Controlled mechanical ventilation (CMV) is time triggered, flow limited, and volume or pressure cycled. Spontaneous breaths can be taken between the mandatory breaths. However, no additional gas is provided during spontaneous breaths. Therefore, the work of breathing is markedly increased in the spontaneously breathing patient. This mode of ventilation is no longer used.

Intermittent mandatory ventilation (IMV) is time triggered, volume or pressure limited, and either time, volume, or pressure cycled. A rate is set, as is a volume or pressure parameter. Additional inspired gas is provided by the ventilator to support spontaneous breathing when additional breaths are desired. Unlike CMV, IMV mode provides additional inspired gas to the patient to support spontaneous breathing, during spontaneous breaths. IMV is particularly beneficial in patients who do not have a respiratory drive, such as those who are neurologically impaired or pharmacologically paralyzed as it ensures adequate ventilation while allowing for some spontaneous breathing. Work of breathing is still elevated with this mode in the awake and spontaneously breathing patient.

In the synchronized intermittent mandatory ventilation (SIMV) mode, the ventilator synchronizes IMV breaths with the patient’s spontaneous breaths ( Fig. 6.8 ). Small, patient-initiated negative deflections in airway pressure (pressure triggered) or decreases in the constant ventilator gas flow (bias flow) passing through the exhalation valve (flow triggered) provide a signal to the ventilator that a patient breath has been initiated. Ventilated breaths are timed with the patient’s spontaneous respiration, but the number of supported breaths each minute is predetermined and remains constant. Additional constant inspired gas flow is provided for use during any other spontaneous breaths. Advances in neonatal ventilators have provided the means for detecting small alterations in bias flow. Therefore, flow-triggered SIMV can be applied to newborns, which appears to enhance ventilatory patterns and allows ventilation with reduced airway pressures and FiO ₂ . ^, SIMV may be associated with a reduction in the duration of ventilation and the incidence of air leak in newborns in general, as well as in those premature infants with bronchopulmonary dysplasia (BPD) and intraventricular hemorrhage. ^,

Pressure, volume, and flow waveforms observed during intermittent mandatory ventilation (IMV) and synchronized IMV (SIMV). In this case, an end-inspiratory pause (P) has been added. Note the difference between peak (PIP) and end inspiratory (EIP) or plateau pressure. Arrows, Triggering variables; open circles, cycling variables.

With permission, Decker Intellectual Properties. Adapted from Bartlett RH. Use of the mechanical ventilator: surgery. In: Wilmore D, et al., eds. Care of the Surgical Patient . Scientific American; 1988.

In the spontaneously breathing patient, brain stem reflexes dependent on cerebrospinal fluid levels of CO ₂ and pH can be harnessed to determine the appropriate breathing rate. As in SIMV, with assist-control ventilation (ACV) the assisted breaths can be either pressure triggered or flow triggered. The triggering-mechanism sensitivity can be set in most ventilators. In contrast to SIMV, the ventilator supports all patient-initiated breaths. This mode is similar to IMV but allows the patient inherently to control the ventilation and minimizes patient work of breathing in adults and neonates. ^, Occasionally, patients may hyperventilate, such as when they are agitated or have neurologic injury. Heavy sedation may be required if agitation is present. A minimal ventilator rate below the patient’s assist rate should be established in case of apnea.

Pressure support ventilation (PSV) is a pressure- or flow-triggered, pressure-limited, and flow-cycled mode of ventilation. It is similar in concept to ACV, in that mechanical support is provided for each spontaneous breath and the patient determines the ventilator rate. During each breath, inspiratory flow is applied until a predetermined pressure is attained. As the end of inspiration approaches, flow decreases to a level below a specified value (2–6 L/min) or a percentage of peak inspiratory flow (at 25%). At this point, inspiration terminates. Although it may apply full support, PSV is frequently used to support the patient partially by assigning a pressure limit for each breath that is less than that required for full support. For example, in the spontaneously breathing patient, PSV can be sequentially decreased from full support to a PSV 5–10 cmH ₂ O above PEEP, facilitating successful weaning while providing partial support with each breath. ^, Thus, V _t during PSV may depend on patient effort. PSV provides two advantages during ventilation of spontaneously breathing patients: it provides excellent support and decreases the work of breathing associated with ventilation; it lowers PIP and P _aw while higher V _t and cardiac output levels may be observed. ^{, ,}

