Effects of positive airway pressure on basilic vein diameter and venous flow velocity in healthy volunteers.

INTRODUCTION: The placement of vascular catheters of adequate size in accordance to catheter-to-vein ratio (CVR) recommendations represents one of the cornerstones of catheter-related upper vein thrombosis prevention. However there is scarcity of data on its effect on the venous dynamics of the basilic vein, a common site for long-term catheter placement. This study investigates the effects of the application of positive airway pressure on the diameter and blood flow velocity of basilic vein. We also measured the effects of under-armpit straps, a device commonly used to keep continuous positive airway pressure (CPAP) helmets in place. METHODS: We enrolled 28 healthy volunteers. Basilic vein diameter and minimum/maximum blood flow velocity, according to respiratory venous flow oscillation, were measured by ultrasound on the midpoint of their dominant arm during spontaneous breathing and during breathing in a CPAP helmet with 10 cm H2O of airway pressure applied, with the helmet kept in place either through armpit straps or by tying the helmet to the bed. RESULTS: The application of 10 cm H2O of positive airway pressure significantly increased basilic vein diameter by 0.9 ± 0.2 mm, while reducing minimum blood flow velocity by 1.8 ± 0.4 cm/s. These effects were amplified by the application of under armpit straps. CONCLUSIONS: Breathing with positive airway pressure increases basilic vein diameter while reducing blood flow-velocity. This phenomenon might lead to an incorrect assessment of CVR, misleading the operator into choosing improperly large catheters.

A lung rescue team improves survival in obesity with acute respiratory distress syndrome.

BACKGROUND: Limited data exist regarding ventilation in patients with class III obesity [body mass index (BMI) > 40 kg/m2] and acute respiratory distress syndrome (ARDS). The aim of the present study was to determine whether an individualized titration of mechanical ventilation according to cardiopulmonary physiology reduces the mortality in patients with class III obesity and ARDS. METHODS: In this retrospective study, we enrolled adults admitted to the ICU from 2012 to 2017 who had class III obesity and ARDS and received mechanical ventilation for > 48 h. Enrolled patients were divided in two cohorts: one cohort (2012-2014) had ventilator settings determined by the ARDSnet table for lower positive end-expiratory pressure/higher inspiratory fraction of oxygen (standard protocol-based cohort); the other cohort (2015-2017) had ventilator settings determined by an individualized protocol established by a lung rescue team (lung rescue team cohort). The lung rescue team used lung recruitment maneuvers, esophageal manometry, and hemodynamic monitoring. RESULTS: The standard protocol-based cohort included 70 patients (BMI = 49 ± 9 kg/m2), and the lung rescue team cohort included 50 patients (BMI = 54 ± 13 kg/m2). Patients in the standard protocol-based cohort compared to lung rescue team cohort had almost double the risk of dying at 28 days [31% versus 16%, P = 0.012; hazard ratio (HR) 0.32; 95% confidence interval (CI95%) 0.13-0.78] and 3 months (41% versus 22%, P = 0.006; HR 0.35; CI95% 0.16-0.74), and this effect persisted at 6 months and 1 year (incidence of death unchanged 41% versus 22%, P = 0.006; HR 0.35; CI95% 0.16-0.74). CONCLUSION: Individualized titration of mechanical ventilation by a lung rescue team was associated with decreased mortality compared to use of an ARDSnet table.

Silver-Coated Endotracheal Tubes Cleaned With a Mechanism for Secretion Removal.

