Breathing Assessment and Oxygen Therapy

SECTION 1

Historical Context & Motivation

The ability to rapidly assess a patient's breathing and deliver supplemental oxygen is now considered a cornerstone of prehospital emergency medicine, yet this was not always the case. For centuries, clinicians relied on rudimentary observations—counting chest movements, listening for audible wheezing, or simply noting skin color changes—without standardized tools or protocols. The evolution of breathing assessment and oxygen therapy from informal observation to a structured, evidence-based process has been driven by advances in physiology, technology, and the formalization of emergency medical services (EMS). Understanding this history helps contextualize why each element of the modern primary assessment exists and why specific oxygen delivery devices are matched to particular clinical scenarios.

1774

Discovery of Oxygen

Joseph Priestley isolates oxygen, calling it 'dephlogisticated air.' Shortly after, Antoine Lavoisier names the element and demonstrates its role in combustion and respiration, laying the chemical foundation for understanding why supplemental oxygen can sustain life.

1917

Oxygen in Combat Medicine

John Scott Haldane develops practical methods for delivering oxygen to soldiers suffering from chlorine gas exposure during World War I. His work establishes flow-rate principles and rudimentary masks that become precursors to modern oxygen delivery devices.

1960

Pulse Oximetry Invented

Takuo Aoyagi develops the principle of pulse oximetry in Japan, allowing noninvasive, real-time measurement of arterial oxygen saturation (SpO₂). This technology eventually becomes a standard prehospital monitoring tool, transforming how EMTs quantify respiratory status.

1971

National EMS Systems Act

The United States begins formalizing EMS through federal legislation, establishing training standards that include systematic breathing assessment. The National Registry of Emergency Medical Technicians (NREMT) develops competency exams that codify the primary assessment sequence.

2010s

Evidence-Based Oxygen Guidelines

Research reveals that excessive oxygen administration can cause harm in certain conditions such as myocardial infarction and stroke. EMS protocols shift toward titrated oxygen therapy guided by SpO₂ targets, replacing the earlier practice of high-flow oxygen for all patients.

This historical arc reveals a central question that shapes modern EMT practice: How do we systematically determine whether a patient's breathing is adequate, and when it is not, how do we select and deliver the appropriate level of oxygen support? Answering this question requires integrating clinical observation, quantitative monitoring, and a working knowledge of oxygen delivery devices—skills that form the heart of the primary assessment.

SECTION 2

Core Principles of Breathing Assessment

The breathing component of the primary assessment follows a look, listen, and feel paradigm that rapidly integrates visual, auditory, and tactile findings to determine whether ventilation is adequate, inadequate, or absent. This evaluation occurs immediately after assessing the airway and before moving to circulation. The EMT must evaluate both the rate and quality of breathing because a patient may breathe at a normal rate yet still ventilate inadequately if tidal volume is severely reduced. The following foundational concepts anchor the entire assessment process.

Rate Assessment

Normal adult respiratory rate is 12–20 breaths per minute. Rates below 12 (bradypnea) or above 20 (tachypnea) signal potential respiratory compromise. Pediatric norms are age-dependent and generally higher.

Quality & Depth

Assess chest rise symmetry, depth of inspiratory effort, and use of accessory muscles (sternocleidomastoid, intercostals, abdominal muscles). Shallow, labored, or asymmetric breathing indicates inadequate ventilation regardless of rate.

Auscultation

Bilateral lung sounds are evaluated for equality, clarity, and the presence of abnormal sounds such as wheezes, crackles (rales), rhonchi, or stridor. Absent or diminished sounds on one side suggest pneumothorax, hemothorax, or mainstem intubation.

Pulse Oximetry (SpO₂)

SpO₂ provides a quantitative measure of hemoglobin oxygen saturation. Values of 94–99% are normal; values below 94% generally warrant supplemental oxygen. Be aware of limitations including poor perfusion, carbon monoxide exposure, and nail polish interference.