Pressure-triggered SIMV and PSV can be applied to newborns. Inspiration is terminated when the peak airway flow decreases to a set percentage between 5% and 25%. This flow cutoff for inspiration, known as the termination sensitivity , can be adjusted. The higher the termination sensitivity value, the shorter the inspiratory time. The termination sensitivity function may also be disabled, at which point ventilation is time cycled instead of flow cycled. There is a reduction in work of breathing and sedation requirements when SIMV with pressure support is applied to newborns.

Volume support ventilation (VSV) is similar to PSV except that a volume, rather than a pressure, is assigned to provide partial support. Automation with VSV is enhanced because there is less need for manual changes to maintain stable tidal and minute volume during weaning. In pediatric patients both VSV and PSV are valuable strategies and equally effective at weaning infants and children from the ventilator.

Volume-assured pressure support ventilation (VAPSV) attempts to combine volume- and pressure-controlled ventilation to ensure a desired V _t within the constraints of the pressure limit. It has the advantage of maintaining inflation to a point below an injurious PIP level while maintaining V _t constant in the face of changing pulmonary mechanics. Work of breathing may be markedly decreased while C _eff is increased during VAPSV.

Proportional assist ventilation (PAV) is an intriguing approach in the spontaneously breathing patient. It is based on the concept that the combined pressure generated by the ventilator ( P _aw ) and respiratory muscles ( P _mus ) is equivalent to that required to overcome the resistance to flow of the endotracheal tube/airways ( P _res ) and the tendency for the inflated lungs to collapse.

With PAV, airway pressure generation by the ventilator is proportional at any instant to the respiratory effort ( P _mus ) generated by the patient. Small efforts, therefore, result in small breaths, whereas greater patient effort results in development of a greater V _t . Inspiration is patient triggered and terminates with discontinuation of patient effort. Rate, V _t , and inspiratory time are entirely patient controlled. The predominant variable controlled by the ventilator is the proportional response between P _mus and the applied ventilator pressure. This proportional assist ( P _aw / P _mus ) can be increased until nearly all patient effort is provided by the ventilator. Patient work of breathing, dyspnea, and PIP are reduced. ^, Elastance and resistance are set, as is applied PEEP. V _t is variable, and the risk of atelectasis is present. PAV produces similar gas exchange with lower airway pressures when compared with conventional ventilation in infants. Compared with preterm newborns being ventilated with the assist-control mode and with IMV, preterm newborns managed with PAV maintained gas exchange with lower airway pressures and a decrease in the oxygenation index by 28% in one study. Chest-wall dynamics are also enhanced. PAV represents an exciting first step in servoregulating ventilators to patient requirements. Additional studies using neurally adjusted ventilation are also under way, and certain populations (obstructive lung disease and small children) may benefit from the increased patient-ventilator synchrony. ^,

An Edi waveform is captured using a specialized catheter with electrodes placed into the distal esophagus near the diaphragm and translated to a trigger on and cycle off each breath. The waveform controls the pressure delivered to provide synchronized, proportional breaths with the patient’s needs. It helps to visualize spontaneous breathing effort and adjust the settings for synchrony. To set the level of support, starting with an NAVA level of 0.5 cmH ₂ O/μV, with steady increases of 0.5–1 cmH ₂ O/μV, every 10–15 seconds, to a maximum of 4 cmH ₂ O/μV, leads to an increase in the PIP and V _t until a plateau is reached with downregulation of Edi to 70% of the peak level—the “breakpoint.” A backup ventilation mode is set for when the Edi level remains flat with accidental catheter dislodgement or apnea. A vigorous Edi confirms a spontaneous ventilation and can be used as an extubation criterion and maintained on NIV-NAVA. ^,

