The evolution of approach in the resuscitation of neonates born with meconium-stained amniotic fluid: a tale of two countries, China and U.S.A., in the past 60 years

Abstract

Neonates born through meconium-stained amniotic fluid (MSAF) may develop complications including meconium aspiration syndrome, persistent pulmonary hypertension of newborn and death. The approach to the resuscitation of these neonates has significantly evolved for the past few decades. Initially, under direct visualization technique, neonates with MSAF were commonly suctioned below the vocal cords soon after delivery. Since 2015, Neonatal Resuscitation Program (NRP^®) of the American Academy of Pediatrics has recommended against "routine" endotracheal suctioning of non-vigorous neonates with MSAF but favored immediate resuscitation with positive pressure ventilation via face-mask bagging. However, the China neonatal resuscitation 2021 guidelines continue to recommend routine endotracheal suctioning of non-vigorous neonates born with MSAF at birth. This review article discusses the differences and the rationales in the approach in the resuscitation of neonates with MSAF between Chinese and American NRP^® guidelines over the past 60 years.

Meconium-stained amniotic fluid (MSAF) is a condition in which neonates have passed meconium in amniotic fluid, and this happens in 5% to 15% of all deliveries^[1], among which 8% to 20% of neonates are depressed and non-vigorous^[2-3]. It was reported that 3% to 5% of neonates born through MSAF developed meconium aspiration syndrome (MAS)^[4]. Studies have found that MSAF is associated with fetal death^[5-6], stillbirth^[7], abnormal fetal heart rate tracings and low Apgar scores^[5]. Neonates with MAS may also have airway obstruction, neonatal hypoxic-ischemic encephalopathy, neonatal sepsis, and seizures^[6]. Hence, the approach in the resuscitation of neonates with MSAF in delivery room is very important^[8-9]. Two major interventions were (routinely) used including the suctioning of the oropharynx and nasopharynx at birth and postnatal intubation with endotracheal suctioning of MSAF. The latter procedure has been used traditionally to clear the airway and to decrease MAS^[10-11]. However, recommendations for these practices have changed several times in the past 60 years due to emerging evidence that the procedures were not beneficial and might even be harmful. This review discusses the consensus of science that supports the current recommendations in U.S.A. and China.

1. Review methods

A detailed review of guidelines from the Neonatal Resuscitation Program^® (NRP^®) of the American Academy of Pediatrics (AAP) and the American Heart Association (AHA), the International Liaison Committee on Resuscitation (ILCOR) and Consensus on Science and Treatment Recommendations (CoSTR) was conducted. Guidelines from Department of Maternal and Child Health and Community Health, China Neonatal Resuscitation (CNR) Program Task Force, and AAP/AHA textbooks of neonatal resuscitation were also obtained for reference.

