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Weaning from mechanical ventilation
- 1. Weaning from Mechanical Ventilation Dr.Ram Gopal Maurya
- 2. • Weaning isthe process of withdrawing mechanical ventilatory support and transferring the work of breathing from the ventilator to the patient. • The process of gradually reducing mechanical ventilatory support must be individualized for each patient.
- 3. • Weaning Success:Weaning success is defined as absence of ventilatory support 48 hours following the extubation. • CLASSIFICATION OF WEANING: 1. simple weaning : patients who proceed from initiation of weaning to successful extubation on the first attempt. 2. difficult weaning: patients who fail initial weaning and require up to 7 days from the first SBT to achieve successful weaning. 3. prolonged weaning: require more than 7 days from the first SBT to achieve successful weaning.
- 4. • The simpleweaning group represents 60%- 70% of ventilated patients, the difficult group includes 20%-25% of patients, and the prolonged group includes the remaining 5%- 15% of patients. • Weaning Failure: defined as either the failure of spontaneous breathing trial (SBT) or the need for reintubation within 48 hours following extubation.
- 5. PATIENT CONDITION PRIORTO WEANING • Before weaning, the patient should have recovered from the acute phase of the disease leading to mechanical ventilation and be able to assume adequate spontaneous breathing.
- 6. WEANING CRITERIA • Weaningcriteria are used to evaluate the readiness of a patient for a weaning trial and the likelihood of weaning success. a. Clinical criteria b. Ventilatory criteria c. Oxygenation criteria d. Pulmonary reserve and measurements
- 7. Clinical criteria • Resolutionof acute phase of disease • Adequate cough • Absence of excessive secretions • Cardiovascular and hemodynamic stability
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- 10. QS/QT • physiologic shuntto total perfusion (QS/QT) ratio is used to estimate how much pulmonary perfusion is wasted. • Shunted pulmonary perfusion cannot take part in gas exchange due to mismatch of ventilation (e.g., atelectasis).
- 11. • In clinicalsettings, a calculated physiologic shunt of 10% or less is considered normal. Shunt of 10% to 20% indicates mild physiologic shunt, and shunt of 20% to 30% shows significant physiologic shunt. Greater than 30% shunt reflects critical and severe shunt. • Since physiologic shunt in mechanical ventilation is usually intrapulmonary in origin (inadequate ventilation in relation to pulmonary perfusion), weaning failure becomes likely when spontaneous ventilation cannot keep up with the pulmonary perfusion.
- 12. P(A-a)O2. • The alveolar-arterialoxygen tension gradient (P(A-a)O2) is used to estimate the degree of hypoxemia and the degree of physiologic shunt. • This gradient is directly related to the degree of hypoxemia or shunt (a larger gradient reflects more severe hypoxemia or shunt). • On room air, the P(A-a)O2 should be less than 4 mm Hg for every 10 years in age. • On 100% oxygen, every 50 mm Hg difference in P(A-a)O2 approximates 2% physiologic shunt (Barnes, 1994; Burton et al., 1997; Shapiro et al., 1994).
- 13. • In mechanicalventilation, P(A-a)O2 of less than 350 mm Hg while on 100% oxygen suggests a likelihood of weaning success. P(A- a)O2 of 350 mm Hg while on 100% oxygen approximates 14% shunt and values of greater than 350 mm Hg may hinder the weaning process.
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- 16. Combind weaning indices •Rapid shallow breathing index ( RSBI ) • Simplified weaning index ( SWI ) • Compliance rate oxygenation and pressure ( CROP ) index
- 17. RAPID SHALLOW BREATHINGINDEX (RSBI) • The rapid shallow breathing index (RSBI) or f/VT index has been used to evaluate the effectively of the spontaneous breathing pattern. • The RSBI (f/VT index) is calculated by dividing the spontaneous breathing frequency (breaths/min) by the average spontaneous VT (L). • When the RSBI or f/VT index is greater than 100 breaths/min/L (rounded from 105 breaths/min/L), it correlates with weaning failure. On the other hand, absence of rapid shallow breathing (f/VT ratio ,100 breaths/min/L), is an accurate predictor of weaning success
- 20. • When SWIis less than 9/min,highly predictive (93%) of weaning success • And when SWI is more than 11/min, 95% probability of weaning failure.
- 22. WEANING PROCEDURE • Weaningcan be done using:- 1. Spontaneous breathing trials 2. Pressure support Ventilation 3. Synchronised Mandatory Intermittent Ventilation (SIMV)– Not Recommended alone
- 23. Spontaneous breathing trial(SBT) • An evaluation of a patient’s readiness for weaning from mechanical ventilation and extubation. • SBT is the major diagnostic test to determine if patients can be successfully extubated and weaned from mechanical ventilation. • Spontaneous breathing may be augmented with lowlevel (≤ 8 cm H2O) of pressure support, CPAP, or automatic tube compensation (ATC). • SBT may last up to 30 minutes.
