LUNG ULTRASOUND AS AN ASSESSMENT TOOL FOR THE INDICATION OF NONINVASIVE MECHANICAL VENTILATION AFTER CARDIAC SURGERY.

Autores:
¹ Marcelo Azeredo Terra;
² Michele Vaz Canena;
³ Nágela Simão Vinhosa Nunes;
⁴ Sérgio Nogueira Nemer.

¹Mestre em Ciências da Atividade Física e Fisioterapeuta rotina da Unidade CardioIntensiva do Complexo Hospitalar de Niterói.
²Mestre em neurociência Doutoranda em ciências da saúde, fisioterapeuta do hospital universitário Dr. Miguel Riet Corrêa Júnior.
³Mestre em Cardiologia pela UFF, Médica plantonista da Unidade Coronariana do HUAP, Médica responsável pelo Serviço de Síncope do CHN
⁴Doutor em pneumologia pela Universidade de São Paulo, especialista em Fisioterapia respiratória e neurológica.

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Abstract

Background: The aim of this study was to verify whether LUS can assist in indication of NIV in patients undergoing CS and whether this has an impact on the length of stay in the Intensive Care Unit (ICU) and hospital. Methods: An observational, retrospective study was conducted for compare data among patients in the postoperative period of CS who used or not NIV after evaluation with LUS. The normality of the variables was tested by the Shapiro-Wilk test. The significance level was considered p=0.05 in the Mann Whitney test. Results: 111 patients (men, n.83) were included and divided into two groups. Group 1 (n.74) patients who used NIV and in Group 2 (G2 n.37) those who did not. The duration of mechanical ventilation, length of stay in the ICU and hospital were, respectively: (G1) 11.3 ± 30.3 X (G2) 6.3 ±8.2 hours (p=0.002); (G1) 6.7 ±6.2 X (G2) 4.7 ±2.0 days (p=0.01) and (G1) 14.4 ±12.3 X (G2) 11.4 ±9.9 days (p=0.02). Conclusions: Results of this study suggest that LUS makes it possible to early identify pulmonary complications and facilitate indication of NIV to reverse dysfunctions of the respiratory system in patients undergoing CS.

Keywords Lung Ultrasound, Lung Complications, Cardiac Surgery, Physiotherapy, Noninvasive Mechanical Ventilation.

Introduction

Cardiac surgery (CS) has as main objectives, the reduction of symptoms, increase in survival, and improve the quality of life of cardiac patients [1-3]. Even though adverse effects and mortality in the postoperative period have been reduced due to advances in modern surgery, pulmonary complications after the surgical procedure alter the function of the respiratory system and are often associated with adverse outcomes [4-5]. The main pulmonary complications in the postoperative period of CS are atelectasis, pleural effusion, pneumonia, and pulmonary congestion. Their incidence depends on the criteria adopted for diagnosis, around 15.8% [4-6-7].

The early identification of pulmonary dysfunctions caused by postoperative complications is of extreme importance for the proper initiation of treatment. The assessment with lung ultrasound (LUS) seems to influence the decision-making in postoperative [8]. When compared to other evaluation methods, such as chest radiography or computed tomography, LUS has advantages such as no radiation exposure, low cost, and the provision of dynamic images in real time at the bedside which facilitates the appropriate treatment choice.

LUS is considered a precise tool in the diagnosis of pulmonary complications in the postoperative period, with a specificity of 82.8% and a sensitivity of 95.5% [9]. Noninvasive ventilation (NIV) is indicated to revert the pulmonary dysfunction resulting from these complications [10]. Thus, LUS could provide important complementary information for the proper indication of NIV, sometimes avoiding its inappropriate use. Therefore, this study aimed to analyze whether the evaluation of pulmonary aeration by USP for the indication of NIV in patients undergoing CS caused an impact on the length of stay in the ICU and in the hospital.