2. The evolution of NRP^® management of neonates born with MSAF in U.S.A

The first reference to tracheal suctioning dates back to 1960 when Dr. Stanley James^[12] postulated in a neonatal resuscitation textbook that "if meconium had been aspirated into trachea, it should be suctioned out" and affirmed by a prospective study by Gregory et al^[10] in 1974. This study by Gregory et al included 88 neonates with MSAF (8.8%) in a cohort of 1 000 consecutive live neonates born during a period of 6 months. Glottis visualization, intubation and endotracheal suctioning was performed in 80 neonates. The authors observed that a total of 46 cases (57%) with meconium in the trachea (0.5~7.7 mL). Although they did not report the incidence of MAS in these 88 neonates with MSAF who all survived, 16 (all had meconium in trachea) were sick who required supplemental oxygen or pneumothorax or pneumomediastinum. Gregory et al commented that "The mere presence of meconium in the trachea does not necessarily presage respiratory problems. Two thirds of those neonates from whom meconium was recovered had no respiratory difficulties, although half had abnormal chest roentgenograms"^[10]. In 1976, Carson et al^[11] compared the incidence of MAS in 273 neonates with MSAF who received intrapartum or opharyngeal and nasopharyngeal suctioning before the delivery of shoulders with that of 947 historic controls (no intrapartum suctioning) and reported a significantly lower incidence of MAS in the study group (1/273[0.4%] vs18/947[1.9%] of controls, P<0.05). These studies contributed to adopting universal intrapartum suctioning of the oropharynx and nasopharynx and postnatal intubation with endotracheal suctioning for thick or particulate meconium as standard of care for neonates born through MSAF and has been included in Textbook of Neonatal Resuscitation from 1987 to 1994 (1^st, 2^nd and 3^rd edition of AAP NRP^® textbooks^[13-15]). However, in 1988, Linder et al^[16] performed a single center randomized controlled trial (RCT) to evaluate the effect of intubation and suctioning on 572 vigorous neonates delivered vaginally with MSAF. Endotracheal suctioning did not decrease the incidence of MAS and there were some complications (hoarseness, stridor) related to intubation of vigorous neonates in the delivery room. This was the initial evidence that endotracheal intubation and suctioning might not be beneficial to vigorous neonates, but international guidelines on neonatal resuscitation did not change.

In 2000, Wiswell et al^[17] reported the findings of a large international RCT which evaluated the effects of intubation of 2 094 apparently vigorous full term neonates born through MSAF regardless of consistency. The study showed that intubation and endotracheal suctioning of MSAF in the vigorous infant was not beneficial (Supplementary Table 1), leading to the new 2000 guidelines^[18] and the 4^th edition textbook of Neonatal Resuscitation^[19]: limited endotracheal intubation and suctioning to non-vigorous neonates; and stopped routine intubation and endotracheal suctioning in vigorous neonates with MSAF.

Table 1.

Comparison of resuscitation algorithms between U.S.A. and China for neonates born through meconium-stained amniotic fluid

