Diaphragmatic Dysfunction

Answer 1

• Transdiaphragmatic pressure = pressure difference across thoracic/abdominal cavities; proportional to muscle fiber tension.
• Diaphragmatic dysfunction- reduction in the force generating capacity of the diaphragmatic fibres.
  *

Question 2

Measurement of Diaphragmatic dysfunction in ICU

Answer 2

=>Three methods:
1) BAMPS(Bilateral Anterior Magnetic Phrenic Stiulation)
2) Ultrasound to measure change in Diaphragmatic thickness
3) Airway occlusion and measurement of inspiratory pressures generated.

Question 2

BAMPS (bilateral anterior magnetic phrenic nerve stimulation)

Answer 2

=>Gold-standard method.
->Causes isolated diaphragm twitch → measure change in transdiaphragmatic or airway pressure.
->DD defined as ↓ ability to generate negative inspiratory pressure, usually <11 cm H₂O.
->Limitation: requires specialist equipment → limited widespread use.

DD- Diaphragmatic Dysfunction

Question 2

Ultrasound

Answer 2

->Widely used in ICU.

->Key measurements:
* Diaphragm thickness
* Thickening fraction (TF) = fractional ↑ in thickness during inspiration
* Diaphragm excursion (only valid during non-assisted breathing)
* TF <30% = diagnostic of diaphragmatic dysfunction.
* Excursion <1 cm during non-assisted breathing = DD.

Question 3

Occlusion pressures

Answer 3

=>Uses airway pressure during maximal inspiratory effort against occluded airway.

->Respiratory muscle weakness defined as maximal inspiratory pressure <30–40 cm H₂O, age-adjusted.

Question 4

Magnitude of the problem

Answer 4

->DD is extremely common in mechanically ventilated patients.
->Up to 63% have DD within 24 hours of admission & intubation.
->Severity correlates with number/magnitude of organ failures.
->At weaning: DD present in 63–80%.
& in 80% ICU pts with critical illness polyneuropathy.
->Mean transdiaphragmatic pressures in ventilated patients: 7–10 cm H₂O (normal = 28–30).

Question 5

Pathophysiology / Course

Answer 5

->DD severity correlates strongly with duration of ventilation.

->Reflects multiple overlapping insults → variable waxing/waning muscle injury over ICU stay.

->Contributing Factors:
* Sepsis
* Metabolic Factors
* Drugs
* Mechanical ventilation

Question 6

Pathophysiology cont..
Sepsis

Answer 6

Sepsis
Impairs muscle function via multiple mechanisms:
* Inflammatory mediators impair contractile proteins (including diaphragm).
* ↑ nitric oxide synthase → ↑ NO production → ↓ force generation.
* Redistribution of oxygen away from diaphragm.

Question 6

Mechanical Ventilation

Answer 6

Several mechanisms:
1. Over-assistance → disuse atrophy

2.	Under-assistance → excessive load/injury

3.	Patient–ventilator dyssynchrony
*	Reverse triggering, ineffective triggering → abnormal contraction patterns.

4.	Atelectasis + regional injury
uneven ventilation → localized diaphragm injury.

5.	Prolonged ventilation
*	Severity of DD strongly correlates with duration of ventilation.

Bottom line:
Mechanical ventilation causes rapid, severe, and progressive diaphragm atrophy, often within 24–48 hours.

Question 6

Pathophysiology cont..

Metabolic Factors

Answer 6

=>Common critical illness derangements worsen diaphragm weakness:
* Hypercapnia
* Hypoxaemia
* Hypokalaemia
* Hypophosphataemia
* Malnutrition
* Shock states worsen respiratory muscle fatigue by diverting oxygen to vital organs.

Question 7

Pathophysiology cont..
Pharmacologic Exposures

Answer 7

->Sedatives can directly injure diaphragm or cause muscle disuse.
* Example: propofol → exacerbates diaphragm weakness (animal models).
->Corticosteroids:
* Known to cause atrophy and activate proteolytic pathways.
* Relationship to ICU-acquired diaphragm weakness is unclear but suspected.

Question 8

Clinical outcomes
->Weaning Failure
->Prolonged Mechanical Ventilation

Answer 8

->Weaning Failure
* D D strongly predicts failure of SBTs.
* Associated with ⬆️ed risk of reintubation.
* Weaning times –>significantly prolonged.

->Prolonged Mechanical Ventilation:
* Any early ↑ or ↓ in diaphragm thickness =
→ 2× risk of remaining ventilated at day 21.
* DD -> major driver of prolonged ventilation and ICU stay.

Question 8

Clinical outcomes

Answer 8

• Weaning Failure
• Prolonged Mech. ventilation
• Mortality
• Long term Functional outcomes

Question 9

Clinical outcomes
->Mortality & Prognosis
->Long-Term Functional Impairment

Answer 9

=>Mortality & Prognosis
->DD at ICU discharge → significantly ↑ risk of:
* ICU or hospital readmission within 7 days
* 1-year mortality
* Long-term outcomes significantly worse in patients with DD.

⸻

=>Long-Term Functional Impairment
* Diaphragm weakness may persist months to years.
* Strong contributor to poor long-term quality of life and functional impairment.
* May explain persistent dyspnoea despite normal pulmonary function tests.

Question 10

Potential Therapies & Prevention of Diaphragmatic Dysfunction

Answer 10

=>No proven therapies yet for diaphragmatic dysfunction after mechanical ventilation.

=>Approaches focus on prevention

=>General Prevention Principles
* Avoid oversedation.
* Avoid excessive ventilator unloading.
* Maintain safe inspiratory effort.
* Avoid neuromuscular blockade unless essential.
* Provide adequate metabolic support.

2. Prevention Strategies (Mechanistic)

A) Diaphragm-Protective Ventilation

B) Phrenic Nerve Stimulation

C) Pharmacologic Approaches (Experimental)

Question 11

Prevention Strategies

Answer 11

A) Diaphragm-Protective Ventilation

B) Phrenic Nerve Stimulation

C) Pharmacologic Approaches (Experimental)

Question 12

Diaphragm-Protective Ventilation

Answer 12

=>Addresses Disuse atrophy

• Adjust ventilation + sedation -> maintain safe level of inspiratory effort.
• Moderate inspiratory effort (similar to healthy resting breathing) associated with: Shorter duration of ventilation
• Both too little and too much inspiratory effort associated with prolonged ventilation.

->Clinical challenge:
* Must balance avoiding lung injury (protective tidal volume) vs ensuring adequate inspiratory effort.

Question 13

Phrenic Nerve Stimulation

Answer 13

• Activates diaphragm while allowing controlled ventilation and deep sedation.
• Prevents development of diaphragm atrophy (animal models, cardiac surgery patients).
• Uncertain clinical role – more research needed on patient selection and dosing.

Question 14

Pharmacologic Approaches
Experimental

Answer 14

• No agents yet validated in clinical settings.

Question 15

Treatment Approaches (Not yet proven)

Answer 15

1) Inspiratory Muscle Training (IMT)
* Recruits diaphragm and auxiliary respiratory muscles for rehabilitation.

• Systematic review →
  
  • IMT improves inspiratory and expiratory muscle function.
  • Associated with shorter ventilation & ICU stay (needs confirmation in larger trials).

2) Early mobilization
* May recruit diaphragm and improve muscle performance.

3) Treatment of underlying contributors
* Control sepsis, correct metabolic derangements, address drug effects, minimize ventilator dys-synchrony.