3.1 Respiratory Disorders Overview

What the CEN Tests in Respiratory

The Certified Emergency Nurse (CEN) examination, administered by the Board of Certification for Emergency Nursing (BCEN), devotes roughly 11% of its 175 items (about 17 scored questions) to respiratory emergencies. This domain rewards nurses who can recognize respiratory failure early, interpret arterial blood gases, and select the right level of oxygenation and ventilation support for the underlying disease.

The tested conditions cluster into five families:

Most questions are written as scenarios: a patient with a set of vital signs and an ABG, and you choose the next best action. Memorizing definitions is not enough — you must apply them under time pressure.

Oxygenation Versus Ventilation

The single most important distinction in this chapter is oxygenation (getting O2 into the blood) versus ventilation (clearing CO2). They fail independently.

• Type I (hypoxemic) failure: PaO2 < 60 mmHg on room air despite adequate respiratory effort. Caused by V/Q mismatch, shunt, or diffusion problems — pneumonia, ARDS, pulmonary edema, PE.
• Type II (hypercapnic) failure: PaCO2 > 50 mmHg with pH < 7.35. The pump fails — the patient cannot move enough air. Seen in COPD, severe asthma, opioid overdose, and neuromuscular weakness.

A patient can be hypoxemic with a normal or low CO2 (early), then progress to hypercapnia as they tire. That conversion is the warning sign of impending arrest.

Normal Adult ABG Reference

A "normalizing" PaCO2 in an asthmatic who was previously hyperventilating (low CO2) is ominous — it means the patient is tiring and CO2 is climbing back toward 40, not that they are getting better.

Bedside Monitoring Tools

Pulse oximetry (SpO2) measures oxygenation only, and it lags. On high-flow oxygen, SpO2 can read 98% while the patient is severely hypoventilating and accumulating CO2 — the oxygen masks the problem. SpO2 is also unreliable with carbon monoxide poisoning (it reads carboxyhemoglobin as oxygenated), poor perfusion, or dark nail polish.

Capnography (end-tidal CO2, EtCO2) displays ventilation breath-to-breath. Normal EtCO2 is 35-45 mmHg. A waveform that flattens or disappears after intubation signals esophageal placement or arrest. A "shark-fin" upsloping waveform suggests bronchospasm (asthma/COPD). Rising EtCO2 with sedation warns of hypoventilation before SpO2 falls.

Assessment Priorities

1. Airway patency and protective reflexes
2. Work of breathing: accessory muscle use, tripoding, retractions, paradoxical (abdominal) movement
3. Air movement: breath sounds, a silent chest in asthma = near-total obstruction
4. Adjuncts: ABG, capnography, chest x-ray, bedside ultrasound

Use domain weight and your practice-test miss pattern to decide how much review time respiratory needs.

Reading a Respiratory Patient at a Glance

Before any monitor is attached, an experienced emergency nurse forms an impression from across the room. The presence and severity of distress is judged by position, speech, and effort. A patient who is tripoding — leaning forward, hands braced on the knees — is recruiting accessory muscles because the diaphragm alone is failing. Counting how many words the patient can say between breaths is a fast severity scale: full sentences suggest mild distress, short phrases suggest moderate distress, and single words or an inability to speak suggest severe, potentially pre-arrest distress.

Skin color and mental status complete the picture. Cyanosis is a late and unreliable sign because it requires roughly 5 grams per deciliter of deoxygenated hemoglobin, so an anemic patient may be profoundly hypoxic without turning blue. Far more sensitive is a change in mentation: anxiety and restlessness are early signs of hypoxia, while drowsiness and confusion suggest rising carbon dioxide. The classic teaching is that the hypoxic patient is agitated and the hypercapnic patient is sleepy, and a patient who quiets down after a period of agitation may be deteriorating rather than calming.

Why the Underlying Cause Drives Treatment

The CEN repeatedly tests the principle that the same symptom — shortness of breath — demands different interventions depending on cause. Pulmonary edema responds to preload reduction and positive pressure; bronchospasm responds to bronchodilators; embolism responds to anticoagulation; and a collapsed lung responds to decompression. "** Anchoring each vignette to that question prevents the common error of reaching for oxygen as a one-size-fits-all answer when the patient actually needs a chest tube, a clot-busting drug, or noninvasive ventilation.

Throughout this chapter, every workflow is built around matching the intervention to the mechanism rather than to the symptom. Keep in mind that emergency patients often have more than one mechanism at once: a septic pneumonia patient may have both a shunt from consolidated lung and a pump problem from exhaustion, and a trauma patient may have both a hemothorax draining blood and hypovolemic shock from elsewhere. The CEN expects you to identify the most immediately life-threatening mechanism, address it first, and then continue reassessing, because the patient who is stabilized in one domain can decompensate in another within minutes.