Mechanical VentilationMechanical Ventilation PROBLEMSPROBLEMS
Patiparn Toomtong
Department of Anesthesiology
Siriraj Hospital Mahidol University
Although life-saving, IPPV may be associated with many complications, including:
Consequences of PPVAspects of volutraumaAdverse effects of intubation and tracheostomy
Optimal Ventilatory Care Optimal Ventilatory Care RequiresRequires
Attention to minimizing adverse hemodynamic effectsAverting volutraumaEffecting freedom from IPPV as early as possible
Common ScenariosCommon Scenarios
• New development of hypotension
• Acute respiratory distress (fighting)
• Repeated sounding of High pressure alarm
• Hypoxaemia
• Blood from the endotracheal tube
• Problem of diagnosing VAP
BarotraumaBarotrauma or VolutraumaVolutrauma
• High Paw alone insufficient to cause alveolar rupture
• Excessive alveolar volume the likely factor leading to alveolar rupture and air dissection
• More frequent in younger age group• May be difficult to detect if small in CXR• “Stretch-induced” Acute lung injury
Patient-ventilator SynchronyPatient-ventilator Synchrony
Flow-targeted breath requires careful adjustmentConstant flow of 40-60 lpm not always adequateMonitor: patient response, airway pressure/flow graphicsUsing decelerating flow pattern may be helpful
Patient-ventilator SynchronyPatient-ventilator Synchrony
Pressure-targeted breath is better?• Rapid pressurisation of the airway with high initial gas flow• Match Ppl change quicker than flow pattern• Flow is continuously adjusted by the ventilator to maintain a constant airway pressure
Patient-ventilator SynchronyPatient-ventilator Synchrony
Any problems from pressure Any problems from pressure breaths?breaths?• Max initial flow may not be optimal in all patients depending on drive• Adjustment of the rate of rise may be beneficial• Pressure of what? Proximal airway vs Ppl by muscular effort• So! Carinal or pleural triggering helpful• variable minute ventilation!
Weaning from Mechanical Ventilation
Definition of Weaning
The transition process from
total ventilatory support
to spontaneous breathing.
This period may take many forms ranging from abrupt withdrawal to gradual
withdrawal from ventilatory support.
Weaning
Discontinuation of IPPV is achieved in most patients without difficulty
up to 20% of patients experience difficulty
requires more gradual process so that they can progressively assume spont. respiration
the cost of care, discontinue IPPV should proceed as soon as possible
Reversible reasons for prolonged mechanical
ventilation
• Inadequate respiratory drive
• Inability of the lungs to carry out gas exchange effectively
• Psychological dependency
• Inspiratory fatigue
Weaning
• Patients who fail attempts at weaning constitute a unique problem in critical care
• It is necessary to understand the mechanisms of ventilatory failure in order to address weaning in this population
Why patients are unable to sustain spontaneous
breathing
• Concept of Load exceeding Capacity to breathe
• Load on respiratory system
• Capacity of respiratory system
Balance Load vs Capacity
• Most patients fail the transition from ventilator support to sustain spont. breathing because of failure of the respiratory muscle pump
• They typically have a resp muscle load the exceeds the resp neuromuscular capacity
Load on Respiratory System
• Need for increase ventilation
increased carbon dioxide production
increased dead space ventilation
increased respiratory drive• Increased work of breathing
Causes of Inspiratory respiratory muscle fatigue
• Nutrition and metabolic deficiencies: K, Mg, Ca, Phosphate and thyroid hormone
• Corticosteroids• Chronic renal failure• Systemic disceases; protein synthesis, degradation, glycogen stores• Hypoxemia and hypercapnia
Capacity of respiratory system
• Central drive to breathe• Transmission of CNS signal via Phrenic
nerve• Impairment of resp muscles to generate
effective pressure gradients• Impairment of normal muscle force
generation
Evidence based Evidence based medicinemedicine
• When to start weaning When to start weaning process?process?
• Decision making, any Decision making, any guideline? How long it will guideline? How long it will take?take?
When to begin the weaning process?
