Mechanical Ventilation in Neonates (B1)

Transcription

1 Title of Guideline (must include the word Guideline (not protocol, policy, procedure etc) Author: Contact Name and Job Title Directorate & Speciality Date of submission Mechanical Ventilation in Neonates (B1) Dr Dushyant Batra (Consultant Neonatologist) Dr Bernard Schoonakker (Consultant Neonatologist) Dr Craig Smith (Consultant Neonatologist) Neonatal Intensive Care Unit, Family Health May 2015 Explicit definition of patient group to which it applies (e.g. inclusion and exclusion criteria, diagnosis) Infants admitted to the Neonatal Unit requiring Mechanical Ventilation Version 3 If this version supersedes another clinical guideline please be explicit about which guideline it replaces including version number. Statement of the evidence base of the guideline has the guideline been peer reviewed by colleagues? Evidence base: (1-6) 1 NICE Guidance, Royal College Guideline, SIGN (please state which source). 2a meta analysis of randomised controlled trials 2b at least one randomised controlled trial 3a at least one well-designed controlled study without 3b randomisation at least one other type of well-designed quasiexperimental study 4 well designed non-experimental descriptive studies (ie comparative / correlation and case studies) 5 expert committee reports or opinions and / or clinical experiences of respected authorities 6 recommended best practise based on the clinical experience of the guideline developer Consultation Process Ratified by: Date: Target audience 2 2a, 2b, 3b, 4 Nottingham Neonatal Service Staff and Clinical Guideline Meeting. Nottingham Neonatal Service Staff and Neonatal Task & Finish Guideline group. February 2017 Staff of the Nottingham Neonatal Service. 1

2 Review Date: (to be applied by the Integrated Governance Team) May 2020 A review date of 5 years will be applied by the Trust. Directorates can choose to apply a shorter review date, however this must be managed through Directorate Governance processes. This guideline has been registered with the trust. However, clinical guidelines are guidelines only. The interpretation and application of clinical guidelines will remain the responsibility of the individual clinician. If in doubt contact a senior colleague or expert. Caution is advised when using guidelines after the review date. This policy should be read in conjunction with guidelines covering early care (A8), surfactant therapy (B5), BPD (B8), hypoxic respiratory failure (B6), nitric oxide(b10), HFOV (B9) and CPAP (B15). Key points: 1. Each ventilated baby should have a clear ventilation strategy, which should be guided by clinical condition, information from bed-side monitoring, regular blood gases and pulmonary graphics. 2. Always check that all equipment is ready before ventilation - ensure that system check and breathing circuit check is done before connecting the baby to the ventilator. 3. If there are problems with ventilation review the patient, consider all possible causes (BOLDPEEP) and involve senior colleagues if unsure or things are not improving. 2

3 Contents Nottingham Neonatal Service Clinical Guidelines Guideline No B1.. Error! Bookmark not defined. Glossary... 4 Section 1: Ventilation algorithms... 5 Section 2: Practical aspects of ventilation Introduction and patient groups Introduction Patient Groups Correct assessment of Clinical need for respiratory support Aims of Intubation and Ventilation Initiation of ventilation Ventilator Choice Initiation of Ventilation (Algorithm 1.1) Continuation of ventilation (Algorithm 1.2) Weaning ventilation (Algorithm 1.3) Deterioration on ventilator Approach to common alarms Extubation Section 3: Ventilation parameters and modes of ventilation Ventilation parameters Modes of ventilation Section 4: Volume Targeted Ventilation Section 5: Oxygenation and ventilation physiology CO 2 removal Oxygenation Summary box and level of evidence Audit points: REFERENCES: APPENDIX 1:

4 Glossary AC= Assist control ventilation BP= Blood pressure C= Compliance CDH= Congenital diaphragmatic hernia CMV= Continuous mandatory ventilation CPAP= Continuous positive airway pressure CXR= Chest x-ray ECMO= Extracorporeal membrane oxygenation ELBW= Extremely low birth weight ET= Endotracheal FiO 2 = Fraction of inhaled O 2 FRC= Functional residual capacity HFO= High frequency oscillation HIE= Hypoxic ischaemic encephalopathy HR= Heart rate I:E= Inspiratory-expiratory ratio IVH= Intraventricular haemorrhage MAP= Mean airway pressure MV= Minute ventilation NEC= Necrotising enterocolitis NGT= Nasogastric tube OI= Oxygenation index PC= Pressure controlled PS= Pressure support PSV= Pressure support ventilation PEEP= Positive end-expiratory pressure PIP= Peak inspiratory pressure Pmax= Maximum peak inspiratory pressure PPROM= Preterm Prelabour rupture of membranes PVL= Periventricular leukomalacia R aw = Airway resistance RDS= Respiratory distress syndrome RR= Respiratory rate SIMV= Synchronised intermittent mandatory ventilation TC= Time constant Te= Expiratory time Ti= Inspiratory time TV= Tidal volume TVe= Expiratory tidal volume VG= Volume guarantee VILI= Ventilator induced lung injury VTV: Volume targeted ventilation 4

5 Section 1: Ventilation algorithms ALGORITHM 1.1: INITIATION OF VENTILATION* Does the patient need ventilation? 1. Early care guideline (<26 weeks gestation) 2. Need for surfactant (significant RDS) 3. Significant lung disease (e.g. meconium aspiration, pneumonia, exacerbation of chronic lung disease) 4. Refractory apnoeas, sepsis 5. Complex surgical problems (e.g. congenital diaphragmatic hernia, postoperative care) 6. Airway protection (e.g. poor neurological states, severe HIE) 7. Significant cardiovascular compromise (e.g. hypotension, sepsis, NEC) Initiate ventilation with SIMV mode 1. Ensure appropriate FiO2, PIP, PEEP, Ti, and rate for lung recruitment, oxygenation and ventilation. Slope should be set at Monitor saturations, tidal volume, chest movement, ET leak and haemodynamic status 3. Consider volume guided ventilation once lungs recruited and above parameters stable (see section 5) 4. Blood gas (arterial or capillary) in minutes 5. Consider Assist control mode if good respiratory drive Reassess and review Is the patient likely to remain ventilated for > 12 hours? Yes Follow Algorithm 1.2 No Follow Algorithm 1.3 * Use in conjunction with section 2 (See Glossary for details of abbreviations) 5

