Special Techniques & Mechanical Ventilation Notes

Drains

  • Open: Penrose
  • Closed: Jackson-Pratt

Biopsy & Mass Removal

  • Needle Punch (Tru-cut): Used for soft tissue masses; provides a core sample for histological evaluation.
  • Bone (Jamshidi needle): Specifically designed for bone marrow biopsies; allows for the extraction of a cylindrical bone marrow sample.

Laser Surgery

  • Precautions:
    • Exposed skin (burns): Use protective barriers or avoid direct exposure.
    • Flammable ignition: Ensure no flammable materials are near the laser; use appropriate scavenging systems.
    • Smoke plume inhalation: Use smoke evacuators and wear appropriate masks.
    • Safety eyewear required due to visible and invisible laser radiation: Specific to the laser type; must be used by all personnel in the room.

Endoscopy

  • Examine internal body structures via an orifice using optical instruments: Allows for visualization of the GI tract, respiratory tract, etc.
  • Examine tissues directly, remove foreign bodies: Biopsies can be taken; foreign objects can be retrieved.
  • General anesthesia needed: Ensures patient doesn't move and is comfortable during the procedure.
  • Proper fasting before procedure: Prevents regurgitation/aspiration during anesthesia.

Local Anesthesia

  • Benefits:
    • Better pain control (multi-modal analgesia): Can be combined with systemic analgesics.
    • Lower analgesic dose requirements: Reduces risk of side effects from systemic medications.
    • Minimize chronic pain incidence: Prevents wind-up.
    • Decrease cardiovascular depression: Safer for compromised patients.
    • Pre-emptive analgesia: Administered before a painful stimulus.
    • Inexpensive, minimal side effects, fast onset: Makes it a practical choice for many procedures.
  • Desirable Characteristics:
    • Good penetration into tissues, high potency, rapid onset, long duration.
    • Low systemic toxicity, non-irritating, reversible action.
  • Mechanism:
    • Membrane stabilizing agents, block Na+Na^+ inflow, prevent nerve cell depolarization.
  • Site of Action:
    • Small fibers affected more rapidly than large fibers.
    • Non-myelinated fibers blocked more rapidly than myelinated (nodes of Ranvier).
  • Order of Blockade:
    • 1. Pain, 2. Cold, 3. Warmth, 4. Touch, 5. Joint, 6. Deep pressure (reverse order for return).
  • Absorption:
    • Poor through intact skin; variable from injured skin, mucous membranes, etc.
  • Toxicity:
    • Rapid IV injection or excessive dose causes excitation then depression.
    • Clinical signs: hypotension, cardiovascular collapse, seizures.
  • Agents:
    • Lidocaine:
    • Dog: 5 mg/kg, Cat: 2.5 mg/kg
    • Onset: 10 mins, Duration: 1-2 hours
    • Toxic dose: 10 mg/kg, Conc: 20 mg/ml (2%)
    • Bupivacaine:
    • Dog: 2 mg/kg, Cat: 0.5 mg/kg
    • Onset: 20 mins, Duration: 3-6 hours
    • Toxic dose: 2 mg/kg, Conc: 5 mg/ml (0.5%)
  • Applications:
    • Topical, local infiltration, peripheral nerve blocks, intra-articular.

Epidurals

  • Indications:
    • Long-term analgesia caudal to the neck when anesthesia is already planned.
  • Contraindications:
    • Pyoderma at the skin site, septicemia, spinal trauma, coagulopathies.
  • Benefits:
    • Lower MAC, prolonged analgesia (10-20 hrs for morphine).
  • Anatomy:
    • Agent placed in the potential space surrounding the spinal cord.
  • Materials:
    • Clippers, scrub, gloves, syringes, needles, saline, analgesic agent, assistant.
  • Calculating drugs:
    • Use lower dose than parenteral; 1mL per 4.5kg (10 lbs) rule of thumb.
  • Possible Side Effects:
    • Prolonged paresis, urine retention, pruritus, transient respiratory depression.
  • Technique:
    • Positioning: lateral or sternal recumbency with spine parallel to table; pull pelvic limbs forward.
    • Advance needle, expect two pops; remove stylet; attempt "hanging drop" technique.

Mechanical Ventilation

  • Definitions:
    • Assisted ventilation: patient initiates inspiration, anesthetist ensures adequate volume.
    • Controlled ventilation: anesthetist controls rate, volume, and pressure; patient makes no efforts.
    • Mechanical ventilation: forced delivery of gases; intermittent mandatory ventilation.
    • Manual ventilation: squeezing reservoir bag; periodic or intermittent mandatory ventilation.
  • Tidal volume: 10mL/kg10mL/kg
  • Respiratory minute volume: tidal volume x respiratory rate.
  • Atelectasis: airway and air sacs collapse.
  • Normal Respiratory Pattern:
    • Chest expands, creating negative pressure; air is pulled in; gas exchange occurs; surfactant prevents alveolar collapse.
  • Problems Under Anesthesia:
    • Hypercarbia (elevated PaCO2PaCO_2), hypoxemia, atelectasis.
  • Patients at Increased Risk:
    • Prolonged anesthesia, obesity, pregnancy, head trauma, neuromuscular blockers, chest/diaphragm surgery, large animals.
  • Options for Ventilation:
    • Negative Pressure: requires ability to change atmospheric pressure; non-invasive (e.g., Iron Lung).
    • Positive Pressure: requires sealed intubation; invasive (bellows for lung expansion).
  • Manual Ventilation:
    • Anesthetist uses reservoir bag; done every 2-5 minutes to reduce atelectasis.
  • Mechanical Ventilation Parameters:
    • Inspiratory time, expiratory time, I:E ratio, respiratory rate, peak inspiratory pressure, PEEP.
  • Normal Settings:
    • Inspiratory time: ~1 sec; Expiratory time: 2-3x inspiratory; I:E ratio: 1:2 or 1:3; Respiratory rate: 6-12 bpm; Peak inspiratory pressure: 12-20 cmH2O.
  • SAV2500 Ventilator Setup:
    • Leak check anesthesia machine.
    • Connect oxygen, WAG line, and flexible h