Modes of mechanical ventilation

Modes of mechanical ventilation

1. Modes of Mechanical Ventilation Dr. Dharmraj Singh SR, Cardiac surgical intensive care

2. Objectives Understand how ventilators control breath delivery, phase and control variables. Understand the basic modes of ventilation. Combinations, tailor-making, mix and match…

3. Parameters to be observed Type of patient – Neoante / Pediatric / Adult Mode – PRVC/ VCV/ PCV/ SIMV/ CPAP /PSV Tidal volume – inspiratory and expiratory Ventilatory rate – set and actual Airway pressure PEEP High airway pressure alarm Pressure support or pressure control above PEEP Trigger Flow range

4. goal's OF MECHANICAL VENTILATION GOAL TARGET 1. Improve gas exchange Reverse hypoxia Relieve acute respiratory acidosis 2. Relieve respiratory distress Reduce oxygen cost of breathing Reduce respiratory muscle fatigue 3.Improve pulmonary mechanics Prevent and reverse atelectasis Improve compliance Prevent lung injury 4. Permit lung and airway healing Maintain lung and airway functions 5. Avoid complications Protect lung and airway Prevent disuse respiratory muscle atrophy

5. Indications for mechanical ventilation Indications Examples 1. Acute ventilatory failure Apnea or bradypnea, ALI, ARDS pH< 7.30, PaCO 2 > 50mmHg (higher for COPD) 2. Impending ventilatory failure Progressive acidosis and hypoventilation to pH< 7.30 and PaCO 2 > 50 mmHg (increasing trend) Tidal volume < 3-5 mL/kg Frequency > 25-30/min, labored or irregular Minute ventilation > 10L/min Vital capacity < 15mL/kg MIP < -20 cmH 2 O 3. Severe hypoxemia PaO2 < 60mmHg at FiO 2 > 50%, or PaO2 < 40mmHg at any FiO 2 PaO 2 /FiO 2 (P/F ratio): 300 mmHg for ALI, 200 mmHg for ARDS Indications Examples 1. Acute ventilatory failure Apnea or bradypnea, ALI, ARDS pH< 7.30, PaCO 2 > 50mmHg (higher for COPD) 2. Impending ventilatory failure Progressive acidosis and hypoventilation to pH< 7.30 and PaCO 2 > 50 mmHg (increasing trend) Tidal volume < 3-5 mL/kg Frequency > 25-30/min, labored or irregular Minute ventilation > 10L/min Vital capacity < 15mL/kg MIP < -20 cmH 2 O 3. Severe hypoxemia Contd … MIP- maximum inspiratory pressure

6. Indications for mechanical ventilation 4. Prophylactic ventilatory support Post-anesthesia recovery Muscle fatigue, neuromuscular disease Reduce risk of pulmonary complications Prolonged shock Head injury Smoke inhalation Reduce hypoxia of major body organs Hypoxic brain Hypoxia of heart muscle Reduce cardiopulmonary stress Prolonged shock Coronary artery bypass surgery Other thoracic or abdominal surgeries

7. Airway resistance (R aw ) Airflow obstruction in the airway Simplified Poiseuille’s Law △P= V/r 4 Driving pressure to maintain the same airflow (V) must increase by a factor of 16-fold when the radius (r) of the airway is reduced by only half of its original size. Length, size, patency of airway, ET tube, and ventilator circuit Normal value- 0.5 to 2.5 cmH2O/L/sec at a flow rate of 30L/min (0.5L/sec) Healthy adults- 1.6cmH2O/lit/sec [Flow(V) = Pr4t/8 L]  

8. Work of Breathing (WOB) Work= Force Distance = Pressure Area Distance = Pressure Volume WOB= Change in pressure Change in volume Work (WOB per unit time)= P cmH2O V (minute volume in mL) P- pressure change during the respiratory cycle in cmH2O V- minute volume in mL Normal value of resting individual is 2.5-3 J/min. 10-15 J/min is considered to be maximum sustainable WOB, above this level patients require respiratory support.  

