Mechanical ventilation

mechanical ventilation basic modes

1. Mechanical Ventilation: Basic Modes Dr. Shahnawaz Alam Guided by:-Dr. Vikas Chandra Jha HOD Neurosurgery Moderated by:- Dr.Saraj kumar Singh Asst.Prof .(Dept. of Neurosurgery)

2. Objectives To understand the basic modes of ventilator. The basics of Invasive positive pressure ventilation (IPPV) & Noninvasive positive pressure ventilation (NIPPV). How ventilator helps in reducing the work of breathing & restore adequate gas exchange. The principles of bedside monitoring: Pressure and volume alarms/Flow and pressure time curves.

3. “OUTCOME IN ICU DEPENDS ON VENTILATOR SETTINGS” “AS A NEUROSURGERY RESIDENT/NEUROGURGEON, WOULD BE PRIMARILY RESPONSIBLE FOR PATIENT CARE IN NEURO-ICU”

4. What are ventilator ? A machine that generates a controlled flow of gas into a patient’s airways by assisting or replacing spontaneous breathing. Supportive role to buy time. Negative pressure ventilation Positive pressure ventilation: Simple pneumatic system/New generation microprocessor controlled systems.

5. Who needs a ventilator? Can’t oxygenate (low PaO 2 /SpO 2 ). Can’t ventilate (high PaCO 2 ). Can’t generate enough tidal volume due to muscle or nerve weakness → high PaCO 2 /low SpO 2. Can’t participate or protect airway (low GCS ). If you’re not sure whether or not the patient needs a ventilator → the patient needs a ventilator!

6. Goals of Mechanical Ventilation Correct hypoxemia – PO 2 > 60mmHg or SpO 2 > 90 %. Correct hypercapnia – PCO 2 ~ 40mmHg. Reduce work of breathing Provide rest to respiratory muscles and reduce oxygen cost of breathing.

7. Basic Ventilator Parameters Tidal volume( Vt ) Frequency (f) FiO2 SPO2 Airway pressure Positive End Expiratory Pressure(PEEP) I:E Ratio Ve = Vt x f Ve = PaCO2

8. Tidal Volume Volume of air needed to adequately remove CO 2 from the blood. Usually 6-10 ml/kg of body weight. Current literature lower tidal volume practice.

9. Frequency The frequency that the tidal volume must be delivered to adequately remove CO2. Usually 12-14/min may be increased or decreased as indicated by arterial CO2 levels. Actual rate may be higher than the set rate if the patent is initiating spontaneous breaths.

10. FiO 2 FiO2 is the amount of oxygen delivered to the patient. Oxygen concentrations of greater than 0.50 (50%) increase the risk of oxygen toxicity if delivered for more than 24 hours.

11. POSITIVE END EXPIRATORY PRESSURE(PEEP ) Elevation of baseline Paw above Patm . Not a standard mode of ventilation but used as adjunct to other modes. Hazards of PEEP: Lowers venous return, CO Barotrauma (PEEP>10 cm H2O) Increased CVP, ICP

12. I:E Ratio The normal ratio of inspiration to expiration is 1: 1.5 - 1: 2. Longer Ti → opening of stiff alveoli units → improves oxygenation . Shorter Ti → encourages lung emptying. Te → prevent alveoli from collapse → intrinsic PEEP → reduction of shunting. Thus , adjustments in I:E ratios are goal oriented. Ratios >1 inverse ratio ventilation.

13. Pressure Waveforms Depicts changes in airway pressure over time Baseline is normally zero. If PEEP is applied, the baseline pressure will equal the PEEP.

14. Starting a ventilator-Mode Mode denotes interplay b/w patient and the ventilator. Describes the style of breath support based on relationship between the various possible types of breath and inspiratory phase variables.

