Bronchoscopy in Dogs and Cats

Introduction #

Bronchoscopy in cats and dogs requires careful anesthetic management to ensure patient safety while providing optimal visualization of the airways. This procedure demands specific considerations for airway access, depth of anesthesia, oxygenation, and monitoring. The anesthetic protocol must balance adequate immobilization and analgesia with minimal respiratory depression. Emergency preparedness for apnea, hypoxia, or airway obstruction is extremely important.

Patient Assessment and Preparation #

Prior to bronchoscopy, a thorough physical examination and pre-anesthetic bloodwork are essential. Particular attention should be paid to cardiopulmonary function, as patients requiring bronchoscopy often have underlying respiratory disease. Stabilization of critical patients with supplemental oxygen, fluid therapy, or bronchodilators may be necessary before proceeding with anesthesia.

Fasting for 8-12 hours is recommended to reduce the risk of regurgitation and aspiration. A shorter fasting period (4-6 hours) may be appropriate for pediatric patients. Water can be offered until 2-4 hours before the procedure.

Premedication #

Mild sedation can be achieved with opioids (butorphanol 0.2-0.4 mg/kg IV or hydromorphone 0.05-0.1 mg/kg IV). Alpha-2 agonists should be used with caution or avoided in patients with significant cardiovascular compromise.

Induction Options #

Propofol (4-6 mg/kg IV in dogs, 6-8 mg/kg IV in cats) remains the induction agent of choice due to its smooth, rapid onset and short duration. It can be titrated to effect and produces excellent muscle relaxation. Alfaxalone (1-2 mg/kg IV in dogs, 2-3 mg/kg IV in cats) is an excellent alternative, particularly in patients with cardiovascular disease.

Ketamine/diazepam combinations are not generally used for patients because they may not provide the same degree of muscle relaxation and gag reflex inhibition. Mask induction with inhalants is generally avoided due to stress, environmental contamination, and potential for laryngospasm.

Intubation Considerations #

Intubation for bronchoscopy presents unique challenges as the bronchoscope must share the airway with the endotracheal tube. Several approaches can be employed:

1. Special endotracheal tubes with side channels for bronchoscope insertion-not common
2. Oversized endotracheal tubes with the bronchoscope passing inside-useful for large dogs.
3. Jet ventilation and tracheal oxygen insufflation techniques-useful if the endotrachal tube must be removed during scope passage
4. Intermittent apnea with temporary extubation

For standard bronchoscopy in medium to large dogs, an endotracheal tube 2-4 mm larger than normally indicated can be used, allowing the bronchoscope to pass alongside it. For smaller dogs and cats, extubation with tracheal insufflation or jet ventilation may be necessary.

Alternatively, in some cases, especially for sampling or visualization of proximal airways, a laryngeal mask airway (LMA) can be used, providing airway control while allowing bronchoscope passage. Sterile tubes are useful if sampling for bacteriology is likely.

Maintenance of Anesthesia #

Inhalant Anesthesia #

Inhalant anesthetics (isoflurane or sevoflurane) are commonly used for maintenance due to their predictable depth control and rapid adjustability. However, they present challenges during bronchoscopy:

• Inhalant delivery may be interupted during extubation
• Higher doses required for immobility can cause dose-dependent respiratory depression
• Environmental contamination is common during extubation or scope passage

Sevoflurane offers advantages over isoflurane with faster induction and recovery, making it preferable for brief procedures or when rapid depth adjustments are needed. However, the slower recovery from isoflurane may provide more time if frequent extubation is necessary.

Injectable Anesthesia #

Total intravenous anesthesia (TIVA) offers several advantages for bronchoscopy:

• Eliminates dependence on inhalant delivery through compromised airways
• Provides consistent anesthetic depth regardless of ventilation
• Potentially less respiratory depression at equipotent doses

Propofol CRI (0.1-0.4 mg/kg/min in dogs, 0.1-0.2 mg/kg/min in cats) provides excellent control but may accumulate with prolonged administration in cats. Alfaxalone CRI (0.07-0.1 mg/kg/min) is an excellent alternative with less respiratory depression but recovery may be less smooth and longer than with propofol.

Combining propofol with opioid infusions (fentanyl 1-5 μg/kg/h) allows for reduced propofol dosing, improved analgesia, and less gag reflex at light planes of anesthesia.

Oxygen Supplementation #

Adequate oxygenation is critical during bronchoscopy as patients often have compromised respiratory function and the procedure interferes with normal ventilation. Several approaches can be used:

1. High oxygen flow (3-5 L/min) through specialized endotracheal tubes
2. Intermittent positive pressure ventilation or tracheal oxygen insufflation via the biopsy port or a urinary catheter placed alongside the bronchoscope
3. High-flow nasal or flowby oxygen during brief periods of extubation

Pre-oxygenation for 5 minutes before induction is helpful. Monitoring oxygen saturation continuously helps guide interventions.

Ventilation Management #

Hypoventilation is common during bronchoscopy due to anesthetic-induced respiratory depression and physical interference with ventilation. Strategies to address this include:

1. Short periods of apnea (30-60 seconds) during critical visualization or sampling
2. Manual ventilation between examination periods

End-tidal CO₂ should be closely monitored, maintaining values between 35-45 mmHg when possible. Temporary hypercapnia may be acceptable during brief examination periods.

Monitoring Requirements #

Comprehensive monitoring is essential during bronchoscopic procedures:

• Continuous ECG to detect arrhythmias that may occur with hypoxemia or vagal stimulation
• Pulse oximetry to monitor oxygen saturation (maintain SpO₂ > 90%)
• Capnography to assess ventilation (when possible with the breathing system used)
• Blood pressure monitoring (direct arterial measurement preferable)
• Depth of anesthesia assessment (spontaneous movement must be prevented)

Arterial blood gas analysis should be considered for patients with severe hypoxia or patients with significant respiratory compromise.

Recovery Considerations #

Patients should be carefully monitored during recovery, with continued oxygen supplementation until fully awake. Extubation should occur only when the patient has a strong swallow reflex and can maintain oxygen saturation on room air.

Respiratory compromise may be exacerbated post-procedure due to airway inflammation, sedation, or bronchoconstriction. Equipment for re-intubation and positive pressure ventilation should remain readily available.

Conclusion #

Successful anesthesia for bronchoscopy in cats and dogs requires careful consideration of patient status, procedure requirements, and anesthetic technique. The combination of appropriate premedication, induction methods, maintenance technique, and thorough monitoring maximizes safety while providing optimal conditions for airway examination. The choice between inhalant and injectable maintenance, along with creative approaches to intubation and oxygen delivery, should be tailored to the individual patient and specific procedural needs.