Lesson 11, Volume 14Which Developments in Mechanical Ventilation Will Outlast the Next Decade?

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1 Lesson 11, Volume 14Which Developments in Mechanical Ventilation Will Outlast the Next Decade? By Robert M. Kacmarek, PhD, RRT, FCCP Click to go to Poststudy Questions Information on Submitting Answers for CME Credit Objectives Outline patient selection and appropriate application of noninvasive positive pressure ventilation. Define and describe the use of lung protective ventilatory strategies. Discuss the development of combined pressure-volume targeted modes of mechanical ventilation. Discuss the use of prone positioning in the management of ARDS. Describe the use of tracheal gas insufflation to manage PaCO 2 and airway pressure. Key words combined modes of ventilation; lung protective ventilatory strategies; noninvasive positive pressure ventilation; prone positioning; tracheal gas insufflation; ventilator-induced lung injury Abbreviations LPVS = lung protective ventilatory strategies; NIPPV = noninvasive positive pressure ventilation; PEEP = positive end-expiratory pressure; TGI = tracheal gas insufflation; VT = tidal volume Introduction Over the last decade a number of innovative approaches or adjuncts to mechanical ventilation have been actively researched, many of which show some promise in improving our ability to provide ventilatory support. Which of these innovations will outlast the next decade? I have identified for discussion five different innovations that I believe will outlast the next decade. Specifically, I believe noninvasive positive pressure ventilation (NIPPV), lung protective ventilatory strategies (LPVS), combined pressure-volume targeted modes of ventilation, prone positioning, and tracheal gas insufflation (TGI) will outlast the next decade. These developments all have common elements, which form the basis of my confidence that they will survive the decade. They all are intended either to minimize exposure to high pressures and volumes during ventilatory support, minimizing the potential for induced injury, or to improve patient comfort and synchronization with the ventilator. file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (1 de 10) [24/09/ :40:16]

2 NIPPV Of all the innovations listed, I have the greatest confidence that NIPPV will outlast the next decade. This approach is not new; in fact, a face mask was used on the first patient I ever ventilated in the mid-1960s. Limited use of NIPPV in acute settings during the 1970s and 1980s was primarily a result of poor technology, poor patient selection, and little understanding of how to apply NIPPV. Today, there is more level-one data supporting the use of NIPPV than any other aspect of mechanical ventilation. 1-7 As shown in Table 1, at least seven randomized controlled trials have compared NIPPV to other methods of managing the ventilatory status of critically ill patients. Table 1Randomized Trials of NIPPV in Acute Respiratory Failure Author Patient Type No. NIPPV/Control % Intubated NIPPV/Control Mortality NIPPV/Control Bott et al 1 COPD 26/30 0/0 3.8%/27.0% Kramer et Mixed 16/15 31%/73% 6.3%/13.0% al 2 Wysocki et Mixed PaCO 2 > al 3 45 mm Hg 21/20 11/6 62%/70% 36%/100% 33%/50% 9%/66% Brochard et COPD 43/42 26%/74% 9%/29% al 4 Barbe et al 5 COPD 14/10 0/0 0/0 Nava et al 6 COPD 25/25 88%*/68%* 8%/23% Antonelli et al 7 Hypoxemic respiratory failure *Percentage weaned by day 30. All intubated by protocol. 32 / 32 31%/100% 28%/47% NIPPV has been most successful in the COPD patient with an uncomplicated acute exacerbation. Indeed, five of the six randomized controlled trials that primarily involved COPD patients have resulted in significantly greater benefit for the NIPPV group. 1-6 In the one negative trial, 5 patient selection must be questioned. Although there were no differences in intubation rates or mortality rates between groups, not a single patient in either the control or treatment group required endotracheal intubation, nor did a single patient die. As emphasized by Keenan et al 8 in a meta-analysis, NIPPV in the COPD patient with uncomplicated acute exacerbation decreases the frequency of intubation and mortality. In addition, NIPPV has been shown to decrease ICU length of stay, length of hospitalization, and cost of managing patients. 1-4 With the strength of the current data, NIPPV in select COPD patients should be considered the standard of care. In fact, considering the beneficial outcomes, no patient in this category should be file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (2 de 10) [24/09/ :40:16]

