Question Answer
Weaning success is defined as effective spontaneous breathing without any mechanical assistance for 24 hours
Medical (ICU) patients Often have coexisting problems and usually take more time to complete weaning than surgical patients
The minimum VC and spontaneous tidal volume are 10 to 15 ml/kg IBW and 5 to 8 ml/kg respectively
Vital capacity is effort dependent and requires proper teaching and coaching for accurate measurements
For successful weaning outcomes, the QS/QT should be < 20% (pulmonary shunt)
QS/QT calculation Qs/Qt = (PAO2 – PaO2)0.003/(CaO2 – CVO2) + (PAO2 – PaO2)0.003
On 100%, every 50 mmHg difference in P(A-a)O2 approximates 2% physiologic shunt
P(A-a)O2 should be _____ while on 100% < 350 mmHg
PaO2/FiO2 index should be .200 mmHg
Vd/Vt ratio should be < 60%
F/Vt should be < 100 cycles/L (very accurate)
a/A ratio is better > 0.8
PO.1Max Pressure max < 6%
Basic Methods for Discontinuing Ventilatory Support Increasing periods of spontaneous breathing IMV or SIMV PSV Single daily spontaneous breathing trials (SBT)
SBT and PSV are _____ _____ than other methods more effective
define weaning gradual reduction in the level of ventilatory support
define discontinuing ventilatory support overall process of removing the patient from the ventilator regardless of method
Need for Mechanical Ventilation Apnea – drug overdose, trauma, cardiac arrest, pneumonia, ARDS, COPD, Neuromuscular Impending failure Severe oxygenation problems
Ventilator work load refers to demand of ventilatory muscles
Ventilator work load is determined by 1) Level of ventilation needed 2) Compliance of lung & thorax 3) Resistance to flow in airways 4) Imposed WOB (ventilation)
Increased Demand & Level of Ventilation Required is determined by 1) Metabolic rate (sepsis) 2) CNS drive 3) Ventilatory deadspace
Decreased compliance Atelectasis, pneumonia, fibrosis, pulmonary edema, and ARDS Decreased thoracic compliance: obesity, ascites, abdominal distension, & pregnancy
Increased resistance Bronchospasm, mucosal edema, and secretions Artificial airways: ET and trach tubes Other factors: circuits, demand flow systems, inappropriate vent flow or sensitivity settings
Ventilatory capacity CNS drive – most have increased except neuromuscular and drug induced Ventilatory muscle strength Ventilatory muscle endurance
Factors reducing ventilatory drive Decreased PaCO2 Metabolic alkalosis Pain Electrolyte imbalance Narcotics, sedatives Fatigue Neurologic or Neuromuscular disease
Respiratory muscle strength is influenced by age, sex, muscle bulk and overall health
Controlled ventilation can lead to ventilation muscle atrophy
Ventilatory muscle endurance is a fuction of energy supply vs demand
Ventilatory demand is related to the amount of work performed and is a function of minute ventilation (Ve), compliance, and resistance
Once ventilatory muscles fatigue, they must be rested for 24 hours to recover
Factors considered for successful weaning Ventilatory workload vs capacity Oxygenation status Cardiovascular status Psychological factors
Careful pt evaluation is required to determine? which patients are ready to be removed quickly, which may need a prolonged ventilatory phase, and which are not ready for discontinuation of ventilatory support
Patients receiving support for 72 hours or less often can be removed quickly from the ventilator
Patients who need longer than 72 hours of support may require a more structured approach for weaning
Current guidelines recommend pts requiring > 24 hours of M.V. be carefully assessed to determine all causes of ventilator dependence
Considerations for discontinuing vent support 1) reason for instituting m.v. 2) pts baseline functional status 3) vent workload vs vent capacity 4) oxygenation status 5) cardio status 6) overall organ systems 7) duration of critical illness 8) duration of m.v. 9) psychological factors
Patient evaluation criteria 1) evidence of rev of condition that caused the need for m.v. 2) oxygenation: PaO2 > 60 on < 40 – 50%; PEEP of 5 – 8 cm H2O or less; PaO2/FiO2 ratio > 150 – 200; pH > 7.25
Patient evaluation criteria for hemodynamics Absence of acute myocardial ischemia Absence of marked hypotension Adequate Bp without vasopressor treatment
Patients must be able to initiate? inspiratory effort and breath spontaneously
Weaning Indices PaO2/FiO2 ratio > 150 – 200 (PAO2-PaO2) < 350 mmHg MIP (NIF) > -20 to -30 cmH2O VC > 10 – 15 ml/kg MVV > 20L or 2 x Ve (f/Vt) < 105 b/min/L PO.1 < 6 cmH2O
Ventilation evaluation Presence of palpable scalene muscle use on inspiration; Irregular ventilation pattern; palpable abdominal muscle tension during expiration; inability to alter breathing pattern
Patients having none of the ventilation evaluation signs have 90% chance of success
Patients having one or two signs of ventilation evaluation will need continued support
Patients having three or more signs of ventilation evaluation indicate pt is unstable


