Mechanical Ventilation (2)

SEMINAR ON MECHANICAL VENTILATION Guide Dr. G.Singh (MS) Co-Guide Dr. A.M. Lakra (MD) -Rajan Kumar

Introduction Cornerstone for intensive care medicine Ventilate is derived from Latin word “ventus” meaning wind. Ventilation is movement of air into and outside the body The ventilators must overcome the pressure generated by the elastic recoil of the lung at end inspiration plus the resistance to flow at the airway. Ventilators provide infusion of a blend of air or oxygen into the circuit.

History In 1543, Vesalius demonstrated the ability to maintain the beating heart in animals with open chest. In 1780, such technique were first applied to humans In 1887, fell-o-dwyer apparatus was used for translaryngeal ventilation via a bellows. In 1928, the drinker–Shaw iron lung based on negative pressure ventilation From 1930-1950 – such machines were the mainstay in ventilation of victims of polio epidemics

Respiratory physiology Tidal volume Respiratory rate Minute volume Inspiratory Reserve Volume Expiratory Reserve Volume Inspiratory Capacity (IRV + TV) Residual Volume Functional Residual Capacity (ERV + RV) Vital capacity (IRV + TV + ERV) Total Lung Capacity (IRV + TV + ERV + RV) Compliance Dead space

MECHANICAL VENTILATOR Ventilators are specially designed pumps that can support the ventilatory function of the respiratory system and improve oxygenation through application of high oxygen content gas and positive pressure.

Components Bacterial filter Pneumotachometer, valves & solenoids Humidifier Heater/ thermostat Oxygen analyser Pressure manometer Chamber for nebulising drug Compressor Battery

Goals Achieve and maintain adequate pulmonary gas exchange Minimise the risk of lung injury Reduce patient work of breathing Optimise patient comfort

Classification 1. ICU Ventilators The condition of lung is poor 2. Anaesthetic ventilators The condition of lung is good 3. Transport ventilator The ventilator is compact and used for transportation of victim/patients from one site to other 4. Other/special (a) High frequency ventilator (i) High frequency positive pressure ventilator (ii) High frequency jet ventilator (iii) High frequency oscilitation ventilator

ICU ventilator A. Positive pressure ventilation (PPV) (a) Non invasive PPV (i) Nasal mask (ii) Facial mask These has less complications and as effective as invasive ventilators (b) Invasive PPV (i) Nasotracheal tube (ii) Oro tracheal tube (iii) Tracheostomy

B.Negative pressure ventilation Iron lung machine The machine creates a negative pressure to expand the chest wall so that the lungs can expand inside it with the negative intrapleural pressure.

Ventilator cycle pause pause inspiration expiration

Principles Gas flows only down the pressure gradient, i.e. from areas of high pressure to low pressure. Exhalation is a passive process, ventilators expend energy only during inhalation

Mechanical ventilation is produced through the interaction of only 5 variables Time Volume Pressure inspiratory: expiratory (I:E) ratio Flow

Objectives Improve O2 &CO2 gas exchange Reverse hypoxemia Prevent progressive hypercapnia Reverse acute respiratory acidosis Improve ventilation distribution Prevent and reverse lung collapse Reduce venous admixture

Assist respiratory muscle Decreased O2 cost of breathing Relieve resp. distress Improve lung compliance Increase alveolar recruitment - Return lung to resting lung volumes

Indications On the basis of blood gas analysis 1. PO2 <50mmHg on room air <60mmHg on oxygen support (FIO2 >50%) 2. PCO2 >50mmHg 3. pH <7.25 4. PO2/FIO2 <250mmHg 5. p (A-a ) O2 gradient >350 mmHg on 100% O2.

On the basis of pulmonary function Resp. Rate >35/min Vital capacity <15ml/kg Dead space volume (VD/VT) >0.6 (60%) Tidal volume <5ml/kg

Basic physics related to mechanical ventilation Paw = flow× resistance + volume ∕ compliance + PEEP Pressure at point B is equivalent to the alveolar pressure and is determined by the volume inflating the alveoli divided by the compliance of the alveoli plus the baseline pressure (PEEP). Pressure at point A (equivalent to airway pressure measured by the ventilator) is the sum of the product of flow and resistance due to the tube and pressure at point B.