3 denied access to this therapy. It can be argued that COPD patients in acute respiratory failure should be ventilated with NIPPV (both full-face mask and nasal mask), with endotracheal intubation reserved for those failing NIPPV. In those patients who are failing weaning trials, extubation and initiation of NIPPV should be considered. In fact, Nava et al 6 recently demonstrated that COPD patients extubated to NIPPV, compared to those remaining intubated after a weaning trial failure, had a shorter weaning period and a significantly lower nosocomial infection rate. The frustration experienced by many attempting to initiate NIPPV should be decreased somewhat with the recent introduction of newer ventilators designed to provide NIPPV and newer full-face and nasal masks. An appropriate mask with minimal leakage and a low incidence of facial trauma should help to lower the failure rate. In addition, better education of all practitioners involved in the provision of NIPPV clearly improves outcome. There is a lengthy learning curve associated with the use of NIPPV, and it takes time to reach the > 70% success rate that has been demonstrated in published trials. The indications for NIPPV are not completely defined. Most would agree with those given in Table 2, but many groups are attempting NIPPV in populations other than COPD patients. Case series of patients with acute asthma, 9 cystic fibrosis, 10 and those awaiting lung transplantation have been published. Antonelli et al 7 showed that NIPPV outperformed endotracheal intubation in a randomized comparison of patients with acute hypoxemic respiratory failure but not COPD. These additional indications are controversial and await further study before they can be recommended with the same enthusiasm as in the COPD patient. Table 2Indications and Potential Contraindications for NIPPV Indications Respiratory distress Rapid rate Use of accessory muscles Abdominal paradox Severe dyspnea Acute respiratory acidosis ph < 7.30 PCO 2 > 50 mm Hg Contraindications Respiratory arrest or need for immediate intubation Hypertension Uncontrolled cardiac arrhythmias Facial trauma Upper airway obstruction Inability to clear secretions file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (3 de 10) [24/09/ :40:16]

4 NIPPV will outlast the next decade because it clearly demonstrates improved patient outcome and is noninvasive and because our knowledge of successful NIPPV application is still increasing. LPVS We all know that mechanical ventilation can be life-saving; however, only during the last 10 to 15 years have data demonstrated that mechanical ventilation can also induce an injury (volutrauma) similar to ARDS. 11 Even more recently, data identifying the potential of mechanical ventilation to cause or extend multiple organ system dysfunction have become available This information has led many to recommend the use of a LPVS for all patients requiring ventilatory support regardless of etiology. 15 LPVS can best be defined as an approach to ventilation that minimizes tidal volume (VT), maintaining peak alveolar pressure below the upper deflection point on the pressure-volume curve of the respiratory system and applying sufficient positive end-expiratory pressure (PEEP) to avoid opening and closing of unstable lung units (above the lower inflection point of pressure-volume curve). 15 In the animal laboratory, it has been clearly established that two factors influence the epithelial injury observed during mechanical ventilation: overdistending tidal volumes, and the opening and closing of unstable lung units. 11,15 The ventilatory pattern that does not avoid these limits causes a disruption of the alveolar capillary membrane with the development of interstitial and intra-alveolar edema, disruption of surfactant production, and generalized inflammation. 11 A number of groups have also demonstrated activation of inflammatory mediators and rupture of pulmonary capillaries. 