Methods

Study Design and Subjects. This is a cross-sectional, observational, retrospective, and unicentric study of data analysis from medical records obtained through the assessment of pulmonary aeration with LUS of patients undergoing elective CS from January 2016 to August 2020 and who were admitted to the Cardiac ICU of the Niterói Hospital Complex – Rio de Janeiro – Brazil. The study was approved by the Human Research Ethics Committee under the number 3360532; CAAE 13906419.8.0000.5283. Patients of both genders were included, with age over 18 years old and submitted to elective CS [Myocardial revascularization (MR), valve replacement (VR), combined surgery (MR + VR) and other surgical procedures (aneurysmectomy, myxoma removal, atrioplasty, closure of interatrial communication and aortic aneurysm repair)] via median sternotomy and who used cardiopulmonary bypass during the procedure.

The following exclusion criteria were adopted: patients who were not assessed with LUS after the surgical procedure during the ICU stay, those who were not tolerant to NIV for the treatment of pulmonary dysfunctions because they presented claustrophobia when wearing the mask or other complaints, those who presented some hemodynamic disorder such as refractory hypotension (systolic pressure < 90 mmHg), as well as those who died in the ICU after CS.

Lung Ultrasound Protocol. The SonoSite M-Turbo device (FUJIFILM SonoSite Inc. Bothell, WA – USA) with 5-10 MHz curvilinear transducer (L38xi) was used for LUS assessment. The assessment was performed on the first postoperative day, here considered the first 24 hours after the patient\’s arrival in the ICU, later daily assessments were performed for follow-up during the ICU stay until discharge to the ward.

The assessment was performed with the patient in a semi-inclined position, with the head of the bed elevated from 30° to 45°, suggested by the international consensus on pulmonary ultrasonography published by Volpiceli and collaborators [11] entitled \”International evidence based recommendations for point-of-care lung ultrasound\”, which defined the use of eight-regions of the chest as positive criteria for examination, with 4 regions of each hemithorax. It was also used in a study that replaced the original Lung Ultrasound Score protocol with the mLUSS [12].

The scoring system adopted distinguishes four patterns of lung aeration as follows: normal aeration (Profile A; presence of lines A and less than two isolated lines B), moderate loss of lung aeration (Profile B; more than two lines B spaced and well defined), severe loss of lung aeration (Profile B\’; multiple coalescing lines B) and pulmonary consolidation (Profile C; presence of pulmonary consolidation). Scores from 0 to 3 points were assigned respectively to the four categories (0 point for Profile A, 1 point for Profile B, 2 points for Profile B\’ and 3 points for Profile C) and for each region, the worst visible pattern was recorded (table 1). The total score for all areas ranged from 0 to 24 points, Table1 [27].

In the assessment, a scan was performed in the anterior region of the chest, delimited by the parasternal line and the anterior axillary line, and also divided into upper and lower regions, separated by the line at nipple height, where we observe the areas: (1) anterosuperior and (2) anteroinferior, and in the lateral region of the thorax delimited by the anterior axillary line and the posterior axillary line also divided into upper and lower where we observe the areas: (3) upper lateral and (4) lower lateral.

LUS was performed by an intensive care physiotherapist with experience in the use of the tool and later by an intensive care cardiologist who also has experience for data confrontation. We consider experienced with the use of LUS intensivists who performed more than 100 bedside examinations in the ICU, as suggested by Reissig and collaborators in their study [28]. The analyzed data that had consensus among the evaluators were computed in the medical records with the total score of each patient. Patients who presented moderate to severe alteration of lung aeration besides areas of consolidation started the NIV protocol.

Non-Invasive Ventilation Protocol. The NIV protocol was initiated early by the physiotherapist, after analysis of the results of the two evaluators with LUS. Patients with NIV indications were guided through the procedure before its initiation, being adapted to a face mask (HSiner noninvasive ventilation face mask number 5) connected to a mechanical ventilator (Dräger SAVINA® 300 Dräger Medical, Lübeck, Germany) in the NIV preadjusted pressure support mode. The daily assessment occurred until discharge from the ICU, so in the presence of any hemodynamic complication, such as a drop in StO2 < 90%, increased work of breathing, RR greater than 30 ipm, use of accessory muscles of respiration, even without indication with the mLUSS protocol, the NIV was initiated on any day other than the first postoperative.

Statistical Analysis. The categorical variables were described by percentage and the numerical ones by mean and standard deviation. The statistical tests used for the categorical variables were the chi-square test, and the t or Mann-Whitney U tests for the numerical variables. The normality of the variables was tested by the Shapiro-Wilk test.