Nation	Category of neonatal resuscitation guidelines/textbook of neonatal resuscitation	Algorithm
U.S.A.	1st edition,textbook of neonatal resuscitation(1987)[13]	(1) Meconium thin, watery: no special management; (2) Meconium thick, particulate: suction mouth,oropharynx and hypopharynx at the perineum as soon as head is delivered by a suction catheter. On radiant warmer, clear hypopharynx, intubate and suction trachea under direct visualization. Repeat till clear.
	2nd edition, textbook of neonatal resuscitation (1990)[14]	Same as above and to minimize hypoxia when suctioning, free flow oxygen should be provided via oxygen tubing.
	3rd edition, textbook of neonatal resuscitation (1994)[15]	(1) Suction mouth, pharynx at the perineum as soon as head is delivered; (2) Thin meconium with active infant: no special management; (3) Thin meconium with depressed infant or thick particulate meconium: clear hypopharynx, intubate and suction trachea under direct visualization.
	4 th edition, textbook of neonatal resuscitation, and guideline of AHA/AAP (2000)[18-19]	Suction the mouth, pharynx, and nose as soon as the head is delivered (intrapartum suctioning) regardless of whether the meconium is thin or thick. Either a large-bore suction catheter (12 F to 14 F) or bulb syringe can be used. Vitality of MSAF neonates is evaluated then. Vigorous: clear mouth and nose of secretion, keep warming, drying and stimulate. Non-vigorous: suction mouth and suctioning of residual meconium from the hypopharynx (under direct vision) and intubation/suction of the trachea.
	5 th edition, textbook of neonatal resuscitation (2006), guidelines of AHA/AAP (2005) [22-23]	(1) No longer advise routine intrapartum oropharyngeal and nasopharyngeal suctioning; (2) Endotracheal suctioning for infants who are not vigorous should be performed immediately after birth.
	6 th edition, textbook of neonatal resuscitation (2011), guideline of AHA/AAP/ILCOR (2010) [24-25]	Same as above
	7 th edition, textbook of neonatal resuscitation (2016), guideline of AHA/AAP/ILCOR (2015) [26-27]	(1) Vigorous: gentle clearing of meconium from the mouth and nose with a bulb syringe may be done if necessary; (2) Non-vigorous: PPV should be initiated if the infant is not breathing or the heart rate is less than 100/min after the initial steps of resuscitation are completed. Routine intubation for tracheal suction in this setting is not suggested; (3) Appropriate intervention to support ventilation and oxygenation should be initiated as indicated for each individual infant. This may include intubation and suction if the airway is obstructed.
	8 th edition, textbook of neonatal resuscitation (2021), guideline of AHA/AAP/ILCOR (2020) [38-40]	(1) Routine oral, nasal, oropharyngeal, or endotracheal suctioning of newly born babies is not recommended; (2) For non-vigorous newborns (presenting with apnea or ineffective breathing effort), routine laryngoscopy with or without tracheal suctioning is not recommended; For non-vigorous newborns who have evidence of airway obstruction during PPV, intubation and tracheal suction can be beneficial.
China	1st edition, suggestions of resuscitation of neonatal asphyxia (1965)[46]	Preliminary mentioned
	2nd edition, suggestions of resuscitation of neonatal asphyxia (1983)[47]	(1) Suction mouth, pharynx, nose at the perineum as soon as head is delivered; (2) Hold the chest tightly to avoid breathing or crying for all MSAF newborns; (3) Suction residual meconium from the hypopharynx under direct vision by a suction catheter or a long cotton swab to roll out the thick meconium. Intubation/suction of the trachea for massive MSAF below the cords might also be required and repeated until the endotracheal suctioning was clear. No stimulation should be performed before the suction became clear completely.
	3rd edition, suggestions of resuscitation of neonatal asphyxia (1994)[50]	Same as 1983
China	4th guideline of resuscitation of neonatal asphyxia (2005)[57]	(1) Suction mouth, pharynx and nose at the perineum as soon as head is delivered. Vitality of MSAF neonates is evaluated then; (2) Vigorous: continue to initial resuscitation; (3) Non-vigorous: endotracheal intubation and suctioning by a meconium aspirator.
	5th guideline ofresuscitation of neonatal asphyxia (2007)[59]	(1) Stop routine intrapartum oro-nasopharyngeal suctioning before shoulders delivered;. (2) Vitality of MSAF neonates is evaluated first after birth, regardless thin or thick meconium; (3) Vigorous: continue to initial resuscitation; (4) Non-vigorous: endotracheal intubation and suctioning with a meconium aspirator.
	6th guideline of neonatal asphyxia (2011)[60]	Same as 2007
	7th guideline of CNR (2016)[61]	(1) Stop routine intrapartum oro-nasopharyngeal suctioning before shoulders delivered. Clearing mouth and nose secretion with bulb syringe or a 12 F or 14 F suction catheter if needed (massive MSAF orairway obstruction); (2) Vitality of MSAF neonates is evaluated first after birth; (3) Vigorous: continue to initial resuscitation; (4) Non-vigorous: intubation and endotracheal suctioning with an aim to finish the procedure within 20 sec. If the practitioner is not competent in intubation within 20 sec and/or equipment is not available for non-vigorous neonates. PPV is suggested after quick suctioning of mouth and nose.
	8th guideline of CNR (2021)[62]	Same as 2016

Note: [AHA] American Heart Association; [AAP] American Academy of Pediatrics; [ILCOR] International Liaison Committee on Resuscitation; [MSAF] meconium-stained amniotic fluid; [PPV] positive pressure ventilation; [CNR] China neonatal resuscitation guidelines.

Later in 2004, a large landmark multicenter RCT^[20] in 11 hospitals in Argentina and one in U.S.A. including 2 514 full term neonates with MSAF showed that routine intrapartum oropharyngeal and nasopharyngeal suctioning was not beneficial. Based on this, the American College of Obstetricians and Gynecologists revised the guidelines in 2007^[21]: no longer advised routine intrapartum oropharyngeal and nasopharyngeal suctioning for neonates born to mothers with MSAF. Nevertheless, endotracheal intubation and suctioning for non-vigorous neonates was still recommended due to insufficient evidence to change practice in 2005 and 2010^[22-25].

