Neonatal Acid-Base Status Following General Anesthesia for Emergency Abdominal Delivery with Halothane or Isoflurane BettyLou K. Mokriski, MD,* Andrew M. Malinow, MD”f Department

of Anesthesiology,

University

of Maryland

School of Medicine, Bal-

timore, MD.

Study Objective: To determine whether halothane or isoflurane as anesthesia for emergency abdominal delivery is associated with better fetal acid-base parameters. Design: Randomized study. Setting: Inpatient Level III perinatal referral center in a university hospital. Patients: Sixty-six gravidas undergoing emergency abdominal delivery under general anesthesia for fetal distress. Interventions: Randomization to receive halothane or isofluran,e at 0.7 minimum alveolar concentration as part of a standard anesthetic technique. Measurements and Main Results: Umbilical artery and vein blood gases were obtained and compared for hydrogen ion concentration, partial pressure of carbon dioxide, partial pressure of oxygen, and base deficit. There were no significant differences between the isoflurane and halothane groups. Conclusions: There is no difference in the frequency or severity of acidosis associated with isoflurane or halothane when used for general anesthesia for emergency abdominal delivery of a distressed fetus.

Keywords: Anesthesia, obstetric; halothane; isoflurane; obstetrics.

blood gas analysis;

cesarean

section;

*Assistant Professor of Anesthesiology TAssistant Professor of Anesthesiology and Obstetrics and Gynecology Address reprint requests to Dr. Mokriski at the Department of Anesthesiology, University of Maryland School of Medicine, 22 S. Greene Street, Baltimore, MD 2 120 1, USA. Received for publication March 15, 1991; revised manuscript accepted for publication August 7, 1991. 0 1992 Butterworth-Heinemann J. Clin. Anesth. 497-100,

1992.

Introduction Isoflurane, halothane, and enflurane have been safely used to prevent maternal awareness during the period prior to elective abdominal delivery. The choice of volatile drug does not affect fetal outcome in the elective situation as measured by Apgar scores, blood-gas tensions, acid-base balance, lactate values, and Early Neonatal Neurobehavioral Scores at 2 to 4 hours.’ There are no human data comparing volatile anesthetic drugs for emergency abdominal delivery. Data from animal models of asphyxia are conflicting.2-5 We designed this study to determine whether halothane or isoflurane was associated with greater acidosis when administered to a gravida undergoing emergency abdominal delivery.

J. Clin. Anesth.,

vol. 4, March/April

1992

97

Original Contribution5

Materials and Methods Sixty-six patients undergoing emergency abdominal delivery requiring general anesthesia were included in our protocol, which was approved by the University of Maryland Human Volunteers Research Committee (exempt from the need for patient consent). All patients received 30 ml of a nonparticulate antacid. After denitrogenation with 100% oxygen (0,) by mask, anesthesia was induced in a rapid-sequence manner with thiamylal 4 mg/kg intravenously (IV) followed by succinylcholine 1 to 1.5 mg/ kg. After tracheal intubation, patients randomly received halothane or isoflurane at 0.7 minimum alveolar concentration (MAC) in 50:50 nitrous oxide (N,O) in 0, (N,O/O,) until delivery. Fresh gas flow was 8 to 10 L/ min. Randomization was computer generated. A tidal volume of 10 ml/kg was delivered mechanically at a rate of 10 breaths per minute. Umbilical artery and vein blood samples from a segment of cord double-clamped at delivery were analyzed with an AVL 945 (AVL, Graz, Austria) or ABL 2 (Radiometer America, Paramus, NJ) blood gas analyzer. Maternal epidemiologic data of age, parity, height, and weight were recorded. Fetal estimated gestational age, weight, and Apgar scores at 1 and 5 minutes were noted, along with the indication for emergency delivery, induction to delivery time, uterine incision to delivery time, presence of meconium, and estimated blood loss. If additional information was learned at the time of delivery, the patient was classified to reflect this information. Fetal heart rate (FHR) changes consisted of prolonged bradycardia or persistent late decelerations. For purposes of analysis, acidosis by pH was defined as an umbilical artery pH less than 7.15 or an umbilical vein pH less than 7.20. Acidosis by base deficit was a base deficit greater than 7 mmol/L in the umbilical artery or greater than 5 mmol/L in the umbilical vein. Table 1.

Maternal

and Operative

(in) Maternal

0 to 7

(Table 6).

Discussion We have shown that in the emergency situation, isoflurane and halothane are associated with similar levels of acidosis in the distressed fetus. This is similar to what has been seen in the elective situation in spite of experimental data that have suggested exaggerated acidosis

Isoflurane

p-value NS NS

24.7

h 6

0 to 8 24.5 t 7

61.8

+ 6

64.2

t

3

77.4

+ 20

71.6

f

17

NS

4

NS

5.3 2 3

NS

1.4 + 0.7

NS

0.046

age 35 + 5

(wk) Induction to delivery time (min) Uterine incision to delivery (min) Estimated blood loss (ml) Fetal weight (g)

5.3

1,042 2,398 SD.

