Newer modes of ventilation Dr Babu K Abraham MD, MRCP(UK) Senior Consultant Department of Critical Care Medicine Apollo Hospitals, Chennai

Newer Modes Dual Mode – Modes that try to deliver the benefit of both volume and pressure targeted breaths Try to guarantee control of both pressure & volume settings Partial Ventilatory Support – Pressure targeted modes Allow spont breathing during both high & low pressure setting Closed Loop System Intelligent automated modes PRVC BiLEVEL/BIPAP APRV NAVA

Pressure Regulated Volume Control (PRVC) Maquet Servo-i Also known by other names Adaptive pressure control AutoFlow - Dräger Medical AG Adaptive Pressure Ventilation - Hamilton Galileo Volume Control + - Puritan Bennett Volume Targeted Pressure Control/ Pressure Controlled Volume Guaranteed - Engström, General Electric Pressure targeted breaths (PCV) Has a target VT Time cycled

Machine adjusts the inspiratory pressure to deliver the set minimal VT If the VT is ↑ above the set target the machine ↓ the inspiratory pressure & vice versa Problems – The inspiratoy pressure is set based on the preceding VT If pt’s effort is large the VT will ↑ despite the inspiratory pressure ↓

Settings for PRVC VT – minimal desired RR – minimal desired Ti or I:E ratio Upper pressure limit - Machine will deliver a maximum pressure < 5 cm set Inspiratory rise time FiO2 PEEP

? Benefits of using PRVC Guarantees a minimum average VT Flow benefits of PCV retained – so better flow synchrony Less ventilatory manipulation required Near automatic weaning Evidence Compared to VCV – lower Ppeak* Compared to PCV – no difference even in Ppeak** No study on outcome*** May be less comfortable than PSV**** Relatively easy to use and set Can increase WOB in pts with increased resp drive – Eg Metabolic Acidosis. This is because these pts take large Vt due to their increased resp drive. The machine decrease the inspiratory pressure to maintain the target Vt. This then leads to inapp shifting of WOB onto the pt. Crit Care 1997;1(2):75-77* J Crit Care1998;13(1):21-25** Respir Care 2007;52:478-485*** Respir Care 2008;53:879-902****

Biphasic Intermittent Positive Airway Pressure (BIPAP) Also called Bilevel Bivent DuoPAP These modes deliver pressure-controlled breaths time-triggered time-cycled breaths using a set-point targeting scheme

There are two pressures to be set Phigh Plow This mode maintains a constant pressure (set point) even in the face of spontaneous breaths There are two pressures to be set Phigh Plow There are two time intervals to be set Time spent on Phigh – Thigh Time spent on P low - T low Pt can breath spontaneously at both these pressures T high T low

CPAP PCV BIPAP Phigh Unrestricted spontaneous breathing TIME T high T low PCV BIPAP Phigh improves oxygenation promotes alveolar recruitment Unrestricted spontaneous breathing Allows reduced sedation and promote weaning Plow Allows exhalation Maintains recruitment

The difference between the two P high & P low The difference between the two Two levels of functional FRC Creates a driving pressure Determines the VT Permit gas to enter the lung units Represents the difference between airway pressure (Paw) and alveolar pressure (Palv) T high T low PCV

Settings for BiLEVEL Clinician needs to set Phigh and Plow Thigh and Tlow Thigh and Tlow can be adjusted independently of the 2 pressure levels Recommendation for changing over Plow equivalent to PEEP Phigh equivalent to the Pplat or 12 to 16 cm H2O above the Plow Cycling – time cycling that approximately maintain a 1:1- I:E ratio Careful consideration of the patient’s underlying pathophysiology is required when adjusting these settings – ARDS vs COPD

APRV Concept same as Bi LEVEL There are some distinct differences Plow level In BIPAP – kept at PEEP In APRV – kept at 0 Relation between Thigh and Tlow In BIPAP – traditional to 1:1 In APRV - inverse ratio Original description Thigh 1.8 sec Tlow 1.3 sec APRV extended - Thigh 4 to 6 seconds Tlow 0.8 sec