6 ALGORITHM 1.2: CONTINUATION OF VENTILATION* Q1 Does the patient need significant ventilation? MAP >12cm of H 2 O FiO 2 50% Examples: Significant RDS/ Sepsis Pulmonary haemorrhage Meconium aspiration Complex surgical diagnosis like CDH, Eventration, post-operative NEC Yes Use PC-SIMV Consider PC-HFO Back-up rate based on clinical condition to provide adequate ventilation and target pco 2 Consider Surfactant Optimise sedation, consider muscle relaxants Consider adjuvant treatments e.g. Nitric oxide Go to Q3 Q2 No Can the respiratory rate be delegated to the patient? Yes Time cycled, patient triggered modes usually preferred PC-AC with back up rate typically 30bpm Go to Q3 Q3 Is the patient: Stable/ improving ET tube leak<50% Lungs well recruited Yes No PC-SIMV with rate 30-60bpm usually preferred Go to Q3 Consider Volume guarantee (Vte set 4-6ml/kg) Consider PC-PSV Go to Q4 No Address ET tube leak (consider the cause, change ET tube if indicated) Optimise lung recruitment, review PEEP, PIP Reconsider Volume guarantee Go to Q4 Q4 Is the patient ready for weaning? Yes Follow Algorithm 3 for weaning No * Use in conjunction with section 2 (See Glossary for details of abbreviations) Continue previous mode and reassess for weaning 6

7 ALGORITHM 1.3: WEANING VENTILATION* Is the patient ready for weaning? Stable and acceptable O 2 requirements Acceptable MAP (generally <9cm H 2 O) Haemodynamic stability (stable BP off inotropes or low dose inotropes No contraindications for extubation (e.g. continued muscle relaxation, surgical plan to continue ventilation after major surgery Review the mode of ventilation Weaning with PC-AC or PSV usually preferred Back up rate typically 30bpm Consider volume guarantee (typically 4-6ml/kg) if pre-requisites met (See Algorithm 1.2 and section 5 Monitor MAP, it should wean itself as lung mechanics improve Optimise systemic care Wean sedation as appropriate and ensure good respiratory drive Consider Caffeine if indicated Patient should be off inotropes Ready for extubation assessment Improving/ stable blood gas (arterial or capillary) Improving or stable respiratory diagnosis Improving baby with good respiratory drive Non-respiratory support available (if indicated) Post-extubation care Good positioning and minimise handling as appropriate Repeat blood gas (arterial/ capillary) after 30-60min * Use in conjunction with section 2 (See Glossary for details of abbreviations) 7

8 Section 2: Practical aspects of ventilation 2.1 Introduction and patient groups Introduction Modern neonatal respiratory care is aimed at both optimisation of respiratory care and prevention of severe respiratory morbidity. This has been possible by improving our understanding of antenatal and perinatal care as well as benefiting from modern technology. This document provides guidance on when and how to initiate ventilation, and how to optimise the choice of different modes of ventilation and ventilation strategies. It should be read in conjunction with the self-learning package for Draeger ventilator Patient Groups Neonates may need intubation and ventilation for a variety of reasons. In some situations, the decision to intubate may not be straightforward and close observation and senior advice can be extremely helpful. The common indications include: Extremely preterm ( 26wks gestation) neonates (early care guideline) Preterm and term neonates with RDS requiring surfactant Worsening respiratory failure where non-invasive support is failing Neonates with inadequate respiratory drive/strength or inability to maintain airway Neonates requiring cardiovascular support (e.g. inotropes) Certain surgical conditions directly or indirectly affecting airway/ respiratory status e.g. Congenital Diaphragmatic Hernia, NEC, post-operative period etc Correct assessment of Clinical need for respiratory support The clinician initiating ventilation should be clear about why the baby requires respiratory support and for how long. Consideration of the following factors allows more precise tailoring of ventilatory requirements from the beginning: Gestational age and weight Age and respiratory course since birth Antenatal history (e.g. long history of PPROM) Previous respiratory history (if older) Current CXR (if available) Current gas exchange and oxygen requirements Other problems (e.g. NEC) Transport Aims of Intubation and Ventilation Secure patent airway Support infant s own respiratory efforts when possible Improve oxygenation and establish acceptable CO 2 clearance Avoid or minimise Ventilator Induced Lung Injury (VILI) with the principle of permissive hypercapnia Stabilise an acutely sick baby Prepare for Surgery or Transportation 8

