DISCONTINUATION OF VENTILATORY Dr Mehdi Hasan Mumtaz

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					 DISCONTINUATION OF
VENTILATORY SUPPORT


  Prof. Mehdi Hasan Mumtaz
     DISCONTINUATION OF
    VENTILATORY SUPPORT
   Weaning – Discontinuing mechanical
    ventilation.
   Strict Sense – Weaning refers to a slow
    decrease in the amount of ventilator
    support with the patient gradually
    assuming a greater proportion of overall
    ventilation.
     PATHOPHYSIOLOGICAL
        DETERMINANTS

A.   Adequacy of pulmonary gas exchange.

B.   Performance of the respiratory muscle
     pump.

C.   Psychological factors.
ADEQUACY OF PULMONARY
    GAS EXCHNAGE

   Hypoventilation.

   Impaired Pulmonary Gas Exchange.

   O2 Content of Venous Blood.
    RESPIRATORY MUSCLE
         PERFORMANCE
a. Neuromuscular capacity.
   – Respiratory centre output.
   – Phrenic nerve dysfunction.
   – Respiratory muscle stregth/endurance.
         Hyperinflation.
         Chest wall motion abnormaliteis.
         O2 supply.
         Malnutrition.
         Respiratory acidosis.
         Metabolic abnormalities.
         Endocrinopathy.
         Drug induced abnormalities.
         Disease muscle atrophy.
         Respiratory muscle fatigue.
    RESPIRATORY MUSCLE
         PERFORMANCE

B. Respiratory Muscle Pump Load.
   –  Ventilatory Requirements.
          CO2 Production.
          Dead Space Ventilation.
         Inappropriately  Respiratory Drive.

   –  Work of Breathing.
RESPIRATORY N/MUSCULAR
        CAPACITY
   Respiratory Centre Output.
    – Respiratory acidosis.
    – Indices of drive.
          Airway occlusion pressure at0.1sec.
          Mean inspirtory flow (Po.1 VT/T1.

    – CO2 recruitment threshold.
PHREMIC NERVE FUNCTION

        Coronary Bypass Operation.

   Hypothermic injury.
   Inadvertent sectioning.
   Stretching & compression of nerve.
   BF To vasavasorum of nerve
RESPIRATORY MUSCLE FUNCTION
            “Hyperinflation”
             Adverse Effects
   Respiratory muscles operate at
    unfavrourable position of their length –
    tension curve.
   Flattening of diaphragm radius.
   Efficacy due to medial & horizontal
    orientation of fibres.
   Inwardly directed elastic recoil of chest
    wall – added elastic load.
ABNORMALITIES IN CHEST
    WALL MOTION


       Asynchrony
         Paradox
            
     In Energy Cost.
            O2 SUPPLY
    CO.
                         Hypoxaemia.
   O2 content
                           Anaemia
   O2 extraction – Sepsis.
   LVEJ.
ACUTE RESPIRATORY
    ACIDOSIS


     Contractibility



    Endurance Time
           METABOLIC
         ABNORMALITIES

   Hypokalaemia.

   Hypophosphataemia.

   Hypercalcaemia

   Hypomagnisaemia.
ENDOCINE DISTURBANCE

   Hyperthyroidism.

   Hypothyroidism.

   Corticosteroid therapy.
RSP MUSCLE PUMP LOAD
   Ventilatory Requirements.
    – CO2 production.
    – VD ventilation.
    – Elevated respiratory drive.
          Drive – Hypo ventilation.
          Drive – Fatigue.
    – VD/VT >0.6 significant.
    – Cimpliance.
                         Work of breathing
    – Resistance.
    WORK OF BREATHING
 (Determinant of Weaning Outcome)
 Compliance.
 Resistance.
 O2 Cost of Breathing.

Total O2 consumption Total O2 consumption
Spontaneous breathing  on mechanical ventilation

Normal <5% of total body O2 consumption
Weaning >50%.
PSYCHOLOGICAL FACTORS

   Cmv (dependence).
    – Insecurity.
    – Anxiety.
    – Fear.
    – Agony.
    – Panic
      PREDICTING WEANING
           OUTCOME
         “objective measurements”
            “predictive indices”
   Why?
   Avoid unnecessary prolongation.
   Identify fail trial.
   Prevent premature weaning.
   Suggest alterations in managements.
 PREDICTIVE VARIABLES.
1. Gas Exchange.
                           PaO2
  a.   PaO2>60(FIO2<35)= ----------
                           PAO2
  b.   P(A-a)O2 < 350.
  c.   PaO2 /
              FIO2 > 200.
  d.   PaO2/
             PAO2 > .97.
 PREDICTIVE VARIABLES.
2. Ventilation Pump
   a. VC>10-15ml/kg.
   b. Maximum inspiratory Pressure < -30cmH2O.
   c. MV < 10<.
   d. MV < twice.
   e. P0.1.
   f. f/VT.
PREDICTIVE VARIABLES


       CROP Index.



