Modes of Modes of Mechanical VentilationMechanical Ventilation

Mohamad S Ahmad, M.D. Mohamad S Ahmad, M.D. Lecturer of Anaesthesia and

Intensive CareAin Shams University Cairo, Egypt

2008

IntroductionIntroduction

VentilationVentilation • The goal of ventilation is to facilitate CO2 release The goal of ventilation is to facilitate CO2 release

and maintain normal PaCO2and maintain normal PaCO2• Minute ventilation (VE)Minute ventilation (VE)

– Total amount of gas exhaled/min.Total amount of gas exhaled/min.– VE = (RR) x (TV)VE = (RR) x (TV)– VE comprised of 2 factorsVE comprised of 2 factors

• VA = alveolar ventilationVA = alveolar ventilation• VD = dead space ventilationVD = dead space ventilation

– VD/VT = 0.33VD/VT = 0.33• VE regulated by brain stem, responding to pH and VE regulated by brain stem, responding to pH and

PaCO2PaCO2

Oxygenation

• The primary goal of oxygenation is to The primary goal of oxygenation is to maximize O2 delivery to blood (PaO2)maximize O2 delivery to blood (PaO2)

• Alveolar-arterial O2 gradient (PAO2 – Alveolar-arterial O2 gradient (PAO2 – PaO2)PaO2)– A-a gradient measures efficiency of A-a gradient measures efficiency of

oxygenationoxygenation

• PaO2 partially depends on ventilation PaO2 partially depends on ventilation but more on V/Q matchingbut more on V/Q matching

Adjustments

• To affect To affect oxygenation, oxygenation, adjust:adjust:

– FiOFiO22

– PEEPPEEP

– I timeI time

– PIPPIP

• To affect To affect ventilation, adjust:ventilation, adjust:

– Respiratory Respiratory

RateRate

– Tidal VolumeTidal VolumeMAP

VE

COMPLIANCECOMPLIANCE = = Volume / Volume / Pressure Pressure

If volume is set, pressure varies…..if pressure If volume is set, pressure varies…..if pressure is set, volume variesis set, volume varies

Goals of MechanicalVentilation

• Achieve and maintain adequate Achieve and maintain adequate pulmonary gas exchangepulmonary gas exchange

• Minimize the risk of lung injuryMinimize the risk of lung injury

• Reduce patient work of breathingReduce patient work of breathing

• Optimize patient comfortOptimize patient comfort

Ideal Mode of Ventilation

• Synchronizes with the patient’s Synchronizes with the patient’s spontaneous respiratory effortspontaneous respiratory effort

• Maintains adequate and consistent tidal Maintains adequate and consistent tidal volume and minute ventilation at low volume and minute ventilation at low airway pressuresairway pressures

• Responds to rapid changes in pulmonary Responds to rapid changes in pulmonary mechanics or patient demandmechanics or patient demand

• Provides the lowest possible WOBProvides the lowest possible WOB

Ideal Ventilator Design

• Achieves all the important goals of mechanical Achieves all the important goals of mechanical ventilationventilation

• Provides a variety of modes that can ventilate Provides a variety of modes that can ventilate even the most challenging pulmonary diseaseseven the most challenging pulmonary diseases

• Has monitoring capabilities to adequately Has monitoring capabilities to adequately assess ventilator and patient performanceassess ventilator and patient performance

• Has safety features and alarms that offer lung Has safety features and alarms that offer lung protective strategiesprotective strategies

MODESMODES• Ventilator mode can be defined as a set of operating Ventilator mode can be defined as a set of operating

characteristics that control how the ventilator characteristics that control how the ventilator functionsfunctions

• Operating mode can be described by (1)the way a Operating mode can be described by (1)the way a ventilator is triggered into inspir. and cycled into ventilator is triggered into inspir. and cycled into expir., (2)what variables are limited during expir., (2)what variables are limited during inspiration, (3)and whether or not the mode allows inspiration, (3)and whether or not the mode allows mand., spont. breaths or both.mand., spont. breaths or both.

• spontaneous, PEEP, CPAP, BiPAP, CMV, AC, IMV, spontaneous, PEEP, CPAP, BiPAP, CMV, AC, IMV, SIMV, MMV, PSV, PCV, APRV, IRVSIMV, MMV, PSV, PCV, APRV, IRV

SPONTANEOUSSPONTANEOUS• Not an actual mode since rate and tidal volume Not an actual mode since rate and tidal volume

during spont. breathing are determined by during spont. breathing are determined by patientpatient

• Role of ventilator during spont. vent. is to Role of ventilator during spont. vent. is to provide the (1) flow to the pt. in a timely provide the (1) flow to the pt. in a timely manner, (2) flow adequate to fulfill a patient’s manner, (2) flow adequate to fulfill a patient’s insp. demand, and (3) provide adjunctive insp. demand, and (3) provide adjunctive modes such as PEEP to complement the spont. modes such as PEEP to complement the spont. effort effort

• Apnea ventilation is a safety feature used for Apnea ventilation is a safety feature used for spontaneous modespontaneous mode