Flow, volume and pressure are variables while resistance and compliance are constants. It follows from the relationship between pressure, flow and volume that by setting one of pressure, volume or flow and the pattern in which it is delivered which includes the time over which it is delivered the other two become constants. It also follows that it is not possible to present more than one of these variables at a time.

Cycling Time cycled Pressure cycled Volume cycled

Time cycled – these cycle to expiration once a predetermined time is elapsed since inspiration. Tidal volume is determined by set inspiratory flow and inspiratory time Used in Operation theaters In neonates

Pressure cycled These cycled to expiration once a predetermined pressure is reached, so if there is leak in circuit the predetermined pressure will not reached and pt. will remain in inspiration conversely, if airway pressure is high, bronchospasm or tube kinking there will be premature end of inspiration and patient can be hypoventilated.

Volume cycled – Inspiration is terminated when a preset tidal volume is delivered. So theoretically, the patient cannot be hypoventilated even if the lung compliance (airway pressure) changes but actually this is not the case, a portion of tidal volume is lost (120-150ml) in the ventilator breathing circuit and if patient’s pulmonary compliance is decreased (peak inhalation pressure will increase) the delivered tidal volume can further be decreased.

The accurate, tidal volume reaching to patients can only be calculated by putting a spirometer at the endotracheal tube. e.g. most commonly used in ICUs Disadvantage – they deliver fixed tidal volume so if airway pressure becomes high and still same tidal volume is be delivered the chances of barotrauma are increased. Dual control – can work in both volume control and pressure control mode and can switch over from one mode to other depending on requirements.

Modes of mechanical ventilations Characterized by three variables The parameter used to initiate or ‘ trigger ’ a breath The parameter used to ‘ limit ’ the size of breath, and the parameter used to terminate inspiration or ‘ cycle ’ the breath.

In controlled ventilation modes – time triggered Inspiratory phase is concluded once a desired volume, pressure or flow is attained but the expiratory time (Et) will form the difference between the inspiratory time (It) and the preset respiratory cycle time. In Assist mode – the ventilator is pressure or flow triggered The magnitude of the breath is controlled or limited by one of three variables Volume, pressure or flow.

Controlled mode ventilation(CMV)/ intermittent positive pressure ventilation (IPPV): in this mode patient’s own effort is nil. Only ventilator is delivering the preset tidal volume at preset frequency Assist controlled ventilation(AC): in this mode assist means the ventilator supplementation of patient initiated breath (which itself doesnot have adequate tidal volume) and control means back up rate which is set up by clinician.

Synchronized intermittent mandatory ventilation (SIMV ): in this mode ventilator will deliver only between patient’s efforts or to coincide with the beginning of spontaneous effort. Advantages of SIMV over CMV Less haemodynamic depression Patient on CMV/IPPV need heavy sedation or muscle relaxant. Less V/Q mismatch No sense of breathlessness between ventilatory cycles More rapid weaning

Disadvantages 1.increased work of breathing can cause muscular fatigue. 2.increased chances of hypocapnia (due to hyperventilation) Positive end expiratory pressure (PEEP) indications pulmonary edema ARDS In thoracic surgery to minimize postoperative bleeding. Physiological PEEP (in normal intubated patient to prevent atelectasis)

Mechanism of PEEP Positive pressure given at end expiration prevents alveoli to collapse and small airways to close. So more time is available for gaseous exchange Side effects of PEEP Hypotension and decrease in cardiac output: PEEP compresses venules in alveolar septa leading to decreased venous return. So optimal PEEP is the value which maintain oxygen saturation >90% without decreasing the cardiac output significantly. Increased pulmonary artery pressure and right ventricular strain: it is due to compression of capillaries in alveolar septa. Increased dead space because of overdistension of normal alveoli. Increased pleural and mediastinal pressure. These increased pressures can cause pulmonary barotrauma

Inverse ratio ventilation (IRV): ratio of inspiration to expiration is reversed(2:1, while normal ratio is 1:2). Prolonged inspiration will maintain positive pressure. So more or less it acts like PEEP. It is better than PEEP and there is even distribution of ventilation. Pressure support ventilation (PSV ): if a patient is on spontaneous respiration with adequate frequency but not adequate tidal volume,this mode is helpful in increasing the tidal volume.

