How would you prepare the KCl for peripheral administration and at what rate should it be administered? (3 marks)

To prepare 10mEq/100ml from a 20mEq/50ml stock solution:

- Take out 25ml of stock solution to obtain 10mEq KCl.

- Then dilute with 75ml of water for injection to obtain 10mEq in 100 ml.

Patient requires 40 mEq KCl -> i.e. 4 x 10mEq/100ml

Administer at the max rate 10mEq/100ml/hr for four hours to deliver 40 mEq KCl.

NB. Equivalents is an American term.

What is the total osmolarity (mOsm/L) of the above IV solution if 0.9% NaCl was used as the diluent. (KCl=74.5; NaCl=58.4) (3 marks)

To get the answer in mOsm/L, calculate quantity of KCl and NaCl as if you have 1L of the above soln.

KCl:

• 1mEq K⁺ = 1mmol K⁺
• 10mEq/100ml => 100mEq K⁺ in 1000ml.
• 100mEq = 100 mmol K⁺
• 1 mol K⁺Cl^- = 2 Osm KCl
• 100mmol KCl= 200 mOsm KCl

NaCl:

• Calculate the number of moles of NaCl in the above soln:
• 25ml of KCl stock is diluted with 75ml 0.9% NaCl to get 10mEq KCl/100ml.
• Therefore in 1000ml of the made up solution there is 750ml of 0.9% NaCl.
• 0.9% NaCl (Normal Saline) means 9g NaCl in 1 L. Therefore in 750ml of NS there is 0.75*9 = 6.75g of NaCl.
• No moles= 6.75/58.4 = 0.1156 mol or 115.6 mmol
• 1 mmol NaCl = 2 mOsm
• 115.6*2 = 231 mOsm NaCl

Total osmolarity of the above solution:

200+231 = 431 mOsm/L