Mechanical Mechanical VentilationVentilationBY: Jonathan PhillipsBY: Jonathan Phillips

IntroductionIntroduction

Conventional mechanical ventilation Conventional mechanical ventilation refers to the delivery of full or refers to the delivery of full or partial ventilatory support by a partial ventilatory support by a volume –cycled mechanical volume –cycled mechanical ventilator or by pressure support. It ventilator or by pressure support. It can include the maintenance of can include the maintenance of positive airway pressure at the end positive airway pressure at the end of exhalation i.e.. PEEP.of exhalation i.e.. PEEP.

IndicationsIndications The decision to initiate mechanical The decision to initiate mechanical

ventilation entails potentially serious ventilation entails potentially serious complications. complications.

The main indication for mechanical The main indication for mechanical ventilation is ARF. ventilation is ARF.

The parameters needed include The parameters needed include respiratory rate >35, inspiratory force < respiratory rate >35, inspiratory force < 25cm H2O, vital capacity < 10-15ml/kg, 25cm H2O, vital capacity < 10-15ml/kg, PaO2 <60 mm Hg with FIO2 >60%, PaO2 <60 mm Hg with FIO2 >60%, PaCO2 >50mmHg, with pH < 7.35. and PaCO2 >50mmHg, with pH < 7.35. and an absent gag or cough reflex.an absent gag or cough reflex.

Common disorders for Common disorders for Mechanical ventilationMechanical ventilation

Acute pulmonary parenchymal Acute pulmonary parenchymal diseases, pneumonia, ARDSdiseases, pneumonia, ARDS

Cardiogenic pulmonary edemaCardiogenic pulmonary edema Neuromuscular disorders: myasthenia Neuromuscular disorders: myasthenia

gravis, Guillian Barre syndrome, gravis, Guillian Barre syndrome, poliomyelitis, and spinal cord traumapoliomyelitis, and spinal cord trauma

Systemic illnesses include shock and Systemic illnesses include shock and sepsissepsis

Volume cycled Volume cycled ventilationventilation

The controlled variables of tidal The controlled variables of tidal volume and inspiratory flow determine volume and inspiratory flow determine airway pressure and inspiratory time. airway pressure and inspiratory time. Variations in airway resistance or lung Variations in airway resistance or lung compliance alter airway pressures but compliance alter airway pressures but do not affect minute ventilation.do not affect minute ventilation.

Controlled mechanical ventilationControlled mechanical ventilation Assist-control Assist-control Intermittent mandatory ventilationIntermittent mandatory ventilation

Controlled mechanical Controlled mechanical ventilationventilation

Minute ventilation is completely Minute ventilation is completely dependent upon the rate and tidal dependent upon the rate and tidal volume set on the ventilator. Any volume set on the ventilator. Any respiratory efforts made by the patient respiratory efforts made by the patient do not contribute to minute ventilation.do not contribute to minute ventilation.

CV is required in patients who are not CV is required in patients who are not making respiratory effort, spinal cord making respiratory effort, spinal cord injury, OD or pharmacologic paralysisinjury, OD or pharmacologic paralysis

CMVCMV

Combined neuromuscular paralysis Combined neuromuscular paralysis and controlled mechanical ventilation and controlled mechanical ventilation can also be used to avoid volutrauma can also be used to avoid volutrauma in patients with ARDS and to avoid in patients with ARDS and to avoid baratrauma in asthmatics who are baratrauma in asthmatics who are difficult to ventilate.difficult to ventilate.

In these settings hypercapnia is In these settings hypercapnia is accepted provided that oxygenation accepted provided that oxygenation is maintained.is maintained.

Assist controlAssist control In A/C mode the ventilator senses an inspiratory effort by In A/C mode the ventilator senses an inspiratory effort by

the patient and responds by delivering a preset tidal the patient and responds by delivering a preset tidal volume. volume.

Every inspiratory effort that satisfies the ventilators Every inspiratory effort that satisfies the ventilators demand valve trigger threshold, initiates delivery of the demand valve trigger threshold, initiates delivery of the preset tidal volume.preset tidal volume.

