Acute effects of tidal volume strategy on hemodynamics, fluid balance, and sedation in acute lung injury*

Current Practice Review in the Management of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) presents as an acute inflammatory lung injury characterized by refractory hypoxemia and non-cardiac pulmonary edema. An estimated 10% of patients in the intensive care unit and 25% of those who are mechanically ventilated are diagnosed with ARDS. Increased awareness is warranted as mortality rates remain high and delays in diagnosing ARDS are common. The COVID-19 pandemic highlights the importance of understanding ARDS management. Treatment of ARDS can be challenging due to the complexity of the disease state and conflicting existing evidence. Therefore, it is imperative that pharmacists understand both pharmacologic and non-pharmacologic treatment strategies to optimize patient care. This narrative review provides a critical evaluation of current literature describing management practices for ARDS. A review of treatment modalities and supportive care strategies will be presented.

Acute Respiratory Distress Syndrome in Cancer Patients

Acute respiratory distress syndrome (ARDS) is a heterogeneous form of acute, diffuse lung injury that is characterized by dysregulated inflammation, increased alveolar-capillary interface permeability, and non-cardiogenic pulmonary edema. In the general population, the incidence and mortality associated with ARDS over the last two decades have steadily declined in parallel with optimized approaches to pneumonia and other underlying causes of ARDS as well as increased utilization of multimodal treatment strategies that include lung-protective ventilation. In the cancer settings, significant declines in the incidence and mortality of ARDS over the past two decades have also been reported, although these rates remain significantly higher than those in the general population. Epidemiologic studies identify infection, including disseminated fungal pneumonias, as a major underlying cause of ARDS in the cancer setting. More than half of cancer patients who develop ARDS will not survive to hospital discharge. Those who do survive often face a protracted and often incomplete recovery, resulting in significant long-term physical, psychological, and cognitive sequelae. The residual organ dysfunction and poor functional status after ARDS may delay or preclude subsequent cancer treatments. As such, close collaboration between the critical care physicians and oncology team is essential in identifying and reversing the underlying causes and optimizing treatments for cancer patients with ARDS. This chapter reviews the diagnosis and common causes of ARDS in cancer and gives an update on the general management principles for cancer patients with ARDS in the ICU.

Acute Respiratory Distress Syndrome: Etiology, Pathogenesis, and Summary on Management

The acute respiratory distress syndrome (ARDS) has multiple causes and is characterized by acute lung inflammation and increased pulmonary vascular permeability, leading to hypoxemic respiratory failure and bilateral pulmonary radiographic opacities. The acute respiratory distress syndrome is associated with substantial morbidity and mortality, and effective treatment strategies are limited. This review presents the current state of the literature regarding the etiology, pathogenesis, and management strategies for ARDS.

Tidal volume in acute respiratory distress syndrome: how best to select it

Mechanical ventilation is the type of organ support most widely provided in the intensive care unit. However, this form of support does not constitute a cure for acute respiratory distress syndrome (ARDS), as it mainly works by buying time for the lungs to heal while contributing to the maintenance of vital gas exchange. Moreover, it can further damage the lung, leading to the development of a particular form of lung injury named ventilator-induced lung injury (VILI). Experimental evidence accumulated over the last 30 years highlighted the factors associated with an injurious form of mechanical ventilation. The present paper illustrates the physiological effects of delivering a tidal volume to the lungs of patients with ARDS, and suggests an approach to tidal volume selection. The relationship between tidal volume and the development of VILI, the so called volotrauma, will be reviewed. The still actual suggestion of a lung-protective ventilatory strategy based on the use of low tidal volumes scaled to the predicted body weight (PBW) will be presented, together with newer strategies such as the use of airway driving pressure as a surrogate for the amount of ventilatable lung tissue or the concept of strain, i.e., the ratio between the tidal volume delivered relative to the resting condition, that is the functional residual capacity (FRC). An ultra-low tidal volume strategy with the use of extracorporeal carbon dioxide removal (ECCO₂R) will be presented and discussed. Eventually, the role of other ventilator-related parameters in the generation of VILI will be considered (namely, plateau pressure, airway driving pressure, respiratory rate (RR), inspiratory flow), and the promising unifying framework of mechanical power will be presented.

Severe hypoxemia: which strategy to choose

BACKGROUND

Acute respiratory distress syndrome (ARDS) is characterized by a noncardiogenic pulmonary edema with bilateral chest X-ray opacities and reduction in lung compliance, and the hallmark of the syndrome is hypoxemia refractory to oxygen therapy. Severe hypoxemia (PaO2/FiO2 < 100 mmHg), which defines severe ARDS, can be found in 20-30 % of the patients and is associated with the highest mortality rate. Although the standard supportive treatment remains mechanical ventilation (noninvasive and invasive), possible adjuvant therapies can be considered. We performed an up-to-date clinical review of the possible available strategies for ARDS patients with severe hypoxemia.

