Unit 8.3: Fluid Balance and Electrolytes

• Topic 01

  Fluid Balance Charts

  45 questions
• Topic 02

  Normal Electrolyte Ranges and Clinical Significance

  45 questions
• Topic 03

  IV Fluid Prescribing

  87 questions
• Topic 04

  Recognising and Responding to Dehydration and Fluid Overload

  45 questions

A few questions from this unit, with the answer and a full explanation. The complete bank is available when you start practising.

1. What term is used to describe urine output below 0.5 mL/kg/hr in an adult?

   • A
     Anuria
   • B
     Polyuria
   • C
     Haematuria
   • D
     Oliguria
     Correct answer
   Explanation

   Oliguria is defined as urine output below 0.5 mL/kg/hr (or less than approximately 400 mL per 24 hours in an adult). It is an important clinical indicator of reduced renal perfusion or renal dysfunction, commonly seen in dehydration, acute kidney injury, and cardiac failure. Anuria means no urine output (<100 mL/24 hr). Polyuria is excess urine production. Haematuria is blood in urine. Nocturia is frequent nocturnal urination. Dysuria is painful urination.

2. A 75 kg patient with pneumonia has had a temperature fluctuating between 38.5 °C and 40.0 °C over 24 hours. For fluid balance calculation purposes, the nurse decides to use the midpoint temperature of 39.25 °C. Their baseline insensible loss is 700 mL/24 hr. Calculate the estimated total insensible loss for the 24-hour period. Additionally, the patient has tachypnoea (RR 26/min); the nurse adds a further 150 mL for increased respiratory losses. What is the final adjusted insensible loss estimate?

   • A
     Without tachypnoea: 925–1,025 mL (700 + 225–325 for 2.25 °C rise). With tachypnoea: 1,075–1,175 mL
     Correct answer
   • B
     Without tachypnoea: 850 mL (using minimum 100 mL/°C only); with tachypnoea: 1,000 mL
   • C
     Without tachypnoea: 700 mL (midpoint averaging negates the pyrexia adjustment); with tachypnoea: 850 mL
   • D
     Without tachypnoea: 1,050–1,200 mL (700 + 350–500 for 3.25 °C rise); with tachypnoea: 1,200–1,350 mL
   Explanation

   Midpoint temperature rise = 39.25 − 37 = 2.25 °C above 37 °C. Pyrexia adjustment: $2.25 \times 100 = 225 mL (minimum) to \2.25 \times 150 = 337.5$ mL ≈ 338 mL (maximum). Total without tachypnoea = 700 + 225 = 925 mL to 700 + 338 = 1,038 mL ≈ 1,025 mL (rounded). With tachypnoea (+150 mL): 925 + 150 = 1,075 mL to 1,025 + 150 = 1,175 mL. The use of midpoint temperature in fluctuating pyrexia is a pragmatic clinical approach rather than re-calculating for each temperature reading. This multi-step calculation tests the ability to apply the per-degree formula, use a midpoint, and add an additional adjustment — reflecting realistic NMC CBT numeracy demands.

3. A student nurse lists the following as outputs to include in a fluid balance chart: urine, wound drainage, nasogastric aspirate, insensible losses, and loose stool. Which item should the mentor correct?

   • A
     Wound drainage — this is recorded in the input column, not the output column
   • B
     Nasogastric aspirate — this is only recorded if it exceeds 200 mL in volume
   • C
     Urine — this is only recorded if the patient is catheterised
   • D
     Insensible losses — these cannot be directly measured and are not entered on the bedside chart
     Correct answer
   Explanation

   Insensible losses (skin evaporation, respiratory moisture) cannot be measured at the bedside and are not entered on the fluid balance chart. Urine (including from non-catheterised patients using calibrated containers), wound drainage, nasogastric aspirate, and loose stool (estimated) must all be recorded in the output column. Urine does not require catheterisation — it can be measured using a calibrated jug.