VENTILATION STRATEGIES FOR THE CRITICALLY UNWELL

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1 VENTILATION STRATEGIES FOR THE CRITICALLY UNWELL Dr Nick Taylor Visiting Emergency Specialist Teaching Hospital Karapitiya Senior Specialist and Director ED Training Clinical Lecturer, Australian National University Canberra Hospital, Australia

2 CASE 1 19 yo with severe hypoxia Widespread B profile on USS lung Intubated with sucker through cords

3 HOW WILL YOU VENTILATE HIM?

4 CASE 2 25 yo female with severe asthma Intubated Sudden drop in sats, high pressures and low BP

5 HOW WILL YOU VENTILATE HER?

6 INTRO Traditional ventilation teaching is often complicated and difficult to understand There are only 2 main reasons for respiration

7 Supplying Oxygen Getting Rid of CO2

8 There are also essentially only two main types of lung pathology requiring ventilation

9 TWO TYPES OF VENTILATION LUNG INJURY (Oxygen Supply is the problem) LUNG OBSTRUCTION (Getting rid of CO2 is the problem)

10 Today we will learn to apply these principles to a critically unwell patient You can use these principles for NIV or IPPV

11 FIRST: VERY SIMPLE PULMONARY PHYSIOLOGY

12 HOW DO WE MEASURE VENTILATION? Minute Volume = Tidal Volume x Respiratory Rate

13 MINUTE VOLUME FOR A NORMAL CO2 Around 60mL/kg in spont breathing pt Because of dead space it s closer to mL/kg when intubated

14 How does our body control ventilation?

15 PRIMARY SERVO CONTROL OF MINUTE VENTILATION Respiratory centre in the medulla (brain stem) ph sensitive cells (dissolved CO2 changes ph in CSF) Responds to changes in arterial CO2, and adjusts minute volume accordingly As CO2 rises we ventilate more, if CO2 falls, we ventilate less

16 CO2 is inversely proportional to MV Thus when ventilating a patient, we guide ventilation adequacy with ETCO2

17 Note ETCO2 will differ from PaCO2 It is usually lower by 5-10 but varies substantially with different circuits and lung pathology This is because of non ventilated dead space or shunt

18 BACK UP PLAN Hypoxic respiratory drive Need PO2 < 50 Clearly not your day to day ventilation controller!

19 OTHER VARIABLES What is the inevitable 3 rd major variable which goes along with TV and RR? Pressure

20 HOW DOES PRESSURE VARY WITH MV? Lung dynamics (particularly compliance) and coexisting pathology play a major role in how the lung will respond to a given RR and TV

21 COMPLIANCE Change in pressure for a given volume Low compliance = high elastic recoil and difficult to expand - a thick balloon (hard to inflate, easy to deflate) High compliance = low elastic recoil, Easy to expand - a plastic bag (easy to inflate, hard to deflate)

22 PRESSURES PIP (Peak inspiratory pressure) and EEP (end expiratory pressure) PIP is less useful as a measure of barotrauma than Alevolar pressure Plateau pressures (alveolar pressures) can be measured using an inspiratory breath hold Plateau pressures should be kept <30mmHg

23 Notice oxygen hasn t been mentioned in regards to ventilation yet

24 OXYGENATION Depends on: FiO2 Quality and size of surface area available for gas exchange Perfusion of lungs Oxygen carrying capacity of blood Tissue perfusion at end-organ

25 Positive end expiratory pressure PEEP Use PEEP to prevent derecruitment of alveolar units (decrease shunt) Increase FRC (functional residual capacity) eg in the obese patient Also reduces venous return (Preload) as mean intrathoracic pressure rises Predominately helps oxygenation

26 PEEP CONTINUED PEEP of 3-5 cmh 2 O thought to be physiological when ETT insitu Thus all patients except those with extremely high auto PEEP (severe asthma) should have around 5 of PEEP

27 AUTO PEEP All lungs have a low amount of auto-peep which rises in disease states like asthma Measure with expiratory breath hold Difference between applied PEEP and Exp pressure is the auto PEEP

28 FLOW RATE Is the speed at which VT is delivered Normal setting L/min Flow rate sets Tinsp and thus I:E ratio High flow > 60 L/min good for asthma (shorter Tinsp) but may increase Peak inspiratory Pressure (PiP) Low flow rates (20 to 50 L/min) = increase inspiratory time with improved distribution gases

29 I:E RATIOS Normal 1:2 Shorter insp times increase dead space ventilation Longer insp times improve oxygenation but increase haemodynamic instability Dependant on flow rate, inspiratory time and frequency

30 RISE TIME (RAMP) The amount of time it takes for set pressure to be reached from beginning inspiration Adjusts the peak inspiratory flow rate

