Detection of Residual Pulmonary Alterations With Lung Ultrasound and Effects on Postoperative Pulmonary Complications for Patients With Asymptomatic SARS-CoV-2 Infection Undergoing Surgeries

Susana González-Suárez; Antonio Barbara Ferreras; Melissa Caicedo Toro; Macarena Aznar de Legarra


BMC Anesthesiol. 2022;22(186) 

In This Article


Ethics Statement and Registration

The Ethics Committee approved this prospective observational single-center study at the Vall d'Hebron University Hospital, Barcelona, Spain (PR (AG)346/2020) and retrospective registered at on June 11, 2021 (registration number: NCT04922931). All participants signed written informed consent forms before enrolment in the study. All methods were carried out following relevant guidelines and regulations.

Study Design and Participants

We defined post-COVID-19 patient as a patient who previously had a positive PCR test from oronasopharyngeal swab, and then had one negative test performed at least 4 days before surgery and the absence of symptoms (fever, dyspnea, cough, and digestive disorders) at time of surgery.

We included all consecutive post-COVID-19 patients ≥ 18 years underwent various elective surgery (general surgery, urology, neurology, otolaringology, gynecology, cardiac, thoracic, and vascular surgery) and anesthetic techniques (general, local, neuraxial and peripheral regional anesthesia) from June 30, 2020, to February 18, 2021. Moreover, the included patients did not have baseline pulmonary pathology prior to COVID-19.

Exclusion criteria were as follows: patients under the age of 18 years old, pregnant, patients with hemodynamic instability parameters (mean arterial pressure < 60 mmHg and need for vasopressors), patients undergoing pulmonary surgery (lung neoplasms) or who previously had chest surgery, patients with pulmonary pathology before SARS-CoV-2 infection (obstructive or restrictive pulmonary pathology), patients with a documented medical history of any degree of pulmonary arterial hypertension (both primary or secondary), heart failure or active respiratory infection. Figure 1 shows the flow diagram of the inclusion/exclusion process.

Figure 1.

Flow diagram of exclusion/inclusion criteria

Pulmonary Ultrasonography Procedure and Determination of Pulmonary Static Compliance

The anesthesiologists used the Sonosite portable ultrasound system and a 2- to 5 MHz convex transducer for lung ultrasound (LUS) procedure. During study researchers utilized higher frequencies for evaluation of the pleural line to determine pleural thickening (defined as being greater than 3 mm in width, with or without irregular margins)[12] as well as a linear probe 6–15MHz if it was deemed necessary. The scanning system included the approach of 10 thoracic areas with 5 in each hemithorax. Specifically, areas 1 and 2 denoted the upper anterior and lower anterior chest areas respectively; areas 3 and 4 denoted the upper lateral and basal lateral chest areas, respectively, and area 5 denoted posterior area located posterior of the axillary line, at the point at which the diaphragm and adjacent lung segment were accessible in a supine position with slight lateralization of the patient. The anterolateral areas were delimited by three longitudinal lines: para-sternal line, anterior axillary line, and posterior axillary line. A breast line delimited the upper and lower areas resulting in five punctures of exploration (modified from Volpicelli et al..[13]

During the LUS procedure, the probe was placed vertically perpendicular to the ribs at a depth of 9–12 cm in the anterior plane and 12–20 cm in the lateral plane, and the focus was placed at the pleural level.

During operation, the static compliance was determined by respirators (Drager Perseus A500 and MAQUET ventilator) in patients with general anesthesia. The controlled ventilation was performed with tidal volumes of 7ml/kg adjusted for ideal body weight, with a PEEP (Positive End-Expiratory Pressure) of 5 mm Hg and in a neuromuscular blocking state after orotracheal intubation in a supine position. The static compliance value was calculated depending on the formula that is available in anesthesiology textbook[14] as follows: Cs = VT/P plateau – PEEP where Cs denotes static compliance, VT denotes tidal volume, and P plateau denotes plateau pressure.

Study Outcomes

We used as the main outcome the proportion of patients having the residual pulmonary alterations detected by lung ultrasound and static pulmonary compliance before operation, and the relationship between these injuries with the clinical course of SARS-CoV-2 infection (cough, dyspnea, fever, digestive disorders, pneumonia, thrombotic-associated complications (PTE, myocardial infarction, stroke, venous thrombosis), ARDS, need for mechanical ventilation, need for vasoactive drugs and days of hospitalization and admission to Intensive Care Unit).

The secondary outcomes were the postoperative occurrence of respiratory complications during hospital stay (ARDS, PTE, pneumonia, pneumothorax, atelectasis, bronchospasm) and determine whether the incidence of residual pulmonary injuries detected before surgery are associated with the appearance of PPC.

