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ALOK SINHA Department of Medicine Manipal College of Medical Sciences Pokhara, Nepal.

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Presentation on theme: "ALOK SINHA Department of Medicine Manipal College of Medical Sciences Pokhara, Nepal."— Presentation transcript:

1 ALOK SINHA Department of Medicine Manipal College of Medical Sciences Pokhara, Nepal

2 Inability of the lungs to perform the function of gas exchange- the transfer of oxygen from inhaled air into the blood and the transfer of carbon dioxide from the blood into exhaled air Defined as a PaO 2 value of less than 60 mm Hg while breathing air PaO 2 value of less than 60 mm Hg while breathing air or a PaCO 2 of more than 50 mm Hg or a PaCO 2 of more than 50 mm Hg

3 Classification Type 1 Type 1 hypoxemic respiratory failure Type 2 Type 2 hypercapnic respiratory failure Acute Chronic

4 Respiratory failure is caused by: 1. failure to oxygenate characterized by decreased PaO 2 characterized by decreased PaO 2 2. failure to ventilate characterized by increased PCO 2 characterized by increased PCO 2

5 1. Failure to oxygenate: due to ecreased inspired O 2 tension increased CO 2 tension ventilation perfusion mismatch Pneumonia Oedema P E reduced O 2 diffusion capacity due to interstitial edema fibrosis thickened alveolar wall Deoxygenated blood from pulmonary artery

6 V – Q Mismatch V/Q incresed = physiological dead space V/Q incresed = physiological dead space Pulmonary embolism Pulmonary embolism Obliteration of blood vessels Obliteration of blood vessels emphysema emphysema V/Q reduced = physiological shunt V/Q reduced = physiological shunt Collapse of alveoli – atelectasis Loss of surfactant Airway obst. - COPD Fluid filling Anatomical shunt increased – anastomosis between pulmonary & systemic vessels

7 2. Failure to ventilate Causes: Airway Respiratory muscles Chest wall Respiratory centers

8 Hypoxemic (type I) PaO2 <60 mm Hg PaO2 <60 mm Hg CO2 level may be normal CO2 level may be normal or low or low associated with virtually all acute diseases of lung with associated with virtually all acute diseases of lung with V/Q mismatch Common causes C.O.P.D. C.O.P.D. Pneumonia Pneumonia Pulmonary edema Pulmonary edema Pulmonary fibrosis Pulmonary fibrosis Asthma Asthma Hypercapnic (type II) PaCO2 of >50 mm Hg pH depends on the level of bicarbonate, dependent on the duration of hypercapnia caused by- Alveolar hypoventilation C.O.P.D. Neuromuscular disorders Guillain-Barré syndrome Diaphragm paralysis Amyotrophic lateral sclerosis Muscular dystrophy Myasthenia gravis severe obstruction with a FEV1 of less than 1 L or 35% of normal

9 Pulmonary embolism Pulmonary embolism Pulmonary arterial hypertension Pulmonary arterial hypertension Pneumoconiosis Pneumoconiosis Granulomatous lung diseases Granulomatous lung diseases Cyanotic congenital heart disease Cyanotic congenital heart disease Bronchiectasis Bronchiectasis Adult respiratory distress syndrome Adult respiratory distress syndrome Fat embolism syndrome Fat embolism syndrome Chest wall deformities Kyphoscoliosis Ankylosing spondylitis Central respiratory drive depression Drugs - Narcotics, benzodiazepines, barbiturates Neurologic disorders - Encephalitis, brainstem disease, trauma Primary alveolar hypoventilation Obesity hypoventilation syndrome (Pickwickian Syn)

10 730 KG BMI 252 Carol Yager (1960 – 1994)

11 Acute and chronic respiratory failure Acute respiratory failure develops over minutes to develops over minutes toHours No time for renal compen. No time for renal compen. pH is less than 7.3. pH is less than 7.3. clinical markers of chronic clinical markers of chronicHypoxemia- polycythemia polycythemia cor pulmonale cor pulmonale Are absent Chronic respiratory failure develops over several days allowing time for renal compensation develops over several days allowing time for renal compensation an increase in bicarbonat conc. an increase in bicarbonat conc. pH -only slightly decreased. pH -only slightly decreased. clinical markers of chronic clinical markers of chronic hypoxemia hypoxemia polycythemia cor pulmonale Are present

12 Alveolar-to-arterial PaO 2 difference ( A-a Gradient) Determines the efficiency of lungs at carrying out of respiration Aa Gradient = ( /4(PCO 2 )) - PaO 2 Aa Gradient = ( /4(PCO 2 )) - PaO 2 Normal < 10mm increase in alveolar-to-arterial PO 2 above 15- increase in alveolar-to-arterial PO 2 above mm Hg indicates pulmonary disease as the cause of hypoxemia Normal in Hypoventilation Normal in Hypoventilation