During CPAP pressures exceeding ambient levels are continuously applied to the airways to enhance alveolar distention and oxygenation. This mode can substantially reduce both airway resistance and work of breathing. Caution is necessary for untreated conditions such as pneumothorax. Because ventilation is unsupported, this mode requires that the patient provide all the work of breathing and CPAP should be avoided in patients with hypovolemia, untreated pneumothorax, lung hyperinflation, or elevated intracranial pressure and in infants with nasal obstruction, cleft palate, tracheoesophageal fistula, or untreated congenital diaphragmatic hernia. CPAP is frequently applied via nasal prongs, although it can be delivered with a nasal mask.

Bubble CPAP (bCPAP) is a variation using continuous flow, similar to ventilator-derived CPAP, as opposed to the variable flow systems commonly used with nasal CPAP. ^, Heated, humidified air is delivered to the infant with the distal expiratory tubing submerged to the appropriate depth of pressure. The bubbling in the water chamber is thought to create chest vibrations that enhance gas exchange. The low-amplitude, high-frequency oscillations generated by bCPAP enhance gas exchange in patients after extubation or with chronic lung disease. Limitations of CPAP include lack of pressure alarms; pressure-release valves; injury to skin, nose, and nasal septum from pressure of the nasal prongs or masks; and the risk of “CPAP belly,” a condition where air leaks from the airway into the stomach and digestive tract. ^,

Although sometimes used in the setting of acute lung injury, bilevel control of positive airway pressure (BiPAP) is more commonly used for home respiratory support by varying airway pressure between one of two settings: the inspiratory positive airway pressure (IPAP) and the expiratory positive airway pressure (EPAP). ^, With patient effort, a change in flow is detected, and the IPAP pressure level is developed. With reduced flow at end expiration, EPAP is reestablished. The BiPAP system provides both ventilatory support and airway distention during the expiratory phase. However, BiPAP should only support spontaneously breathing patients. In a randomized trial of NIV in a subset of pediatric patients with lung injury, NIV improved hypoxemia and decreased the rate of endotracheal intubation. In neonates, a multicenter randomized trial demonstrated decreased days of mechanical ventilation, chronic lung disease, and mortality when early CPAP was used instead of intubation and surfactant in preterm infants.

Enhancing alveolar distention reduces hypoxemia and shunt and is helpful in the management of respiratory failure. One means to accomplish this is to maintain the inspiratory plateau pressure for a longer proportion of the breath. The inspiratory time may be prolonged to the point at which the I/E ratio may be as high as 4:1. In most circumstances, however, the I/E ratio is maintained at approximately 2:1. Inverse ratio ventilation (IRV) is usually performed during pressure-controlled ventilation (PC-IRV), although prolonged inspiratory times can be applied during volume-controlled ventilation by adding a decelerating flow pattern or an end-inspiratory pause to the volume-controlled ventilator breath. One advantage of IRV is the ability to recruit alveoli that are associated with high-resistance airways that inflate only with prolonged application of positive pressure. Unfortunately, IRV is associated with a profound sense of dyspnea in patients who are awake and spontaneously breathing. Therefore, heavy sedation and pharmacologic paralysis is required when using this ventilator mode.

As expiratory time ( E _t ) is reduced, the risk for incomplete expiration, identified by the failure to achieve zero-flow conditions at end expiration, is increased. This results in “auto-PEEP” or a total PEEP greater than that of the preset or applied PEEP. Clinicians should actively monitor for the presence of auto-PEEP and incorporate it into the ventilation strategy to avoid barotrauma. IRV may also negatively affect cardiac output and therefore decrease DO ₂ . Some studies on IRV have shown increased P _aw and oxygenation, alongside lung protection through reduced PIP. Other reports suggest that early implementation of IRV in severe ARDS enhances oxygenation and allows reduction in FiO ₂ , PEEP, and PIP. On the other hand, a number of studies have failed to demonstrate enhanced gas exchange with this mode of ventilation. Some series have suggested that IRV is less effective at enhancing gas exchange than is application of PEEP to maintain the same P _aw . Overall, it appears that oxygenation is determined primarily by the P _aw rather than specifically by the application of IRV. Thus, the usefulness of IRV remains in question.

