炭酸水素ナトリウム
**炭酸水素ナトリウム**は、獣医の救急および集中治療、ならびに特定の疾患の慢性管理に広く使用される全身性および尿アルカリ化剤です。 - **救急時の酸塩基管理**：主に、根本的な原因が急速に改善できず、血中pHが危険なレベルに低下した場合の重度な代謝性アシドーシスの補正に使用されます。 - **電解質異常の危機**：生命を脅かす**高カリウム血症**（カリウムを細胞内に移動させる）および**高カルシウム血症**の補助治療として機能します。 - **尿のアルカリ化**：尿のpHを上昇させることで、特定の尿石（尿酸塩、シスチンなど）の管理または予防のために経口投与されます。 > **臨床のポイント**：心肺蘇生（CPR）および糖尿病性ケトアシドーシス（DKA）における炭酸水素ナトリウムのルーチン使用は推奨されなくなりました。DKAでは細胞内低カリウム血症を悪化させ、逆説的な中枢神経系アシドーシスを引き起こす可能性があります。CPRでは、患者の換気が不十分な場合、高炭酸ガス血症を引き起こす可能性があります。
作用機序: Sodium bicarbonate acts as an exogenous source of bicarbonate anion (**$HCO_3^-$**), which is the primary extracellular buffer in the body. - **Buffering Acidosis**: $HCO_3^-$ combines with free hydrogen ions ($H^+$) to form carbonic acid ($H_2CO_3$), which then dissociates into water ($H_2O$) and carbon dioxide ($CO_2$). - **Pathway**: **$HCO_3^-$ + $H^+$ → $H_2CO_3$ → $H_2O$ + $CO_2$** (The $CO_2$ must be exhaled via the lungs, highlighting the need for adequate ventilation). - **Hyperkalemia Management**: By increasing blood pH, it stimulates the $Na^+/H^+$ exchanger and subsequently the $Na^+/K^+$-ATPase pump, driving **potassium into cells** and rapidly lowering serum potassium levels. - **Urinary Alkalinization**: Bicarbonate is excreted in the urine, raising the pH. This increases the solubility of weak acids (like uric acid and cystine) and decreases the solubility of weak bases.
動物種別の用量
- Acidosis (Ruminants) · 2-5 mEq/kg IV for a 4-8 hour period · IV · Once · Over 4-8 hours
- Acidosis (Ruminants) · 2-5 mEq/kg IV for a 4-8 hour period · IV · Once · Over 4-8 hours
- Severe metabolic acidosis · mEq of bicarbonate required = 0.5 x body weight in kg x (desired total CO2 mEq/L minus measured total CO2 mEq/L). Give 1/2 of the calculated dose slowly over 3-4 hours IV. · IV · Once · Over 3-4 hours · Recheck blood gases and assess clinical status. Avoid over-alkalinization.
- Metabolic acidosis secondary to uremia · 0.3 x body weight (kilograms) x the base deficit. Administration of one third of this dose slowly IV and the rest placed in the intravenous fluids. OR 1-2 mEq/kg of bicarbonate can be given as a slow IV bolus if blood gas is not possible. · IV · Once · Over several hours · Avoid rapid IV boluses. Recheck blood gas after 2-4 hours.
- Adjunctive therapy of diabetic ketoacidosis · Dose (in mEq) = body weight in kgs. x 0.4 x (12 - patient's bicarbonate) x 0.5. Give above dose over 6 hours in IV fluids. · IV · Once · Over 6 hours · Only if plasma bicarbonate is <=11 mEq/L. Recheck and repeat if still <=11 mEq/L. Use is controversial.
- Adjunctive treatment of hypercalcemic crisis · mEq of bicarbonate required = 0.3 x body weight in kg x (desired plasma bicarbonate mEq/L - measured plasma bicarbonate mEq/L); or 1 mEq/kg IV every 10-15 minutes; maximum total dose: 4 mEq/L · IV · q10-15m · Until effect or max dose
- Adjunctive therapy for hyperkalemic crises · 2-3 mEq/kg IV over 30 minutes (if decreased tissue perfusion/renal failure and no DKA) OR 1-2 mEq/kg IV slowly · IV · Once · Over 30 minutes or slowly · Must be used judiciously.
投与経路
禁忌
- Metabolic or respiratory alkalosis
- Excessive chloride loss secondary to vomiting or GI suction
- Patients at risk for development of diuretic-induced hypochloremic alkalosis
- Hypocalcemia (alkalosis may induce tetany)
- Hypoventilating patients
- Hypercapnoeic patients
- Animals unable to effectively expel carbon dioxide
有害事象
- Metabolic alkalosis
- Hypokalemia
- Hypocalcemia
- 'Overshoot' alkalosis
- Hypernatremia
- Volume overload
- Congestive heart failure
- Shifts in the oxygen dissociation curve (decreased tissue oxygenation)
- Paradoxical CNS acidosis leading to respiratory arrest
- Hypercapnia (if not well ventilated during CPR)
- Predisposition to ventricular fibrillation
- Hypernatraemia
- Congestive heart failure (due to sodium load)
- Decreased tissue oxygenation (shift in oxygen dissociation curve)
- Paradoxical CNS acidosis
- Respiratory arrest
薬物相互作用
- Anticholinergic agents · Concomitant oral sodium bicarbonate may reduce absorption; administer separately
- Azole antifungals (ketoconazole, itraconazole) · Concomitant oral sodium bicarbonate may reduce absorption; administer separately
- Ciprofloxacin, Enrofloxacin · Solubility is decreased in an alkaline environment; monitor for signs of crystalluria
- Corticosteroids · Patients receiving high dosages of sodium bicarbonate and ACTH or glucocorticoids may develop hypernatremia
- Diuretics (e.g., thiazides, furosemide) · Concurrent use in patients receiving potassium-wasting diuretics may cause hypochloremic alkalosis
- Ephedrine · When urine is alkalinized, excretion may be decreased
- Histamine2 blocking agents (e.g., cimetidine, ranitidine) · Concomitant oral sodium bicarbonate may reduce absorption; administer separately
- Iron products · Concomitant oral sodium bicarbonate may reduce absorption; administer separately
- Oral medications (general) · Can increase or reduce absorption rate/extent; avoid giving other drugs within 12 hours of oral sodium bicarbonate
- Quinidine · When urine is alkalinized, excretion may be decreased
- Salicylates · When urine is alkalinized, excretion of weakly acidic drugs may be increased
モニタリング
- Acid/base status (venous or arterial blood gases)
- Serum electrolytes (especially potassium, calcium, and sodium)
- Urine pH (if being used to alkalinize urine)
- Blood gas analysis (pH, pCO2, HCO3-)
- Serum electrolytes (Na+, K+, Ca2+)
- Respiratory rate and effort
- Clinical signs of fluid overload or congestive heart failure
過量投与
Overdose or overly rapid administration can cause **severe alkalosis**, leading to irritability, muscle twitching, or **tetany** (due to a sudden drop in ionized calcium). - **Mild Overdose**: May only require discontinuing the bicarbonate therapy or using a rebreathing mask. - **Severe Alkalosis**: May require intravenous calcium therapy to treat tetany. - **Electrolyte Correction**: Sodium chloride or potassium chloride may be necessary if hypokalemia or hypochloremia is present. > Always thoroughly check dosages and frequently monitor electrolyte and acid/base status during administration.
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