9. Lung compliance Volume change (lung expansion) per unit pressure change (work of breathing) C= △V/△P Static Compliance (C ST ) = Corrected Tidal Volume/ (Plateau Pressure-PEEP), absent airflow- elastance of lung and chest wall Dynamic Compliance (C DYN )= Corrected Tidal Volume/ (Peak Inspiratory Pressure-PEEP), airflow present- condition of airway, elastance of lung and chest wall C ST = 40-60 mL/cmH2O C DYN = 30-40 mL/cmH2O Total compliance is combination of lung and chest wall is normally 100mL/cmH2O

10. Frequency (Resp. rate) Initial frequency set between 10-12 /min Frequency= Estimated minute volume/ Tidal volume Minute Volume (Male)= 4 (BSA) Minute Volume (Female)= 3.5 (BSA) Estimate the ventilator frequency needed to achieve a certain PaCO 2 New frequency= Frequency /Desired PaCO 2  

11. Tidal volume FiO 2 Tidal volume usually between 10-12 ml/kg of predicted body weight Predicted body weight (Kg): Males: PBW = 50 + [2.3 ✕(height in inch-60)] Females: PWB = 45.5 + [2.3 ✕(height in inch-60)] Usually start with low tidal volume 6-8 ml/kg Severe hypoxemia, Post-resuscitation, ARDS keep initial FiO2 may be 100% Maintain PaO2 80-100 mmHg Keep FiO2 below 50 % to avoid oxygen induced lung injury

12. Pip, PEEP PIP- maximum pressure, usually at end of respiratory cycle Increases FRC, useful to treat refractory hypoxia Initial PEEP level- 5 cmH2O Pplat - pressure at alveolar level

13. Inspiratory pause, I:E ratio and inspiratory rise time I:E ratio (normal-1:2)is the duration of inspiratory and expiratory phases, represent compromise between ventilation and oxygenation. All abnormal I:E ratios uncomfortable and require deep sedation. More inspiratory time (I:E 1:1.5 or 1:1) increases Pmean , and favours better better oxygenation, at the cost of CO2 clearance. Disadvantage- more hemodynamic instability and the possibility of gas trapping. Oxygenation may paradoxically worsen due to change in pulmonary blood flow: particularly in volume dependent patients.

14. I:E ratio to improve oxygenation  

15. I:E ratio Range 1:2 – 1:4 (Pediatric 1:1:5) I time and I:E ratio inversely related Using flow to changed the I:E ratio Given : (minute volume) MV= 12L/min Desired I:E ratio= 1:3 Flow= MV ✕ sum of I:E ratio= 12L/min ✕ (1+3)= 48 L/min Using I Time to change the I:E ratio Given: f= 16/min, desired I:E ratio= 1:4 Time for each breath= 60 sec/16= 3.75 sec I Time= Time for each breath ✕ [I Ratio / Sum of I:E Ratio] = 3.75✕[1/(1+4)]= 0.75 sec Using I Time % to set I:E Ratio Given: desired I:E ratio= 1:3.5 I Time= I Ratio/ Sum of I:E Ratio= 1/(1+3.5)= 22 %

16. I:E ratio More expiratory time (I:E 1:4 and higher) expiratory CO2 clearance and favours better ventilation Disadvantage- possibility of atelectasis  

17. Inspiratory pause (0-30%) Period during inspiration, during which flow ceases This decreases CO2 clearance in scenarios of high airway resistance In ARDS, the decreased alveolar dead space instead improve s CO2 clearance

18. Inspiratory rise time (0-.4sec, 0-20%) Rate at which the ventilator achieves the pressure control variable should be left short (shortest possible) to WOB and patient-ventilator dyssynchrony One may decrease the inspiratory rise time to decrease the rate of inspiratory flow if PIP is high due to excessive resistance  

19. Flow pattern Square (constant), accelerating (ascending), decelerating (descending), sine wave Square flow may be used initially upon setting up the ventilator. Prove even, constant peak flow during entire inspiratory phase Accelerating- partial airway obstruction Decelerating- improve distribution of tidal volume and gas exchange, COPD Sine wave- more physiological, improve distribution of ventilation and gas exchange

20. Ventilatory phases Inspiration: Inspiratory valve opens and expiratory valve is closed Inspiratory pause: Inspiratory valve and expiratory valve closed Expiration: Inspiratory valve closed and expiratory valve open Expiratory pause: Inspiratory valve and expiratory (or PEEP) valve closed at end of expiration

21. What is mode ? Method or the way of delivering a breath by changing available variables. Components of a Mode: Type of breath- mandatory, assist, support, spontaneous Control variables- pressure, volume, dual Phase variables- trigger, limiting, cycling, baseline Conditional variables

22. variables Control variables Pressure controller Volume controller Flow controller Time controller Phase variables Trigger variable- Control: Time-Triggered, Pressure-Triggered, Flow-Triggered Limit Variable, Cycle Variable, Conditional Variable

23. Phase variables: Trigger, Limit and cycling Phase variables Trigger: ventilator (time)- triggered or patient (pressure or flow) triggered Limit: flow-limited or pressure-limited Cycling: volume, time or pressure cycled.