BACKGROUND: Biofilm on the surface of endotracheal tubes (ETTs) is associated with ventilator-associated pneumonia. The use of silver-coated ETTs has been suggested to reduce the occurrence of ventilator-associated pneumonia by preventing biofilm formation. However, mucus accumulation can reduce the antibacterial activity of silver-coated ETTs by isolating bacterial colonies from the silver surface. We hypothesized that, in mechanically ventilated subjects, periodic removal of secretions through the use of a cleaning device would enhance the antimicrobial properties of silver-coated ETTs and thus reduce bacterial colonization. METHODS: Subjects were randomized to either standard suctioning (blind tracheal suctioning, control group) or blind tracheal suctioning plus cleaning maneuver every 8 h (treatment group). Tracheal aspirates were collected immediately before extubation for microbiological culture. After extubation, ETTs were collected for both cultural and non-cultural microbiological analysis and biofilm isolation. RESULTS: 39 subjects expected to be ventilated for > 48 h were enrolled; 36 ETTs (18 control, 18 treatment) and 29 tracheal samples (15 control, 14 treatment) were collected. Among the ETTs positive for bacterial colonization (15 vs 9, P = .18), cleaning maneuvers did not reduce microbial load, shown as the decimal logarithm of colony-forming units (CFU) per mL (1.6 ± 1.2 vs 0.9 ± 1.2 logCFU/mL, P = .15). There was a trend toward decreased biofilm deposition (439.5 ± 29.0 vs 288.9 ± 157.7 mg, P = .09) in the treated ETTs. No significant differences were observed in the number of positive tracheal aspirates (13 vs 10, P = .39) or in the microbial load (4.8 ± 4.0 vs 4.2 ± 3.8 logCFU/mL, P = .70) of tracheal secretions. Finally, no differences in the microbial load of Gram-positive organisms, Gram-negative organisms, or yeasts were found between the ETTs and tracheal aspirates of the 2 groups. CONCLUSIONS: In 39 critically-ill subjects intubated with silver-coated ETTs, periodic cleaning maneuvers did not decrease bacterial colonization of the ETTs and did not lower respiratory tract colonization compared to the standard suctioning. (Clinicaltrials.gov registration NCT02120001.).

Transpulmonary Pressure Describes Lung Morphology During Decremental Positive End-Expiratory Pressure Trials in Obesity.

OBJECTIVES: Atelectasis develops in critically ill obese patients when undergoing mechanical ventilation due to increased pleural pressure. The current study aimed to determine the relationship between transpulmonary pressure, lung mechanics, and lung morphology and to quantify the benefits of a decremental positive end-expiratory pressure trial preceded by a recruitment maneuver. DESIGN: Prospective, crossover, nonrandomized interventional study. SETTING: Medical and Surgical Intensive Care Units at Massachusetts General Hospital (Boston, MA) and University Animal Research Laboratory (São Paulo, Brazil). PATIENTS/SUBJECTS: Critically ill obese patients with acute respiratory failure and anesthetized swine. INTERVENTIONS: Clinical data from 16 mechanically ventilated critically ill obese patients were analyzed. An animal model of obesity with reversible atelectasis was developed by placing fluid filled bags on the abdomen to describe changes of lung mechanics, lung morphology, and pulmonary hemodynamics in 10 swine. MEASUREMENTS AND MAIN RESULTS: In obese patients (body mass index, 48 ± 11 kg/m), 21.7 ± 3.7 cm H2O of positive end-expiratory pressure resulted in the lowest elastance of the respiratory system (18.6 ± 6.1 cm H2O/L) after a recruitment maneuver and decremental positive end-expiratory pressure and corresponded to a positive (2.1 ± 2.2 cm H2O) end-expiratory transpulmonary pressure. Ventilation at lowest elastance positive end-expiratory pressure preceded by a recruitment maneuver restored end-expiratory lung volume (30.4 ± 9.1 mL/kg ideal body weight) and oxygenation (273.4 ± 72.1 mm Hg). In the swine model, lung collapse and intratidal recruitment/derecruitment occurred when the positive end-expiratory transpulmonary pressure decreased below 2-4 cm H2O. After the development of atelectasis, a decremental positive end-expiratory pressure trial preceded by lung recruitment identified the positive end-expiratory pressure level (17.4 ± 2.1 cm H2O) needed to restore poorly and nonaerated lung tissue, reestablishing lung elastance and oxygenation while avoiding increased pulmonary vascular resistance. CONCLUSIONS: In obesity, low-to-negative values of transpulmonary pressure predict lung collapse and intratidal recruitment/derecruitment. A decremental positive end-expiratory pressure trial preceded by a recruitment maneuver reverses atelectasis, improves lung mechanics, distribution of ventilation and oxygenation, and does not increase pulmonary vascular resistance.

Optimization of Mechanical Ventilation in a 31-Year-Old Morbidly Obese Man With Refractory Hypoxemia.

Morbidly obese, critically ill patients are prone to develop hypoxemic respiratory failure and ventilator dependency. The best method for recruiting the lungs of these patients and keeping alveoli open without causing injury remains unclear. We present the case of a 31-year-old patient with severe refractory hypoxemia reversed by lung recruitment maneuvers and subsequent application of positive end-expiratory pressure (PEEP) at a level determined by a decremental PEEP trial. The patient was extubated at a high PEEP level of 22 cm H2O followed by noninvasive ventilatory support after extubation. This case suggests that a recruitment maneuver followed by PEEP titration is necessary in obese patients for optimizing mechanical ventilation. Extubation to noninvasive ventilatory support with the identified optimal PEEP may decrease an inappropriate increased work of breathing and the risk of reintubation.

