Lecture 18: Assisted Breathing Methods

Question 1

What is the main inspiratory muscle and what muscle fibres does it consist of?

Answer 1

• diaphragm
• fatigue resistance slow-twitch type I and fast twitch II a myofibres

Question 2

List some central and peripheral that can cause loss of control of one or both hemidiaphragms

Answer 2

Central causes:
* brain or brainstem stroke, Amyotrophic Lateral Sclerosis (ALS)
* spinal cord injury, syringomyelia, polio
* autoimmune (MS, Guillain-Barré)

Peripheral causes:
* phrenic nerve trauma from surgery, radiation, tumor
* phrenic neuropathy, viral or bacterial infections, idiopathic (unknown origin)

Question 3

What % is the diaphragm active during breathing

Answer 3

duty cycle: active 30-40% of the time

Since they’re busy all the time, they’re susceptible to inactivity or disuse

Question 4

Describe early negative pressure mechanical ventilation

Answer 4

aka Iron Lung or Cuirass ventilators sealed pressurized vessel, only thing that came out was the person’s head. machine is snug around neck

vacuum in the chamber causes subatmospheric pressure, causes the chest to expand, allowing airflow into the lungs. then chamber would pressurize, causing the chest to deflate, allowing for exhalation

Question 5

Describe early positive pressure mechanical ventilation - why was it created?

Answer 5

During the 1952 polio epidemic, iron lung ventilators were in short supply.

Anesthetist discovered bellows could provide positive pressure and keep polio patients alive

Hired teams of volunteers (medical students), to keep people alive by squeezing bellows to keep patients allive

Question 6

central apnea

Answer 6

a sleep disorder that causes breathing to repeatedly stop and start during sleep

somewhat related to positioning. also related to central nervous system control

baby suddenly stops breathing

Question 7

obstructive sleep apnea

Answer 7

overweight. tongue falls back and is an obstacle to breathing
Throat muscles relax and block airway

Question 8

What is positive pressure ventilation?
* What can positive pressure ventilation assist with?

Answer 8

Pressurized air is forced into the airways, through modulating the applied pressure (pressure control) or the supplied volume (volume control).

The ventilator can
* Provide a mandatory breath,
* Assist a patient who can initiate a breath, or
* do combinations of the above.

Patients can vary between being deeply comatose to alert and interactive.

Question 9

List 4 harms of positive pressure ventilation

Answer 9

• Ventilator-induced lung injury – VILI (or VALI). 3 types: volutrauma/biotrauma, barotrauma, atelectasis,
• Ventilator-associated pneumonia – VAP
• Ventilator-induced diaphragmatic dysfunction (or atrophy/due to atrophy) – VIDD
• Ventilator-associated brain injury - VABI

Question 10

Describe the following type of ventilator induced lung injury: volutrauma/biotrauma

Answer 10

Volutrauma/biotrauma:
End-inspiratory volume is too large and causes direct lung damage and inflammation. This also increases epithelial and microvascular permeability leading to fluid filtration into the alveoli. Results in pulmonary edema.

Question 11

Describe the following type of ventilator induced lung injury: barotrauma

Answer 11

Barotrauma: positive airway pressure is too large causing lung overdistension resulting in** gross tissue injury**. A pneumothorax can occur and air will transfer into the interstitial tissues from the proximal airways

Question 12

Describe the following type of ventilator induced lung injury: atelectasis

Answer 12

atelectasis: a complete or partial collapse of a lung/lobe that develops when alveoli within the lung become deflated

inhomogenous pressure distribution from positive pressure ventilation and extrinsic weight of chest wall and intrinsic compression from the superior portions of the lung and the mediastinal contents causes parts of the lung to collapse.

If collapse is cyclical with each breath, the re-popening of terminal lung units induces inflammation and damage through recurrent shear stress and alterations of local surfactant.

After using the ventilator for a while and being taken off of it, alveoli can remain permanently collapsed, resulting in insufficient lung capacity –> can lead to Acute respiratory distress syndrome (ARDS)

ARDS: fluid builds up inside the tiny air sacs of the lungs, and surfactant breaks down

Question 13

What are the components a respiratory therapist may have to monitor to reduce ventilator associated lung injury and decrease the incidence of acute respiratory distress syndrome
* define: end expiratory pressure
* define: plateau pressure

Answer 13

Overalll: avoid giving too much volume or pressure while still adequately oxygenating patient.