Skin Signs & Mental Status

Cyanosis (bluish discoloration of lips, nail beds) indicates significant hypoxemia. Altered mental status—anxiety, confusion, or unresponsiveness—can reflect cerebral hypoxia and is an early warning sign that ventilation is failing.

✦ KEY TAKEAWAY

Think of breathing assessment like checking a garden hose. The rate is how often you turn the nozzle on and off, and the depth (tidal volume) is how wide you open the nozzle each time. A hose that clicks on and off quickly but barely opens still delivers inadequate water, just as tachypneic shallow breathing fails to deliver adequate oxygen to the alveoli. The EMT must assess both parameters simultaneously to determine whether the patient's ventilation is truly effective.

SECTION 3

Visual Explanation — The Breathing Assessment Algorithm

The breathing assessment algorithm begins with look-listen-feel observations and proceeds to a decision point based on rate and quality. Absent breathing requires immediate BVM ventilation with high-flow oxygen. Inadequate breathing (slow, shallow, or labored) requires assisted ventilation or a non-rebreather mask at 15 LPM. Adequate breathing is monitored with pulse oximetry; if SpO₂ falls below 94%, supplemental oxygen via nasal cannula is initiated.

The flowchart above represents the systematic decision-making process that the EMT follows during the breathing portion of the primary assessment. Notice that the algorithm is hierarchical: observation precedes quantification, and intervention is matched to severity. The most critical branch—absent breathing—demands the most aggressive intervention (bag-valve-mask with supplemental oxygen), while adequate breathing may require nothing more than monitoring. This tiered approach ensures that limited resources are directed where they will have the greatest impact on patient survival.

SECTION 4

How Breathing Assessment and Oxygen Therapy Work

Physiology of Ventilation and Oxygenation

To understand why specific assessment findings matter, one must appreciate the distinction between ventilation and oxygenation. Ventilation is the mechanical process of moving air in and out of the lungs; oxygenation is the gas exchange process by which oxygen diffuses across the alveolar-capillary membrane into the blood. A patient can ventilate adequately (normal rate and depth) yet still suffer poor oxygenation if the alveolar membrane is damaged (e.g., pulmonary edema). Conversely, a patient receiving 100% oxygen can still die if ventilation ceases because CO₂ accumulates and fresh gas never reaches the alveoli.

MINUTE VENTILATION

V̇E = f × VT

Where V̇E = minute ventilation (mL/min), f = respiratory frequency (breaths/min), and VT = tidal volume (mL/breath). Normal adult V̇E ≈ 12 breaths/min × 500 mL = 6,000 mL/min. A rate of 30 with a tidal volume of only 150 mL yields only 4,500 mL/min, much of which is dead-space ventilation.

ALVEOLAR VENTILATION

V̇A = f × (VT − VD)

Where V̇A = alveolar ventilation (mL/min) and VD = dead space volume (≈ 150 mL in adults). This equation explains why shallow breathing is dangerous: if VT approaches VD, effective alveolar ventilation approaches zero regardless of respiratory rate.

Fraction of Inspired Oxygen (FiO₂)

Room air provides an FiO₂ of approximately 0.21 (21% oxygen). Each oxygen delivery device increases this fraction by a predictable amount depending on its design and the set flow rate. The nasal cannula (NC) adds roughly 4% per liter of flow (FiO₂ ≈ 0.24 at 1 LPM up to ≈ 0.44 at 6 LPM). The non-rebreather mask (NRB) with a reservoir bag at 15 LPM delivers an FiO₂ of approximately 0.90–0.95. The bag-valve-mask (BVM) connected to 15 LPM oxygen with a reservoir can deliver nearly 1.00 FiO₂. These values are estimations because actual FiO₂ varies with mask seal quality and patient breathing pattern.

NASAL CANNULA FiO₂ ESTIMATE

FiO₂ ≈ 0.20 + (0.04 × Flow Rate in LPM)

This approximation applies for flow rates of 1–6 LPM. At 4 LPM: FiO₂ ≈ 0.20 + (0.04 × 4) = 0.36 (36%). Flow rates above 6 LPM via nasal cannula cause mucosal drying and are not recommended.

