Ventilatory supportin special situations Dr.Balamugesh.T, MD, DM Dept. of Pulmonary Medicine, CMC, Vellore.
And the Lord God formed man of the dust of the ground, and breathed into his nostrils and breath of life, and man become a living soul. Genesis 2:7
ARDS • COPD • Bronchial asthma • Bronchopleural fistula
ARDS • Acute onset • Hypoxia- PaO2/FiO2<200 • Bilateral infiltrates on CXR • Absence of left atrial hypertension Mortality - 26% to 74%
Ventilation Induced Lung Injury • Volutrauma – over distention of alveoli • Barotrauma – high inflation pressures • Atelectrauma - repetitive opening and closing of alveoli • Biotrauma - up-regulated cytokine release • Oxygen toxicity
Ventilation in ARDS • Which mode? • How much FiO2? • How much PEEP? • How much VT? • Target? • What if refractory ARDS?
Which mode? • Volume assist/control commonly used • Plateau-pressure goal ≤30 cm of water ARDS Clinical Trials Network
How much FiO2? • Least FiO2 to achieve Oxygenation goal • PaO2 55–80 mm Hg • SpO2 88–95% • FiO2 > 60% risk of oxygen toxicity.
How much Tidal volume? ARDS Network Mortality • Low tidal volume -31% (6 mL/kg predicted body weight) • Conventional tidal volume -40% (12 mL/kg)
PEEP • Improves oxygenation by providing movement of fluid from the alveolar to the interstitial space, • Prevent cyclical alveolar collapse • Recruitment of small airways collapsed alveoli, • Increase in FRC
Open Lung Ventilation (OLV) • Objective - maintenance of adequate oxygenation and avoidance of cyclic opening and closing of alveolar units by selecting a level of PEEP that allows the majority of units to remain inflated during tidal ventilation • Trade off - Hypercapnia
PEEP…. • The lower inflection point on the static pressure–volume curve represents alveolar opening (or “recruitment”). • “optimal PEEP” - The pressure just above this point, is best for alveolar recruitment • usually 10 to 18 mmHg
optimal PEEP J J Cordingley, Thorax 2002;57
How much PEEP? • Low PEEP(8.3±3.2 cm of water) • High PEEP (13.2±3.5 cm) No difference in outcomes if VT- 6ml/kg and Plat. Pressure <30cm N Engl J Med 2004;351
Permissive hypercapia – • usually well tolerated • Consequences • myocardial depression, • Pulmonary hypertension • Raised ICT • Increase RR • Judicious bicarbonate • Tracheal gas insufflation – to wash out dead space CO2
Protective lung ventilation protocol from the ARDSNet study • Initial tidal volume – 6ml/kg • Plat. Pressure <30cm H20 • Oxygenation goal PaO2 = 55 - 80 mmHg or pulse oximetry oxygen saturation 88–95% • I:E ratio 1:1–1:3 • Goal arterial pH = 7.30–7.40 • If pH < 7.30, increase respiratory rate up to 35 breaths/min • If pH < 7.30 and respiratory rate = 35, consider starting intravenous bicarbonate
Refractory hypoxia • 1. Neuromuscular blocking agents (if not already in use) • 2. Prone position ventilation • 3. Recruitment maneuvers • 4. Inverse ratio ventilation, • 5. Miscellaneous – • nitric oxide, • high-frequency ventilation, • extracorporeal membrane oxygenation, or • partial liquid ventilation
Prone position ventilation • Improve oxygenation • Better FRC • Recruitment of dorsal lung • Better clearance of secretion • Better ventilation-perfusion matching • Potential problems • facial oedema, eye damage • dislodgment of endotracheal tubes and intravascular catheters • Difficulty in resuscitation No differences in clinical outcome
Recruitment manoeuvres • Sigh function in ventilators • By ambu bag • Sustained inflation or CPAP of 30-45 cm H20 for 20-120 sec.
Inverse ratio ventilation • Prolongation of the inspiratory time as a method of recruitment • Pressure control ventilation to increase the I:E ratio to 1:1 or 2:1 • hyperinflation and the generation of intrinsic PEEP
Obstructive lung disease • COPD • Asthma
Indications for NIV for AE-COPD GOLD 2005
Exclusion criteria GOLD 2005
Think twice • Reversibility of the precipitating event, • Patient’s/relative’s wishes, and • Availability of intensive care facilities • Failure to wean Mortality among COPD patients with respiratory failure is no greater than mortality among patients ventilated for non-COPD causes GOLD 2005
Post-Intubation hypotension • Reduced venous return secondary to positive intrathoracic pressure due to bagging • Direct vasodilation and reduced sympathetic tone induced by sedative agents
Mechanical ventilation • Avoid overcorrection of respiratory acidosis and life threatening alkalosis. • Prolonged expiratory time. I:E – 1:2.5 to 1:3. • Low Respiratory Rate- 10-14/mt. • Limited tidal volume
PEEP • PEEPe beneficial • Reduce gas trapping by stenting open the airways • Reduce the work to trigger inspiratory flow • As PEEPe is applied, tidal volume will increase without an increase in airway pressure until PEEPe exceeds PEEPi
Allow early extubation Prevent post extubation respiratory failure Post extubation NIV
NIV in asthma • Few trials • Trial of NIV over 1–2 hours in an ICU if there are no contraindications
NIV in acute bronchial asthma • FEV1<40%, PaCO2 <40mm Hg • Conventional medical management Vs BiPAP 15/5 for 3 hours Chest. 2003;123
NIV in asthma…. • 80% NIV group increased FEV1 by >50% as compared to baseline, vs 20% of control patients (p < 0.004) • alleviate the attack faster, and • significantly reduce the need for hospitalization.
Endotracheal intubation • Absolute indications • Cardiopulmonary arrest and • Deteriorating consciousness • Relative • Progressive deterioration, hypercapnia with increasing distress or physical exhaustion
Intubation performed/supervised by experienced anaesthetists or intensivists • Use larger endotracheal tube
• FiO2= 1.0 (initially) • Long expiratory time (I:E ratio >1:2) • Low tidal volume 5–7 ml/kg • Low ventilator rate (8–10 breaths/min) • Set inspiratory pressure 30–35 cm H2O on pressure control ventilation or limit peak inspiratory pressure to <40 cm H2O • Minimal PEEP <5 cm H2O
Aerosol delivery Metered dose inhaler (MDI) system • Spacer or holding chamber • Location in inspiratory limb rather than Y piece • No humidification (briefly discontinue) • Actuate during lung inflation • Large endotracheal tube internal diameter • Prolonged inspiratory time
Jet nebuliser system • Mount nebuliser in inspiratory limb • Consider continuous nebulisation • Increase inspiratory time and decrease respiratory rate • Use a spacer • Stop humidification • Delivery may be improved by inspiratory triggering
Air escaping through the BPF • delays healing of the fistulous track • significant loss of tidal volume, jeopardizing the minute ventilation and oxygenation
Measures to reduce air-leak • Limit the amount of PEEP • Limit the effective tidal volume, • Shorten inspiratory time, • Reduce respiratory rate. • Use of double-lumen intubation with differential lung ventilation,
Chest tube • To add positive intrapleural pressure during the expiratory phase to maintain PEEP • Occlusion during the inspiratory phase to decrease BPF flow
High-frequency ventilation (HFV) • Useful in patients with normal lung parenchyma and proximal BPF • Limited value in patients with distal disease and parenchymal disease.