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14 Underlying disease process (pneumonia, pulmonary edema, asthma, COPD) associated hypoxemia hypercapnia

15 Hypoxemia Symptoms shortness of breath confusion & restlessness Seizures coma Signs Cyanosis variety of arrhythmias from hypoxemia & acidosis Polycythemia – in long-standing hypoxemia

16 Hypercapnia Vasodilation leading to Morning headache flushed skin & warm moist palms full & bounding pulse Extrasystoles & other arrythmias muscle twitches flapping tremors - asterixis drowsiness Asterix

17 Now answer this question- If you are forced to choose one of these, which one you will like to have HypoxiaHypercapnia ?

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19 . A.B.G. (arterial blood gases) complete blood count anemia anemia contribute to tissue hypoxia contribute to tissue hypoxia polycythemia polycythemia indicate chronic hypoxemic respiratory failure indicate chronic hypoxemic respiratory failure Associated organ involvement R.F.T. R.F.T. L.F.T. L.F.T.

20 Chest radiograph frequently reveals the cause of respiratory failure distinguishes between cardiogenic cardiogenic noncardiogenic pulmonary edema noncardiogenic pulmonary edemaEchocardiography when cardiac cause of acute respiratory failure is suspected when cardiac cause of acute respiratory failure is suspected left ventricular dilatation left ventricular dilatation regional or global wall motion abnormalities regional or global wall motion abnormalities severe mitral regurgitation severe mitral regurgitation provides an estimate of right ventricular function and pulmonary artery pressure in patients with chronic hypercapnic respiratory failure provides an estimate of right ventricular function and pulmonary artery pressure in patients with chronic hypercapnic respiratory failure

21 Other Tests PFT in the evaluation of chronic respiratory failure in the evaluation of chronic respiratory failure ECG to evaluate the possibility of a cardiovascular cause of respiratory failure to evaluate the possibility of a cardiovascular cause of respiratory failure dysrhythmias resulting from severe hypoxemia and/or acidosis dysrhythmias resulting from severe hypoxemia and/or acidosis

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23 Hypoxemia major immediate threat to organ function oxygen supplementation and/or ventilatory assist devices The goal is to assure adequate oxygen delivery to tissues, generally achieved with a The goal is to assure adequate oxygen delivery to tissues, generally achieved with a PaO 2 of 60 mm Hg or more SaO 2 of greater than 92%

24 Supplemental oxygen administered via nasal prongs face mask in severe hypoxemia, intubation and mechanical ventilation often are required Airway management Adequate airway vital in a patient with acute respiratory distress The most common indication for endotracheal intubation (ETT) is respiratory failure What is the role of tracheostomy??

25 Hypercapnia without hypoxemia generally well tolerated not a threat to organ function hypercapnia should be tolerated until the arterial blood pH falls below 7.2 hypercapnia and respiratory acidosis managed by correcting the underlying cause providing ventilatory assistance Treatment of coexisting condition with approptiate drugs

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27 Mechanical ventilation is a method to Mechanical ventilation is a method to mechanically assist mechanically assist or or replace spontaneous breathing replace spontaneous breathing

28 Mechanical Ventilatior What is it? Mechanical Ventilatior What is it? Machine that generates a controlled flow of gas into a patients airways Machine that generates a controlled flow of gas into a patients airways Oxygen and air are received from cylinders or wall outlets blended according to the prescribed inspired oxygen tension (FiO 2 ) Oxygen and air are received from cylinders or wall outlets blended according to the prescribed inspired oxygen tension (FiO 2 ) Delivered to the patient using one of many available modes of ventilation.The magnitude of rate and duration of flow are determined by the operator Delivered to the patient using one of many available modes of ventilation.The magnitude of rate and duration of flow are determined by the operator

29 INDICATIONS FOR TRACHEAL INTUBATION AND MECHANICAL VENTILATION Body_ID: B Protection of airway Removal of secretions Hypoxaemia PaO 2 < 60 mmHg SpO Hypercapnia if conscious level impaired or risk of raised intracranial pressure Increased Alveolar-arterial gradient of oxygen tension (A-a DO 2 ) with 100% oxygenation Vital capacity falling below 1.2 litres in patients with neuromuscular disease Removing the work of breathing in exhausted patients

30 Ventilatory workload is increased by loss of lung compliance Ventilatory workload is increased by loss of lung compliance inspiration/ventilation is usually supported to reduce O2 requirements and increase patient comfort inspiration/ventilation is usually supported to reduce O2 requirements and increase patient comfort