MAIN RESULTS

In summary, in moderate-to-severe ARDS or in the presence of other organ failure, noninvasive ventilatory support presents a high risk of failure: in those cases the risk/benefit of delayed mechanical ventilation should be evaluated carefully. Tailoring mechanical ventilation to the individual patient is fundamental to reduce the risk of ventilation-induced lung injury (VILI): it is mandatory to apply a low tidal volume, while the optimal level of positive end-expiratory pressure should be selected after a stratification of the severity of the disease, also taking into account lung recruitability; monitoring transpulmonary pressure or airway driving pressure can help to avoid lung overstress. Targeting oxygenation of 88-92 % and tolerating a moderate level of hypercapnia are a safe choice. Neuromuscular blocking agents (NMBAs) are useful to maintain patient-ventilation synchrony in the first hours; prone positioning improves oxygenation in most cases and promotes a more homogeneous distribution of ventilation, reducing the risk of VILI; both treatments, also in combination, are associated with an improvement in outcome if applied in the acute phase in the most severe cases. The use of extracorporeal membrane oxygenation (ECMO) in severe ARDS is increasing worldwide, but because of a lack of randomized trials is still considered a rescue therapy.

CONCLUSION

Severe ARDS patients should receive a holistic framework of respiratory and hemodynamic support aimed to ensure adequate gas exchange while minimizing the risk of VILI, by promoting lung recruitment and setting protective mechanical ventilation. In the most severe cases, NMBAs, prone positioning, and ECMO should be considered.

Recent advances in mechanical ventilation in patients without acute respiratory distress syndrome

While being an essential part of general anesthesia for surgery and at times even a life-saving intervention in critically ill patients, mechanical ventilation has a strong potential to cause harm. Certain ventilation strategies could prevent, at least to some extent, the injury caused by this intervention. One essential element of so-called ‘lung-protective’ ventilation is the use of lower tidal volumes. It is uncertain whether higher levels of positive end-expiratory pressures have lung-protective properties as well. There are indications that too high oxygen fractions of inspired air, or too high blood oxygen targets, are harmful. Circumstantial evidence further suggests that spontaneous modes of ventilation are to be preferred over controlled ventilation to prevent harm to respiratory muscle. Finally, the use of restrictive sedation strategies in critically ill patients indirectly prevents ventilation-induced injury, as daily spontaneous awakening and breathing trials and bolus instead of continuous sedation are associated with shorter duration of ventilation and shorten the exposure to the injurious effects of ventilation.

A ventilator strategy combining low tidal volume ventilation, recruitment maneuvers, and high positive end-expiratory pressure does not increase sedative, opioid, or neuromuscular blocker use in adults with acute respiratory distress syndrome and may improve patient comfort

BACKGROUND

The Lung Open Ventilation Study (LOV Study) compared a low tidal volume strategy with an experimental strategy combining low tidal volume, lung recruitment maneuvers, and higher plateau and positive end-expiratory pressures (PEEP) in adults with acute respiratory distress syndrome (ARDS). Herein, we compared sedative, opioid, and neuromuscular blocker (NMB) use among patients managed with the intervention and control strategies and clinicians' assessment of comfort in both groups.

METHODS

This was an observational substudy of the LOV Study, a randomized trial conducted in 30 intensive care units in Canada, Australia, and Saudi Arabia. In 16 centers, we recorded daily doses of sedatives, opioids, and NMBs and surveyed bedside clinicians about their own comfort with the assigned ventilator strategy and their perceptions of patient comfort. We compared characteristics and outcomes of patients who did and did not receive NMBs.

RESULTS

Study groups received similar sedative, opioid, and NMB dosing on days 1, 3, and 7. Patient comfort as assessed by clinicians was not different in the two groups: 93% perceived patients had no/minimal discomfort. In addition, 92% of clinicians were comfortable with the assigned ventilation strategy without significant differences between the two groups. When clinicians expressed discomfort, more expressed discomfort about PEEP levels in the intervention vs control group (2.9% vs 0.7%, P <0.0001), and more perceived patient discomfort among controls (6.0% vs 4.3%, P = 0.049). On multivariable analysis, the strongest associations with NMB use were higher plateau pressure (hazard ratio (HR) 1.15; 95% confidence interval (CI) 1.07 to 1.23; P = 0.0002) and higher daily sedative dose (HR 1.03; 95% CI 1.02 to 1.05; P <0.0001). Patients receiving NMBs had more barotrauma, longer durations of mechanical ventilation and hospital stay, and higher mortality.

CONCLUSIONS

In the LOV Study, high PEEP, low tidal volume ventilation did not increase sedative, opioid, or NMB doses in adults with ARDS, compared with a lower PEEP strategy, and appeared at least as comfortable for patients. NMB use may reflect worse lung injury, as these patients had more barotrauma, longer durations of ventilation, and higher mortality.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT00182195.

Use of sedation and neuromuscular blockers in critically ill adults receiving high-frequency oscillatory ventilation

BACKGROUND

Nearly all patients receive sedation and neuromuscular blockers (NMBs) during high-frequency oscillatory ventilation (HFOV).

OBJECTIVE

To describe analgo-sedation and NMB use prior to and during HFOV in adults with acute respiratory distress syndrome.

METHODS

Retrospective single-center study of 131 consecutive adults whose care was managed with HFOV from 2002 to 2011.