A control mode back up rate is set on the ventilator to A control mode back up rate is set on the ventilator to prevent hypoventilationprevent hypoventilation

Patient work is required to trigger the ventilator, and Patient work is required to trigger the ventilator, and continues during inspiration. In the presence of auto-peep continues during inspiration. In the presence of auto-peep the effective trigger threshold is increased by the amount the effective trigger threshold is increased by the amount of auto-peep present.of auto-peep present.

An ACCP consensus statement cautioned against the initial An ACCP consensus statement cautioned against the initial use of A/C in awake patients with obstructive airway use of A/C in awake patients with obstructive airway disease, since this can lead to progressive hyperinflation.disease, since this can lead to progressive hyperinflation.

Intermittent Mandatory Intermittent Mandatory ventilationventilation

IMV, the degree of ventilator IMV, the degree of ventilator support is determined by the select support is determined by the select IMV rate. At regular intervals, the IMV rate. At regular intervals, the ventilator delivers a breath based ventilator delivers a breath based upon a preset tidal volume and rate.upon a preset tidal volume and rate.

The patient is allowed to breathe The patient is allowed to breathe spontaneously through the ventilator spontaneously through the ventilator circuit at a tidal volume and rate circuit at a tidal volume and rate according to need and capacity.according to need and capacity.

IMVIMV

Most present day ventilators synchronize Most present day ventilators synchronize the intermittent mandatory ventilation the intermittent mandatory ventilation breaths with inspirtatory effort by the breaths with inspirtatory effort by the patient, a modality termed synchronized patient, a modality termed synchronized IMV or SIMV. IMV or SIMV.

This modification requires a trigger This modification requires a trigger modality, either a demand valve or flow-modality, either a demand valve or flow-by, both of which need patient effort to by, both of which need patient effort to trigger and therefore increase the work trigger and therefore increase the work of breathing.of breathing.

Pressure Support Pressure Support VentilationVentilation

PSV is flow-cycled in that, once triggered by PSV is flow-cycled in that, once triggered by a demand valve, the preset pressure is a demand valve, the preset pressure is sustained until the inspiratory flow tapers, sustained until the inspiratory flow tapers, usually to 25% of its maximal value.usually to 25% of its maximal value.

PSV tends to be a comfortable ventilatory PSV tends to be a comfortable ventilatory modality because the patients has greater modality because the patients has greater control over ventilator cycling and flow control over ventilator cycling and flow rates.rates.

Close monitoring is required whenever PSV Close monitoring is required whenever PSV is used alone because neither tidal volume or is used alone because neither tidal volume or minute ventilation is guaranteed.minute ventilation is guaranteed.

PSV is more appropriate during weaning PSV is more appropriate during weaning from mechanical ventilation.from mechanical ventilation.

Vent managementVent management FIO2-hypoxia is more dangerous than is FIO2-hypoxia is more dangerous than is

brief exposure high levels of O2.brief exposure high levels of O2. The initial FIO2 should be 100%The initial FIO2 should be 100% FiO2 can be made to achieve a PaO2 FiO2 can be made to achieve a PaO2

greater than 60mmHg or SaO2 >90%.greater than 60mmHg or SaO2 >90%. Attempts should be made to utilize the Attempts should be made to utilize the

lowest possible fraction of FIO2 that lowest possible fraction of FIO2 that maintains the arterial oxygen saturation maintains the arterial oxygen saturation >90% or PO2 >60%>90% or PO2 >60%

An FIO2 below 0.5 is preferable to An FIO2 below 0.5 is preferable to minimize oxygen toxicity.minimize oxygen toxicity.

Vent ManagementVent Management Respiratory rate of 10-15 breaths per minute to Respiratory rate of 10-15 breaths per minute to

begin. begin. In COPD patients, minute ventilation should be In COPD patients, minute ventilation should be

adjusted to achieve baseline PaCO2 and not adjusted to achieve baseline PaCO2 and not necessarily a normal PaCO2.necessarily a normal PaCO2.