• keep tidal volume to a narrow range of 6-8mL/kg of predicted body weight (to avoid volumtrauma)
• follow positive end-expiratory pressure guidelines to limit atelectasis (lower end of range) and barotrauma (higher end of range)

end expiratory pressure: the pressure remaining in the lungs when you exhale

maintain plateau pressure: <30 cm H2O

plateau pressure: pressure applied at the end of inspiration to small airways and alveoli

minimize FiO2 (fraction of inspired oxygen) to avoid absorption atelectasis and oxygen toxicity

Question 14

One study reviewed the following ventilator parameter complications, what did they find?

• low VT, low PEEP
• high VT, low PEEP
• low VT, high PEEP

Answer 14

Lung Protective Ventilation cannot eliminate VILI. No matter how you fiddle with these parameters, something in the lung will be suboptimal.

Low VT and low PEEP: higher amountsof atelectasis are present at end-expiration and end-inspiration with minimal areas of overinflation

High VT and low PEEP: less atelectasis is present at end-expiration and end-inspiration, but there are
increased areas of overinflation at end-inspiration. Furthermore, a higher amount of tissue cyclical collapse during breathing is present (this can cause inflammation and damage due to sheer stress).

Low VT and higher PEEP: less atelectasis is present. However, higher overinflation occurs at end-inspiration and end- expiration. volutrauma possible –> pulmonary edema

Question 15

Ventilator-associated pneumonia (VAP)

• Exogeneus sources
• mechanism
• length of time to develop
• problem with VAP
• how does VAP differ from community acquired pneumonia

Answer 15

• hands of healthcare worker, ventilator circuit, biofilm of endotracheal tube
• colonized secretions are inhaled into the lungs through the endotracheal tube
• 48+ hours after mechanical ventilation is applied
• increased lengths of ICU stay and up to 20-30% higher death rates. Different strains of VAP can be drug resistant, making it difficult to treat
• The microbiologic flora responsible for VAP is different from that of the more common community-acquired pneumonia (CAP).

Question 16

Describe the clinical manifestations of ventilator associated brain injury

Answer 16

cyclic alveolar collapse and overstretching –> local and systemic inflammation –> hippocampal neuronal cell apoptosis

• delirium
• coma
• disability
• impaired quality of life
• long-term cognitive impairment

Question 17

Work in multiple animal models showed a significant
reduction of _______ that was
proportional to duration of mechanical ventilation.

Answer 17

diaphragmatic force-generating capacity

Question 18

What is the typical thickness of the diaphragm of a 50-
year-old man, 1.75 m tall, weighs 75 kg, and never smoked?

What would be the diaphragm thickness of his twin brother, of same height and weight, but who has smoked 2 packs of cigarettes per day since he was 15 years old

What would be the diaphragm thickness of the first man, the non-smoker, one week after becoming seriously ill with
Covid-19 and being connected to a mechanical ventilator?

Answer 18

2mm

3-4mm; muscle is overexercised; emphysema

• diaphragm drops to half its size in 3 days (1 mm).

Question 19

Describe the study where they reviewed the histology of diaphragm fibres in brain dead donors who were on a ventilator for 18-69 hours vs the histology of diaphragm fibres in surgery patients kept on a MV for only 2-3 hours

Answer 19

on average, cross section of diaphragm fibres (both slow twitch and fast twitch) reduced by over half in the patients on ventilators for 18-69 hours (less than 3 days)

there was rapid disuse atrophy

Question 20

What is daily vacation from sedation? What has been found despite this protocol being established?

Answer 20

Standard protocol weaning trial where they lighten the anesthetic for a patient and attempt to see if they can breathe on their own

encourages voluntary ventilation as soon as it is feasible

However, despite patients being on voluntary mode of ventilation (ventilation only provides support), they continue to have a decay in diaphragmatic force.

Essentially, there is no clinically available way to avoid VIDD

Question 21

What % of patients that have been on a ventilator for 4 days or more fail to wean off of it?

Answer 21

30% of patients who have been on a ventilator for 4 or more, fail to wean off of it

Question 22

What are the possible ways electrodes can be applied to stimulate the diaphragm

Answer 22

1 Transcutaneous
2 Surgically Implanted
3 Laparoscopically Implanted
4. Transvascular (next lecture)

Question 23

Describe transcutaneous activation of the phrenic nerve
* method of application
* pitfalls
* suitable for

Answer 23

can be electrical or magnetic

• Cumbersome.
• Can only be applied manually and maintaining long term positioning is difficult in an ICU patient as it is applied to neck
• Not selective enough to stimulate the phrenic nerves
  without also recruiting brachial plexus branches.
• Suitable for assessment of diaphragm function to see if ur phrenic nerve is healthy and connected to ur diaphragm
• unreliable for therapeutic stimulation

Question 24

Describe surgically implanted activation of the phrenic nerve
* what is the most famous one?
* what is it purported to be useful for?
* describe the system components

