NEWER MODES OF VENTILATION DR.PRATHEEBA DURAIRAJ,M.D,D.A 5.12.2007
Discovery of the potential for mechanical ventilation to produce ventilator-associated lung injury has resulted in the development of new lung protective strategies
AIM • To enhance respiratory muscle rest • Prevent deconditioning / atrophy of muscles • Improve gas exchange • Prevent lung damage • Improve patient synchrony • Help in weaning process
Volume Ventilation • Stable, consistent tidal volume delivery and minute ventilation, which is independent of patient’s lung mechanics BUT • Pressures variable and difficult to control • Resultant high peak pressure • Slow rise to peak pressure, distribution of ventilation may not be optimized • Set flow rate may not match patient’s demand • Increased muscle workload from flow asynchrony, may compromise patient comfort gas exchange cardiac function
Simple Volume System Volume 500 ml Pressure 3500 cm H20 Volume 500 ml
Pop! Simple Volume System Volume 2000 ml Pressure 3500 cm H20
PressureControl Ventilation Benefits • Variable flow capability for patient demand • Reduced patient inspiratory muscle workload • Lower peak inspiratory pressures • Adjustable inspiratory time • Rapid filling of the alveoli • Improved gas distribution, V/Q matching,and oxygenation Disadvantages • Delivered tidal volume is variable and depends upon the patient’s lung mechanics including changes in airway resistance and lung compliance • May have adverse effects on volume delivery
NEWER MODES VOLUME PRESSURE
Clinicians Want the Best of All Possible Worlds Advantages of both pressure and volume ventilation • “You can’t always get what you want,” (Rolling Stones), so…get what you need. • What’s new?
Basic principles • Trigger –machine & patient [flow / presssure ] • Flow triggerig – less work –prefered • Too sensitive – auto triggering • Limit variable [ pressure / volume ] • Cycle variable –volume ,flow ,pressure ,time
TYPES INVASIVE • APRV • BIPAP • Self adaptive modes • Proportional assist ventilation • Independent ventilation • High frequency ventilation • Extracorporeal membrane oxygenation • Liquid ventilation NONINVASIVE
NON INVASIVE VENTILATION • Negative pressure ventilators (Tank and Cuirass ventilators) were the only non-invasive methods of assisting ventilation for many years mainly for ventilating large number of victims of Polio during their acute illness. • use of NIMV has increased in last decade in various conditions to avoid complications of intubation.
Types • Positive Pressure Ventilation • Negative Pressure Ventilation
Mechanism of Action • Improvement in pulmonary mechanics and oxygenation In COPD, oxygen therapy often worsens hypercarbia and respiratory acidosis. Augments alveolar ventilation and oxygenation without raising PaCO2 • Partial unloading of respiratory muscles Reduces trans-diaphragmatic pressure, pressure time index of respiratory muscles and diaphragmatic electromyographic activity - Alteration in breathing pattern with an increase in tidal volume, decrease in respiratory rate and increase in minute ventilation. • NIMV also overcomes the effect of intrinsic PEEP
Advantages of NIMV • Preservation of airway defense mechanism • Early ventilatory support: an option • Intermittent ventilation possible • Patient can eat, drink and communicate • Ease of application and removal • Patient can cooperate with physiotherapy
Contd… • Improved patient comfort • Reduced need for sedation • Avoidance of complications of endotracheal intubation: upper airway trauma, sinusitis, otitis, nosocomial pneumonia • Ventilation outside hospital possible • Correction of hypoxaemia without worsening hypercarbia • Ease to teach paramedics and nurses
Disadvantages • Mask uncomfortable/claustrophobic • Time consuming for medical and nursing staff • Facial pressure sores • Airway not protected • No direct access to bronchial tree for suction if secretions are excessive • Less effective?