NS = not significant.

vol. 4, March/April

f

3

1.5 + 1

Note: Data are means t

J. Clin. Anesth.,

In the prospective patient group, 32 patients received halothane and 34 received isoflurane. Patient groups were similar for maternal and operative characteristics (except for height) (Table 1). Indications for abdominal delivery were similar in both groups (Table 2). All patients who were listed as placental abruption, chorioamnionitis, or cord prolapse had a coexisting abnormal FHR tracing and/or a fetal scalp pH less than 7.20. The frequency of meconium-stained amniotic fluid was similar in both groups (Table 3). Apgar scores were the same in both groups (Table 3). There were no significant differences in the umbilical artery (Table 4) and umbilical vein (Table 5) blood gas analysis parameters between the groups. More umbilical cord blood samples were defined as acidemic when the base deficit criteria were used than when the pH criteria were used. There was no difference in acidosis defined by pH or base deficit between the groups

weight

(kg) Estimated gestational

98

Results

Characteristics

HaIothane Parity (range) Maternal age (yr) Maternal height

Data were subjected to Student’s t-test, the Wilcoxon rank sum test, or Fisher’s exact test, as appropriate. The Wilcoxon rank sum test was used for ordinal data and interval data with unequal variances. Fisher’s exact test was used for analysis of Apgar scores and the presence of meconium. A value of p < 0.05 was considered significant. Data are expressed as means + SD.

1992

+ 287 f 972

36 t

988 2,466

+- 232 + 909

NS NS

Neonatal acid-base status following halo&me or isojlurane: Mokriski and Malinow

Table 2.

Table 5.

Indication for Delivery Halotbane

Isoflurane

19 6 2 2

22 3 4 3

1 1

1 1

1

0

Fetal heart rate tracing abnormalities Placental abruption Scalp pH < 7.20 Cord prolapse Placenta previa with vaginal bleeding Chorioamnionitis Biophysical profile score of 2 of 10

Umbilical Vein Blood Gas Data Halotbane

[H+] (nmol/L) pH range PCO, (mmHg) PCO, range PO, PO, Base Base

58 6.71 48 33 32 15 -7 -26

(mmHg) range deficit (mmol/L) deficit range

+ to k to + to r to

6 7.40 13 100 10 60 6 1

Isoflurane 55 7.11 48 36 34 14 -6 -12

+ to f to + to f to

6 7.40 8 74 10 55 3 -1

Note: Data are means + SD; p > 0.05.

Note: p > 0.05.

H+ = Hydrogen ion concentration; PCO, = partial pressure of carbon dioxide; PO, = partial pressure of oxygen.

Table 3.

Table 6.

Apgar Scores and Meconium

Infants with Apgar score < 7 at 1 minute Infants with Apgar score < 7 at 5 minutes Infants with meconium-stained amniotic fluid

HaIotbane

Isoflurane

20 (63)

21 (62)

8 (25)

4 (12)

‘As defined by umbilical artery pH < 7.15 or umbilicalvein pH < 7.20.

8 (25)

7 (21)

bAs defined by umbilical artery base deficit > 7 or umbilical vein base deficit > 5.

Note: Data are expressed as number of infants (percentage of infants); p > 0.05.

Table 4.

Acidosis

Umbilical Artery Blood Gas Data

Halothane Isoflurane

Note: Data are expressed patients); p > 0.05.

PH

Base Deficitb

4 (13) 6 (18)

17 (53) 17 (50)

as number

of patients (percentage

of

Again, acidosis was exaggerated with a longer administration of anesthesia. Yarnell et aL5 administered halothane for 15 minutes; Palahniuk et ~1.~ administered halothane at an inspired concentration of 4% for an unspecified time greater than 15 minutes. Thus, the optimal choice of isoflurane or halothane is not clear from the animal data. The clinical situation does differ due to the limited duration of anesthesia exposure and the avoidance of maternal hypotension. Maternal hypotension may worsen acidosis by itself.6 A decrease in maternal MAP affects fetal pH by decreasing uteroplacental perfusion. In the clinical situation without hypotension or prolonged exposure, we have shown that the choice of halothane or isoflurane does not affect fetal acid-base parameters. Our results do not eliminate the possibility that both drugs exaggerate fetal acidosis to a similar degree. We have no way of measuring fetal umbilical cord blood gases prior to the administration of the volatile drug. We also chose not to include a control group of patients who would not receive a volatile drug. Such a group would have required our patients to give informed consent (due to the known 17% frequency of awareness in mothers receiving only N,O/O, 50:50*). To obtain informed consent during the time interval between the decision to perform an emergency abdominal delivery and induction of general anesthesia would significantly compromise patient care. In our institution, this time period is

al5

Halotbane [H+] (nmol/L) pH range PCO, (mmHg) PCO, range PO, (mmHg) PO, range Base deficit (mmol/L) Base deficit range

