Metabolic

Diabetes Mellitus

Patients are often seen by the endocrine service preoperatively and already have a sliding insulin scale written (Table 32.5).

Patients on multiple inotropes may need a more generous insulin dose.

Potassium (K+)

Only 2% of total body K+ is extracellular (70 meq of 3500 meq total lean body weight) and measured by serum levels (normal serum K+ = 2 - 4 meq/L).

There is a nonlinear relationship between total body K+ and serum K+ (Table 32.6). Depletion causes less change in serum K+ due to intracellular

Table 32.5. Insulin scale for perioperative hyperglycemia blood sugar (mmoles/l)

blood sugar (mg/100ml)

infusion rate

300-400 200-300 <100

none translocation to replenish stores while excess results in a better correlation with serum K+.

Estimate deficit as decrease 1 meq/L in serum K+ causes a 10% decrease in total body K+ (50 meq/L lean body weight).

Calcium (Ca2+)

Normal serum levels are indicated in Table 32.7.

Hypoalbuminemia decreases the protein bound fraction and results in a decrease in total serum calcium but no change in serum ionized Ca2+. Correction factor is every decrease of 1 mg/dl albumin increases total serum Ca2+ by 0.8 mg/dl.

Ionized calcium be should measured quickly at body temperature with minimal heparin in sample as a measured decrease may be reported with alkaline pH, low serum sodium or heparin.

Magnesium (Mg2+)

Magnesium is the second most abundant intracellular cation (Table 32.8) but uneven distribution in the body: 1000 mmoles total in body, serum 2.6 mmoles (0.3%), bone 530 mmoles (53%). Serum levels are not checked routinely at TTH as there is a poor correlation with total body levels. Urinary Mg is likely a better indicator of total body stores.

Measured low serum levels are treated with magnesium sulfate 2.0-4.0 g i.v. This is also of therapeutic value in patients with atrial or ventricular arrhythmias and normal serum levels.

Metabolic Acidosis

Calculation of anion gap is based on serum levels of Na+ - (Cl- + HCO32-) = 10 - 12 mmol/L = 140 - (105 + 25).

Most common cause in CVICU is hypoperfusion (increased lactate), renal failure or diabetes (increased ketones) (Table 32.9).

Physiological correction involves for every decrease in HCO3 by 1 meq/L causes a decrease in pCO2 by 1.1 mm Hg (though pCO2 can not be < 10 mm Hg).

Table 32.6. Potassium homeostasis

Rx IV

Ddx Transcellular shift ^ B agonists (epinephrine, dobutamine), alkalosis

K+ depletion ^ diuretics, NG, vomit, low CO2, cirrhosis, steroids, diarrhea

Sx muscle weakness, CNS changes, AV block, ST segment depression

"u" wave, T wave flat, potentiate digoxin-toxic arrhythmias postoperative protocol based on urine output and initial K+ = 4.0-5.0meq/L

0-50

50-100

meq KCl

5-lO

lO-l5

l5-2O

if K+ > 5.0 KCl is held and recheck level if K+ < 4.0 patients get 10 meq KCl/ h

PO liquid: Kaochlor (10%)/Kciel: 15 cc = 20 meq tablets: Slow K 1 tab = 8 meq, KDur 1 tab = 10 meq correct acidosis (increase PCO2, decrease HCO3) avoid > 40 meq KCL/L/ hour through central line give magnesium sulfate if refractory hypokalemia

Sx Rx

Hyperkalemia (>5.5 meq/L)

Ddx Transcellular shift ^ myonecrosis, insulin lack, acidosis, drugs (p-blockers, succinylcholine, digoxin toxicity) J Renal excretion ^ renal insufficiency, adrenal insufficiency, drugs (ACEI, diuretics, NSAIDS, heparin) Pseudohyperkalemia ^ hemolysis, increased platelets or WBC

skeletal muscle weakness, diarrhea peaked T wave, J p wave, \ PR, \ QRS, asystole should treat if > 6.0 meq/L or if any ECG changes consider a) CaCl2 1.0 gm i.v.

b) NaHCO3 1 amp i.v. (only if able to eliminate additional CO2 produced)

c) Humulin R 10 units i.v. bolus with D50W if low glucose d) hyperventilate, salbutamol inhalation (renal failure)

e) Furosemide 10-20 mg i.v.