9 2.2 Initiation of ventilation Ventilator Choice In Nottingham, the Draeger VN500 is used is the ventilator of choice. It provides very useful information from various pulmonary measurements and graphics. It can be used as a conventional time cycled/pressure limited ventilator or in modes supporting volume guided ventilation, which may help reduce lung injury. VN500 can also provide HFO and can be used in conjunction with Nitric Oxide Initiation of Ventilation (Algorithm 1.1) At the time of initiation, the Draeger ventilator requires a system check and a circuit check (See self-learning package for details) following on-screen instructions and enter the details of the ET tube size and patient s weight. SIMV mode is usually preferred at initiation especially if the baby has a poor respiratory drive or is muscle relaxed. The initial ventilator settings will depend on the patient assessment (See Background and patient groups above and Section 3), pressures/ FiO 2 needed with T-piece (neopuff ) ventilation and the previous respiratory history. Most preterm babies being admitted to NICU after stabilisation and surfactant can be started on: PEEP 5 cmh2o and PIP 18 cmh2o and FiO2 21% Inspiratory time 0.33 sec and Rate 40-60/min These settings including FiO 2 should then be adjusted according to O2 saturations, tidal volume (TV), chest movement/ air entry, pulmonary graphics and other bedside monitoring results. Blood gas (arterial/ capillary) should be done in 20-30min, which along with chest x-ray may guide the ventilator settings. The ventilation mode may be changed to Assist control mode in presence of good respiratory drive. Add volume guarantee if all the pre-requisites are met (see section 5). There should be clear strategy for ventilation from the time the decision for ventilation is made. The duration of ventilation can vary depending on the clinical situation. If the expected duration of ventilation is short e.g. a preterm infant with an isolated lung disease who has responded very well to surfactant, consideration should be given to weaning process (Section 2.2.4) including a need for adjuvant treatments like Caffeine (See Caffeine guideline) and weaning from sedation if appropriate. 2.3 Continuation of ventilation (Algorithm 1.2) Many of the patients will need ventilation for longer than 12 hours. These may include neonates with significant pulmonary compromise, haemodynamic compromise, and pre or post-operative surgical conditions like CDH and NEC. Each of these babies should have an individualised ventilation strategy guided by the senior clinicians based on the clinical situation, ventilatory parameters, bedside monitoring, investigation results and expected course. Sedation, typically with Morphine infusion should be started in an appropriate dose. Algorithm 1.2 suggests a framework for ventilation. There are four key questions: i) Does the patient need a mean airway pressure of 12 cm H 2 O and/ or FiO 2 of 50%? The clinical management of patients with significant lung disease is guided by the clinical situation. Preterm infants in first 24 hours of their life may be benefitted by additional dose(s) of surfactant. Appropriate size/ position of ET tube, 9

10 optimisation of patient synchrony, sedation and muscle relaxation as indicated can help stabilising a sick patient. Choosing the right mode of ventilation is important. Typically, SIMV mode is used in this setting to have a better control, usually with a higher rate (typically 40-60). Some patients may need high frequency Oscillation (HFO) ventilation (Guideline B9) and/ or further advanced treatment like nitric oxide or ECMO (Guideline B6). ii) Can the respiratory rate be delegated to the patient? Patients with a good respiratory drive and stable clinical condition usually synchronise better with patient triggered modes like Assist control (AC) or Pressure support ventilation (PSV) with a low backup rate (typically set at 30bpm). Low backup rates to delegate the respiratory rate to the patient may not be appropriate for the most unwell patients especially when consideration for muscle relaxation is being considered. Patient comfort during ventilation is crucial and is usually achieved with Morphine. Overzealous dosage of Morphine however can be counterproductive and can worsen the ventilator asynchrony. iii) Is the patient well recruited, stable/ improving? Once the patient is stable/ improving and lungs are well recruited consideration should be given to addition of volume guarantee (VG). The time phase between initiation and consideration for VG could vary from a few minutes (preterm infant after receiving surfactant) to many days (e.g. infants with severe PPHN or some patients with exacerbation of chronic lung disease). Section 5 provides the details of Volume targeted ventilation (VTV) but one of the prerequisites is ET leak being <50%. Lung recruitment can be assessed by clinical assessment including observation of chest, input from bedside monitoring including O2 saturations, and pulmonary graphics. Chest x-ray (CXR) provides objective information on lung recruitment when in doubt. iv) Is the patient ready for weaning? Readiness for weaning (Algorithm 1.3) is guided by clinical improvement in respiratory parameters including mean airway pressure (MAP) and FiO 2 stability, as well as systemic condition of the patient. 2.4 Weaning ventilation (Algorithm 1.3) Weaning process should be guided by the clinical condition, input from bedside monitoring and blood gases. AC/ PSV with low backup rate (typically 30bpm) with added VG is preferred mode for weaning. Caffeine, if indicated, should be started or continued to support the respiratory drive of preterm infants (Caffeine guideline). Sedation should be weaned as appropriate. Patients on VTV typically autowean with improvement in peak inspiratory pressure (PIP) and MAP as the lung compliance improves (Section 4). 10

11 2.5 Deterioration on ventilator The success of meeting the aims of ventilation depends on complex interactions between patient, equipment as well as the staff looking after them. Ventilator alarms provide an important feedback on this interaction; must never be ignored and should warrant patient review. The mnemonic BOLDPEEP may help in gathering information and direct an approach to deterioration on ventilator. B.O.L.D.P.E.EP Common Findings Bad RDS/lung disease Significant lung disease on CXR History of worsening gases and rising oxygen Declining flow and volumes on trend waveform Flat V/P loop Minimal/no chest movement Reduced/squeaky air entry bilaterally Improvement seen over 30 seconds with Neopuff at higher pressures (improved expansion and air entry) Obstructed ETT Possibly, history of secretions, blood in ETT or bad BPD Declining flow and volumes on trend waveform Blunted flows in real time, Flat V/P loop Minimal/no chest movement Reduced/squeaky air entry bilaterally Rising resistance (>200) Minimal improvement with Neopuff at higher pressures, if obstruction is partial Look for water in ventilator tubing Look for response to suction Long ETT CXR evidence/previous use of dental rolls Asymmetrical air entry/chest expansion Agitated baby, never completely settled Improvement with easing ETT back Dislodged ETT Sudden change, sudden events Leak heard No chest movement with ventilator Gas flow in stomach Agitated baby Ventilator registers leak-high flows to compensate and low VTe (make sure low VTe alarm is on and set) No improvement with Neopuff Pneumothorax Bad / worsening lung disease (RDS/Meconium) No antenatal steroids No Surfactant or late surfactant Asymmetric chest shape Decreased expansion/possibly asymmetrical Asymmetrical air entry Volume/time waveform doesn t return to base line V/P loop doesn t complete (subtle) Positive Transillumination Equipment problem Water in tubing? Pneumotach left out of circuit (no volume or flow data!!) Water in pneumotachograph? Kinked ETT due to weight of pneumotach connection? Check waveforms, check alarm settings Equipment/Patient interaction (sedation/paralysis) Bad lung disease? Long ETT? Profound Acidosis? Consider use of more sedation or paralysis ONLY when you are clear what the underlying cause e.g. Bad RDS requiring higher pressures and control of pulmonary hypertension 11