It was considered a 95% significance level, using the Stata version 16 program.

Results:

Subjects characteristics. Elective CS was performed within the selected study period, from January 2016 to August 2020, in 220 patients and only 126 patients were evaluated with LUS. Fifteen patients were excluded due to intolerance to the use of NIV (n. 11) or death (n. 4). The final sample consisted of 111 patients, 75 men (67.5%), with an average age of 59.9 ± 11.7 years, submitted to MR (n.45), VR (n.43), combined surgery (n.13), and other procedures (n.10), with mean CPB time of 75.3 ± 28.6 minutes, expressed in Table 2. The patients were divided into two groups: group 1 (G1 n.74), patients who after assessment with LUS used NIV, and group 2 (G2 n.37) patients who did not make use of NIV, represented in Table 2.

Incidence of pulmonary complications. In the total population studied, 57 (51.3%) patients had one or more pulmonary complications. The complications detected with LUS were pleural effusion (43%), atelectasis (30%), pulmonary consolidation (21%), pulmonary congestion (2.7%) and pneumothorax (1.8%). The patients presented with pneumothorax after surgery were contraindicated for the use of NIV, and were thus excluded from the study, Table 2.

Analysis of the results. The average time of invasive MV use after ICU arrival was (G1)

11.3 ± 30.3 h and (G2) 6.3 ± 8.2 h, (p=0.002). The length of stay in ICU was: (G1) 6.7 ±

6.2 days and (G2) 4.7 ± 2.0 (p=0.017), and hospital stay: (G1) 14.4 ± 12.3 days and (G2)

11.4 ± 9.9 days, (p=0.022). After the implementation of LUS for the assessment of patients, there was a reduction of 33.3% in the number of NIV procedures compared to the previous protocol used in this ICU. The number of patients who were readmitted to the ICU after discharge to the ward for presenting some postoperative pulmonary complication was: (G1) n.19 (33%) and (G2) n.6 (11%) patients, (p=0.261). The results are expressed in Table 3.

Discussion

This study retrospectively analyzed the impact of using pulmonary assessment, by ultrasound, on the indication or none of NIV and if modified the length of stay of patients after CS, both in the ICU and in the total hospital stay.

Currently, the two most prevalent types of CS are myocardial revascularization and valve replacement [1]. In this study, the majority of the sample, 88 (79%) patients, were submitted to these procedures. Surgical interventions are part of the procedures for the therapeutics of cardiac patients. This type of intervention may involve alterations in the pulmonary parenchyma and in the breathing biomechanics, which, when early identified and treated, result in a better prognosis of the patient.

The CPB time is a factor of increased morbidity in the postoperative period of CS. The mean CPB time of the patients analyzed in this study (75.3 ± 28.6 minutes) is in accordance with what we find in the literature as normal (risk increased to time > 90 minutes), and the occurrence of pulmonary complications in the postoperative period is also in agreement with the literature in this type of intervention, around 51.3% of patients [11-13].

Factors that have an important impact on the morbidity and mortality of these patients are pulmonary complications that can be related to several factors. Cavayas and collaborators in a sample of 115 patients observed an incidence of 29.6% of postoperative respiratory system complications, including atelectasis, pneumonia, and prolonged MV. These complications were associated with a longer ICU and hospital stay [5]. These complications were also observed in the study of Alcântara and NavesSantos [14], where the incidence of pleural effusion was 57% and atelectasis ranged from 10% to 70% of patients undergoing CS. In our study, we observed as postoperative complications the pleural effusion (43%) and the atelectasis (30%) in higher incidences and it seems to have significantly influenced the results regarding the ICU and hospital length of stay. Patients who presented these complications stayed longer in the ICU and the hospital.

Daniel Lichtenstein and collaborators described the diagnostic accuracy of LUS of 93% for pleural effusion, 97% for alveolar consolidation, and 95% for alveolar-interstitial syndrome, compared with lung auscultation and the chest radiograph [22]. The efficacy of LUS, greater than the traditional methods of lung aeration assessment, such as lung auscultation and chest radiography, are already well documented. Touw and collaborators [5] identified in 177 patients, 159 (90%) pulmonary complications on the day of hospitalization, compared to 107 (61%) identified with chest radiographs (p <0.001). They also observed that LUS identified 11 out of 17 patients (65%) and radiography 7 out of 17 patients (41%) with clinically relevant postoperative pulmonary complications (p <0.001). Thus, LUS can be used with primary imaging technique for evaluation of postoperative pulmonary complications and evolutionary follow-up of patients in the ICU.

