Dean R. Hess

Rationale: Higher positive end-expiratory pressure (PEEP) levels may reduce atelectrauma, but increase over-distention lung injury. Whether higher PEEP improves clinical outcomes among patients with acute respiratory distress syndrome (ARDS) is unclear. Objectives: To compare clinical outcomes of mechanical ventilation strategies using higher PEEP levels versus lower PEEP strategies in patients with ARDS. Methods: We performed a systematic review and meta-analysis of clinical trials investigating mechanical ventilation strategies using higher versus lower PEEP levels. We used random effects models to evaluate the effect of higher PEEP on 28-day mortality, organ failure, ventilator-free days, barotrauma, oxygenation, and ventilation. Results: We identified eight randomized trials comparing higher versus lower PEEP strategies, enrolling 2,728 patients with ARDS. Patients were 55 (±16) (mean ± SD) years old and 61% were men. Mean PEEP in the higher PEEP groups was 15.1 (±3.6) cm H2O as compared with 9.1 (±2.7) cm H2O in the lower PEEP groups. Primary analysis excluding two trials that did not use lower Vt ventilation in the lower PEEP control groups did not demonstrate significantly reduced mortality for patients receiving higher PEEP as compared with a lower PEEP (six trials; 2,580 patients; relative risk, 0.91; 95% confidence interval [CI] = 0.80–1.03). A higher PEEP strategy also did not significantly decrease barotrauma, new organ failure, or ventilator-free days when compared with a lower PEEP strategy (moderate-level evidence). Quality of evidence for primary analyses was downgraded for precision, as CIs of outcomes included estimates that would result in divergent recommendations for use of higher PEEP. Secondary analysis, including trials that did not use low Vt in low-PEEP control groups, showed significant mortality reduction for high-PEEP strategies (eight trials; 2,728 patients; relative risk, 0.84; 95% CI = 0.71–0.99), with greater mortality benefit observed for high PEEP in trials that did not use lower Vts in the low-PEEP control group (P = 0.02). Analyses stratifying by use of recruitment maneuvers (P for interaction = 0.69), or use of physiological targets to set PEEP versus PEEP/FiO2 tables (P for interaction = 0.13), did not show significant effect modification. Conclusions: Use of higher PEEP is unlikely to improve clinical outcomes among unselected patients with ARDS.

Rationale: Trials investigating use of lower tidal volumes and inspiratory pressures for patients with acute respiratory distress syndrome (ARDS) have shown mixed results. Objectives: To compare clinical outcomes of mechanical ventilation strategies that limit tidal volumes and inspiratory pressures (LTV) to strategies with tidal volumes of 10 to 15 ml/kg among patients with ARDS. Methods: This is a systematic review and meta-analysis of clinical trials investigating LTV mechanical ventilation strategies. We used random effects models to evaluate the effect of LTV on 28-day mortality, organ failure, ventilator-free days, barotrauma, oxygenation, and ventilation. Our primary analysis excluded trials for which the LTV strategy was combined with the additional strategy of higher positive end-expiratory pressure (PEEP), but these trials were included in a stratified sensitivity analysis. We performed metaregression of tidal volume gradient achieved between intervention and control groups on mortality effect estimates. We used Grading of Recommendations Assessment, Development, and Evaluation methodology to determine the quality of evidence. Results: Seven randomized trials involving 1,481 patients met eligibility criteria for this review. Mortality was not significantly lower for patients receiving an LTV strategy (33.6%) as compared with control strategies (40.4%) (relative risk [RR], 0.87; 95% confidence interval [CI], 0.70–1.08; heterogeneity statistic I 2 = 46%), nor did an LTV strategy significantly decrease barotrauma or ventilator-free days when compared with a lower PEEP strategy. Quality of evidence for clinical outcomes was downgraded for imprecision. Metaregression showed a significant inverse association between larger tidal volume gradient between LTV and control groups and log odds ratios for mortality (β, −0.1587; P = 0.0022). Sensitivity analysis including trials that protocolized an LTV/high PEEP cointervention showed lower mortality associated with LTV (nine trials and 1,629 patients; RR, 0.80; 95% CI, 0.66–0.98; I 2 = 46%). Compared with trials not using a high PEEP cointervention, trials using a strategy of LTV combined with high PEEP showed a greater mortality benefit (RR, 0.58; 95% CI, 0.41–0.82; P for interaction = 0.05). Conclusions: The trend toward lower mortality with LTV ventilation in the primary analysis and the significant relationship between the degree of tidal volume reduction and the mortality effect together suggest, but do not prove, that LTV ventilation improves mortality among critically ill adults with ARDS.

