conditions of chest such as intrathoracic abscess or granuloma

- Likely due to overproduction of vascular endothelial growth factor (VEGF)

Prognosis of equine thoracic neoplasia?

- Guarded to poor

Describe the prevalence of EIPH in racehorses.

- Over 80% of TB and STB racehorses when examined after each of 3 consecutive races

Clinical signs of EIPH?

- Epistaxis (<9% of racehorses; Not reliable)

- Poor performance (if severe bleeding)

- Frequent swallowing

What signalment of horses commonly get EIPH?

- Racehorses

- Increases in frequency with age

Describe the pathophysiology of EIPH.

- Failure of pulmonary capillaries at maximal exercise (Marked increase in stress in the alveolar wall → rupture of capillaries; High blood pressure in tiny vessels and very negative pressure in thorax leads to burst of vessels)

- Physiologic mechanisms rather than pathologic

- Additional suspected contributors are upper airway obstructions (DDSP, laryngeal hemiplegia - increase negative pressure in thorax to overcome obstruction) and lower airway obstructions (Asthma)

True or false: With EIPH, recurrence is likely. Why or why not?

- True

- Hemorrhage into airways and interstitium once causes inflammation -> develop fibrosis and decreased compliance -> Reoccurence

Methods for diagnosis of EIPH?

- PE

- Endoscopy (30-120 mins after exercise)

- BAL (Macrophages with hemosiderin inside = Hemosiderophages)

Treatment for EIPH?

- Furosemide 4 h pre-race to decrease severity of bleeding

- Rest - mandated by some racing jurisdiction for up to 2 weeks (optimal duration unknown)

- Anti-inflammatories (NSAIDS)

- Treat any other respiratory disease such as upper airway abnormality or equine asthma

What injury can result from smoke inhalation?

- Thermal injury - upper airway (Burns)

- Chemical injury - CO exposure

- Low PAO2 causes pulmonary vasoconstriction and hypoxemia

Following smoke inhalation, it may take ____________ to develop clinical signs of respiratory disease.

- 24 to 48 hours

In addition to respiratory signs, what other issues in other body systems can smoke inhalation lead to?

- MODS

- SIRS

- Sepsis

- Hypermetabolism

Describe phase 1 of the pathophysiology of smoke inhalation following exposure.

- 0 to 36hrs after exposure

- Acute pulmonary insufficiency due to CO and hypoxia

- Upper airway edema and necrosis (airway obstruction)

- Bronchoconstriction (due to noxious products burned)

- Altered pulmonary blood flow (hypoxic bronchosconstriction)

Describe phase 2 of the pathophysiology of smoke inhalation following exposure.

- 48-72 hours after exposure

- Pulmonary edema, lower airway obstruction, and parenchymal lesions due to release of inflammatory mediators from macrophages and neutrophils

Describe phase 3 of the pathophysiology of smoke inhalation following exposure.

- 1-2 weeks after exposure

- Bronchopneumonia: impaired immune system locally and systemic

Diagnostics for smoke inhalation?

- PE

- CBC/ Chem

- Arterial blood gas (Hypoxia?)

- Endoscopy of upper airway and tracheobronchial tree

- 1-2 weeks later - may develop pneumonia -> Do tracheal aspirate (cytology, C/S), and thoracic radiographs or US

Treatment of smoke inhalation?

- Humidified Oxygen

- Tracheotomy if upper airway obstruction

- Bronchodilation

- Furosemide (for pulmonary edema)

- Anti-inflammatories (NSAIDs vs. corticosteroids, consider immunosuppression)

- Hyperbaric oxygen chambers

- If IV fluids are needed - be judicious due to risk of pulmonary edema

- ABX if documented pneumonia

Poor prognostic indicators associated with smoke inhalation?

- Tachypnea (>50 bpm)

- Dehydration (PCV>50%)

- Opaque nasal discharge

- Persistent severe hypoxemia despite O2 supplementation (PaO2 <60 mmHg)

True or false: Horses with smoke inhalation are often in severe acute respiratory distress following exposure.

- False; Horses may be "normal" at presentation

Define bronchopneumonia.

- Infection of the bronchi extending into the parenchyma

Define pleuropneumonia.

- Extension of parenchymal infection to the pleural space

- Fluid and/or fibrin over lung/in thorax

- Presence of pleural effusion

True or false: Spontaneous pneumonia is uncommon in adult horses.

- True

Predisposing factors to adult equine pneumonia?

- Long distance transport (Stress and head elevation, poor drainage)

- Aspiration - choke, dysphagia

- General anesthesia

- Viral respiratory infections

- Strenuous exercise

- Penetrating wounds

Clinical signs associated with adult equine pneumonia are dependent on what?