Pressure controlled ventilation (PCV): in this mode pressure is preset and ventilator terminates inspiration once preset pressure is achieved. So if airway pressure varies patient is prone for ventilation but advantage is that chances of barotrauma is less and there is choice of extending inspiratory time, facilitating better oxygen.

BIPAP : bipap means positive pressure both during inspiration and expiration. Typical setting is 8-20 cm H2O positive pressure during inspiration and 5 cm H2O during expiration.it is combination of PSV and PEEP. Airway pressure release ventilation (APRV) applied to patient on CPAP where there is periodic release of CPAP to decrease the incidence of barotrauma and hypotension.

High frequency ventilation : this mode is applicable in conditions in which adequate tidal volume cannot be delivered. So minute volume is maintained by high frequency.

TYPES OF WAVES FORMS Pressure waveforms Rectangular Exponential rise Sine Volume waveforms Ascending ramp Sinusoidal Flow waveforms Rectangular Sinusoidal Ascending ramp Descending ramp Exponential decay

Setting of ventilator Tidal volume I:E ratio Frequency PEEP Trigger sensitivity (for assist mode) FIO2 5-7 ml/kg 1:2 10-12 bpm 3–5 cmH2O -1 to -2 cmH2O 50%

Normal ABG Values pH PaCO2 PaO2 SaO2 HCO3 ¯ Base excess 7.35 - 7.45 35 – 45 mmHg 70 – 100 mmHg 93 - 98% 22 – 26 mEq/L -2.0 to 2.0 mEq/L

Ventilator parameters adjustment according to blood gases _____ PO2 _____ PO2 ____ ____ PCO2 ____ ____ PCO2 Ti FiO2 RATE PEEP PIP Goals

Monitoring Clinical Radiological Biochemical Bacteriological others

Clinical monitoring General Appearance Level of activity Response to stimulus Eye opening Posture Perfusion Color Edema

Movement of chest Retractions Synchronization Air entry Adequacy of mechanical breath

Pulse oximetry EtCO2 monitoring ABG analysis Capillary gas determination Transcutaneous monitoring Oxygenation indices Monitoring of O2 & CO2 status

Ventilator Parameters PIP PEEP MAP RR Ti & I:E Ratio FiO2 VT Trends of Ventilator Parameters Pulmonary Graphics

Hemodynamic Stability Oxygenation Adequacy of Circulation

Radiological Monitoring When to do Chest X-ray ? At the start of ventilation Before surfactant administration After ET tube change Sudden deterioration Prior to extubation Post extubation

Biochemical Monitoring Blood Gases Blood Sugar Serum calcium Serum electrolytes

Bacteriological Monitoring Blood culture ET tube culture

Other Monitoring Humidification & warming of ventilator circuit gases Position of patient Skin Fluid & electrolytes Nutrition status Sensorium Infection control

Sedation in Mechanically Ventilated Patients Benzodiazepines Opioids Neuroleptics Propofol Ketamine Dexmedetomidine

Maintenance of Sedation Titrate dose to ordered scale Motor Activity Assessment Scale MAAS Sedation-Agitation Scale SAS Modified Ramsay Sedation Scale Rebolus prior to all increases in the maintenance infusion Daily interruption of sedation

NEUROMUSCULAR BLOCKING AGENTS Difficult to asses adequacy of sedation Polyneuropathy of the critically ill Use if unable to ventilate patient after patient adequately sedated Have no sedative or analgesic properties