Hypercapnic acute respiratory failure Acute exacerbation of COPD Post extubation Weaning difficulties Post surgical respiratory failure Thoracic wall deformities Cystic fibrosis Status asthmaticus Obesity hypoventilation Syndrome Hypoxaemic acute respiratory failure Cardiogenic pulmonary oedema Community acquired pneumonia Post traumatic respiratory failure ARDS Weaning difficulties Chronic Respiratory Failure Immunocompromised Patients Indications of NIMV
Contraindications • Respiratory arrest • Unstable cardiorespiratory status • Uncooperative patients -confused ,agitated • Unable to protect airway- impaired swallowing and cough • Facial Oesophageal or gastric surgery • Craniofacial trauma/burn • Anatomic lesions of upper airway • Vomiting • Impaired conciousness
Relative Contraindications • Extreme anxiety • Massive obesity • Copious secretions • Need for continuous or nearly continuous ventilatory assistance
Prerequisites for successful Non-Invasive support • Patient is able to cooperate • Patient can control airway and secretions • Adequate cough reflex • Patient is able to co-ordinate breathing with ventilator • Patient can breathe unaided for several minutes • Haemodynamically stable • Blood pH>7.1 and PaCO2 <92 mmHg • Improvement in gas exchange, heart rate and respiratory rate within first two hours • Normal functioning gastrointestinal tract
Interface • Interfaces are devices that connect ventilator tubing to the face allowing the entry of pressurized gas to the upper airway. • Nasal and oronasal masks and mouth pieces, CPAP helmet are currently available interfaces. • Masks - made from a non irritant material such as silicon rubber. - minimal dead space and a soft inflatable cuff to provide a seal with the skin. • Nasal mask - better tolerated but less effective – leak • Face masks are more useful in acute respiratory failure • Nasal masks,Mouth piece ,CPAP helmet are used most often in chronic respiratory failure
Advantages FiO2 can be set Alarm & monitoring back up Back up ventilation Separate insp & exp limbs – prevent rebreathing Inspiratory pressure > 20 cm H2O can be set Disadvantages Expensive Less flexible &portable Leak compensation not present – requires tight interface Ventilators - conventional
Advantages cheaper flexible &portable Leak compensation present – does not requires tight interface Inspiratory pressure of 20 cm H2Ois maximum available Disadvantages FiO2 cannot be set Due to leak – high oxygen flows Single limb – rebreathing NPPV Ventilators
Modes of Ventilation • CPAP • It is not a true ventilator mode as it does not actively assist inspiration. • CPAP by nasal mask provides pneumatic splint which holds the upper airway open in patients with nocturnal hypoxaemia due to episodes of obstructive sleep apnoea. • CPAP increases FRC and opens collapsed alveoli. • CPAP reduces left ventricular transmural pressure therefore increases cardiac output. – effective for treatment of pulmonary oedema. • Pressures are usually limited to 5-12 cm of H2O - higher pressure tends to result in gastric distension
BILEVEL POSITIVE AIRWAY PRESSURE [ BI LEVEL PAP] • Unique flow triggering &leak compensation • Spontaneous mode –cycle between IPAP (Up to 30 cm H2O)& EPAP (Up to 15 cm of H2O)- PATIENT TRIGGERED PRESSURE SUPPORTED • IPAP = PEEP +PS / EPAP = PEEP in PCV SPECIAL MACHINES • Have blower unit to compensate air leaks upto 180 L /mt • Pressure limited back up • Adjustable sensitivities ,maximum inspiratory time ,adjustable FiO2 -available
INDICATIONS Worsening hypoventilation/ hypoxemia Chronic ventilatory muscle dysfunction Post intubation difficulty Upper airway obstruction –laryngeal oedema,strictures CONTRA INDICATIONS Unstable Haemodynamics Vomiting Neurologically abnormal Pneumothorax Deterioratingrespiratory parameters BI LEVEL PAP[contd…]
PSV • Non-invasive PSV can be administered with standard critical care ventilator or bilevel portable devices. -patient triggered,pressure limited ,flow cycled ventilation • PSV mode has unique ability to vary inspiratory time breath by breath, permitting close matching with the patient's spontaneous breathing pattern Advantages (a) Patient-ventilator synchrony (b) Improved patient comfort (c) Reduced diaphragmatic work
Volume limited ventilation • ventilators are usually set in assist-control mode with high tidal volume (10-15 ml/kg) to compensate for air leak. • suitable in obesity or chest wall deformity who need high inflation pressure neuromuscular diseases who need high tidal volume for ventilation Proportional assist ventilation (PAV) • This is a newer mode of ventilation. • In this mode ventilator has capacity of responding rapidly to the patients' ventilatory efforts. • By adjusting the gain on the flow and volume signals, one can select the proportion of breathing work that is to be assisted.
Goals of NIMV Short Term • Relieve symptoms • Reduce work of breathing • Improve or stabilize gas exchange • Good patient-ventilator synchrony • Optimize patient comfort • Avoid intubation Long Term • Improve sleep duration and quality • Maximize quality of life • Enhance functional status • Prolong survival
Protocol for Non Invasive Ventilation • Explain to the patient what you are doing and what to expect • Setup the ventilator by the bed side • Keep the head of the patient's bed at >45 degree angle • Choose the correct interface • Turn on the ventilator and dial in the settings • Attach O2 at 2 litres per minute • Hold the mask gently over the patient's face until the patient becomes comfortable with it. Strap the face mask on using the rubber head strap and minimize air leak without discomfort. • Connect humidification system.
