Maternal and cord blood at delivery

Maternal and cord blood at delivery Ill. Parameters of respiratory exchange (Apgar score)

J.

S E L W Y N C R A W F 0 R D , F . :\ A . . R . C: . S . *

Chicago, Illinoi1

tween thC' number of points scored and certain parameters of acid-base status. HowPver, it is now \vel! understood that clinically apparent dPpression of a neonate may rPstdt from two causes, acting together or separately: asphyxia and a drug. There has to date been no clear statement as to how these factors rnig·ht individually affect the constitution and the smn of the Apgar score, or of the influence of drng· activity on the correlation between total score and the severity of biochemical asphyxia. In this n•gard, it is a striking fact that, apparently. there has been little or no attempt to assess the significance of each of the component scores which go to provide thP total. The study presented here was undertaken in au at tempt to remedy these deficiences. The cases to be discussed, and the various methods of investigation employed, have been described in the initial paper in this series." Briefly, only cases in which a mature infant was delivered vaginally were studied. A loop of umbilical cord was secured between clamps immediately subsequeni w complete delivery of the infant. Samples of blood were rapidly obtained from the ttrnbilical \·ein and ttrnbilical artery. Analyses of the acid-base paranwters were carried out with the aiel of the Astrup apparatus. and OX)f(l'll saturatio11 was determined by means of the Kipp IH'mnrpflpctor. The Apgar scnn's \\'t'rt' assesst'tl. <1! pnTisclv 1 minute and !i tninutcs 'ml)S('(jllent lo complete delinT\', hv a singlf' observer, and were immediatE'Iy n·corded. togdher with the appropriate clinical data, 011 a specially designed card. The belief was expressed in the Parlier

T H ERE c AN be few who would deny that the introduction of the Apgar method of assessing the status of the newborn infant 1 was a spectacular contribution to the study and practice of perinatal care. As James 2 has remarked, one important effect has been to encourage clinicians to give increased attention to the child during the period immediately subsequent to delivery. A second advantage offPred by the systematized method of assessing the status of the infant has been the provision of a scale of measurement which permits, within limits, a comparison between neonates born in different institutions. Apgar and her associates 1 • 3 • 4 have demonstrated the meaningfulness of the latter point by showing that a negative correlation exists between the total points scored and the degree of asphyxia as evidenced by analyses of cord blood: that is, that there is an arithmetic relationship be-

From the Chicago Lying-in Hospital. The project was supported by the Otho S. A. Sprague Memoria/Institute Grant and by United States Public Health Service General Research Support Grant 1-501-FR-05367-01. Computations were accomplished with the assistance of the Biological Science.< Computation Center, University of Chicago, under United States Public Health Service Grant FR 00013, from the Division of Research Facilities and Resources, of the Nationalimtitutes of Health. The great assistance rendered by Mr. R. R. Blough in this regard is warmly acknowledged. *Present address: Research Department of Anaesthetics, Royal College of Sur.r?.eons of Enl!,land, Lincoln's Inn Fields, London,-W. C. 2, England.

382

Maternal and cord blood at delivery

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paper" that the points allotted for color in the original score provided no information of merit, and thus attention should be paid only to the Apgar minus color (A-C) score. It seems, therefore, fitting that an investigation of this matter be presented here first.

383

(Demerol) and, or, a single dose of tranquilizing agent). The possibility that cord around the neck might be associated with a change in the pattern of correlations was also investigated. Of the 73 cases in which meperidine had been administered, 20 had a nuchal cord. There was a cord around the neck in 26 of the 89 cases which had not received meperidine (Table I). No correlation greater than 0.35 between the points awarded at 1 minute for color and any of the biochemical attributes was found. A similar lack of statistically significant correlations existed with respect to the ."> minute score. The points awarded for color did not correlate well with the total points gained in the other four categories of the score, and the correlation between the 1 minute and 5 minute scores for color did not exceed 0.45 in any of the groups of cases. There remained the possibility that points for color might provide information of significance in cases in which the infant earned a less-than-perfect Apgar minus color score. Therefore, analyses similar to those enumerated above were conducted on those cases in \~:hich the (""~~(;) i score \vas either 7 or was less than 7. Once more there was a lack of significant levels of correlation Table I). It might well be reasoned. however. that