Airway pressure release ventilation (APRV) is a unique approach to ventilation in which CPAP at high levels is used to enhance mean alveolar volume while intermittent reductions in pressure to a “release” level provide a period of expiration ( Fig. 6.9 ). Reestablishment of CPAP results in inspiration and return of lung volume back to the baseline level. The advantage of APRV is a reduction in PIP of approximately 50% in adult patients with ARDS when compared with other more conventional modes of mechanical ventilation. ^, Spontaneous ventilation is also allowed throughout the cycle, which may enhance cardiac function and renal blood flow. ^, Some data suggest that V ˙ E matching may be improved and dead space reduced. ^, In performing APRV, V _t is altered by adjusting the release pressure. Conceptually, ventilator management during APRV is the inverse of other modes of positive-pressure ventilation in that the PIP, or CPAP, determines oxygenation and the expiratory pressure (release pressure) is used to adjust V _t and CO ₂ elimination.

Typical pressure and volume waveforms observed during airway pressure release ventilation. CPAP, Continuous positive airway pressure.

APRV is very similar to modes of ventilation, such as IRV, that use prolonged I/E ratios. However, APRV appears to be better tolerated when compared with IRV in patients with acute lung injury/ARDS, as demonstrated by a reduced need for paralysis and sedation, increased cardiac performance, decreased pressor use, and decreased PIP requirements. In one study, APRV improved the lung perfusion, as measured by pulmonary blood flow and oxygen delivery, in infants who underwent repair of tetralogy of Fallot or cavopulmonary shunt. Despite these benefits, clinical experience with APRV in the pediatric population remains limited. ^,

A decrease in pulmonary compliance and FRC is seen in the patient with acute lung injury (PaO ₂ /FiO ₂ ratio, 200–300) or ARDS (PaO ₂ /FiO ₂ ratio, <200). This is secondary to alveolar collapse and a decrease in the volume of lung available for ventilation, which leads to decreased pulmonary compliance. As a result, higher ventilator pressures are necessary to maintain V _t and V ˙ E . However, any attempt to ventilate the patient with respiratory insufficiency due to parenchymal disease with higher pressures can result in compromise of cardiopulmonary function and the development of ventilator-induced lung injury.

Patients who received mechanical ventilation have been known to have had concomitant lung injury. In 1952, mechanical damage to lungs from mechanical ventilation was described and in 1967 “respirator lung,” extensive alveolar infiltrates and hyaline membrane, was shown in autopsy studies. The modern concept of ventilator-induced lung injury was first identified in 1974 in vivo studies demonstrating the detrimental effects of ventilation at PIP of 45 cmH ₂ O in rats. Electron microscopy has been used to document an increased incidence of alveolar stress fractures in ex vivo, perfused rabbit lungs exposed to transalveolar pressures more than 30 cmH ₂ O. Other studies have demonstrated increases in albumin leak, elevation of the capillary leak coefficient, enhanced wet-to-dry lung weight, deterioration in gas exchange, and augmented diffuse alveolar damage on histologic examination with application of increased airway pressure (45–50 cmH ₂ O) in otherwise normal rats and sheep over a 1- to 24-hour period. ^{, ,} Pulmonary exposure to high pressures may potentially worsen nascent respiratory insufficiency and, ultimately, lead to the development of pulmonary fibrosis.