PEEPPEEP• PEEP increases the end-expiratory or baseline airway PEEP increases the end-expiratory or baseline airway

press. to a value greater than atmos. and is often used to press. to a value greater than atmos. and is often used to improve the pt.’s O2 status, esp. if refractoryimprove the pt.’s O2 status, esp. if refractory

• PEEP is not a stand-alone mode, but is used in PEEP is not a stand-alone mode, but is used in conjunction with other modesconjunction with other modes

• Two major indication for PEEP are:Two major indication for PEEP are:

- Intrapulmonary shunt- Intrapulmonary shunt

- Decreased FRC and lung compliance- Decreased FRC and lung compliance

• Complications assoc. with PEEP include Complications assoc. with PEEP include

- Decrease venous return and C. O.- Decrease venous return and C. O. - Barotrauma- Barotrauma

- Incr. ICP- Incr. ICP - Alterations of renal, hepatic blood - Alterations of renal, hepatic blood flowflow

CPAPCPAP

• Is PEEP applied to a spont. breathing pt.Is PEEP applied to a spont. breathing pt.

• Indications are same as PEEP but in addition Indications are same as PEEP but in addition pt. must have adequate lung function to sustain pt. must have adequate lung function to sustain eucapnic ventilationeucapnic ventilation

• Can use in with ET tube or facemaskCan use in with ET tube or facemask

BiPAPBiPAP

• Allows one to apply IPAP and EPAP Allows one to apply IPAP and EPAP

• IPAP provides positive pressure breaths and it IPAP provides positive pressure breaths and it improves hypoxemia and/or hypercapniaimproves hypoxemia and/or hypercapnia

• EPAP (essentially PEEP) improves EPAP (essentially PEEP) improves oxygenation by increasing the FRC and oxygenation by increasing the FRC and enhancing alveolar recruitmentenhancing alveolar recruitment

• Indications for BiPAP:Indications for BiPAP:

- preventing intubation of end-stage COPD - preventing intubation of end-stage COPD patientpatient

- supporting patients with chronic ventilatory - supporting patients with chronic ventilatory failurefailure

- patient’s with restrictive chest wall disease- patient’s with restrictive chest wall disease

- neuromuscular disease- neuromuscular disease

- nocturnal hypoventilation- nocturnal hypoventilation

CMVCMV

• Ventilator delivers the preset tidal volume at a Ventilator delivers the preset tidal volume at a set time intervalset time interval

• should only be used when the pt. is properly should only be used when the pt. is properly medicated with a combination of sedatives, medicated with a combination of sedatives, respiratory depressants and neuromuscular respiratory depressants and neuromuscular blockersblockers

• Indicated if pt. “fights” the vent., seizure, Indicated if pt. “fights” the vent., seizure, complete rest for pt. for 24 hr., chest injurycomplete rest for pt. for 24 hr., chest injury

Assist Control (A/C)Assist Control (A/C)

• Pt. always receives a mechanical breath, either Pt. always receives a mechanical breath, either timed or assisted timed or assisted

• Indicated when full ventilatory support is Indicated when full ventilatory support is needed, used when pt. has a stable needed, used when pt. has a stable respiratory drive (10-12 spont. rate)respiratory drive (10-12 spont. rate)

• Advantages include a very small WOB Advantages include a very small WOB when sens. and flow are set properly, and when sens. and flow are set properly, and this mode allows the pt. to control the RR this mode allows the pt. to control the RR

• Disadvantage include alveolar hypervent.Disadvantage include alveolar hypervent.

IMVIMV

• Pt. breaths spont. at any tidal volume between Pt. breaths spont. at any tidal volume between the mechanical breathsthe mechanical breaths

• Primary disadvantage is chance for breath Primary disadvantage is chance for breath stacking, therefore care should be taken to set stacking, therefore care should be taken to set high press. limit properly to reduce risk of high press. limit properly to reduce risk of barotraumabarotrauma

SIMVSIMV• A mode in which the vent. delivers mandatory A mode in which the vent. delivers mandatory

breaths to the pt. at or near the beginning of a spont. breaths to the pt. at or near the beginning of a spont. breath, mandatory breaths are synchronized with the breath, mandatory breaths are synchronized with the pt.’s spont. efforts to avoid breath stackingpt.’s spont. efforts to avoid breath stacking

• ““synchronized window” refers to the time synchronized window” refers to the time just prior to time triggering in which the just prior to time triggering in which the vent. is responsive to the pt.’s effort (0.5 sec vent. is responsive to the pt.’s effort (0.5 sec is typical)is typical)

• Advantages include maintaining resp. Advantages include maintaining resp. muscle strength, reduces V/Q mismatch, muscle strength, reduces V/Q mismatch, decreases mean airway press., helps wean decreases mean airway press., helps wean ptpt

PSVPSV• Used to lower the WOB and augment a Used to lower the WOB and augment a

patient’s spont. tidal volumepatient’s spont. tidal volume

• When PSV is used with SIMV, it lowers the When PSV is used with SIMV, it lowers the O2 consumption because of the decr. WOBO2 consumption because of the decr. WOB