31 Respiratory failure is caused by 1. Failure to ventilate characterized by increased PCO 2 characterized by increased PCO 2 2. Failure to oxygenate characterized by decreased PaO 2 characterized by decreased PaO 2

32 Failure to ventilate Increase the patients alveolar ventilation Increase the patients alveolar ventilation rate rate depth of breathing depth of breathing by using mechanical ventilation

33 Failure to oxygenate Restoration and maintenance of lung volumes by using recruitment maneuvers Recruitment maneuvers are used to reinflate collapsed alveoli: due to pressure generated by ventilator during inspiration alveoli are inflated PEEP is used to prevent derecruitment

34 What do we mean by PEEP ? Girls changing room

35 PEEP amount of pressure above atmospheric pressure present in the airway at the end of the expiratory cycle amount of pressure above atmospheric pressure present in the airway at the end of the expiratory cycle PEEP improves gas exchange by preventing alveolar collapse recruiting more lung units increasing functional residual capacity redistributing fluid in the alveoli

36 Dangers of PEEP Overdistension of lungs – Barotrauma Will increase intracranial tension Reduce venous return to right side of heart leading to reduced cardiac out put & hypotension The ideal level of PEEP is that which prevents derecruitment of the majority of alveoli, while causing minimal overdistension The ideal level of PEEP is that which prevents derecruitment of the majority of alveoli, while causing minimal overdistension

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38 Modes of ventilation: Air flow continues until Air flow continues until a predetermined volume has been delivered – volume controlled a predetermined volume has been delivered – volume controlled airway pressure generated – pressure controlled airway pressure generated – pressure controlled

39 Flow reverses, when the machine cycles into the expiratory phase, the message to do this is Flow reverses, when the machine cycles into the expiratory phase, the message to do this is either at a preset time either at a preset time preset tidal volume preset tidal volume preset percentage of peak flow preset percentage of peak flow

40 Mechanical breaths may be Mechanical breaths may be Controlled ( Controlled ( Controlled mandatory ventilation -CMV) ventilator is active ventilator is active patient passive patient passive assisted ( assisted ( Synchronised intermittent mandatory ventilation - SIMV) patient initiates and may or may not participate in the breath patient initiates and may or may not participate in the breath

41 Controlled mandatory ventilation (CMV) Most basic classic form of ventilation Pre-set rate and tidal volume Does not allow spontaneous breaths Appropriate for initial control of patients with little respiratory drive severe lung injury circulatory instability

42 Synchronized Intermittent Mandatory Ventilation (SIMV) method of partial ventilatory support to facilitate liberation from mechanical ventilation method of partial ventilatory support to facilitate liberation from mechanical ventilation patient could breathe spontaneously while also receiving mandatory breaths patient could breathe spontaneously while also receiving mandatory breaths As the patients respiratory function improved, the number of assisted is decreased, until the patient breaths unassisted As the patients respiratory function improved, the number of assisted is decreased, until the patient breaths unassisted

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44 Iron Lung

45 CONDITIONS REQUIRING MECHANICAL VENTILATION Post-operative After major abdominal or cardiac surgery Respiratory failure ARDS Pneumonia COPD Acute severe asthma Aspiration Smoke inhalation, burns Circulatory failure Following cardiac arrest Pulmonary oedema Low cardiac output-cardiogenic shock Neurological disease Coma of any cause Status epilepticus Drug overdose Respiratory muscle failure (e.g. Guillain-Barré, poliomyelitis, myasthenia gravis) Head injury-to avoid hypoxaemia and hypercapnia, and to reduce intracranial pressure Bulbar abnormalities causing risk of aspiration (CVA, myasthenia gravis) Multiple trauma

46 TERMS USED IN MECHANICAL VENTILATORY SUPPORT Controlled mandatory ventilation (CMV) Most basic classic form of ventilation Pre-set rate and tidal volume Does not allow spontaneous breaths Appropriate for initial control of patients with little respiratory drive, severe lung injury or circulatory instability Synchronised intermittent mandatory ventilation (SIMV) Pre-set rate of mandatory breaths with pre-set tidal volume Allows spontaneous breaths between mandatory breaths Spontaneous breaths may be pressure-supported (PS) Allows patient to settle on ventilator with less sedation Pressure controlled ventilation (PCV) Pre-set rate; pre-set inspiratory pressure Tidal volume depends on pre-set pressure, lung compliance and airways resistance Used in management of severe acute respiratory failure to avoid high airway pressure, often with prolonged inspiratory to expiratory ratio (pressure controlled inverse ratio ventilation, PCIRV) Pressure support ventilation (PSV) Breaths are triggered by patient Provides positive pressure to augment patient's breaths Useful for weaning Usually combined with CPAP; may be combined with SIMV Pressure support is titrated against tidal volume and respiratory rate