NRP^® guidelines was revised in 2015^[26-27] and it recommended that routine intubation and endotracheal suctioning of non-vigorous neonates born through MSAF was not required, only if airway obstruction was suspected. The recommendation was based on 9 low quality observational studies^[28-36] which demonstrated no improvement in survival and/or incidence of MAS when neonates (both depressed and/or vigorous) born through MSAF were intubated for tracheal suctioning. After that, a RCT of 122 neonates^[37] showed no benefit in reducing mortality and/or MAS in non-vigorous neonates born through MSAF with endotracheal suctioning, compared with those neonates without endotracheal suctioning.

In 2020, NRP^® guideline in this approach of neonates born through MSAF was reaffirmed^[38-40] and supported by a systematic review^[41]: for non-vigorous neonates (presenting with apnea or ineffective breathing effort) delivered through MSAF, routine laryngoscopy with or without tracheal suctioning is not recommended because routine suctioning of the airway is likely to delay initiating ventilation. However, a low certainty of evidence was noted. A total of 812 patients were included, 581 came from the RCTs^[37,42-44] (Supplementary Table 2) and 231 from the observational study^[3]. All 4 RCTs were from India and were single center studies; the observational study was from U.S.A. and reported multi-center data. No significant differences were observed between the group treated with endotracheal suctioning compared with immediate resuscitation regarding survival at discharge, hypoxic ischemic encephalopathy and MAS. But some differences in the methodology and the patient characteristics were noted among the 4 RCTs. The intubation attempts were mostly performed by trainees in 4 RCTs and only 1 trial (Singh et al^[43]) used a meconium aspirator device. Details of the data on the success or complications of intubation were not provided. Late preterm neonates were included in 2 trials. Oropharyngeal suctioning was also performed before endotracheal suctioning in the Nangia et al^[42] and Kumar et al^[44] trials. Interestingly, the cohort study^[3] of 231 non-vigorous neonates born through MSAF at four centers in Texas compared neonatal intensive care unit (NICU) admissions among neonates ≥35 weeks' gestation before and after adoption of the 2015 guidelines and observed a statistically significant increase in admissions for respiratory distress or failure (40% vs 22%, OR=2.2, 95%CI=1.2-3.9) although the increase in admissions for MAS that was not statistically significant (11% vs 5%, OR=2.3, 95%CI=0.83-6.2). Furthermore, risks of imprecision and bias were high in these trials^[41], the recommendation was therefore classified as weak^[38].

3. The evolution of management of neonates born with MSAF in China and comparing CNR with NRP^® guidelines

Endotracheal intubation during the resuscitation of neonatal asphyxia in China was first described by Dr. Shi SZ in 1965^[45]. This study contributed to the recommendations of the resuscitation of neonatal asphyxia in 1965^[46] and was the initial reference on the management of neonates born through MSAF. After 20 years, the 2^nd edition of recommendations of the resuscitation of neonatal asphyxia was released and published in 1983^[47]. This edition first described the resuscitation in details including the suction of mouth, pharynx, nose at the perineum as soon as head was delivered and before delivery of the shoulder. It also suggested to hold the chest tightly to avoid breathing or crying for all neonates with MSAF, intubation and endotracheal suctioning before stimulation and repeated until the endotracheal suctioning was clear (Table 1). This proposal abandoned the methods used in old era and ushered in a new era of neonatal resuscitation in China^[48-49].

In 1994, the 3^rd edition of resuscitation of neonatal asphyxia was released without further changes while this guideline first suggested pediatric or neonatal physicians to attend the resuscitation in high risk deliveries with midwives^[50].