⚠ Clinical Pearl

Pulse oximetry readings can be falsely elevated in carbon monoxide (CO) poisoning because standard pulse oximeters cannot distinguish carboxyhemoglobin (COHb) from oxyhemoglobin. In suspected CO exposure, treat the patient, not the number—apply high-flow oxygen via NRB regardless of the SpO₂ reading.

SECTION 5

Oxygen Delivery Devices — Classification and Selection

Selecting the correct oxygen delivery device is a clinical decision that depends on the patient's respiratory status, the target FiO₂, and whether the patient is breathing spontaneously. The EMT scope of practice includes three primary devices: the nasal cannula, the non-rebreather mask, and the bag-valve-mask. Each device occupies a distinct position on the continuum from low-flow supplementation to full positive-pressure ventilation.

This diagram plots the three primary EMT-level oxygen delivery devices against their flow rate ranges and approximate FiO₂ outputs. The nasal cannula occupies the low-flow/low-FiO₂ range (24–44%). The non-rebreather mask provides high-flow delivery (60–95% FiO₂). The BVM with oxygen reservoir approaches 100% FiO₂ and is reserved for patients requiring positive-pressure ventilation.

Comparison of EMT-level oxygen delivery devices

Device	Flow Rate	FiO₂	Indications	Key Considerations
Nasal Cannula	1–6 LPM	24–44%	Mild hypoxemia; SpO₂ 90–94%; patient tolerates NC	Do not exceed 6 LPM (mucosal drying). Humidification for prolonged use.
Non-Rebreather Mask	10–15 LPM	60–95%	Significant hypoxemia; SpO₂ < 90%; respiratory distress	Pre-fill reservoir bag before applying. Minimum 10 LPM to prevent CO₂ rebreathing.
Bag-Valve-Mask (BVM)	15 LPM (with reservoir)	~100%	Apnea; inadequate ventilation; respiratory failure	Maintain proper mask seal (C-E technique). Ventilate over 1 second per breath. Avoid hyperventilation.

SECTION 6

Worked Example — Field Breathing Assessment

Consider the following scenario: You arrive on scene to find a 62-year-old male sitting in a tripod position on his porch. He is conscious and anxious, speaking in two- to three-word sentences. His skin appears pale with slight cyanosis around the lips. You are performing your primary assessment.

Primary Assessment — Breathing Evaluation and Intervention

Step 1 — LookObserve the patient's chest for rise and fall. You note that chest rise is present but shallow, and both the sternocleidomastoid and intercostal muscles are retracting visibly. The tripod position and accessory muscle use are clinical signs of respiratory distress. You also observe circumoral cyanosis, indicating significant hypoxemia.

Findings: Shallow breathing, accessory muscle use, cyanosis → suggests inadequate ventilation

Step 2 — ListenPlace your stethoscope on the midaxillary line bilaterally. You auscultate bilateral wheezes with diminished air entry at the bases. Wheezes indicate bronchoconstriction (possibly asthma or COPD exacerbation). Diminished bases suggest reduced tidal volume or fluid accumulation.

Findings: Bilateral wheezes with diminished bases

Step 3 — Count Respiratory RateCount respirations for 30 seconds and multiply by two (or count for a full 60 seconds if the rhythm appears irregular). You count 14 breaths in 30 seconds, yielding a respiratory rate of 28 breaths per minute. This tachypnea combined with shallow depth indicates the patient is working hard but achieving poor alveolar ventilation.

Respiratory rate: 28 breaths/min (tachypneic)

Step 4 — Apply Pulse OximetryPlace the pulse oximeter on the patient's finger. After allowing the waveform to stabilize, the SpO₂ reads 86%. This is significantly below the 94% threshold and confirms the clinical picture of inadequate oxygenation. You verify adequate peripheral perfusion by checking capillary refill at the fingertip (2 seconds—acceptable).

