Ward pt.2

Question 1

What is CPAP?

Answer 1

• A type of positive airway pressure that is used to deliver a set pressure (PEEP) to the airways that is maintained throughout the respiratory cycle, during both inspiration and expiration in people who are breathing spontaneously
• CPAP is a way of delivering PEEP but also maintains the set pressure throughout the respiratory cycle, during both inspiration and expiration
• A CPAP machine essentially delivers constant PEEP (normally adjusted between 5-12 cm H2O during sleep and is useful for at-home treatment of obstructive sleep apnea (OSA). By providing constant positive pressure to the airway, it splints open its upper and lower portions, preventing the collapse of tissues that may occur at or after exhalation

Question 2

What happens in the alveoli when you breath?

Answer 2

• As inspiration occurs (1) the alveoli expands to allow the air in. Gas exchange can then take place as the blood supply moves past the wall of the alveoli.
• During expiration the alveoli contracts down (2). It does not completely collapse, partly due to the presence of a substance called surfactant (3). This decreases the surface tension within the alveoli ensuring that complete collapse cannot take place

Question 3

What happens to alveoli when a patient is ventilated? How is this avoided?

Answer 3

• Unfortunately, ventilation of a patient tends to inactivate the pulmonary surfactant which then leads to collapse of the alveoli (4), making gas exchange more difficult as the surface area of the lung is now reduced.
• The ventilator also causes an increase in alveolar capillary permeability and causes the activation of inflammatory cells and the release of cytokines
• The consequence of this is that the alveoli are opening and collapsing much more than they would normally and will also be subject to higher pressures in order to reopen them with each breath. This combination will damage the alveoli further.
• Positive end expiratory pressure (PEEP), is a pressure applied by the ventilator at the end of each breath to ensure that the alveoli are not so prone to collapse. This ‘recruits’ the closed alveoli in the sick lung and improves oxygenation

Question 4

Benefits of PEEP

Answer 4

So PEEP:

Reduces trauma to the alveoli
Improves oxygenation by ‘recruiting’ otherwise closed alveoli, thereby increasing the surface area for gas exchange.
Increases the functional residual capacity- the reserve in the patients lungs between breaths which will also help improve oxygenation.
Ventilation/perfusion mismatches are improved.
Increases the compliance of the lung- compliance is the relationship between the change on volume and the change in pressure in the lung. With PEEP, less pressure is needed to get the same volume of air into the lung as the alveoli are already partially inflated and therefore do not need that high initial pressure to open them. (Remember the balloon analogy- hard to blow up initially, but then much easier to inflate after the initial breath).

Question 5

Problems with PEEP

Answer 5

• PEEP can cause some problems for those patients who have some airway obstruction i.e. Asthmatics and those with COPD
• The other problem PEEP can cause is a drop in cardiac output

Question 6

Problems of PEEP in airway obstruction

Answer 6

• If we look at the alveoli of a person with obstructive disease we can see the obstruction on the airway (3) and the ventilator is blowing air down into the alveoli (1).
• Once the ventilator has finished putting air into the lung, expiration is then a passive process, relying on the passive recoil of the chest wall and lung (2).
• But because the obstruction is there, this air takes longer to get out of the lung. The ventilator does not wait for the air to come out before it delivers the next breath. This means in the obstructed patient that not all the air will come out of the alveoli before the next breath comes in.
• The air that is left over will exert a pressure on the alveolar walls, helping to keep them open (4).
• As continued breaths come in the alveoli will become larger, so exerting more pressure on the internal walls of the alveoli (4). The increased force on the inside tends to then increase the recoil exerted by the lung tissue on the outside of the alveolar wall (5). This increased recoil will help push some more air out of the alveoli past the obstruction.
• This process will continue until a steady state is reached, where the amount of air coming in is equal to the amount of air coming out (6).
• This balancing of pressure, with the ventilators involvement, keeps the alveoli open and is referred to as Auto-PEEP and the lung volumes, which were higher than before, are referred to as Dynamic Hyperinflation.
• The phenomenon of not being able to get one breath out of the lung before the next breath comes in is known as Breath Stacking.

