642 SECTION V Pediatric Critical Care Pulmonary The ultrasonic nebulizer uses a piezoelectric crystal that produces a highly concentrated output of aerosol particles The metered dose inhaler uses a pr[.]
642 S E C T I O N V Pediatric Critical Care: Pulmonary The ultrasonic nebulizer uses a piezoelectric crystal that produces a highly concentrated output of aerosol particles The metereddose inhaler uses a pressurized canister that dispenses a single bolus of aerosolized medication Such inhalers are convenient, cost effective, and versatile, and generally have an effective deposition rate of 10% to 15% The canister is actuated into the spacer and the medication remains suspended in the chamber until inhaled by the patient A dry-powder inhaler delivers a large bolus of medication during a single inspiration maneuver, producing therapeutic effects similar to a metered-dose inhaler and aerosol nebulizer The dry-powder medication, released from a capsule and deposited into a small canister, is delivered to the lungs during inspiration Weaning From Mechanical Ventilation and Extubation Weaning and liberation from mechanical ventilation requires resolution of the underlying reason for intubation, ability to demonstrate effective gas exchange with minimal support, and appropriate neurologic state to support spontaneous breathing and airway protection Avoiding both premature extubation and unnecessary prolongation of mechanical ventilation is important It is the patient who dictates the initiation and pace of the weaning process Improvement of the underlying disease process can be assessed with indices of gas exchange, pulmonary mechanics, ventilation-perfusion relationships, and chest radiograph findings If the patient is intubated for primary lung disease, resolution of the underlying disease process will result in improved compliance and/or lower airway resistance, which will, in turn, present as lower peak pressures to achieve target tidal volumes The patient will gradually be able to take on an increasing fraction of the work of breathing without distress; the ventilator support should be decreased accordingly Reduced dead space fraction and V/Q mismatch may be measured directly but will also be inferred by the capability to wean Fio2 while maintaining an adequate peripheral capillary oxygen saturation Chest radiography and airway secretions will be additional markers for disease improvement and the ability to wean toward extubation Other organ systems that must be optimized for best chance of extubation success include cardiovascular status and heart function, nutritional status, and neurologic/neuromuscular status In cases of significant debility, the respiratory muscles may be strengthened with progressive pressure support trials that allow the patient to take more of the respiratory workload From a neurologic standpoint, sedation should be lightened such that the patient demonstrates spontaneous breathing without distress as well as a strong cough and, if developmentally appropriate, the ability to follow commands Extubation Readiness Trial Currently, there are three methods of extubation readiness trials (ERTs; also called spontaneous breathing trials): (1) T-piece trials, (2) CPAP trials, and (3) minimal pressure-support trials.63 In TABLE Extubation Readiness Trial Parameters 54.3 Indications Decreasing ventilator support over last 12 h PEEP 5–8 cm H2O Fio2 # 0.5 Hemodynamically stable Spontaneous respiratory drive PEEP settings cm H2O Pressure support to compensate for tube resistancea ETT Size Pressure Support 3–3.5 mm ID 4–4.5 mm ID mm ID 10 cm H2O cm H2O cm H2O Signs of failure Apnea Exhaled Vt # mL/kg IBW Tachypnea for age Increased respiratory effort Desaturation below target Spo2 Unstable hemodynamics a Many clinicians have abandoned the application of pressure support during extubation readiness trials (ERTs), since tube resistance is not significantly increased in properly sized small-diameter endotracheal tubes and pressure support could mask ERT failure ETT, Endotracheal tube; Fio2, fraction of inspired oxygen; IBW, ideal body weight; ID, internal diameter; PEEP, positive end-expiratory pressure; Spo2, peripheral capillary oxygen saturation; Vt, tidal volume T-piece trials, the patient’s endotracheal tube is disconnected from the ventilator and connected to corrugated tubing carrying a constant flow of humidified air Because of the lack of mechanical alarm system, this method is less commonly used in children More commonly, a patient is placed in either a straight CPAP mode or a pressure support with minimal pressure Table 54.3 summarizes indications, settings, and signs of failure of extubation readiness testing Extubation If the patient successfully passes an ERT, extubation should be considered Reasons to delay extubation might include lack of protective reflexes, including cough and gag, copious or thick secretions that may not be managed well without an endotracheal tube, concerns about hemodynamic neurologic or metabolic status, and/or planned operative procedures in the next 12 to 24 hours Providers should strive to liberate patients from mechanical ventilation to avoid unnecessary morbidity However, patients requiring reintubation experience longer ICU stays and higher mortality; thus, providers must also be thoughtful about avoiding premature extubation Extubation failure (commonly defined as need for reintubation within 48 hours) is highly associated with simple measures of respiratory function, such as inspiratory drive, lung mechanics, gas exchange, and level of ventilator support before extubation Table 54.4 lists threshold values