• Numerous trials performed to develop criteria for success weaning, however, not useful to predict when to begin the weaning
• Physicians must rely on clinical judgement• Consider when the reason for IPPV is stabilised and
the patient is improving and haemodynamically stable• Daily screening may reduce the duration of MV and
ICU cost
Evidence-based medicine
Recommendation 1. Search for all the causes that may contribute to ventilator dependence in all patients with longer than 24 h of MV support, particularly who has fail attempts. Reversing all possible causes should be an integral part of discontinuation process.
Daily Screening
• Resolution/improvement of patient’s underlying problem
• Adequate gas exchange (SaO2 > 90%, PaO2/FiO2 >200)
• Respiratory rate < 35/ min• Absence of fever, temperature < 38C• Adequate haemoglobin concentration,
> 8-10 g/dl• Stable cardiovascular function: heart
rate < 140/min, 180>SBP>90
Daily Screening (cont.)
• Indices suggesting an adequate capacity of the ventilatory pump: respiratory rate of less than 30/ min, Maximum inspiratory pressure < -20 to -30 cmH2O
• Correction of metabolic and electrolyte disorders
• Normal state of consciousness
Evidence-based medicine
Recommendation 2. Patients receiving MV for respiratory failure should undergo a formal assessment of discontinuation potential if the criteria are satisfied.
Reversal of cause, adequate oxygenation, haemodynamic stability, capability to initiate respiratory effort. The decision must be individualized.
Predictions of the outcome of weaning
Variables used to predict weaning success: Gas exchange
• PaO2 of > 60 mmHg with FiO2 of < 0.35
• A-a PaO2 gradient of < 350 mmHg
• PaO2/FiO2 ratio of > 200
Weaning success predictionVentilation Pump• Vital capacity > 10- 15 ml/kg BW• Maximal negative insp pressure
< -30 cmH2O
• Minute ventilation < 10 l/min• Maximal voluntary ventilation more than
twice resting MV
Weaning success prediction
• Tidal volume > 325 ml• Tidal volume/BW > 4 ml/kg• Dynamic Compliance > 22 ml/cmH2O
• Static compliance > 33 ml/cmH2O
• Rapid shallow breathing index < 105 breaths/min/L
Clinical observation ofthe Respiratory Muscles
• Initially thought to be reliable in predicting subsequent weaning failure
• from inductive plethysmographic studies not necessary
• a substantial increase in load will effect on the rate, depth, and pattern of breathing
• a manifestation of fatigue
Both respiratory rate and minute ventilation initially increase, may
be followed by a paradoxical inward motion of the anterior
abdominal wall during inspiration which indicates the insufficient diaphragmatic contraction to
descend and move the abdominal content downward
Cyclic change in breathing patterns with either a chest wall
motion or a predominantly abdominal wall motion are another indicator, called
respiratory alternans
Duration of weaning prior to initial episode offatigue (days) 2.5 (0.25–7.5)Fatigue criteriaHypoxia (PaO2 < 60, SpO2 <90%) 11 (31%)Hypercarbia (PaCO2 > 50 mmHg) 9 (25%)Pulse rate > 120/min 17 (47%)SBP > 180 or < 90 mmHg 2 (6%)Respiratory rate > 30/min 33 (92%)Clinical respiratory distress 27 (75%)
Fatigue Criteria
1. Maximal expiratory pressure2. Peak expiratory flow rate3. Cough strength4. Secretion volume5. Suctioning frequency6. Cuff leak test 7. Neurological function (GCS)
Parameters that assess airway patency and protection
Evidence-based medicine
Recommendation 3. The removal of the artificial airway from a patient who has successfully been discontinued from ventilatory support should be based on assessment of airway patency and the ability of the patient to protect the airway.
Methods of Weaning
• Abrupt Discontinuation• T- tube trials• SIMV• Pressure support
Spontaneous breathing protocol• Communicate with patient, weaning is about
to begin, allow pt to express fear whenever possible
• Obtain baseline value and monitoring clinical parameters; vital signs, subj distress, gas exchange, arrhythmia
• Ensure a calm atmosphere, avoid sedation• Sit the patient upright in bed or chair• Fit T-tube with adequate flow, observe for 2
hr
For How long I will have to For How long I will have to monitor the weaning monitor the weaning process with SBT in my process with SBT in my patient?patient?