12 2.6 Approach to common alarms Ventilator alarms are designed to alert the healthcare professionals caring for a ventilated infant about unexpected changes in the Ventilator-infant unit and may have significant impact on the infant e.g. disconnection or a dislodged tube. Alarms in red must be attended immediately and alarms in yellow have medium priority. Never set the lower limit of minute ventilation to zero. The table below provides information about common alarms but as a common approach: 1. Review the patient and ask for help if required 2. Review bedside monitoring including saturations, heart rate etc. 3. Check for disconnection, chest movement/ air entry 4. Does the baby need resuscitation: remember ABC (Airway, breathing, circulation) 5. Check minute ventilation values and trends, may provide vital information about sudden or gradual deterioration 6. Check pulmonary graphics (see appendix 1) S No Alarm Possible common causes Approach 1. Low minute volume 2. High minute volume 3. Set TV not reached 4. Flow sensor alarms 5. Respirator y Rate High 6. Respirator y Rate Low 1. Disconnection 2. Change in ventilator leak 3. Lack of respiratory drive with inappropriate mode 4. Worsening lung disease 5. Blocked tube 6. Splinting 1. Incorrect weight entered 2. Change in lung compliance 3. Inappropriate mode, rate 4. Auto-triggering Seen during Volume guided modes 1. Inappropriately low P max 2. Worsening lung disease 3. Significant leaks 4. Inadequate PEEP 5. Derecruitment 1. Condensation of water in the flow sensor 1. False triggering by secretions or water in the circuit 2. High back up rate 3. Seizures 1. Poor respiratory drive with low back up rate 2. Splinting 3. Blocked tube 7 Apnoea 1. Dislodged/ obstructed tube 2. Splinting 1. Review patient 2. Auscultate both lungs 3. Check breathing circuit, ventilator settings, mode, and pulmonary graphics 4. Consider T-piece ventilation 1. Review patient 2. Auscultate both lungs 3. Review mode of ventilation, back up rate 1. Review patient 2. Auscultate both lungs 3. Check ventilator settings, lung recruitment, pulmonary graphics 1. Keep the flow sensor in upright position 2. Recalibrate flow sensor 3. Consider changing the flow sensor 1. Review patient and auscultate both lungs 2. Review breathing circuit and ventilator circuit 1. Review patient and auscultate both lungs 2. Review ventilator circuit 3. Review ventilator settings and pulmonary graphics 1. Review the patient 2. Auscultate both lungs for air entry 3. Ask for help 4. Review the mode of ventilation and ventilation settings 12

13 2.7 Extubation (See also CPAP guideline, B15): This is best performed with close liaison between the medical and nursing teams. Attempt to wean the baby at the earliest opportunity after consideration of the factors listed in section 4-6. Weaning is generally achieved by using VTV. Key factors include open lungs, falling MAP and stable FiO 2. Checklist for extubation: Stable on minimal ventilatory settings with a stable FiO 2. Is breathing comfortably off sedation Has been loaded with caffeine if appropriate (See Caffeine guideline) Stomach emptied by aspirating the NGT Potential airway obstruction removed (secretions) CPAP immediately available if required Good respiratory drive Post extubation CPAP or No CPAP: Many babies <28 weeks or <1 kg benefit from nasal CPAP or NSIMV. CPAP should be applied prior to extubation. The use of nasal CPAP increases the likelihood of maintaining a successful extubation. Caution is needed while using CPAP in babies with necrotising enterocolitis and abdominal pathology. Please refer to CPAP guideline (B15). Failure of Extubation Failure to maintain extubation is usually explained by loss of lung volumes, excessive secretions, poor seal or poor respiratory drive. However if recurrent, consider the following: 1. Decreased respiratory drive. Excessive sedation Need for caffeine CNS infection CNS abnormality IVH/PVL. Hypocapnia 2. Muscular dysfunction Muscle weakness Severe electrolyte disturbances 3. Neuromuscular Diaphragmatic dysfunction Prolonged neuromuscular blockade Myotonic dystrophy Cervical spinal injury 4. Airway/Lung problem Mucus plug/secretions Consolidation/ sepsis Nasal obstruction Post-extubation stridor (Laryngeal oedema, sub-glottic stenosis) Section 3: Ventilation parameters and modes of ventilation 13