15. The ventilator circuit

16. ventilatory phases Each ventilatory breath has four phases: Initiation phase Inspiratory phase Plateau phase Expiratory phase

17. Variables Respiration is a dynamic process in which pressure, volume and flow are function of time . They are called as variables. There are two kinds of variables- Control variables & Phase variables . Control Variables Control the delivery of a breath. The clinician can choose to keep either volume or pressure constant from breath to breath. The control variables are used to describe modes of ventilation - Volume-controlled (VC) ventilation Pressure-controlled (PC) ventilation

18. Phase Variables How the ventilator controls the phases of the respiratory cycle depends upon the phase variables. Four phase variables are - Trigger variable Limit variable Cycle variable Baseline variable

19. Trigger Variables Determine how a breath is started. A breath can be initiated (triggered) either by: The ventilator The patient Ventilator-triggered breaths: initiated in response to a timer inside the ventilator. The exact time interval is determined by the set rate.

20. Patient-triggered breaths are termed as: Spontaneous breath: completely regulated by the patient with no contribution by the ventilator. Assisted breath: initiated by the patient, but all other aspects of the breath are controlled by the ventilator. Supported breath: initiated and ended by the patient, but the breath is delivered under positive pressure by the ventilator . Trigger variables: pressure/flow/volume/time.

21. Cycle Variables Determine how a breath ends. The change over from inspiration to expiration and from expiration to inspiration is called cycling . It can be determined by : • Volume cycle (desired volume met) • Flow cycle (desired flow met) • Pressure cycle (desired pressure met) • Time cycle (elapsed time met )

22. Limit Variable

23. Baseline Variable

24. CONTROLLED Vs ASSISTED VENTILATION Controlled breaths are time triggered breaths. Patient cannot initiate breath sequence irrespective of effort. May be volume or pressure targeted. Patient cannot control RR, VT or Paw. Assisted breaths are triggered by patients’ effort (Flow / Pressure) Once breath is initiated, pre-set VT or Paw attained by the ventilator. Patient can control RR but not VT or Paw.

25. BREATH TYPE: Spontaneous vs Mechanical vs Assisted

26. INVASIVE IPPV FULL SUP P ORT CMV VOLUME CONTROL PRE S SURE CONTROL PARTIAL SUP P ORT S I M V PSV

27. Basic Modes of Ventilation Controlled Mandatory Ventilation (CMV ): Pressure control(PC) or Volume control(VC) Asst-Control Mandatory Ventilation (ACV ) Intermittent Mandatory Ventilation(IMV) Synchronized Intermittent Mandatory Ventilation(SIMV) Pressure Support Ventilation (PSV ) Combinations: SIMV(PC)+PS / SIMV(VC)+PS

28. PATIENT COMFORT SCALE + - Spontaneous Breathing Controlled Mechanical Ventilation Assist Control Ventilation Synchronized Intermittent Mechanical Ventilation Pressure Support Ventilation Pressure Control Ventilation

29. Controlled mandatory ventilation(CMV) D elivers Preset Vt (or pressure) at a time triggered (preset) RR(f). As it controls both V t (pressure) and f Ve Patient cann’t breath spontaneously/change the ventilator ‘f’ Suitable when no breathing efforts/disease or Under heavy sedation and muscle relaxants. Asynchrony and increased work of breathing. Not suitable in awake or has respiratory efforts. Cann’t be used during weaning.

30. Volume Control Ventilation V entilator delivers a pre-set TV. Pressures may vary with changes in R and CL but volume remains constant. Inspiration ends when the pre-set TV is reached/certain time elapses (inspiratory hold). Time triggered, Flow limited, Time/Volume cycled ventilation.

31. Settings: Vt , f, Flow/ Time and FiO2 VT: 6 – 12 ml/kg f: 10 – 15 bpm FiO2: lowest possible to achieve oxygenation. I:E : 1:2 – 1:4 Monitoring and alarms: PIP and P plat relates to CL. High/Low pressure alarm: 5 – 10 cm H 2 O above/below ventilating pres. Low pressure and volume alarms signify leak in system.

32. Pressure Control Ventilation Provides pre-set pressure to the airways, not exceeding the set level irrespective of changes in CL and R. Vt is variable depending on compliance, Raw , set pressure and patient effort. Expiration occurs once a pre-set Ti has elapsed. Time triggered, Pressure limited, Time cycled ventilation.

33. Settings Pressure: < 30 cm H2O f : 10-15 bpm I:E ratio: 1:2 - 1:4 Ti and flow rate depend on I:E ratio and f Monitoring and alarms: Low Volume alarm: increased resistance or decreased compliance (in VCV signifies leak). Low pressure alarm: ≈10 cm H2O below patients ventilation pressure leak in the system.

