DISCONTINUATION OF VENTILATORY SUPPORT Prof Mehdi Hasan Mumtaz

DISCONTINUATION OF VENTILATORY SUPPORT Prof. Mehdi Hasan Mumtaz

DISCONTINUATION OF VENTILATORY SUPPORT q q 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 q Hypoventilation. q Impaired Pulmonary Gas Exchange. q O 2 Content of Venous Blood.

RESPIRATORY MUSCLE PERFORMANCE a. Neuromuscular capacity. – Respiratory centre output. – Phrenic nerve dysfunction. – Respiratory muscle stregth/endurance. u u u u u Hyperinflation. Chest wall motion abnormaliteis. O 2 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. u CO 2 Production. u Dead Space Ventilation. u Inappropriately Respiratory Drive. – Work of Breathing.

RESPIRATORY N/MUSCULAR CAPACITY q Respiratory Centre Output. – Respiratory acidosis. – Indices of drive. u Airway occlusion pressure at 0. 1 sec. u Mean inspirtory flow (Po. 1 VT/T 1. – CO 2 recruitment threshold.

PHREMIC NERVE FUNCTION Coronary Bypass Operation. q q Hypothermic injury. Inadvertent sectioning. Stretching & compression of nerve. BF To vasavasorum of nerve

RESPIRATORY MUSCLE FUNCTION “Hyperinflation” Adverse Effects q q 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.

O 2 SUPPLY q CO. Hypoxaemia. q O 2 content q Anaemia O 2 extraction – Sepsis. LVEJ. q

ACUTE RESPIRATORY ACIDOSIS Contractibility Endurance Time

METABOLIC ABNORMALITIES q Hypokalaemia. q Hypophosphataemia. q Hypercalcaemia q Hypomagnisaemia.

ENDOCINE DISTURBANCE q Hyperthyroidism. q Hypothyroidism. q Corticosteroid therapy.

RSP MUSCLE PUMP LOAD q Ventilatory Requirements. – CO 2 production. – VD ventilation. – Elevated respiratory drive. u u Drive – Hypo ventilation. Drive – Fatigue. – VD/VT >0. 6 significant. – Cimpliance. Work of breathing – Resistance.

WORK OF BREATHING (Determinant of Weaning Outcome) q Compliance. q Resistance. q O 2 Cost of Breathing. Total O 2 consumption Spontaneous breathing on mechanical ventilation Normal <5% of total body O 2 consumption Weaning >50%.

PSYCHOLOGICAL FACTORS q Cmv (dependence). – Insecurity. – Anxiety. – Fear. – Agony. – Panic

PREDICTING WEANING OUTCOME “objective measurements” “predictive indices” q q q Why? Avoid unnecessary prolongation. Identify fail trial. Prevent premature weaning. Suggest alterations in managements.

PREDICTIVE VARIABLES. 1. Gas Exchange. a. b. c. d. Pa. O 2>60(FIO 2<35)= -----PAO 2 P(A-a)O 2 < 350. Pa. O 2 / FIO 2 > 200. Pa. O 2/ PAO 2 >. 97.

PREDICTIVE VARIABLES. 2. Ventilation Pump a. VC>10 -15 ml/kg. b. Maximum inspiratory Pressure < -30 cm. H 2 O. c. MV < 10<. d. MV < twice. e. P 0. 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) q Attractive features. – – Easy to measure. Independent of effort. Accurate. Rounded off value (100)

RIB CAGE – ABDOMINAL MOTION “Cohen et al” MCA ---- = VT Maximum Compartmental Amplitude -----------------------Tidal volume Integrative Indices

INTEGRATIVE INDICES CROP Index = Cdyn X P 1 max X (Pa. O 2/PAO 2) ---------------------Respiratory Rate Integrative index = PT 1 X (VE 40/VT sb)

PHYSICAL EXAMINATION q q 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 q Auscultation. q Dyspnoea Level. q Mental Status. q Blood Pressure. q Heart Rate. q Rhythm. q Cyanosis.

METHODS “discontinuing mechanical ventilation” q Older – Spontaneous breathing trial. q 1970 s – Intermittent mandatory ventilation. q 1980 s – Pressure support ventilation. q Continuous positive airway support.

METHODS Spontaneous Breathing Trials “T-Piece Trial” q q q 5 min trial. FIO 2 – 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 The Fatiguing Process Weaning & Ventilatory Failure

FACTORS THAT MAY IMPAIR RSP MUSCLE STRENGTH IN CRITICALLY ILL PATIENTS q q q q q Hypophosphataemia. Hypomagnisaemia. Hypocalcaemia. Hypoxia. Hypercarbia. Acidosis. Infection. Muscle atrophy. Malnutrition.

FACTORS ing THE LOAD ON RESPIRATORY MUSCLES IN PATIENTS IN ICU q q q Bronchoconstriction. Left Ventricular Failure. Hyperinflation. Intrinsic +ve End Expiratory Pressure. Artificial Airways. Ventilator Circuits.

STEP-1 ASSESSMENT PRIOR TO WEANING Able to oxygenate with stable, low inspired O 2 concentrations? No Reventilate patient with weaning mode Yes Patient able to breath spontaneously for 10 min? No

STEP-2 INITIAL ASSESSMENT OF BREATHING Rapid Shallow Breathing Measure f/VT ratio after 5 min of breathing on CPAP circuit

STEP-3 INITIAL ASSESSMENT f/ VT < 80 Measure f/VT ratio after 5 min of breathing on CPAP circuit f/VT <80 Continue spontaneous breathing with CPAP f/VT >80 but <105 Reassess after 30 min No f/VT <80 Yes Extubate after trial of T-piece breathing-9 Yes f/VT <80

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 & orientated? Is Patient triggering ventilator? Is Patient overventilated? Check Pa. CO 2/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 < -20 cm. H 2 O Measure Inspiratory Mouth Pressure PI Max < -20 cm. H 2 O

STEP-7 LOAD APPLIED TO THE RESPIRATORY MUSCLES Measure Applied Load Cdyn < 50 mls/cm H 2 O No Wean Cautiously Recognising Likely Failure