3 Objectives To understand: Indications for Positive Pressure VentilationInvasive Positive pressure ventilationNon-invasive Positive Pressure VentilationHow positive pressure ventilation helpsReduce the work of breathingRestore adequate gas exchangeThe basics ofInvasive positive pressure ventilation (IPPV)Basic Vent ModesNoninvasive positive pressure ventilation (NIPPV)ObjectivesTo understand the of how positive pressure ventilation restores adequate gas exchange and reduces work of breathing for the patient.To evaluate the basic cocepts of IPPV and NIPPVAnd to increase understanding of ventilator alarms, and some of the wave forms and curves displayed on the ventilator
4 Indications and Rationale for Initiating IPPV Decreased mental status (unable to protect airway)Hypercapnic respiratory failureHypoxic respiratory failureIntubation to facilitate procedurePulmonary toiletThere are many indications for intubating patients and achieving a definitive airway.Some patients, due to a decreased mental status cannot protect their own airway. This may be due to drugs, alcohol, head injury, seizure or other mental status altering condition.Work of breathing may become too much for some patients and the will develop hypercapnic respiratory failure. This maybe do to neurologic disorders such as Myistnia Gravis, Multiple Sclerosis or non-neurologic problems that increase the patient’s work of breathing beyond what the can tolerate.Hypoxemia or a low PaO2 is another reason to intubate someone. In an intubated patient you can deliver 100%FiO2 as well as recruit collapsed alveoliSome patients require frequent suctioning and are intubated for pulmonary toilet.Some procedures (both surgical and non-surgical) require intubation.
5 Approach to MV Is MV indicated ? NO YES Conservative treatment and periodic reassessmentNOContraindication to NIPPV ?YESNIPPVYESInvasive MVSuccess ?NO
6 Important Pitfalls and Problems Associated with PPV Potential detrimental effects associated with PPVHeartDecreased pre-loadLungsBarotraumaPneumothoraxGas exchangeMay increase dead space (compression of capillaries)Intubation and positive pressure ventilation is not a benign procedure and one should watch for the potential side effects and complications.The effects of positive pressure ventilation are seen mostly with in the thorax. Positive pressure in the airways and lungs increases the intrathoracic pressure and thereby decreasing cardiac pre-load. This can lead to hypotension and decreased cardiac output especially in the hypovolemic patient.High airway pressure can lead to barotrauma and lung injury in some patients. Simple and tension pneumothoracies are potential complications as well.If the pressure in the alveoli excedes the pressure of the capillaries in the parenchyma of the lungs then the capillaries will collapse and the dead space will increase.
7 Important Hemodynamic Effects Associated with PPV Decreased preloadDecreased afterloadOther factors effecting hemodynamics:As lung and chest wall compliance decrease so does venous return to the heartAs discussed, increasing airway pressures will decrease preload and potentially blood pressure and cardiac output.Positive pressure ventilation will also reduce afterload. This happens because as the intrathoraic pressure rises it helps push the blood out of the chest creating less resistance for the heart to pump against. This may creat an improved stroke volume depending on the patients cardiac status. Due to the reduction in both preload and afterload, PPV is very helpful in patients with cardiogenic pulmonary edema.Marini, Wheeler. Crit Care Med. The Essentials
8 Common Modes of Ventilation Volume targeted ventilation (flow controlled, volume cycled)ACPressure targeted ventilationPCV (pressure controlled, time cycled)PSCombination modesSIMV with PS and either volume or pressure-targeted mandatory cyclesThere are two basic types of ventilation modes, volume ventilation like assist control and pressure modes such as pressure control ventilation and pressure support.Some modes combine pressure and volume settings like SIMV with pressure support.