Question 7

How does PEEP affect cardiac output

Answer 7

• Venous return to the heart is very dependent on the difference in pressure between that in the thoracic cavity (Pt), where the heart is enclosed, and that in the circulatory system (Pet)
• VR = Pet – Pt
• PEEP will cause a rise in the intra thoracic pressure, meaning the difference between the two pressures will fall, causing a reduction in the venous return.
• The respiratory system in normal breathing is a negative pressure system. The drop in pressure in the thorax causes the air to move in. This drop in pressure also relieves some of the pressure on the right side of the heart allowing it to fill more easily.
• By applying PEEP we are reducing that drop in pressure. The consequence of this is that we also then affect the right side of the heart potentially reducing cardiac output.
• The increased pressure in the thoracic cavity also increases the pressure in the pulmonary system, meaning that the right side of the heart has higher pressures to push against to get the blood through the lungs.
• This in turn makes the right side become bigger, which then pushes against the left side of the heart which will then reduce cardiac output.

Question 8

Benefits of CPAP

Answer 8

The application of CPAP maintains PEEP, can decrease atelectasis (partial or complete collapse of a lung or part of a lung), increases the surface area of the alveolus, improves V/Q matching, and hence, improves oxygenation

Question 9

What is PEEP?

Answer 9

Positive end-expiratory pressure (PEEP) is the pressure in the alveoli above atmospheric pressure at the end of expiration

Question 10

Difference between CPAP and BPAP

Answer 10

CPAP differs from bilevel positive airway pressure (BiPAP) where the pressure delivered differs based on whether the patient is inhaling or exhaling. These pressures are known as inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP)

Question 11

Indications of CPAP

Answer 11

• Airway collapse can occur from various causes, and CPAP is used to maintain airway patency in many of these instances. Airway collapse is typically seen in adults and children who have breathing problems such as obstructive sleep apnea (OSA), which is a cessation or pause in breathing while asleep. OSA may arise from a variety of causes such as obesity, hypotonia, adenotonsillar hypertrophy, among others.[2]
• CPAP may be used in the neonatal intensive care unit (NICU) to treat preterm infants whose lungs have not yet fully developed and who may have respiratory distress syndrome from surfactant deficiency.[3][4] Physicians may also use CPAP to treat hypoxia and decrease the work of breathing in infants with acute infectious processes such as bronchiolitis and pneumonia or for those with collapsible airways such as in tracheomalacia.
• It is used in hypoxic respiratory failure associated with congestive heart failure in which it augments the cardiac output and improves V/Q matching.
• CPAP can aid oxygenation via PEEP prior to placement of an artificial airway during endotracheal intubation.
• It is used to successfully extubate patients that might still benefit from positive pressure but who may not need invasive ventilation, such as obese patients with obstructive sleep apnea (OSA) or patients with congestive heart failure.

Question 12

Contraindications of CPAP

Answer 12

• CPAP cannot be used in individuals who are not spontaneously breathing. Patients with poor respiratory drive need invasive ventilation or non-invasive ventilation with CPAP plus additional pressure support and a backup rate (BiPAP).

The following are relative contraindications for CPAP:
- Uncooperative or extremely anxious patient
- Reduced consciousness and inability to protect their airway
- Unstable cardiorespiratory status or respiratory arrest
- Trauma or burns involving the face
- Facial, esophageal, or gastric surgery
- Air leak syndrome (pneumothorax with bronchopleural fistula)
- Copious respiratory secretions
- Severe nausea with vomiting
- Severe air trapping diseases with hypercarbia asthma or chronic obstructive pulmonary disease (COPD)

Question 13

What is positive pressure ventilation?

Answer 13

A form of respiratory therapy that involves the delivery of air or a mixture of oxygen combined with other gases by positive pressure into the lungs.

Question 14

How can positive pressure ventilation be delivered?

Answer 14

Positive pressure ventilation can be delivered in two forms: non-invasive positive pressure ventilation (NIPPV), which is delivered through a special face mask with a tight seal (air travels through anatomical airways), or invasive positive pressure ventilation (IPPV), which involves the delivery of positive pressure to the lungs through an endotracheal tube or tracheostomy (or any other device that delivers gas bypassing parts of the anatomical airway)

Question 15

Which conditions respond most to NIPPV?