Such injury may be prevented during application of high PIPs by strapping the chest, thereby preventing lung overdistention, suggesting that alveolar distention or volutrauma is the injurious element, as opposed to the application of high pressures or barotrauma. A low- V _t (6 mL/kg) approach to mechanical ventilation in rabbits with Pseudomonas aeruginosa–induced acute lung injury was found to be associated with enhancement in oxygenation, increase in pH, increase in arterial blood pressure, and decrease in extravascular lung water when compared with a high V _t group (15 mL/kg). A relationship may also exist between ventilator gas flow rate and the development of lung injury. In another study, positive blood cultures were found in five of six animals exposed to high EIP but rarely in those with low EIP.

Together, these data suggest that the method of ventilation has an effect on lung function and gas exchange as well as a systemic effect, which may include translocation of bacteria from the lungs. Therefore, avoidance of high PIPs and lung overdistention should be a primary goal of mechanical ventilation. Although the animal data suggest that high PIPs and volumes may be deleterious, two multicenter studies have attempted to randomize patients with ARDS to high and low peak pressure or volume strategies. The first study failed to demonstrate a difference in mortality or duration of mechanical ventilation in patients randomized to either the low-volume (7.2 ± 0.8 mL/kg) or the high-volume (10.8 ± 1.0 mL) strategy, although the applied PIP was not elevated to what would commonly be considered injurious levels in either group (low, 23.6 ± 5.8 cmH ₂ O; high, 34.0 ± 11.0 cmH ₂ O). Another study found similar results, but had similar design limitations. A survival increase from 38% to 71% at 28 days, a higher rate of weaning from mechanical ventilation, and a lower rate of barotrauma have been demonstrated in patients in whom a lung-protective ventilator strategy was used. This strategy consisted of lung distention to a level that prevented alveolar collapse during expiration (see later) and avoidance of high distending pressures. One study identified a statistically significant reduction over time in bronchoalveolar lavage (BAL) concentrations of polymorphonuclear cells, interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-8, and IL-6, and in the plasma concentration of IL-6 ( P < .002) among 44 patients randomized to receive a lung-protective strategy rather than a conventional approach. The mean number of ventilator-free days at 28 days in the lung-protective strategy group was higher than in the control group (12 ± 11 vs. 4 ± 8 days, respectively; P < .01). However, mortality rates at 28 days from admission were not different.

The NIH’s Acute Respiratory Distress Network convincingly demonstrated that mortality was reduced with the use of a low-volume (6 mL/kg, mortality of 31%) when compared with a high-volume (12 mL/kg, mortality of 39%; P = .005) ventilator approach ( Fig. 6.10 ). Interestingly, no difference was found in gas exchange or pulmonary mechanics between groups to account for the difference in mortality. Most clinicians are now convinced that avoidance of high PIP and support of lung recruitment through the application of appropriate levels of PEEP (see later) should be a primary goal of any mechanical ventilatory program.

Probability of survival and of being discharged home and breathing without assistance during the first 180 days after randomization in patients with acute lung injury and the acute respiratory distress syndrome. The status at 180 days or at the end of the study was known for all but nine patients.

From The Acute Respiratory Distress Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med . 2000;342:1301–1308.

The concept of permissive hypercapnia was applied to avoid ventilator-induced lung injury. Application of this concept has shown decreased pulmonary morbidity, particularly in pediatric patients. ^, With this approach, PaCO ₂ is allowed to increase to levels as high as 120 mmHg as long as the blood pH is maintained in the 7.1–7.2 range by the administration of buffers. In an adult study, mortality was reduced to 26% when compared with that expected (53%; P < .004) based on Acute Physiology and Chronic Health Evaluation II (APACHE II) scores when low-volume, pressure-limited ventilation with permissive hypercapnia was applied in the setting of ARDS. In a burn study in children, the mortality rate was only 3.7% despite a high degree of inhalation injury when a ventilator strategy used a PIP of 40 cmH ₂ O and accepted an elevated PaCO ₂ as long as the arterial pH was greater than 7.20. Another study suggested that a strategy of high-frequency (40–120 breaths/min) ventilation with a low V _t , low PIP, high PEEP (7–30 cmH ₂ O), and mild hypercapnia (PaCO ₂ from 45 to 60 mmHg) enhances the survival rate in children with severe ARDS.