Evidence-based medicine
Recommendation 4. Formal assessments should be done during SBT rather than receiving substantial support. The criteria to assess patient tolerance during SBTs are respiratory pattern, gas exchange, hamodynamics stability and patient comfort. The tolerance of SBTs lasting 30 to 120 minutes should prompt for permanent ventilator discontinuation.
SIMV Protocol• Switch to SIMV from assist mode or decrease RR• Begin with RR 8/min decrease SIMV rate by two
breaths per hour unless clinical deterioration • if assume to fail, increase SIMV rate to previous
level, until stable• if stable at least 1 hour of rate 0/ min extubate• in patient without respiratory disorders, decrease
rate with half an hour interval, 2 hr extubate
Pressure Support Protocol• Switch to PSV or decrease PS• Begin PSV at 25 cmH2O, decrease PS by 2-4
cmH2O every hour unless clinical deterioration appears, adjust pressure until stable, if stable of PSV = 0 for at least one hour fit with T-tube or CPAP and then observe
• In patient without resp problems, decrease pressure at half an hour interval, if able to tolerate PSV = 0 for 2 hours, can be extubated
Failed to Wean
• Associated with intrinsic lung disease
• Associated with prolonged critical illness
• Incidence approximately 20%• Increased risk in patient with longer
duration of mechanical ventilation• Increased risk of complications,
mortality
Evidence-based medicine
Recommendation 5. Patients receiving MV who fail an SBT should have the cause determined. Once causes are corrected, and if the patient still meets the criteria of DS, subsequent SBTs should be performed every 24 hours.
Evidence-based medicine
Recommendation 6. Patients receiving MV for respiratory failure who fail an SBT should receive a stable, nonfatiguing, comfortable form of ventilatory support.
Weaning Protocol
Reduced ventilator timeReduced weaning time; early beginning by non-physician healthcare workersReduced costReduced complications: VAP
Evidence-based medicine
Recommendation 7. Weaning protocols designed for nonphysician health care professionals should be developed and implemented by ICUs. Protocols aimed at optimizing sedation should also be developed and implemented.
Evidence-based medicine
Recommendation 8. Tracheostomy should be considered after period of stabilization on the ventilator when it becomes apparent that the patient will require prolonged MV. Tracheostomy should be performed when the patient appears likely to gain one or more benefits from the procedure.
Evidence-based medicine, cont.
• Required high levels of sedation to tolerate tube
• With marginal respiratory mechanics, lower resistance
• Derive psychological benefit from the ability to eat orally, communicate by articulated speech, enhanced mobility
• Assist physical therapy efforts
Evidence-based medicine
Recommenation 9. Unless there is evidence for clearly irreversible disease, a patient requiring prolonged MV should not be considered permanently ventilator-dependent until 3 months of weaning attempts have failed.
Patient subgroups
Evidence-based medicine
Recommendation 10. Anaesthesia/sedation strategies and ventilator management aimed at early extubation should be used in postsurgical patients.
SEMIQUANTITATIVE ASSESSMENT OF NEED FOR AIRWAY CARE
Spont. cough
Gag Sputum Quantity
0 Vigorous
0 Vigorous 0 None1 Modera
te1 Moderate 1 1 pass
2 Weak 2 Weak 2 2 passes3 None 3 None 3 > 3 passesSputum Viscosity
Suctioning Frequency ( per last 8 h)
Sputum Character
0 Watery 0
> 3 h 0
Clear1 Frothy 1 q 2-3 h 1 Tan2 Thick 2 q 1-2 h 2 Yellow3 Tenacio
us3 < q 1 h 3 Green
EXUTBATION DELAY IN THE 136 PATIENTSNo
DelayDelay
p Valu
en (%) 99 (73%)
37 (27%)Days of delay NA 3 (2-
