Innovative Practices Of Ventilatory Support With Pediatric .
Innovative practices of ventilatory support with pediatric patientsGiuseppe A. Marraro, MDObjectives: The recognition that alveolar overdistension ratherthan peak inspiratory airway pressure is the primary determinantof lung injury has shifted our understanding of the pathogenesisof ventilator-induced side effects. In this review, contemporaryventilatory methods, supportive treatments, and future developments relevant to pediatric critical care are reviewed.Data Synthesis: A strategy combining recruitment maneuvers,low-tidal volume, and higher positive end-expiratory pressure(PEEP) decreases barotrauma and volutrauma. Given that appropriate tidal volumes are critical in determining adequate alveolarventilation and avoiding lung injury, volume-control ventilationwith high PEEP levels has been proposed as the preferable protective ventilatory mode. Pressure-related volume control ventilation and high-frequency oscillatory ventilation (HFOV) havetaken on an important role as protective lung strategies. Furtherdata are required in the treatment of children, confirming thepreliminary results in specific lung pathologies. Spontaneousbreathing supported artificially during inspiration (pressure support ventilation) is widely used to maintain or reactivate spontaneous breathing and to avoid hemodynamic variation. Volumesupport ventilation reduces the need for manual adaptation toMechanical ventilation wasfirst introduced during thepolio epidemics of the1950s and since then hasbeen of undoubted value in improving thesurvival of many patients, including newborns and children. However, problems canstem from its use, particularly if inappropriate ventilatory modes are chosen. Thiscan result in pressure and volume damageto the lungs, hemodynamic instability, oxygen toxicity, and nosocomial infection.Ventilation-Induced Lung InjuryVentilatory modes should be carefullyselected to minimize ventilator-inducedFrom the Pediatric Intensive Care Unit, Fatebenefratelli and Ophthalmiatric Hospital, Milan, Italy.Address requests for reprints to: Giuseppe A. Marraro,MD, Pediatric Intensive Care Unit, Fatebenefratelli andOphthalmiatric Hospital, Milan, Italy. E-mail:gmarraro@picu.itCopyright 2003 by the Society of Critical CareMedicine and the World Federation of Pediatric Intensive and Critical Care SocietiesDOI: 10.1097/01.PCC.0000044993.63927.DE8maintain stable tidal and minute volume and can be useful inweaning. Prone positioning and permissive hypercapnia havetaken on an important role in the treatment of patients undergoingartificial ventilation. Surfactant and nitric oxide have been proposed in specific lung pathologies to facilitate ventilation and gasexchange and to reduce inspired oxygen concentration. Investigation of lung ventilation using a liquid instead of gas has openednew vistas on several lung pathologies with high mortality rates.Results: The conviction emerges that the best ventilatory treatment may be obtained by applying a combination of types ofventilation and supportive treatments as outlined above. Earlytreatment is important for the overall positive final result. Lungrecruitment maneuvers followed by maintaining an open lungfavor rapid resolution of pathology and reduce side effects.Conclusions: The methods proposed require confirmationthrough large controlled clinical trials that can assess the efficacyreported in pilot studies and case reports and define the optimalmethod(s) to treat individual pathologies in the various pediatricage groups. (Pediatr Crit Care Med 2003; 4:8 –20)KEY WORDS: hemofiltration; plasma filtration; sepsislung injury. The recognition that alveolaroverdistension rather than high proximalairway pressure is the primary determinant of lung injury (i.e., volutraumarather than barotrauma) has constituteda substantial shift in the pathogenesis ofventilator-induced side effects (1– 6).Mechanical ventilation with high pressure and volume induces changes in endothelial and epithelial permeability, formation of pulmonary edema, and alterationsin pulmonary microvascular permeability.Severe alveolar damage, alveolar hemorrhage, and hyaline membranes have beennoted in animals that die after lung overinflation injury (4, 7–9) and in a series ofventilated adult patients (10). The most important factors that have been proposed asbeing responsible for ventilation-inducedlung injury are, first, high lung volumeassociated with elevated transpulmonarypressure and alveolar overdistension, andsecond, repeated alveolar collapse and reopening because of low end-expiratory volume. Other factors that contribute to injury include preexisting lung damageand/or inflammation, high inspired oxygenconcentration, the level of blood flow, andthe local production and systemic release ofinflammatory mediators (11–13).Innovative and protective lung strategies are proposed to avoid alveolar overdistension by limiting tidal volume and/or plateau pressure. Lung overstretching andoverdistension are significant in causinglung injury rather than high pressuresalone; volume trauma is at least as important as barotrauma (14). Acute respiratorydistress syndrome (ARDS) (15–19), asthma(20), acute lung injury (21), and severe airflow obstruction (20, 21) should be takeninto account, with tidal volumes and peakpressures reduced to a minimum.Positive end-expiratory pressure(PEEP) should be used appropriately tomaintain alveolar recruitment throughout the respiratory cycle (2, 3, 22), andcomplementary therapies such as nitricoxide and surfactant should be used toimprove ventilation and oxygenation.Lower end points for ventilation may beaccepted, e.g., a PaO2 of 50 – 60 mm Hgand moderate hypercapnia (45–50 mmHg). Ventilation should be adapted toPediatr Crit Care Med 2003 Vol. 4, No. 1
changing lung pathology and supportivetreatments, such as physiotherapy andprone positioning, nitric oxide, and surfactant, used to improve the lung pathology and to reduce the duration of mechanical ventilation (23–25).CONTROLLED VENTILATIONSmall Tidal Volume—HighRespiratory Rate: ContinuousPositive Volume-ControlledVentilationLocal inhomogeneities of ventilation result in large shear forces applied to lungunits undergoing cyclic opening andclosing. The repeated collapse and reopening of the lung units at low lungvolume may contribute to ventilationinduced lung injury. A strategy combining recruitment maneuvers, low-tidalvolume, and higher PEEP have beendemonstrated to decrease the incidenceof barotrauma (6, 9, 26 –30).Given that appropriate tidal volumesare critical in determining adequate alveolar ventilation and also in avoiding lunginjury, volume-control ventilation is thesafer and preferable ventilatory mode.Pressure-limited ventilation is not highlyindicated in pediatric patients and forneonatal ventilation because the tidal volume cannot be controlled in every breathand reduced tidal volume (hypoventilation) can be alternated to large tidal volume (hyperdistention). This method iswidely applied in neonatology because ofthe simplicity of use and because lungbarotrauma is supposed to be connectedwith peak inspiratory pressure.In volume-controlled ventilation, thetarget tidal volumes (6 – 8 mL/kg or 5mL/kg, if necessary) are selected based onideal body weight and lung pathologywhile minute volume remains stable. It isadjusted to maintain the pressurevolume curve below the upper inflectionpoint. It should be noted that tidal volume less than or close to total deadspacecan produce an insufficient exchange ofalveolar gases (hypercapnia). By usinguncuffed endotracheal tubes, a large discrepancy between set and delivered tidalvolumes is present. To avoid hypoventilation, this discrepancy and poor compliance of infant lung compared with theventilatory circuit compliance must beevaluated.Respiratory rate can be adapted to maintain normocarbia in case of contraindicaPediatr Crit Care Med 2003 Vol. 4, No. 1tion of permissive hypercapnia (human immunodeficiency virus in premature babies,brain hemorrhage, pulmonary hypertension). Generally, the respiratory rate for aspecific patient is increased by 20% to 25%of the normal range.PEEP has to be adjusted to maintainthe pressure-volume curve above thelower inflection point, to avoid repeatedalveolar collapse and reopening resultingfrom low end-expiratory volume, and tomaintain alveolar recruitment throughout the respiratory cycle. Hemodynamicimplications can be reduced by maintaining an euvolemia and avoiding highPEEP levels.Pressure-Regulated VolumeControl (PRVC) VentilationPRVC ventilation is a mode of ventilationnow