- Severity/duration of illness and presence/absence of pleuritis

Possible clinical signs associated with adult equine pneumonia?

- Fever

- Anorexia

- Bilateral nasal discharge

- Cough

- Exercise intolerance

- Tachycardia, tachypnea, increased effort

- Pleurodynia: pawing, stiff, reluctant to move (Can look like colic)

- Weight loss

- Ventral edema

- Epistaxis

- Halitosis

Diagnostics for adult equine pneumonia?

- History/PE (thoracic auscultation, thoracic percussion, tracheal auscultation, +/- rebreathing exam)

- Labs: CBC, Chem, blood gas

- Imaging: US, radiographs, endoscopy

- Respiratory fluid sampling

When presented with a horse with suspected pneumonia, (pleuropneumonia or bronchopneumonia), what fluid sample is best to submit for culture?

- Tracheal wash

Methods of obtains a tracheal wash sample? Briefly describe benefits/limitations.

- Endoscopic: Convenient with good visualization, accessibility may be limiting factor

- Transtracheal: More invasive but more sterile and doesn't require specialize equipment

What cytologic findings may be consistent with pneumonia on a tracheal wash sample? What other diagnostics should be performed on the sample?

- Increased neutrophils, degenerative neutrophils, intracellular bacteria

- Perform gram stain and aerobic/anaerobic culture

When a thoracocentesis is performed, what findings are suggestive of septic pleuritis?

- High cell count and protein with degenerative neutrophils or intracellular bacteria

- Low fluid pH (<7.1) and low glucose (<40mg/dl)

A foul smell in a thoracocentesis sample is suggestive of what?

- Anerobes

What ABX therapy is appropriate for pneumonia?

- Broad spectrum antibiotics (Don't wait on culture)

- Combination antibiotic therapy: Penicillin + gentamicin

- Rifampin aids tissue penetration

Common ABX for gram positive coverage?

- Penicillin

- Ceftiofur or ampicillin

Common ABX for gram negative coverage?

- Gentamicin

- Amikacin (foals)

- Enrofloxacin

- Ceftiofur

- Trimethoprim sulfamethoxazole/sulfadiazine

- Chloramphenicol

- Tetracyclines - doxy, mino

Common ABX for anaerobe coverage?

- Penicillin (except Bacteroides fragilis)

- Metronidazole (PO)

- Chloramphenicol (PO)

- Tetra-/doxy-/minocycline

How long should ABX therapy be continued for management of equine pneumonia?

- Until resolved - clinical signs, inflammatory indicators on lab work and imaging (may take weeks to months)

What adjunct treatments can be used for management of equine pneumonia in addition to ABX?

- NSAIDs - endotoxic/SIRS & pain

- Additional analgesia - butorphanol, lidocaine

- IV fluids

- Deep bedding and ice boots if endotoxic/SIRS

- Oxygen

What is the purpose of pleural effusion drainage in management of equine pneumonia?

- Facilitate lung expansion and reduce hypoxemia

- Removes cells and protein that can create adhesions and loculation

How often should pleural effusion drainage be performed in equine pneumonia patients?

- Repeat q 1-2 days or use indwelling drains

- Note: Large volumes (20 L) often removed

When is pleural lavage indicated in equine pneumonia patients?

- If thick viscous pleural fluid is present -> Remove fibrinous effusion

Complications of equine pneumonia?

- Thrombophlebitis

- Laminitis

- DIC

- Pleural/pulmonary/mediastinal abscess

- Bronchopleural fistula (pneumothorax; Often cough during pleural lavage)

- Pericaridits

- ABX induced colitis

Prognosis of equine pneumonia?

- Overall survival of ~ 75%

- Performance (i.e., racing future) often unaffected

Negative prognostic indicators for equine pneumonia?

- Anaerobic infection

- Complications and severe disease

Common cause of equine fungal pneumonia in the PNW?

- Cryptococcus gattii

What is equine multi-nodular pulmonary fibrosis?

- Nodular form of interstitial pneumonia - fibrosis

Clinical signs of equine multi-nodular pulmonary fibrosis?

- Fever

- Cough

- Weight loss

- Exercise intolerance that can progress to respiratory distress

- Inflammatory CBC - leukocytosis, hyperfibrinogenemia

EMPF has been associated with what?

- EHV-5 (Positive PCR lung biopsies and BAL)

Treatment of equine multi-nodular pulmonary fibrosis?

- Corticosteroids

Prognosis of equine multi-nodular pulmonary fibrosis?

- Poor; Progressive condition