In 1995, a single-center retrospective cohort study^[51] observed 121 asphyxial neonates (74 with MSAF) with and without tracheal intubation, and found that there was no significant difference in the incidence of MAS between the two groups. However, the patients in the non-tracheal intubation group were more serious and needed ventilator-assisted ventilation for a longer time (76.5 h vs 16.25 h, P<0.05). Yu et al reported a lower mortality of MAS (6.25%) in comparison of their historical cohort^[52] (7.07%, 8 deaths in 113 cases of MSAF with endotracheal suctioning in 1985-1990). They concluded that endotracheal suctioning could avoid or shorten the duration of ventilator-assisted ventilation and reduce the mortality of MAS. Endotracheal lavage (2 mL of normal saline) was also used to dilute the thick meconium for difficult suction in this study. Later, there were several studies on the prevention and treatment of MAS by endotracheal lavage in China^[53-54]. The authors commented that although endotracheal suctioning of MSAF after birth could reduce the incidence of MAS in most neonates, i.e. the development of aspiration pneumonia and the prognosis was better, it could not solve the problem of in utero aspiration of meconium and MAS. Therefore, to better prevent MAS, it was not only necessary to timely and thoroughly clear the airway and to perform endotracheal suctioning after birth, but also more importantly to prevent and correctly manage fetal distress in utero ^[52].

In 2002, China's Ministry of Health identified perinatal asphyxia as a health priority and sought partners to develop an educational program to reduce intrapartum-related neonatal mortality^[55]. Due to the success and widespread implementation of the NRP^® in U.S.A. and other countries, the decision was to adopt and potentially adapt the NRP^® for use in China. Following this, China Neonatal Resuscitation Program Task Force was established in 2003^[56], and CNR Program was developed in 2004. The 4^th edition of resuscitation guidelines was drafted in 2005 in Beijing^[57] which was translated from NRP^® guidelines^[18] of AHA/AAP in 2000 (Table 1). Meconium consistency was no longer used as an indication for tracheal intubation. Vitality of MSAF neonates was first evaluated after birth, and endotracheal suctioning by meconium aspirator was used for non-vigorous neonates. This guideline first suggested the use of meconium aspirator. Comparing effects on neonates with thick MSAF treated by endotracheal suctioning (n=249) and by endotracheal lavage (n=246) in a RCT, Su et al^[58] found that the incidence of severe MAS was significantly lower in endotracheal suctioning group than that of endotracheal lavage group. There were no difference in the incidence and complications of MAS. The study provided evidence-based practice and promoted the widespread use of meconium aspirator in China.

After that, two revisions in the China guidelines of neonatal resuscitation^[59-60] were released and published in 2007 and 2011 which were the same as the NRP^® guidelines in 2005^[22] and 2010^[24].

As mentioned above that there was a significant change in the NRP^® guidelines in 2015 and 2020^{[26, 38]}, controversy has swirled since the guidelines were released. In addition to the observed increase in NICU admissions for respiratory distress or failure, Chiruvolu et al^[3] reported significantly higher proportions of neonates who needed oxygen therapy, mechanical ventilation, and surfactant therapy. There were no differences in the incidence of other outcomes including MAS. Another multicenter, large sample retrospective cohort study^[9] showed that in the subgroup of MSAF neonates with a 1-minute Apgar score ≤3, the use of surfactant in the non-intubation group was significantly higher than that in the endotracheal suctioning group (36.0% vs 27.7%, RR=1.30, 95%CI=1.09-1.55), inhaled nitric oxide treatment (21.9% vs 16.2%, RR=1.35, 95%CI=1.08-1.69) and the incidence of moderate to severe hypoxic-ischemic encephalopathy (20.1% vs 12.1%, RR=1.67, 95%CI=1.27-2.19). It suggested that the decrease in meconium suction rate after the implementation of the new guidelines was related to the concerning increase in the incidence of severe MAS and moderate to severe hypoxic-ischemic encephalopathy.

