Oxygenation - Basics

Oxygenation keeps cells alive by getting air to the alveoli, moving O₂ across the membrane, loading it onto hemoglobin, and delivering it with adequate blood flow—then clearing CO₂ on the way out. These notes are clinical job aids you can use at the bedside to spot what’s failing (Ventilation, Diffusion, or Perfusion), choose the right device or action, and re-assess quickly.

Safety anchors: ABCs • Targeted SpO₂ (per unit policy) • Precise device setup • Upright positioning for V/Q • Clear SBAR handoffs • Reassess after every change

Clinical judgment: Collect cues → identify which part of the O₂ pathway is failing (V–D–P) → choose & sequence actions (position, airway clear, O₂ titrate, circulation support) → re-evaluate

Use this pack: Scan tables • practice Quick Checks • test yourself with the NGN mini-item + answer keys

Policy note: Follow local protocols for O₂ targets, device selection, humidification, ABG indications, and escalation.

🫁 Oxygenation

1) Foundations 📘

1.1 The O₂ Pathway (air → lungs → blood → tissues)

Essential	What it does	If it fails, you’ll see…
Lungs	Move air in/out; exchange gases	↑WOB, abnormal sounds, low SpO₂
Heart	Pushes oxygenated blood	Hypotension, poor perfusion
Blood vessels	Deliver blood to/from alveoli & tissues	Cool skin, poor cap refill
Hemoglobin (RBCs)	Carries O₂	Anemia → low O₂ delivery

Memory aid — V-D-P: Ventilation • Diffusion • Perfusion — always ask, “Which one is failing?”

1.2 Three Core Processes

Process	Plain definition	Bedside cues	First moves
Ventilation	Air movement in/out of lungs	Slow/shallow or very fast breathing; ↑CO₂	Sit upright, coach breathing, open airway
Diffusion	O₂/CO₂ crossing alveoli–blood	Crackles, edema/pneumonia, rising O₂ needs	Elevate HOB, lung expansion, treat fluid/infection per orders
Perfusion	Blood flow to pick up/drop off gases	Clear lungs but low SpO₂, shock/anemia	Support circulation; check Hgb; consider PE if sudden dyspnea

1.3 Gas Basics (why O₂ moves)

• Gases move from higher to lower partial pressure.

• Air is humidified in the trachea; alveolar O₂ is lower than room air.

• “Dissolve until equal” (gas ↔ blood): what’s in alveoli shapes the ABG.

1.4 Respiratory Drive (why we breathe)

• Primary: remove CO₂.

• Secondary: low O₂ (hypoxic drive).

• ⚠️ Titrate O₂ thoughtfully in likely CO₂ retainers—use your target range.

2) Structure & Mechanics ⚙️

2.1 Pressures & Phases

Term	Where	Inhale	Exhale
Atmospheric	Outside body	—	—
Intrapulmonary	Inside lungs	Negative (air in)	Positive (air out)
Intrapleural	Pleural space	Slightly negative	Slightly negative

2.2 Airway Resistance & Compliance

• Resistance changes with airway radius (narrow = hard), volume, and flow speed.

• Compliance = stretchiness

  • Low (stiff): fibrosis, edema, ARDS → hard to inflate

  • High (floppy/over-stretch): emphysema → easy in, hard out (air trapping)

Memory aid — M.E.C.H.: Mechanics (pressures) • Elasticity (compliance) • Caliber (resistance) • Humidity (airways like moisture)

2.3 Gravity & Perfusion

• Upright: more blood to the lung bases, less to the apices (use positioning to your advantage).

3) Oxygen Transport in Blood 🚚

3.1 Hemoglobin = the O₂ taxi

• 1 hemoglobin binds 4 O₂; each RBC carries a huge O₂ load when saturated.

3.2 Oxyhemoglobin Curve (how PaO₂ maps to sat)

Zone	Rough PaO₂	What it means	Nursing action
Plateau	> ~70 mmHg	Sat stays high & stable	Monitor; don’t overtreat
Steep	< ~40 mmHg	Small PaO₂ drop → big sat fall	Act fast; escalate support

Right shift (lets go of O₂ in tissues): ↑CO₂, ↑H⁺ (↓pH), ↑Temperature, ↑2,3-DPGMemory aid — R.I.G.H.T.: Raised CO₂ • Increased H⁺ • Greater Temp • High 2,3-DPG → Tissues get O₂

4) V/Q Matching 🔄 (getting air & blood to the same place)

State	What’s wrong	Classic clues	First nursing moves
Normal	Air & blood match	Stable sat	Routine care
Low V/Q (shunt)	Blood arrives, air doesn’t	Crackles, dependent changes, mucus	Sit up, IS/C&DB, airway clearance; consider CPAP/PEEP per orders
High V/Q (dead space)	Air arrives, blood doesn’t	Sudden dyspnea, clear lungs, PE risk	Support circulation, evaluate for PE, notify provider
Silent unit	Neither air nor blood	Severe distress/asymmetry	Urgent correction (e.g., pneumothorax protocol)

👉 Big shunt (>~20%) → severe hypoxia: O₂ alone won’t fix it; treat the cause.