RESULTS

During the first 4 days of HFOV, 89% and 95% of patients received sedation and opioids, respectively. Upon HFOV initiation, 119 (90.8%) patients received fentanyl doses higher than 200 µg/h; of these, 48 also received more than 20 mg/h of midazolam. Analgo-sedation doses increased significantly over time such that doses were double by day 3. Factors independently associated with fentanyl doses higher than 200 µg/h were NMB ever used (OR 4.43; 95% CI 1.26-15.65, p = 0.02), pH less than 7.15 (OR 2.08; 95% CI 1.22-3.5, p = 0.007), worsening partial pressure of oxygen/fraction of inspired oxygen (OR 1.05; 95% CI 1.00-1.10, p = 0.04), and Acute Physiology and Chronic Health Evaluation (APACHE) II score (OR 0.87; 95% CI 0.79-0.97, p = 0.009). Deep sedation was commonly administered when NMBs were not being used, with 99.2% of sedation-agitation scores of 1 or 2. Eighty-six patients (65.6%) received NMBs and use was greatest on day 1 (59.5%). Train-of-Four was measured every hour for 53.4% of patients; 29.2% of the measurements were 0 of 4. NMB use declined over the 10-year study period.

CONCLUSIONS

High analgo-sedation doses were associated with APACHE II scores, worsening gas exchange, and NMB use. Two thirds of patients received NMBs; use was highest on day 1 and subsequently declined. The percentage of patients who received NMB during HFOV in our study was lower than that previously reported. Future research should evaluate patient outcomes with and without use of NMBs, as well as the potential to manage patients with less sedation.

Association between tidal volume size, duration of ventilation, and sedation needs in patients without acute respiratory distress syndrome: an individual patient data meta-analysis

PURPOSE

Mechanical ventilation with lower tidal volumes (≤6 ml/kg of predicted body weight, PBW) could benefit patients without acute respiratory distress syndrome (ARDS). However, tidal volume reduction could be associated with increased patient discomfort and sedation needs, and consequent longer duration of ventilation. The aim of this individual patient data meta-analysis was to assess the associations between tidal volume size, duration of mechanical ventilation, and sedation needs in patients without ARDS.

METHODS

Studies comparing ventilation with different tidal volume sizes in patients without ARDS were screened for inclusion. Corresponding authors were asked to provide individual participant data. Patients were assigned to three groups based on tidal volume size (≤6 ml/kg PBW, 6-10 ml/kg PBW, or ≥10 ml/kg PBW). Ventilator-free days, alive at day 28, and dose and duration of sedation (propofol and midazolam), analgesia (fentanyl and morphine), and neuromuscular blockade (NMB) were compared.

RESULTS

Seven investigations (2,184 patients) were included in the analysis. The number of patients breathing without assistance by day 28 was higher in the group ventilated with tidal volume ≤6 ml/kg PBW compared to those ventilated with tidal volume ≥10 ml/kg PBW (93.1 vs. 88.6%; p = 0.027, respectively). Only two investigations (187 patients) could be included in the meta-analysis of sedation needs. There were neither differences in the percentage of study days that patients received sedatives, opioids, or NMBA nor in the total dose of benzodiazepines, propofol, opioids, and NMBA.

CONCLUSIONS

This meta-analysis suggests that use of lower tidal volumes in patients without ARDS at the onset of mechanical ventilation could be associated with shorter duration of ventilation. Use of lower tidal volumes seems not to affect sedation or analgesia needs, but this must be confirmed in a robust, well-powered randomized controlled trial.

A higher tidal volume may be used for athletes according to measured FVC

We investigated whether professional athletes may require higher tidal volume (Tv ) during mechanical ventilation hypothesizing that they have significantly higher "normal" lung volumes compared to what was predicted and to nonathletes. Measured and predicted spirometric values were recorded in both athletes and nonathletes using a Spirovit SP-1 spirometer (Schiller, Switzerland). Normal Tv (6 mL/kg of predicted body weight) was calculated as a percentage of measured and predicted forced vital capacity (FVC) and the difference (δ) was used to calculate the additional Tv required using the equation: New Tv(TvN) = Tv + (Tv × δ). Professional athletes had significantly higher FVC compared to what was predicted (by 9% in females and 10% in males) and to nonathletes. They may also require a Tv of 6.6 mL/kg for males and 6.5 mL/kg for females during mechanical ventilation. Nonathletes may require a T v of 5.8 ± 0.1 mL/kg and 6.3 ± 0.1 mL/kg for males and females, respectively. Our findings show that athletes may require additional Tv of 10% (0.6/6 mL/kg) for males and 8.3% (0.5/6 mL/kg) for females during general anesthesia and critical care which needs to be further investigated and tested.

Cardiac index and oxygen delivery during low and high tidal volume ventilation strategies in patients with acute respiratory distress syndrome: a crossover randomized clinical trial

INTRODUCTION

The beneficial effect of low tidal volume (TV) ventilation strategy on mortality in patients with acute respiratory distress syndrome (ARDS) has been attributed to the protective effect on ventilator-induced lung injury, and yet its effect on cardiovascular function might also play an important role. The aim of this study was to assess whether low TV ventilation improves cardiac output and oxygen delivery compared with high TV ventilation strategy in patients with ARDS.