14 3.1 Ventilation parameters PIP (Peak inspiratory pressure) Peak inspiratory is the maximum pressure delivered by the ventilator during inspiration. Different situations may warrant a wide range of PIP s (12-40 cmh 2 O). In established or worsening lung disease or when resting lung volumes need to be generated (lung expansion), short periods of high pressures may be needed (30-40 cmh 2 O) in conjunction with surfactant. The difference between PIP and PEEP (see below) determines the tidal volume. The initial PIP setting should be guided by looking at the chest movement, air entry, O 2 saturations with T piece ventilation during the peri-intubation period, and information from CXR (if available). In preterm newborns; start at cm H 2 O and adjust immediately depending on the degree of chest movement 1, oxygen saturations, blood gas status, TV, MV values and CXR estimation of lung disease and lung volumes. The PIP may need to be decreased quickly after administration of surfactant. Volume targeted ventilation (See Section 4) is now routinely used and provides the benefit of minimizing volutrauma, especially in situations with changing lung compliance. Overzealous PIP may lead to overdistension and reduced lung perfusion and cardiac output as well as inappropriate carbon dioxide clearance. PEEP (Positive end expiratory pressure): It is the positive pressure maintained by the ventilator during expiration and helps maintain the functional residual capacity (FRC) and reduces atelectasis 2. It is usually set at 4-6cm H 2 O. PEEP of up to 8cm H2O may be needed in specific situations like pulmonary haemorrhage, significant abdominal distension. Too high a PEEP can reduce CO 2 clearance and venous return/ cardiac output. Supra-physiologic FRC alters pulmonary mechanoreceptor mediated prolongation of expiratory time and may reduce neonate s spontaneous respiratory rate 3. RATE: Changes in rate alter alveolar minute ventilation (MV). Alveolar minute ventilation = Rate X (TV- Dead Space) Initial frequency of breaths (RR) should be set at 40-60/min. The mode of ventilation should be considered when setting the rate (see section 2 above). SIMV at low rates (in comparison with Assist Control mode) can be associated with erratic tidal volume delivery and increased blood pressure fluctuations 4,5. Preterm infants with RDS have low compliance but a normal resistance leading to a low time constant. Time Constant (TC) = Resistance X Compliance High rates are useful especially in the initial phase of RDS. Even rates above 60 with short Ti can be successfully used during conventional ventilation as a short term measure 6,7 however, beware of inadvertent PEEP and a reversed I:E ratio at high ventilator rates. Inspiratory and Expiratory time: Inspiratory time (Ti) should normally be set at sec (range ). The aim is to keep the Ti and expiratory time (Te) about 3-5 times their respective time constants (normal time constants in newborns with RDS is typically sec 8. Infants with BPD have longer time constants and may sometimes need somewhat longer Ti ( ). Flow waveforms can be used to optimize the inspiratory time. Always look at the inspiratory/ expiratory (I:E) ratio and rate after changing the inspiratory time. A shorter Ti is more likely to result in 14

15 the infant breathing in synchrony with the ventilator and therefore decreasing the incidence of air leaks especially in lungs with low compliance 9. Manipulation of the Ti will alter the Mean Airway Pressure (MAP). 3.2 Modes of ventilation The modes of ventilation commonly used are described in this section. These modes differ in their degree of their interaction and co-ordination with infant s own efforts. Figure 1 shows the degree of patient control in various modes. CMV (Continuous Mandatory Ventilation) This is a fixed rate, time cycled and pressured limited mode of ventilation. The ventilator works independent of the patient, hence asynchrony is common. Transport ventilators can currently only deliver this mode. In the neonatal unit, this mode should only be used if the neonate is muscle relaxed. Synchronised Intermittent Mandatory Ventilation (SIMV) In this mode of ventilation the mechanically delivered breaths are synchronised to the onset of spontaneous patient breaths. The Ventilator provides a minimum number of fully supported breaths per minute. The patient can take additional breaths from the continuous flow in the ventilator circuit but these breaths are only supported by PEEP. This mode provides better synchrony with the ventilator but at lower rates (<30bpm) may increase work of breathing and be counterproductive as the patient is required to breathe against the resistance of the ET tube and inspire from residual flow within the ventilator circuit. The mode may be used for rapid weaning, often where there is no or minimal lung disease. In some term infants, weaning may be achieved at a lower back-up rate by addition of pressure support (PS) to SIMV. This however, should not be used in ELBW infants, as it may not achieve the target of minimum ventilation. Reyes et al 10 reported a reduced need of ventilation at 28 days of life in ELBW preterm infants subjected to SIMV with PS as compared to SIMV alone. However there was no difference in total days of mechanical ventilation and supplemental oxygen in the two groups. Assist Control Ventilation (AC) This mode uses flow sensor technology, which detects spontaneous patient inspiration with a preset sensitivity and delivers synchronised mechanical breaths. The ventilator supports each spontaneous respiratory effort achieving the set sensitivity threshold. In the absence of respiratory effort, ventilation is maintained at the set backup rate. This feature is helpful in synchronising the expiration and avoids auto-cycling or auto-triggering. The latter occurs because of false triggering that may occur because of expiratory asynchrony, condensation in the circuit, hiccups, seizures or in the presence of significant air leaks. This mode may be useful in the presence of static lung disease, where significant ventilator support is anticipated in an awake and active patient. The weaning is achieved by reducing the PIP or altering the trigger sensitivity setting. This mode is often used with Volume Guarantee (VG). Comparison of SIMV to AC during weaning has been made in a few randomised trials 4,11. This demonstrated that ACV was associated with faster weaning; the median duration of weaning was 24 vs. 50 hours when the SIMV rate was reduced below 20 inflations per minute 4. Weaning is prolonged when the number of spontaneous breaths supported by ventilator inflations is reduced, as this effectively increases the work of breathing necessary to overcome the resistance of the endotracheal tube