9 Pressure and Volume Targeted Ventilation In pressure-targeted ventilation: an airway pressure target and inspiratory time are set, while flow and tidal volume become the dependent variables.In volume targeted ventilation (flow-controlled, volume cycled), a target volume and flow (or inspiratory time in certain ventilator) are preset and pressure and inspiratory time (or flow in the ventilator where inspiratory time is preset) become the dependent variables.The tidal volume is the integral of the flow during inspiration = area under the curve of the flow time curve during inspiration (see next slide).With pressure targeted ventilation, the operator needs to set a pressure and a time making flow and tidal volume dependent variables.With volume ventilation the volume and flow are set on the ventilator and pressure and time become the dependent variables.When looking at the flow time cureve on the ventilator display, the area under the curve equals the tidal volume
10 Pressure and Volume Targeted Ventilation As you can see from the pressure and flow wave forms, with pressure-targeted ventilation, the pressure remains constant and the flow peaks early in the cycle and decreases over time.In Volume ventilation with a constant flow profile, the pressure increase with time and the flow remains constant. A decelerating flow pattern yields a more rounded pressure curve.VTMarini, Wheeler. Crit Care Med. The Essentials
11 Assist-control Set variables Volume, TI or flow rate, frequency, flow profile (constant or decel)PEEP and FIO2Mandatory breathsVentilator delivers preset volume and preset flow rate at a set back-up rateSpontaneous breathsAdditional cycles can be triggered by the patient but otherwise are identical to the mandatory breath.A common mode of ventilation is Assist Control.The operator must set a tidal volume, a respiratory rate, a flow profile (constant or decelerating), a FiO2 and a PEEP.In Assist Control ventilation, the ventilator will deliver the set number of breaths at the set tidal volume to the patient. It will also deliver the set tidal volume to the patient with every spontaneous breath.
12 Assist-control Advantages Increased ventilatory support / decreased work of breathingDisadvantagesHyperventilationHemodynamic effectsVent-patient mismatchAdvantages to AC is that it provides support and helps decease work of breathing. AC, however, delivers a full tidal volume as the set rate and when the patient triggers a breath, therefore, this mode can lead to hyperventilation and low PaCO2 leading to alkalosis.
13 SIMVKey set variablesTargeted volume (or pressure target), flow rate (or inspiratory time, Ti), mandated frequencyPEEP, FIO2, pressure supportMandatory breathsVentilator delivers a fixed number of cycles with a preset volume at preset flow rate. Alternatively, a preset pressure is applied for a specified TiSpontaneous breathsUnrestricted number, aided by the selected level of pressure supportSyncronized Intermitant Mandatory Ventilation is another commonly used ventilator mode. Like assist cintrol, the ventilator delivers the set number of breaths at the set tidal volume. Unlike AC, however, SIMV does not give a full tidal volume breath with the patient’s spontaneous respiration.When used as a volume targeted mode, just like in assist control, you set a tidal volume, a rate, a FiO2 and a PEEP. SIMV can also be used as a pressure targeted mode and you would then need to set a pressure target, an inspiratory time, a respiratory rate, and FiO2 and a PEEP.Weather using SIMV as a Volume or Pressure mode an additional setting of pressure support is needed. This pressure support assists the patient with his or her spontaneous respirations.
14 SIMVAdvantagesIncreased ventilatory support / decreased work of breathingLess risk of hyperventilationDisadvantagesMore work of breathing than assist-controlSIMV also provides decreased work of breathing and vent support to the patient in respiratory failure. SIMV onlys provides a set tidal volume to the machine breaths. Any patient triggered breaths are unassisted unless pressure support is added, therefore, SIMV decreases the risk for hyperventilation, but increases the work of breathing compared with assist-control.
15 Pressure Support Pressure = set variable. Mandatory breaths: none. Spontaneous breathsVentilator provides a preset pressure assist, which terminates when flow drops to a specified fraction (typically 25%) of its maximum.Patient effort determines size of breath and flow rate.Pressure Support is, just as its name implies, a support mode only there are no cycles provided by the ventilator. The patients breaths spontaneously and the ventilator provides pressure to assist with respirations. The patient determines the flow, respitatory and to some degree the length of the breath. The ventilator stops the pressure when the flow drops to a specific fraction of its maximum. This is usually 25%. PS is often combined with Continuous Positive Airway pressure or CPAP.
