NMS. Surgery

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Chapter 1 ♦ Principles of Surgical Physiology

3. Treatment a. First-line therapy: Aggressive isotonic resuscitation, leading to diuresis and calcium excretion; if unsuccessful, then add furosemide. b. Medical therapy: Medications to stop osteoclastic activity are the mainstay of therapy (i.e., bisphosphonates, calcitonin, and steroids).

Quick Cuts • Two-thirds rule: Total body water = 2/3 total body weight. • Adequate urine output is ½ mL/kg/hr or 250 mL per 8 hour shift.

• Maintenance fluid estimate: 60 mL/hr + 1 mL/kg/hr for each kg above 20 kg. • Hyperkalemia is life threatening: Treat aggressively to shift K intracellularly, and then work on potassium excretion. • Severe, symptomatic hypocalcemia is life threatening and should be treated with calcium supplementation.

ACID–BASE DISTURBANCES Regulatory Systems

I. Carbon dioxide: CO 2 production can exceed 15,000 mmol/day from metabolic processes (e.g., lung excretion). If Pco 2 increases, then water dissociates into HCO 3 − and H + based on the Henderson–Hasselbalch equation , thus decreasing pH. Either a loss of bicarbonate or a gain in protons can cause acidosis. II. Strong ions: Ions that completely dissociate in water (e.g., Na + , Cl − , Ca ++ , Mg ++ , K + ). In a pure salt solution, ion concentrations are equal, and pH is neutral. In plasma, cations outnumber anions. To maintain electrical neutrality, water dissociates, H + is excreted, and HCO 3 − concentration increases, creating a pH of 7.4, not 7.0. III. Weak acids: Weak acids can exist as negatively charged molecules or accept H + and exist uncharged. These buffering systems include proteins and phosphates. Acidosis The body’s pH decreases when the Pco 2 increases, the concentration of HCO 3 − decreases, the concentration of strong anions increases, or the concentration of weak acids increases. A pH less than 7.35 is considered pathologic. I. Respiratory acidosis A. Causes 1. Decreased ventilation: Leads to increased CO 2 concentration. 2. Increased CO 2 production: Excess enteral or parenteral carbohydrate administration increases the respiratory quotient and production of CO 2 . B. Treatment: Increase alveolar ventilation. Most alveolar hypoventilation requires intubation with mechanical ventilation.