f) Kayexalate 20-50 g in 20% Sorbitol PO or PR q3 h g) dialysis (if renal failure)

Table32.7Calcium homeostasis normal serum calcium levels mg/dl mmol/L

total serum calcium 8.5-10.2 2.1-2.5

ionized serum calcium 4.8-7.2 1.1-1.3 NB. Conversion factor to SI units is 0.25 x traditional unit

Ionized hypocalcemia

Ddx sepsis, alkalosis, acute pancreatitis (i PTH)

Hypomagnesemia (i PTH) ^ Rx magnesium renal failure (T phosphorus) ^ Rx by lowering phosphate miscellaneous: blood transfusion, CPB, burns, drugs

Sx neuromuscular excitability hypotension, left ventricular failure, increase QT interval

Rx if heart failure or hypotension may promote vasoconstriction may decrease ventricular compliance and worsen diastolic dysfunction Calcium chloride (CaCl2 10%) ^ 272 mg (13.6 meq) Ca2+ Calcium gluconate (10%) ^ 90 mg (4.5 meq) Ca2+ initial dose 1 ampule CaCl2 over 10 minutes

Hypercalcemia

Ddx hyperparathyroidism, malignancy

Sx altered mental status, coma, ileus, hypotension, renal failure

Rx Rx > 13 mg/dl a) diuresis with saline and loop diuretics b) calcitonin 4 U/kg IM or SQ q12h x 2 doses (decrease bone resorption)

c) mithramycin 25 ^g/kg i.v. bolus q 2 days x 2 doses d) dialysis

Treatment depends on the underlying cause and hemodynamic profile of the patient.

• calculate total meq deficit of bicarbonate by using the measured base deficit on arterial blood gases and either of the following formulas. ^HCO3 deficit x 40% TBW(where TBW = 60% total body weight) ^HCO3 deficit x 0.3 x weight

• Remember that administered sodium bicarbonate (NaHCO3) is converted to carbon dioxide increasing the patient's pCO2. Give NaHCO3 only if the patient can eliminate the additional CO2 produced.

• Correct by administering 1 ampoule of NaHCO3 (50 cc) which contains 44 meq HCO3. Aim to correct at least one half the calculated deficit.

Table 32.8. Magnesium homeostasis

Normal serum levels = 0.8-1.2 mmol/L = 1.6 -2.4 meq/L

NB. Conversion factor to SI units is 0.50 x traditional unit

Hypomagnesemia

Ddx diuretics (loop, osmotic), alcohol, aminoglycosides, amphotericin, decrease intake (i.v. poor Mg), diarrhea

Sx decreased serum potassium, phosphate, sodium, calcium arrhythmias in acute MI, intractable arrhythmias digitalis cardiotoxicity, \ QT on ECG muscle weakness, seizures tremors

Rx normal 1 mmol = 2 meq deficit ^ 1-2 meq/Kg (70-140 meq)

MgSO4 5 g (40 meq) q 12h reduce by 50% with renal insufficiency should normalize serum levels over 24 h

Hypermagnesemia

Ddx renal failure + Mg, diabetic ketoacidosis, pheochromocytoma

Sx hypotension (3.0-5.0 meq/L)

complete heart block (> 7.5 meq/L) respiratory depression, coma (> 10 meq/L)

Rx i.v. calcium loop diuretics and volume

Table 32.9 Differential diagnosis of anion gap

normal anion gap (f chloride)

f anion gap (normal chloride)

HCO3 loss

H+ gain

gut ^ diarrhea, small intestine/ pancreas, ureterosigmoid, ileal loop renal ^ renal tubular acidosis, carbonic anhydrase inhibitor, HCl ketoacidosis: starvation, alcohol, diabetes, lactate: a = hypoperfusion, b = no hypoperfusion intoxication: salicylate, methanol, ethylene glycol, paraldehyde, uremia gut ^ diarrhea, small intestine/ pancreas, ureterosigmoid, ileal loop renal ^ renal tubular acidosis, carbonic anhydrase inhibitor, HCl ketoacidosis: starvation, alcohol, diabetes, lactate: a = hypoperfusion, b = no hypoperfusion intoxication: salicylate, methanol, ethylene glycol, paraldehyde, uremia

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