31 LUNG INJURY VENTILATION

32 Injury ventilation is for basically everything except obstruction and thus includes ARDS, APO, pneumonia, contusions etc Oxygenation is the primary problem

33 NIV Mode CPAP PEEP start at 5-10 and increase by 2-3 every 5-10 minutes FiO2 depends on starting sats Aim to lower to <0.5 ASAP

34 IPPV MODE SIMV in Volume control mode

35 TV 6-8 ml/kg of ideal body weight This is a lung protective strategy For ARDS aim 6mL/kg

36 For ventilation Start at 18 Why 18? Dead space As a proportion of TV it s higher at lower TVs Need to compensate with rate to achieve MV RATE

37 PEEP/FIO2 For oxygenation Use PEEP tables No mortality diff high vs low PEEP but high PEEP may oxygenate better

38 IFR AND I:E Flow rates 50-80ml/min I:E ration 1:1.5-2

39 PERMISSIVE HYPERCAPNOEA Don t try and chase the CO2 unless acidosis (ph <7.15) becomes an issue

40 PLATEAU PRESSURES FOR INJURY Alveolar pressure Keep <30 cm H20 as associated with lower mortality

41 FIXING P PLAT Check P plat after changing TV /PEEP or q4h If Pplat > 30 cm H2O: decrease VT by 1ml/kg steps (minimum = 4 ml/kg). If Pplat < 25 cm H2O and VT< 6 ml/kg, increase VT by 1 ml/kg until Pplat>25cmH2OorVT =6ml/kg. If Pplat < 30 and breath stacking or dys-synchrony occurs: increase VT in 1ml/kg increments to 7 or 8 ml/kg if Pplat remains < 30 cm H2O.

42 LUNG INJURY SALVAGE

43 RECRUITMENT Maybe useful when unable to achieve adequate oxygenation Multiple different methods described Pros/cons to doing it Simplest is PEEP 30-40cm/H2O for 1-2 minutes PRONING is another recruitment method which can decrease mortality on the very critically hypoxic

44 Volume mode Start at 8ml/kg TV SUMMARY INJURY VENTILATION Set initial rate for goal MV Reduce TV over 1-2 hours to 6ml/kg Adjust TV and RR for P plat and CO2 goals

45 OBSTRUCTION

46 Commonest causes are asthma and COPD Failure to expel CO2 A Ventilation problem

47 NIV Bi-Level mode Start at 10/4 Start with FiO2 0.4 or so Increase IPAP/PS by 2-3cm H20 every 10-15minutes using MV and CO2 goals to guide you

48 IPPV MODE SIMV VC (PC if you like, no real difference)

49 TV Start at 8mL/kg of ideal body weight

50 RATE Start at 10 bpm and be ready to lower it Time in expiration is important

51 I:E AND IFR Use high IFR of L/min Aim to get I:E 1:4-5

52 PERMISSIVE HYPERCAPNOEA ph >7.1 is OK

53 PEEP/FIO2 0 added PEEP Check auto PEEP with Expiratory Breath Hold FiO2 at 0.4 to start

54 Breath stacking DYNAMIC HYPERINFLATION Leads to High intrathoracic pressures and decreased venous return sometimes to arrest

55 OBSTRUCTION RESCUE STRATEGIES If BP drops profoundly or pressures rise dramatically think pneumothorax or dynamic hyperinflation Disconnect from ventilator Allow sec apnoea Lung USS with slow RR for PTx May need chest compressions to reduce hyperinflation

56 OBSTRUCTION SUMMARY Low RR High IFR Long I:E ratio Moderate TVs Permissive hypercapnoea Watch out for dynamic hyperinflation

57 CASE 1 19 yo with severe hypoxia Widespread B profile on USS lung Intubated with sucker through cords

58 CASE CONTINUED Handbagged with PEEP valve no suction!!! When connected to ventilator: TV 60mL with PIP 50 What can you do??

59 Return to hand bagging CAN T VENTILATE LUNG INJURY Raise P limit of ventilator to 50 Set VC initially in CMV Rapid exchange back to vent circuit No suctioning!!! PEEP for 1-2 minutes Ventilate with ARDS PEEP/FiO2 tables and injury strategy

60 CASE 2 25 yo female with severe asthma Intubated and ventilated with obstruction strategy Sudden drop in sats, high pressures and low BP

61 WHATS SHOULD YOU DO Hand bag at slow rate Pressures very high Lung USS done: Normal BP 50/25 Apnoea trialled no success 5 slow chest compressions with audible exhalation BP increased Return to ventilator at RR 6, I:E 1:5

62 THANKYOU! QUESTIONS?

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