BTS sleep Course. Module 13 Introduction to elective use of non-invasive ventilation (prepared by J Stradling)

Transcription

1 BTS sleep Course Module 13 Introduction to elective use of non-invasive ventilation (prepared by J Stradling) What is NIV Uses of NIV Theoretical aspects Available technology Interfaces Specific uses Patient assessment Ventilator settings

2 This module will only consider NIV in the elective setting. It is intended that it accompanies a practical session on mask fitting and setting up the actual ventilator.

3 Non-invasive ventilation (or NIV) is simply the artificial ventilation (full or partial) of a patient without having to intubate or perform a tracheostomy. Usually delivered via a nasal, or face, mask.

4 Aims of non-invasive ventilation 1) Support ventilation and improve the patient s ventilatory function 2) If abnormal, bring down the PaCO 2 and raise the PaO 2 3) Thus improving symptoms and increasing lifespan

5 There are lots of different names for this medical intervention. NIV, NIPPV, BiPAP, NIPPY, Pressure support etc. Don t be confused! Essentially ventilation occurs when a ventilator delivers an inspiratory pressure that is more than the expiratory (in contrast to CPAP continuous positive airway pressure). NIV is the best term, BiPAP and NIPPY are trade names, and the anaesthetists have lots of other names to confuse you. For a tutorial, try:- - not for the faint hearted!

6 3) Acute usage in hospital patients presenting in ventilatory failure who will be weaned off it. (Not subject of this module). e.g. in acute exacerbations of COPD Uses of NIV 1) Long term support of ventilation, typically overnight, sometimes during the day as well. e.g. in patients with neuromuscular weakness, scoliosis, obesity, many of whom have developed type II respiratory failure i.e. a raised arterial PaCO 2 (> 6kpa). 2) Temporary support with subsequent conversion to CPAP when better. e.g. in patients with overlap syndrome (OSA, COPD and PaCO 2 >6kPa).

7 Theory Ventilators drive air in and out of the lungs, in mainly two different ways. Either by switching between two pressure levels, where the inspiratory (IPAP) is higher than the expiratory (EPAP) so called pressure cycled Or by pushing a set volume of air in and out of the lungs (almost regardless of the pressure needed to do this), so called volume cycled. Most domiciliary ventilators are pressure cycled

8 Pressure cycled Inspiratory pressure of approximately 15cmsH 2 O (IPAP) with an expiratory pressure (EPAP) usually very low (e.g. <4 cmsh 2 O). Pressure (and breaths/min, f) set to ensure adequate ventilation. Main advantages Machine usually smaller Compensates for mask leaks by keeping up the pressure during the inspiratory cycle Disadvantage If lungs get stiffer less air blown in may under ventilate the patient

9 Volume cycled Volume (Tidal volume,v T ) blown in with each inspiration approximately 500 to 800 mls. Volume (and breaths/min, f) set to ensure adequate ventilation. Main advantages Same volume delivered despite changes in lung stiffness useful perhaps during chest infections Main disadvantage Cannot compensate for mask leaks Larger machines (although smaller versions becoming available)

10 Pressure cycled versus volume cycled In practice no real difference. Given that for stable patients mask leaks may be a greater issue, and pressure machines are usually smaller and quieter, most units use pressure machines. ERJ 1993;6:1060-4

11 Pressure cycled ventilators Breathing circuit types Expiratory valve ventilator blows in, and during expiration a valve opens to let out the exhaled air (prevents rebreathing of CO 2 ). Older type. Blow off valve between mask and tubing Blow off holes in mask shell Bypass - No valve but requires a blow off hole so that during expiration (when the pressure drops) the CO 2 is adequately flushed out of the system. Commoner. Exhalation valve with activation line from ventilator Patient end Airway pressure sensor line Ventilator end

12 Adjustable settings on pressure cycled ventilators (1) Varies with the make can be confusing! Essentially need to be able to vary both the size of each breath, and how often the breath is given, if the patient does not breathe often enough themselves. Expiratory pressure (EPAP/PEEP) usually set as low as possible, it is the minimum mandatory pressure required to generate enough flow to blow out the CO 2 through the blow off holes during expiration usually about 4 cmsh 2 O.

