Carbonic anhydrase inhibitors

Acetazolamide, Dichlorphenamide, Methazolamide, Ethoxzolamide

Mechanism of Action

1.    Carbonic anhydrase (CA) facilitates excretion of H+ and recovery of bicarbonate by the proximal renal tubule and ciliary epithelium of the eye. Sodium is recovered in exchange for H+. 
2.    Inhibitors block CA block sodium recovery. A very mild diuresis is produced (this is really a side effect of their use in glaucoma) because relatively unimportant mechanism for Na recovery and because proximal tubule site means that other sodium recovery mechansims continue to process their normal fraction of the sodium load.
 

Example calculations of maximum local anesthetic doses for a 15-kg child

Articaine

5 mg/kg maximum dose × 15 kg = 75 mg

4% articaine = 40 mg/mL

75 mg/(40 mg/mL) = 1.88 mL

1 cartridge = 1.8 mL

Therefore, 1 cartridge is the maximum

Lidocaine

7 mg/kg × 15 kg = 105 mg

2% lidocaine = 20 mg/mL

105 mg/(20 mg/mL) = 5.25 mL

1 cartridge = 1.8 mL

Therefore, 2.9 cartridges is the maximum

Mepivacaine

6.6 mg/kg × 15 kg = 99 mg

3% mepivacaine = 30 mg/mL

99 mg/(30 mg/mL) = 3.3 mL

1 cartridge = 1.8 mL

Therefore, 1.8 cartridges is the maximum.

Prilocaine

8 mg/kg × 15 kg = 120 mg

4% prilocaine = 40 mg/mL

120 mg/(40 mg/mL) = 3 mL

1 cartridge = 1.8 mL

Therefore, 1.67 cartridges is the maximum

Osmotic diuretics

An osmotic diuretic is a type of diuretic that inhibits reabsorption of water and sodium. They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate.

Mechanism(s) of Action

1.    Reduce tissue fluid (edema) 
2.    Reflex cardiovascular effect by osmotic retention of fluid within vascular space which increases blood volume (contraindicated with Congestive heart failure) 
3.    Diuretic effect

o    Makes H2O reabsorption far more difficult for tubular segments insufficient Na & H2O capacity in distal segments
o    Increased intramedullary blood flow (washout)
o    Incomplete sodium recapture (asc. loop). this is indirect inhibition of Na reabsorption (Na stays in tubule because water stays) 
o    Net diuretic effect: 
    Tubular concentration of sodium decreases 
    Total amount of sodium lost amount increases 
    GFR unchanged or slightly increased

Toxicity

Circulatory overload, dilutional hyponatremia,  Hyperkalemia, edema, skin necrosis

Agents
Mannitol

Isoflurane (Forane) MAC 1.3%, Blood/gas solubility ratio 1.4
- Better muscle relaxation than with the other halogenated anesthetic agents.
- Isoflurane markedly potentiates the action of the neuromuscular blocking agents.
- Produces rapid onset and recovery of anesthesia.
- Does not sensitize the heart to catecholamines.
- Produces respiratory depression, but produces less cardiovascular depression
- than does halothane.
- It has an extremely low degree of metabolism and is apparently relatively
- nontoxic.

DOPAMINE

It is an immediate metabolic precursor of noradrenaline. It activates D1 receptors in several vascular beds, which causes vasodilatation. It acts on dopaminergic and other adrenergic receptors (α & β1).

Adverse effects of dopamine include nausea, vomiting, ectopic beats, anginal pain, tachycardia, palpitation and widened QRS.
Contraindications are atrial or ventricular tachyarrhythmias, hyperthyroidism and pheochromocytoma.

Midazolam -Intravenous Anesthetics
 Midazolam is a benzodiazepine used for preoperative sedation, induction of anesthesia, or maintenance of anesthesia in short procedures.