24. Phase variables: Trigger What causes the breath to begin (signal to open inspiratory valve) Machine (controlled): the ventilator will trigger regular breath at a frequency which will depend on the set respiratory rate, i.e. they will be ventilator time triggered . Patient (assisted): If the patient does make an effort to breath and the ventilator can sense it (by eighter sensing a negative inspiratory pressure or an inspiratory flow ) and deliver a breath, it will be called a patient-triggered breath.

25. Phase variables: Trigger

26. Phase variables: Limit Factor which controls the inspiration inflow Flow Limited: a fixed flow rate and pattern is set and maintained throughout inspiration. An adequate tidal volume ( Ti dependent) Pressure will be variable (compliance and resistance dependent) Pressure limited: the pressure is not allowed to go above a preset limit The tidal volume will be variable (compliance and resistance dependent)

27. Phase variables: Cycling Signal that stop the inspiration and start the expiration . Without inspiratory pause: one signal With inspiratory pause: two cycling signals (one to close inspiratory valve and the second to open the expiratory valve) Volume Time Flow Pressure: back-up from of cycling when the airway pressure reaches the set high-pressure alarm level

28. Control variables Pressure: Pressure signal is the feedback signal (Pressure Preset) Volume : Volume signal is the signal usually measure the flow and turn it into volume signal electronically. (volume preset) Time Flow Combinations

29. Basic Modes of Ventilation Controlled Mechanical Ventilation- Assist Control Ventilation- Intermittent Mandatory Ventilation Synchronized Intermittent Mandatory Ventilation Pressure Support- Combination Volume Control Pressure Control PRVC SIMV (VC+PS) SIMV (PC+PS) SIMV (PRVC)+PS Pressure Support/CPAP Bi-Vent Auto Mode NAVA

30. Initial ventilator settings Parameter Setting Notes Mode Assist/ Control or SIMV Provide ventilatory support. f 10-12/min Primary control to regulate ventilation. Guided by PaCO 2 V T 1—12 mL/kg PIP is directly related to the V T setting. FiO 2 100% for severe hypoxemia or compromised cardiopulmonary status 40% for mild hypoxemia or normal cardiopulmonary status. PEEP 5cmH 2 O for refractory hypoxemia Monitor patient and notes cardiovascular adverse effect. I:E 1:2-1:4 1:4 for patients needing longer E time due to air trapping. Flow pattern Constant Other floe pattern for lower PIP and better gas distribution. Parameter Setting Notes Mode Assist/ Control or SIMV Provide ventilatory support. f 10-12/min Primary control to regulate ventilation. Guided by PaCO 2 V T 1—12 mL/kg PIP is directly related to the V T setting. FiO 2 100% for severe hypoxemia or compromised cardiopulmonary status 40% for mild hypoxemia or normal cardiopulmonary status. PEEP Monitor patient and notes cardiovascular adverse effect. I:E 1:2-1:4 1:4 for patients needing longer E time due to air trapping. Flow pattern Constant Other floe pattern for lower PIP and better gas distribution.

31. Initial ventilator settings for neonate Parameter Normal Compliance Low Compliance PIP 15-20 cmH2O 20-30 cmH2O PEEP 3-5 cmH2O Up to 8 cmH2O V T 4-8 mL/kg 6-10 mL/kg frequency 25-40 /min Up to 150/min (esp. with air leak) Flow Rate 6-8 L/min 6-8 L/min I Time 0.3-0.5 sec Change according to frequency to maintain an I:E ratio of 1:1 I:E Ratio 1:1.5 -1:2 At least 1:1 (to prevent inverse I:E ratio) FiO2 Set to keep patient pink with SpO 2 from 90-95% Set to keep patient pink with SpO 2 from 90-95% Use with appropriate PEEP level if necessary

32. Effects of ventilator setting changes Settings Ventilation* Oxygenation** Frequency (f) Tidal Volume (V T ) FiO 2 Unchanged or PEEP Unchanged or PSV Pressure gradient (e.g., BiPAP, APRV) Settings Ventilation* Oxygenation** * Ventilation= ** Oxygenation=  

33. Volume control ventilation ( Vcv ) In general volume control favours the control of ventilation Advantages Disadvantage Guaranteed tidal volumes produces a more stable minute volume The minute volume remains stable over a range of changing pulmonary characteristic Initial flow rate is lower than in pressure-controlled modes, i.e. it avoids a high resistance-related early pressure peak The mean airway pressure is lower with volume control ventilation Recruitment may be poorer in lung units with poor compliance. In the presence of a leak, the mean airway pressure may be unstable Insufficient flow may give rise to patient-ventilator dyssynchrony .

