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Anaesthesia and dead space

  1. Anatomical dead space: Extends from, nose to alveolar ducts it is 2 ml/kg or 30% of tidal volume or 150 ml
     
    ↑ ed in
    1. Sitting position
    2. Old age
    3. Neck extension & jaw protrusion
    4. ing lung volume
    5. Bronchodilators
    6. IPPV and PEEP
    7. Anaesthesia mask, circuits
↓ ed in
  1. Intubation
  2. tracheostomy
  3. hyperventilation
  4. bronchoconstrictors
  1. Physiological dead space (total dead space)
    1. Anatomical dead space + Alveolar dead space (Alveoli which are ventilated but not perfused)
    2. Alveolar dead space is negligible in supine position & 60 – 80 ml in standing position
    3. All conditions causing V/Q mismatch increases the alveolar dead space
    4. During General Anesthesia, FRC is decrease by 15 to 20%
↓ in vital capacity with position
 
Lithotomy  by 18%
Trendelenburg  by 14%
Rt. Lateral by 12%
Lt. Lateral by 10%
Prone by 10%

Complications for different positions

  1. Lithotomy:
    1. Nerve injuries
      1. Peroneal N. injury (compressed b/w head of fibula; & bar)
      2. Saphenous N. injury (pressure over medial condyle)
      3. Femoral N. injury (angulation of thigh)
      4. Obturator N. injury ( angulation of thigh)
    2. Muscle injury
      1. Compartment syndrome of leg (extreme tightening of straps)
      2. Compartment syndrome of hand (compressed between buttocks & table)
      3. Chemical burns
    3. Increase Venous return Increase cardiac load
    4. Respiration - decrease FRC
  2. Lateral & Lateral oblique
    1. Transient Homer syndrome
    2. Brachial plexus injury
    3. Radial & ulnar N.; injuries
    4. Compartment syndrome of hand
    5. Extreme flexion of neck can compromise spinal blood flow
    6. Breast injury
    7. Genitalia injury
Trendelenburg
  1. ↑ CVP ↑ i c p, ↑ i. o. p
  2. Cardiac load (V.R)
  3. FRC
  4. Cerebral H’ age
  5. Venous congestion in face- swelling of face conjunct eyelids
  6. Lingual & buccal neuropathy
  1. Sitting
    1. Extreme flexion of neck can cause Spinal Cord ischemia
    2. Branchial plexus injury (weight of arm decrease GA stretched branchial plexus)
    3. Femoral & obturator N. injury
    4. Sciatic N. injury
    5. VENOUS AIR EMBOLISM commonly seen in posterior fossa surgery

Deliberate\induced\controlled hypotension

  1. Definition: Reduction of systolic BP to 80 – 90 mm Hg or mean arterial pressure to 50 – 65 mm Hg or reduction of BP by 1/3 of its preoperative value:
  2. Techniques
    1. Spinal & epidural
    2. Inhaled anaesthetic
      1. Isoflurane
      2. Enflurane
    3. Vasodilators- Sodium nitroglycerine
  3. Sodium nitroprusside –
    1. acts on arterioles
    2. very dangerous S/E cyanide poisoning
    3. Rx sodium nitrite Sodium thiosulfate

Hyperbaric o2

Uses:
  1. Poisonings
    1. Carbon monoxide (at 2.5 atm tl/2 of CO is 19 mm while at I atm it is 214 .min)
    2. Cyanide
  2. Gas bubble disease
    1. Air embolism
    2. Decompression sickness
  3. Infections
    1. Clostridial
    2. Refractory osteomyelitis
    3. Mucormycosis
  4. Ischemia
    1. Crush injury
    2. Ischemic ulcers
    3. Radiation necrosis
  5. Acute hypoxia

Pain management

  1. Pain assessment: visual analogue scale
  2. Chronic pain conditions
     
    For neurolytic blocks 5% phenol or 100% alcohol are used
  3. Trigeminal neuralgia
     
    D. O. C. Carbamazepine 200 mg/day by 200 mg to a max. of 1500 mg
     
    Other modalities: Radio frequency Ablation
     
    Neurolytic blocks
  4. Post herpetic neuralgia
     
    D.O.C. fluphenazine other Amitriptyline, Desimipramine,
     
    Other – Desensitization tech.
    1. TENS
    2. Intercostal blocks
    3. Topical aspirin in ether

Anaesthesia for Day Care Surgery

  1. Patient selection:
    1. ASA I or II
    2. Age 6 months — 70 years
    3. Short duration procedures
    4. Procedures not associated with post-operative complications
    5. Accompanied by attendant Investigations- nil for ASAI
  2. Premedication: Reserved for very anxious patients
    1. Drugs: I/V agent — propofol Opioid—Alfentanil
    2. Inhalational — Desflurane
    3. Muscle relaxant — Mivacurium
    4. Benzodiazepine — Midazolam
    5. Regional — Beirs/LA
  3. Discharge:
    1. No (or minimal) nausea
    2. Pain (controllable on oral analgesics)
    3. Well oriented
    4. Accept liquids
    5. Able to void
    6. Able to sit
    7. No active bleeding
    8. Accompanied by attendant

Anaesthesia For laparoscopy

Gas used – CO2
  1. Complication
    1. Decrease cardiac output (30 – 40%), Intra-abdominal pressure should be 12 – 14 mmHg
    2. Arrythmia
    3. Hypercapnia (so I. C. T)
    4. V/Q mismatch
    5. Pneumothorax (manage conservatively
    6. CO2 embolism.
  2. Contraindication
    1. ↑ I. C. T.
    2. IHD
    3. CHF
    4. Severe hypovolemia
    5. VP shunt

Pulmonary Aspiration of Gastric contents (Preventable complication)

  1. Incidence 1 in 3,000
  2. Mortality after aspiration 5-70%
  3. Predisposing factors
    1. A,. Depressed consciousness
    2. Full stomach
    3. Conditions Lower esophageal sphincter tone.
      1. Pregnancy (Progesterone relaxes LES, impaired gastroesophegeal angle)
      2. Hiatus hernia
      3. Nasogastri c tubes
      4. besity
      5. Drugs:-
        • Atropine, glycopyrrolate
        • Dopamine
        • Sodium nitroprusside
        • Halothane
        • Thiopentone
        • Opoids
        • Ganglion blockers
    4. Condition  gastric emptying
      1. DM
      2. Hypothyroidism
      3. Narcotics
      4. Anxiety, pain




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