The 7^th edition of 2016 and the 8^th edition of 2021 CNR guidelines^[61-62] continued to recommend routine intubation and endotracheal suctioning for non-vigorous neonates born through MSAF with an aim to finish the procedure within 20 sec to minimize hypoxia. It however allows no intubation if the attending practitioner is not competent in intubation within 20 sec and/or equipment is not available. In the latter situation, immediate positive pressure ventilation (PPV) is suggested after quick suctioning of mouth and nose.

4. Discussion

Why is there a difference between the two latest versions of China and American guidelines in the resuscitation of non-vigorous neonates born through MSAF? We believe that the main reason is the rapid development of perinatal medicine and rapid improvement of resuscitation skills in China. Despite the decreasing neonatal mortality, the incidence of severe MAS remains high. Therefore, timely adjustments of China's resuscitation guidelines are required according to China's health care system.

A Lancet commission on women's reproductive, maternal, newborn, child, and adolescent health in China over the past 70 years was released in June 2021^[63]. In this report, since its establishment, China has made remarkable achievements in lowering maternal and children mortality. The maternal mortality rate has decreased from around 1 500 cases to 17.8 cases per 100 000 births in 1949 and in 2019, and the infant mortality rate has been lowered from around 200 cases to 5.6 cases per 1 000 births in 1949 and in 2019, respectively. The neonatal mortality rate in China was 4 folds of that of North America and European countries in 1990 but decreased to 1.7 times in 2015. Interestingly, it was shown that since the set-up of Neonatal Resuscitation Program Task Force in 2003 and the development of CNR program after 2004, the decrease in neonatal mortality rate was fast^[64]. The proportion of neonatal mortality out of infant mortality decreased from 71.63% in 2004 to 66.32% in 2013^[65].

However, China is a developing country, as in other low- and middle-income countries, with limited medical resources, inadequate perinatal surveillance, high rate of neglected pregnancies, and late second stage arrival of mothers with prolonged fetal distress^[66]. While the neonatal survival rate was increasing with the rapid improvement of resuscitation skills, the incidence of MAS and its complications remained high. The mortality of MAS was about 15%^[67] and up to 39.5% among severe MAS^[68]. In contrast, U.S.A. is a developed country with institutional deliveries, antenatal monitoring and universal perinatal surveillance during labor. The incidence of MAS has declined in developed countries due to improved obstetric practices and perinatal care^[66]. As early as 2000, the incidence of MAS in MSAF neonates was only 3% to 4%^[17,20], and the mortality of MAS was about 8%^[17]. A California Perinatal Quality Care Collaboration (CPQCC)^[69] database showed that the incidence of MAS in California was 1.02 per 1 000 births from 2013 to 2015, and decreased to 0.78 per 1 000 births in 2017. Based on the low incidence of MAS, the AAP/AHA considered more weight on the potential complications of endotracheal intubation (e.g. apnea, bradycardia, airway injury and stridor) and the risk due to a delay in starting PPV ^[38-40]. CPQCC showed that among MAS neonates, endotracheal intubation rate at delivery room decreased from 2013-2015 to 2017 (44.3% vs 35.1%; P=0.005), but similar proportions in invasive ventilation rate (80.1% vs 80.8%), inhaled nitric oxide rate (28.8% vs 28.4%), and extracorporeal membrane oxygenation (0.81% vs 0.35%), respectively^[69]. Although the incidence of MAS decreased, the incidence of severe MAS remained the same. China is composed of many provinces, cities, autonomous prefectures and counties. Due to the uneven economic development between the eastern and western regions, there is a significant difference in neonatal mortality between eastern and western regions (3.1 vs 9.5 per 1 000 live births, respectively)^[70]. Medical resources in the western regions and remote areas including conventional/high-frequency oscillatory ventilators, nitric oxide and other instruments and equipment are limited. Therefore, it is conceivable that it is difficult to treat severe MAS in the western regions and remote areas as that in developed countries, where the use of invasive ventilators was as high as 80% and the inhaled nitric oxide was nearly 30% as reported in California^[69]. In fact, the complications of endotracheal intubation were low. In addition, a manikin study recently showed a statistically significant but clinically irrelevant delay in starting PPV^[71]. Taken together, in China the concern with severe MAS outweighs the minimal risk of endotracheal intubation and suctioning and delay in starting PPV. Indeed, Su et al^[58] observed the severity of MAS was related to the amount of endotracheal MSAF suctioned. CNR therefore continues to recommend routine intubation and endotracheal suctioning in non-vigorous neonates with MSAF.

