Electrolyte Imbalance QnA for HO

 House Officers must know in ward 

- Electrolyte imbalance

Q1: 50year old, 70 kg, male with persistent diarrhea and vomiting for 3days due to food poisoning. He is dehydrated. Vitals are stable, looks lethargic. Na: 128mmol/L

a. How to correct his hyponatremia

    - calculate first

• Na deficit (mmol) : (desired Na level - serum Na) x bw x fraction
• 0.6 x kg x (desired Na - serum Na)
• desired Na :  135-145
• Na deficit is 0.6 because extracellular comprises 60%. 
• If its potassium (intracellular) therefore 0.4 cause it is 40%
• 0.6 x 70 x (135-128) = 294mmol/L

    - to add with daily requirement

• infusion = deficit + requirement
• requirement: 1-2mmol/kg/d (we usually use the lower range when calculating)
• infusion: 294 + 70 = 364 mmol/L

- then how do we deliver 364mmol/L to pt?

• 1 pint NS = 77mmol/ L
• 1L NS = 154mmol/L
• 364 / 77 = 4.7 pints, 
• therefore 5 pints of normal saline over 24 hours is needed.

b. the next day his repeated Na is normal: 136, 

how do you plan for fluid regime ? for maintenance?

• normally a person need 30-40ml/kg/d (fluid requirement)
• general normal weight for man: 70kg,  normal weight for woman : 60kg

• if we take the middle value fluid requirement (35ml/kg/d), 
• the man will need 2450ml (around 5 pint as well)
• women is 2100ml, around 4pint. 

thats why usually we see usually 

• 5 pint (2/3 pint NS + 2/3 pint D5%) given to man, 
• 4 pint(2 pint NS + 2 pint D5%) given to women. 

** WHY 2 or 3 pint NS? for example a 70kg man we take 140mmol Na requirement, 1 pint NS is 77mmol, therefore the man only need 2 pint NS. but his fluid requirement is 5 pints a day, that's why we need to add another 3 pint D5 to complete his daily fluid requirement. 

Q2. what should you watch out during sodium correction?

• Na correction should not exceed 10mmol/L/24 hours
• thats why we use the lower normal when correcting sodium
• even in severe hyponatremia, if Na only 120, your aim of correction is only up to 130, and not up to 135 in 24 hours. 
• if there are hypernatremia (rare), mostly we try to find out the associated conditions/ related underlying issues. usually will be given diuretics to excrete excess sodium. 

Q3: 50year old, 70 kg, male with persistent diarrhea and vomiting for 3days due to food poisoning. looks lethargic, no ecg changes.  K: 3.2mmol/L

a. how to correct his potassium?

• Deficit = (desired K - measured) x Body Weight (BW) x 0.4
• (3.5-3.2) x 70 x 0.4 = 8.4mmol
• 70 for maintanence , 
• maintanence + deficit = infusion
• 70+8.4 = 78.4
• 78.4/13.3 = 5.8gm
• we take normal daily requrement of K : 1mmol/kg/d, therefore we need to convert into gm  by dividing 13.3
• 1gm = 13.3mmol
• so we need to correct at least 5 gm first
• can correct with 1g KCL in each pint NS (total 5gm)/24hours

b. what is the maximum/ safe dilution of K+ in 1 pint of NS?

• dilution cannot exceed 40mmol/L
• which also means cannot exceed 20mmol/pint = 20/13.3 = 1.5gm KCl
• we cannot give more than 1.5gm KCl in a pint of NS

c. what is the safe titration of K+?

• titration of potassium cannot exceed 10mmol / hour
• if we need fast correction due to symptomatic, 
• max is 1gm KCl in 100cc NS over 1 hour, not faster than that

• If need 2gm infusion, it must be in 2 hours.
• never bolus correction, must always use safe titration
• 2gm KCl infusion in 200cc NS over 2 hours

• OTHERWISE can cause CARDIAC ARREST! 

Q4: How do we know the patient has hyperkalemia?

• Cut off point for hyper K: 
• K+ > 5.5
• symptomatic ECG changes: tall tented T waves, absence of P wave, broad QRS, PR prolong
• it became dangerous when the ECG changes go towards heart block type of ECG with tall tented T wave --> severe hyperkalemia --> lead to arrythmia then asystole

Q5. what is the fx of each components in lytic coctail? 

• lytic cocktail: treatment for hyperkalemia
• Calcium gluconate - 10ml 10% calcium gluconate
• for cardio protection
• Insulin / actrapid 10u : 
• drive K+ into cell together with glucose
• Glucose/ D50 - 50ml : 
• K+ transporter
• we need to administer calcium gluconate follow by insulin then D50

Q5a. so why we cannot give insulin first instead of glucose?

• Potassium cannot enter the cell by itself, thats why we need glucose first ,since it is the transporter it can allow the insulin to drive the K into the cell. 
• GLucose is the transporter
• so we need to load the excess potassium onto the glucose
• Insulin cannot push the K directly, they need transport. therefore they need glucose first, then insulin will push both into the cells. 

Q5b. how many times can we give lytic cocktail?

• every 6 hourly
• if the potassium is still not corrected, Hemodialysis (HD) is needed

But we could not just correct potassium with just lytic coctail,  have to correct the cause of hyperK as well. 

Q5c. what are the common cause of HyperK in surgery?

• Acute Kidney Injury (AKI)
• severe dehydration, sepsis can cause AKI. 
• If there are evidence of sepsis, we need to find the source and remove its source of infection
• antibiotics
• If there are acidosis, we need to find the cause and solve it from there as well. 

Q6. what are the common antibiotics used in Gastrointestinal - GI sepsis?

• cefobid and flagyl

• common organism in GI
• gram negative : E.Coli, Klebsiella, Enterobacter
• GI accomodates a broad spectrum of gram negative organisms
• anaerobes

• 1st generation of cephalosporin covers gram positive
• exp: cephalexin
• 2nd generation covers gram positive and a bit of gram negative (narrow spectrum)
• cefuroxime
• 3rd generation covers broad spectrum of gram negative
• cefobid/ cefoperazone

• Metronidazole: covers anaerobes

• If patient has carbuncle, abscess or soft tissue infection / sepsis, the choice of antibiotic should be covering skin organism: 
• empirical antibiotic
• penicillin based: cloxacillin, etc. 
• for Urology patient, usually have narrow spectrum of organism, 
• common: E. Coli
• can use cefuroxime as empirical antibiotic, unless they have sepsis, so may need to consider quinolones to cover for broader/ other pathogens

Q6a. so when do we change antibiotics? 

• observe if antibiotic works, after 3-5 days
• usually the patient will show clinical improving and total white cell count (TWC) will reduce
• but if no changes after 3 days, we might need to consider changing to a higher efficacy antibiotic
•