Avi Nahum

Prone positioning attenuates and redistributes ventilator-induced lung injury in dogs

Background: We previously demonstrated a markedly dependent distribution of ventilator‐induced lung injury in oleic acid‐injured supine animals ventilated with large tidal volumes and positive end‐expiratory pressure ≥10 cm H2O. Because pleural pressure distributes more uniformly in the prone position, we hypothesized that the extent of injury induced by purely mechanical forces applied to the lungs of normal animals might improve and that the distribution of injury might be altered with prone positioning. Objective: To compare the extent and distribution of histologic changes and edema resulting from identical patterns of high end‐inspiratory/low end‐expiratory airway pressures in both supine and prone normal dogs. Design/Setting: We ventilated 10 normal dogs (5 prone, 5 supine) for 6 hrs with identical ventilatory patterns (a tidal volume that generated a peak transpulmonary pressure of 35 cm H2O when implemented in the supine position before randomization, positive end‐expiratory pressure = 3 cm H2O). Ventilator‐induced lung injury was assessed by gravimetric analysis and histologic grading. Measurements and Main Results: Wet weight/dry weight ratios (WW/DW) and histologic scores were greater in the supine than the prone group (8.8 ± 2.8 vs. 6.1 ± 0.7; p = .01 and 1.4 ± 0.3 vs. 1 ± 0.3; p = .037, respectively). In the supine group, WW/DW and histologic scores were significantly greater in dependent than nondependent regions (9.4 ± 1.9 vs. 6.7 ± 0.9; p = .01 and 2.0 ± 0.4 vs. 0.9 ± 0.4; p = .043, respectively). In the prone group, WW/DW also was greater in dependent regions (6.7 ± 1.1 vs. 5.8 ± 0.5; p = .054), but no significant differences were found in histologic scores between dependent and nondependent regions (p = .42). Conclusion: In this model of lung injury induced solely by mechanical forces, the prone position resulted in a less severe and more homogeneous distribution of ventilator‐induced lung injury. These results parallel those previously obtained in oleic acid‐preinjured animals ventilated with higher positive end‐expiratory pressure.

Time required for partial pressure of arterial oxygen equilibration during mechanical ventilation after a step change in fractional inspired oxygen concentration

Abstract Objective: To determine the time required for the partial pressure of arterial oxygen (PaO2) to reach equilibrium after a 0.20 increment or decrement in fractional inspired oxygen concentration (FIO2) during mechanical ventilation. Setting: A multi-disciplinary ICU in a university hospital. Patients and methods: Twenty-five adult, non-COPD patients with stable blood gas values (PaO2/FIO2 ≥ 180 on the day of the study) on pressure-controlled ventilation (PCV). Following a baseline PaO2 (PaO2b) measurement at FIO2 =0.35, the FIO2 was increased to 0.55 for 30xa0min and then decreased to 0.35 without any other change in ventilatory parameters. Sequential blood gas measurements were performed at 3, 5, 7, 9, 11, 15, 20, 25 and 30xa0min in both periods. The PaO2 values measured at the 30thxa0min after a step change in FIO2 (FIO2 =0.55, PaO2[55] and FIO2 =0.35, PaO2[35]) were accepted as representative of the equilibrium values for PaO2. Each patients rise and fall in PaO2 over time, PaO2(t), were fitted to the following respective exponential equations:xa0PaO2b + (PaO2[55]-PaO2b)(1-e-kt) and PaO2[55] + (PaO2[35]-PaO2[55])(e-kt) where t refers to time, PaO2[55] and PaO2[35] are the final PaO2 values obtained at a new FIO2 of 0.55 and 0.35, after a 0.20 increment and decrement in FIO2, respectively. Time constant k was determined by a non-linear fitting curve and 90% oxygenation times were defined as the time required to reach 90% of the final equilibrated PaO2 calculated by using the non-linear fitting curves. Results: Time constant values for the rise and fall periods were 1.01±0.71xa0min–1, 0.69±0.42xa0min–1, respectively, and 90% oxygenation times for rises and falls in PaO2 periods were 4.2±4.1xa0min–1 and 5.5±4.8xa0min–1, respectively. There was no significant difference between the rise and fall periods for the two parameters (p>0.05). Conclusion: We conclude that in stable patients ventilated with PCV, after a step change in FIO2 of 0.20, 5–10xa0min will be adequate for obtaining a blood gas sample to measure a PaO2 that will be representative of the equilibrium PaO2 value.

Effects of expiratory tracheal gas insufflation in patients with severe head trauma and acute lung injury

ObjectiveThis study analyzed the effect of phasic tracheal gas insufflation at mid- to end-expiration in patients with severe head trauma and acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).Design and settingA prospective interventional study in a 16-bed intensive care unit.PatientsSeven patients with severe head trauma (Glasgow Coma Scale <9) and ALI/ARDS.InterventionsPatients were ventilated in assist/control mode with a ventilatory strategy providing adequate oxygenation (PaO2 >70xa0mmHg) and normocapnia (PaCO2 between 35–40xa0mmHg). Mid to end expiratory tracheal gas insufflation at 8xa0l/min flow rate was delivered for 90xa0min while normocapnia was maintained by simultaneous reductions in tidal volume. We measured (hemodynamics, oxygenation, lung mechanics, and cerebral parameters) in basal situation and during and after tracheal insufflation.Measurements and resultsTracheal gas insufflation allowed a significant decrease in tidal volume from 9.1 to 7.2xa0ml/kg, with associated reduction in driving pressure (plateau pressure minus positive end-expiratory pressure, PEEP) from 18.1 to 13.2xa0cmH2O. Total PEEP increased from 9.3 to 12.7xa0cmH2O due to the generation of lung hyperinflation. Oxygenation improved slightly during tracheal gas insufflation, and this improvement remained after stopping tracheal insufflation. No changes in hemodynamic or cerebral parameters were observed during the study.ConclusionsIn patients with severe head trauma and ALI receiving mechanical ventilation, expiratory tracheal gas insufflation allowed the targeted arterial PCO2 level to be maintained together with a substantial reduction in tidal volume.

