Low tidal volume ventilation strategies for patients with respiratory failure from acute lung injury may lead to breath stacking and higher volumes than intended.To determine frequency, risk factors, and volume of stacked breaths during low tidal volume ventilation for acute lung injury.Prospective cohort study of mechanically ventilated patients with acute lung injury (enrolled from August 2006 through May 2007) treated with low tidal volume ventilation in a medical intensive care unit at an academic tertiary care hospital.Patients were ventilated with low tidal volumes using the Acute Respiratory Distress Syndrome Network protocol for acute lung injury. Continuous flow-time and pressure-time waveforms were recorded. The frequency, risk factors, and volume of stacked breaths were determined. Sedation depth was monitored using Richmond agitation sedation scale.Twenty patients were enrolled and studied for a mean 3.3 +/- 1.7 days. The median (interquartile range) Richmond agitation sedation scale was -4 (-5, -3). Inter-rater agreement for identifying stacked breaths was high (kappa 0.99, 95% confidence interval 0.98-0.99). Stacked breaths occurred at a mean 2.3 +/- 3.5 per minute and resulted in median volumes of 10.1 (8.8-10.7) mL/kg predicted body weight, which was 1.62 (1.44-1.82) times the set tidal volume. Stacked breaths were significantly less common with higher set tidal volumes (relative risk 0.4 for 1 mL/kg predicted body weight increase in tidal volume, 95% confidence interval 0.23-0.90).Stacked breaths occur frequently in low tidal volume ventilation despite deep sedation and result in volumes substantially above the set tidal volume. Set tidal volume has a strong influence on frequency of stacked breaths.
To evaluate the efficacy of continuous infusions of lorazepam vs. midazolam for sedation in the intensive care unit (ICU). Design: Prospective, randomized study. Setting: Large, urban university hospital. Patients: Twenty adult medical ICU patients receiving mechanical ventilatory support. Interventions: Patients were randomized to receive either lorazepam or midazolam. The infusion rate was adjusted at the bedside by the ICU nurse according to a standardized study protocol to achieve and maintain sedation at Ramsay's sedation level 2 or 3. Measurements and Main Results: Ten patients were randomized to receive lorazepam and ten to receive midazolam. The groups were similar in demographics, Acute Physiology and Chronic Health Evaluation (APACHE) II scores, ICU admission diagnosis, underlying disease processes, and supplemental analgesic administration. The mean time to achieve initial adequate sedation was 124 mins for lorazepam and 105 mins for midazolam. The mean infusion rate at the point of initial sedation was 0.06 mg/kg/hr for lorazepam and 0.15 mg/kg/hr for midazolam. The maximum and mean infusion rates for the entire study period were 0.1 and 0.06 mg/kg/hr, respectively, for lorazepam and 0.29 and 0.24 mg/kg/hr, respectively, for midazolam. The number of infusion rate adjustments per day was 1.9 mg/kg/hr for lorazepam and 3.6 mg/kg/hr for midazolam. Of the surviving patients, the mean time to return to baseline mental status after discontinuation of the benzodiazepine infusion was 261 mins for lorazepam and 1815 mins for midazolam. The mean volume of fluid per day required to deliver the maximum dose of benzodiazepine was 1.2 L for lorazepam (maximum 2.4 L) and 1.3 L for midazolam (maximum 3.6 L). Conclusions: While there was a tendency to a longer time required for return to baseline mental status in patients receiving midazolam, this was not statistically signficant. Findings of interest concerning both midazolam and lorazepam were: a) time to achieve sedation in medical ICU patients is often prolonged; b) actual dose requirements necessary to maintain sedation in this patient population are larger than the current literature describes; c) time to awaken after discontinuation of the infusion was occasionally delayed for >24 hrs; d) large volumes of fluid were required to deliver these doses of drug via this route of administration. (Crit Care Med 1994; 22:1241–1247)
We implemented a new policy at our institution where the responsibility for intensive care unit (ICU) patient transports to the operating room (OR) was changed from the anesthesia to the ICU service. We hypothesized that this approach would be associated with increased on-time starts and decreased turnover times.