Respiratory Management of Perioperative Obese Patients.

With a rising incidence of obesity in the United States, anesthesiologists are faced with a larger volume of obese patients coming to the operating room as well as obese patients with ever-larger body mass indices (BMIs). While there are many cardiovascular and endocrine issues that clinicians must take into account when caring for the obese patient, one of the most prominent concerns of the anesthesiologist in the perioperative setting should be the status of the lung. Because the pathophysiology of reduced lung volumes in the obese patient differs from that of the ARDS patient, the best approach to keeping the obese patient's lung open and adequately ventilated during mechanical ventilation is unique. Although strong evidence and research are lacking regarding how to best ventilate the obese surgical patient, we aim with this review to provide an assessment of the small amount of research that has been conducted and the pathophysiology we believe influences the apparent results. We will provide a basic overview of the anatomy and pathophysiology of the obese respiratory system and review studies concerning pre-, intra-, and postoperative respiratory care. Our focus in this review centers on the best approach to keeping the lung recruited through the prevention of compression atelectasis and the maintaining of physiological lung volumes. We recommend the use of PEEP via noninvasive ventilation (NIV) before induction and endotracheal intubation, the use of both PEEP and periodic recruitment maneuvers during mechanical ventilation, and the use of PEEP via NIV after extubation. It is our hope that by studying the underlying mechanisms that make ventilating obese patients so difficult, future research can be better tailored to address this increasingly important challenge to the field of anesthesia.

Endotracheal Tubes Cleaned With a Novel Mechanism for Secretion Removal: A Randomized Controlled Clinical Study.

INTRODUCTION: Intubation compromises mucus clearance, allowing secretions to accumulate inside the endotracheal tube (ETT). The purpose of this trial was to evaluate a novel device for ETT cleaning. We hypothesized that its routine use would reduce tube occlusion due to mucus accumulation, while decreasing airway bacterial colonization. METHODS: Subjects were randomized to either the use of the device every 8 h, or the institutional standard of care (blind tracheal suction) only. ETTs were collected at extubation and analyzed with high-resolution computed tomography (HRCT) for quantification of mucus volume. Microbiological testing was performed on biofilm samples. Vital signs and ventilatory settings were collected at the bedside. In-hospital follow-up was conducted, and a final evaluation survey was completed by respiratory therapists. RESULTS: Seventy-four subjects expected to remain intubated for longer than 48 h were enrolled (77 ETTs, 37 treatment vs 40 controls). Treated tubes showed reduced mucus accumulation (0.56 ± 0.12 vs 0.71 ± 0.28 mL; P = .004) and reduced occlusion (6.3 ± 1.7 vs 8.9 ± 7.6%; P = .039). The HRCT slice showing the narrowest lumen within each ETT exhibited less occlusion in cleaned tubes (10.6 ± 8.0 vs 17.7 ± 13.4%, 95% CI: 2-12.1; P = .007). Data on microbial colonization showed a trend in the treatment group toward a reduced ETT-based biomass of bacteria known to cause ventilator-associated pneumonia. No adverse events were reported. The staff was satisfied by the overall safety and feasibility of the device. CONCLUSION: The endOclear is a safe and effective device. It prevents luminal occlusion, thereby better preserving ETT nominal function.

Microbiome, biofilms, and pneumonia in the ICU.

PURPOSE OF REVIEW: Lower respiratory tract infections remain one of the leading causes of death in the world. Recently, the introduction of molecular methods based on DNA sequencing and microarrays for the identification of nonculturable microorganisms and subspecies variations has challenged the previous 'one bug - one disease' paradigm, providing us with a broader view on human microbial communities and their role in the development of infectious diseases. The purpose of this review is to describe recent understanding of the role of microbiome and bacterial biofilm in the development of lung infections, and, at the same time, to present new areas of research opportunities. RECENT FINDINGS: The review describes recent literature in cystic fibrosis patients, chronic obstructive pulmonary disease patients, and literature in mechanically ventilated patients that helped to elucidate the role of microbiome and biofilm formation in the development of pneumonia. SUMMARY: The characterization of the human microbiome and biofilms has changed our understanding of lower respiratory tract infections. More comprehensive, sensitive, and fast methods for bacterial, fungal, and viral detection are warranted to establish the colonization of the lower respiratory tract in healthy individuals and sick patients. Future research might explore the global bacterial, fungal, and viral pulmonary ecosystems and their interdependence to target novel preventive approaches and therapeutic strategies in chronic and acute lung infections.