Score for color

Consideration is gtven to 162 cases in which the infant, mature by birth weight, was delivered vaginally without the aid of ~eneral anesthesia. The following correlations were examined: Between the points scored for color at 1 lllinute, and the Apgar minus color score at I minute and at 5 minutes, and each of three independent parameters of neonatal asphyxia: oxygen saturation, base excess, and carbon dioxide tension in umbilical artery blood. Between the points scored for color at 5 minutes and all of the above (including the I minute score for color). A similar correlation was made of the observation recorded in those cases in which the mother had received no depressant agent durin.g the period of 6 hours prior to delivery~ and in those in which a drug had been administered (no patient received more than one injection of 50 to 100 mg. meperidine

1

Table I. Correlations of var·ious attributes with the score for color at 1 minute* ---~----·----,----------,-------.-----------------------

Coefficients of correlation (r) of 1 minute score for color No. of cases

c,t

All cases With drugs Without drugs

162

0.43 0.+5 0.42

Cases without nuchal cord

With drugs Without drugs

53 63

Total series excluding

All cases With drugs Without drugs

+2

0.28

21

0.3B

All cases With drugs (A-C),= 8 or 7 Without drugs

30 16 I+

Total series

tA--rl. \ ._, / . ~ ~

=R ......

Total series exeluding

73

39

21

I

(A -c M

I

(A -c M

Umbilical arterv blood

--o-,-.,------B-.-E----'-c--1-P-c~"-.o-,

I

-0.30 -0.31 -0.30 -0.33 -0.3+ -0 32

-0.28

0.36

0.3+

*Only correlations greater than 0.24 have been noted (statistical significance can be attached only to coefficients greater than 0.60). tC~.. scon~ for color at 5 minutes. :i:(A ~ Cl1 and

(A~

C).-.. Apgar minus \.olor score at

l minute and at 5 minutes, res.pectivt·ly.

384

Ucrohe: 1,

Crawford

within a relatively small series of cases it is unlikely that a good correlation would bl' found hetw<'en a biochemical Yaluc and a scoring system limited to three points ( 0, I, or 2 for color). A. s a further atte1npt to find significance in the color score, attention was directed to only those cases in which an A - (: score of 8 at 1 minute had been recorded. The base excess in umbilical artery blood was taken as a guide to the degree of biochemical asphyxia suffered by tl1l' infant. Because the numbers comprising the subg-roups were rather small, only the results derived from the total series an· presented (Table II). The difference between the means are not significant, but the possibility remains, that when an infant is judged to haYt' attained the maximum score for muscle tone, respiratory effort, rdiex irritability and heart rate, then the points allotted for color might correlate reasonably w
As a first step, the total A- C scores at I and 5 minutes (A-· C) 1 and (A- C), were analyzed in a manner comparable to that employed in im'estigating tlw score for color. In no instance did the correlation between the oxygen saturation in umbilical artery blood and the A-- C scores reach a level of statistical significance (r> 0.60). Significant

l~hh

.\111. J. Clh<>t & l ;,111·,

Table II. A

C scores of f\ at

J

mimw·

A1 ean base ex£ es.,

In umbilical No. (A-C), of 8, no points for color ( . ·\:-C)l of 8, 1 point for color (A C), of il. 2 points for color

mtery blood (mEq./L.)

h.

)(j

· ') H6

correlation between the (A ···C) 1 score and l!Hlbilical artery PCO., was observed only within the group of cases without nuchal cord and in which, in addition, no meperidint· had been given ( r equal to -0.77). Thus only the correlations between the ~core and tlw \·alue of base excess and of pH in uterine artery blood need be further considerPd. The correlation between (A- C: 1 , and umbilil'al artery base excc:;s in the total serie~ of !62 cases was 0.47. the correlation of A (: , 1 with umbilical artery pH was 0.49. Howe\·cr. when the series was considered in "eparate group,,. as in tlw previous section. ·Table difl"eren t cia ta were oht;tirwd 1.