34. ASSIST /CONTROL MODE A set Vt (VC) or a set pressure and time (PC) is delivered at a minimum rate. Additional ventilator breaths are given if triggered by the patient. Mandatory breaths: Ventilator delivers preset volume and preset flow rate at a set back-up rate. Spontaneous breaths: Additional cycles can be triggered by the patient but otherwise are identical to the mandatory breath.

35. Vt of each delivered breath is the same, whether it is assisted or controlled breath. Minim. breath rate is guaranteed (controlled breaths with set Vt ).

36. Pros: Asynchrony taken care of to some extent. Low WOB as every breath is supported and Vt is guaranteed. Cons: Hyperventilation Natural breaths are not allowed Breath stacking High volumes and pressures C/I: Irregular RR/Hiccoughs/Brainstem injury Hyperventilation and breath stacking can be overcome by choosing optimal ventilator settings and appropriate sedation

37. Intermittent Mandatory Ventilation(IMV) Machine breaths are delivered at a set rate (volume or pressure limit). Patient is allowed to breath spontaneously from either a demand valve or a continuous flow of gases but not offering any inspiratory assistance. Patient’s capability determines Vt of spontaneously breaths. Some freedom to breath naturally even on mechanical ventilator.

38. Pros : Freedom for natural spontaneous breaths even on machine. Lesser chances of hyperventilation. Cons : Asynchrony/Random chance of breath stacking. Increase WOB. Random high airway pressure (barotrauma) and lung volume ( volutrauma ). The con’s have been addressed in newer modes like SIMV and PSV and IMV is not an option in most modern ventilators.

39. Synchronized Intermittent Mandatory Ventilation (SIMV) Ventilator delivers either patient triggered assisted breaths or time triggered mandatory breath in a synchronized fashion so as to avoid breath stacking. If the patient breathes between mandatory breaths, the ventilator will allow the patient to breathe a normal breath by opening the demand ( inspiratory ) valve but not offering any inspiratory assistance . If patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath.

40. Synchronisation window Time interval just prior to time trigger when the ventilator is sensitive to patient effort and assisted breath is delivered. V aries in different manufacturers but 0.2-0.5 sec bfr time trigger is standard. If the patient makes a spontaneous inspiratory effort that falls in sync window , the ventilator is patient triggered to deliver an assisted breath and will count it as mandatory breath. If the pt triggers outside this window, vent will allow this spontaneous breath to occur by opening the demand (inspiratory) valve but does not offer any inspiratory assistance.

41. SIMV contin … Mandatory breaths are ‘ sychronised ’ with patient effort. Mandatory breaths may be time triggered (poor RR) or patient triggered (good RR).Thus, mandatory breaths my be assisted or controlled. Mandatory breaths can be set as volume controlled or pressure controlled. The problem of ‘breath stacking’ and dysynchrony addressed But the problems of WOB and Raw during spontaneous breath persisted. This is tackled with use of Pressure Support as adjunct. SIMV and spontaneous mode always used with PSV in modern practice.

42. In SIMV -3 types of breathing: 1. Patient initiated assisted ventilation 2. Ventilator generated controlled ventilation 3. Unassisted spontaneous breath

43. DUAL CONTROL MODES Advantages of Pressure control ventilation (Rapid decelerating flow) + Advantages of volume-control ventilation ( constant MV)

44. PRESSURE REGULATED VOLUME CONTROL(PRVC)/ ADAPTIVE PRESSURE CONTROL (APC)/AUTOFLOW Achieve volume support while keeping PIP lowest possible. Ventilator gives a trial breath and calculates Pplat & compliance . Pressure gradually increased till it reaches set Vt. PIP is kept at lowest by altering the flow rate and inspiratory time in response to changing compliance or Raw.

45. OTHER MODES Inverse Ratio Ventilation (IRV ) Longer inspiratory time; I:E = 2:1 – 4:1. Beneficial in ARDS by – reducing intrapulmonary shunt, reduced dead space ventilation , Better V/Q matching. Higher MAP - more chances of barotrauma. May worsen pulmonary edema. Requires sedation and paralysis.