APRV in ARDS pts shown to ** What is the evidence? BiLEVEL -Shown to be beneficial in patients during the acute phase of ALI and ARDS – improves dependent gas distribution* APRV in ARDS pts shown to ** - Improve oxygenation & hemodynamic parameters - ↓ in sedation and inotrope use - ↓ the durations of ventilation and ICU stay AJRCCM1999;159:1241–1248* AJRCCM 2001;164:43–49**

Closed Loop Systems Advances in microcomputer technique System that allow ventilators to manipulate variables based on feed back Commercially multiple modes available today Advanced version of PSV/PCV Input from neural output of the respiratory centers PAV NAVA

Neurally adjusted ventilatory assistance (NAVA) Advanced version of PSV Pt’s own spontaneous breathing is required Neural output - Electromyographic activity of the diaphragm (Edi) is captured Delivers assist in proportion to and in synchrony with the patient’s Edi signal A specially designed (9 electrodes) esophageal catheter needs to be inserted Amplified on a real-time basis to generate proportional Paw,insp

A spontaneous breath starts with – Impulse generated by the respiratory center Transmitted via the phrenic nerves Excitation of the diaphragm

In a healthy subject only 5% of maximum capacity of neuro ventilatory coupling is used to generate an adequate Vt In a healthy subject, the low amplitude of diaphragm excitation reflects the fact that neuroventilatory coupling is highly efficient and that only about 5% of m In disease, muscle performance may not be up to expectation, leading to an increased output from the respiratory center with the aim of recruiting additional motor units in the diaphrag maximum capacity is used. In this example, the increased signal seen in COPD and post-polio patients thus reflects the fact that a larger part of the muscular reserve is used. Only 5-8% of maximum capacity is used in healthy subjects, while up to 40% is used in COPD patients. If the diaphragm becomes weaker and/or the inspiratory load increases, the diaphragm´s electrical activation must increase to maintain a given volume. (Adapted from Sinderby et al JAP 1998) The electrical activity of the diaphragm (Edi) is measured in μV (micro volt). 1 μV = 10-6V, thus 1,000,000 μV = 1V.

Conventionally a pressure drop or flow reversal is used to initiate the ventilatory support The earliest signal that can be registered is the excitation of the diaphragm Adjusting the support level in synchrony with the rise and fall of the electrical discharge - the ventilator and the diaphragm works with the same signal input Conventional ventilator technology uses a pressure drop or flow reversal to initiate the assist delivered to the patient. This is the last step of the signal chain leading to inhalation and is subject to disturbances such as intrinsic PEEP, hyperinflation and leakage. The earliest signal that can be registered with a low degree of invasivity is the excitation of the diaphragm (as shown on the left-hand side of the picture). The excitation of the diaphragm is independent of pneumatic influence and insensitive to the above problems associated with pneumatic triggering technologies. By following diaphragm excitation and adjusting the support level in synchrony with the rise and fall of the electrical discharge, the ventilator and the diaphragm will work with the same signal input. In effect, this allows the ventilator to function as an extra muscle, unloading extra respiratory work induced by the disease process

A specially designed (9 electrodes) oesophageal catheter needs to be inserted Amplified on a real-time basis to generate proportional Paw,insp

What does the clinician set? Insert Edi Catheter Confirm the position of the catheter Adjust the NAVA Level - gain factor between the Edi and Paw,insp generated Set PEEP Set FiO2 Set Back up ventilation

Few clinical data are available so far with NAVA (especially in patients who have weak EMGdia signal) Studies in healthy subjects found the system able to match perfectly the patient’s timing and generate Paw,insp in proportion to the patient’s Edi* Beneficial effects Better patient–ventilator synchrony Facilitate physiological weaning** Concern - esophageal catheter placement may limit its clinical application Nat Med 1999;5(12):1433–6* Intensive Care Med.2008.**

Conclusion “A mode of ventilation is only as good as the operator who applies it”

Thank you