13 Adjustable settings on pressure cycled ventilators (2) Inspiratory pressure (IPAP) set from 10 to 25 cmsh 2 O this provides the driving pressure, minus the expiratory pressure, to inflate the lungs. In someone with normal lungs and chest wall, they will only need about 8 cmsh 2 O inflation pressure, add in the mandatory expiratory pressure (4 cmsh 2 O), = 12 cmsh 2 O IPAP. 20 cmsh 2 O 10 Airway pressure Inspiratory (12) Expiratory (4) Difference (ie the actual driving pressure, also called the pressure support ) = 8 0

14 Adjustable settings on pressure cycled ventilators (3) Timing either set to take over the ventilation (about 16 to 22 breaths/min, depending on the patients own rate, f), or set to be a backup rate should the patient start to breathe too slowly (about 10/min). Some machines allow you to set the respiratory rate (in breaths per minute, f) Some allow you to set the inspiratory time and expiratory time separately (T i and T e in seconds). To get breaths per minute, add the T i and T e, and then divide into 60 (e.g. T i =1s, T e =2s, 60/3 = 20 breaths/min)

15 Adjustable settings on pressure cycled ventilators (4) Timing having set the respiratory rate, some machines allow you to vary the Ti and the Te adjusts automatically: e.g. if rate = 15 (total breath therefore 4 seconds), and Ti set to 1 second, Te will be 3 secs. Alternatively the Ti to total breath time [Ti/(Ti + Te)] ratio (or % time spent breathing in) can be altered: e.g. if rate = 15, and if Ti/(Ti+Te) = ¼ (25%), then Ti becomes 1 sec and Te becomes 3 secs. Similarly, the I/E ratio, Ti/Te, can be altered on some machines: e.g. if rate = 15, and Ti/Te = 33% (or 0.3) then Ti = 1 sec and Te = 3

16 Adjustable settings on pressure cycled ventilators (5) Rise time - Some machines also allow you to alter the time it takes to reach the inspiratory pressure at the beginning of inspiration. Rapid rise gets to the pressure more quickly and delivers more air, but may be uncomfortable; slow rise may be more comfortable, but time is wasted at lower pressures, so less air goes in per cycle. Some machines make this setting patient adjustable. Rapid rise Slow rise

17 Adjustable settings on pressure cycled ventilators (6) Triggering Some machines allow you to alter the sensitivity of the trigger that senses the start of the patient s breath. This is done by either sensing a drop in pressure at the mask, or an increase in flow through the machine. Some machines adjust this automatically. If it is very sensitive, the ventilator will cut in and help the inspiration really quickly, but may be triggered by spontaneous pressure/flow changes in the mask (e.g. little leaks). If it is not sensitive enough, the patient will feel slightly suffocated at the beginning of inspiration, waiting for the ventilator to cut in. Increased work of breathing.

18 Adjustable settings on pressure cycled ventilators (7) Spontaneous or Timed or Both Spontaneous this setting means that the ventilator will only cut in when the patient takes a breath, but not otherwise only therefore assists a breath. Also known as pressure support, (confusing as this term also refers to the IPAP-EPAP inflation pressure itself). Timed this setting simply ventilates like clockwork with a regular rate, regardless of the patient s own breathing rate (unusual these days in NIV). Spontaneous/timed this setting allows the patient to breathe at their own rate, but will also have a back up rate that will cut in if the patient breathes too slowly (usual setting).

19 Healthdyne Quantum ventilator Sets mode:- CPAP, spontaneous ventilation, or spontaneous and timed Mask pressure reading Estimate of ventilation Numbers show setting Sets expiratory pressure Trigger set automatically Sets inspiratory pressure Sets speed of rise of inspiratory pressure Sets machine s ventilatory rate Sets % of total breath time spent on inspiration

20 NIPPY II ventilator Expiratory pressure not adjustable Sets inspiratory pressure Sets trigger sensitivity * Sets inspiratory time Sets maximum expiratory time Mask pressure reading * Some machines have alarms designed to detect a mask leak or obstruction to the tubing, or some other fault. Some work on pressure detection, some on flow detection

21 Most modern machines now have interactive digital control panels rather than the much more friendly knobs. They are usually accessed by pressing up and down buttons that put you into sub menus that are not always very intuitative. NIPPY 3 ventilator Press to set inspiratory pressure, readout beside it Press to set expiratory pressure, readout beside it Press to set inspiratory time, readout beside it Saime ventilator Press to set back up ventilatory rate, readout beside it Press to set certain features of the breath, readout beside it

22 Many different ventilators on the market, need to get used to one or two if possible.

23 Interfaces

24 Must be comfortable Must not leak Interfaces Key points Must not produce ulceration Must have a vent present if pressure cycled! Missing vent piece Vent piece in place

25 Adjustable head piece allows individual adjustment to minimise nasal bridge pressure Mask adjustment Ensure mask is square on the face Ensure straps are equally tensioned Ensure skirt is not distorted If there is leakage, pull forwards off face and gently replace Soft floppy skirt almost self seals due to pressure within mask without having to pull tight on the face