16 In addition, two groups 17,18 have shown that inappropriate ventilatory patterns can result in the translocation of bacteria from the lung into the systemic circulation. This type of data has led some to speculate that inappropriate ventilatory patterns not only lead to a mechanical disruption of the alveolar-capillary membrane and the activation of pulmonary inflammatory mediators, but also extend and possibly cause multiple system organ failure as a result of translocation of mediators. 19,20 Recent data by Ranieri et al 12 showed that patients ventilated with LPVS (low VT, high PEEP) demonstrated a reduction in both pulmonary and systemic inflammatory mediators after a 36-h ventilation period, while those ventilated with large VT (12 ml/kg) and low PEEP (set based on oxygenation of about 10 cm H 2 O) demonstrated increases in both pulmonary and systemic inflammatory mediators. In fact, Slutsky and Tremblay 20 have speculated that the lung may be the engine that drives multiple system organ failure. Three randomized controlled trials comparing LPVS to standard ventilator management have been published In the study by Amato et al, 21 a large improvement in survival occurred with LPVS, whereas the studies of Stewart et al 22 and Brochard et al 23 showed no difference in outcome. As indicated in Table 3, the reason for this discrepancy is most likely the fact that the actual VT and plateau pressures were only different between groups in the study by Amato et al and that these investigators set PEEP (about 16 cm H 2 O) based on the pressure-volume curve in the LPVS group. In all other groups of all three trials, PEEP was set based on oxygenation (8 to 10 cm H 2 O). In addition, Amato et al used a 35 to 40 cm H 2 O for 30 to 40 s continuous positive airway pressure recruitment maneuver whenever the ventilator was disconnected. file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (4 de 10) [24/09/ :40:16]

5 Table 3Randomized Trials Comparing ARDS Ventilator Management: Actual Data From Day 1 Author VT Plat Press PEEP Mortality Rate Amato et al 21 Control 362 ml % LPVS 763 ml % Stewart et al 22 Control 7.0 ml/kg % LPVS 10.7 ml/kg % Brochard et al 23 Control 7.1 ml/kg % LPVS 10.3 ml/kg % At a meeting of the American Thoracic Society, Brower has presented the results of the National Institutes of Health-ARDS net trial (Roy Brower, MD; personal communication; May 1999). In this trial, a 25% decrease in mortality occurred in the group ventilated with a 6 ml/kg VT compared to the group with a 12 ml/kg VT. The mortality rate was 40% in the 12 ml/kg group and 30% in 6 ml/kg group. Based on the strength of the laboratory data and the recent clinical trial data, I would expect LPVS to be the standard for the application of mechanical ventilation well beyond the next decade. There is still room for a refinement in the actual method of application of mechanical ventilation and in the determination of ventilation targets in specific patients, but the concept is now well established. Combined Pressure-Volume Targeted Modes Although there are problems with the inappropriate provision of controlled ventilatory support, it is much easier to manage the mechanical ventilator during controlled ventilation than during assisted ventilation. For assisted ventilation to prevent ventilatory muscle dysfunction, the mechanical ventilator should be in synchrony with the ventilatory demands of the patient. 24 Synchrony is difficult to insure; the recent introduction of new modes of assisted ventilation have all focused on this issue. As shown by Marini et al, 25 peak flow delivery and flow variability greatly affect patient work and synchrony during assisted breathing. This realization has led to the increased use of pressure support ventilation; however, during pressure targeted ventilation, VT, minute ventilation, and PaCO 2 can vary greatly. This has led clinicians to petition manufacturers to provide modes of ventilatory support that combine the desirable features of both pressure (flow variability and pressure limitation) and volume (VT consistency) ventilation. Unfortunately, the best method of doing so has not been determined. There are few or no comparative data to allow us to define the optimal approach. In my opinion, the optimal approach will incorporate closed-loop feedback control. Whether that control file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (5 de 10) [24/09/ :40:16]

