PATIENT-VENTILATORINTERACTION DURING PARTIAL VENTILATORY ASSIST Toshio Fukuoka Dept Emergency and Intensive Care Medicine, Nagoya University JAPAN 1!
Topics in my presentation! Purpose of partial ventilatory support (PVA)! Characteristics of PVA! Unloading WOB (work of breathing) during SIMV! Patient-ventilator synchrony during PVA! Several topics about PSV (pressure support ventilation) and PAV (proportional assist ventilation) 2!
Purpose of partial ventilatory assist! Achieve more comfortable assist for the patient to avoid fighting and deep sedation and/or neuromuscular blockade! Keep respiratory muscle activity to prevent the muscle atrophy during ventilatory assist! Unload the patient work of breathing (WOB) during the weaning process 3!
Spontaneous breathing and total ventilatory assistSpontaneous breathing Total ventilatory assist Airway pressure Flow Pressure provided by Flow ventilator Alveolar pressure Alveolar pressure Pmus Pressure of patient inspiratory muscle 4!
Modes of PVA! Assist ventilation! Synchronized intermittent mandatory ventilation (SIMV)! Pressure support ventilation (PSV)! Proportional assist ventilation (PAV) 6!
Characteristics of PVA methods! Trigger " When will the assist start?! Frequency of support " How many assist will be provided?! Limit of support breath " Does the assist have any limit or target of tidal volume or airway pressure?! Inspiratory-expiratory switching " When will the assist stop for expiration? 7!
PAV! Trigger: Patient inspiratory effort (PIE)! Frequency: PIE! Limit: Pre-set proportion of PIE in pressure! Switching: PIE (?) 11!
Characteristics of PVA methods Frequency Limit of Trigger IE switching of support support breath Pre-set TVACV PIE PIE Pre-set TV (+ pause time) Time Pre-set Pre-set TVIMV Pre-set TV cycle frequency (+ pause time) Pre-set Pre-set TVSIMV PIE Pre-set TV frequency (+ pause time) Pre-setPC-assist PIE PIE Pre-set time pressure Pre-set Pre-setPC-SIMV PIE Pre-set time frequency pressure Pre-setPSV PIE PIE Inspiratory flow pressure Pre-set ratio ofPAV PIE PIE PIE PIE 12!
Unloading WOB during SIMV! In 1970s, IMV and SIMV were introduced as PVA and used widely for weaning process from ventilator.! Weaning by (S)IMV enables a gradual reduction in the amount of support provided by the ventilator and a progressive increase in the amount of respiratory work performed by the patient.! But…. 13!
Unloading WOB during SIMV! Though SIMV showed gradual loading of WOB during reduction of assist rate, one study showed that even at 80% of support of the minute ventilation, the ventilatory muscles continue to perform significant work in patient of ARDS. (Marini JJ et al ARRD 1988; 138: 1169)! In SIMV, decreasing assist rate resulted in increase WOB not only for the spontaneous breaths, but also for the assisted breaths. 14!
EMG during SIMVAssisted breaths and spontaneous breathsEven at the assistedbreaths, EMG activitywas almost same asspontaneous breaths.Imsand C et al. Anesthesiology1994; 80:13 15!
Unloading WOB during SIMV! InSIMV, unloading WOB is far from proportional to assist rate.! Even if ventilator provide most of the minute ventilation, level of WOB would be enough to exhaust the patient. 16!
Clinical implication Unloading WOB in SIMV! Leaving an exhausted patient with SIMV with spontaneous breaths might be a desperate exercise for him/her rather than a rest.! Check the patient condition to avoid unintentional overload due to inappropriate PVA. " However even in PSV, a study showed that tidal volume during the weaning was not a good predictive factor for weaning success in COPD patients.(Stroetz RW, Hubmayr RD. AJRCCM 1995;152: 1034) 17!
Asynchrony during PVA! Frequency and limit " Inadequate or excessive inspiratory flow or volume! Trigger " Trigger failure " Trigger delay " Auto-cycling! IE Switching " Premature termination " Double triggering 18!
Asynchrony during PVA! Frequency and limit " Inadequate or excessive inspiratory flow or volume! Trigger " Trigger failure " Trigger delay " Auto-cycling! IE Switching " Premature termination " Double triggering 19!
To match the ventilatory support to patient inspiratory effort! Matching the ventilator support to patient inspiratory effort is a key of patient-ventilator synchrony during PVA.! Patient ventilatory pattern varies significantly. " However, sometimes patient ventilatory pattern is not reliable. 20!
Tidal volume of spontaneous breathing varies greatly. JAMMES ET AL, BULLETIN EUROPEAN DE PHYSIOPATHOLOGIE RESPIRATOIRE. 15: 527, 1979In 235 healthy subjects, tidal volume (Vt) and respiratory rate(fv) of varies so much. 21!