Troubleshooting Is it working ? Look at the patient !! Listen to the patient !! Pulse Ox, ABG, EtCO 2 Chest X ray Look at the vent (PIP; expired TV; alarms)

Troubleshooting When in doubt, DISCONNECT THE PATIENT FROM THE VENT, and begin bag ventilation. Ensure you are bagging with 100% O2. This eliminates the vent circuit as the source of the problem. Bagging by hand can also help you gauge patient’s compliance

Troubleshooting Airway first: is the tube still in? (may need DL/EtCO2 to confirm) Is it patent? Is it in the right position? Breathing next: is the chest rising? Breath sounds present and equal? Changes in exam? Atelectasis, bronchospasm, pneumothorax, pneumonia? (Consider needle thoracentesis) Circulation: shock? Sepsis?

Troubleshooting Well, it isn’t working….. Right settings ? Right Mode ? Does the vent need to do more work ? Patient unable to do so Underlying process worsening (or new problem?) Air leaks? Does the patient need to be more sedated ? Does the patient need to be extubated ?

Troubleshooting Patient - Ventilator Interaction Vent must recognize patient’s respiratory efforts (trigger) Vent must be able to meet patient’s demands (response) Vent must not interfere with patient’s efforts (synchrony)

Troubleshooting Improving Ventilation and/or Oxygenation can increase respiratory rate (or decrease rate if air trapping is an issue) can increase tidal volume/PAP to increase tidal volume can increase PEEP to help recruit collapsed areas can increase pressure support and/or decrease sedation to improve patient’s spontaneous effort

Ventilator alarms Airway pressure -high/low Tidal volume Inspiratory flow Expiratory flow Triggering FiO2

Weaning from ventilator It means discontinuing the ventilatory support. Guidelines are: 1. pO2 >60 mm Hg (or oxygen saturation > 90%) on FIO2 <50% and PEEP <5mmHg. 2. pCo2 <50 mmHg 3. Respiratory rate <20/min 4. Vital capacity >15ml/kg 5. VD/VT <0.6 6. Tidal volume > 5ml/kg

7. Minute ventilation <10 litres/min 8. Inspiratory pressure <-30 cm H2O 9. rapid shallow breathing index (RSBI) should be <100 = respiratory rate (breaths/min)/tidal volume (in litres) 10. Arterial pH is normal 11. Normal cardiac status 12. Normal electrolytes 13. Adequate nutritional status Method of weaning Although weaning process vary from patient to patient and is possible to wean patient in any mode of ventilation except control mode ventilation

Pulmonary barotrauma Pneumothorax Pneumomediastinum Bronchopleural fistula Pneumocardium Air embolism Complications

infection Pulmonary (ventilator assoc. pneumonia) Urinary Wound infection iv cannula related complications due to prolonged intubation Airway edema Sore throat Laryngeal ulcer and granuloma

GIT stress ulcer paralytic ileus cardiovascular: right ventricular strain or even rt ventricular failure nosocomial infections liver and kidney dysfunction due to decreased cardiac output neuromuscular weakness ciliary activity impairment oxygen toxicity prolonged immobilization bed sores, thromboembolism

Acute Deterioration - DOPE Displaced tube Obstructed Tube ( blocked tube) Pneumothorax Equipment Failure

Gradual Deterioration Increase in primary pathology Infection Anemia Hypo tension Dyselectrolytemia Hypoglycemia Progression to CLD

CARE OF THE PATIENT ON VENTILATOR Care of unconscious patient Sedation Analgesia Care of conscious patient Care of all vascular lines and tubes Nutritional support

Respiratory care Care of ET Tube/Tracheostomy Tube Antibiotic Bronchodilators Mucolytic Physiotherapy - chest - limb Humidification/ warming of airway Prevention of aspiration

TAKE HOME MESSAGE Learned by surgical resident Surgical aetiology decides results Monitoring clinical and laboratory criteria Avoid as far as possible ; difficult weaning Elective ventilation useful armament

Mechanical Ventilation (2)

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Mechanical Ventilation (2)