16 Pressure Support Advantages Increased patient comfort Flow, rate, and volume controlled by patientImproved vent-patient interfaceDecreased work of breathingBetter recruitment of collapsed alveoliDisadvantagesPatient may tireMore work of breathing compared to other modesPressure support is the mode closes to “natural respiration”. The patient controls all aspects fo the breath, so there are many advantages. Because there is not set minute ventilation or tidal volume, the patient may tire due to the work of breathing.
17 Pressure in Volume Targeted Ventilation Mean Airway PressurePressure applied to the lung and chest wall, averaged across both phases of ventilationPeak Airway PressureTotal pressure needed to create the tidal volumeIncludes: resistive pressure of circuit, PEEP, and lung and chest wallPlateau PressurePeak airway pressure – resistive componentTranspulmonary PressurePlateau pressure – pleural pressureMean airway pressure is the pressure measured during passive ventilation in the circuit across both phases of the ventilatory cycle. This is the pressure across both the lung and chest wall.Changes to the ventilator including; minute ventilation, PEEP and inspiratory to expiratory ratio affect mean airway pressure. Mean airway pressure affects pleural pressure and alveolar distention.Changes in mean airway pressure therefore influence arterial oxygenation and cardiac output.Peak airway pressure is the total pressure needed to drive in the tidal volume. It includes the resistive pressure of the circuit, the PEEP left in the lung from the last cycle as well as the elastic recoil of the lung and chest wall.Plateau Pressure is the peak airway pressure minus the resistive pressure. This is measured when the flow from the ventilator is zero. This is a key determinate of alveolar distention.Transpulmonary pressure looks more closely at all the factors that determine alveolar distention. Transpulmonary pressure is the plateau pressure minus the pleural pressure. This means that if a patient has a stiff, non-compliant chest wall, a given plateau pressure will generate a higher pleural pressure (pressure around the lung) but create less alveolar distention.
18 Airway Resistance and Respiratory System Compliance Airway resistance = (Peak airway pressure – Plateau pressure) divided by the flowCompliance = change in volume divided by the change in pressureHigh compliance = easily distended (emphysemia)Low compliance = stiff (ARDS, fibrosis, edema)In a passively ventilated patient, airway resistance is the peak airway pressure minus the plateau pressure divided by the flow.It should be noted that the lung is dynamic and as the airways distend, the resistance decreases.Compliance is defined as a change in volume divided by a change in pressure. Pulmonary or lung compliance looks at how much the lung will inflate based on the pressure applied to it.A lung with low compliance is stiff. Conditions such as ARDS, pulmonary fibrosis and pulmonary edema can cause this. A highly compliant lung is easily distended with a low pressure. High compliance can be seen in patients with emphysema.
19 Noninvasive Ventilation Ventilatory assistance provided via mask without intubationCan be volume or pressure modePatients must meet criteria to be candidatesSome patients with respiratory distress or failure who have a quickly treatable cause such as pulmonary edema, asthma, or a COPD exaserbation can be treated without intubation.BiPAP and CPAP are the most common pressure modes used with NIPPV, however, volume modes can be usedPatients must meet certain criteria to be candidates for non-invasive ventilation
20 Key Differences Between NIPPV and IPPV Advantages of NIPPVDisadvantages of NIPPVAllows the patients to maintain normal functionsSpeechEatingHelps avoid the risks and complications related to:IntubationSedation Less ventilator-associated pneumoniaLess airway pressure is toleratedDoes not protect against aspirationNo access to airway for suctioningNot tolerated by some patientsPressure soresSome advantages to non-invasive ventilation is that it allows the patients to remain awake and continue to be able to eat and communicate. It avoid the risks of intubation and mechanical ventilation including sedatives and VAP.A few of the disadvantages of NIPPV are that you cannot supply the high pressures that are sometimes required for patients with respiratory issues. Aspiration is a risk and pulmonary toilet is not and option. The mask used can be very claustrophobic for some and is not tolerated by some patients.Slide 20
