An injury to the phrenic nerve causes?

UPRVUNL - 2021

Applied Physiology

Easy

Appeared in: UPRVUNL - 2021

Explanation

The phrenic nerve is the primary nerve that controls the diaphragm, the main muscle used for breathing.
An injury to the phrenic nerve can cause the diaphragm to become paralyzed or weakened.
When the diaphragm doesn't function correctly, the lungs cannot expand properly during inhalation, leading to difficulty in breathing (dyspnea).
This is a direct anatomical and physiological consequence, as confirmed by the nerve's origin from C3-C5 spinal roots, which are crucial for respiration.

Option A: Tachycardia (a heart rate over 100 beats per minute) is related to cardiac function and is controlled by the heart's conduction system and the autonomic nervous system, not the phrenic nerve.
Option B: Cardiac arrhythmia (an irregular heartbeat) is a disturbance in the heart's electrical conduction. It is not a direct result of phrenic nerve injury.
Option D: Hyperthermia (high body temperature) is a disorder of thermoregulation, which is controlled by the hypothalamus in the brain. It has no direct connection to the phrenic nerve.

Clinical Relevance

Nursing practice connection: Knowing Physiological effects of phrenic nerve injury helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must conduct vigilant respiratory assessments for patients with conditions that could potentially damage the phrenic nerve, such as cervical spine injuries, neck or chest trauma, or following thoracic surgery.
Key assessments include monitoring respiratory rate, depth, effort, use of accessory muscles, and oxygen saturation (SpO₂). A sudden onset of dyspnea in a high-risk patient is a red flag.
What if? If the injury was bilateral (affecting both the left and right phrenic nerves), the patient would likely experience severe respiratory failure requiring immediate mechanical ventilation, as the diaphragm would be completely paralyzed.

How to Approach the Question

First, identify the key anatomical structure in the question: the 'phrenic nerve'.
Recall or determine the primary function of this nerve. A key mnemonic is 'C3, 4, 5 keeps the diaphragm alive,' which links the nerve to the diaphragm.
Consider the function of the diaphragm, which is the main muscle of respiration.
Logically deduce the consequence of an 'injury' to this nerve. If the nerve controlling the primary breathing muscle is damaged, the most direct and significant effect will be on breathing.
Evaluate the given options. 'Breathing difficulty' is a direct match with your deduction. The other options (Tachycardia, Cardiac arrhythmia, Hyperthermia) relate to different body systems (cardiac, thermoregulatory) that are not directly controlled by the phrenic nerve.

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