Answer 15

• NIPPV can be used in acute hypercapnic respiratory failure so long as the patient’s condition is responsive to this form of therapy
• Conditions that respond the most to NIPPV include exacerbations of chronic obstructive pulmonary disease (COPD) and acute cardiogenic pulmonary edema

Question 16

Lower airway anatomy

Answer 16

The lower airway continues down below the vocal folds to the trachea to form the right and left mainstem bronchi, which further divide into smaller segmental bronchi. These subdivide into even smaller bronchioles that eventually end with the terminal portion of the airway, the alveoli, in which gas exchange occurs

Question 17

Indication of positive pressure ventilation

Answer 17

• Airway protection in a patient who cannot maintain or protect an open airway, e.g., from an altered level of consciousness or trauma
• Hypercapnic respiratory failure
• Hypoxemic respiratory failure
• Circulatory failure

Question 18

Contraindication to NIPPV

Answer 18

Contraindications to NIPPV include:[6]

• The need for intubation
• Encephalopathy or altered mental status
• Hemodynamic instability
• Facial trauma or facial defects
• Airway obstruction secondary to a mass
• Anticipated need for prolonged mechanical ventilation
• Gastrointestinal bleeding

Question 19

Contraindications to invasive positve pressure ventilation

Answer 19

• The patient’s wishes are clearly against ventilatory support
• Situations in which NIPPV is a reasonable alternative to provide respiratory support as there are fewer possible complications associated with its use compared to classic invasive mechanical ventilation (excessive sedation, ventilator-associated pneumonia, barotrauma, and volutrauma).

Question 20

How can NIPPV be delivered?

Answer 20

NIPPV is administered most commonly by a CPAP (continuous positive airway pressure) or BiPAP (bilevel positive airway pressure) machine.

Question 21

Most commonly used form of NIPPV

Answer 21

BiPAP

Question 22

How does BiPAP work?

Answer 22

The machine works similarly to a CPAP machine in that it delivers a constant level of PEEP (usually 3 to 12 mm Hg), but it also provides positive inspiratory pressure (usually 5 to 25 mm Hg) when the patient initiates a breath.

Question 23

Complications of CPAP and BiPAP

Answer 23

• Many and can be quie serious
• Most complications will focus specifically on classic mechanical ventilation as its exact nature is more invasive, and it is important to understand its consequences. However, although rarer, complications can and do occur, with non-invasive positive pressure ventilation.
• Complications include Ventilator-associated Lung Injury and Barotrauma
• Hemodynamic Effects
• Ventilator-associated Pneumonia
• Oxygen Toxicity
• Neuromuscular Complications
• Miscellaneous Injuries Related to Non-invasive Ventilation

Question 24

Ventilator-associated Lung Injury and Barotrauma in positive pressure ventalation

Answer 24

= Barotrauma occurs when there is alveolar damage due to high pressures entering the lungs. Specifically, the transalveolar pressure, which is the difference in pressure between the alveolus and the surrounding interstitial space, is increased to such an extent that the epithelial lining of the alveoli is damaged. With repeated breaths and inappropriate ventilation, the damage often occurs on a microscopic level until it is severe enough to cause an overt pneumothorax, subcutaneous emphysema, or pneumomediastinum, which are all conditions associated with high mortality rates
- Excessively high tidal volumes or inspiratory pressures are some of the underlying culprits in the cause of barotrauma. One of the landmark studies on acute respiratory distress syndrome, known as ARDSNet, demonstrated that using lung-protective strategies with lower tidal volumes (between 4-8 mL/kg based on ideal body weight) have improved mortality benefits and are associated with more ventilator-free days for patients. Additional studies have examined lung protective strategies for patients not suffering from acute lung injury and have also found reduced morbidity and mortality benefits, although additional studies are needed for conclusive evidence

Question 25

Hemodynamic effects of positive pressure ventilation

Answer 25

• Positive pressure ventilation results in physiologic alterations in intrathoracic pressure and cardiac output. One of the most common hemodynamic effects from positive pressure ventilation is a reduction in preload to the heart secondary to increased intrathoracic pressure that impressive the inferior vena cava and right atrium. This effect is more prominent in individuals that may already have reductions in intravascular volume. Likewise, changes in intrathoracic pressure or cardiac output can precipitate an arrhythmia or myocardial ischemia.
• Even though most arrhythmias are related to structural changes in the heart, it is common for them to occur secondary to positive pressure ventilation. This is because ventilated patients often have respiratory and electrolyte derangements, including hypoxemia, hypercapnia, acidemia, alkalemia, hypokalemia, hypomagnesemia, or hypocalcemia. Serial arterial blood gasses are often obtained to identify and correct underlying derangements and prevent arrhythmias. Likewise, mechanical ventilation and critical illness lead to hormonal and catecholamine changes in the body that can precipitate myocardial ischemia. This process can occur at any time while a patient requires mechanical ventilation but is also likely during weaning trials when myocardial oxygen demand is increased, and a patient’s sedation is decreased or turned off to assess their ability to come off the ventilator.