6 will be based on ventilatory pattern, minute ventilation, measurement of work of breathing, or ventilatory demand is yet to be determined. It may not be unreasonable to allow the patient to actively participate in the process of fine tuning the settings of ventilator, since patient comfort and minimization of anxiety are clearly desired outcomes of assisted ventilation. It is difficult to say which of the available approaches will be refined to this level. New modes of assisted ventilation can be grouped into two broad categories: those in which gas delivery is varied within a single breath and those where gas delivery is varied between breaths (Table 4). Those modes that appear most physiologically sound and most likely to survive vary gas delivery within a given breath. Table 4New Modes of Assisted Ventilation Within breath adjustments Volume-assured pressure support Automatic tube compensation Proportional assist ventilation Between breath adjustments Volume support Pressure-regulated volume control Adaptive support ventilation Every patient we ventilate at some time receives assisted ventilatory support, and patient-ventilator synchrony is clearly a major problem with assisted ventilation. Even though I cannot define the best method of providing combined pressure/volume targeted ventilation, I expect that with continued efforts to improve and refine the use of these modes, they will easily outlast the next decade. Prone Positioning Prone positioning could have easily been included under the larger topic of LPVS. However, since it is an independent technique, it may best be considered separately. Numerous reports demonstrated improved Pao 2 in ARDS patients placed in the prone position In about 75% of ARDS patients, prone positioning improves the Po 2 by > 20%. This allows a decrease in the required Fio 2 and PEEP settings, leading most to consider prone positioning a lung recruitment strategy. It is clear that prone positioning results in a more uniform distribution of pleural pressure gradients, resulting in greater ventilation of dependent lung than in supine positioning. 31 The exact mechanism for this improvement is still unclear (Table 5). Does prone positioning improve patient outcome? This is still open to debate, since no randomized controlled trial comparing ventilatory strategies with and without prone positioning has been published, although a number are underway. Table 5Potential Reasons for PaO 2 Improvement With Prone Positioning file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (6 de 10) [24/09/ :40:16]

7 Potential Reasons Change in percentage of dependent lung Change in geometric configuration of the lung Abdominal weight Weight of heart and great vessels Decrease in chest wall compliance I am optimistic that prone positioning will have a positive effect on outcome based on the beneficial effects of recruiting collapsed lung. In addition, although it is labor-intensive, prone positioning can be applied in any hospital with the correct number of practitioners (at least four) available to turn the patient. Tracheal Gas Insufflation A major concern during ventilation with LPVS is the elimination of CO 2. In most ARDS patients, the lower inflection point on the pressure-volume curve is about 15 cm H 2 O and the upper deflection point is 30 to 35 cm H 2 O. As a result, ventilating pressure is limited to 15 to 20 cm H 2 O, producing the low VT (approximately 6 ml/kg) currently recommended. With these low volumes, hypercarbia develops (permissive hypercapnia), even if the ventilatory rate is increased into the mid 20s. It has been clearly shown that hypercarbia is well tolerated by many patients; however, some do not tolerate elevated PaCO 2 levels and the associated acidosis. Patients with sepsis, renal failure, severe cardiovascular disease, or increased intracranial pressure generally are unable to tolerate permissive hypercapnia. It is in this type of patient that TGI is indicated. TGI is the injection of a secondary flow of gas just above the carina to wash out the CO 2 in the anatomic and mechanical dead space during each exhalation. 