Monitor- respiratory rate, heart rate, level of dyspnoea, O2 saturation, blood pressure, minute ventilation, exhaled tidal volume, abdominal distension and ABG • Initial ventilator setting should be very low ie. IPAP of 6 cm H2O, and EPAP of 2 cmH2O • Increase EPAP by 1-2 cm increments till the patient triggers the ventilator in all his inspiratory efforts. • Increase IPAP in small increments, keeping it 4cmH2O above EPAP, to a maximum pressure, which the patient can tolerate without discomfort and major leaks. • Titrate pressure to achieve a respiratory rate of <25 breaths/min and Vt >7ml/kg • Increase FiO2 to improve O2 saturation to 90%
AIR LEAK [80 -100%] MASK RELATED Discomfort Facial skin erythema Claustrophobia Skin necrosis- particularly over bridge of nose Retention of secretions Failure to ventilate Upper airway obstruction FLOW RELATED Nasal congestion Sinus /ear pain Nasal dryness Eye irritation Gastric distension MAJOR COMPLICATIONS Aspiration pneumonia - < 5% Hypotension Pneumothorax Complications and Side effects
MAJOR Respiratory arrest Loss of consciousness Psychomotor agitation Haemodynamic instability Heart rate <50 b/m MINOR Respiratory rate > 35 /mt pH <7.30 Pao2 <45mmHg Intubate when one major / two minor criteria CRITERIA FOR FAILURE OF NPPV
Pressure RegulatedVolume Control [PVRC] • Available on the Servo 300 • Assist control mode • Variable, decelerating flow pattern • Breaths are –patient TRIGGER, time cycled, assist/control Establishes a “learning period” to determine patient’s compliance, which establishes regulation of pressure/volume • Aim – is to deliver preset TV/ MV / frequency with constant pressure [minimum] during the entire inspiration
Pressure RegulatedVolume Control (PRVC) • Inspiratory pressure is regulated based on the Pressure/Volume calculation of the previous breath, compared to a target tidal volume • The ventilator continuously adapts the inspiratory pressure in responses to changing compliance and resistance to maintain the target tidal volume • Results in breath-to-breath variation of inspiratory pressure Limitations: • Only an A/C mode and requires a change to Volume Support for weaning • Only guarantees volume distally and not at patient airway
Applications of PRVC • ALI • Asthma • COPD • Postop patient • Pediatric patient • Pts with no breathing capacity- need initial high flow rates • In whom VT has to be controlled –surfactant therapy
Benefits • Can be used in all populations • Low peak inspiratory pressure • Inspiratory pressure adapts to mechanical properties of lung • ⇩ CVS interference • Improved gas distribution • Less need for sedation • Greater patient comfort
BIPHASIC POSITIVE AIRWAY PRESSURE [BIPAP] • Pressure controlled ventilation allowing spontaneous ventilation • Shifts between two levels of PAP • P low – pressure akin to PEEP In PCV [lowest airway pressure] • P high –pressure above PEEP [P plat] • T high &T low • Subdivisions – CMV to CPAP • Single mode covers entire spectrum • Finer adjustment done after connecting the patient to ventilator in VCV
BIPAP -SUBDIVISIONS • CMV BIPAP-no Spontaneous breathing • IMV –BIPAP –spontaneous breathing at lower level • APRV – BIPAP - spontaneous breathing at higher level • Genuine BIPAP - spontaneous breathing at both levels • CPAP - spontaneous breathing at single CPAP level
Setting up BIPAP • Adjusted with ABG values • High /low PaCO2 /Normal PaO2 • ⇧/⇩ VT/ RR • Alteration of P high /P low – ⇧/⇩VT • Alteration of T high/T low - ⇧/⇩ RR • Decreased PaO2 ⇧mean airway pressure without altering VT/RR equidirectional alteration of P high /P low
ADVANTAGES OF BIPAP • Less sedation • Reduced atelectasis • Ideal mode in pts with inadequate spontaneous effort • In face of deteriorating gas exchange we can increase the invasiveness of ventilation without having to change mode
Airway Pressure Release Ventilation (APRV) • Outlined in 1987 • Continuous positive airway pressure with regular, brief, intermittent releases in airway pressure. • The release phase results in alveolar ventilation and removal of carbon dioxide. • APRV, unlike conventional CPAP, facilitates both oxygenation and CO2 clearance • It is the high CPAP level [referred to as PEEP high or P high] which enhances oxygenation, • Timed releases to the low CPAP level [referred to as PEEP low or P low] aid in CO2 clearance.
APRV –CONTD… • Whereas more conventional modes of ventilation begin the ventilatory cycle at a baseline pressure and elevate airway pressure to accomplish tidal ventilation • APRV commences at an elevated baseline pressure and follows with a measured pressure release. • During APRV, spontaneous breathing may occur at either the plateau pressure or deflation pressure levels. • Available on Dräger and Puritan Bennett ventilators
APRV –CONTD… • Elevated baseline airway pressure during APRV may produce near complete recruitment • Minimizes low volume lung injury from cyclic recruitment • APRV is less likely to produce over-inflation or high-volume lung injury, as airway pressures are lowered (released) to accomplish ventilation. • Needs a High flow CPAP circuit with release valve
Advantages of APRV • Lower peak airway pressures • Lower minute ventilation • Decreased adverse effects upon circulatory function • Spontaneous ventilation the entire ventilatory cycle • Decreased need for sedation • Near elimination of neuromuscular blockade • Recruitment of alveoli
Indications for APRV • ALI or low-compliance lung disease. • patients with airway disease.\ CONTRAINDICATIONS • Patients with Increased airway resistance