26 Starting ventilation electively This used to be done during a hospital admission and could take several days/nights to get right Now, often started as an outpatient with monitoring of overnight oximetry at home if required, or capillary blood gases to plot improvement in PaCO 2

27 Starting ventilation The patient is likely to be petrified Talk the patient through the process and make sure they feel in control of the process Discuss mask choices with the patient Allow the patient to hold mask on their face first before using the straps (machine off, then with it on) Always congratulate patient on progress so far

28 Starting ventilation Encourage longer and longer periods on the ventilator, building up to minutes. Check settings on ventilator are as prescribed, and tolerated comfortably, before patient leaves! Check patient happy to go home with system and report back by phone the following morning

29 Usually not required Added oxygen? Oxygen can be added to the circuit but it is difficult to prescribe a specific % oxygen as the mixing with the ventilator s air is variable. Amount required best done by titration, gradually increasing, starting with 0.25 or 0.5 litres per min initially. Ventilator Bacterial filter O 2 adaptor Tube to patient Some machines have an O 2 inlet already Beware going above an SaO 2 of 92%, may provoke hypoventilation in patients who retain CO 2

30 Usually not required Added humidification? If most of the ventilation occurs through the nose then natural humidification should be enough. Using a face mask for NIV usually means humidification necessary, as mouth breathing likely. Addition of a separate heated humidifier significantly adds to the hassle for the patient. However integral humidifier prevents insertion of filter between ventilator and humidifier. (May need different filter between mask and tubing waterproof or HME Integral heated humidifier Separate heated humidifier

31 Examples of patients requiring long term NIV, with evidence of benefit Post polio syndrome Scoliosis (when vital capacity < 1 litre) Post-thoracoplasty (used to be done for TB, before anti-tuberculosis drugs became available) Neuromuscular diseases, e.g. Acid maltase deficiency Spinal muscular atrophy Motor neurone disease Muscular dystrophy Obesity hypoventilation syndrome

32 Types of presentation in patients with gradually failing ventilatory capacity Shortness of breath awake aware having to make extra effort to breathe (may not be in type II respiratory failure yet) Orthopnoea more breathless on lying down, OK sitting/standing (may not be in type II respiratory failure yet) Sleep disturbance/daytime sleepiness (may not be in type II respiratory failure yet) Conventional type II failure morning headache/cyanosis/ankle swelling/morning confusion

33 Assessment of patients with gradually progressive ventilatory insufficiency History Examination SOB, orthopnoea, headache on awakening, morning confusion, cyanosis, poor sleep, witnessed apnoeas SOB at rest, distribution of weakness in neuromuscular patients (proximal suggests respiratory muscle involvement), orthopnoea, abdominal paradox on breathing/ sniffing, lying and standing VC. Supine VC best predictor of ventilatory failure Tests Respiratory muscles (? any better than lying and standing VC) Oximetry and blood gases (if SaO 2 < 96%) Overnight oximetry (earliest finding is REM hypoxia)

34 Blood gases Measures arterial oxygen levels and carbon dioxide levels Reflects the level of ventilation and gas exchange in the lung Also measures acid/base balance ph 7.36 to 7.44 PaCO 2 4 to 6 kpa (>6 = type II respiratory failure) PaO 2 10 to 14 kpa Base excess +/- 2 meq/l

35 Blood gases Either from an artery (often painful and difficult) Usually radial, sometimes brachial or femoral Or from an arterialised capillary sample (easier and rarely painful) Usually the ear lobe These samples give a good enough PCO 2 but the PO 2 will read variably low. In this situation use an oximeter to estimate arterial oxygen saturation levels Remember, saturation (SaO 2 ) and pressure (PaO 2 ) are different ways of quoting oxygen levels

36 Paradoxical movements in bilateral diaphragm paralysis Lung function >15% fall in VC is probably abnormal Inspiratory and expiratory photos superimposed Arch Phys Med Rehabil Jan;82(1): % fall in VC

37 Supine VC as predictor of three progressive stages of respiratory failure in primary myopathies. VC 60% PN Thorax 2002;57: (REM hypopnoeas) 40% PN (continuous nocturnal hypoventilation) ROC curves 25% PN (awake hypercapnia)

38 Examples of overnight Oximeter tracings Normal Central sleep apnoea REM sleep hypoxia only Hypoxia all the time with REM worsening

39 When should NIV be offered when there is progressive disease e.g. motor neurone disease? Distressing symptoms improved quality of life is aim Prolong life? Newcastle data suggests 3 months on average, 6 months in those with no bulbar symptoms Lancet Neurol Feb;5(2): PaCO 2 > 6 kpa (or base excess >4 mmol/l) implies impending ventilatory failure Lying VC < 40% PN implies impending ventilatory failure (1 to 2 litres depending on patient size etc) (Nocturnal SaO 2 <88% for > 5 mins)