Other secondary outcome measures were the correlation between static pulmonary compliance and B-lines and correlation between lung compliance values and the time elapsed between COVID-19 diagnosis and surgery. Other outcomes for the postoperative period were 30-day survival after surgery; hospital stay; need for IMV and NIMV; need for an emergent intubation.[15] Other outcomes for the postoperative complications were: the influence of the ASA, surgical complexity and type of anesthesia on the incidence of PPC, occurrence of postoperative non-pulmonary complications (PnPC) (need for vasoactive drugs, transfusion requirements, need for a second surgery, thrombotic-associated complications (upper or lower extremity ischemia, intestinal ischemia, acute myocardial infarction and stroke), non-pulmonary infections, acute kidney injury, arrhythmias and heart failure).

Data Collection

We collected demographic characteristics, baseline comorbidities, American Society of Anesthesiologists (ASA) physical status classification, baseline characteristics of the COVID-19 presentation and the number of days from COVID-19 diagnosis to surgery.

LUS data collection comprised the presence of atelectasis, pleural effusion, B lines, pleural thickening, and the presence of both, ≥ 3 B-lines and pleural thickening.

The operative data collected included the static pulmonary compliance values in patients who received general anesthesia, the type of anesthesia performed, the type of surgery, and the risk of surgery according to the National Institute for Clinical Excellence (NICE) classification of the National Health Service UK.

Postoperative data collected included 30-day survival after surgery, hospital stay, need for IMV and NIMV, emergent intubation, type of PnPC and type of PPC.

All items that could be used to identify the patient (clinical record ID number or name) were removed to protect personal data.

Data Measurement

For LUS, each region was scored according to four LUS aeration patterns inspired by Lichtenstein's nomenclature:[16] 0 points—presence of lung sliding with A-lines or one or two isolated B-lines; 1 point—moderate loss of lung aeration with three or four B- lines; 2 points—severe loss of lung aeration with five or more B-lines; and 3 points—presence of a hypoechoic poorly defined tissue characterized by complete loss of lung aeration. The LUS score ranging between 0 and 30 was calculated as the sum of points.

For surgical risk, we classified the surgical procedures according to the following grades:

  1. I: Minor surgical procedures: poor surgical aggressiveness, surgery with low probability of bleeding or easily detectable bleeding (excision of adenopathies, herniorrhaphys, amputation of fingers, lithotripsy, prostate biopsy).

  2. II: Medium surgical procedures: greater probability of bleeding and/or if it occurs could go unnoticed by developing in a cavity (thyroidectomy, embolectomy, tonsillectomy, transurethral resection, tracheostomy, laparoscopy surgery for general, ginecology and urology surgeries).

  3. III: Major surgical procedures: most important degree of surgical aggressiveness with prolonged postoperative need (peripheral bypass-bypass, spinal arthrodesis, laminectomy, open surgery (for resection of the digestive tract, cystectomy, nephrectomy).

  4. IV: Very aggressive surgical procedures: prolonged surgeries with very specialized or critical care in the postoperative period, (open cardiac surgery, aortic surgery, intracranial surgery, aggressive neoplastic surgery (pelviperitonectomy).

We used the following definitions for PCP:

  • ARDS detected by hypoxemia with a relationship between the arterial partial pressure of oxygen and the fraction on inspired oxygen (PaO2/FiO2) less than 200, and bilateral pulmonary infiltrates in both fields on a chest radiograph.

  • PTE was diagnosed by dyspnea clinic and chest computed tomography angiography (CT angiography).

  • Pneumonia when the patient received antibiotics for a suspected respiratory infection and met at least one of the following criteria: fever, new lung opacities, leukocyte count >12.000/μ.

  • Atelectasis when the patient presented lung opacification with a shift of the hilum, hemidiaphragm, or mediastinum toward the affected area on a chest radiograph.

  • Bronchospasm, when the patient presented expiratory wheezing, treated with bronchodilators.

  • Pneumothorax, when the patient presented air in the pleural space on a chest radiograph.

The PnPC were recorded as reported by the attending physicians.

Data Sources and Management

Data was either collected prospectively by the research team (ultrasound findings and pulmonary static compliance) and retrospectively by the research team (clinical course of SARS-CoV-2 infection and postoperative data). Retrospective data were obtained from the patient's medical records.

Statistical Analysis

For categorical variables, frequencies and percentages were displayed for the total sample. Differences in parameters were calculated with Pearson's Chi-squared non-parametric test. The mean, standard deviation, and percentile descriptive were displayed for continuous variables. Differences in parameters were evaluated by Mann-Whitney (non-parametric) test or Student's t tests for two independent (parametric) samples based on the normality of the variables to be tested using the Shapiro-Wilks test. Spearman's correlation coefficient was employed to measure the correlation between two variables. The level of significance used in the analyses was 5% (α-0.05) for two- tailed tests.