Bouhemad and collaborators [23] were the first ones to propose the Lung Ultrasound Score (LUSS) protocol to calculate the patterns of lung aeration in patients with pneumonia associated MV. In subsequent studies, this score was used to predict the outcome of weaning from MV [24-25], with promising results. However, its applicability for the indication of NIV in patients undergoing CS has not yet been described. The reduced length of ICU stay seems to be related to reduced mortality. Ramos and collaborators [13] observed that the mean time of 3 days of ICU stay of patients undergoing CS is a protective factor for death, about 5.4% of the population studied. However, an interesting fact found in this study was a longer length of stay in the ICU compared to the previously mentioned study, an average of 6 days of ICU stay, with lower mortality, only 3% of the studied population.

Among the most commonly used procedures during ICU stay to treat pulmonary dysfunctions caused by postoperative complications is NIV, which in many units have pre-established closed protocols of prophylactic use, however, the use of this resource depends on the adequate assessment of these dysfunctions. Lung aeration assessed with bedside ultrasound seems to influence the decision making of the physiotherapist after identifying postoperative complications for the correct indication of NIV. The results of this study showed that not all patients need NIV after CS with median sternotomy and use of CPB. Also, patients who did not use NIV after assessment with LUS showed a reduction of ICU and hospital length of stay.

In our ICU, patients submitted to CS participated in a pre-established NIV protocol, where all, without exception, performed NIV in 3 periods of 60 minutes during the first 3 days after orotracheal extubation. However, the use of NIV protocols, without the appropriate indication, may provide an increase in the length of stay of these patients and may contribute to increasing mortality and comorbidities related to the hospital stay. With the implantation of USP for assessment of postoperative lung aeration of CS, the number of interventions with NIV was reduced by 33%, and good indicators were presented, such as earlier withdrawal of the patient from bed and the tendency to reduce the length of hospital stay.

The efficacy of NIV, in the postoperative period, seems to depend on the establishment of an institutional program, with proper patient identification, understanding of risks and benefits, and a continuing education program for professionals involved in the election of this therapy [15-17]. Recommendations of the European Respiratory Society and American Thoracic Society (ERS/ATS), through the guideline of clinical practices of NIV, describes that this therapy should be used to reverse the condition of acute respiratory failure in patients, providing improvement in lung capacity and a decrease in breathing work, but also mentions that, in many cases, the supply of adequate oxygen therapy could solve this adversity [15-18].

Its use is controversial, in the same way that an improvement in the pulmonary clinical condition is observed, with a reduction in the length of hospital stay and a contribution to lowering mortality rates, its use, without adequate indication and well-defined protocol, may increase the length of hospital stay and increase the probability of new complications [10,19,20].

Finally, the indication of NIV in a protocol manner where all patients submitted to CS make indiscriminate use seems not to be the best alternative. The efficacy and safety of NIV through the conventional management of closed protocols were not confirmed in patients after CS [15]. The point-of-care ultrasound (POCUS) has gained wide acceptance in the last decades in the ICU [8-27], with increasing use in the assessment of lung aeration and can be useful as an assessment tool for the indication of NIV, with the advantage of enabling continuous patient follow-up, allowing daily assessments in real time, important factors to improve the indication of NIV in the treatment of patients who evolve with pulmonary dysfunction after CS.

This study presents some limitations: as a retrospective study carried out in a single ICU, the variables were extracted from the patients\’ records, some variables may have been affected by causality and information bias. The group with a longer stay in ICU and hospital may have been affected by CPB and MV time. The time of both factors may interfere in the appearance of pulmonary complications and thus in the indication of NIV, providing an increased number of interventions and length of stay in therapy. It is suggested that prospective observational studies should be conducted in order to control the outcome variables. Another limitation presented in our study was the fact that some patients did not tolerate the pre-established NIV time of 60 minutes

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