34. Volume control ventilation ( Vcv )

35. Pressure control ventilation ( pcv ) In general pressure control favours the control of oxygenation Inspiratory pressure- control variable, maintain during inspiratory phase Square waveform Advantages Disadvantages Increased mean airway pressure Increased duration of alveolar recruitment Pressure limited ventilation may protect against barotrauma Work of breathing and patient comfort may be improved Tidal volume is variable and dependent on respiratory compliance Uncontrolled volume may result in volutrauma A high early inspiratory flow may breach the pressure limit if airway pressure is high

36. Pressure control ventilation ( pcv )

37. Controlled Mandatory Ventilation (CMV) The ventilator delivers Preset tidal volume (or pressure) at time triggered (preset) respiratory rate. As the ventilator controls both tidal volume (pressure) and respiratory rate, the ventilator ”controls” the patients minute volume. Patient can not breath spontaneously Patient can not change the ventilatory rate

38. Controlled mandatory ventilation (CMV) Suitable only when patient has no breathing efforts Disease or Under heavy sedation and muscle relaxants Disadvantage: Asynchrony and increased work of breathing Not suitable for patient who is awake or has own respiratory efforts Can not be used during weaning

39. Assist Control Ventilation A set tidal volume (volume control) or set pressure and time (pressure control) is delivered at a minimum rate Additional ventilator breaths are given if triggered by the patient Mandatory breath: Ventilator delivers preset volume and preset flow rate at a set back-up rate Spontaneous breath: Additional cycles can be triggered by the patient but otherwise are identical to the mandatory breath.

40. Assist Control Ventilation Tidal volume (V T ) of each delivered breath is the same, whether it is assisted breath or controlled breath Minimum breath rate is guaranteed (controlled breath with set V T ) Pros: Cons: Asynchrony taken care of to some extent Low work of breathing, as every breath is supported and tidal volume is guaranteed. Hyperventilation Respiratory alkalosis Natural breath are not allowed Breath stacking High volume and pressures

41. Assist Control Ventilation Hyperventilation and breath stacking can usually be overcome by choosing optimal ventilator setting and appropriate sedation Machine breath are delivered at a set rate (volume or pressure limit)

42. Intermittent Mandatory Ventilation (IMV) Patient is allowed to breath spontaneously from eighter a demand valve or a continuous flow of gases but not offering any inspiratory assistance. Patient’s capability determine Tidal volume of spontaneously breaths Some freedom to breath naturally even on mechanical ventilator Random chance of breath stacking and asynchrony: Increased WOB Uncomfortable feeling

43. Intermittent Mandatory Ventilation (IMV) Pros: Freedom for natural spontaneous breath even on machine Lesser chances of hyperventilation Cons: Asynchrony Random chance of breath stacking Increase work of breathing Random high airway pressure (barotrauma) and lung volume ( volutrauma )

44. Synchronized Intermittent Mandatory Ventilation (SIMV) Ventilator delivers eighter patient triggered assisted breath or time triggered mandatory breath in a synchronized fashion so as to avoid breath stacking If the patient breathes b/w mandatory breaths, the ventilator will allow the patient to breath a normal breath by opening the demand (inspiratory) valve but not offering any inspiratory assistance.

45. Synchronization window Time interval just prior to time triggering in which the ventilator is responsive to the patient’s inspiratory effort. If the patient makes a spontaneous inspiratory effort that fall in syn window, the ventilator is patient triggered to deliver an assisted breath and will count it as mandatory breath If patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath.

46. Synchronized Intermittent Mandatory Ventilation (SIMV) If the patient trigger outside the window, vent will allow this spontaneous breath to occur by opening the demand (inspiratory) valve but does not offer any inspiratory assistance. 3 types of breathing: Patient initiated assisted ventilation, Ventilator generated controlled ventilation, Unassisted spontaneous breath.

