How to ventilate obese patients in the ICU

Abstract

Obesity is an important risk factor for major complications, morbidity and mortality related to intubation procedures and ventilation in the intensive care unit (ICU). The fall in functional residual capacity promotes airway closure and atelectasis formation. This narrative review presents the impact of obesity on the respiratory system and the key points to optimize airway management, noninvasive and invasive mechanical ventilation in ICU patients with obesity. Non-invasive strategies should first optimize body position with reverse Trendelenburg position or sitting position. Noninvasive ventilation (NIV) is considered as the first-line therapy in patients with obesity having a postoperative acute respiratory failure. Positive pressure pre-oxygenation before the intubation procedure is the method of reference. The use of videolaryngoscopy has to be considered by adequately trained intensivists, especially in patients with several risk factors. Regarding mechanical ventilation in patients with and without acute respiratory distress syndrome (ARDS), low tidal volume (6 ml/kg of predicted body weight) and moderate to high positive end-expiratory pressure (PEEP), with careful recruitment maneuver in selected patients, are advised. Prone positioning is a therapeutic choice in severe ARDS patients with obesity. Prophylactic NIV should be considered after extubation to prevent re-intubation. If obesity increases mortality and risk of ICU admission in the overall population, the impact of obesity on ICU mortality is less clear and several confounding factors have to be taken into account regarding the "obesity ICU paradox".

Keywords: ARDS; COVID-19; HFNC; Mechanical ventilation; NIV; Obese; Obesity; Prone position; Prone positioning.

Fig. 1

Impedance changes due to regional ventilation in a patient with obesity. Thoracic transversal electric impedance tomography images show impedance changes due to regional ventilation summarized for tidal ventilation cycles in a patient with a body mass index of 57 kg/m². Images were recorded during spontaneous breathing before intubation (a) and about 1 h after extubation (c) in a patient without lung pathology. Note the ventral shift of ventilation during mechanical ventilation with a positive end-expiratory pressure (PEEP) of 5 cmH₂O (b), which is likely due to atelectasis formation in dependent lung areas. Obviously, the PEEP level was insufficient to keep the lung open

Fig. 2

Effect of obesity in main pressures of the respiratory system. The respiratory system includes the lung and the chest wall, and the airway pressure is related to both transpulmonary and transthoracic pressures, which differ in the patient with obesity compared to the patient without obesity. The relative part of pressure due to transthoracic pressure is often higher in the patient with obesity than in the patient without obesity (elevated pleural pressure, which can be estimated by esophageal pressure). The plateau pressure represents the pressure used to distend the chest wall plus lungs. In patients with obesity, elevated plateau pressure may be related to an elevated transthoracic pressure, and not an increase in transpulmonary pressure with lung overdistension. FRC functional residual capacity

Fig. 3

Prone positioning in patients with obesity. ARDS acute respiratory distress syndrome. PaO₂/FiO₂ pressure of arterial oxygen to fractional inspired oxygen concentration

Fig. 4

Main respiratory physiological modifications and suggestions for mechanical ventilation in critically ill patients with obesity. The main respiratory physiological modifications (functional residual capacity decreased, abdominal pressure often increased, pulmonary and chest wall compliance often decreased, cephalic ascension of diaphragm, oxygen consumption and work of breathing increased) lead to shunt via atelectasis and gas exchange impairment. Comorbidities are often associated with obesity: obstructive apnea syndrome and obesity hypoventilation syndrome. Consequences on airway management, potentially difficult, include the preparation of adequate material for difficult intubation as videolaryngoscopes, preoxygenation with noninvasive ventilation in a semi-sitting position, considering adding apneic oxygenation (OPTINIV method), rapid sequence induction and recruitment maneuver following intubation after hemodynamic stabilization. Ventilatory settings include low or limited tidal volume (6–8 ml/kg/PBW or less), moderate to high PEEP (7–20 cmH₂O) if hemodynamically well tolerated, recruitment maneuver (if hemodynamically well tolerated, in selected patients), monitoring of esophageal pressure if possible, use of prone positioning in a trained team in case of severe ARDS, without contra-indicating ECMO. After extubation, CPAP or NIV should be considered early, as implementation of positive pressure therapies at home after evaluation. PBW predicted body weight, PEEP positive end-expiratory pressure, ARDS acute respiratory distress syndrome, ECMO extracorporeal membrane oxygenation, CPAP continuous positive airway pressure, NIV noninvasive ventilation, HFNC high-flow nasal cannula oxygen