available in newer ventilators. Thismethod delivers a controlled tidal andminute volume in a pressure-limitedmanner, using the lowest possible pressure, which is constant during the inspiratory phase. The gas flow is decelerated and pressure and flow constantlyvary, breath by breath, to achieve thepreset tidal volume at a minimum peakinspiratory pressure. It is particularlyuseful in patients ventilated when thereare rapid changes in lung compliance andairway resistance, for instance, when surfactant and bronchodilators are used (31–34).Methodology. The ventilator tests thefirst breath at 5 cm H2O above PEEP andcalculates the compliance. The inspiratory pressure changes breath by breathuntil the preset tidal volume is reached ata maximum of 5 cm H2O below the setupper pressure limit. At this stage, themeasured tidal volume corresponds tothe preset value and the pressure remainsconstant. If the measured tidal volumeincreases above the preset level, inspiratory pressure is reduced until the set tidalvolume is reached.Indications. This mode of ventilationappears to be indicated: a) if within thelung compliance and resistance vary rapidly; b) if there is an initial requirementof high flow to reopen closed pulmonaryareas (e.g., atelectasis, etc.); c) to reducehigh ventilatory peak pressure (e.g., inpremature infants, interstitial emphysema); d) to control ventilatory pressuresfrom the moment nonventilated alveoliand bronchioles are reopened (e.g., surfactant, theophylline, or nitric oxide administration); e) in the presence of bron-chospasms and bronchiole spasms (e.g.,asthma, bronchiolitis); f) in all patients inwhom PEEP levels must be reduced toavoid hemodynamic complications.Advantages of PRVC Ventilation. Thismethod appears to be useful in improvingrespiratory mechanics and gas exchange,in reducing the barotrauma caused bypeak inspiratory pressure, in limiting oxygen toxicity because of the possibility ofusing reduced FIO2 to maintain adequategas exchange compared with conventional mechanical ventilation (34 –36).The use of decelerating gas flows favorsopening of closed areas of the lung andlaminar flow, which allows the reductionof PEEP levels in case of hemodynamicimplications (37– 40). It also appears tobe beneficial when drugs, such as surfactant, bronchodilators, and nitric oxide,which bring about a rapid change in compliance and airway resistance, are used.Clinical controlled trials are requiredto evaluate the benefits of PRVC ventilation in acute lung pathology, in ventilation of healthy lungs (i.e., neurosurgicalpatients), and during weaning from theventilator, in which this method appearsto be indicated.High-Frequency OscillatoryVentilation (HFOV)High-frequency ventilation has been oneof the most studied ventilation techniques during the past two decades. Despite its theoretical benefits, it has notreceived unanimous consensus and hasnot been widely used.The most fundamental difference between high-frequency ventilation and intermittent positive-pressure ventilation isthat with high-frequency ventilation, thetidal volume required is approximately1–3 mL/kg/body weight compared with6 –10 mL with intermittent positivepressure ventilation. During high-frequency ventilation, minute ventilation isproportional to ventilator frequency the square of the tidal volume. The increase in the ventilation rate to frequencies of 60 bpm or more in high-frequencyventilation is obviously mandatory if evencomparable minute volume ventilation isto result (41, 42).Three models are currently under investigation: high-frequency positivepressure ventilation, high-frequency jetventilation, and HFOV (43, 44). The firsttwo are no longer used in intensive caretherapy because of their poor results intrials compared with conventional me9
