Week 9- CPAP

Question 1

The act of respiration encompasses two distinct processes…

Answer 1

Oxygenation and Ventilation

• Both of these processes are dependent on gas moving in and out of the lungs
• Disease such as COPD and CHF result in the need for more work to be done in order to generate airflow or they impair the ability of the lungs to adequately oxygenate the blood and the ability to remove carbon dioxide

Question 2

Oxygenation

Answer 2

• Involves the movement of oxygen from the atmosphere to the alveoli and subsequent diffusion into the blood

Question 3

Ventilation

Answer 3

• Relates to the removal of CO2 from the alveoli after diffusion from the blood

Question 4

How does CPAP work?

Answer 4

• A tight-fitting mask controlled by a regular designed to provide a high flow of variable or fixed oxygen concentration
• The most important feature is a flow restriction device at the exhalation port of the mask, which works the same as Positive End Expiratory Pressure (PEEP)
• This places the patient’s airways under a constant level of pressure throughout the respiratory cycle, causing fluid and other obstructions to be “pushed” back where they belong

Question 5

CPAP provides the most benefits in 2 types of patients:

Answer 5

• those with acute exacerbations of either CHF or COPD

Question 6

What was done before CPAP?

Answer 6

• Prior to the advent of CPAP and alternative or rescue airways, ventilatory support was provided in the field by EMS providers using a bag mask or invasive intervention involving sedation, perhaps paralysis and intubation which led to mandatory intensive care admission

Question 7

How does it work?

Answer 7

• If one exhales against, smaller, dependent airways are “splinted” open at the end of expiration and small membranous bronchi and alveoli don’t collapse
• Keeping these structures open on exhalation allows the muscles that were working to keep them open to be recruited into inspiration
• When alveoli stay open, inspiratory effort does not have to be expended to re-inflate them
• This reduces inspiratory work, relieves respiratory muscle fatigue, and decreases work of breathing
• CPAP gets many patient with severe inspiratory muscle fatigue through their acute crisis without needing to be intubated

Question 8

Results of CPAP

Answer 8

• Increased pressure in the airways also allows for better distribution of gasses that leads to an increase in alveolar pressure and re-expansion of collapsed alveoli which reverses microatelectasis maintaining inspiratory and expiratory pressures above normal results in improved functional reserve capacity, better lung compliance and decreased airway resistance
• This allows a greater volume/ unit of pressure change and positively impacts the ventilation/ perfusion (VA/Q) ratio
• As alveoli stay open, gas exchange time can be doubled increasing oxygen and decreasing CO2 levels in the blood reduces hypoxia

Question 9

CHF and CPAP

Answer 9

• CPAP does not push edema fluid out of the lungs
• Pt’s with acute CHF have an imbalance in the CO of the right and left sides of the heart
• When the left ventricle becomes compromised the right ventricle continues to pump forward a normal volume of blood but the ventricle becomes unable to keep pace
• Fluid backs up into the lungs resulting in capillary leak and pulmonary edema
• With CPAP, the resultant positive intrathoracic pressure decrease venous return
• This reduces right-sided CO to a level that the left heart can equal or even exceed
• Fluid ceases to back up and will even begin to be reabsorbed as left ventricular CO improves
• Pulmonary edema ceases to worsen and may even diminish, often rapidly

Question 10

CPAP and CHF

Answer 10

• A final means by which CPAP benefits patients with acute CHF relates to the decrease in the WOB required by pt
  -CHF causes edematous, stiff, more elastic lungs and indices bronchospasm that increases airway resistance
• Patients with acute CHF need to preform substantially increased WOB. This means more and more CO being diverted to the respiratory muscles, further compromising peripheral perfusion and stressing the already failing heart
• CPAP assist the patient with a resultant decrease in the proportion of CO being sent to the respiratory muscles and improved peripheral perfusion

Question 11

CPAP and COPD

Answer 11

• CPAP overcomes inspiratory work
• CPAP prevents airway collapse during exhalation
• CPAP improves arterial blood gas values
• CPAP may avoid intubation and mechanical ventilation

Question 12

What are the complications of CPAP?

Answer 12

• Pulmonary pressure that are too high can cause a decrease in blood volume circulating through the lungs resulting in a decrease in cardiac output (fall in BP)
• High alveolar pressure can cause an over distension of the alveoli resulting in lung overdistention
• Overdistention of the lungs can reduce the ability of the lungs to move easily (decreased compliance)
• Positive pressure may increase secretions or dry upper airways
• Because a tight mask seal must be maintained, the patient may find it difficult to clear respiratory secretions

Question 13

CPAP Indications

Answer 13

• Severe respiratory distress; and
• S/S of acute pulmonary edema or COPD

Question 14

CPAP conditions

Answer 14

• Age >18 yrs
• LOA N/A
• HR N/A
• RR Tachypnea
• SBP Normotension (> or equal to 100mmHg)
• SPO2 <90% or accessory muscle use

Question 15

CPAP Contraindications

Answer 15

• Asthma exacerbation
• Suspected pneumo
• Unprotected or unstable airway
• Major trauma or burns to the head or torso
• Tracheostomy
• Inability to sit upright
• Unable to cooperate