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- 26. Pressure Support Ventilation •helps to reduce the airflow resistance imposed on the patient by the endotracheal tube and ventilator circuit.
- 27. Weaning using SIMV •Based on the results of the sixth International Consensus Conference on Intensive Care Medicine, synchronized intermittent mandatory ventilation (SIMV) should be avoided as a stand-alone weaning modality (Boles et al., 2007). However, SIMV remains an effective tool in providing partial ventilatory support during continuous mechanical ventilation.
- 28. • Automatic TubeCompensation. Automatic tube compensation (ATC) is a mode in the Evita 4 ventilator (Dräger Medical) that reduces the airflow resistance imposed by the artificial airway (endotracheal or tracheostomy tube). It allows the patient to have a breathing pattern as if breathing spontaneously without an artificial airway. This type of compensation may facilitate breathing efficacy and reduce the work of breathing throughout the weaning process.
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- 30. Termination criteria: • Spontaneousfrequency >35/min for 5 min; • SpO2 < 90%, • Heart rate >140/min or 120% of baseline; • Systolic pressure >180 mm Hg or ,< 90 mm Hg; • Signs of anxiety or use of accessory muscles.
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- 34. CAUSES OF WEANINGFAILURE • Aside from the pathological conditions that lead to the need for mechanical ventilation, weaning failure may occur when the work of spontaneous breathing becomes too great for the patient to sustain. • Weaning failure is generally related to (1) increase of airflow resistance, (2) decrease of compliance, or (3) respiratory muscle fatigue.
- 35. Increase of AirflowResistance • Normal subjects using an endotracheal (ET) tube have an increase of 54% to 240% in the work of breathing, depending on the size of the ET tube and ventilator flow rate. • To minimize this ET tubes of larger size should be used when it is appropriate to the patient’s size & the ET tube may be cut to about an inch from the patient’s lips.
- 36. Other strategies fordecreasing airway resistance • periodic monitoring of the ET tube for kinking or obstructions by secretions, or other devices attached to the ET tube such as a continuous suction catheter, heat and moisture exchanger, or end-tidal CO2 monitor probe. • Endotracheal suctioning to remove retained secretions and use of bronchodilators to relieve bronchospasm have also been used successfully to reduce the airflow resistance.
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- 39. • following topicsshould be evaluated in a diffi cult-towean patient: 1. Airway And Lung Dysfunction, 2. Brain Dysfunction, 3. Cardiac Dysfunction, 4. Diaphragm Dysfunction, And 5. Endocrine Dysfunction.
- 40. Airway and lungdysfunction • Elevated airway resistance, reduced respiratory system com pliance, and impaired gas exchange increase the work of breathing
- 41. Brain dysfunction • Braindysfunction in diffi cult-to-wean patients is related mostly to delirium. • Other psychological disturbances, such as anxiety and depression, may interfere with successful weaning.
- 42. Cardiac dysfunction • The transition from mechanical ventilation to spon taneous breathing imposes an additional load on the cardiovascular system because of intrathoracic pressure changes, which aff ect ventricular preload and afterload and increased oxygen consumption by the respiratory muscles. • In patients with COPD but without cardiac disease, weaning was associated with a signifi cant reduction in left ventricle ejection fraction and this reduction was probably due to increased left ventricular afterload.
- 43. • Diagnostic approach 1.electrocardiography at the fi nal stages of the weaning trial to detect ischemia 2. SvO2 could be used as a screening tool for cardiac dysfunction in difficult weaning. Th e decrease in SvO2 resulted from the inability to improve cardiac output and therefore oxygen transport. 3. BNP 4. Echocardiography.
- 44. Treatment strategies • Indiffi cult-to-wean patients with evidence of cardiac failure, afterload reduction and ultimately the use of inotropes must be considered.
- 45. Diaphragm/respiratory muscle function • Diaphragm/respiratorymuscle weakness can be one of the cause of weaning failure. • It should be kept in mind that dysfunction of the respiratory muscle may result from a lesion anywhere between the aff erent chemo- receptors of the respiratory centers and the contractile proteins. • Some commom etiology: disuse atrophy; Critical illness polyneuropathy and myopathy; malnutrition; electrolyte imbalance; etc
- 46. • Diaphragmatic strengthis obtained by stimulation of the phrenic nerves and recording the resulting transdiaphragmatic pressure (Pdi). Weaning-failure patients have twitch Pdi values below 10cm H2O, whereas values of 35 to 39cm H2O are observed in healthy subjects. • Diaphragmatic rapid shallow breathing index/ diaphragmatic excursion can also be used for weaning.
- 47. Treatment strategies • Mechanicalventilation is a double-edged sword for the respiratory muscles. • Antioxidants: Antioxidant supplementation was associated with a reduction in ventilator- dependent days
- 48. Endocrine and metabolicdysfunction • adrenal insuffi ciency. • Hypothyroidism. • Malnutrition. • Electrolyte abnormalities, including very low plasma levels of phosphate and magnesium, have been shown to aff ect skeletal muscle function.