Answer 24

• Avery Breathing Pacemaker System - suitable for pediatric and adult populations
• SCI patients (c4 or above), congenital central hypoventilation syndrome, central sleep apnea
• electrode cuff on each phrenic nerve. Electrode is connected to an implanted receiver that communicates with antenna on skin. highly flexible monopolar stainless-steel wire, insulated by silicone rubber, with a platinum nerve contact on one end, and a connector that mates with the receiver.
• 2 channel radio transmitter is worn around patient’s belt. Transmitter is connected to an antenna that is applied over the skin. Antenna communicates using radiofrequency with radio receiver.
• radioreceiver converts radiofrequency to electrical impulses that stimulate the phrenic nerve and causes contractions of the diaphragm.

A bipolar configuration is also available for those
patients implanted with other medical devices, such
as a cardiac pacemaker, to provide an additional
margin of electrical isolation.

Question 25

Describe the ATROSTIM Phrenic Nerve Stimulator inventor’s argument for their design

Describe their system design

Answer 25

The phrenic nerves arise bilaterally from cervical segments C3 - C6.
An electrode fixed to the nerve above the clavicle (as seen with Avery Diaphragm Pacing System) in the neck cannot stimulate the fibers coming from segment C6.

Thus, they placed multipole sequential stimulation electrodes in the upper chest instead of lower neck, allowing for the stimulation of the phrenic nerve fibres coming from C6 in addition to the ones from C3-5

Multipole sequential stimulation electrode allows for the recruitment of different subset of diaphragm fibres on rotation. This prevents the diaphragm from fatiguing.

Question 26

Prospective clinical study on effects of mechanical ventilation vs. peripheral nerve stimulation on Respiratory Infection rates.

Answer 26

Peripheral nerve stimulation:
0 respiratory incidents

Mechanical ventialtion:
2 respiratory incidents every 100 days with mechanical ventilation

Question 27

Advantages and disadvantages of phrenic nerve stimulation over mV

Answer 27

advantages
* Increased freedom
* Negative pressure breathing
* Lower risk of ventilator-associated pneumonia (VAP)
* Decreased risk of tracheal
complications
* Pays for itself within 3-4 years of operation

disadvantages
* Lengthy/complex invasive surgery (3-4hrs)
* Possible damage to phrenic nerves during or after electrode placement
* High initial cost (~$60,000 USD)
* Difficult to retrieve device
* Few patients are eligible (must be healthy)

Question 28

Describe the process of placing laparoscopically implanted intramuscular electrodes

Answer 28

• use Hasson ports to expose the diaphragm and and cut falciform ligament of the diaphragm
• pump CO2 into abdominal cavity to visualize diaphragm from below
• connect electrode to a computer system, using probe to hold electrode, apply to several locations on diaphragm, identify areas of maximal contraction and record changes in intraabdominal pressure (as collected and measured by tubing attached to laparoscopic ports that is attached to a pressure sensitive transducer)
• mark places to implant electrode with surgical marker
• place 2 electrodes per hemi-diaphragm, attach to computer system to double-check that location and positioning is appropriate
• if appropriate, electrode wires are attached to stimulation unit

Question 29

Advantages and Disadvantages of Diaphragm Intramuscular Electrodes

Answer 29

• No thoracotomy, lower risk of nerve damage as it is less invasive
• Lower risk of complications such as pneumothorax
• Faster recovery from laparoscopic surgery than open surgery

Disadvantages
- Lengthy, costly surgery, requires full anaesthesia (2-4 hrs)
- Percutaneous wires connect to external control unit –> possible infection
- Critically ill patients are not eligible. only health patients like long term survivors of spinal cord injuries

Question 30

How could diaphragm pacing systems be useful for ALS (Amyotrophic lateral sclerosis)? What did they find?

Answer 30

Rational: slow decline in a patient’s Forced Vital Capacity and delay the onset of respiratory failure

however, turned out to be harmful. patients treated had more than twice increased risk of death during study than others who only had noninvasive ventilation

progressive degeneration of nerve cells result in denervation of the diaphragm. can’t stimulate phrenic nerve

Question 31

Avery Diaphragm Pacer VS Synapse Neurx

Answer 31

Avery Device
* full FDA PMA approval for adults and pediatrics (apnea, ALS, SCI)
* over 45 years of experience
* proven long-term safety record
* reduced risk of infections and need for wound care
* bilateral redundancy

Neurx
* HDE exemption for adults with SCI or ALS only
* little over 12 years of experience
* unknown longterm safety record
* additionl risk of infection due to protruding wires
* no redundancy - single point system failure
* more expensive