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Egans 47 Weaning

Egans Ch. 47 Discontinuing Ventilatory Support

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 fuction 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) overal 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 evaulation signs have 90% chance of success
Patients having one or two signs of ventillation evaluation will need continued support
Patients having three or more signs of ventillation evaluation indicate pt is unstable
Created by: stephnpc