69 6.51 63 42 18 6 -7 -31

k 6 to 7.35 + 16 to 121 +- 7 to 44 k 7 to 0

Isoflurane 65 6.82 61 42 19 5 -6 -16

k 8 to 7.32 + 16 to 128 f 7 to31 5 4 to 0

Note: Data are means + SD; p > 0.05. H+ = Hydrogen ion concentration; PCOs = partial pressure of

carbon dioxide; PO, = partial pressure of oxygen.

with the administration of volatile anesthetics. Biehl et ~1.2 and Baker et aL3 both showed that isoflurane exacerbates acidosis in an asphyxiated fetal sheep model. However, isoflurane required 48 minutes of administration (at an inspired concentration of 2%) to decrease fetal pH in the absence of experimentally produced fetal asphyxia.2 Baker et aZ.3 confirmed acidosis associated with isoflurane after only 19 minutes but also noted significant decreases in maternal mean arterial pressure (MAP). Palahniuk et al.4 demonstrated similar changes with halothane that were not confirmed in a study by Yarnell et

J. Clin. Anesth.,

vol. 4, March/April

1992

99

Original Contributions

usually less than 5 minutes. In addition, it seems unlikely that patients would consent if the possibility of awareness was accurately stated. We thus chose to include only isoflurane and halothane treatment groups. If one of these drugs consistently worsens the fetal condition, this would have been detected by significantly worse blood gases measured at delivery. In summary, we could detect no difference in the frequency or severity of acidosis associated with isoflurane or halothane when used for general anesthesia for emergency abdominal delivery of a distressed fetus.

5.

References

6.

2.

3.

4.

1. Warren TM, Datta S, Ostheimer GW, Naulty JS, Weiss JB, Morrison JA: Comparison of the maternal and neonatal effects of

halothane, enflurane, and isoflurane for cesarean delivery. Anesth An&g 1983;62:516-20. Biehl DR, Yarnell R, Wade JG, Sitar D: The uptake of isoflurane by the foetal lamb in uterot effect on regional blood flow. (Jan Anaesth SocJ 1983;30:581-6. Baker BW, Hughes SC, Shnider SM, Field DR, Rosen MA: Maternal anesthesia and the stressed fetus: effects of isoflurane on the asphyxiated fetal lamb. Anesthesiology 1990;72:65-70. Palahniuk RJ, Doig GA, Johnson GN, Pash MP: Maternal halothane anesthesia reduces cerebral blood flow in the acidotic sheep fetus. Anesth Andg 1980;59:35-9. Yarnell R, Biehl DR, Tweed WA, Gregory GA, Sitar D: The effect of halothane anaesthesia on the asphyxiated foetal lamb in utero. Can Anaesth Sot J 1983;30:474-9. status and clinMarx GF, Cosmi EV, Wollman SB: Biochemical ical condition of mother and infant at cesarean section. Anesth Analg 1969;48:986-94.

Awrtheaia and &al&a-Aagw,

1922

Morbidity and Mortality in Obstetericr as Iafluenced by Ane&eaia* Worhy

Boarao+ MiLti

Jr&W.

Duma,

M. D,

T IS NOT our intention to dwell on the history of anesthesia. Only, it is worthy of mention that not long after the discovery of nitrous oxid, Humphrey Davy, the first superintendent of the Pneumatic Institute of Clifton, England, while working bn the then known gases, noticed that the inhalation of nitrous oxid relieved pain. His friend Southey, the poet, used to visit the lahoratory frequently and inhaled some. So impressed was he that the following eulogy came from his pen to his brother, “Oh Tom! Such a goJ bar Davy dticovered. 1 Oh Tom! I have had sow, it rmzkes w strong, Md JO h@py! So gloriously hukpy! Oh excellent gas bag! Tom, I am Sure tke air of heaven mwt be this The anesthetist of today often rvonder working gw of d&M.”

hears this paraphrased, especiaIly by the parturient women. This was written in 1798 and yet it was not until forty-six years later that this elastic fluid was used as an anesthetic, and theu chidly in dentistry for another twenty-four years, until Joseph Clover, surgeon and anesthetist, adopted nitrous oxid for general use in 1868.

Title

page,

“Morbidity

Anesthesia”,

and

by Wesley

Mortality

Bourne

in Obstetrics

and

searches in Anesthesia and Analgesia, August, permission Cleveland, Ridge,

100

J. Clin.

Anesth.,

International

(Reprinted

History

Journals,

vol. 4, March/April

the

Ohio and Wood

Illinois.

thesiology’s thesia

from

1992

Library-Museum

of Anesthesiology

1989,

Park

Ridge,

Research

Series,

Part

with

Society,

of Anesthesiology, Library-Museum

Reprint IL.)

by

Current Re-

1922. Reproduced

Anesthesia

in the Wood

as influenced

W. Duncan,

James

Park

of Anes19: Anes-