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.