Newer pulse oximetry technology is available that uses multiple wavelengths of light and is thereby able to measure more than 2 forms of hemoglobin, including carboxyhemoglobin (SpCO), methemoglobin (SpMet), and total hemoglobin (SpHb). Several studies have shown relatively low bias, but poor precision, for SpCO compared with HbCO. Evaluations of SpMet have been conducted primarily in normal subjects. Clinical evaluations of SpHb suggest that it might not yet be accurate enough to make transfusion decisions. Respiratory waveform variability of the pulse oximeter plethysmogram might be useful to assess pulsus paradoxus in patients with airway obstruction; it might also be used to measure the breathing frequency. The change in pulse pressure over the respiratory cycle has been used to assess fluid responsiveness in mechanically ventilated patients, and similarly, the pulse oximetry plethysmogram waveform amplitude variability might be used to assess fluid responsiveness. However, there are limitations to this approach, and it remains to be determined how well it can be applied clinically using existing pulse oximetry technology. The pulse oximeter signal is probably useful for applications beyond S pO ₂ . However, the current technology is not mature, and improvements are necessary. With technology improvements, the use of pulse oximetry to detect SpCO, SpMet, SpHb, pulsus paradoxus, breathing frequency, and fluid responsiveness is likely to improve in the future.

The topic of patient safety has received much attention in recent years. There are a number of areas in which the subject of patient safety impacts respiratory care practice. This paper focuses on articles published in 2014 related to pressure injury, handoffs, protocols and multidisciplinary teams, perioperative obstructive sleep apnea, and readmissions.

Respiratory mechanics refers to the expression of lung function through measures of pressure and flow. From these measurements, a variety of derived indices can be determined, such as volume, compliance, resistance, and work of breathing. Plateau pressure is a measure of end-inspiratory distending pressure. It has become increasingly appreciated that end-inspiratory transpulmonary pressure (stress) might be a better indicator of the potential for lung injury than plateau pressure alone. This has resulted in a resurgence of interest in the use of esophageal manometry in mechanically ventilated patients. End-expiratory transpulmonary pressure might also be useful to guide the setting of PEEP to counterbalance the collapsing effects of the chest wall. The shape of the pressure-time curve might also be useful to guide the setting of PEEP (stress index). This has focused interest in the roles of stress and strain to assess the potential for lung injury during mechanical ventilation. This paper covers both basic and advanced respiratory mechanics during mechanical ventilation.

Tracheostomy tubes are used to administer positive-pressure ventilation, to provide a patent airway, and to provide access to the lower respiratory tract for airway clearance. They are available in a variety of sizes and styles from several manufacturers. The dimensions of tracheostomy tubes are given by their inner diameter, outer diameter, length, and curvature. Differences in dimensions between tubes with the same inner diameter from different manufacturers are not commonly appreciated but may have important clinical implications. Tracheostomy tubes can be cuffed or uncuffed and may be fenestrated. Some tracheostomy tubes are designed with an inner cannula. It is important for clinicians caring for patients with a tracheostomy tube to appreciate the nuances of various tracheostomy tube designs and to select a tube that appropriately fits the patient. The optimal frequency of changing a chronic tracheostomy tube is controversial. Specialized teams may be useful in managing patients with a tracheostomy. Speech can be facilitated with a speaking valve in patients with a tracheostomy tube who are breathing spontaneously. In mechanically ventilated patients with a tracheostomy, a talking tracheostomy tube, a deflated cuff technique with a speaking valve, or a deflated cuff technique without a speaking valve can be used to facilitate speech.

Fundamental to respiratory care practice are airway management, noninvasive monitoring, and invasive mechanical ventilation. The purpose of this paper is to review the recent literature related to these topics in a manner that is most likely to have interest to the readers of Respiratory Care.

Evidence-based medicine (EBM) is the integration of individual clinical expertise with the best available research evidence from systematic research and the patient's values and expectations. A hierarchy of evidence can be used to assess the strength upon which clinical decisions are made. The efficient approach to finding the best evidence is to identify systematic reviews or evidence-based clinical practice guidelines. Respiratory therapies that evidence supports include noninvasive ventilation for appropriately selected patients, lung-protective ventilation, and ventilator discontinuation protocols. Evidence does not support use of weaning parameters, albuterol for ARDS, and high frequency oscillatory ventilation for adults. Therapy with equivocal evidence includes airway clearance, selection of an aerosol delivery device, and PEEP for ARDS. Although all tenets of EBM are not universally accepted, the principles of EBM nonetheless provide a valuable approach to respiratory care practice.