40 Newcastle randomised controlled trial of NIV in MND A Entry criteria = orthopnoea, PIMax<60% pred, awake hypercapnia Lancet Neurol Feb;5 (2): B C Survival from randomisation A = all pts, B = Normal/mod impaired bulbar function, C = Severe bulbar impairment

41 Newcastle randomised controlled trial of NIV in MND A Entry criteria = orthopnoea, PIMax<60% pred, awake hypercapnia Lancet Neurol Feb;5 (2): B C Time QOL score >75% baseline A = all pts, B = Normal/mod impaired bulbar function, C = Severe bulbar impairment

42 Examples of patients who may require NIV, but may be changed to CPAP when better Overlap syndrome The combinations of OSA, COPD causing low baseline SaO 2 levels with further falls during sleep, plus superimposed oscillations due to OSA. Obesity (BMI > 40) further complicates. Chance of needing ventilation 1 = low 2 = moderate 3 = high OSA Obesity COPD 1 CO 2 retention is extremely rare in pure OSA

43 Overlap syndrome Low baseline SaO 2 Lower stable levels asleep Extra oscillations due to OSA Overlap syndrome the combination of OSA and COPD

44 Overlap syndrome If patient with COPD/OSA acutely unwell with decompensated ventilatory failure (i.e. has a respiratory acidosis), best to use non-invasive ventilation (NIV) first and consider changing to CPAP when better (if FEV1 < 1 litre more likely to need NIV long term) If patient not acutely unwell, with relatively compensated ventilatory failure (arterial ph OK), then try CPAP first (may need to change to NIV if no improvement in CO 2 ). Oxygen can be added to CPAP/NIV in specific circumstances with careful monitoring of CO 2 levels Place of long term NIV in pure stable hypercapnic COPD not established

45 Are there any rough rules as to the ventilator settings in different conditions? (1) 1) Neuromuscular disease with pure hypoventilation (normal lungs and chest wall, no OSA, therefore easy to ventilate) EPAP (or PEEP) - as low as possible (about 4 cms H 2 O) IPAP usually 10 to 12 cms H 2 O will do Ventilatory rate 18/min, to ensure adequate ventilation Sometimes the rate can be set lower if the patient is breathing adequately, e.g. set at 10/min. This makes the machine more comfortable to use when awake, as it is not cutting in before the patient is ready to take another breath. Thus the patient feels that the machine really is following their breathing.

46 Ventilator settings in different conditions (2) 2) Restrictive chest wall disease, e.g. scoliosis, or pure obesityhypoventilation EPAP low, but may need about 6/7 cmsh 2 O or so to keep lungs expanded and improve gas exchange by stopping areas of lung collapse (so called atelectasis ). This may occur because the chest is so small and the lungs squashed such that the alveoli do not get properly expanded. IPAP usually 12 to 16 cms H 2 O. Higher than with neuromuscular diseases because the lungs and chest wall are stiffer and need more oomph, as well as needing to be a bit higher because the EPAP may be up a bit. Remember that the effective ventilation depends on the IPAP pressure minus the EPAP pressure (also known as the pressure support ). Ventilatory rate 18/min, to ensure adequate ventilation

47 Ventilator settings in different conditions (3) 3) Overlap syndrome COPD and OSA EPAP may need about 8 to 10 cmsh 2 O or so to keep pharynx splinted open, otherwise the patient cannot trigger the ventilator at the beginning of inspiration. IPAP usually 15 to 18+ cms H 2 O. Set higher than usual, as the EPAP is high, and again, remember that the effective ventilation depends on the IPAP pressure minus the EPAP pressure (pressure support). Also the airways obstruction means that again more oomph is required. Ventilatory rate 18/min, to ensure adequate ventilation

48 Ventilator settings in different conditions (4) 4) Pure obstructive lung disease, e.g. COPD EPAP low, may need about 6/7 cmsh 2 O or so. This extra pressure is needed to keep up the lung volume and balance something called intrinsic PEEP. Simply, this pressure helps the patient keep their lung volume up (which helps keep the airways open) and thus reduces work of breathing. IPAP usually 15 to 18+ cms H 2 O. Set higher than usual, as the EPAP is higher, and the airways obstruction means that again more oomph is required. Ventilatory rate 18/min, to ensure adequate ventilation, although the patient may be breathing faster and triggering it themselves.

49 This module has only considered NIV in the elective setting. In the acute setting, e.g. in COPD exacerbations, there are other considerations not covered here. Selection of patients is quite different. is the web address of an excellent tutorial on different types of ventilation not for the faint hearted