Hyperventilation with resultant metabolic alkalosis Hyperventilation with resultant metabolic alkalosis in these patients may be associated with serious in these patients may be associated with serious electrolytes shifts and arrhythmias.electrolytes shifts and arrhythmias.

Initial tidal volumes usually can be set at 10-12 Initial tidal volumes usually can be set at 10-12 ml/kgml/kg

Patients with decreased ling compliance (ARDS) Patients with decreased ling compliance (ARDS) Often need smaller lung volumes 6-8 to minimize Often need smaller lung volumes 6-8 to minimize

peak airway pressures.peak airway pressures.

Vent managementVent managementPEEPPEEP

Positive end-expiratory pressure is Positive end-expiratory pressure is defined as the maintenance of positive defined as the maintenance of positive airway pressure at the end of expiration.airway pressure at the end of expiration.

It can be applied in both CPAP and It can be applied in both CPAP and continuous positive pressure pressure continuous positive pressure pressure ventilation.ventilation.

PEEP increases lung compliance and PEEP increases lung compliance and oxygenation while decreasing the shunt oxygenation while decreasing the shunt fraction and the work of breathing.fraction and the work of breathing.

Vent ManagementVent ManagementPEEPPEEP

The main goal of PEEP is to achieve a The main goal of PEEP is to achieve a PaO2 greater than 55-60 mm HG with a PaO2 greater than 55-60 mm HG with a FIO2 less than or equal to 60%.FIO2 less than or equal to 60%.

PEEP is applied in 3-5 cm H2O PEEP is applied in 3-5 cm H2O increments.increments.

PEEP >10 should not have their PEEP PEEP >10 should not have their PEEP removed abruptly, because removal can removed abruptly, because removal can result in collapse of distal lung units, result in collapse of distal lung units, worsening of shunt, and potentially life worsening of shunt, and potentially life threatening hypoxemia.threatening hypoxemia.

Vent managementVent managementInspiratory flow rateInspiratory flow rate

Low flow rates can be associated Low flow rates can be associated with prolonged inspiratory times with prolonged inspiratory times that can lead to the development of that can lead to the development of auto-PEEP.auto-PEEP.

The resultant hyperinflation can The resultant hyperinflation can affect patient hemodynamics affect patient hemodynamics adversely by impairing venous adversely by impairing venous return to the heart.return to the heart.

Vent ManagementVent ManagementTrigger sensitivityTrigger sensitivity

Pressure triggering to initiate either a Pressure triggering to initiate either a machine assisted breath or to permit machine assisted breath or to permit spontaneous breathing between IMV spontaneous breathing between IMV breaths, or during trials of CPAP.breaths, or during trials of CPAP.

The patient must generate a decrease in The patient must generate a decrease in the airway circuit pressure equal to the the airway circuit pressure equal to the selected pressure sensitivity.selected pressure sensitivity.

The smallest trigger sensitivity should be The smallest trigger sensitivity should be selected, allowing the patient to initiate selected, allowing the patient to initiate mechanical or spontaneous breaths mechanical or spontaneous breaths without causing the ventilator to autocycle.without causing the ventilator to autocycle.

Vent ManagementVent ManagementFlow-byFlow-by

Refers to triggering of the ventilator by Refers to triggering of the ventilator by changes in airflow as opposed to changes changes in airflow as opposed to changes in airway pressure.in airway pressure.

▪▪ Flow sensitivity, the rate of inhaled flow Flow sensitivity, the rate of inhaled flow that triggers the ventilator to switch from that triggers the ventilator to switch from base flow to either a machine delivered or a base flow to either a machine delivered or a spontaneous breath.spontaneous breath.

▪▪Flow by triggering requires less work of Flow by triggering requires less work of breathing when used with patients breathing when used with patients receiving CPAP.receiving CPAP.

▪▪However it offers no advantage over However it offers no advantage over demand valve triggering when using demand valve triggering when using pressure support ventilation.pressure support ventilation.