Nevertheless, the NRP^® recommendations^[38] imply some neonates born through MSAF may be benefited from endotracheal suctioning. It is important to further understand the rationale and pathophysiology of MSAF and MAS.

Meconium aspiration may occur before, during, or after delivery. It can result in partial airway obstruction with a ball-valve effect causing alveolar over-distension and air-leak or complete obstruction with atelectasis. Meconium in the alveoli can trigger inflammation, surfactant deficiency and pulmonary vasoconstriction leading to ventilation-perfusion mismatch and hypoxemic respiratory failure^[72], which can worsen acidosis. The fetal hypoxia and acidosis contribute to pulmonary vasoconstriction and vascular remodeling resulting in persistent pulmonary hypertension and severe hypoxemia. Asphyxia in neonates born through MSAF is commonly associated with MAS, contributes to ventricular dysfunction^[73], which causes refractory hypoxemia and complicates pulmonary hypertension secondary to intrapulmonary shunts (bronchial vasculature to pulmonary vein shunts that bypass the alveoli)^[74-75]. In short, while aspiration of MSAF is a perinatal event, breathing and/or immediate PPV may lead to rapid and distal migration of meconium. Endotracheal suctioning may potentially prevent such migration, but can also delay resuscitation of a compromised, hypoxic fetus. The clinical decision of intubation and endotracheal suctioning is a balance between hemodynamic and respiratory pathophysiology of meconium aspiration and consequences of delaying resuscitation and early administration of PPV^[75]. That is the rationale for the NRP^® approach against routine intubation and endotracheal suctioning in the resuscitation of non-vigorous neonates born with MSAF. As routine endotracheal suctioning of non-vigorous neonates is likely to delay initiating ventilation, it is important to first initiate ventilation as soon as possible in apneic or ineffectively breathing neonates born through MSAF. Should initial attempts in ventilation be unsuccessful then airway obstruction is probably the cause. Direct laryngoscopy inspection and suction should be considered. Some infant may require endotracheal intubation and suctioning to relieve airway obstruction^[38-40]. Interestingly, the amount of endotracheal suctioning of MSAF in non-vigorous neonates averaged 1.65 mL and ranged from 0.2 to 10 mL^[58]. Indeed, it was demonstrated that endotracheal suctioning of MSAF remained to be effective after PPV^[76].

In conclusion, we reviewed American and China resuscitation guidelines of neonates born through MSAF from 1960 to 2021. Recent studies do not support either benefit or risk of a strategy based on immediate laryngoscopy with or without endotracheal suctioning compared to immediate resuscitation for non-vigorous neonates delivered through MSAF, especially in the context of different health care systems. A large and high quality RCT for this question would be a challenging endeavor, and strategies that involve a cluster randomized approach are likely required. Meanwhile, large observational cohort studies may also provide further evidence of the approach that better improves neonatal resuscitation.