47. Synchronized Intermittent Mandatory Ventilation (SIMV) It allows patients to assume a portion of their ventilatory drive: Weaning is possible Greater work of breathing than AC ventilation and therefore some may not consider it as initial ventilator mode Friendly cardiopulmonary interaction: Negative inspiratory pressure generated by spontaneous breathing leads to increased volume return, which theoretically may help cardiac output and function

48. Pressure Support Ventilation Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drop to a specified fraction (typically 25%) of its maximum. Patient effort determines size of breath and flow rate.

49. Pressure Support Ventilation It augments spontaneous V T decreases spontaneous rates and WOB Used in conjunction with spontaneous breath in any modes of ventilation No guarantee of tidal volume with changing respiratory mechanics, No back up ventilation in the event of apnea. Provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the respiratory valve and other mechanical aspects of ventilatory support Allows for titration of patient effort during weaning Helpful in assessing extubation readiness

50. Ventilator management in ARDS Protocol for Lung Protective Ventilation 1 st stage: Calculate patient’s PBW→ Set TV at 8mL/kg of PBW→ add PEEP of 5cmH2O→ select lowest FiO2 that achieve an SpO2 of 88-95%→ Reduce TV by 1mL/kg every 2 hours until TV= 6mL/kg 2 nd stage: When TV= 6mL/kg, measure plateau pressure (Ppl) → if Ppl >30 cmH2O, decrease TV in 1mL/kg increments until Ppl < 30 cmH2O or TV= 4 mL/kg. 3 rd stage: Monitor ABG for respiratory acidosis→ If pH = 7.15-7.30, increase RR until pH> 7.30 or RR= 35 bpm → If pH <7.15, increase RR to 35 bpm, if pH is still < 7.15, increase TV in 1 mL/kg increments until pH> 7.15. Optimal goals: TV= 6 mL/kg, Ppl  30cmH2O, SpO2= 88-95%, pH= 7.3– 7.45

51. Ventilator management in COPD Dynamic hyperinflation Positive pressure ventilation Intrinsic PEEP Contd …

52. Ventilator management in COPD Ventilate with low tidal volume (6mL/kg) using lung protective ventilation protocol Maximize the time for expiration by: 1. preventing rapid respiratory rate (with sedation, if possible, or neuromuscular paralysis, if necessary). 2. monitoring I:E ratio of 1:2 or higher.

53. Thank you

54. Neurally adjusted ventilatory assist (NAVA) Patient’s electrical activity of diaphragm ( EAdi or Edi) is used to guide optimal functions of ventilator. Neural control of respiration originated in the patient’s respiratory center are sent to diaphragm via phrenic nerves. Bipolar electrodes are used to pick up electrical activity Electrodes are mounted on a disposable EAdi catheter and positioned in esophagus at the level of diaphragm. Available for adults, children, and neonates Used successfully in the mx of mechanically ventilated patients with spinal cord injury. Contd..

55. Neurally adjusted ventilatory assist (NAVA) Others uses- head injury, COPD, H/O ventilator dependency patients Rapidly reduce or eliminates the incidence of disuse atrophy of diaphragm.

56. High frequency oscillatory ventilation (HFOV) Utilizes the highest frequencies range (8-30 Hz), piston pump produces oscillatory waves that deliver the gas to the lungs. Produces both positive as well as negative stroke, which assist both inspiration and expiration. Pendelluft phenomenon: when inflated alveolar units equilibrate gases by swinging ventilations between them.

57. Clinical conditions for HFOV Clinical condition Notes Failing conventional ventilation Unable to maintain acceptable blood gas Deteriorating clinical condition Increasing ventilation requirement FIO2 >50%, frequency >30/min, and PIP >20 cm H2O for infants <1,000 g (PIP in high 20 cm H2O for infants >1,500 g) Rapidly increasing FiO2 requirement (without pneumothorax) Oxygen index >10 (e.g., patent ductus arteriosus Chest radiograph consistent with diffuse, homogenous lung disease (without air trapping) Hyaline membrane disease (HMD) Pulmonary hypertension Nitric oxide candidates, oxygen index 15 Clinical condition Notes Failing conventional ventilation Unable to maintain acceptable blood gas Deteriorating clinical condition Increasing ventilation requirement FIO2 >50%, frequency >30/min, and PIP >20 cm H2O for infants <1,000 g (PIP in high 20 cm H2O for infants >1,500 g) Rapidly increasing FiO2 requirement (without pneumothorax) Oxygen index >10 (e.g., patent ductus arteriosus Chest radiograph consistent with diffuse, homogenous lung disease (without air trapping) Hyaline membrane disease (HMD) Pulmonary hypertension