Although application of high, overdistending airway pressures appears to be associated with the development of lung injury, a number of studies have demonstrated that application of PEEP or high-frequency oscillatory ventilation (HFOV) may prevent lung injury by the following mechanisms: (1) recruitment of collapsed alveoli, which reduces the risk for overdistention of healthy units; (2) resolution of alveolar collapse, which in and of itself is injurious; and (3) avoidance of the shear forces associated with the opening and closing of alveoli. ^, In the older child with injured lungs, a pressure of 8–12 cmH ₂ O is required to open alveoli and begin V _t generation. ^{, ,} Alveoli will subsequently close unless the end-expiratory pressure is maintained at such pressures, and cyclic opening and closing is thought to be particularly injurious because of application of large shear forces. One way to avoid this process is through the application of PEEP to a point above the inflection pressure ( P _flex ), such that alveolar distention is maintained throughout the ventilatory cycle ( Fig. 6.11 ). ^, As mentioned previously, it has been demonstrated that the distribution of infiltrates and atelectasis in the supine patient with ARDS is predominantly in the dependent regions of the lung. This is likely the result of compression due to the increased weight of the overlying edematous lung. It has been shown that when the superimposed gravitational pressure from the weight of the overlying lung exceeded the PEEP applied to a given region of the lung, end-expiratory lung collapse increased, resulting in derecruitment. Thus, application of PEEP may result in recruitment of these atelectatic lung regions, simultaneously enhancing pulmonary compliance and oxygenation. PEEP and prone positioning are more effective if the need for ventilation is of extrapulmonary etiology rather than pulmonary etiology.

Static pressure/volume curve demonstrating the P _flex point in a patient with acute respiratory distress syndrome. Positive end-expiratory pressure should be maintained approximately 2 cmH ₂ O above that point. The upper inflection point (UIP) indicates the point at which lung overdistention is beginning to occur. Ventilation to points above the UIP should be avoided in most circumstances.

As a result of these new data and concepts, the approach to mechanical ventilation in the patient with respiratory failure has changed drastically over the past few years ( Box 6.1 ). Time-cycled, pressure-controlled ventilation has become favored because of the ability to limit EIP to noninjurious levels at a maximum of 35 cmH ₂ O. In infants and newborns, this EIP limit is set lower, at 30 cmH ₂ O. The V _t should be maintained in the range of 6 mL/kg. A lung-protective approach also incorporates lung distention and prevention of alveolar closure. Pressure/volume curves should be developed on each patient at least daily so the P _flex can be identified, and the PEEP maintained above P _flex . If a pressure/volume curve cannot be determined, Pflex can be assumed to be in the 7–12 cmH ₂ O range and PEEP (at that level or up to 2 cmH ₂ O higher) can be applied. ^{, ,} Recruitment maneuvers that use intermittent sustained inflations of approximately 40 cmH ₂ O for up to 40 seconds often can be beneficial by initially inflating collapsed lung regions. The inflation obtained with the recruitment maneuver is then sustained by maintaining PEEP greater than P _flex .

Both PIP and PEEP are increased; therefore, enhancements in compliance and reductions in V _d / V _t and shunt are to be expected. If they are not observed, then one should suspect the presence of overdistention of currently inflated alveoli instead of the desired recruitment of collapsed lung units. Application of increased levels of PEEP may also result in a decrease in venous return and cardiac output due to increased intrathoracic pressure. In addition, West’s zone I physiology, which predicts diminished or absent pulmonary capillary flow in the nondependent regions of the lungs at end inspiration, may be exacerbated with application of higher airway pressures. This may be especially detrimental, because it is the nondependent regions that are best inflated and to which one would wish to direct as much pulmonary blood flow as possible. As a result, parameters of DO ₂ should be carefully monitored during application of increased PEEP. One approach for monitoring delivery is by applying close attention to the S V ˙ E O ₂ whenever the PEEP is increased to more than 5 cmH ₂ O.