for the respiratory parameters associated with low-risk (,10%) and high-risk (.25%) extubation failure.64–66 CHAPTER 54 Mechanical Ventilation and Respiratory Care TABLE 54.4 Predictors of Extubation Failure Respiratory Parameter Low Risk (#10%) High Risk (25%) Spontaneous tidal volume (mL/kg) 6.5 ,3.5 Fio2 ,0.3 0.4 Mean airway pressure (cm H2O) ,5 8.5 Peak inspiratory pressure (cm H2O) ,25 30 Dynamic compliance (mL/kg/cm H2O) 0.9 ,0.4 Dead space ratio (Vd/Vt) ,0.5 0.65 Percentage of the total minute ventilation provided by the ventilator (%) ,20 30 Mean inspiratory flow (mL/kg/s) 14 ,8 Fio2, Fraction of inspired oxygen; Vd, dead space ventilation; Vt, tidal volume Key References Chatburn RL Understanding mechanical ventilators Expert Rev Respir Med 2010;4(6):809-819 Cheifetz IM Invasive and noninvasive pediatric mechanical ventilation Respir Care 2003;48(4):442-453; discussion 453-448 643 Gilstrap D, MacIntyre N Patient-ventilator interactions Implications for clinical management Am J Respir Crit Care Med 2013;188(9): 1058-1068 Hupp SR, Turner DA, Rehder KJ Is there still a role for high-frequency oscillatory ventilation in neonates, children and adults? Expert Rev Respir Med 2015;9(5):603-618 Kacmarek RM Proportional assist ventilation and neurally adjusted ventilatory assist Respir Care 2011;56(2):140-148; discussion 149-152 Newth CJ, Venkataraman S, Willson DF, et al Weaning and extubation readiness in pediatric patients Pediatr Crit Care Med 2009;10(1): 1-11 Panitch HB Airway clearance in children with neuromuscular weakness Curr Opin Pediatr 2006;18(3):277-281 Pediatric Acute Lung Injury Consensus Conference Group Pediatric acute respiratory distress syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference Pediatr Crit Care Med 2015;16(5):428-439 Rimensberger PC, Cheifetz IM, Pediatric Acute Lung Injury Consensus Conference Group Ventilatory support in children with pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference Pediatr Crit Care Med 2015;16(5 suppl 1):S51-S60 Turner DA, Ofori-Amanfo G, Williford WL, Cheifetz IM Lung protective ventilation: a summary of the current evidence from the 2012 American Association for Respiratory Care International Congress Expert Rev Respir Med 2013;7(3):209-212 West JB Respiratory Physiology: The Essentials 9th ed Baltimore: Williams & Wilkins; 2012 The full reference list for this chapter is available at ExpertConsult.com e1 References Polgar G, Weng TR The functional development of the respiratory system from the period of gestation to adulthood Am Rev Respir Dis 1979;120(3):625-695 Lumb AB, Nunn JF Nunn’s Applied Respiratory Physiology 6th ed Edinburgh; Philadelphia: Elsevier Butterworth Heinemann; 2005 West JB Respiratory Physiology: The Essentials 9th ed Baltimore: Williams and Wilkins; 2012 Friedman ML, Nitu ME Acute respiratory failure in children Pediatr Ann 2018;47(7):e268-e273 Chatburn RL Understanding mechanical ventilators Expert Rev Respir Med 2010;4(6):809-819 Mireles-Cabodevila E, Hatipoglu U, Chatburn RL A rational framework for selecting modes of ventilation Respir Care 2013; 58(2):348-366 Cheifetz IM Invasive and noninvasive pediatric mechanical ventilation Respir Care 2003;48(4):442-453; discussion 453-448 Turner DA, Ofori-Amanfo G, Williford WL, Cheifetz IM Lung protective ventilation: a summary of the current evidence from the 2012 American Association for Respiratory Care International Congress Expert Rev Respir Med 2013;7(3):209-212 Williams DC, Cheifetz IM Emerging approaches in pediatric mechanical ventilation Expert Rev Respir Med 2019;13(4):327-336 10 Murias G, Villagra A, Blanch L Patient-ventilator dyssynchrony during assisted invasive mechanical ventilation Minerva Anestesiol 2013;79(4):434-444 11 Stein H, Firestone K, Rimensberger PC Synchronized mechanical ventilation using electrical activity of the diaphragm in neonates Clin Perinatol 2012;39(3):525-542 12 Pediatric Acute Lung Injury Consensus Conference Group Pediatric acute respiratory distress syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference Pediatr Crit Care Med 2015;16(5):428-439 13 Rimensberger PC, Cheifetz IM, Pediatric Acute Lung Injury Consensus Conference Group Ventilatory support in children with pediatric acute respiratory distress syndrome: proceedings from the Pediatric Acute Lung Injury Consensus Conference Pediatr Crit Care Med 2015;16(5 suppl 1):S51-S60 14 Selim B, Ramar K Advanced positive airway pressure modes: adaptive servo ventilation and volume assured pressure support Expert Rev Med Devices 2016;13(9):839-851 15 Vagiakis E, Koutsourelakis I, Perraki E, et al Average volumeassured pressure support in a 16-year-old girl with congenital central hypoventilation syndrome J Clin Sleep Med 2010;6(6):609-612 16 Guttmann J, Haberthur C, Mols G, Lichtwarck-Aschoff M Automatic tube compensation (ATC) Minerva Anestesiol 2002;68(5):369-377 17 Turner DA, Rehder KJ, Cheifetz IM Nontraditional modes of mechanical ventilation: progress or distraction? 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Physiology: The Essentials 9th ed Baltimore: Williams & Wilkins; 2012 The full reference list for this chapter is available at ExpertConsult.com e1 References Polgar G, Weng TR The functional development... Burns KEA, Soliman I, Adhikari NKJ, et al Trials directly comparing alternative spontaneous breathing trial techniques: a systematic review and meta-analysis Crit Care 2017;21(1):127 64 Wratney... intensive care unit Proper management of respiratory support is essential to achieve optimal outcomes This chapter couples basic respiratory physiologic principles with the technical aspects of invasive