47 Continuous positive airways pressure (CPAP) Positive airway pressure applied throughout the respiratory cycle, via either an endotracheal tube or a tight-fitting facemask Improves oxygenation by recruitment of atelectatic or oedematous lung Mask CPAP discourages coughing and clearance of lung secretions; may increase the risk of aspiration Bi-level positive airway pressure (BiPAP/BIPAP) Describes situation of two levels of positive airway pressure (higher level in inspiration) In fully ventilated patients, BiPAP is essentially the same as PCV with PEEP In partially ventilated patients, and especially if used non-invasively, BiPAP is essentially PSV with CPAP Non-invasive intermittent positive pressure ventilation (NIPPV) Most modes of ventilation may be applied via a facemask or nasal mask Usually PSV/BiPAP (typically cmH 2 O) often with back-up mandatory rate Indications include acute exacerbations of COPD

48 Of mechanical ventilation

49 Large tidal volumes overstretch alveoli and injure the lungs Small tidal volumes increase the contribution to dead space – wasted ventilation

50 Large PEEP overstretch alveoli and injure the lungs Small PEEP does not correct V/Q mismatch & derecruitment

51 There is no ideal mode of ventilation for any particular patient There is no ideal mode of ventilation for any particular patient The science of mechanical ventilation is to optimize pulmonary gas exchange The art is to achieve this without damaging the lungs.

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54 Major immediate complication 1. Hypotension due to vasodilatory effects of hypnotic drugs due to vasodilatory effects of hypnotic drugs Treated with vasoconstrictors Treated with vasoconstrictors have an ampule of phenylephrine (a selective alpha adrenoceptor agonist) at hand to reverse vasodilatory hypotension have an ampule of phenylephrine (a selective alpha adrenoceptor agonist) at hand to reverse vasodilatory hypotension Increase in intrathoracic pressure Increase in intrathoracic pressure Treated with fluid boluses Treated with fluid boluses Always have an intravenous fluid drip running and be prepared to run in a liter or more of fluid quickly Always have an intravenous fluid drip running and be prepared to run in a liter or more of fluid quickly

55 2. Barotrauma Pneumothorax Pneumothorax subcut emphysema subcut emphysema 3. VALI (Ventilator Associated Lung Injury) 4. O2 toxicity 5. From prolonged immobility and inability to eat normally venous thromboembolic disease venous thromboembolic disease skin breakdown skin breakdown atelectasis atelectasis Late complications

56 6. From endotracheal intubation ventilator-associated pneumonia (VAP) ventilator-associated pneumonia (VAP) tracheal stenosis tracheal stenosis vocal cord injury vocal cord injury tracheal-esophageal or tracheal-vascular fistula tracheal-esophageal or tracheal-vascular fistula

57 Measures to reduce complications Elevating the head of the bed to > 30° decreases risk of ventilator-associated pneumonia Elevating the head of the bed to > 30° decreases risk of ventilator-associated pneumonia routine turning of patient every 2 h decreases the risk of skin breakdown routine turning of patient every 2 h decreases the risk of skin breakdown Keep the PEEP & TV in optimal range Keep the PEEP & TV in optimal range All patients receiving mechanical ventilation should receive deep venous thrombosis prophylaxis All patients receiving mechanical ventilation should receive deep venous thrombosis prophylaxis

58 Some special techniques 1. Inhaled nitric oxide very short-acting pulmonary vasodilator very short-acting pulmonary vasodilator Delivered to the airway in concentrations of between 1 and 20 parts per million Delivered to the airway in concentrations of between 1 and 20 parts per million Improves blood flow to ventilated alveoli, thus improving V/Q mismatch, Oxygenation can be improved markedly Improves blood flow to ventilated alveoli, thus improving V/Q mismatch, Oxygenation can be improved markedly benefit only lasts for 48 hours and outcome is not improved benefit only lasts for 48 hours and outcome is not improved

59 2. techniques 2. techniques to reduce the high inflation pressures resulting from the stiff lungs (low compliance) 1. Low tidal volumes to reduce inflation pressures (6 ml/kg ideal body weight compared to 12 ml/kg) reduces mortality Minute ventilation reduced PaCO2 rises – permissive hypercapnia

60 3. Inverse ratio ventilation : may improve oxygenation PCO 2 may rise further 4. Prone positioning: improves oxygenation in ~70% of patients with ARDS


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