Fundamentals Exam 2: Medical Gases, Cylinders & Humidity

dry room air components

78% nitrogen, 21% oxygen, 1% trace gases

oxygen flammability

nonflammable, but supports combustion

Three characteristics of oxygen

Colorless, odorless, nonflammable oxidizer

Clinical role of heliox

lower gas density may reduce turbulent flow resistance

used for airway obstruction

Two common heliox mixes

80% He/20% O₂

70% He/30% O₂

80/20 heliox correction factor

1.8 on O₂ calibrated flowmeter

70/30 heliox correction factor

1.6 on O₂ calibrated flowmeter

What device would you use to give heliox to a non-intubated patient?

non-rebreather

Action of inhaled nitric oxide

selective pulmonary vasodilation, doesn't recruit new alveoli but makes what is already working work overtime

Two nitric oxide toxicities to monitor

NO₂ formation and methemoglobinemia

Medical use of nitrous oxide

Anesthetic / analgesic agent

CO₂ purpose in gas analysis

calibration and laboratory diagnostic mixtures

atmospheric role of N₂

78% of room air

How does fractional distillation separate gases?

Different boiling points after liquefying air

PSA

Pressure swing adsorption, creates medical grade O₂ from room air

PSA removes ______ from air

Nitrogen, via molecular sieve

Typical PSA oxygen purity

above 90%; varies by concentrator

bulk medical oxygen purity

approx 99%

oxygen cylinder color

green

room air cylinder color

yellow

nitrous oxide cylinder color

teal and black

nitric oxide cylinder color

navy blue

helium cylinder color

brown

carbon dioxide cylinder color

gray

nitrogen cylinder color

black

What does PISS stand for?

Pin Index Safety System

Oxygen pin positions in PISS?

2 and 5

PISS

pin-index system

Small portable cylinders (E tanks)

ASSS

gas specific threaded connections

Large high-pressure cylinders (H and K tanks)

DISS

Gas-specific diameter/bore connections

wall outlets and equipment

hospital medical gas pressure

50 psig from wall

gravity dependent flowmeter

Thorpe tube, variable orifice

non gravity dependent flowmeter

Bourdon gauge, fixed-orifice

Bourdon gauge backpressure hazard

Kinks may make flow indication falsely high

pressure-reducing valve function

reduce cylinder pressure to safe working pressure

zone valve function

Isolate part of hospital medical gas pipeline

Safety priority before closing a zone valve

secure independent gas support for patients

DOT-3AA cylinder material

Steel; magnetic

DOT-3AL cylinder material

Aluminum alloy; not magnetic

star stamp means _______

approved for 10-year retest interval

plus stamp means _______

can be filled up to 10% over its service pressure

D cylinder conversion factor

0.16 L/psig

E cylinder conversion factor

0.28 L/psig

H cylinder conversion factor

3.14 L/psig

compressed cylinder duration formula

[(start − end psig) × factor] / flow.

typical cylinder reserve

200 psig

1 L liquid O₂. = _______ gas O₂

860 L

1 L liquid O₂ weight

2.5 lbs

1 lb liquid O₂ = __________ gas O₂

344 L

liquid O₂ duration formula (in lbs)

(lb × 344 L/lb) / flow

absolute humidity

actual water vapor mass per volume of air (mg/L)

relative humidity formula

Actual AH / max AH at same temp × 100

BTPS

body temperature, ambient pressure, saturated

saturated gas humidity at 37°C

44 mg/L at 100% RH

isothermic saturation boundary

when inspired gas reaches 37°C and 100% RH

_______ can shift ISB further distally

Cold/dry air or bypassed upper airway

inspissated secretions

dried, thickened mucus

harmful effects of underhumidification

Poor ciliary clearance and mucus plugging

HME means

Heat and moisture exchanger

Is an HME passive or active?

passive, uses exhaled heat and moisture

HME moisture output

about 20-30 mg/L

HME mechanical dead space

approx 30-90 mL

HME contraindication indicators

Copious secretions and large tidal-volume leak

HME concern with very low VT

extra dead space can reduce alveolar ventilation

Heated passover moisture source

External water, heat, and vapor evaporation

Heated passover maximal output

44 mg/L at 37°C

bubble humidifier primary use

comfort when using low-flow oxygen systems

unheated bubble humidifier output

15-20 mg/L.

Purpose of bubble humidifier pop-off valve

pressure relief for downstream obstruction

wick humidifier

humidifier that uses capillary action

rainout

condensation inside humidified breathing circuit

Main danger of pooled circuit condensate

Accidental airway lavage and contamination

Humidifier vs nebulizer

a humidifier has vapor molecules and a nebulizer has suspended aerosol droplets

need for humidification with an ETT

ETT bypasses normal upper-airway conditioning

Aerosol

Solid/liquid particles suspended in gas

MMAD

Mass median aerodynamic diameter

MMAD divides

Half aerosol mass above, half below diameter

Where do ≥10 micron particles deposit?

mainly nose, mouth, upper airway

Where do 5-10 micron particles deposit?

upper and larger conducting airways

Where do 2-5 micron particles deposti?

lower airways (bronchioles)

inertial impaction

deposition of particles by collision, happens when larger/ heavier particles reach a bend

Sedimentation

gravity-driven particle settling

Brownian diffusion matters for ______

Extremely small particles

inhalation breath hold

10 second breath hold, gives time for sedimentation/deposition

pMDI inspiration pattern

Slow, deep inhalation with actuation coordinated

DPI inspiration pattern

Quick, forceful, deep inhalation

VHC means

valved holding chamber

VHC benefits

easier coordination, less throat deposition

after an inhaled corticosteroid you have to _______

Rinse mouth and spit

residual volume

amount of drug remaining in nebulizer after treatment

SVN infection-control

correct cleaning/disinfection and sterile fluids

aerosol-induced bronchospasm indicators

Increasing wheeze, distress, or airflow obstruction

clinical measures of bronchodilator response

Symptoms, breath sounds, WOB, peak flow/FEV₁

most important thing to assess with pMDI

technique and device function.