SpO₂: 86% — severe hypoxemia confirmed

Step 5 — Select Oxygen Delivery DeviceThe patient is breathing spontaneously but inadequately. With an SpO₂ of 86%, accessory muscle use, and cyanosis, this patient requires high-flow oxygen. Apply a non-rebreather mask at 15 LPM after pre-filling the reservoir bag. If the patient's condition deteriorates—respiratory rate drops below 12 or patient becomes unresponsive—be prepared to transition to BVM-assisted ventilation. Reassess SpO₂ every 2 minutes and continue monitoring mental status.

Intervention: Non-rebreather mask at 15 LPM; monitor for deterioration; prepare BVM

SECTION 7

Strengths and Limitations of Assessment Findings

No single assessment finding is definitive in isolation. Each element of the breathing assessment carries inherent strengths and limitations that the EMT must understand to avoid diagnostic pitfalls. For example, pulse oximetry is enormously useful as a screening tool but can mislead in the presence of carbon monoxide poisoning, methemoglobinemia, or severe peripheral vasoconstriction. Similarly, respiratory rate alone can be misleading: a patient breathing at 16 breaths per minute appears normal by rate criteria alone, yet if tidal volume is only 200 mL, effective alveolar ventilation is dangerously low.

Strengths and limitations of breathing assessment components

Assessment Finding	Strengths	Limitations
Respiratory Rate	Quick to obtain; requires no equipment; reliable indicator of respiratory effort	Does not reflect tidal volume or oxygenation; can be normal in early compensation
Chest Rise/Fall	Immediate visual indicator of tidal volume; reveals asymmetry (pneumothorax)	Difficult to assess in obese patients or under clothing; subjective
Auscultation	Identifies abnormal sounds (wheezes, crackles); detects unilateral pathology	Noisy environments interfere; requires practice; absent sounds can indicate either absent ventilation or severe obstruction
Pulse Oximetry (SpO₂)	Objective, continuous, quantitative; noninvasive; guides titration of O₂ therapy	Unreliable in CO poisoning, poor perfusion, hypothermia, nail polish; lags behind acute changes by 30–60 seconds
Skin Signs (Cyanosis)	Visible indicator of severe hypoxemia; requires no equipment	Late finding; difficult to detect in dark-skinned patients; absent in anemia despite hypoxemia

✦ KEY TAKEAWAY

Think of breathing assessment findings like instruments on an aircraft dashboard. No pilot relies on a single gauge; they cross-reference the altimeter, airspeed indicator, and attitude indicator to build a complete picture of the aircraft's state. Similarly, the EMT must integrate multiple findings—rate, depth, lung sounds, SpO₂, skin signs, and mental status—because each parameter compensates for the blind spots of the others. A normal SpO₂ does not guarantee adequate ventilation, and a normal rate does not guarantee adequate oxygenation.

SECTION 8

Connection to Advanced Airway Management and ALS Interventions

The breathing assessment and oxygen therapy skills covered in this lesson form the EMT-level foundation upon which advanced life support (ALS) providers build more sophisticated interventions. Understanding where your scope ends and ALS capabilities begin allows for better patient advocacy, smoother handoffs, and more informed requests for ALS intercept. The table below contrasts EMT-level assessment and intervention with the expanded tools available at the Advanced EMT (AEMT) and Paramedic levels.