• Typically used in the SIMV mode to help Typically used in the SIMV mode to help weaning by (1) increasing spont. tidal volume weaning by (1) increasing spont. tidal volume (2) decreasing spont. RR (3)decreasing WOB(2) decreasing spont. RR (3)decreasing WOB

PCVPCV

• The pressure controlled breaths are time The pressure controlled breaths are time triggered by a preset resp. ratetriggered by a preset resp. rate

• Once inspir. begins, a pressure plateau is Once inspir. begins, a pressure plateau is created and maintained for a preset inspir. timecreated and maintained for a preset inspir. time

• Typically used in ARDS where it takes Typically used in ARDS where it takes excessive press. in volume cycled modes to excessive press. in volume cycled modes to ventilate a pt., leading to barotraumaventilate a pt., leading to barotrauma

ALTERNATIVE MODES OF ALTERNATIVE MODES OF MECHANICAL VENTILATIONMECHANICAL VENTILATION

• Dual-control ventilation modes were Dual-control ventilation modes were designed to combine the advantages of designed to combine the advantages of volume-control ventilation with pressure-volume-control ventilation with pressure-control ventilationcontrol ventilation

• These dual-control modes attempt to These dual-control modes attempt to increase the safety and comfort of increase the safety and comfort of mechanical ventilation mechanical ventilation

pressure-regulated volume-control (PRVC)

• a desired tidal volume is preset and the a desired tidal volume is preset and the ventilator delivers a pressure-limited ventilator delivers a pressure-limited (controlled) breath until that preset tidal (controlled) breath until that preset tidal volume is achieved volume is achieved

• ↑ ↑ VtVt ↓ PIP↓ PIP & ↓ Vt & ↓ Vt ↑ PIP↑ PIP

• provides the opportunity to deliver provides the opportunity to deliver minimum minute ventilation at the lowest minimum minute ventilation at the lowest peak airway pressures possiblepeak airway pressures possible

volume support ventilation (VSV) • The patient triggers every breath, controlling his The patient triggers every breath, controlling his

own respiratory frequency and inspiratory time own respiratory frequency and inspiratory time but the machine can guarantee minute ventilationbut the machine can guarantee minute ventilation

• The pressure support is automatically adjusted up The pressure support is automatically adjusted up or down according to patient's lung compliance or down according to patient's lung compliance and/or resistance to deliver a preset tidal volumeand/or resistance to deliver a preset tidal volume

• This mode cannot be used in a patient who lacks This mode cannot be used in a patient who lacks spontaneous breathing effortspontaneous breathing effort

• This mode is considered as a self-weaning mode This mode is considered as a self-weaning mode

Automode

PRVCPRVC

VSVVSV• designed for automatic weaning from pressure designed for automatic weaning from pressure

control to pressure support depending on the control to pressure support depending on the patient's effortpatient's effort

Volume-assured pressure support ventilation (VAPSV)

PSVPSV

VCVVCV• Advantages include a reduction in the work Advantages include a reduction in the work

of breathing, lowered airway resistance, and of breathing, lowered airway resistance, and lowered intrinsic PEEP lowered intrinsic PEEP

Automatic tube compensation(ATC)

Designed to overcome the resistance of the Designed to overcome the resistance of the endotracheal tube by means of continuous endotracheal tube by means of continuous calculations calculations

Proportional assist ventilation(PAV)

• This mode adjusts airway pressure in This mode adjusts airway pressure in proportion to the patient's effortproportion to the patient's effort

• If patient's effort and/or demand are If patient's effort and/or demand are increased, the ventilator support is increased, the ventilator support is increased, and vice versa, to always give a increased, and vice versa, to always give a set proportion of the breath set proportion of the breath

High-frequency ventilation (HFV)• HFV is time-cycled positive pressure HFV is time-cycled positive pressure

ventilation that delivers a high frequency (60–ventilation that delivers a high frequency (60–120 breathes per min) of small tidal volumes 120 breathes per min) of small tidal volumes (1.5 mL/kg) that are usually less than the (1.5 mL/kg) that are usually less than the anatomic dead space anatomic dead space

• 3 different modes: high-frequency positive-3 different modes: high-frequency positive-pressure ventilation (HFPPV), high-frequency pressure ventilation (HFPPV), high-frequency jet ventilation (HFJV), and high-frequency jet ventilation (HFJV), and high-frequency oscillatory ventilation (HFOV) oscillatory ventilation (HFOV)

APRV (airway pressure release ventilation)

• Is similar to CPAP in that the pt. is allowed Is similar to CPAP in that the pt. is allowed to breathe spont. without restrictionto breathe spont. without restriction

• Combines two separate levels of CPAP and Combines two separate levels of CPAP and the pt. may breathe spont. from both levelsthe pt. may breathe spont. from both levels

• Periodically, pressure is dropped to the Periodically, pressure is dropped to the lower level, reducing mean airway press.lower level, reducing mean airway press.

• During spont. expir. the CPAP is dropped During spont. expir. the CPAP is dropped (released) to a lower level which simulates (released) to a lower level which simulates an effective expirationan effective expiration

ThankYou