prescribing fluids

Question 1

Intravenous fluids may be divided into

Answer 1

• Crystalloid solutions - clear fluids made up of water and electrolyte solutions; Will cross a semi-permeable membrane e.g Normal, hypo and hypertonic saline solutions; Dextrose solutions; Ringer’s lactate and Hartmann’s solution.

• Colloid solutions – Gelatinous solutions containing particles suspended in solution. These particles will not
form a sediment under the influence of gravity and are largely unable to cross a semi-permeable membrane. e.g. Albumin, Dextrans, Hydroxyethyl starch [HES]; Haemaccel and Gelofusine

Question 2

different types of saline

Answer 2

(1) 0.9% Normal Saline – Think of it as ‘Salt and water’
• Principal fluid used for intravascular resuscitation and replacement of salt loss e.g diarrhoea and vomiting

2) 0.45% Normal saline = ‘Half’ Normal Saline = HYPOtonic saline
• Reserved for severe hyperosmolar states E.g. H.O.N.K and severe dehydration
Leads to HYPOnatraemia if plasma sodium is normal

(3) 1.8, 3.0, 7.0, 7.5 and 10% Saline = HYPERtonic saline
• Reserved for plasma expansion with colloids
• In practice rarely used in general wards; Reserved for high dependency, specialist areas

Question 3

different types of dextrose solution

Answer 3

(1) 5% Dextrose (often written D5W) – Think of it as ‘Sugar and Water’
• Primarily used to maintain water balance in patients who are not able to take anything by mouth; Commonly used post-operatively in conjuction with salt retaining fluids ie saline; Often prescribed as 2L D5W: 1L N.Saline [‘Physiological replacement’ of water and Na+ losses]
• Provides some calories [ approximately 10% of daily requirements]
• Regarded as ‘electrolyte free’ – contains NO Sodium, Potassium, Chloride or Calcium
• Distribution: 66% intracellular
• When infused is rapidly redistributed into the intracellular space; Less than 10% stays in the intravascular space therefore it is of limited use in fluid resuscitation.
• For every 100ml blood loss – need 1000ml dextrose replacement [10% retained in intravascular space
• Common cause of iatrogenic hyponatraemia in surgical patient

(2) Dextrose saline – Think of it as ‘a bit of salt and sugar’
• Similar indications to 5% dextrose; Provides Na+ 30mmol/l and Cl- 30mmol/l Ie a sprinkling of salt and sugar!
• Primarily used to replace water losses post-operatively
• Limited indications outside of post-operative replacement – ‘Neither really saline or dextrose’; Advantage – doesn’t commonly cause water or salt overload.

Question 4

what are colloids

Answer 4

• The colloid solutions contain particles which do not readily cross semi-permeable membranes such as the capillary membrane
• Thus the volume infused stays (initially) almost entirely within the intravascular space
• Stay intravascular for a prolonged period compared to crystalloids
• However they leak out of the intravascular space when the capillary permeability significantly changes e.g. Severe trauma or sepsis
• Until recently they were regarded as the gold standard for intravascular resuscitation (see next slide)
• Because of their gelatinous properties they cause platelet dysfunction and interfere with fibrinolysis and coagulation factors (factor VIII) – thus they can cause significant coagulopathy in large volumes.

Question 5

colloid or crystalloid - which should you choose?

Answer 5

Recommendations:

• Colloid should NOT be used as the sole fluid replacement in resuscitation; Volumes infused should be limited because of side effects and lack of evidence for their continued use in the acutely ill.
• In severely ill patients – principally use crystalloid and blood products; Colloid may be used in limited volume to reduce volume of fluids required or until blood products are available
• In elective surgical patients – replace fluid loss with ‘physiological Hartmann’s and Ringer’s solutions; Blood products and colloid may be needed to replace intravascular volume acutely

Question 6

key elements you need to write down when prescribing any drug

Answer 6

Key elements
 – Drug name
– Dose
– Frequency of administration – Route of administration
– Start/Stop date
– (Indication)

Question 7

details you need to write down when prescribing a fluid

Answer 7

not all drug charts are the same but likely:

• date and time
• route of administration
• type of fluid (e.g. 0.9% saline)
• volume of infusion (1L)
• drug added (e.g. 20mmol KCL)
• infusion rate (eg 8hrly)
• signature and bleep no