Medical Gases & Oxygen Therapy – Part 2 (RC121)

57 vocabulary flashcards summarizing key terms, devices, hazards, calculations, and monitoring concepts from the lecture on Medical Gases and Oxygen Therapy.

Oxygen Therapy

Administration of supplemental oxygen to correct or prevent hypoxemia and reduce work of the heart and breathing.

Hypoxemia

Abnormally low arterial oxygen tension (PaO₂) leading to tissue oxygen deficiency.

Goals of Oxygen Therapy

Correct hypoxemia, decrease work of the heart, decrease work of breathing.

Indications for Oxygen Therapy

Documented or suspected hypoxemia, specific conditions (post-op, CO poisoning, shock, trauma, AMI, some premature infants).

Laboratory Measures of Oxygenation

SpO₂ (pulse oximetry), SaO₂ (arterial saturation), PaO₂ (ABG – most accurate).

Clinical Manifestations of Hypoxia

Tachypnea, tachycardia, cyanosis, distress appearance.

Tachycardia

First cardiovascular sign of hypoxia; elevated heart rate.

Oxygen Toxicity

Cellular injury caused by high FiO₂ and/or prolonged exposure; mainly affects lungs and CNS.

Factors Affecting Oxygen Toxicity

Inspired oxygen fraction (FiO₂) and exposure time.

Symptoms of Oxygen Toxicity

Substernal pain, uncontrollable cough, dyspnea, anxiety, numbness.

Pulmonary Effects of O₂ Toxicity

Pulmonary edema, alveolar wall damage, hyaline membrane formation, fibrosis, decreased vital capacity, O₂-induced pneumonia.

Vicious Circle of High FiO₂

High FiO₂ → lung toxicity → ↑ shunting → ↓ PaO₂ → need for even higher FiO₂.

Rule of Thumb for High FiO₂

Limit 100 % O₂ to <24 h; lower to ≤70 % within 2 days and ≤50 % within 5 days.

O₂-Induced Hypoventilation

Depression of ventilation in COPD when high PaO₂ suppresses hypoxic drive, raising PaCO₂.

Hypoxic Drive

Ventilatory stimulus from peripheral chemoreceptors sensing low PaO₂ when hypercapnic drive is blunted.

Retinopathy of Prematurity (ROP)

Retinal vasoconstriction and vessel necrosis in premature infants exposed to high PaO₂ (>80 mmHg).

Absorption Atelectasis

Alveolar collapse from nitrogen washout when FiO₂ ≥50 %, especially with low tidal volumes.

Low-Flow Oxygen System

Device supplying O₂ that mixes with room air; variable FiO₂ (24–44 %).

Anatomic Reservoir

50 mL of O₂ temporarily stored in naso-/oropharynx during low-flow therapy.

Nasal Cannula

Two-prong device; ¼–6 L min⁻¹; FiO₂ ≈24–44 %; easy, low cost, prone to dislodgement/dryness.

Nasal Cannula FiO₂ Rule

Approx. FiO₂ = 24 % at 1 L min⁻¹, +4 % for each additional L min⁻¹ up to 6 L min⁻¹.

Transtracheal Oxygen Catheter

Catheter in trachea; ¼–4 L min⁻¹; FiO₂ 22–35 %; lower O₂ use, improved mobility; surgical placement required.

Reservoir Oxygen System

Device that stores O₂ between breaths; variable FiO₂ 24–100 %.

Simple Mask

Mask reservoir; 5–10 L min⁻¹ (≥5 to flush CO₂); FiO₂ 35–55 %.

Partial Rebreather Mask

Mask with reservoir bag; 10–15 L min⁻¹; permits rebreathing first 1/3 exhaled gas; FiO₂ 60–80 %.

Nonrebreather Mask (NRB)

Mask with one-way valves; 10–15 L min⁻¹; FiO₂ 80–100 %.

High-Flow Oxygen System

Device providing flow ≥ patient inspiratory demand (≥40 L min⁻¹); fixed FiO₂.