Egan’s Chapter 47 Practice Questions:

1. Advantages of adding continuous positive airway pressure (CPAP) to T-tube weaning include all of the following: improved blood oxygenation, decreased work of breathing, compensation for auto-PEEP

2. Advantages of noninvasive positive-pressure ventilation include? preserves airway defenses, allows intermitent use, allows speech or swallowing

3. All of the following factors will increase ventilatory demand (workload)? 1. Severe hypoxemia, 2. Pulmonary Infection, 3. Bronchospasm,

4. Common causes for weaning failure include?: myocardial ischemia, critical illness, polyneuropathy, psychological dependence

5. The following are advantages of using pressure-supported ventilation for weaning: reduced work of breathing, respiratory muscle fatigue prevented, better patient comfort and synchrony

6. The following are disadvantages of using intermittent mandatory ventilation for weaning?: potentially high work of breathing, weaning time possibly prolonged, patient ventilator dyssynchrony

7. The following are disadvantages of using the T-tube method for weaning: more staff time required, abrupt transition sometimes difficult, lack of alarm systems

8. The following are useful strategies in managing the psychological problems encountered in weaning some patients from ventilator support: secure a psychiatric consult, decrease environmental stress, teach relaxation methods

9. The following drug categories can depress ventilatory drive and hinder weaning?: analgesics, narcotics, hypnotics

10. The following factors can reduce a patient’s ventilatory drive?: respiratory alkalosis, depressant drugs, decreased metabolism

11. The following indicates that an adult patient is ready to be weaned from ventilatory support?: VD/VT = 0.55, MIP = -33 cm H2O, PO2 = 76 mm Hg on 40% O2

12. The following indicates that an adult patient is ready to be weaned from ventilatory support?: VC = 1.9 L, Qs/Qt = 8%, MIP = -45 cm H2O

13. The following indicates that a patient’s renal function is adequate for weaning?: no major weight gain, no edema present, normal electrolytes

14. The following weaning methods provide the best respiratory muscle strength conditioning?: pressure-supported ventilation, intermittent mandatory ventilation, volume-assured pressure support (VAPS)

15. Limitations of noninvasive positive-pressure ventilation include?: requires patient cooperation, limits access to the airway, causes mask-related problems

16. Treatment options for severe postextubation stridor include?: nebulized racemic epinephrine, nebulized dexamethasone, He-O2 mixtures

17. Ventilatory capacity is determined by all of the following?: central nervous system (CNS) drive, muscle strength, muscle endurance

18. When is ventilator dependence likely to occur?: when arterial hypoxemia is present, when the patient is malnourished, when the cardiovascular system is unstable

19. Which of the following is TRUE about artificial tracheal airways and weaning?: There are decreases in tube inner diameter (ID) and increases in VE increase the work of breathing. The added work due to artificial airways can increase ventilator dependence. Artificial airways can increase the work of breathing nearly threefold.

20. Which of the following is true about noninvasive positive-pressure ventilation (NIPPV)?: NIPPV can support ventilation without a tracheal airway. NIPPV should not be used with patients at risk for aspiration. NIPPV can be used to prevent reintubation when weaning fails.

21. Which of the following is true about the P0.1 measure?

A P0.1 correlates well with central respiratory drive.

B P0.1 is the airway pressure measured 100 ms after occlusion.

C Chronic obstructive pulmonary disease (COPD) patients with a P0.1 greater than 6 cm H2O are difficult to wean.

22. While monitoring a patient being weaned through a T-tube protocol, signs indicating that mechanical ventilation should be restored include: development of cardiac arrhythmias, asynchronous or paradoxical breathing, development of severe hypotension