32 Over time, this results in a decrease in PaCO 2 without a change in ventilator settings. Numerous animal models have demonstrated the efficacy of TGI in ARDS during permissive hypercapnia In addition, TGI can be used to decrease airway pressure while maintaining eucapnia in the patient who is unable to tolerate an elevated Pco 2 and who has high airway pressures. 37 There are only limited clinical data 38,39 on the use of TGI, and no controlled trials have been reported because there are no commercially available products in the United States that allow for the safe application of TGI. Ideally, TGI should only be administered during exhalation to prevent increases in both delivered VT and airway pressure, and to appropriately coordinate with both pressure and volume ventilation. 40,41 In addition, alarms and automatic discontinuation of the TGI system are mandatory in the event of an artificial airway occlusion. In spite of the current limitation in clinical data, because of the need to provide LPVS and to avoid permissive hypercapnia in selected patients, I believe that TGI will outlast the next decade. Currently, there are a number of manufacturers developing systems. file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (7 de 10) [24/09/ :40:16]

8 Other Innovations Space does not allow comment on other techniques that may outlast the next decade. Partial liquid ventilation, and high-frequency oscillation in adults all have the potential of also outlasting the next decade. However, I am much more confident that NIPPV, LPVS, combined pressure-volume targeted modes, prone positioning, and TGI will outlast the next decade than I am for any of these other innovations. Click to go to Poststudy QuestionsLesson 11, Volume 14 References Bott J, Carroll MP, Conway JH, et al. Randomized control trial of nasal ventilation in acute ventilatory failure due to chronic obstructive airway disease. Lancet 1993; 341: Kramer N, Meyer TJ, Meharg J, et al. Randomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure. Am J Respir Crit Care Med. 1995; 151: Brochard L, Mancebo J, Wysocki M, et al. Noninvasive ventilation for acute exacerbations of chronic obstructive pulmonary disease. N Engl J Med 1995; 333: Wysocki M, Tric L, Wolff M, et al. Noninvasive pressure support ventilation in patients with acute respiratory failure. Chest 1995; 107: Barbe F, Togores B, Rubi M, et al. Noninvasive ventilatory support does not facilitate recovery from acute respiratory failure in chronic obstructive pulmonary disease. Eur Respir J 1996; 9: Nava S, Ambrosino N, Clini E, et al. Noninvasive mechanical ventilation in the weaning of patients with respiratory failure due to chronic obstructive pulmonary disease. Ann Intern Med 1998; 128: Antonelli M, Conti G, Rocco M, et al. A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure. N Engl J Med 1998; 339: Keenan SP, Kernerman PD, Cook DJ, et al. Effect of noninvasive positive pressure ventilation on mortality in patients admitted with acute respiratory failure: a meta-analysis. Crit Care Med 1997; 25: Meduri GU, Cook TR, Turner RE, et al. Noninvasive positive pressure ventilation in status asthmaticus. Chest 1996; 110: Gozal D. Nocturnal ventilatory support in patients with cystic fibrosis: comparison with supplemental oxygen. Eur Respir J 1997; 10: Dreyfuss D, Saumon G. Ventilator-induced lung injury: lessons from experimental studies. Am J Respir Crit Care Med 1998; 157: Ranieri VM, Suter PM, Tortorella C, et al. Effect of mechanical ventilation on inflammatory mediators in patients with acute respiratory distress syndrome [abstract]. Am J Respir Crit Care Med 1998; 157:A694. file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (8 de 10) [24/09/ :40:16]

