Speciatly Gases

Question 1

Nitric Oxide Properties

Answer 1

• Colorless gas at room temperature
• Non-flammable but supports combustion
• A free radical with a half life of 3-5 sec
• Highly diffusible and lipid soluble

Question 2

NO effects in the body

Answer 2

• Will be produce endogenously in vascular endothelial cells
• Is important mediator of physiologic functions
  
  • Vasodilation
  • Neurotransmission
  • Long term memory
  • immunologic defense

Question 3

Effects of NO

Answer 3

• When inhaled in small concentration NO is a potent pulmonary vasodilator
  
  • Considered to be a selective pulmonary vasodilator as it only affects ventilated alveoli
  • Thus NO increases blood flow only to ventilated alveoli by relaxing the smooth muscle of the capillaries supplying these alveoli
  • This vasodilation results in a decrease PVR, so that we can get a decrease PVR without a decrease SVR

Question 4

Pulmonary Vasodilation of NO

Answer 4

• The pulmonary vasodilation results in
  
  • Decreased intrapulmonary shunting
  • Improved oxygenation
  • Decreased PVR
  • Decreased pulmonary artery pressure
• The effects are limited to the pulmonary circulation because after diffusing into the capillaries NO immediately binds to hemoglobin
• This forms nitrosylhemoglobin which is rapidly oxidized to methemoglobin (metHb)

Question 5

NO Potential Uses

Answer 5

ARDS

Pulmonary Hypertension

Heart Transplantation

Acute pulmonary embolism

COPD

Bronchodilation

Congenital diaphragmatic hernia

Congenital heart disease

Testing pulmonary vascular responsiveness

Question 6

Most Common Uses of NO

Answer 6

• Pulmonary Vasodilation
  
  • PPHN
  • Congenital heart defects
  • ARDS
• For Bronchodilation
  
  • Usually to reverse methacholine or histamine induced bronchoconstriction

NO is primarily used for its selective pulmonary vasodilatory effects

Question 7

NO Dosing

Answer 7

• Therapeutic dose range 2-80 ppm (Neo – 20 ppm)
• Beneficial effects appear to peak at about 10 ppm in adult ARDS patients

Question 8

Calgary Health Region Adult NO Dose

Answer 8

• Start at 10 ppm and do an ABG 5 min after initiation
• If no response (PaO2 increases <10 mmHg, SpO2 increases <2% or MPAP does not decrease by at least 5 mmHg) then increase to 20 ppm
• If still no response:
  
  • For ARDS—discontinue NO (treatment failure!)
  • For pulm. HTN—increase to 40 ppm and assess response

Question 9

Optimizing NO

Answer 9

• Wean NO by 2-4 pm Q5min while monitoring SpO2 and mean PAP
• If SpO2 falls by >2% or mean PAP increase by >5 mmHg return to last effective dose

Question 10

NO Toxicity

Answer 10

• In high concentration (5000-20,000 ppm) NO causes acute pulmonary edema and can lead to death
• Lower concentrations are associated with direct cellular damage and impaired surfactant production

Question 11

NO by products

Answer 11

• Most toxic effects are due to its by-products:
  
  • NO2
  • Nitric Acid
  • Methemoglobin

Question 12

NO2 and Nitric Acid

Answer 12

• NO2
  
  • (Nitrogen dioxide) is produced when NO reacts with oxygen
  • Is a reddish-brown gas
  • More toxic than NO
• Nitric Acid
  
  • Forms when NO reacts with H2O

The higher the FiO2 the more NO2 formed!

Question 13

NO Can Cause

Answer 13

• Cell damage
• Chemical pneumonitis
• Hemorrhage
• Pulmonary edema
• Death

Question 14

Want to keep NO2 below

Answer 14

Clinically the goal is to keep NO2 < 2 ppm!