     Integrative Index.
AIRWAY OCCLUSION
    PRESSURE




      P 0.1
            RAPID SHALLOW
              BREATHING
          (F/VT Ratio= Breaths/min/L)

   Attractive features.
     –   Easy to measure.
     –   Independent of effort.
     –   Accurate.
     –   Rounded off value (100)
      RIB CAGE – ABDOMINAL
             MOTION

                 “Cohen et al”

MCA          Maximum Compartmental Amplitude
-------- =   -----------------------------------------------
 VT                            Tidal volume



                Integrative Indices
    INTEGRATIVE INDICES

                         Cdyn X P1 max X (PaO2/PAO2)
CROP Index =          -------------------------------------------
                               Respiratory Rate



Integrative index =   PT1 X (VE 40/VT sb)
PHYSICAL EXAMINATION
   Careful physical examination.
   Elevated RR.
   Bed side VT.
   Clinical impression – Work of breathing.
     –   Nasal flaring.
     –   Accessory muscle use.
     –   Suprasternal recession.
     –   Intercostal recession.
     –   Paradoxical movement.
PHYSICAL EXAMINATION
   Auscultation.
   Dyspnoea Level.
   Mental Status.
   Blood Pressure.
   Heart Rate.
   Rhythm.
   Cyanosis.
               METHODS

“discontinuing mechanical ventilation”


   Older – Spontaneous breathing trial.
   1970s – Intermittent mandatory ventilation.
   1980s – Pressure support ventilation.
   Continuous positive airway support.
               METHODS
       Spontaneous Breathing Trials
             “T-Piece Trial”
   5min trial.
   FIO2 – 0.4.
   Duration.
   Expiratory limb 12” added.
   Flow twice x MV.
   Monitor – Blood gases.
             CNS Output
           Respiratory Drive



 Pump        Respiratory            Load on the
Capacity    Muscle Pump                Pump


                                   The Fatiguing
                                      Process


                                  Weaning &
                               Ventilatory Failure
FACTORS THAT MAY IMPAIR RSP MUSCLE
STRENGTH IN CRITICALLY ILL PATIENTS

   Hypophosphataemia.
   Hypomagnisaemia.
   Hypocalcaemia.
   Hypoxia.
   Hypercarbia.
   Acidosis.
   Infection.
   Muscle atrophy.
   Malnutrition.
    FACTORS ing THE LOAD ON
RESPIRATORY MUSCLES IN PATIENTS
             IN ICU
   Bronchoconstriction.
   Left Ventricular Failure.
   Hyperinflation.
   Intrinsic +ve End Expiratory Pressure.
   Artificial Airways.
   Ventilator Circuits.
                     STEP-1
 ASSESSMENT PRIOR TO WEANING
                    No
Able to oxygenate
 with stable, low
   inspired O2
 concentrations?
                              Reventilate patient
                              with weaning mode
        Yes

  Patient able to
      breath
spontaneously for
     10min?         No
             STEP-2
INITIAL ASSESSMENT OF BREATHING

   Rapid Shallow Breathing

      Measure f/VT ratio
    after 5min of breathing
        on CPAP circuit
                 STEP-3
          INITIAL ASSESSMENT
                 f/
                   VT < 80             Measure f/VT ratio
                                     after 5min of breathing
      f/VT <80                           on CPAP circuit


Continue spontaneous
breathing with CPAP                     f/VT >80 but <105


Reassess after 30 min

                          No          Reassess after 30 min
      f/VT <80
           Yes
Extubate after trial of        Yes          f/VT <80
 T-piece breathing-9
           STEP-4
  FOLLOWING A WEANING TRIAL
Reventilate patient
with weaning mode


                      Is the patient
                          awake?
                                       No
                                            Volume cycled
                                                SIMV
                              Yes


           Inspiratory Pressure Support
                   STEP-5
               CONSCIOUS LEVEL
  Patient awake &              Is Patient triggering ventilator?
    orientated?


                                      Is Patient overventilated?

    Check PaCO2/ABG’s

                                    Adjust IPPV to Normocapnia

Is Patient triggering ventilator?

             No            Continue IPPV until conscious level 
         STEP-6
ASSESSMENT OF RESPIRATORY
 MUSCLE STRENGTH (PI max)

      PI Max < -20cmH2O



         Measure
        Inspiratory
          Mouth
         Pressure

      PI Max < -20cmH2O
       STEP-7
 LOAD APPLIED TO THE
RESPIRATORY MUSCLES

  Measure Applied Load


  Cdyn < 50mls/cm H2O
                 No



     Wean Cautiously
 Recognising Likely Failure

				
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posted:10/29/2012
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