Weaning StrategiesWeaning Strategies

The level of support ventilation is The level of support ventilation is decreased gradually, and the patient decreased gradually, and the patient assumes more of the work of assumes more of the work of ventilation.ventilation.

IMV –allows a change from IMV –allows a change from mechanical ventilation to mechanical ventilation to spontaneous breathing by spontaneous breathing by decreasing the ventilator rate decreasing the ventilator rate gradually. gradually.

Weaning strategiesWeaning strategies

T-Tube intersperses periods of T-Tube intersperses periods of unassisted spontaneous breathing unassisted spontaneous breathing through a T-Tube with periods of through a T-Tube with periods of ventilator support.ventilator support.

Short daytime periods 5-15 minutes 2-Short daytime periods 5-15 minutes 2-6 times a day with increasing periods.6 times a day with increasing periods.

Extubation may be appropriate when Extubation may be appropriate when the patient can tolerate more than 30-the patient can tolerate more than 30-90 minutes of T-tube ventilation90 minutes of T-tube ventilation

Weaning strategiesWeaning strategies

PSV is used when respiratory muscle PSV is used when respiratory muscle weakness appears to be compromising weakness appears to be compromising weaning success.weaning success.

A decrease in respiratory rate with A decrease in respiratory rate with achieved tidal volumes of 10-12 ml/kg achieved tidal volumes of 10-12 ml/kg signals that the optimal PSV level has signals that the optimal PSV level has been reached. At this point PSV can be been reached. At this point PSV can be reduced.reduced.

Once PSV level 5-8 cm H2O is reached Once PSV level 5-8 cm H2O is reached the patient can be extubated.the patient can be extubated.

ExtubationExtubation

Should be performed early in dayShould be performed early in day Patient should be told to coughPatient should be told to cough Elevate head to 30-45 degreesElevate head to 30-45 degrees Oropharynx should be suctionedOropharynx should be suctioned Cuff deflatedCuff deflated Patient extubated and face mask Patient extubated and face mask

placedplaced Patient encouraged to deep breath Patient encouraged to deep breath

and cough with HHN to followand cough with HHN to follow

Competency Competency ExamExam

QuestionsQuestions

1. Which is the main indication for 1. Which is the main indication for vent management?vent management?

A. Acute respiratory failureA. Acute respiratory failure B. Severe COPDB. Severe COPD C. CO2 retentionC. CO2 retention D. Severe pneumoniaD. Severe pneumonia

QuestionsQuestions

1. Which is the main indication for 1. Which is the main indication for vent management?vent management?

A. Acute respiratory failureA. Acute respiratory failure B. Severe COPDB. Severe COPD C. CO2 retentionC. CO2 retention D. Severe pneumoniaD. Severe pneumonia

QuestionsQuestions

2. Which is not a guideline for 2. Which is not a guideline for withdraw of mechanical ventilation?withdraw of mechanical ventilation?

A. PaO2 >60A. PaO2 >60 BB. FIO2<50%. FIO2<50% C.PEEP >10C.PEEP >10 D.Vital capacity >10D.Vital capacity >10

QuestionsQuestions

2. Which is not a guideline for 2. Which is not a guideline for withdraw of mechanical ventilation?withdraw of mechanical ventilation?

A. PaO2 >60A. PaO2 >60 BB. FIO2<50%. FIO2<50% C.PEEP >10C.PEEP >10 D.Vital capacity >10D.Vital capacity >10

QuestionsQuestions

3. An FIO2 below this value is 3. An FIO2 below this value is preferable to minimize oxygen preferable to minimize oxygen toxicity?toxicity?

A.80%A.80% B.70%B.70% C.60%C.60% D.50%D.50%

QuestionsQuestions

3. An FIO2 below this value is 3. An FIO2 below this value is preferable to minimize oxygen preferable to minimize oxygen toxicity?toxicity?

A.80%A.80% B.70%B.70% C.60%C.60% D.50%D.50%

End of LectureEnd of Lecture