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.

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SummaryWith 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.

Rationale: Obesity is characterized by elevated pleural pressure (P PL) and worsening atelectasis during mechanical ventilation in patients with acute respiratory distress syndrome (ARDS). Objectives: To determine the effects of lung recruitment maneuver (LRM) in the presence of elevated P PL on hemodynamics, left and right ventricular pressures and pulmonary vascular resistance. We hypothesized that elevated P PL protects the cardiovascular system against high airway pressures and prevents lung overdistension. Methods: First, an interventional crossover trial in adult subjects with ARDS and BMI≥35 kg/m 2 (n=21) was performed to explore the hemodynamic consequences of LRM. Second, cardiovascular function was studied during low/high PEEPs in a model of swine with ARDS and high P PL (n=9) versus healthy swine with normal P PL (n=6). Measurements and Main Results: Subjects with ARDS and obesity (BMI=57±12 kg/m 2) following LRM, required an increase in PEEP of 8[7, 10] cmH 2 O above traditional ARDSnet settings to improve lung function, oxygenation and ventilation/perfusion matching, without impairment of hemodynamics or right heart function. ARDS swine with high P PL demonstrated unchanged transmural left ventricle pressure and systemic blood pressure after LRM protocol. Pulmonary artery hypertension decreased 8[13, 4] mmHg, as did vascular resistance 1.5[2.2, 0.9] WU, and transmural right ventricle pressure 10[15, 6] mmHg during exhalation. LRM and PEEP decreased pulmonary vascular resistance and normalized ventilation/perfusion ratio.

Objectives: The impact of tidal volume (V T) on outcomes in mechanically ventilated children with pediatric acute respiratory distress syndrome (PARDS) remains unclear. To date, observational investigations have failed to calculate V T based on standardized corrections of weight. We investigated the impact of V T on mortality and probability of extubation in PARDS using ideal body weight (IBW)-adjusted V T. Design: Retrospective analysis of an ongoing prospective cohort of PARDS patients. V T was calculated based on actual body weight (ABW) and two different formulations of IBW. Setting: Pediatric intensive care unit at a large, tertiary care children's hospital. Patients: PARDS patients on conventional ventilation with a documented height or length. Interventions: None. Measurements and Main Results: There were 483 patients with a measured height or length at PARDS onset included in the final analysis, with 73 (15%) non-survivors. At 24 hours, there remained 400 patients on conventional ventilation. When calculating V T based on IBW by either method, volumes were larger both at onset and at 24 hours compared to V T based on ABW (all p < 0.001) and the proportion of patients being ventilated with tidal volumes > 10mL/kg based on IBW was larger both at onset (12.4% and 15.5%) and 24 hours (10.3% and 11.5%) compared to ABW at onset (3.5%) and 24 hours (4.0%) (all p < 0.001). V T , based on both ABW and IBW, was not associated with either increased mortality or decreased probability of extubation after adjusting for oxygenation index in the whole cohort, while associations between higher V T and poor outcomes were seen in subgroup analyses in overweight children and in severe PARDS.

In 39 critically-ill subjects intubated with silver-coated ETTs, periodical cleaning maneuvers did not decrease bacterial colonization of the ETTs and did not lower respiratory tract colonization compared to the standard suctioning.

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