III I. A precisely similar pattern emerged when consideration was given to oulv cases wiLlr a 11 (A · (:) , score of less than B and to those· \\·ith a score of less than 7. The pattern was repeated with n'SI:Wct lo the 5 minute score I Table IV'. The medication received during labor hy the patients who comprised this series way !t'gitimatcly be termed conserYative : althoug·h, eYen so, it would undoubtedlv ha\·c been preferable to ha\"e accompanied each injection of meperidine with level of statistical significance. Undoubtedlv. tlw employment of heavier medication (and almost certainly. the use of a tc~chniquc of general anesthesia in which is incorporated an inhalational agent other than nitrous oxide) would seriously diminish tlw \·altw ,,f

Maternal and cord blood at delivery 385

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Table III. Correlation between (A- C h and umbilical artery blood at 1 minute Umbilical artery blood ------------------pH Base excess

All cases in which meperidine had been administered All cases in which meperidine had not been administered Cases without nuchal cord but with meperidine Cases without nuchal cord and without meperidine

l

0.39

0.31

0.56

0.59 J

0.48

o.42

0.78

0. 75

Significantly different at the 5 per cent level

I

,. Significantly different at the 5 per cent level

Table IV. Correlation between (A- C) 1 and umbilical blood at 5 minutes Umbilical artery blood

pH

Base excess

Total series

All cases With meperidine Without meperidine

0.34 0.19 0.46

0.31 0.19 0.43

r;xcluding cases with nuchal cord

With meperidine Without meperidine

0.11 0.70

0.18 0.64

Significantly different at the 5 per cent level

----

the Apgar score as an indicator of biochemical asphyxia of the infant. On the other hand, when consideration is given only to cases in which depressant drug administration had been withheld, the correlation between the (A- C) 1 score and the parameters of biochemical asphyxia virtually reaches the level of statistical significance (taken as 0.60). The presence of a nuchal cord quite obviously, and as expected, introduces a nonsystematized variation in the immediate clinical and biochemical pictures, and if cases of cord around the neck are excluded from consideration, together with cases in which meperidine had been administered, the correlation between the (A- C) 1 and the pH and base excess in umbilical artery becomes very high (0.78 and 0.75, respectively). The argument may be presented in another \vay. The rneans of base excess in umbilical artery blood of the cases not receiving meperidine, who scored less than 8, and less than 7, at one minute were -11.88 mEq. per liter and -12.36 mEq. per liter, respectively. The values in respect to the cases in

which meperidine had been provided during labor were -9.52 and -10.36 mEq. per liter. Thus, roughly, it may be said that the administration of meperidine (50 to 100 mg.) during the 6 hour period prior to delivery will, on the average, be associated with a degree of neonatal depression (as defined in clinical terms) equivalent to that provoked by an increase in asphyxia by -2 mEq. per liter base excess. The influence of nuchal cord on the (A-C) 5 score occasioned some surprise. The relevant data are summarized in Table V. Of the 46 cases in which a nuchal cord was present, 20 had a history of meperidine administration during labor, and 5 of these infants were depressed at 5 minutes. Onlv one of the infants out of the group of 26 cases of nuchal cord whose mothers had received no meperidine during labor. scored less than the maximum number of points at 5 minutes. It had been the clinical impn:ssion of the writer that cord around the neck tended to cause an acute episode of depression from vvhich the infant rapidly recovered. A.p-

386

Crawford

\11.1

Table V. Nuchal cord influence on (A

r.

( ktolwr 1. I ~-lbb ()hst & (;ynt•('

C),, score Mean umbiltcal artery i,·; ,), in rleprP."nl infant,

Cases with (kC), br than 8 No.

No.

~~-

Base exce.1 i

•'

{mEq./J .. )

plf

l.ti

1 fi . ·~

7 .I) )I'

(I

No nuchal cord, no meperidine

6'',)

No nuchal cord, with meperidine

5:!

:l

.i.il

!6.H

/.(ijh

Nuchal cord

46

6

J:Ul

9.1

7.19:!

parently, on the basis of these findings, the combination of the presence of a nuchal cord and the exhibition of meperidine during the 6 hour period prior to delivery is associated with a relatively high incidence of prolonged neonatal depression despite a relatively mild degree of biochemical asphyxia. The individual point-loss

