Is the Perioperative Change in Ultrasound-based Diaphragmatic Inspiratory Amplitude Predictive of Postoperative Atelectasis: A Prospective Observational Study in Obese Patients Undergoing Bariatric Surgery
Phase: NA
Conditions: Postoperative Pulmonary Atelectasis, Morbid Obesity
Sponsor: University of Roma La Sapienza

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Title: Is the perioperative change in ultrasound-based diaphragmatic inspiratory amplitude 
predictive of postoperative atelectasis? A prospective observational study in obese 
patients undergoing bariatric surgery. 
Protocol 994/19 
 
 

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Introduction 
Obese patients undergoing bariatric surgery, are at high risk for postoperative respiratory 
complications but predictive variables, risk factors and criteria for postoperative ICU admission are 
debated (1-3). In these patients, postoperative respiratory complications are related to various 
pathophysiological mechanisms that include: decreased lung volumes, respiratory muscle 
dysfunction and atelectasis (4). Very recently it has also been demonstrated a possible role of 
molecules that would mediate the fibro-adipogenic remodeling of the diaphragm in the obese, thus 
increasing the respiratory disability (5). 
Pulmonary atelectasis appears within minutes after anesthesia induction, complicate 85-90% of 
the cases -involving up to 15% of the lungs and inducing a 5 to 10% of cardiac output intra 
pulmonary shunting- and determine an increased incidence of postoperative morbidity (with higher 
incidence of pneumonia) (6-11). Furthermore, in the perioperative period, obese patients are more 
likely to develop atelectasis that resolves more slowly than in non-obese patients (12). Surgical 
handling of sub diaphragmatic region, as during sleeve gastrectomy, can impair diaphragmatic 
excursions thus contributing to postoperative pulmonary dysfunction (12-17). The same upper 
abdominal surgery represents a risk factor for the development of pulmonary complications in the 
perioperative period and alteration of the respiratory function indices (18).  
Ultrasounds (US) imaging is a real-time, bedside, non-invasive technique that allows the 
quantitative evaluation of amplitude, force and velocity of diaphragmatic movement, including: 
diaphragmatic inspiratory amplitude (DIA) and diaphragmatic thickening (19). The US-DIA is a 
qualified quantitative approach to assess diaphragmatic function and has been reported to linearly 
correlate with vital capacity (20-26). In obese patients undergoing sleeve gastrectomy there are no 
conclusive criteria for discharge and indications to postoperative ICU admission, as recently 
defined for patients with OSAS (27,28). We hypothesize that perioperative change in US-DIA 

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predicts postoperative atelectasis, thus providing a clinically useful tool to stratify the need for 
higher intensity monitoring including ICU admission (3,27).  
Aim of this prospective observational study, in obese patients undergoing sleeve 
gastrectomy, is to evaluate the relationship between pre to postoperative changes in US-DIA and 
PaO2/FiO2. 
 
Methods 
After IRB approval from the University of Rome and having the patient’s written consent, 40 
consecutive patients morbidly obese (BMI >30 Kg/m2), aged >18 years, undergoing laparoscopic 
sleeve gastrectomy will be enrolled in this prospective observational study. Exclusion criteria will 
be any of the following: sign and symptoms of heart failure, neuromuscular diseases or previous 
thoracic surgery, American Society of Anesthesiology physical (ASA) status >III.  
 
Study protocol 
Perioperative monitoring will include continuous 3-lead electrocardiogram, heart rate (HR), 
invasive (arterial line) systolic, diastolic and mean arterial pressure (MAP), SpO2, end-Tidal CO2, 
end-Tidal desflurane, diuresis and body temperature. In all patients anesthesia will be induced, 
according available guidelines, with propofol (2 mg/kg of IBW) and fentanyl (2 mg/kg of IBW) (4). 
To facilitate endotracheal intubation and mechanical ventilation, neuromuscular block will be 
induced with rocuronium dose (0.6 mg/kg) based on the patient’s real body weight, and will be 
monitored throughout anesthesia using an acceleromyographic train-of-four stimulus to the 
adductor pollicis (3). After anesthesia induction trachea will be intubated, and mechanical 
ventilation with intermittent positive pressure ventilation (IPPV) will be started at a Tidal volume of 
7 mL/kg of IBW and with 12 breaths per minute. Lungs will be ventilated with air/O2 mixture to 
keep PaO2 between 100 and 200mm Hg. After the beginning of mechanical ventilation, desflurane 
will be started maintaining a minimum alveolar concentration (MAC) of 6% and a fresh gas flow of 