21 Clinical Use of NIPPV in Intensive Care Decompensated COPD (Hypercapnic Respiratory Failure)Cardiogenic pulmonary edemaHypoxic respiratory failureOther possible indicationsWeaning (post-extubation)Obesity hypoventilation syndromePost-surgeryAsthmaThe key to using NIPPV is that you have to select the appropiate patients. They have to have a fairly quickly quickly reversible pathology, usually within hours. A patient who runs out of her steroids at home and goies into a COPD exaserbation or a patient who receives too much IVF and develops pulmonary edema are good examples.An elderly patient who come to the hospital with pneumonia and respiratory failure is not a good candidate. It will take several days for the antibiotics to work. A head trauma patient with decreased mental status, GCS of 8, is also not a good choice for NIPPV due the the fact that he cannot protect his airway.Other potential uses for NIPPV are post extubation in patients who require more support than anticipated, sleep apnea patients, asthmaics, as well as others.Adapted from: Am J Respir Crit Care Med. 2001;163:
22 Contraindications to NIPPV Cardiac or respiratory arrestNonrespiratory organ failureSevere encephalopathy (e.g., GCS < 10)Severe upper gastrointestinal bleedingHemodynamic instability or unstable cardiac arrhythmiaFacial surgery, trauma, or deformityUpper airway obstructionInability to cooperate/protect the airwayInability to clear respiratory secretionsHigh risk for aspirationAny patient who cannot cooperate with their own care, cannot protect their airway, is hemodynamically unstable or in shock or is at risk fro aspiration is NOT a cadidate for non-invasive ventilation.Adapted from: Am J Respir Crit Care Med. 2001;163:
23 Initiating NIPPV Initial settings: Spontaneous trigger mode with backup rateStart with low pressuresIPAP cmH2OEPAP cmH2OAdjust inspired O2 to keep O2 sat > 90%Increase IPAP gradually up to 20 cm H2O (as tolerated) to:alleviate dyspneadecrease respiratory rateincrease tidal volumeestablish patient-ventilator synchronyThe usual settings for NIPPV include an inspiratory positive airway pressure or IPAP and expiratory possitive airway pressure or EPAP. EPAP is sometimes refered to as PEEP. One also needs to set the FiO2.Depending on the reason for respiratory failure (i.e. hypercarbic or hypoxic) on choses the initial settings. It is customary to chose an IPAP of between 8-12 cmH2o pressure. With hypoxemic resp fail, you want to use a higher EPAP than you would in patients with hypercapnic resp failure. The initial EPAP setting is usualy between 3-5 cmH2O.Remember the higher the IPAP, the greater the driving pressure but the less comfortable it is for the patient. The higher the EPAP, the more PEEP you are leaving in the lungs, but it is harder for the patient to exhale against the end-expiratory pressure.
24 Success and Failure Criteria for NIPPV Improvements in pH and PCO2 occurring within 2 hours predict the eventual success of NPPV.If stabilization or improvement has not been achieved during this time period, the patient should be considered an NIPPV failure and intubation must be strongly considered.Other criteria for a failed NIPPV trial include: worsened encephalopathy or agitation, inability to clear secretions, inability to tolerate any available mask, hemodynamic instability, worsened oxygenation.If a patient does not show improvement in their ABG quickly, NIPPV is not going to work.If a patient decompensates or becomes hemodynamically unstable, NIPPV has failed.Changing you management plan and intubating a patient after they have failed NIPPV is not a sign of weakness or a poor initial management decision. A therapy was tried and it simply did not work. Always do what is safest for the patient and obtain a definitive airway if it becomes necessary.
25 Case Study Case Study Skip The following is a case study reflective of this lecture. You will have the opportunity to do a self assessment to test your knowledge. You will only be able to take this self assessment once. You will have another chance to take it again after you review the Mechanical Ventilation Part 2 module.Case StudySkip
27 ReferencesHubmayr RD, Abel MD, Rehder K. Physiologic approach to mechanical ventilation. Crit Care Med. 1990;18:Tobin MJ. Mechanical ventilation. N Engl J Med. 1994;330;Marini JJ. Monitoring during mechanical ventilation. Clin Chest Med. 1988;9:Brochard L. Noninvasive ventilation for acute respiratory failure. JAMA. 2002;288:Calfee CS, Matthay MA. Recent advances in mechanical ventilation. Am J Med. 2005;118: