Question 1

Which of the following medications contributes to an increased right-to-left intrapulmonary shunting?

Accepted Answer

The intravenous vasodilators nitroprusside and prostacyclin will relax pulmonary vasculature globally,reducing pulmonary vascular resistance,but will also increase pulmonary blood flow past nonfunctioning alveoli and intrapulmonary right-to-left shunt.

Question 2

The respiratory therapist has initiated nitric oxide for an infant with severe refractory hypoxemia.The initial dose was 20 ppm and titrated up to 30 ppm for the last 4 hours due to lack of response.However,there still is no response.What should the therapist do?

Accepted Answer

Studies have suggested that optimal dosing is usually in the 20- to 30-ppm range.Some infants will not respond positively.The Neonatal Inhaled Nitric Oxide Study (NINOS)trial indicated that only 6% of nonresponders will demonstrate a positive response when given NO at 80 ppm.Typically,a response would be seen almost immediately;however,it is recommended that the time allotted for determining an infant's response last no longer than 4 hours to limit the exposure to NO.

Question 3

The therapist taking care of an infant on iNO observes that the NO₂ levels have been increasing.In order to correct the situation he increases the inspiratory flow of the ventilator.What will be some of the limitations associated with this change?
I.It reduces time of contact between NO and O₂.
II.It affects the mean airway pressure because it changes the inspiratory time.
III.It may increase the delivered tidal volume.
IV.It reduces the mean airway pressure and increases the inspiratory time.

Accepted Answer

Decreasing the NO or oxygen concentration is usually not an option;therefore,to reduce NO₂ delivery to the patient,reduce the duration of contact between NO and oxygen.Two methods accomplish this: (1)increase the inspiratory flow or (2)add the NO as close to the patient as possible.Each of these methods has practical limitations.Increasing the ventilator flow will reduce the time of contact between NO and oxygen before reaching the patient,but it may also affect inspiratory time,tidal volume,mean airway pressure,and so on.

Question 4

Although very small amounts of NO₂ are present at the bedside,which health care workers need to exert special precautions to minimize exposure to NO₂?

Accepted Answer

At first,scavenging was advocated to reduce the possible harmful inhalation of nitrogen dioxide by other personnel in the vicinity.Studies have shown this to be unnecessary because of the relatively small amounts of NO₂ present at the bedside.Modern hospitals have adequate room air exchange rates,and the chance of NO or NO₂ accumulation is remote.A possible caveat involves interfacility transport.Pressurized aircraft may not allow an adequate cabin air exchange rate to ensure safety.The aircraft crew must be made aware of this so that proper measures are taken to reduce this risk.

Question 5

During the administration of aerosol therapy,how does a heliox mixture compare with an air-oxygen mixture as a carrier gas?

Accepted Answer

Patients who use the helium-oxygen mixtures show more improvement in expiratory peak flows than a group using air.Aerosol has deeper and prolonged deposition in the lung when it is delivered with heliox as the carrier gas.

Question 6

The therapist is treating a very irritable young child with upper airway obstruction.Which oxygen device will be the most appropriate to administer the greatest concentration of helium?

Accepted Answer

Spontaneously breathing patients with upper or lower airway obstruction can be given heliox via mask.Because the goal of heliox therapy is to reduce the density of the inspired gas,it is important to deliver the greatest concentration of helium.Therefore,the patient must be able to tolerate the lowest possible fractional concentration of inspired oxygen (FiO₂),and room air entrainment must be minimized,resulting in a higher fractional concentration of inspired helium (FiHe).Nasal cannulas (with the exception of high flow nasal cannulas)and simple masks allow far too much room air entrainment,thereby diluting the helium concentration.Therefore,a close-fitting nonrebreathing mask should be used.This limitation makes the treatment of young patients difficult.Children in distress may not tolerate the tightly fitting mask required to minimize air entrainment.

Question 7

After increasing the inspiratory flow of the ventilator to decrease the generation of NO₂ the therapist notices many changes in the ventilator parameters.The therapist adds the NO into the inspiratory limb of the ventilator circuit close to the patient.What will be a limitation of the procedure?

Accepted Answer

Adding NO into the inspiratory limb of the ventilator circuit close to the patient will reduce contact time,but it also creates monitoring difficulties.The practitioner must allow an adequate distance for proper mixing to ensure accurate NO measurement.

Question 8

Which of the following parameters of mechanical ventilation are affected negatively by the use of heliox?

Accepted Answer

The primary obstacle to heliox delivery via a mechanical ventilator is error in volume and flow measurement.Many mechanical ventilators rely on gas density to measure flows and volumes.Most errors result from underestimation of flow due to the low-density characteristics of helium.Volume is typically a mathematical integration of flow and time;therefore,volumes will be equally affected.

Question 9

What is the purpose of administering helium-oxygen gas mixtures to patients?

Accepted Answer

It is important to note that helium is not used to treat the underlying cause of increased airway resistance but rather to decrease the work of breathing until more definitive therapies are effective.When helium is combined with oxygen,the resulting gas mixture density is one third that of air.

Question 10

The respiratory therapist has initiated iNO at 20 ppm for an infant with pulmonary hypertension.After 2 hours a blood gas test reveals a 10% improvement in SaO₂.What should the therapist do?

Accepted Answer

Several studies have used an increase in oxygen saturation of 20% over baseline as an indication that the infant is responsive.

Question 11

Vascular smooth muscle is largely dependent on which of the following
Intracellular ions?

Accepted Answer

Current understanding suggests that vascular smooth muscle is largely dependent on intracellular calcium ion (Ca²⁺)concentration.Smooth muscle tissue comprises bundles of myofibrils,threadlike contractile fibers encased by the sarcoplasmic reticulum,a network of tubes or channels that store Ca²⁺.

Question 12

The therapist is evaluating a small tachypneic infant receiving heliox mixture 70:30 through an infant hood.Although the SpO₂ has improved,the child shows signs of worsening work of breathing.What is the most probable mechanism to explain this situation?

Accepted Answer

Stillwell and colleagues investigated the use of heliox mixtures delivered through an infant hood.Not surprisingly,they found a greater concentration of helium at the top of the hood (due to its lower gas density),away from the infant's nose and mouth.This resulted in a lower FiHe and therefore a denser gas being delivered to the infant.

Question 13

What is the potential benefit of adding heliox to patients who have status asthmaticus while undergoing mechanical ventilation?

Accepted Answer

The use of heliox mixtures has been advocated to minimize air trapping and hemodynamic compromise and to reduce peak inspiratory pressures.

Question 14

The therapist is using an oxygen flowmeter to deliver an 80:20 heliox mixture to a patient.The reading on the flowmeter is 10 L/minute.What is the actual flow received by the patient?

Accepted Answer

An 80:20 heliox mixture is 1.8 times more diffusible than oxygen.To correct for the difference in gas density,the indicated flow on the flowmeter is multiplied by 1.8.A 70:30 heliox mixture is 1.6 times more diffusible than oxygen.To obtain the accurate flow rate for this mixture,the indicated flow is multiplied by 1.6.

Question 15

What is the primary physiologic activity of inhaled nitric oxide?

Accepted Answer

The underlying principle of inhaled nitric oxide (iNO)is its selectivity as a pulmonary vasodilator.Inhaled NO will relax only pulmonary smooth muscle adjacent to functioning alveoli.Atelectatic or fluid-filled lung units will not participate in iNO uptake.

Question 16

An infant has been receiving iNO for the last 3 days.Which important level should be monitored when ordering a co-oximetry?

Accepted Answer

The half-life of iNO is extremely short,about 5 seconds.Once NO crosses the vascular endothelium,it is rapidly bound by hemoglobin,forming nitrosyl hemoglobin (methemoglobin).Methemoglobin production results from the oxidation of the iron in the hemoglobin.The quantity of methemoglobin depends on iNO concentration and concurrent nitrate-based drug therapy (e.g. ,nitroprusside,nitroglycerin).If the methemoglobin level is excessive,a reduction in iNO or other nitro-based vasodilators is warranted.

Question 17

Which of the following substances prevents the release of Ca²⁺ from the sarcoplasmic reticulum?

Accepted Answer

In the body,the process of smooth muscle relaxation uses cyclic guanosine monophosphate (cGMP)to reduce Ca²⁺ levels.In smooth muscle cells cGMP activates cGMP-dependent kinase,preventing the release of Ca²⁺ from the sarcoplasmic reticulum,resulting in smooth muscle relaxation.In the early 1980s researchers reported a potent smooth muscle-relaxing agent,endothelium-derived relaxing factor (EDRF),now understood to be endogenous nitric oxide.

Question 18

An infant on high-flow nasal cannula also requires administration of albuterol every 6 hours.The flow of the cannula was adjusted from 4 to 5 liters per minute.How could this affect the aerosol delivery to this infant?

Accepted Answer

Heliox has been shown to reduce turbulence and improve aerosol delivery in a range of clinical settings.Ari and colleagues assessed the effects of heliox on medication delivery by comparing with 100% oxygen while testing the infant,pediatric cannulas running at flows of 3 and 6 Lpm,and adult cannulas running at 10 and 30 Lpm.At higher flows they found that heliox increased aerosol deposition compared to oxygen.At lower flows there was less benefit from the use of heliox compared to oxygen in the pediatric and adult cannulas and no benefit for the infant.

Question 19

What is the product of the reaction between oxygen and nitric oxide?

Accepted Answer

When combined with oxygen,NO produces NO₂,a toxic gas.Although rare,the patient as well as health care providers can be adversely affected.Factors influencing NO₂ production are oxygen concentration,NO concentration,and time of contact between NO and oxygen.

Question 20

Inhaled NO has been administered to an infant for nearly 4 hours.The respiratory therapist notices suboptimal response and suggests HFOV.What is the principle behind the potential benefit of adding this ventilatory modality to this infant?

Accepted Answer

If lung volume is optimized with HFOV,this could further enhance the effects of iNO.The use of HFOV improves oxygenation response to iNO.

Quiz 18: Administration of Gas Mixtures