Management of VF arrest

Passive rewarming

• Temperature is very important during rewarming as temperature commonly overshoots normal. Warming the patient too quickly or allowing continued shivering causes dangerous electrolyte shifts, leading to potentially lethal arrhythmias. 
• Controlled rewarming of 0.15° to 0.5° C per hour is recommended. 
• To maintain tight temperature control throughout rewarming a neuromuscular blockade is usually employed.  
• Careful fluid monitoring during rewarming is crucial because of the vasodilation that accompanies a body temperature rise. Volume replacement may be needed to prevent fluid deficit and hypotension.
• Electrolytes shift out of the cells back into the serum during rewarming, so frequent electrolyte monitoring is needed during this phase to prevent critically elevated levels. Slow, controlled rewarming allows the kidneys to excrete excess potassium, preventing hyperkalemia. 
• Hypoglycemia can occur during rewarming as the insulin resistance of earlier hypothermia phases diminishes. Glucose levels must be monitored frequently, with insulin titration and dextrose boluses used as needed to maintain the patient within ordered ranges.

References

• http://www.americannursetoday.com/article.aspx?id=8014&fid=7986
• http://ccforum.com/content/16/S2/A25/ 

Hartmann's (Compound Sodium Lactate)

Components (in mmols):

• Na 129
• K 5
• Ca 2
• Cl 109
• bicarb 29
  

IV Fluids

Standard fluid regime for NBM patients:

• N/2 * 2 bags
• 4 % dextrose + N/5 + 30mmol KCl

In terms of fluid requirements,

• 65% of body is water (TBW)
• 2/3 of this is intracellular, 1/3 extracellular

Ways you can lose electrolytes:

• Vomiting → loss of K
• Diarrhoea→ loss of K
• Sweat→ loss of NaCl
• Burns → loss of protein and Na
• Third space losses → loss of NaCl + H20

Ways to assess dehydration:

• Urine dipstick - concentration
• ↑ Ur and ↑ Na

Correction of hypernatremia begins with a calculation of the fluid deficit. Predicted insensible and other ongoing losses are added to this number and the total is administered over 48 hours. Recheck serum electrolyte levels frequently during therapy. To avoid cerebral edema and associated complications, the serum sodium level should be raised by no more than 1 mEq/L every hour. In patients with chronic hypernatremia, an even more gradual rate is preferred.

Free Water Deficit (L) = Body Weight (kg) X Percentage of Total Body Water (TBW) X ([Serum Na / 140] - 1)

Percentage of TBW should be as follows:

• Young men - 0.6%
• Young women and elderly men - 0.5%
• Elderly women - 0.4%

Example:

• A serum sodium level of 155 in a 60-kg young man represents a fluid deficit of 60 X 0.6 X ([155 / 140] - 1) or 3.9 L
  

• With another 900 mL of insensible losses, the patient requires 4.8 L of fluid in the next 48 hours, resulting in an infusion rate of 100 mL/h.

SIADH

• Pure water depletion and ↑ Na → use 4% D + N/5 to treat it.
• Stimulating the bowel e.g. abdo surgery → release of ADH → SIADH

References

• http://www.merck.com/mmpe/print/sec12/ch156/ch156e.html
• http://emedicine.medscape.com/article/766683-treatment
  

Electrolyte imbalances that occur in diabetes

• Hypocalcaemia - kidney doesn't activate vitamin D -> decreased GIT absorption of Ca
  
• Hyponatraemia
• Hyperphosphataemia - it can't be excreted. Treatment is by giving a phosphate binder e.g. mylanta.