Question 15

Methemoglobin

Answer 15

• Any NO diffusing into the capillaries immediately binds to Hb resulting in metHb
• High levels of metHb reduce the oxygen carrying capacity of the blood
• Normal metHb is < 2%
• Methemoglobinemia is defined as metHb > 2%
  
  • In the CHR metHb levels are assessed at least Q12h.
  • Methemoglobinemia is not commonly seen at the therapeutic dose of NO
• Causes blood to appear rusty brown in colour
• MetHg >30% can be treated with methylene blue
• Oximetry readings may be erroneously high.

Question 16

Treatment of Methemoglobin

Answer 16

Normals and methemoglobinemia values: CBRC (Also says high levels < 35% usually well tolerated and not treated).

When MethBlue given then should see cyanosis resolved within the hour.

Question 17

Adverse Effects of NO

Answer 17

• Poor or paradoxical response
  
  • Some patients will experience worse hypoxemia
    
    • May be due to a worsening V/Q when no shunt was initially present
• Platelet inhibition
• Increased left ventricular filling pressures
• Rebound Effect
  
  • Seen during the withdrawal of NO therapy
  • May result in worse hypoxemia and pulmonary HTN then before therapy

Question 18

What will NO do to FiO2

Answer 18

• Adding NO will reduce the FiO2, the FiO2 must be analyzed distal to where NO is added

Question 19

NO Delivery for a Ventilated Patient

Answer 19

• Typically NO is administered in a ventilated patient
  
  • Must have an oxygen analyzer downstream from the T in point as NO will effect FiO2
  • An NO/NO2 analyzer must also be used

Question 20

NO Delivery for a Spontaneously breathing patient

Answer 20

• This is now being done using the INOvent delivery system!
• Not commonly done
• Simple circuit of corrugated tubing with NO, air and O2 blended to get desired FiO2 and ppm of NO
• Again, FiO2, NO and NO2 are analyzed prior to the patient

Question 21

NO Removal of Care Steps

Answer 21

• Care must be taken to prevent the rebound effect!
• Steps:
  
  • NO reduced to lowest effective dose
    
    • Ideally £ 5 ppm
  • Pt should be hemodynamically stable with adequate oxygenation on FiO2 £ 0.40 and low level PEEP
  • Pt should be hyperoxygenated (FiO2 0.60-0.70) just prior to discontinuation
  • Exception: if the patient was a non-responder.

Question 22

Flolan

Answer 22

• Epoprostenol sodium
• Naturally occurring metabolite of arachidonic acid
• It is a prostaglandin with several profound effects
  
  • Inhibits natural platelet aggregation
  • Reduces pulmonary hypertension (some systemic action as well)
• Low dose may cause some vagally mediated bradycardia but at higher doses may cause a rebound tachycardia
• May be referred to as a prostacyclin in some literature

Question 23

Heliox

Answer 23

• Helium is light
  
  • Viscosity is higher than air
  • Hydrogen only gas that is lighter
• Odorless, tasteless, non-flammable
• Low density gas used to decrease the WOB!

Question 24

Heliox Combinations

Answer 24

• Must be combined with oxygen
  
  • Common mixtures
  • 20% O2, 80% helium
  • 30% O2, 70% helium

Question 25

Upper and Lower Airway Flow

Answer 25

• Upper airway
  
  • Turbulent flow in large airways is affected more by gas density than viscosity
  • Breathing a low density gas improves flow through these airways
• Lower airways?
  
  • Have laminar flow, flow affected more by viscosity than density

Question 26

Clinical indications for Heliox

Answer 26

• Upper airway obstruction
  
  • Airway Tumor
  • Post extubation stridor
  • Pediatric airway obstructions
• Lower airway
  
  • Severe COPD/Asthma
  • Combined with NIPPV and/or mech vent
  • Evidence is not clear, but promising.

Question 27

Heliox Delivery Mechanism

Answer 27

• If using Heliox mixture (20%O2/80%Helium)
  
  • Use tight fitting NRM
• If using separate oxygen/helium tanks
  
  • Must monitor FIO2
  • Ensure adequate FiO2 delivered to patient
• For aerosol delivery
  
  • Increase flow to ensure nebulizer power is adequate
  • May improve aerosol penetration
• Mech vents
  
  • May alter Vt measurement
  • Some vents now have Heliox option