chanical ventilation. High-frequency jetventilation has found an important placein tracheobronchial surgery. HFOV isproving to be highly successful, mainlybecause adequate equipment capable ofsolving the problem of humidification ofventilated gases is now available.High-Frequency Positive-PressureVentilation. Tidal volume is delivered viaa normal sized tracheal tube, with inspiration being the only active part of theventilatory cycle (i.e., expiration achievedby passive lung recoil). Frequencies areusually in the range of 60 –120 cpm (1–2Hz).High-Frequency Jet Ventilation. Tidalvolume is delivered via a narrow cannulaor injector, resulting in a jet of high velocity gas, normally at frequencies of 60 –600 cpm (1–10 Hz).High-Frequency Oscillation. Tidalvolume is delivered via normal sized tracheal tubes, and both inspiration and expiration are active and of approximateequal power, such as would occur with anoscillating piston or loudspeaker-basedventilator. Frequencies range from 2 Hzto 50 Hz (300 –3000 cpm). Prototype ventilators with a frequency range of 100 Hz(6000 cpm) have been described (45).High-Frequency OscillationHigh-frequency oscillation differs in several respects from the other two techniques. Cyclic pressure changes are applied to the trachea by connecting apiston pump or the cone of a loudspeakersystem driven by an electronic oscillator,directly to the patient’s endotracheal tubeto generate approximately a sinusoidalflow waveform. The pump is used to produce a reciprocating flow in the airways,whereas an auxiliary gas flow (bias flow)is used to clear the extracted carbon dioxide and to provide fresh gases to thesystem. These systems behave as a Tpiece circuit, and the efficiency of carbondioxide removal is a function of the magnitude of the bias flow.Both inspiration and expiration are active, in contrast to high-frequency jetventilation and high-frequency positivepressure ventilation, in which expirationis passive and the flow profiles have asquare or triangular waveform, respectively. From this, it follows that the inspiratory/expiratory ratio is usually fixedat 1:1, but pumps with variable ratios arenow available.There are a number of mechanismsproposed to explain the gas exchange in10HFOV. Direct alveolar ventilation,asymmetric velocity profiles, Taylor dispersion, pendelluft, cardiogenic mixing, accelerated diffusion, and acousticresonance appear to participate in gasexchanges both individually and/or together (42, 46).Clinical ConsiderationsGas Trapping. Tidal volume amplification resulting from pressure swings inthe alveoli, delivering a larger tidal volume than the one generated by the oscillator, may contribute to gas trapping. Airtrapping may occur if the ventilatory frequency increases and if the expiratorytime is reduced to 250 msec.Gas trapping is less likely to occur inHFOV systems in which expiration is assisted. The shorter the expiratory periodand the greater the respiratory time constants, the lower the frequency at whichgas trapping becomes a problem.A modest degree of gas trapping is notalways undesirable, and the term “autoPEEP” may give a more balanced view ofthis effect. The proximal airway pressureis not a real indicator of true intrathoracic pressure during HFOV, and esophageal pressure may be a better index forclinical use.Humidification During HFOV. Theneed for good humidification (90% relative humidity) in HFOV is essential toavoid severe irreversible damage to thetrachea. On one hand, viscous secretionscan obstruct alveoli and one bronchi, deteriorating ventilation; on the otherhand, excessive humidification can leadto condensation in the child’s circuit, theendotracheal tube, and the airways, reducing the effect of HFOV. At present, themost advanced humidifiers available(e.g., Fischer Paykel) are able to solve themajority of HFOV-related humidificationproblems, avoiding those difficulties thatwere seen with high-frequency jet ventilation use.Cooling Effects of High-FrequencyVentilation. There is no documented evidence for such a claim, provided thatadequate humidification is provided. Thegas flows used in HFOV may be high, butthe thermal capacity of gases is very low.In contrast, the latent heat of vaporization of water is considerable. In highfrequency jet ventilation, for example, attypical clinically used minute volumes,the cooling effect from the gas alone isthe equivalent of about 250 kcal 1 (about7% to 10%) of the daily calorie require-ment. The cooling effect that would result from the use of dry gas, with theconsequent latent heat losses from evaporation, would be approximately 3000 –3500 kcal/day 1. Thus, simple warmingof the inspired gas would produce littleclinical benefit.Prevention of Aspiration. In paralyzed,deeply sedated children, HFOV can prevent aspiration of pharyngeal contents byits auto-PEEP effect, so