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3.0 l/min. Intraoperative normothermia will be warrant with forced air systems. The total amount of 
remifentanil infused through a dedicated venous line during the surgical procedure will be 
recorded. At the end of anesthesia, neuromuscular block will be reversed with sugammadex. The 
dose of sugammadex used will depend on the level of neuromuscular block to antagonize 
according to the following modalities. If the recovery from the rocuronium-induced block will reach 
a value of at least 1-2 PTC (Post tetanic count), the dose of sugammadex used will be 4 mg/kg 
bw. In the presence of a spontaneous recovery reached until the reappearance of T2 the dose 
used will be 2mg/kg. The median time to restore a value of 0.9 of the ratio T4/T1 will be registered, 
then inhalational anesthesia will be discontinued. After skin closure and reversal of neuromuscular 
block, desflurane administration will be stopped and to speed up anesthetic washout the fresh gas 
flow will be increased to 10 l/min. Postoperatively, supplemental O2 will be provided with the 
minimal FiO2 needed to keep SpO2 >93% as prescribed by guidelines on OSAS (27). 
 
Measurements  
Demographics (age, gender, BMI) and clinical characteristics including: ASA and comorbidities 
and pre and post operative respiratory function [PaO2/FiO2 ratio, Blood gas analysis (BGA)] and 
US-DIA will be recorded. These data will be collected according to time sequence: 
T0: preoperative <24hours before surgery: US-DIA, BGA while the patient is breathing minimal 
supplement FiO2 needed to keep SpO2 >93%. 
T1: Post op: at 60 min after extubation: Aldrete, US-DIA, BGA. 
T2: Post op at 240 min: Aldrete, BGA. 
Occurrence and severity of postoperative atelectasis, duration of surgery, RASS, Aldrede score, 
VAS, intraoperative fluid balance, premedication and intraoperative use of opioids and 
neuromuscular blocking drugs used will be also recorded. 

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Primary endpoint will be to detect the relationship between perioperative changes in DIA during 
forced breath and occurrence and severity of postoperative atelectasis (PaO2/FiO2) at 240 min 
after extubation (T2).  
Secondary endpoints will be: amount of muscle relaxants, opioids and fluids used intraoperatively,  
BGA at T0, T1 and T2 with PaCO2 and ph, difference in pre and postoperative DIA during a quite  
breath, incidence of pneumonia at second postoperative day, LOS, needs of postoperative ICU 
recovery, mortality at hospital discharge.  
 
Ultrasound evaluation 
In eligible patients, a preoperative baseline ultrasound evaluation of the diaphragm and lungs is 
accomplished. A Philips HD7X3 (Philips Medical Systems, Bothell, WA, USA) US machine will be 
used and equipped with a 4 MHz convex probe. Evaluation will be performed by a single operator, 
blinded to the arterial blood gas analysis values. In a semi recumbent position (bed slope of 45°) 
patients will be asked to rest and breath quietly with their eyes closed. An anterior approach will be 
carried out applying freehand transducer on abdomen at the right midclavicular line immediately 
below the costal margin with firm pressure, steering in cranial direction. A B-mode transverse 
scanning will be performed looking across the liver for inferior vena cava (IVC) on the right of the 
screen and gallbladder in the middle. Measurements will be recorded by the M-mode frozen 
images using the US machine calibration and algorithm. The M-mode modality will be used to 
study DIA, regulating the lowest possible gain setting to enhance the trace: the best sinusoidal 
curve will be considered for measurements. During resting and forced breathing, measurement of 
DIA will be recorded drawing a vertical line from the leading edge of the inspiratory peak on the 
sinusoidal curve to the leading edge of the imaginary horizontal line passing through the baseline, 
corresponding to the end of normal expiration. The inspiratory and expiratory times will be finally 
measured both during resting (t0, t1 respectively) and forced breathing (T0, T1 respectively). 

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Moreover, to reduce the measurement error and calculate the intraobserver variability, every 
recording will be taken three times, both during resting and forced breathing: the highest value of 
these three measurements will be considered. Data on pre and post operative spirometry will be 
recorded when available. 
 
 

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