17)NA
Intubation duration at readiness day, d
2 (1-8) 2 (1-6) 0.03Spontaneous cough Readiness date 1 (0-3) 1 (0-3) 0.34 Extubation date 1 (0-3) 1 (0-3) 0.29Gag Readiness date 1.0 (0-
3)1.5 (0-
2)0.04
Extubation date 1.0 (0-3)
2.0 (0-3)
0.002Sum of airway care
assessments
Readiness date 8.0 (1-12)
9.0 (5-11)
0.04 Extubation date 7.5 (1-
12)9.0 (2-
16)0.01
Glasgow Coma Scale (GCS) Readiness date 10 (4-
11) 7 (3-11)
< 0.001
Extubation date 10 (4-11)
8 (3-11)
0.006Coma (GCS < 8)
Readiness date 31/99 (31%)
29/37 (78%)
< 0.001
Extubation date 28/99 (28%)
21/37 (57%)
0.002
EXBUTATION DELAY AND OUTCOME No Delay Delay p
n (%) 99 (73%) 37 (27%)Pneumonia (%) 21.2% 37.8% 0.0
48ICU length of stay 3 (1-15) 8 (3-22) < 0.001
Hospital LOS 11 (1-39) 17 (3-61) 0.009Cost, $ 41,824 70,881 < 0.001Mortality, n (%) 12.1% 27.0% 0.04Tracheotomy, n (%) 4 (4.0%) 0 (0.0%) 0.6
FACTORS ASSOCIATED WITH SUCCESSFUL EXTUBATION
IN NEUROSURGICAL PATIENTS AFTER FIRST EXTUBATION ATTEMPT
Parameter
Univariate Analysis
Multivariate Analysis
OR 95% CIp
ValueOR 95% CI
p Value
GCS score
1.35
(1.2-1.5)
< 0.0001
1.24
(1.1-1.4) 0.0006f/VT
ratio0.99
(0.98-0.99)
< 0.0001
0.99
(0.985-0.997)
0.0050P/F
ratio1.01
(1.00-1.01)
0.0001
1.01
(1.002-1.007)
< 0.0001
MV 0.89
(0.85-0.94)
< 0.0001
0.92
(0.845-0.981)
< 0.0116
GCS and prediction of successful weaning, AJRCCM 2001
ODDS OF SUCCESSFUL EXTUBATION FOR NEUROLOGIC AND RESPIRATORY PREDICTORS
Parameters OR 95% CI p Value
f/VT ratio < 105 10.3 1.2-87 0.02
P/F ratio > 200 3.3 1.8-6 0.0001
GCS score > 8 4.9 2.8-8.3 < 0.001P/F ratio, GCS score, f/VT ratio 5.1 3.1-8.4 < 0.001
P/F ratio, GCS score 4.8 2.9-8 < 0.001f/VT ratio, GCS score 4.9 2.9-8.5 < 0.001
Nursing role in Weaning from
mechanical ventilation
Nurse-led weaningPsychological preparation
Nurse-led weaning
• ICCN 2001: Limited evidence suggesting that nurse-led weaning may reduce ventilation time; however, not clear whether it was nurse-led aspect or the clinical protocol that produced the effect
• Superior to doctor-led weaning, has huge implications for intensive care practice
Nurse-led weaning
• ICCN 2002; Retrospective study in patients with MV longer than 7 days, reduced average duration of MV support
• Some delays occurred: sedation; protocol needed, epidural analgesia, tracheostomy; surgical vs percutaneous, some staff lacked confidence and knowledge: continuous education programme
Daily Screening
• Resolution/improvement of patient’s underlying problem
• Adequate gas exchange (SaO2 > 90%, PaO2/FiO2 >200)
• Respiratory rate < 35/ min• Absence of fever, temperature < 38C• Adequate haemoglobin concentration,
> 8-10 g/dl• Stable cardiovascular function: heart
rate < 140/min, 180>SBP>90
Daily Screening (cont.)• Indices suggesting an adequate
capacity of the ventilatory pump: respiratory rate of less than 30/ min, Maximum inspiratory pressure < -20 to -30 cmH2O
• Correction of metabolic and electrolyte disorders
• Normal state of consciousness
Oriented, Mental ease, Positive attitude
Psychological preparation• Knowing the patient; personal resources,
motivation levels, and styles of coping, comes from continued and close contact with the patient
• Oriented; understanding what will happen and being informed of progress, able to control negative responses
• Mental ease; absence of anxiety and fear arising from being informed, reassured and supported
• Positive attitude; being motivated and co-operating
Last year Meeting (2oo3)
• SIMV 2nd CPAP 3rd, T-piece 1st choice
• SIMV 25%, CPAP 19.82%, T-piece 50.29%
• Physician-led weaning approx. Nurse-led weaning
• T-piece duration 15 min to 4 hours
• Mainly tidal volume less than 10 ml/kg.
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