Permissive hypercapnia (PH) may result from mechanical ventilation (MV) strategies that intentionally reduce minute ventilation. Sedative doses required to tolerate PH have not been well characterized. With increased attention to lung-protective ventilation, characterization of sedative requirements with PH and determination of sedative dose changes with PH are needed.Retrospective analysis.Tertiary care university hospital.We evaluated 124 patients randomized in a previous study to either propofol or midazolam. PH was employed in ten of 60 patients receiving propofol and 13 of 64 patients receiving midazolam.We analyzed dosing of propofol and midazolam in patients undergoing PH through a retrospective analysis of an existing database on MV patients. Total sedative (propofol and midazolam) dose was recorded for the first three days of MV. Linear regression analysis (dependent variable: sedative dose) was used to analyze the following independent variables: PH, age, gender, daily sedative interruption, type of respiratory failure, presence of hepatic and/or renal failure, Acute Physiology and Chronic Health Evaluation II score, morphine dose, and Ramsay sedation score.Propofol dose was higher in PH patients (42.5+/-16.2 vs. 27.0+/-15.3; p=.02); Midazolam dose did not differ between PH and non-PH patients (0.05 [0.04, 0.14] vs. 0.05 [0.03, 0.07]; p=.17). By univariate linear regression analysis, propofol dose was significantly dependent on PH, age, type of respiratory failure, morphine dose, and Ramsay score, with PH (regression coefficient, 11.7; 95% confidence interval, 1.2-22.7; p=.03) and age (regression coefficient, -0.3; 95% confidence interval -0.5 to -0.08; p=.005) remaining significant by multivariate linear regression. By univariate linear regression analysis, midazolam dose was dependent on age, morphine dose, and Ramsay score, but not PH; only morphine dose (regression coefficient, 0.44; 95% confidence interval, 0.22-0.67 for a 0.1-unit increase in morphine dose; p<.001) was significant by multivariate linear regression.We conclude that higher doses of propofol but not midazolam are required to sedate patients managed with PH.
Rationale:Patients with COVID-19 frequently develop severe respiratory disease and may require invasive mechanical ventilation. A study of primarily white patients intubated for COVID-19 associated respiratory failure found predictors of 28-day mortality to be respiratory system compliance, age, tidal volume, arterial pH and heart rate. Little is known about the outcomes of minority populations with severe COVID-19 pneumonia. Therefore, we present an analysis of the predictors of mortality in a group of primarily African American patients with COVID-19 associated respiratory failure. Methods:All adult patients admitted to the University of Chicago COVID-19 intensive care unit receiving invasive mechanical ventilation between March 1st and June 31st, 2020 were identified. Patients were included in the study if they had at least one recorded measure of plateau airway pressure while receiving volume-controlled ventilation allowing determination of driving pressure and lung compliance. Univariable analysis was conducted comparing survivors with those who died in-hospital followed by construction of a multivariable logistic regression model predicting in-hospital mortality based on significant factors from univariable analysis, excluding colinear variables. Results:Eighty-five patients were included in this retrospective study. Patients were primarily African American (n=73, 86%). Among all study patients, median tidal volume was 6.0 cc/kg ideal body weight (IQR 5.8-6.2), PEEP was 8 cm H2O (IQR 5.0-10), and driving pressure was 14 cm H2O (IQR 11-16). Median respiratory system compliance was 27 ml/cm H2O (IQR 21-34). Salvage therapies for refractory hypoxemia in the cohort included prone positioning (27%), paralysis (27%), inhaled pulmonary vasodilators (19%), and extracorporeal membrane oxygenation (1%). In the multivariable logistic regression model, age (OR 1.077, 95% CI 1.031 to 1.125, p=0.001) and driving pressure (OR 1.174, 95% CI 1.009 to 1.366, p=0.038) were found to be independent predictors of mortality. Conclusions:In a predominantly African American patient population with COVID-19 pneumonia requiring invasive mechanical ventilation, higher driving pressure was predictive of overall mortality. These finding are consistent with the work of Botta et al (2020), who demonstrated reduced lung compliance was predictive of mortality among a largely white group of patients with severe COVID-19 pneumonia. While minority populations infected with COVID-19 have been found worse outcomes, early lung mechanics appear to be comparable to white patients. These findings support that higher driving pressures and low lung compliance are indicative of serious lung injury which may lead to death.