Question 26

VAP in positive pressure ventilation

Answer 26

• The most common infection among mechanically ventilated patients receiving positive pressure ventilation is ventilator-associated pneumonia (VAP)
• An endotracheal tube serves the purpose of protecting a patient’s airway from aspiration and providing a path for the flow of air between the patient and the ventilator. However, it also serves as a conduit between the world and the normally sterile lower respiratory tract. In the setting of critical illness and reduced immune system function, bacteria often invade and colonize the lower respiratory tract of patients causing VAP.

Question 27

Mortality rate of VAP

Answer 27

The mortality rate is high and can range between 20% to 50%

Question 28

Common pathogens in VAP

Answer 28

Common pathogens include gram-negative bacteria such as Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter species, and gram-positive bacteria such as Staphylococcus aureus

Question 29

Oxygen toxicity in positive pressure ventilation

Answer 29

• Critically ill patients that require positive pressure ventilation or mechanical ventilation are often hypoxemic and require high levels of inspired oxygen (FIO2).
• However, not all conditions that require a patient to be mechanically ventilated require high levels of oxygen therapy.
• In fact, high levels of oxygen can be toxic to the human body.
• Areas of the lungs with ventilation-perfusion mismatches under high FIO2 can actually lead to a phenomenon known as re-absorption atelectasis that will further aggravate any ventilation-perfusion mismatches.
• High oxygen levels are also associated with increased vasoconstrictive effects on coronary circulation and increased mortality from cardiac causes.

Question 30

Neuromuscular complications of positive pressure ventilation

Answer 30

• Patients that require mechanical ventilation often need sedation due to the stimulating nature of the endotracheal tube. Likewise, the act of being on a ventilator can be a traumatic experience. Some patients that are in desynchrony with the ventilator, colloquially known as “fighting the vent,” may require paralytic medications such as rocuronium, vecuronium, or cisatracurium so that they can be safely ventilated to treat their underlying condition.
• However, important neurochemical changes occur within patients’ bodies, such as the depletion of bioenergetic neuron reserves, altered sodium channel activation, and increased inflammatory cytokines, which lead to changes such as atrophy of the diaphragm or critical illness myopathy
• These changes make it difficult to wean patients off the ventilator and may require the patient to undergo a separate surgical procedure known as a tracheostomy to create an opening in the neck to place a tracheostomy tube for further ventilatory support based on the patient’s underlying critical illness. These patients often require prolonged mechanical ventilation

Question 31

Miscellaneous Injuries Related to Non-invasive Ventilation

Answer 31

Non-invasive ventilation, by its very nature, is associated with fewer risks than invasive mechanical ventilation, but not all patients can benefit from its use. Nevertheless, it is important to be aware of some of the common complications. Facial ulcers and lacerations occur in approximately 13% of patients.[18]

A tight seal is required to properly ventilate patients, but it is important to be aware that the seal is not too tight as to cause injury to the face. Other issues that arise include eye irritation, dry airway passages, and gastric distention.[19] Thus, if there is any concern for aspiration, it is safer to intubate a patient to protect their airway and to avoid gastric distention.

Question 32

BiPAP indications

Answer 32

According to the latest ATS/ERJ guidelines from 2020 for acute respiratory failure, NPPV carries a strong recommendation for the following in the setting of acute respiratory failure (ARF):

BPAP for acute or acute-on-chronic respiratory acidosis secondary to COPD exacerbation where pH </= 7.35
BPAP is the prevention of endotracheal intubation and mechanical ventilation in a patient that is not immediately deteriorating
BPAP or continuous positive airway pressure (CPAP) for cardiogenic pulmonary edema

ATS/ERJ guidelines carry a conditional recommendation for the following in the setting of ARF:
Early NIV for immunocompromised patients with ARF
Post-operative ARF
As palliation to dyspneic patients in the setting of terminal cancer or other terminal conditions
Chest trauma patients with ARF
Prevention of post-extubation respiratory failure in high-risk patients
In addition, NPPV has been effective in treating various chronic respiratory diseases. These diseases include chronic stable COPD with hypercapnia, obesity hypoventilation syndrome, obstructive sleep apnea, respiratory failure secondary to neuromuscular disease, and restrictive thoracic disorders