46. Spontaneous Modes Three basic means of providing support for continuous spontaneous breathing during mechanical ventilation: Pressure Support Ventilation-PSV Continuous positive airway pressure- CPAP INDICATIONS Spontaneously breathing patients who require additional ventilatory support to help overcome - WOB, CL, Raw Respiratory muscle weakness Weaning

47. Pressure Support Ventilation Applicable on Spontaneous breaths/No mandatory breaths. Pressure (or Pressure above PEEP) is the setting variable. The ventilator provides a constant pressure during inspiration once it senses that the patient has made an inspiratory effort. Patient effort determines size of breath and flow rate. Patient triggered, pressure targeted, flow cycled mode of ventilation .

48. ADVANTAGES Full to partial venti . support / Facilitates weaning Augments the patients spont Vt . Decreases patient WOB by overcoming the resistance of the artificial airway, vent circuit and demand valves . May be applied in any mode that allows spontaneous breathing, e.g., VC-SIMV, PC-SIMV. DISADVANTAGES Requires consistent spont ventilation. Patients in stand-alone mode should hv back-up ventilation. Vt variable and dependant on lung characteristics and synchrony. Fatigue and tachypnea if PS level is set too low.

49. ASSESMENT OF READYNESS TO WEAN General preconditions: Reversal of primary problem Patient is awake and responsive ability to cough No or minimal inotropic support Normalising metabolic status Adequate Hb concentration Objective values: Vital Capacity > 10 ml/kg RR <35 Tidal volume > 5ml/kg Max inspiratory pressure <-25 cm H2O RR / Vt <100 b/min/L { Rapid Shallow Breathing Index ( RSBI) } PaCO2 < 50 mmHg PaO2 > 90 mm Hg at FiO2 0.4 PaO2/ FiO2 > 200

50. Causes of failure to wean: Hypoxemia: Diffuse pulmonary/Focal pulmonary disease (Pneumonia) /Pulmonary edema Insufficient Ventilatory Drive: d/t to metabolic alkalosis/Inadequate CNS drive (Ex: sedatives, malnutrition) Excessive Ventilatory Drive:Excessive CO2 production (sepsis, agitation, fever, high carbohydrate intake) Respiratory Muscle Weakness: Neuromuscular disease/Malnutrition / Drugs (Neuromuscular blocking agents, Corticosteroids,aminoglycosides ) Excessive WOB: Airway obstruction/Bronchospasm/Secretions/Increased Raw ( ETT)/ETT too small/Chest motion restriction (pain, bandages ) Phrenic nerve Injury : especially with contralateral pulmonary disease

51. Bedside Monitoring

52. Bedside Monitoring

53. Important Pitfalls and Problems Associated with PPV Heart and circulation - Reduced venous return and afterload - Hypotension and reduced cardiac output Lungs: Barotrauma /VILI/Air trapping Gas exchange - May increase dead space (compression of capillaries) - Shunt (e.g., unilateral lung disease - the increase in vascular resistance in the normal lung associated with PPV tends to redirect blood flow in the abnormal lung)

54. Barotrauma M icroscopic rupture of the alveolus with subsequent entry of air into the pleural space (pneumothorax) and/or the tracking of air along the vascular bundle to the mediastinum ( pneumomediastinum ), 6-25%. Large TV and elevated PIP and Pplat are risk factors. PIP <45 mm Hg and Pplat < 30-35 mm Hg are recommended.

55. Volutrauma local over distention of normal alveoli. over distention-an inflammatory cascade causing additional damage to previously unaffected alveoli. ARDS like clinical scenario. PEEP may be beneficial in preventing this type of injury. P rotective lung ventilation strategy is recommended in all patients with ARDS or acute lung injury .

56. Oxygen toxicity Complication has been reported in patients given a maintenance FIO2 of 50% or above for longer duration. Cause a variety of complications-mild tracheobronchitis , absorptive atelectasis, hypercarbia , and diffuse alveolar damage that is indistinguishable from ARDS. Encouraged to use the lowest FIO2 that accomplishes the needed oxygenation. If necessary, PEEP should be considered a means to improve oxygenation while a safe FIO2 is maintained.