METHODS

In this crossover randomized clinical trial 16 ARDS patients were recruited in an intensive care unit at a university-affiliated hospital. Each patient was ventilated for 30 min with low (6 mL/kg) and 30 min with high (12 mL/kg) TV. The two experimental periods, applied in random order and with allocation concealment, were separated by 30 min of basal ventilation. Minute ventilation was constantly maintained by appropriate respiratory rate changes.

RESULTS

Compared with high TV ventilation, low TV ventilation showed decreased pH (7.37 vs. 7.41, P = 0.001) and increased PaCO₂ (49 vs. 43 mmHg; P = 0.002). Cardiac index and oxygen delivery index were increased with low compared with high TV ventilation (3.9 vs. 3.5 L.min⁻¹.m⁻², P = 0.012, and 521 vs. 463 mL.min⁻¹.m⁻², P = 0.002, respectively), while oxygen extraction ratio decreased (0.36 vs. 0.44, P = 0.027). In four patients oxygen extraction ratio was >0.5 during high TV but not during low TV strategy. The magnitude of the change in cardiac index was positively associated with PaCO₂ variation (P = 0.004), while it was unrelated to the magnitude of changes in TV and airway pressure. The decrease of cardiac index was predicted by PaCO₂ reduction, with and area under ROC curve of 0.72.

CONCLUSIONS

Our findings suggest that a low TV ventilation strategy increases cardiac index and oxygen delivery, thus supporting the hypothesis that the beneficial effect of low TV ventilation in patients with ARDS could be partially explained by hemodynamic improvement. In other words, low tidal volume ventilation could be protective also for the cardiovascular system and not only for the lung. The slight increase of PaCO₂ during low TV ventilation seems to predict the increase of cardiac index.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00713713.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

Analytic reviews: managing the agitated patient in the ICU: sedation, analgesia, and neuromuscular blockade

Physical and psychological distress is exceedingly common among critically ill patients and manifests generically as agitation. The dangers of over- and undertreatment of agitation have been well described, and the intensive care unit (ICU) physician must strike a balance in the fast-paced, dynamic ICU environment. Identification of common reversible etiologies for distress may obviate the need for pharmacologic therapy, but most patients receive some combination of sedative, analgesic, and neuroleptic medications during the course of their critical illness. As such, understanding key pharmacologic features of commonly used agents is critical. Structured protocols and objective assessment tools can optimize drug delivery and may ultimately improve patient outcomes by reducing ventilator days, ICU length of stay, and by reducing cognitive dysfunction.

Sedation and analgesia for the mechanically ventilated patient

Mechanically ventilated patients in the intensive care unit routinely require sedative and analgesic medications to manage pain and anxiety. These medications may have unpredictable effects with long-term use. Strategies that may help to improve patient outcomes include thoughtful selection of medications, use of objective sedation and pain scales, and implementation of protocolized sedation.

Cost-effectiveness of implementing low-tidal volume ventilation in patients with acute lung injury

BACKGROUND

Despite widespread guidelines recommending the use of lung-protective ventilation (LPV) in patients with acute lung injury (ALI), many patients do not receive this lifesaving therapy. We sought to estimate the incremental clinical and economic outcomes associated with LPV and determined the maximum cost of a hypothetical intervention to improve adherence with LPV that remained cost-effective.

METHODS

Adopting a societal perspective, we developed a theoretical decision model to determine the cost-effectiveness of LPV compared to non-LPV care. Model inputs were derived from the literature and a large population-based cohort of patients with ALI. Cost-effectiveness was determined as the cost per life saved and the cost per quality-adjusted life-years (QALYs) gained.

RESULTS

Application of LPV resulted in an increase in QALYs gained by 15% (4.21 years for non-LPV vs 4.83 years for LPV), and an increase in lifetime costs of $7,233 per patient with ALI ($99,588 for non-LPV vs $106,821 for LPV). The incremental cost-effectiveness ratios for LPV were $22,566 per life saved at hospital discharge and $11,690 per QALY gained. The maximum, cost-effective, per patient investment in a hypothetical program to improve LPV adherence from 50 to 90% was $9,482. Results were robust to a wide range of economic and patient parameter assumptions.

CONCLUSIONS

Even a costly intervention to improve adherence with low-tidal volume ventilation in patients with ALI reduces death and is cost-effective by current societal standards.

Review of A Large Clinical Series: Association of Cumulative Fluid Balance on Outcome in Acute Lung Injury: A Retrospective Review of the ARDSnet Tidal Volume Study Cohort

Objective: To evaluate the independent influence of fluid balance on outcomes for patients with acute lung injury. Design: Secondary analysis of a prospective cohort study conducted between March 1996 and March 1999. Setting: The study involved 10 academic clinical centers (with 24 hospitals and 75 Intensive Care Units). Patients: All patients for whom fluid balance data existed (844) from the 902 patients enrolled in the National Heart Lung Blood Institute's ARDS Network ventilator-tidal volume trial. Interventions: The study had no interventions. Measurements/Results: On the first day of study enrollment, 683 patients were, on average, more than 3.5 L in positive fluid balance compared to 161 patients in negative fluid balance (P < .001). Cumulative negative fluid balance on day 4 of the study was associated with an independently lower hospital mortality (OR, 0.50; 95% CI, 0.28-0.89; P < .001) more ventilator and intensive care unit—free days. Conclusions: Negative cumulative fluid balance at day 4 of acute lung injury is associated with significantly lower mortality, independent of other measures of severity of illness.