16 Pressure Support Ventilation (PSV) This mode is a patient triggered and flow cycled mode of ventilation. The ventilated neonate will get set inspiratory pressure support until the inspiratory flow decreases to a predetermined fraction of its peak value (typically 15%). Synchrony is improved as the patient modulates the Ti (often shortens the Ti). HFO Ventilation (see separate HFO guideline) In Nottingham, all babies requiring ventilation are initially managed with conventional ventilation modes. Depending on the response, those with significant pressure requirements or high oxygen requirements (as markers of significant lung disease) may be better managed with HFO. HFO may allow better lung recruitment and less VILI in this setting. Please refer to HFO guideline (B9). Figure 1: Conventional mechanical ventilation modes and patient control. CMV= continuous mandatory ventilation; SIMV = Synchronised intermittent mandatory ventilation; Section 4: Volume Targeted Ventilation It is now well accepted that volume rather than pressure per se causes lung injury 13,14. Advances in technology have made it possible to accurately measure small tidal volumes. This has renewed interest in volume targeted ventilation (VTV). A recent Cochrane review 15 showed reduced rate of death, BPD, pneumothorax and cranial ultrasound abnormalities with volume targeted ventilation as compared to pressure controlled ventilation. VTV reduces the variability of TV delivery, volutrauma, atelectotrauma and CO 2 fluctuations 16, 17 The studies included in the meta-analysis had a significant variation with regards to patient groups, modes and ventilation, types of ventilator and ventilation strategies. Further studies may improve our understanding of this mode and inform us about its impact on long term especially neurodevelopmental outcomes in patients. VN500 has volume target options with triggered (SIMV, AC, PSV) as well as nontriggered (CMV) modes. The Draeger with a sensitive volume sensor (Accuracy of 0.5ml in TV of up to 5ml and 10% above TV of 5ml) has more uniform triggering and TV delivery as compared to some other ventilators 18. Setting up VTV: There are certain prerequisites for the successful use of VTV 19 (Table 1). Ventilators can compensate for some leak but a leak of more than 50% will make expiratory TV measurements unreliable. Draeger measures the tidal volume via the flow sensor at the ET tube end of the ventilation circuit. It displays the tidal volume information on the screen. Use the expiratory TV (TVe) as more accurate record of tidal volume. Note that the sensor works better in a vertical position. 16

17 Table 1: Pre-requisites of VTV ETT leak <50% Pmax Ti PEEP Set TV set 5-10cm above the working PIP high enough so that PIP reaches a plateau before expiration Level for optimum FRC 4-6ml/kg The attending Doctor sets the TVe (usually 4-6ml/kg). In acute RDS, a TVe of 4-5ml/kg is usually adequate. Infants on prolonged ventilation in 2 nd to 3 rd week or with BPD may need higher set TV (5-7ml/kg) 20. Pmax: The Ventilator derives information from the current breath and uses it to plan the next breath. If the measured TVe is below 90% of the set value, the PIP is automatically increased by 3cm of water. The information from each breath is sequentially measured until the desired TV is reached or a set Pmax is reached. It is important to carefully select Pmax (typically 5-10cm above the average PIP used) to achieve the desired TV over a period of close observation. PIP needed to achieve the TVe should be monitored and Pmax should not routinely be set above 30cm H 2 O. Patients consistently needing high pressures to achieve the set TVe should be evaluated. The common causes include worsening lung disease; increased airway resistance e.g. partially blocked tube; and patient asynchrony. Too low a Pmax may result in lower TV delivery, atelectasis and repeatedly alarming. VN500 ventilator includes a safety mechanism by which the peak pressure is cut off if the TV reaches 130% of the set value. Ti: In all modes except PSV, Ti is set by the operator, which should be usually set at sec (See Section 7). PSV mode synchronises inspiration as well as expiration with the patient s effort and is therefore determined by the patient. Tmax of s should be set to prevent hyperinflation. Rate: If the patient has good respiratory effort then the back-up rate can be low (20-35) to improve synchrony. Occasionally this will lead to underventilation if the baby has worsening lung disease, is unwell or heavily sedated. Trigger Sensitivity: It can be adjusted on VN500 ventilator by going in to additional settings under Ventilation settings. The sensitivity should be optimised for each patient. Auto-triggering should be looked for and minimised. Slope: Usually set at , dictates the rate of rise from PEEP to PIP. PEEP: Adequate PEEP, usually 4-6cm of H 2 O, is essential for maintenance of functional residual capacity. Higher PEEP is required in severe BPD, Pulmonary Haemorrhage and persistent bilateral collapse/consolidation. See above (Section III.3). Weaning: Use of VTV automatically adjusts for improving compliance by using a lower PIP to achieve the same TV. The backup rate and Ti needs to be reviewed and optimised to increase patient comfort and synchrony. With SIMV mode, weaning the rate below 30 may lead to increased work of breathing for unsupported breaths. 21,22 17

18 Section 5: Oxygenation and ventilation physiology CO 2 Removal Oxygenation Minute Ventilation (MV) Mean Airway Pressure (MAP) Resp Rate TV Te Ti PIP-PEEP I:E Ti PIP PEEP Figure 2: Main factors contributing to Oxygenation and Ventilation (I:E= Inspiratory to expiratory time ratio) 5.1 CO 2 removal It is a function of minute ventilation: Minute Ventilation = Rate x Tidal Volume ( ml/kg/min) (40-60/min) (4-6ml/kg) Tidal volume is dependent on the amount of air moved with each inspiratory breath. This is dependent on breath size (PIP-PEEP), Ti, Time Constant (TC) and the amount of dead space. Therefore to increase the minute ventilation (CO 2 clearance) the following can be changed: Optimise lung inflation/alveolar recruitment first! Increase Rate Increase PIP (or decrease PEEP) Hypocarbia should be avoided and is common in ventilated patients with Hypoxic ischaemic encephalopathy, following administration of surfactant (especially if on pressure controlled mode without volume guarantee), pain and in muscle relaxed patients. 5.2 Oxygenation Oxygenation is improved by increasing the FiO 2 or the Mean Airway Pressure Mean Airway pressure (MAP) equates to MAP = (Ti x PIP) + (Te x PEEP) Ti + Te 18