57. VENTILATOR ASSOCIATED PNEUMONIA (VAP) Defined as pneumonia occuring > 48 hrs after intubation and mechanical ventilation. Estimated incidence is 10-25 %, mortality of 33-76 %. Early onset (2-5 days) – S.Pneumoniae , H. Influenzae,MSSA , E.Coli , Klebsiella . Late onset (> 7 days) – P. Aeruginosa , Acinetobacter , MRSA , other MDR pathogens.

58. VAP Contn … DIAGNOSIS Presence of a new or progressive infiltrate in CXR plus two of the following: Fever > 38 C. Leukocytosis/ Leukopenia. Purulent tracheobronchial secretions. Respiratory tract sampling using BAL, mini BAL, tracheo -bronchial aspiration for microscopy and quantitative culture.

59. PREVENTION ‘bundled approach ’ has shown to reduce the incidence of VAP by 95%. Components : Appropriate cuff/Change of circuit every 7 days. HME filter and suction devices changed daily. ETT with dorsal lumen for sub- glottic secretions. Elevation of head 30-45 o. Strict hand hygiene/Oropharyngeal decontamination. Sedative vacation; early extubation . Non invasive ventilation. Prophylactic antibiotics are not recommended.

60. TREATMENT: Emperical antibiotic therapy after sampling. Choice of antibiotic depends on local prevalance of organisms and the patient’s risk for MDR infection. Low risk – Ceftriaxone/ Levo , ciprofloxacin/ Ampicillin sulbactam / Ertapenem . High risk – Antipseudomonal ( Cefipime / Ceftazidime / carbapenems / Piperacillin TZ) + Fluroquinolone / Aminoglycoside + Linezolid/ Vancomycin .

61. NON- INVASIVE PPV NIPPV is ventilator support provided without invasive airway control-No tracheostomy /No ETT. M ostly used to provide pressure support during spontaneous ventilation, BiPAP , CPAP. Also used as an option for weaning .

62. ADVTG: Allows the patients to maintain normal functions-Speech/Eating. Helps avoid the risks and complications related to: Intubation/Sedation. Less ventilator-associated Pneumonia. DISADVTG: Less airway pressure is tolerated. Does not protect against aspiration. No access to airway for suctioning.

63. Continuous positive airway pressure (CPAP) PEEP applied to spontaneous breathing patient. Can be applied via ETT/face mask/nasal mask. Less adverse effects than PEEP because of spontaneous rather than PPV. Bilevel positive airway pressure ( BiPAP ) Inspiration positive pressures to inspiration (IPAP) and expiration (EPAP). IPAP provides pressure support during inspiration and EPAP helps in recruitment and FRC. Initially IPAP – 8 cm H2O, EPAP – 4 cm H2O; maybe increased or decreased in 2cm.

64. Clinical Use of NIPPV in ICU Decompensated COPD ( Hypercapnic Respiratory Failure ). Cardiogenic pulmonary edema. Hypoxic respiratory failure. Other possible indications: Weaning ( post- extubation )/Obesity hypoventilation syndrome.

65. Contraindications to NIPPV Cardiac or respiratory arrest/Non-respiratory organ failure. Severe encephalopathy (e.g., GCS < 10 ). Severe upper gastrointestinal bleeding. Hemodynamic instability or unstable cardiac arrhythmia. Facial surgery, trauma, or deformity Upper airway obstruction. Inability to cooperate/protect the airway. Inability to clear respiratory secretions/High risk for aspiration.

66. SUMMARY Ventilator is a support measure, not a treatment modality. So pay more attention at the disease that created ventilator dependency rather than at the knob of ventilator. Proper understanding of ventilator function and modes are vital to provide individualized therapy to a wide range of patients. Ventilator graphics can provide valuable information regarding settings and pulmonary characteristics. Early weaning is the norm. VILI and VAP are dreaded complications - prevention is better than cure.

67. REFERENCES 1 . Clinical Application of Mechanical Ventilation – David W Chang, 4 th Edition 2. The ICU book – Paul L. Marino, 4th edition THANKS !!