Is there a best way to set tidal volume for mechanical ventilatory support?

Tidal breaths are an important component of mechanical ventilation. However, an inappropriate tidal volume setting can overstretch and injure the lung. Maximal stretch, tidal stretch, frequency of stretch, and rate of stretch are all implicated in such injury. Clinical trials have shown that limiting maximal and tidal stretch improves outcomes, even if gas exchange is partially compromised. Thus, current strategies should focus on limiting tidal and maximal stretch as much as possible.

Intensive care management of life-threatening avian influenza A (H5N1)

A large proportion of patients with avian influenza A (H5N1) develop life-threatening manifestations, often including ARDS, acute renal failure and multiple organ failure that requires aggressive intensive care management. The pace of development of respiratory failure is often rapid and can occur in previously healthy hosts, mandating close observation and timely intervention of infected individuals. Use of standard, contact, droplet and airborne isolation precautions is recommended to protect healthcare workers. Key components of ARDS management encompass appropriate mechanical ventilation including limiting tidal volume to </=6 mL/kg of predicted body weight, maintaining transpulmonary pressures </=30 cm H(2)O, and utilizing positive end-expiratory pressure to limit alveolar deflation and to improve oxygenation. Additional strategies include conservative fluid management and using nutrition supplemented with antioxidants. Use of corticosteroids is controversial for both early and late ARDS and although often used for avian influenza, beneficial effects on outcomes have not been demonstrated for corticosteroids. Prone positioning can improve oxygenation temporarily and might be useful as rescue therapy for severe hypoxemia. Administration of inhaled nitric oxide and high frequency oscillatory ventilation can improve oxygenation but have not been demonstrated to improve survival in ARDS-their role in avian influenza is uncertain and availability limited. Management of multiple organ failure may include vasopressor support for septic shock and renal replacement therapy for acute renal failure.

Use of sedatives, opioids, and neuromuscular blocking agents in patients with acute lung injury and acute respiratory distress syndrome

OBJECTIVE

The use of sedatives, opioids, and neuromuscular blocking agents (NMBAs) may delay weaning and prolong intensive care unit length of stay. We hypothesized that in patients on higher positive end-expiratory pressure (PEEP), sedatives, opioids, and NMBAs are used in a higher proportion of patients and in higher doses and that the use of these medications is associated with prolongation of weaning and mortality.

DESIGN

Retrospective analysis.

SETTING

The ALVEOLI trial.

PATIENTS

Five hundred forty-nine patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) who were enrolled in the ALVEOLI trial.

INTERVENTIONS

We analyzed prospectively collected data regarding the impact of sedatives, opioids, and NMBAs in ALI/ARDS patients on duration of mechanical ventilation, time to weaning landmarks, and mortality.

MEASUREMENTS AND MAIN RESULTS

Sedatives and opioids were used in >80% of the patients in similar proportion in the two groups. The use of sedatives and opioids, but not the use of NMBAs, was associated with longer time on mechanical ventilation and an increased time to achieve a 2-hr spontaneous breathing trial (p < .0001). Sedatives were also associated with increased time to achieve unassisted breathing. NMBAs were used for a short period of time, in a higher proportion of patients in the lower PEEP group, and for a longer time (0.23 days).

CONCLUSIONS

Sedatives and opioids use was similar in the higher and lower PEEP groups. The use of sedatives and opioids, but not NMBAs, was associated with a longer time to achieve important weaning landmarks.

Mechanical ventilation with lower tidal volumes does not influence the prescription of opioids or sedatives

Introduction

We compared the effects of mechanical ventilation with a lower tidal volume (V_T) strategy versus those of greater V_T in patients with or without acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) on the use of opioids and sedatives.

Methods

This is a secondary analysis of a previously conducted before/after intervention study, which consisting of feedback and education on lung protective mechanical ventilation using lower V_T. We evaluated the effects of this intervention on medication prescriptions from days 0 to 28 after admission to our multidisciplinary intensive care unit.

Results

Medication prescriptions in 23 patients before and 38 patients after intervention were studied. Of these patients, 10 (44%) and 15 (40%) suffered from ALI/ARDS. The V_T of ALI/ARDS patients declined from 9.7 ml/kg predicted body weight (PBW) before to 7.8 ml/kg PBW after the intervention (P = 0.007). For patients who did not have ALI/ARDS there was a trend toward a decline from 10.2 ml/kg PBW to 8.6 ml/kg PBW (P = 0.073). Arterial carbon dioxide tension was significantly greater after the intervention in ALI/ARDS patients. Neither the proportion of patients receiving opioids or sedatives, or prescriptions at individual time points differed between pre-intervention and post-intervention. Also, there were no statistically significant differences in doses of sedatives and opioids. Findings were no different between non-ALI/ARDS patients and ALI/ARDS patients.