If oxygenation remains inadequate with application of higher levels of PEEP, FiO ₂ should be increased to maintain SaO ₂ greater than 90%, although levels as low as 80% may be acceptable in patients with adequate DO ₂ . As mentioned previously, one of the most effective ways to enhance DO ₂ is with transfusion. All attempts should be made to avoid the atelectasis and oxygen toxicity associated with FiO ₂ levels greater than 0.60. Extending FiO ₂ to levels more than 0.60 often has little effect on oxygenation, because severe respiratory failure is frequently associated with a large transpulmonary shunt. If inadequate DO ₂ persists, a trial increase in PEEP level should be performed or the institution of extracorporeal life support (ECLS) considered. Inflation of the lungs can be enhanced by prolonging the inspiratory time by PC-IRV. Pharmacologic paralysis and sedation are required during PC-IRV, and paralysis may have the additional benefit of decreasing oxygen consumption and enhancing ventilator efficiency. PaO ₂ may improve with application of PC-IRV. ^, Monitoring the effect on DO ₂ and S V ˙ E O ₂ is critical to ensure the benefit of this intervention. The advantages of the alveolar inflation associated with a decelerating flow waveform during pressure-limited modes of ventilation should also be used.

Initiating early mobilization, defined as within the first 2–5 days of ICU admission, is correlated with significant reductions in ventilator days, ICU and hospital lengths of stay, and improvements in functional status culminating in enhanced patient survival rates. Though much of the literature comes from the adult population, pediatric patients similarly derive marked benefits from early mobilization including increased functional exercise capacity and cognitive ability, interaction with care providers, decreased pain scores, and greater independence in self-care tasks (e.g., suctioning oneself). Mobilization strategies encompass both active approaches– such as sitting upright, using bed cycles, dangling transfers, tilting up, and ambulation—and passive techniques involving motion machines to maintain range of motion. Mobilization is also possible with patients on mechanical ventilation, vasopressors, or continuous renal replacement therapy and with femoral catheters.

Specific pediatric considerations include complex medical histories, multiple cognitive and functional abilities, and special mobility devices. A concerning finding from a recent study revealed that more than half of pediatric ICU patients (54.6%) were not mobilized during their stay, underscoring a critical need for intervention. Therefore, consultation with physical therapists, investment in equipment and training, and changing the culture of care providers is paramount. Incorporating age-appropriate activities such as virtual reality or interactive gaming consoles is also important and can enhance engagement. A comprehensive analysis estimates net cost savings estimated at $817,836 attributable to reduced ICU and hospital lengths of stay and decreased medical and patient consumables, emphasizing the economic viability of early mobilization programs.

Altering the patient from the supine to the prone position appears to enhance gas exchange. ^, Enhanced blood flow to the better-inflated anterior lung regions with the prone position would logically appear to account for this increase in oxygenation. However, data in oleic acid lung-injured sheep suggest that the enhancement in gas exchange may be due predominantly to more homogeneous distribution of ventilation, rather than to redistribution of pulmonary blood flow, because lung distention is more uniform in the prone position. This effect may be reversed after a number of hours. Enhanced posterior region lung inflation frequently accounts for persistent increases in oxygenation when the patient is returned to the supine position. Therefore, benefit may be seen when the prone and supine positions are alternated, usually every 4–6 hours.141 A randomized, controlled, multicenter trial evaluating the effectiveness of the prone position in the treatment of patients with ARDS was recently completed. One group was placed in the prone position for 6 or more hours daily for 10 days while the control group remained in the supine position. Although the PaO ₂ /FiO ₂ ratio was greater in the prone position when compared with the supine group (prone, 63.0 + 66.8, vs. supine, 44.6 + 68.2; P = .02), no difference in mortality was noted between groups. It is clear that some patients will not respond to altered positioning, in which case this adjunct should be discontinued. Meticulous attention to careful patient padding and avoidance of dislodgement of tubes and catheters is of the utmost importance in successful implementation of this approach.