Fixed-Performance Device

High-flow apparatus delivering stable, precise FiO₂ regardless of breathing pattern.

Air-Entrainment (Venti) Mask

High-velocity jet entrains air through ports; FiO₂ 24–50 % precise; flow varies.

Air Entrainment Mechanism

Shear forces at jet orifice draw room air into O₂ stream, diluting O₂ and boosting total flow.

Blending System

Mixes pressurized air and O₂ with blender; delivers precise FiO₂ and high flow to aerosol device.

Tandem (Manual) Setup

Two flowmeters joined via Y-connector to create ≥40 L min⁻¹ high-flow mixture.

High-Flow Nasal Cannula (HFNC)

Heated, humidified O₂ up to 60 L min⁻¹ with precise FiO₂; flushes upper airway, offers mild PEEP.

HFNC Benefits

Meets inspiratory demand, increases FRC, washes out dead space, better tolerated than CPAP/BiPAP.

Isolette (Incubator)

Servo-controlled heated enclosure for infants; 8–15 L min⁻¹; variable FiO₂; provides thermal regulation.

Oxyhood

Head enclosure; flow ≥7 L min⁻¹; FiO₂ 21–100 %; fixed performance; allows infant body access.

Oxygen Tent

Plastic canopy for children; 12–15 L min⁻¹; FiO₂ 40–50 %; provides humidity; prone to leaks.

Molecular Sieve Concentrator

Home device using Zeolite pellets to remove N₂, delivering >90 % O₂.

Membrane Concentrator

Vacuum draws air through semipermeable membrane; supplies ≈40 % O₂ for home use.

Hyperbaric Oxygen Therapy (HBO)

Breathing O₂ at >1 ATA (usually 2–3 ATA) in monoplace or multiplace chamber.

Monoplace Chamber

Transparent cylinder enclosing one patient at 100 % O₂ under pressure.

Multiplace Chamber

Large tank for several occupants; only patient may breathe O₂ via mask/hood.

Physiological Effects of HBO

Bubble reduction, hyperoxygenation, vasoconstriction (↓edema), immune enhancement, neovascularization.

Indications for HBO

Decompression sickness, air embolism, CO or cyanide poisoning, gangrene, problem wounds, etc.

Complications of HBO

Barotrauma, oxygen toxicity, gas embolism, fire, visual changes, claustrophobia, ↓ cardiac output.

Oxygen Analyzer

Device that verifies and adjusts delivered FiO₂; placed close to patient.

Physical/Paramagnetic Analyzer

Measures attraction of O₂ to magnetic field; works with any gas; intermittent use only.

Electric (Thermal Conductivity) Analyzer

Compares cooling of heated wires by sample vs. room air; cannot be used with flammable gases.

Polarographic Analyzer

Electrochemical sensor using battery-driven reaction; provides continuous monitoring.

Galvanic Fuel Cell Analyzer

Battery-free electrochemical sensor generating current from O₂ reduction; continuous monitoring.

Two-Point Calibration

Quality control: calibrate analyzer to 21 % (room air) and 100 % O₂, then re-check 21 %.

Pulse Oximetry (SpO₂)

Non-invasive continuous estimate of Hb saturation using spectrophotometry and plethysmography.

Spectrophotometry

Technique measuring light absorption at two wavelengths to determine Hb saturation.

Plethysmography

Detection of arterial pulse waveform amplitude to isolate arterial blood signal.

Sources of Error in Pulse Oximetry

Sensor misalignment, ambient light, low perfusion, motion, dark skin, nail polish, COHb/MetHb.

FiO₂ Mixing Formula

FiO₂ = [(air flow × 0.21) + (O₂ flow × 1.0)] ÷ total flow.

Air/O₂ Entrainment Ratio

Liters air : O₂ = (100 – FiO₂)/(FiO₂ – 21); e.g., 30 % → 8 : 1.

Total Flow Calculation

Add parts of air/O₂ ratio, multiply by set O₂ flow; must be ≥40 L min⁻¹ for high-flow needs.