There were 42 infants who failed to score 8 at 1 minute, and in half of these instances meperidine had been administered during labor. In 12 cases only one point was lost: in all the meperidine cases ( 7), this point was for respiratory effort (mean umbilical artery pH 7.246 and mean umbilical artery base excess -6.7 mEq. per liter); in 4 of the 5 "non-drug" cases the point lost was for muscle tone (mean umbilical artery pH 7.170 and mean umbilical artery base excess -10.7 mEq. per liter). When 2 or 3 points were lost, deductions had been made for both respiratory effort and muscle tone. Only when the (A ~ C) 1 score was 6 or less were points lost for reflex irritability (mean urnbilical artery pH and base excess of 14 "non-drug" cases 7.123 and -12.4 mEq. per liter, and of 16 cases receiving meperidine 7.159 and -10.3 mEq. per liter, respectively). The series is obviously too small to provide definitive data, but it seems fair to conclude that the earliest clinical sign of depression due to biochemical asphyxia is some loss of muscle tone, and that the earliest clinical manifestation of drug-induced depression is on the respiratory activity. Reflex irritability is reduced only after muscle tone and respiratory effort have both been depressed ( ir-

respective of whether the depression is due to biochemical asphyxia or to drugs ! . Thi~ attribute was affected in 13 cases of the present series. Only when points have h!:'t'n lost in all other categories docs bradycardia, as defined in the Apgar score, make its appearance. In the present series, the heart rat<:' vvas found to be below 100 beats per minute in only 2 cases. The 5 minute score was less than 8 in 1U instances. In 6 of these cases •.including; those in which meperidine had been givf:'n, only I point was lost and that was for musclt· tone. The score at 5 minutes is obviomly closely dependent upon the form of resuscitation. However, it is possibly fair to sav that it is easier to stimulate respiration than it i;, to provoke a return of mu~ck tone, and that it is likely that achievement of adequatf' toll\' is the final clinical indication of the recovny of a severely depressed infant. Conclusions

Based on the findings obtained frorn a series of 162 patients wlHl wPre de!iv<:'red \ aginally without the aid of g·eneral an<·sthesia, tht? following conclusions hm t~ been drawn: The points allotted for color at I minute and 5 minutes have befn shown not to provide a significant increment to the information offered hy the remainer of the <>core, except, possibly, in the circumstance that the maximum number of points in the remainder of the score has been achieved. Therefore, it is suggested that reference be made only to the "Apgar minus color" (A C) score.

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The A- C score, at both 1 and 5 minutes, offers a good indication of the degree of neonatal asphyxia, provided that the mother had received no unbuffered narcotic during the 6 hours prior to delivery. If even 50 mg. of unbuffered meperidine had been given to the mother, the correlation between A- C score and asphyxia is reduced significantly. The relationship between the biochemical state of the infant and the A- C score at 1 minute and at 5 minutes in cases in which drugs have not been given and in which nuchal cord is not present is very close. An increase in the predelivery dose of unbuffered meperidine from 50 mg. to 75 to 100 mg. is associated with an increased likelihood that the infant will lose scoring points without being rendered more biochemically asphyxiated at birth. Loss of a point for muscle tone is the first single feature of depression due to asphyxia, whereas loss of a point for respiratory effort stigmatizes depression due to meperidine. Loss of points for both of these attributes

REFERENCES

1. Apgar, V.: Anesth. & Analg. 32: 260, 1953. 2. James, L. S.: Devel. Med. Child Neurol. 4: 196, 1962. 3. Apgar, V., Holaday, D. A., James, L. S.,

Maternal and cord blood at delivery

387

occurs before reflex irritability is reduced, and loss of a point for heart rate occurs only after all the three other attributes have been affected. Loss of points from the 5 minute A- C score appears to be associated prominently with the combination of predelivery medication (with unbuffered meperidine) and cord around the neck. Summary

Examination of correlations between the Apgar score and the biochemical status of the infant at delivery suggests that there is good correlation provided that the infant is not depressed by drugs received from the mother prior to delivery. "Muscle tone" is the attribute first to be affected by asphyxia, "respiratory effort"" the first to be affected by meperidine. The score for color contributes little to the value of the scoring system. The technical assistance of Marie Bagan and Susanna Rudofsky is gratefully asknowledged.

Weisbrot, I. M., and Berrien, C.: J. A. M. A. 168: 1925, 1958. 4. Apgar, V., and James, L. S.: Am. J. Dis. Child. 104: 419, 1962. 5. Crawford, J. S.: Bioi. Neonat. 8: 65, 1965.