19 . Figure 3: Pressure against time curve. Mean airway pressure (MAP) is the area under the pressure curve. 1-5 show different ways to increase MAP: 1. Increasing rate of rise of PIP by reducing slope/ increase gas flow rate 2. Increasing PIP 3. Increasing Ti 4. Increasing PEEP 5. Inadvertent effect of too fast respiratory rate on MAP due to change in I:E ratio Oxygenation may be improved by working on any of these factors but changes in PEEP and PIP are commonly used. Avoid supra-physiological inspiratory times, square wave ventilation (increased flow). Figure 3 shows different factors impacting on MAP. Mean Airway Pressure (MAP) Mean airway pressure is the area under curve of the respiratory cycle and determines the oxygenation. It usually cannot be individually set but is extrapolated from PEEP, PIP, Ti and gas flow rate within the ventilator circuit. Time constant (TC) It is a measure of how quickly the infant s alveolar and proximal airway pressures equilibrate during inspiration and expiration. It is dependent on compliance and resistance. TC = C x R aw C: Compliance, Raw: Airway Resistance Expiratory time constant is defined as the time it takes the alveoli to discharge 63% of its TV. By the end of three TC s, 95% of TV is discharged. In normal newborn, TC is 0.15sec and in RDS about sec. It emphasises that during mechanical ventilation, the expiratory time should be long enough to avoid air trapping. The Inspiratory TC is usually half the expiratory value. Time constants are lower in early RDS and prolonged in chronic lung disease. Slope Draeger ventilators provide continuous gas flow. The peak gas flow rate decides the speed of attaining peak pressure. High flow rates lead to square wave ventilation, and the peak pressure is maintained for longer duration during inspiration resulting in higher MAP (Figure 3). On the Draeger, reducing the slope will reduce the time to 19

20 PIP. Slope is typically set at Lower slopes should only be used in exceptional circumstances. Oxygenation Index (OI) OI = MAP (cm of water) x FiO 2 (%) x 100 PaO 2 (kpa) x 7.5 (1 Kpa = 7.5 mm of Hg.) It is a good practice to record OI in infants on mechanical ventilation who have arterial access. Please refer to Hypoxic respiratory failure guideline (B6) if OI is worsening. Some of these patients may need other treatment strategies like Nitric oxide or may be eligible for ECMO. 5.3 Monitoring and Minimising Ventilator Induced Lung Injury Continuous HR, RR, Saturation monitoring Continuous or frequent BP monitoring Blood gases (Frequency is guided by clinical condition, changes made and senior advice) Transcutaneous or end tidal CO 2 can be useful in severe lung disease or Truncus arteriosus Appendix 1 details the information about use of pulmonary graphics as a bedside tool to help with ventilated patients. The general aims in premature baby with RDS are (some exceptions including Persistent Pulmonary Hypertension of Newborn) Aim to keep ph > Aim to keep arterial CO kpa (upper limit depends on ph and respiratory history). Aim to keep arterial PO 2 between 6-10 kpa. Summary box and level of evidence Summary Reference Level of evidence Infants ventilated using volume targeted ventilation modes have 15 A reduced death and chronic lung disease compared with infants ventilated using pressure control modes. Patient triggered modes (AC/ PSV) associated with reduction in 5-7 B median duration of weaning when compared with SIMV mode at low back-up rates. Using a lower backup rate during Assist control mode results in better patient triggering of ventilator breaths. 21 B Audit points: 1. Use of volume targeted ventilation in eligible infants 2. Use of oxygenation index in patients with arterial access 3. Ventilation modes and parameters in the initiation, continuation and weaning phases. 4. Extubation preparedness and success 20

21 REFERENCES: 1. Aufricht C, Huemer C, Frenzel C, Simbruner G. Respiratory compliance assessed from chest expansion and inflation pressure in ventilated neonates. American journal of perinatology Mar;10(2): Thome U, Topfer A, Schaller P, Pohlandt F. The effect of positive endexpiratory pressure, peak inspiratory pressure, and inspiratory time on functional residual capacity in mechanically ventilated preterm infants. European journal of pediatrics Oct;157(10): Ambalavalan N SR, Carlo AC. Ventilation Strategies. In: Goldsmth JP KE, Siede BL, editor. Assisted Ventilation of the Neonate. St. Louis: Elsevier Saunders; pp Chan V, Greenough A. Comparison of weaning by patient triggered ventilation or synchronous intermittent mandatory ventilation in preterm infants. Acta Paediatr Mar;83(3): Hummler H, Gerhardt T, Gonzalez A, Claure N, Everett R, Bancalari E. Influence of different methods of synchronized mechanical ventilation on ventilation, gas exchange, patient effort, and blood pressure fluctuations in premature neonates. Pediatric pulmonology Nov;22(5): Chan V, Greenough A, Hird MF. Comparison of different rates of artificial ventilation for preterm infants ventilated beyond the first week of life. Early human development Oct;26(3): Mireles-Cabodevila E, Chatburn RL. Mid-frequency ventilation: unconventional use of conventional mechanical ventilation as a lung-protection strategy. Respiratory care Dec;53(12): Carlo WA GA, Chatburn RL. Advances in conventional mechanical ventilation In: Boyton BR CW, Jobe AH, West JB, editor. New Therapies for Neonatal Respiratory Failure: A Physiological Approach. New York: Cambridge University Press; pp Reyes ZC, Claure N, Tauscher MK, D'Ugard C, Vanbuskirk S, Bancalari E. Randomized, controlled trial comparing synchronized intermittent mandatory ventilation and synchronized intermittent mandatory ventilation plus pressure support in preterm infants. Pediatrics Oct;118(4): Dimitriou G, Greenough A, Griffin F, Chan V. Synchronous intermittent mandatory ventilation modes compared with patient triggered ventilation during weaning. Arch Dis Child Fetal Neonatal Ed 1995; 72: F Rozé JC, Liet JM, Gournay V, Debillon T, Gaultier C. Oxygen cost of breathing and weaning process in newborn infants. Eur Respir J 1997; 10: Bjorklund LJ, Ingimarsson J, Curstedt T, John J, Robertson B, Werner O, et al. Manual ventilation with a few large breaths at birth compromises the therapeutic effect of subsequent surfactant replacement in immature lambs. Pediatric research Sep;42(3): Hernandez LA, Peevy KJ, Moise AA, Parker JC. Chest wall restriction limits high airway pressure-induced lung injury in young rabbits. J Appl Physiol May;66(5): Wheeler Kevin KC, McCallion Naomi, Morley Colin J, Davis Peter G. Volume-targeted versus pressure-limited ventilation in the neonate. Cochrane Database of Systematic Reviews: John Wiley & Sons, Ltd; Herrera CM, Gerhardt T, Claure N, Everett R, Musante G, Thomas C, et al. Effects of volume-guaranteed synchronized intermittent mandatory ventilation in preterm infants recovering from respiratory failure. Pediatrics Sep;110(3): Keszler M, Abubakar K. Volume guarantee: stability of tidal volume and incidence of hypocarbia. Pediatric pulmonology Sep;38(3): Liubsys A, Norsted T, Jonzon A, Sedin G. Trigger delay in infant ventilators. Ups J Med Sci 1997;102: Klingenberg C, Wheeler KI, Davis PG, Morley CJ. A practical guide to neonatal volume guarantee ventilation. J Perinatol Sep;31(9): Keszler M, Nassabeh-Montazami S, Abubakar K. Evolution of tidal volume requirement during the first 3 weeks of life in infants <800 g ventilated with Volume Guarantee. Archives of disease in childhood Jul;94(4):F Wheeler KI, Morley CJ, Hooper SB, Davis PG. Lower back-up rates improve ventilator triggering during assist-control ventilation: a randomized crossover trial. J Perinatol Feb;32(2):