Conclusion

Concerns regarding sedation requirements with use of lower V_T are unfounded and should not preclude its use in patients with ALI/ARDS.

Barriers to low tidal volume ventilation in acute respiratory distress syndrome: survey development, validation, and results

OBJECTIVE

To evaluate perceived attitudes, knowledge, and behaviors regarding the use of low tidal volume ventilation in acute respiratory distress syndrome among physicians, nurses, and respiratory therapists in intensive care units.

DESIGN

Cross-sectional, self-administered survey.

SETTING

Large Acute Respiratory Distress Syndrome Network teaching hospital in Baltimore, MD.

PARTICIPANTS

Attending, fellow, and resident physicians; staff nurses; and respiratory therapists in three intensive care units.

INTERVENTIONS

A survey was designed to assess barriers related to clinicians' perceived attitudes, knowledge, and behaviors related to low tidal volume ventilation in acute respiratory distress syndrome and intensive care unit organization-related barriers. Survey development was guided by a published framework of barriers to clinician adherence to practice guidelines; individual items were derived through literature review and refined through pilot testing. Content validity, face validity, and ease of use were verified by local clinicians. Psychometric properties were assessed and regression analyses were conducted to examine differences in perceptions and knowledge level by provider discipline and training level.

MEASUREMENTS AND MAIN RESULTS

There were 291 completed surveys with a response rate of 84%. Validity and acceptable psychometric properties were demonstrated. Barriers related to clinician attitudes, behaviors, and intensive care unit organization were significantly higher among nurses and respiratory therapists vs. physicians. Knowledge-related barriers also were significantly higher among nurses vs. physicians and respiratory therapists. Barriers were lower and knowledge test scores higher among fellows and attending physicians vs. residents. Similarly, barriers were lower and knowledge test scores higher among nurses with >10 yrs of experience vs. <10 yrs of experience.

CONCLUSIONS

Important organizational and clinician barriers, including knowledge deficits, regarding low tidal volume ventilation were reported, particularly among nurses and resident physicians. Addressing these barriers may be important for increasing implementation of low tidal volume ventilation.

Patient-ventilator synchrony during pressure-targeted versus flow-targeted small tidal volume assisted ventilation

PURPOSE

Low tidal volume (V(T)) delivered by flow-targeted breaths reduces ventilator-induced lung injury but may increase patient breathing effort because of limited flow. We hypothesized that a variable-flow, pressure-targeted breath would improve breathing effort versus a fixed flow-targeted breath.

MATERIALS AND METHODS

We compared pressure assist-control ventilation and volume assist-control ventilation (VACV) in 12 patients with acute respiratory failure receiving 6 to 8 mL/kg V(T). Backup frequency, V(T), inspiratory time, applied positive end-expiratory pressure and fraction of inspired oxygen were held constant. Patient breathing effort was assessed by airway pressure (Paw) drop below baseline 0.1 second after the breath initiation (P(0.1)), the maximal Paw drop during the triggering phase (Ptr), the magnitude of ventilator work during flow delivery, and the presence of an active expiratory effort during cycling and air trapping judged by the magnitude of residual flow at end-expiration.

RESULTS

Compared with VACV, pressure assist-control ventilation decreased P(0.1), Ptr (by 25% and 16%, respectively), and evidence for trapped gas but not ventilator work during flow delivery or cycle dys-synchrony. Peak inspiratory flow was comparable between the 2 modes.

CONCLUSIONS

In patients receiving small V(T) VACV with increased breathing effort, variable-flow, pressure-targeted ventilation may provide more comfort by decreasing respiratory drive during the triggering phase.

Acute lung injury and the acute respiratory distress syndrome: a clinical review

Acute respiratory distress syndrome and acute lung injury are well defined and readily recognised clinical disorders caused by many clinical insults to the lung or because of predispositions to lung injury. That this process is common in intensive care is well established. The mainstay of treatment for this disorder is provision of excellent supportive care since these patients are critically ill and frequently have coexisting conditions including sepsis and multiple organ failure. Refinements in ventilator and fluid management supported by data from prospective randomised trials have increased the methods available to effectively manage this disorder.

Oral and nasal enteral tube placement errors and complications in a pediatric intensive care unit

OBJECTIVE

To report five cases of errors in the placement of oral/nasal enteral tubes in a pediatric intensive care unit, and to review literature on placement techniques and complication rates.

DESIGN

Case series and review of the literature.

SETTING

A 19-bed pediatric intensive care unit in a tertiary care pediatric hospital.

PATIENTS

A 14-yr-old male with respiratory distress following a near drowning, a 10-yr-old male with recurrent acute lymphocytic leukemia and Pneumocystis carinii pneumonia, a 16-yr-old female with complex congenital heart disease and respiratory failure, a 16-yr-old male with status asthmaticus, and a 2-yr-old male with congenital heart disease.

INTERVENTIONS

None.

