3.4 York等[18]的研究表明:对于极低出生体重儿,动脉血氧饱和度波动是ROP的高危因素,其研究的数据亦未给出适宜的血氧饱和度波动幅度。血氧饱和度波动幅度与ROP的发生是否有关系,如果有关系,在多大幅度的波动下,能更好的降低ROP的发病率。
3.5 Askie等[19]做了一项系统评价,仅有1个试验符合这个系统评价,即Bedrossian1954。试验包括的是出生体重低于4磅的婴儿。这些婴儿的胎龄没有统计。第1天,一部分婴儿就停止供氧。符合标准的婴儿住院时就被登记。登记的内容:被分配到每一组的数量、随机分配后的死亡情况和追踪的丢失情况。生存的、符合标准的婴儿,试验组(缓慢停氧)24例,对照组(突然停氧)25例。结果是RR 0.22, 95% CI(0.07~0.68),突然停氧和缓慢停氧对ROP的发生无统计学意义。结论是:结合对易发生ROP的早产儿和低出生体重儿早期暴露于高氧中这个系统评价的结果提供了另外的证据。然而,由于数据不足和传统的血氧监测技术,尚不能提供更多的关于在现代新生监护设备的条件下对于逐渐停氧和骤然停氧最适宜的方法的证据。
3.6 如果能保证血氧在安全范围内,早和晚停氧是否与ROP发病率有关,早和晚的界定如何。Askie等[20]做了一项系统评价,仅有1个试验符合这个系统评价,即Engle 1955,结果:早和晚停氧对ROP的发生无统计学意义[RR 3.06,95% CI (0.31~73.34)]。结论是:这个系统评价没有提供一个有利的证据证明在早产儿和低出生体重儿中,早期停氧是有益还是有害。将来的研究方向应该是对早期新生儿和晚期新生儿寻找适合血氧饱和度范围,而不是早停氧还是晚停氧的问题。
3.7 动脉氧分压、经皮氧分压和经皮氧饱和度与ROP关系的研究。早期通过控制吸氧浓度来预防视网膜病变并认为吸氧浓度<40%是比较安全的[21],但由于吸入氧浓度并不能真正反映出体内组织的氧含量,于是人们开始用动脉导管置管法来监测动脉氧分压,由于这是一种有创性的检查方法,且不能持续监测,于是持续经皮氧分压监测法得到了广泛的应用,并发现出生4周内如果用这种方法测出的氧分压>80 mm Hg(1 mm Hg=0.133 kPa),则视网膜病变的发生率较高[22],而目前在临床上采用最多的是脉冲式血氧定量法,即利用双色光电比色法测定动脉血中的血氧饱和度,采用此原理的血氧饱和度监测仪因其无创的优点的确免去了反复穿刺动脉的麻烦,不过必须注意使用这种方法测得的血氧饱和度和实际动脉氧饱和度及氧分压是有一定差异的,如测得氧饱和度在85%~94%时通常表示氧分压波动在50~70 mm Hg;然而当氧饱和度指示94%时,氧分压波动的范围可以为9~17 kPa,如果以氧分压80 mm Hg为诱发视网膜病变阈值,则测得的血氧饱和度94%时,实际的血氧分压都有可能超过该阈值[23]。另外,Tin等[24]调查了英国100家医疗机构设定的氧饱和度上下限报警值,并发现视网膜病变的发生和血氧饱和度上下限报警值有一定的关系。
综上所述,就目前对ROP与吸氧关系诸多问题的研究现状和相关数据来看,彻底解决这些问题,需要多中心前瞻性研究才能完成,这是解决吸氧与ROP因果关系诸多问题的科学、有效、快速的方法。首先,进行多中心前瞻性研究,尽快解决上述问题,以给临床医生初步的用氧规范;第二,以上述结果为依据,生产持续经皮氧分压监测仪、经皮氧饱和度监测仪厂家应对其仪器进行校对,找出动脉氧分压与经皮氧分压和经皮氧饱和度之间的关系,并将结果提供给各医院,各医院在应用持续经皮氧分压监测仪和经皮氧饱和度监测仪的过程中再次对动脉导管置管法的氧分压与持续经皮氧分压和氧饱和度的关系进行校对,在试验结果达到统计学意义的时候,将结果在核心期刊上公布。同时进一步间断进行资料搜集,以进行累积Meta分析,更好地指导临床用氧。
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