A Prospective Evaluation of Benzodiazepine Guidelines in the Management of Patients Hospitalized for Alcohol Withdrawal

Our institution adopted guidelines for the selection of benzodiazepines to be administered to patients hospitalized for alcohol withdrawal. We assessed the guidelines impact on prescribing habits, benzodiazepine dosage requirements and costs, and length of intensive care unit (ICU) stay. A 6‐month prospective, observational study was performed in 50 patients who exhibited signs of alcohol withdrawal and received benzodiazepine therapy. Appropriate therapy was defined as lorazepam for patients 60 years and older or those with hepatic dysfunction, and chlordiazepoxide for all other patients. Benzodiazepine costs were calculated based on acquisition cost. Based on our guidelines, 76% of patients were appropriate candidates for a long‐acting agent such as chlordiazepoxide; 61% of these candidates actually received such a drug. Using a benzodiazepine conversion to compare doses in chlordiazepoxide equivalents, there was a significant difference in the total mean dose of chlordiazepoxide (1295.5 mg, SD ± 1571) compared with lorazepam (365.5 mg; SD ± 446) (p<0.01). The mean total chlordiazepoxide acquisition cost was

Prolonged Neuromuscular Blockade in Two Critically Ill Patients Treated With Atracurium

61.74 (range

Inspiratory tidal volume sparing effects of tracheal gas insufflation in dogs with oleic acid-induced lung injury

0.03–585.98) per patient (28 patients); prior to adoption of the guidelines, the mean cost of benzodiazepine therapy was

Atracurium Resistance in a Critically Ill Patient

1008.72 (±

A retrospective analysis of long-term use of nondepolarizing neuromuscular blocking agents in the intensive care unit, and guidelines for drug selection.

1554.45). For patients receiving chlordiazepoxide, the mean days of ICU and hospital stay were 1.1 days (range 0–9 days) and 5.6 days (range 1–17 days), respectively; before adoption of the guidelines, the mean number of days of ICU stay was significantly greater (4.1 days, p<0.0001). The guidelines resulted in a substantial change in benzodiazepine prescribing patterns. For the management of patients hospitalized for alcohol withdrawal, chlordiazepoxide can be given safely in higher dosages than previously described, is associated with minimal acquisition costs, and in select patients may facilitate non‐ICU management compared with alternative therapies, and thus result in significant cost savings for the provider institution and third‐party payers.

A retrospective review and assessment of benzodiazepines in the treatment of alcohol withdrawal in hospitalized patients

Recent literature suggests that the risk of prolonged neuromuscular blockade associated with atracurium compared with other nondepolarizing neuromuscular blocking agents may be minimal. Two patients experienced prolonged weakness associated with the administration of atracurium. Both received atracurium 0.5–0.7 mg/kg/hour in combination with methylprednisolone 500–600 mg/day. Electromyographic results and creatine kinase levels were suggestive of muscular weakness in both patients. Despite high‐dose corticosteroid therapy, the electromyographic evidence supporting prolonged weakness did not suggest typical corticosteroid myopathy. Although some clinicians advocate routine administration of atracurium in critically ill patients due to the relative lack of reports of prolonged weakness, this may be premature. Although there are fewer reports of atracurium‐associated prolonged weakness compared with pancuronium and vecuronium, the patients we describe suggest that it may occur.

Improving detection of venous thromboembolism. New technology holds promise for early, precise diagnosis.

PURPOSEnTracheal gas insufflation (TGI) improves the efficiency of conventional mechanical ventilation (CMV) by reducing the series dead space of the airways. Consequently, application of TGI as an adjunct to CMV may permit reducing tidal volume (VT) while limiting CO2 retention. We tested the extent to which panexpiratory TGI allows reduction of VT while maintaining PaCO2 constant in an oleic acid-induced lung injury model.nnnMETHODSnWe studied six anesthetized, paralyzed, and mechanically ventilated dogs. Oleic acid injury was induced by injecting 0.09 mL/kg of oleic acid into the right atrium. After stabilization of lung injury the VT-sparing effect of TGI was tested by progressively increasing catheter flow rate (Vc) from 2 to 5, 10, and 15 L/min while decreasing VT by an amount that maintained PaCO2 constant (approximately 47 mm Hg) with respect to baseline (Vc = 0 L/min).nnnRESULTSnTidal volume was decreased from a baseline value of 0.360 +/- 0.030 L to 0.238 +/- 0.054 L at Vc of 15 L/min. The reduction in VT was associated with a decrement in peak and end-inspiratory plateau airway opening pressure from 32 +/- 3 to 28 +/- 6 cm H2O and from 25 +/- 2 to 21 +/- 3 cm H2O, respectively. Total physiological dead space fraction decreased from a baseline value of 0.60 +/- 0.08 to 0.31 +/- 0.20 during TGI at 15 L/min. TGI did not affect cardiac output, PaO2, or pulmonary venous admixture.nnnCONCLUSIONnWe conclude that TGI can be a useful adjunct to CMV during acute lung injury to limit VT while avoiding CO2 retention.