MAIN RESULTS

Five cases of enteral tube placement errors occurred in our combined medical-surgical pediatric critical care unit within the past year. All five resulted in placement of the feeding tube in the respiratory tract, four occurred despite the presence of cuffed endotracheal tubes. Three of the five patients had subsequent worsening of their respiratory status. One developed a pneumothorax, one developed pulmonary hemorrhage, and one developed an increased oxygen requirement.

CONCLUSIONS

Patients in the pediatric intensive care unit may have characteristics that place them at an increased risk for misplacement of oral or nasal enteral tubes into the respiratory tract. Placement of enteral tubes into the respiratory tract may cause serious morbidity and possibly mortality. Checking the placement of enteral tubes with traditional methods does not prevent misplacement in the respiratory tree, and new techniques should be considered.

Therapy for late-phase acute respiratory distress syndrome

Prolonged hypoxemic respiratory failure and evidence of lung organization and fibrosis are features of an ARDS subgroup that is variably identified as "late," "persistent," or "fibroproliferative" ARDS. Early reports suggested that patients with late ARDS had a high mortality unless treated with corticosteroids. A large recent study with improved methodology has demonstrated that despite improvements of pulmonary physiology, corticosteroids do not change mortality of patients who continue to meet ARDS criteria 7 to 28 days after onset of acute lung injury. Additionally, there is no compelling evidence that persistent ARDS confers a higher mortality than that of ALI/ARDS. Observational and interventional studies are needed to increase understanding of the incidence, best management, and outcomes of patients with persistent ARDS.

Conventional mechanical ventilation in acute lung injury and acute respiratory distress syndrome

Acute lung injury and acute respiratory distress syndrome are inflammatory conditions involving a broad spectrum of lung injury from mild respiratory abnormality to severe respiratory derangement. Regardless of cause (direct or indirect lung injury), pulmonary physiology and mechanics are altered, leading to hypoxemic respiratory failure. the use of positive pressure ventilation itself may cause lung injury (ventilator-induced lung injury, or VILI). VILI may amplify preexisting injury, delay lung recovery, and result in adverse outcomes. This article examines the evidence supporting lung-protective ventilation strategies and addresses the methods, outcomes, and potential obstacles to implementation of such approaches.

Intensive insulin therapy in intensive care: an example of the struggle to implement evidence-based medicine

Schultz and colleagues discuss the factors hindering implementation of intensive insulin therapy.

Hemodynamic effects of different lung-protective ventilation strategies in closed-chest pigs with normal lungs

OBJECTIVE

The benefits of lung-protective ventilation strategies used for acute respiratory distress syndrome in subjects with normal lungs are uncertain. The purpose of this study was to investigate the hemodynamic effects of conventional lung-protective ventilation (CLPV) and high-frequency oscillatory ventilation (HFOV) in a normal lung animal model.

DESIGN

Prospective laboratory investigation.

SETTING

Animal laboratory in a university medical center.

SUBJECTS

Seven landrace pigs (mean weight 41 kg).

INTERVENTIONS

Pigs were ventilated at random conventionally with positive end-expiratory pressure 2-3 cm H2O and tidal volume 10-12 mL/kg (control), with CLPV (positive end-expiratory pressure 10 cm H2O, tidal volume 6 mL/kg), or with HFOV. Hemodynamics were analyzed after insertion of biventricular conductance catheters and a pulmonary artery catheter.

MEASUREMENTS AND MAIN RESULTS

The protective strategies led to higher mean airway pressures and severe hypercapnia with acidosis, which was only significant with CLPV. Compared with control, oxygenation was worse with CLPV and HFOV. With HFOV and CLPV, mean arterial pressure, cardiac output, and stroke volume decreased significantly; pulmonary arterial elastance increased. The slope of the end-diastolic pressure volume relationship for the left and right ventricle remained unchanged (preserved ventricular function), whereas the intercept increased with both protective strategies (augmented intrathoracic pressure); left and right end-diastolic volumes decreased significantly.

CONCLUSIONS

In the absence of a fluid resuscitation strategy, CLPV and HFOV caused decreased mean arterial pressure, cardiac output, and stroke volume and worsened oxygenation in this normal lung animal model. This resulted primarily from a biventricular decrease in preload.

Postoperative acute respiratory distress syndrome development in the thoracic surgery patient

Acute respiratory distress syndrome (ARDS) in the thoracic surgery patient is a dreaded complication that occurs in 4% to 5% of pneumonectomies. This peculiar syndrome is indistinct from other forms of ARDS yet is associated with an exceedingly higher mortality rate. Current management parallels ARDS treatment of other etiologies.

Effects of tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome*

OBJECTIVE

To assess the effects of step-changes in tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS).

DESIGN

Prospective, nonconsecutive patients with ALI/ARDS.

SETTING

Adult surgical, trauma, and medical intensive care units at a major inner-city, university-affiliated hospital.

PATIENTS

Ten patients with ALI/ARDS managed clinically with lung-protective ventilation.