Mean tidal volume of the patients are different and stable during PAV In ventilator dependent patients, tidal volume was so constant withTidal volume(l) different support level of PAV. Note: the difference in tidal volume among the patients Assist levels of PAV(%) MARANTZ ET AL, J. APPL. PHYSIOL 80: 397, 1996 22!
Fluctuation of ventilatory pattern during ventilatory assistEven in ventilator dependent patient, there is a breath-by-breath variability in flow pattern. Younes ARRD 1992 23!
Partial ventilatory assistWhen the patient pulls differently, what would happen? Airway pressure Pressure provided by Flow ventilator Alveolar Synchrony and pressure asynchrony Pressure of patient Pmus inspiratory muscle 24!
Volume pre-set SIMV (or ACV) Airway pressure Pressure When Pmus provided by increases, ventilator Flow ventilator deliver the tidal volume with preset flow rate and airway Alveolar pressure decrease. pressure Pull harder Little push Pressure of patient Pmus inspiratory muscle 25!
Pressure support ventilation Airway pressure Pressure When Pmus provided by increases, ventilator Flow ventilator deliver more inspiratory flow to obtain the targetAlveolar pressure.pressure Pull harder Same push Pressure of patient Pmus inspiratory muscle 26!
Proportional assist ventilation When Pmus Airway pressure increases, ventilator Pressure support level also provided by increases and Flow ventilator inspiratory flow rate and airway pressure increase.Alveolarpressure Pull harder More push Pressure of patient Pmus inspiratory muscle 27!
Synchrony during PVA! PSV and PAV allow the inspiratory flow and time to change in account of the patient inspiratory effort during support breaths! In PAV, airway pressure of support breaths will change according to the patient inspiratory effort. " Though PAV has theoretical advantage over PSV, SIMV and ACV in terms of patient-ventilator synchrony, its efficacy and safety in clinical setting should be evaluated more. 29!
Triggering synchrony! Minimize the delay of trigger and trigger failure " Flow trigger or pressure trigger " Avoid PEEPi and too-much-support " Option: Other trigger signal for PVA? • Esophageal pressure triggering? # Adv: Free from effect of PEEPi # Disadv: Noisy signal (heart beat and esophageal motion) 30!
Pressure trigger or flow trigger? Flow triggering seemed to be better in terms of minimize triggering PTP. NOTE: Difference between ventilator types and trigger levels. Aslanian P et al: AJRCCM 1998; 157: 135 31!
Pressure trigger or flow trigger?! Though flow trigger seems to be better than pressure trigger in terms of trigger synchrony, type of ventilator and setting of trigger level would be also important to avoid trigger delay and asynchrony. 32!
Trigger failure due to (?) PVA! PVA will cause PEEPi in 1) patients with increase airway resistance, 2) tachypneic patients and 3) small patients (premature babies).! To achieve trigger synchrony, decrease the assist level is effective in some occasions.! Several studies showed that in PAV the trigger failure rarely occurred. 33!
Trigger failure (trigger asynchrony) during assist ventilation*: trigger failureThe patient had severe airway obstruction.Note: Expiratory flow at the start of inspiration. Chao DC et al. Chest 1997; 112: 1592-1599 34!
PSV and PAV for tachypneicRATE patient Pressure support level (cmH2O)RATE Younes, M.35! 1997 PAV assist level
Effect of reducing support level to trigger failureIn PSV, triggering failure could be eliminated byreducing support level. Giannouli E et al. AJRCCM 1999; 159: 1716 36!
Clinical implication! Decreasing respiratory rate in PVA might be a sign of trigger failure.! To avoid trigger failure, decrease the ventilatory assist would be effective if the patient is tolerable for the reduction.! For avoid trigger failure, PAV showed advantage in some studies. 37!
One more topic about PAV! Decreasing mean airway pressure without ABG worsening.! PAV for small babies. 38!
Decrease in airway pressure during PAV: clinical study In cross over trial of 8 septic patients, during PAV, PIP was decreased significantly and cardiac output increased significantly comparing with in ACV. Younes, M 1992. 39!
Decrease in mean airway pressure during PAV! In cross-over trial of premature babies, PAV successfully reduced mean airway pressure without ABG worsening comparing with conventional mechanical ventilation. (Schulze, A et al. J Pediatr 1999) " Decrease in mean airway pressure might prevent barotrauma and BPD in ventilated premature babies (no clinical trial for this endpoint is available now). 40!
Summary! Characteristics of PVA " Trigger, Frequency, Limit, Switching! Unloading WOB in SIMV " Watch your patient. Do not rely on the assist rate.! Synchrony during PVA " Flow trigger > pressure trigger (?) " (PAV) > PSV > SIMV/ACV " Decrease the respiratory rate during PVA? Then check patient breath rate, or you might miss the asynchrony.! PAV: Promising PVA. Use it with caution today. 41!