22 22. Abubakar K, Keszler M. Effect of volume guarantee combined with assist/control vs synchronized intermittent mandatory ventilation. J Perinatol Oct;25(10):

23 APPENDIX 1: Pulmonary Graphics: The bedside management of a ventilated baby is improved by assessing the waveforms and loops created by the ventilator as well as data on resistance, compliance and volumes. Tidal volume Vs time curve displays tidal volume with each breath. Other graphics include: All the information should be interpreted in the clinical context and not in isolation. A) Airflow against time B) Pressure against time C) Flow against volume D) Pressure against Volume (hysteresis loop) A) Airflow against time: Airflow (litres/min) is plotted against time. This provides an insight into airflow in and out of the airways and lungs. Figure 4a demonstrates a Ti which is too long producing a flat portion at the end of inspiration where inspiratory pressure is being applied with no gas flow. In contrast, Figure 4b shows too short Ti. Figure 4c shows a respiratory rate which is too high or a Te which is too short so that there is air trapping as the expiratory flow does not reach the baseline before the next breath commences. Figure 4a Figure 4b Figure 4c Figure 3: Flow loops: Airflow plotted against time 23

24 B) Pressure versus time Draeger ventilators screens are enabled to show live graphical representation of the airway pressure (Figure 5). Care should be taken in interpreting the graphics in triggered modes like SIMV as the unsupported breaths may show lower pressures. Unexplained differences in pressures as compared to set values warrant clinical review. Caution should be exercised in relying on pressure graphics in isolation as even with dislodged endotracheal tube; the pressure curve may not change however other graphics may show significant changes in flow/ volumes. Figure 5: Airway Pressure against time; X-axis shows time (seconds) and Y-axis shows airway pressure (cm of H 2 O). 24

25 C) Airflow(flow) against Volume (V): It describes the pattern of airflow (L/min) during breaths plotted against tidal volume (ml); Tidal volume being on x-axis and flow rate on y-axis. The inspiration is shown below baseline and expiration above baseline. (Fig 6) Normal peak inspiratory flow occurs during mid-inspiration and peak expiratory airflow occurs before mid-expiration in newborns. Preterm infants with RDS typically show peak expiratory airflow occurring in early expiration (ski slope because of high expiratory airway collapsibility). Other common changes in Flow-Volume waveforms are shown in Figure 6. Figure 6: Flow/Volume loops. a) Normal loop. Expiration is shown above baseline while inspiration is below baseline. The peak inspiratory flow occurs mid inspiration while expiration peaks just ahead of mid expiration, b) High expiratory flow limitation (with normal compliance) typical of RDS, c) Fixed inspiratory and expiratory obstruction (e.g. extra-thoracic airway obstruction). d) Intra-thoracic airflow limitation (e.g. arterial ring), e) Erratic airflow limitation (e.g. secretions, crying), f) Inspiratory and expiratory airway limitation, particularly worse for expiration typically seen with unstable airways, bronchomalacia 25

26 D) Pressure (P x axis) against Volume (V y axis): P-V loops describe the relationship of driving pressure and tidal volume. P-V loop represents the elasticity of the lung. The inspiratory and expiratory portions of P-V loops describe a hysteresis that represents the resistive work of breathing (Figure 7). The PV loops can indicate ET tube leak with discrepancy between inspiration and expiration (normally <10%). High airflow resistance/ air trapping appears as exaggerated expiratory component of hysteresis. Low compliance typical of RDS displays lower slope (Figure E). Figure 7: Pressure-Volume (P-V) loops: a) Normal hysteresis, the lung volume is higher on expiratory limb. The slope of the middle line depicts the compliance, b) Reduced compliance e.g. RDS, Pneumonia, c) Increased expiratory airway resistance (obstructive airway disease), d) Increase resistance work with excessive inspiratory pressure (High PIP/ TV), e) Overdistension due to excessive FRC e.g. air trapping, high PEEP) 26