Supplementary Table 1 Comparison of RCT studies onoutcomes of neonates born through meconium-stained amniotic fluidand received routine tracheal intubation/suction(intervention) and no tracheal intubation/suction(control)

RCT study	Number of participants			Meconium consistency	Gestational age(week)		Death before discharge, n(%)		Respiratory complications				Intubation complications: stridor, n(%)		Low Apgar/HIE, n(%)		P value
									MAS, n(%)		Pneumothorax, n(%)
	Total	Intervention	Control		Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control
Linder[16] 1988	572	308	264	all	>37	>37	0	0	4(1)	0	1(0.3)	0	2(0.6)	0	-	-	<0.025a
Daga[#] 1994	49	26	23	thick	≥34	≥34	1(4)	0	-	-	1(4)	2(9)	-	-	HIE 1(4)	HIE 0	>0.05
Liu[70] 1988	169	77	92	thin	≥37	≥37	0	0	*	*	0	0	0	0	-	-	>0.05
Wiswell[17] 2000	2 094	1 051	1 043	all	≥37	≥37	3(0.3)	2(0.2)	34(3)	28(3)	0	0	-	-	Low Apgar at 1 min 36(4)	Low Apgar at 1 min 14(1)	<0.0018b

Note: [RCT] randomized controlled trial; [MAS] meconium aspiration syndrome; [HIE] hypoxic ischemic encephalopathy. ^a Respiratory complications and intubation complications were compared in intervention group and control group; ^b Low Apgar at 1 min was compared in intervention group and control group; * intervention group vs control group: 2/77(2.6) vs 1/92(1.1) had respiratory symptoms, respectively; ^[#] Daga SR, Dave K, Mehta V, et al. Tracheal suction in meconium stained infants: a randomized controlled study[J]. J Trop Pediatr, 1994, 40(4): 198-200. PMID: 7932931. DOI: 10.1093/tropej/40.4.198.

Supplementary Table 2 Comparison of RCT studies on outcomes of non-vigorous neonates born through meconium-stained amniotic fluidand received routine tracheal intubation/suction (intervention) and no tracheal intubation/suction (control)

RCT study	Number of participants			Gestational age (week)		Death, n(%)		Respiratory complications						P value
								MAS, n(%)		Pneumothorax, n(%)		PPHN, n(%)
	Total	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control
Chettri[37] 2015	122	61	61	≥37	≥37	10(16)	12(20)	20(33)	19(31)	1(2)	1(2)	4(7)	2(3)	>0.05
Nangia[42] 2016	175	87	88	≥37	≥37	9(10)	4(5)	28(32)	23(26)	2(2)	2(2)	-	-	>0.05
Singh[43] 2019	152	75	77	≥34	≥34	4(5)	7(9)	31(41)	44(57)	3(4)	2(3)	6(8)	7(9)	>0.05
Kumar[44] 2019	132	66	66	≥34	≥34	9(14)	5(8)	21(32)	15(23)	-	-	4(6)	2(3)	>0.05

RCT study	(a)Perinatal asphyxia, (b)HIE, n(%)		Need for respiratory support, including noninvasive and invasive, n(%)		Need for mechanical ventilation, n(%)		Duration of hospital stay (day) (mean±SD) (IQR)		P value
	Intervention	Control	Intervention	Control	Intervention	Control	Intervention	Control
Chettri[37] 2015	(a)19(31)	(a)17(28)	-	-	14(23)	15(25)	2.7±2.20	3.4±3.10	>0.05
Nangia[42] 2016	(b)28(32)	(b)27(31)	17(20)	15(17)	11(13)	8(9)	2.99±1.26	2.95±0.86	>0.05
Singh[43] 2019	20(27)	30(39)	-	-	11(15)	13(17)	9.91±3.06	11.17±3.73	>0.05
Kumar[44] 2019	(a)8(12)	(a)10(15)	48(73)	47(71)	9(14)	8(12)	2.25(1.3-5.9)	1.83(1.1-4.3)	>0.05

Note: [RCT] randomized controlled trial; [MAS] meconium aspiration syndrome; [HIE] hypoxic ischemic encephalopathy; [PPHN] persistent pulmonary hypertension of newborn.

Funding Statement

This study was funded by Shenzhen SanMing Project of Medicine (SZSM 201911016).