Evaluation of the Infection-Related Ventilator-Associated Events Algorithm for Ventilator-Associated Pneumonia Surveillance in a Trauma Population.

BACKGROUND: The Centers for Disease Control and Prevention have recently introduced new ventilator-associated pneumonia (VAP) surveillance on the basis of the infection-related ventilator-associated complication (IVAC) definition. We aim to evaluate the accuracy of this new IVAC algorithm for detecting VAP according to the 2008 Centers for Disease Control and Prevention/National Healthcare Safety Network (NHSN) definition as the reference diagnosis (VAP-NHSN) in high-risk trauma patients. METHODS: This retrospective single-center study included all trauma subjects who were admitted to the ICU, required mechanical ventilation for >48 h, and received a blood transfusion. The new IVAC surveillance and the criteria for VAP-NHSN diagnosis were applied. The accuracy of the new IVAC surveillance for detecting VAP-NHSN was determined, and the clinical outcomes were compared between groups. RESULTS: The sensitivity, specificity, and positive and negative predictive values of IVAC for VAP-NSHN identification were 28.12%, 91.45, 58.06%, and 75.14%, respectively. Subjects with IVAC, VAP-NHSN, or both had higher morbidity when compared with those without IVAC and VAP-NHSN. Subjects with IVAC only had lower morbidity compared with those with VAP-NHSN only or those with both IVAC and VAP-NHSN. There was no significant difference in clinical outcomes between subjects with VAP-NHSN only and those with both IVAC and VAP-NHSN. CONCLUSIONS: IVAC criteria had a low accuracy for identifying VAP-NHSN in subjects with high-risk trauma.

Recruitment Maneuvers and Positive End-Expiratory Pressure Titration in Morbidly Obese ICU Patients.

OBJECTIVE: The approach to applying positive end-expiratory pressure in morbidly obese patients is not well defined. These patients frequently require prolonged mechanical ventilation, increasing the risk for failed liberation from ventilatory support. We hypothesized that lung recruitment maneuvers and titration of positive end-expiratory pressure were both necessary to improve lung volumes and the elastic properties of the lungs, leading to improved gas exchange. DESIGN: Prospective, crossover, nonrandomized interventional study. SETTING: Medical and surgical ICUs at Massachusetts General Hospital. PATIENTS: Critically ill, mechanically ventilated morbidly obese (body mass index > 35 kg/m(2)) patients (n = 14). INTERVENTIONS: This study evaluated two methods of titrating positive end-expiratory pressure; both trials were done utilizing positive end-expiratory pressure titration and recruitment maneuvers while measuring hemodynamics and respiratory mechanics. Measurements were obtained at the baseline positive end-expiratory pressure set by the clinicians, at zero positive end-expiratory pressure, at best positive end-expiratory pressure identified through esophageal pressure measurement before and after a recruitment maneuver, and at best positive end-expiratory pressure identified through a best decremental positive end-expiratory pressure trial. MEASUREMENTS AND MAIN RESULTS: The average body mass index was 50.7 ± 16.0 kg/m(2). The two methods of evaluating positive end-expiratory pressure identified similar optimal positive end-expiratory pressure levels (20.7 ± 4.0 vs 21.3 ± 3.8 cm H2O; p = 0.40). End-expiratory pressure titration increased end-expiratory lung volumes (Δ11 ± 7 mL/kg; p < 0.01) and oxygenation (Δ86 ± 50 torr; p < 0.01) and decreased lung elastance (Δ5 ± 5 cm H2O/L; p < 0.01). Recruitment maneuvers followed by titrated positive end-expiratory pressure were effective at increasing end-expiratory lung volumes while decreasing end-inspiratory transpulmonary pressure, suggesting an improved distribution of lung aeration and reduction of overdistension. The positive end-expiratory pressure levels set by the clinicians (11.6 ± 2.9 cm H2O) were associated with lower lung volumes, worse elastic properties of the lung, and lower oxygenation. CONCLUSIONS: Commonly used positive end-expiratory pressure by clinicians is inadequate for optimal mechanical ventilation of morbidly obese patients. A recruitment maneuver followed by end-expiratory pressure titration was found to significantly improve lung volumes, respiratory system elastance, and oxygenation.