EMT vs. ALS breathing assessment and intervention capabilities

Domain	EMT (BLS)	AEMT / Paramedic (ALS)
Ventilation Monitoring	Visual chest rise, respiratory rate, SpO₂	End-tidal CO₂ (EtCO₂) capnography provides real-time ventilation adequacy and confirms tube placement
Airway Devices	OPA, NPA, BVM, suction	Supraglottic airways (King, i-gel), endotracheal intubation, surgical cricothyrotomy
Pharmacology	Supplemental O₂ only; aspirin, glucose, epinephrine auto-injector in some protocols	Bronchodilators (albuterol), sedatives (midazolam), paralytics (succinylcholine) for RSI, IV/IO access for drug delivery
Needle Decompression	Recognize tension pneumothorax; request ALS	Perform needle thoracostomy to relieve pressure
Mechanical Ventilation	Manual BVM ventilation	Transport ventilators with adjustable rate, tidal volume, PEEP settings

As you progress through your EMS career, you may advance to the AEMT or Paramedic level, where tools like capnography (end-tidal CO₂ monitoring) become central to ventilation management. Capnography provides a direct measurement of exhaled carbon dioxide, which reflects both ventilation adequacy and metabolic status—information that pulse oximetry alone cannot provide. For now, recognize that your BLS-level breathing assessment is the critical first link in the chain of respiratory care, and the thoroughness of your evaluation directly influences the decisions made by ALS providers who receive your patient.

SECTION 9

Practice Problems

PROBLEM 1 — CONCEPTUAL

A patient is breathing at a respiratory rate of 18 breaths per minute with very shallow chest rise. An EMT partner states, 'The rate is normal, so the breathing is adequate.' Explain why this assessment may be incorrect and identify what additional findings should be evaluated.

PROBLEM 2 — BASIC CALCULATION

An adult patient is breathing at a rate of 8 breaths per minute with an estimated tidal volume of 400 mL. Calculate the patient's minute ventilation and alveolar ventilation (assume dead space = 150 mL). Are these values adequate?

PROBLEM 3 — INTERMEDIATE

You are treating a 45-year-old female with an asthma exacerbation. She is sitting upright, speaking in short phrases, and has audible expiratory wheezing. Her SpO₂ is 91% on room air and respiratory rate is 26. You apply a nasal cannula at 4 LPM. After 5 minutes, her SpO₂ remains at 91% and she appears more distressed. What is the estimated FiO₂ she is currently receiving, and what should your next intervention be?

PROBLEM 4 — APPLIED

You respond to a house fire and find a 30-year-old male who was trapped in a smoky room. He is conscious and states he feels 'fine.' His SpO₂ reads 99%. A newer EMT on your crew says, 'His sat is great—he doesn't need oxygen.' Do you agree? Justify your clinical decision.

PROBLEM 5 — CRITICAL THINKING

A 70-year-old COPD patient presents with moderate respiratory distress. His baseline SpO₂ (per family report) is typically 88–90%. Current SpO₂ is 87%, respiratory rate is 22, and he has mild accessory muscle use. Some EMS protocols recommend titrating oxygen to a target SpO₂ of 88–92% for known COPD patients rather than the standard ≥ 94%. Analyze the physiological rationale for this lower target, discuss the risks of both under-oxygenation and over-oxygenation in this population, and describe your management approach.

SUMMARY

Lesson Summary

Breathing assessment during the primary assessment is a systematic process that evaluates respiratory rate, depth and quality of ventilation, bilateral lung sounds, pulse oximetry (SpO₂), and skin signs and mental status. The normal adult respiratory rate is 12–20 breaths per minute, and adequate ventilation requires both an appropriate rate and sufficient tidal volume. The concept of minute ventilation (V̇E = f × VT) and alveolar ventilation (V̇A = f × (VT − VD)) explain why shallow breathing can be dangerous even at normal rates.

Oxygen therapy is matched to clinical severity: the nasal cannula (1–6 LPM, 24–44% FiO₂) addresses mild hypoxemia, the non-rebreather mask (10–15 LPM, 60–95% FiO₂) addresses significant hypoxemia, and the bag-valve-mask with oxygen reservoir (15 LPM, ~100% FiO₂) is reserved for patients who are apneic or ventilating inadequately. Key pitfalls include relying on SpO₂ alone (especially in carbon monoxide exposure), and the special consideration of titrated oxygen therapy for COPD patients targeting an SpO₂ of 88–92%. Always integrate multiple assessment findings—never rely on a single parameter—and reassess continuously after every intervention.