Memory aid — M.A.T.C.H.: Move/position • Airway clear • Titrate O₂ • Circulation support • Hunt the cause

5) Numbers That Help 🔢

• Trachea: fully humidified; water vapor pressure = 47 mmHg

• Typical alveolar mix: O₂ ~104 mmHg, CO₂ ~40 mmHg (N₂ dominates the rest)

• Dissolved O₂ rises with PaO₂: e.g., PaO₂ 10 → ~0.03 mL O₂/100 mL plasma; PaO₂ 100 → ~10× that

• Pulmonary circulation: low-pressure system; ~2% physiologic shunt is normal

6) Bedside Assessment Flow 🧑‍⚕️

6.1 Look–Listen–Feel (then measure)

• Look: work of breathing, posture, color, mentation

• Listen: two full breaths per spot; compare sides

• Feel/Check: expansion symmetry, cough strength

• Add percussion & diaphragmatic excursion if skills-checked off

6.2 Monitors & Tests

• SpO₂: clip estimate of how full Hb is with O₂

• ABG (PaO₂/PaCO₂): arterial gas pressures; show how lungs load O₂ & clear CO₂

• ETCO₂: CO₂ at end-exhalation (capnography); mirrors ventilation

Memory aid — O₂-CHAIN: Air → Mechanics → Membrane → Hemoglobin → Flow → Tissues

7) Oxygen Therapy Basics 💨

7.1 Devices (typical ranges)

Device	Flow guide	Typical FiO₂	Notes
Nasal cannula	1–6 L/min	~24–44%	Comfortable; humidify ≥4 L
Simple mask	6–10 L/min	~35–55%	Prevent CO₂ rebreathing (≥6 L)
Venturi mask	As labeled	~24–60%	Precise FiO₂ (colored adapters)
Non-rebreather (NRB)	10–15 L/min	~60–90%	Reservoir must stay inflated
HFNC	Up to ~60 L/min	21–100%	Heated humidified; ↓WOB
CPAP	Set by provider	N/A	Positive pressure keeps alveoli open

7.2 Principles

• Target & check: choose device to meet your unit’s target; reassess SpO₂/ABG/ETCO₂ + symptoms

• Humidify when appropriate (comfort & mucosa)

• Titrate thoughtfully in likely CO₂ retainers (use your target range)

Memory aid — T.I.D.E.: Titrate to target • Identify cause • Device fit/humidify • Evaluate response

8) Common Patterns & First Moves 🧩

Pattern	You might see	Do first
Hypoventilation	High CO₂, sleepy, shallow	Sit up, stimulate/coach, check meds
Diffusion impairment	Crackles, edema, ↑O₂ need	Elevate HOB, lung expansion, follow orders for fluid/infection
Shunt (low V/Q)	Dependent atelectasis/mucus	IS/C&DB, airway clearance, consider CPAP/PEEP per orders
Dead space (high V/Q)	Sudden dyspnea, clear lungs	Support circulation, assess for PE, notify

9) Patient Education 🗣️

• Numbers: “This clip shows how full your blood is with oxygen (SpO₂). Our goal is X–Y%.”

• IS & coughing: “Sit up, slow deep breath to the marker, hold 3–5 s, exhale. Do ~10 breaths each hour you’re awake.”

• Positioning: “Upright helps air reach the best-perfused parts of your lungs.”

• Call for help if: new restlessness, fast breathing, chest pain, bluish lips/fingers.

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10) Documentation & Handoff 🗎

• Device & FiO₂, flow setting, SpO₂ before/after, breath sounds, WOB

• Any ABG/ETCO₂, patient tolerance, interventions, response, plan

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Quick Checks (Retrieval) 🧠✅

1. Define Ventilation, Diffusion, Perfusion in one line each.

2. Give two examples of low compliance conditions.

3. What are typical alveolar partial pressures for O₂ and CO₂?

4. Which V/Q pattern fits mucus plug vs pulmonary embolus? First move for each?

5. On the Hb curve, why is PaO₂ <40 mmHg dangerous?

Answer Key:

1. V = air movement; D = gases crossing alveoli–blood; P = blood flow to exchange gases.

2. Fibrosis, edema/ARDS (stiff lungs).

3. O₂ ~104 mmHg; CO₂ ~40 mmHg (typical).

4. Mucus plug = low V/Q (shunt) → recruit/clear; PE = high V/Q (dead space) → support & evaluate.

5. It’s the steep part—small PaO₂ drops cause big saturation falls.

NGN-Style Mini-Item 🧩

Scenario: Patient on room air becomes restless, SpO₂ 88%, RR 28. Left lung clear; right base has coarse crackles. Which actions require immediate follow-up?

• ☐ Sit the patient up (head of bed ↑)

• ☐ Encourage IS and coughing with splinting

• ☐ Increase O₂ to target without other actions

• ☐ Suction/airway clearance if secretions present

• ☐ Evaluate for pulmonary embolism first

• ☐ Reassess after position/airway maneuvers; consider ABG if unresolved

Correct: ✅ Sit up • ✅ IS/cough • ✅ Suction/clear if secretions • ✅ Reassess/consider ABG

Why: Pattern suggests low V/Q (shunt) at the right base (dependent crackles). Position + recruitment/clearance come first; then titrate O₂ and reassess. Evaluate for PE when presentation suggests dead space (sudden dyspnea with clear lungs).

Glossary 📗

SpO₂ — clip estimate of hemoglobin saturation • PaO₂/PaCO₂ — arterial O₂/CO₂ pressures (ABG) • ETCO₂ — end-tidal CO₂ (ventilation) • FiO₂ — percent of inspired O₂ (room air ≈ 21%) • Compliance — lung/chest stretchiness • Diffusion — gas across alveoli–capillary membrane • Perfusion — blood flow through lung capillaries • V/Q — matching air to blood • Shunt/Dead space/Silent unit — air blocked/blood blocked/both absent • Plateau vs Steep — safe vs risky zones of the oxyhemoglobin curve

Closing Practice Pearls ✨

• Trends beat snapshots. A drifting SpO₂ or rising WOB is louder than a single value.

• Behavior changes early. Restlessness often flags oxygen debt before numbers crash.

• Position is therapy. Upright improves V/Q.

• Pain control unlocks breathing. Patients ventilate better when pain is treated.

• Your presence is a safety device. Verify often; speak up every time.