described forhigh-frequency ventilation (47). Patientswho are capable of voluntary inspirationor coughing can generate a negative tracheal pressure, which could favor aspiration of regurgitated gastric material.The theoretical advantages of HFOVinclude maintaining open airways,smaller phasic volume and pressurechange, gas exchange at significantlylower airway pressures, less involvementof the cardiovascular system, and less depression of endogenous surfactant production. HFOV is recommended to reduce lung barotrauma and theconsequent lung injury in nonhomogeneous lung pathology, in air leaks, inpersistent pulmonary hypertension of thenewborn (PPHN), and in ventilation ofpremature babies (41, 48 –50).Contraindications of HFOV are incases of pulmonary obstruction fromfresh meconium aspiration (danger ofoverinflating the more compliant lungunits), bronchopulmonary dysplasia withclinical evidence of increased expiratoryresistance and respiratory syncytial virusbronchiolitis, and intracranial hemorrhage.There are a limited number of published large clinical trials on the use ofHFOV in pediatric patients (41, 46, 50),but from them, the benefits derivingfrom the reopening of the closed alveoliand maintaining them open, as well asreduction of airleak, have still to be fullydemonstrated. Even though in severalstudies bronchiolitis is excluded frompossible treatment (51), recently published cases have shown a reasonable possibility of successful treatment (52, 53).The described complications of HFOVare connected with overinflation in obstructive lung diseases, intracranial hemorrhages, reduction in heart rate attributed to increased vagal activity,bronchopulmonary dysplasia, necrotizingtracheobronchitis, increased permeability of lung epithelium, and insufficienthumidification of tracheobronchial secretions (48, 54 –56). Adverse neurologicevents have been demonstrated to be conPediatr Crit Care Med 2003 Vol. 4, No. 1
nected with ventilatory strategies morethan with high-frequency devices (57).Although HFOV can maintain adequate gas exchange for prolonged periodsin many situations, there is as yet noclearly defined clinical role for this modeof ventilation. Recent studies in premature babies with hyaline-membrane disease and in term or near-term hypoxemicnewborns have demonstrated an important improvement in oxygenation and areduced incidence of airleak with HFOV.There are no data from randomized,controlled trials supporting the routineuse of rescue HFOV in term or near-terminfants with severe pulmonary dysfunction. Cochrane Review (58) shows no evidence of a reduction in mortality at 28days, in the number of patients requiringextracorporeal membrane oxygenation,days on a ventilator, days receiving oxygen, or days in the hosp
olar ventilation and also in avoiding lung injury, volume-control ventilation is the safer and preferable ventilatory mode. Pressure-limited ventilation is not highly indicated in pediatric patients and for neonatal ventilation because the tidal vol-ume cannot be controll
gender distribution, status at birth and initial ventilatory parameters (Table I). The two groups of infants had similar severity of their RDS as shown by the initial Fi02, mean airway pressure, a/A ratio and ventilatory index. In the control group, pre-trea
to transient hypoxia, and (d) determination of the effects of anemia upon the ventilatory responses to steady-state hypoxia. Effects of anemia on responses to transient hypoxia. Six goats were studied. Initial experiments were performed in duplicate at normal hemoglobin levels for the goa
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Risk of aspiration of oral/ nasal/ pharyngeal secretions - Total Laryngectomy: Anatomy Question 1 Following a total laryngectomy, Mr. John Doe experiences respiratory failure and requires ventilatory support. intubate Mr Doe? Which of the following is the best way to intubate Mr Doe? a) Orotracheal intubation b) Nasotracheal intubation
Monitoring parameters: CO2, VC/IS, NIF 4. If airway and mechanical ventilatory support are not initially required in a patient with tetraplegia or thoracic level paraplegia, evaluation of baseline pulmonary function on admission should be considered with measurement of tidal volume,
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