The amount of air exhaled from lungs as water vapour is about?

ESIC Nursing Officer 2016 (Shift -2)

Applied Physiology

Easy

Appeared in: ESIC Nursing Officer 2016 (Shift -2)

Explanation

The question asks for the approximate amount of water lost as vapor during exhalation, which is a component of insensible water loss.
Physiologically, the body loses about 300-400 mL of water per day through the lungs during respiration.
This occurs because inhaled air is warmed and humidified in the respiratory tract, and this moisture is then expelled during exhalation.
Among the given choices, 500 mL is the closest and most reasonable estimate for this daily water loss, even though it is slightly higher than the typical average.

Option A: 1000 mL is significantly higher than the average daily water loss from the lungs. This volume is closer to the total daily insensible loss from both the skin and lungs combined.
Option B: 1500 mL is a classic distractor. This volume represents the average daily urine output for an adult, which is a form of sensible (measurable) water loss, not insensible loss from the lungs.
Option D: 200 mL is lower than the accepted physiological range for respiratory water loss (300-400 mL). This volume is more representative of the amount of water lost daily in feces or the amount of water produced through metabolism.

Visual 1: Diagram: A flowchart illustrating the daily fluid balance in the human body, showing all routes of intake (ingestion, metabolism) and output (urine, feces, skin, lungs) with their average volumes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Insensible water loss through respiration as background academic context rather than a clinical decision trigger.
A nurse must understand all routes of fluid loss to accurately assess a patient's hydration status. Insensible losses from the lungs and skin are not easily measured but must be accounted for, especially in vulnerable patients.
Conditions like fever or tachypnea (rapid breathing) significantly increase insensible water loss from the lungs. A nurse needs to anticipate increased fluid requirements in such patients to prevent dehydration.
What if the patient is on a mechanical ventilator? The amount of water loss can be altered. If the ventilator provides humidified air, the insensible loss from the lungs will decrease. If it provides dry air, the loss will increase.

How to Approach the Question

Identify the core concept: The question is asking about a specific physiological value related to fluid balance.
Recognize the term 'water vapour' from 'lungs' as referring to insensible water loss through respiration.
Recall the standard physiological values for daily fluid intake and output.
Compare the given options to the known average for respiratory water loss (approximately 300-400 mL/day).
Select the option that is the closest and most reasonable estimate, which is 500 mL.
Eliminate other options by identifying what physiological process they represent (e.g., 1500 mL for urine, 200 mL for feces).

Concept Tested & Keywords

QU6DEAQa_rqbH1S3vApmt-