INTERVENTIONS

Five patients were ventilated at a progressively smaller tidal volume in 1 mL/kg steps between 8 and 5 mL/kg; five other patients were ventilated at a progressively larger tidal volume from 5 to 8 mL/kg. The volume mode was used with a flow rate of 75 L/min. Minute ventilation was maintained constant at each tidal volume setting. Afterward, patients were placed on continuous positive airway pressure for 1-2 mins to measure their spontaneous tidal volume.

MEASUREMENTS AND MAIN RESULTS

Work of breathing and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100). Work of breathing progressively increased (0.86 +/- 0.32, 1.05 +/- 0.40, 1.22 +/- 0.36, and 1.57 +/- 0.43 J/L) at a tidal volume of 8, 7, 6, and 5 mL/kg, respectively. In nine of ten patients there was a strong negative correlation between work of breathing and the ventilator-to-patient tidal volume difference (R = -.75 to -.998).

CONCLUSIONS

: The ventilator-delivered tidal volume exerts an independent influence on work of breathing during lung-protective ventilation in patients with ALI/ARDS. Patient work of breathing is inversely related to the difference between the ventilator-delivered tidal volume and patient-generated tidal volume during a brief trial of unassisted breathing.

Protective effect of endogenous beta-adrenergic tone on lung fluid balance in acute bacterial pneumonia in mice

Some investigators have reported that endogenous beta-adrenoceptor tone can provide protection against acute lung injury. Therefore, we tested the effects of beta-adrenoceptor inhibition in mice with acute Escherichia coli pneumonia. Mice were pretreated with propranolol or saline and then intratracheally instilled with live E. coli (10(7) colony-forming units). Hemodynamics, arterial blood gases, plasma catecholamines, extravascular lung water, lung permeability to protein, bacterial counts, and alveolar fluid clearance were measured. Acute E. coli pneumonia was established after 4 h with histological evidence of acute pulmonary inflammation, arterial hypoxemia, a threefold increase in lung vascular permeability, and a 30% increase in extravascular lung water as an increase in plasma catecholamine levels. beta-Adrenoceptor inhibition resulted in a marked increase in extravascular lung water that was explained by both an increase in lung vascular permeability and a reduction in net alveolar fluid clearance. The increase in extravascular lung water with propranolol pretreatment was not explained by an increase in systemic or vascular pressures. The increase in lung vascular permeability was explained in part by anti-inflammatory effects of beta-adrenoceptor stimulation because plasma macrophage inflammatory protein-2 levels were higher in the propranolol pretreatment group compared with controls. The decrease in alveolar fluid clearance with propranolol was explained by a decrease in catecholamine-stimulated fluid clearance. Together, these results indicate that endogenous beta-adrenoceptor tone has a protective effect in limiting accumulation of extravascular lung water in acute severe E. coli pneumonia in mice by two mechanisms: 1) reducing lung vascular injury and 2) upregulating the resolution of alveolar edema.

Struggle for implementation of new strategies in intensive care medicine: anticoagulation, insulin, and lower tidal volumes

The management of intensive care patients have changed dramatically in the last years: from merely supportive care, it has moved to evidence-based strategies that have been demonstrated to reduce mortality of the severely ill patients. Clinical research have brought numerous positive clinical trials offering intensive care physicians specific therapies to improve outcome of intensive care patients. Among them were the trials that tested the infusion of activated protein C in patients with severe sepsis, tight glycemic control in surgical intensive care patients, and use of lung protective mechanical ventilation by using small tidal volumes in patients with acute lung injury. Although results of these trials were sufficiently strong to, at least, consider implementation of these strategies in critical care medicine, published and yet unpublished reports show that there is significant struggle with implementation of these therapies. This manuscript focuses on the potential reasons that underlie this problem.

Ventilatory strategies in patients with sepsis and respiratory failure

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H2O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.

Low tidal volume ventilation does not increase sedation use in patients with acute lung injury*

OBJECTIVE

Low tidal volume ventilation is associated with reduced mortality in patients with acute lung injury, yet concerns exist about patient comfort and the levels of sedation and analgesia required during its use. We compared the doses and duration of sedatives and opioid analgesics in patients receiving low vs. traditional tidal volumes at our institution.

DESIGN

Secondary analysis of a randomized clinical trial.

SETTING

University-affiliated county hospital in Seattle, WA.

PATIENTS

Sixty-one patients with acute lung injury enrolled in the National Heart, Lung and Blood Institute's ARDS Network tidal volume trial.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Thirty-three patients were randomized to the lower tidal volume arm (6 mL/kg of predicted body weight) and 28 patients were randomized to the higher tidal volume arm (12 mL/kg of predicted body weight). There were no significant differences in the percentage of study days patients received sedatives, opioids, or neuromuscular blockade. When specific study days were examined, there were no significant differences in the proportion of patients receiving benzodiazepines, propofol, haloperidol, and opioids on days 1, 2, 3, and 7 of mechanical ventilation, nor were there differences in the doses of benzodiazepines and opioids on those days.

CONCLUSIONS

At our institution, low tidal volume ventilation was not associated with increased dose or duration of sedatives in patients with acute lung injury. Sedation administration should not be considered a barrier to implementing a lung-protective ventilation strategy.