9 Imai Y, Kawano T, Miyaska K, et al. Inflammatory chemical mediators during conventional ventilation and during high frequency oscillatory ventilation. Crit Care Med 1994; 150: Tremblay L, Valenza F, Ribeiro SP, et al. Injurious ventilatory strategies increase cytokines and c-fos-m-rna expression in an isolated rat lung model. J Clin Invest 1997; 99: Kacmarek RM, Chiche JD. Lung protective ventilation strategies for ARDS the data are convincing! Respir Care 1998; 43: Fu Z, Costello ML, Tsukimoto K, et al. High lung volume increases stress failure in pulmonary capillaries. J Appl Physiol 1992; 73: Nahum A, Hoyt J, Schmitz L, et al. Effect of mechanical ventilation strategy on dissemination of intratracheally instilled Escherichia coli in dogs. Crit Care Med 1997; 25: Verbrugge SJC, Sorm V, Veen A, et al. Lung overinflation without positive end-expiratory pressure promotes bacteremia after experimental Klebsiella pneumoniae inoculation. Intensive Care Med 1998; 24: Dreyfuss D, Saumon G. From ventilator-induced lung injury to multiple organ dysfunction? Intensive Care Med 1998; 24: Slutsky A, Tremblay L. Multiple system organ failure is mechanical ventilation a contributing factor? Am J Respir Crit Care Med 1998; 157: Amato MBP, Barbas CSV, Medeiros DM, et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med 1998; 338: Stewart TE, Meade MO, Cook DJ, et al. Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. N Engl J Med 1998; 338: Brochard L, Roudot-Thoraval F, Roupie E, et al. Tidal volume reduction for prevention of ventilator-induced lung injury in acute respiratory distress syndrome. Am J Respir Crit Care Med 1998; 158: McIntyre NR, Ho L. Effects of initial flow rate and breath termination criteria on pressure support ventilation. Chest 1991; 99: Marini JJ, Rodriquez RM, Lamb V. The inspiratory workload of patient initialed mechanical ventilation. Am Rev Respir Dis 1986; 134: Chatte G, Sab JM, Dubois JM. Prone positioning in mechanically ventilated patients with severe adult respiratory failure. Am J Respir Crit Care Med 1997; 155: Albert RK, Leasa D, Sanderson M, et al. The prone position improves arterial oxygenation and reduces shunt in oleic-acid-induced acute lung injury. Am Rev Respir Dis 1987; 135: Servillo G, Roupie E, DeRobertis E, et al. Effects of ventilation in ventral decubitus position on respiratory mechanics in adult respiratory distress syndrome. Intensive Care Med 1997; 23: Pelosi P, Croci M, Calappi E, et al. The prone positioning during general anesthesia minimally affects respiratory mechanics while improving functional residual capacity and increasing oxygen tension. Anesth Analg 1995; 80: Gattinoni L, Pelosi P, Vitale G, et al. Body position changes redistribute lung computed-tomographic density in patients with acute respiratory failure. Anesthesiology 1991; 74:15-23 file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - Wh...anical Ventilation Will Outlast the Next Decade.htm (9 de 10) [24/09/ :40:16]

10 Lamm WJE, Graham MM, Albert RK. Mechanism by which the prone position improves oxygenation in acute lung injury. Am J Respir Crit Care Med 1994; 150: Ravenscraft SA. Tracheal gas insufflation: adjunct to conventional mechanical ventilation. Respir Care 1996; 41: Nahum A, Ravenscraft SA, Nakos G, et al. Effect of catheter flow direction on CO 2 removal during tracheal gas insufflation in dogs. J Appl Physiol 1993; 75: Imanaka H, Kirmse M, Mang H, et al. Expiratory phase tracheal gas insufflation and pressure control in sheep with permissive hypercapnia. Am J Respir Crit Care Med 1999; 159:49-54 Ravenscraft SA, Shapiro RS, Nahum A, et al. Tracheal gas insufflation: catheter effectiveness determined by expiratory flush volume. Am J Respir Crit Care Med 1996; 153: Nahum A, Ravenscraft SA, Nakos G, et al. Tracheal gas insufflation during pressure-control ventilation. Am Rev Respir Dis 1992; 146: Kirmse M., Fujino Y, Hromi J, et al. Pressure-release tracheal gas insufflation reduces airway pressure in lung-injured sheep maintaining eucapnia. Am J Respir Crit Care Med 1999; 160: Ravenscraft SA, Burke WC, Nahum A, et al. Tracheal gas insufflation augments CO 2 clearance during mechanical ventilation. Am Rev Respir Dis 1993; 148: Kalfon P, Rao GSU, Gallart L, et al. Permissive hypercapnia with and without expiratory washout in patients with severe acute respiratory distress syndrome. Anesthesiology 1997; 87:6-17 Imanaka H, Kacmarek RM, Riggi V, et al. Expiratory phase and volume-adjusted tracheal gas insufflation: a lung model study. Crit Care Med 1998; 26: Imanaka H, Kacmarek RM, Ritz R, et al. Tracheal gas insufflation-pressure control versus volume control ventilation a lung model study. Am J Respir Crit Care Med 1996; 153: Copyright 2000 American College of Chest Physicians file:///d /X. SOLER/TRACK/Lesson 11, Volume 14 - W...nical Ventilation Will Outlast the Next Decade.htm (10 de 10) [24/09/ :40:16]