Comparison of Dexmedetomidine and Clonidine as Adjuvants to Local Anesthetics for Intrathecal Anesthesia: A Meta-Analysis of Randomized Controlled Trials.

The authors performed a meta-analysis to compare the characteristics of clonidine and dexmedetomidine as adjuvants to local anesthetic in intravertebral anesthesia. Four investigators independently searched electronic databases for randomized trials comparing the characteristics of clonidine vs dexmedetomidine as adjuvants to local anesthetic on adults. The endpoints were onset of analgesia, sensory and motor block, and duration of analgesia. A random-effects model was used to perform quantitative analysis. Seven studies comprising 354 subjects were included in this meta-analysis. The onset of sensory block was significantly 40 seconds shorter when dexmedetomidine was added as an adjuvant in the intrathecal injection. The duration of stable sensory block, duration of overall sensory block, and the time before the need for analgesic requirements were significantly extended, 10.8 minutes, 22.3 minutes, and 38.6 minutes, respectively, when dexmedetomidine was used as an adjuvant to local anesthetics (bupivacaine or ropivacaine). No significant differences were detected in the motor block characteristics and the time to achieve peak sensory level between dexmedetomidine and clonidine as adjuvants to local anesthetics. Compared to clonidine, the addition of dexmedetomidine as an adjuvant to local anesthetics is associated with earlier, prolonged sensory block characteristics and later need for analgesic requirements.

Assisted mechanical ventilation: the future is now!

Assisted ventilation is a highly complex process that requires an intimate interaction between the ventilator and the patient. The complexity of this form of ventilation is frequently underappreciated by the bedside clinician. In assisted mechanical ventilation, regardless of the specific mode, the ventilator's gas delivery pattern and the patient's breathing pattern must match near perfectly or asynchrony between the patient and the ventilator occurs. Asynchrony can be categorized into four general types: flow asynchrony; trigger asynchrony; cycle asynchrony; and mode asynchrony. In an article recently published in BMC Anesthesiology, Hodane et al. have demonstrated reduced asynchrony during assisted ventilation with Neurally Adjusted Ventilatory Assist (NAVA) as compared to pressure support ventilation (PSV). These findings add to the growing volume of data indicating that modes of ventilation that provide proportional assistance to ventilation - e.g., NAVA and Proportional Assist Ventilation (PAV) - markedly reduce asynchrony. As it becomes more accepted that the respiratory center of the patient in most circumstances is the most appropriate determinant of ventilatory pattern and as the negative outcome effects of patient-ventilator asynchrony become ever more recognized, we can expect NAVA and PAV to become the preferred modes of assisted ventilation!

Actigraphic monitoring in critically ill patients: preliminary results toward an "observation-guided sedation".

PURPOSE: The aim of this study is to evaluate continuous wrist actigraphy (measurement of limb movements) in intensive care unit patients as a neurologic status monitoring. MATERIALS AND METHODS: This is a prospective, observational study on motor activity of adult patients using wrist actigraphs. Nurses recorded the number of sleep and agitation hours as well as assessed pain and anxiety level (verbal numeric rating) and the agitation/sedation level (Richmond Agitation-Sedation Scale). RESULTS: Thirteen mechanically ventilated patients were studied during their whole intensive care unit stay (total, 165 patients/d). The number of surveyed movements was gathered for each hour, obtaining an estimation of patient motor status. This measure was different between days and nights (33.3 [20.3-49.0] vs 8.5 [4.4-13.8]; P < .001), with a correlation with sleeping hours estimated by nurses (P = .017 during the days [D], P < .001 during the nights [N]), agitation hours (P = .002 D, P = .017 N), Richmond Agitation-Sedation Scale value (P < .001 D and N), pain (P = .012 D), and anxiety (P < .001 D) verbal numeric rating. No differences were found using epochs of 15 or 120 seconds. Compliance with patients and nurses was acceptable. CONCLUSIONS: Patients' limb movements were significantly related to all studied neurologic status indexes. Continuous actigraphy measuring may become important as a clinical tool both to guide utilization of sedative drugs and to enhance early recognition and management of agitation.