The balanced mixture for terminal anesthesia in the parturient

THE

BALANCEII

BIIXTURR IN THE

FOR PARTURIENT

Preliminsry SYLVAN M. SHANE, D.D.S., (From

the Departments

AND

of Anesthesk

AL AN

IA

Report

W. NEWTON LONG, M.D., BALTIMORE, MD. and Obstetsies,

Lutheran

Hospital

of MaryEanJ)

T

HE use of the “balanced mixture ” for anesthesia in general surgery, following a clinical trial in 10,000 cases, has already been reported.’ It was decided to evaluate its usefulness as terminal anesthesia in the parturient. The balanced mixture is a synergistic anesthesia combination consisting of approximately half the anesthetic dose of nitrous oxide (45 per cent) and cyclopropane (10 per cent) administered with 45 per cent oxygen in a semiclosed absorption system, in conjunction with amnesic sedation or a single hypnotic dose of an intravenous barbiturate. The rational pursuant to its use in obstetrics was to have available a general anesthesia technique in the delivery room which would: 1. Serve as a nondepressing general anesthesia alternative for the excessively sedated patient who refused saddle or caudal block. 2. Diminish the incidence of vomiting in the parturient during the induction and maintenance stages of anesthesia. 3. Be simple to administer for inexperienced or occasional anesthetists such as residents and interns. 4. Not unduly depress the fetus. 5. Maintain the patient in a consistent light Plane I anesthesia without the ’ ‘seesaw ” imminence of sudden light and sudden deep anesthesia. 6. Not increase the incidence of postpartum hemorrhage. Technique The balanced mixture is utilized as a terminal general anesthesia to provide unconsciousness during the time of actual delivery and for any postpartum repair. Two types of parturients will enter the delivery room. One type will be sedated with one or more of such drugs as Demerol, scopolamine, Sigmodal, paraldehyde, Seconal, Nembutal, etc. The other type will have had no sedation. The technique differs slightly for each of the two types. The Sed,uteBd Patient.A rubber anesthesia mask is placed on the patient’s face, the exhalation valve always remaining open (Fig. 1). The rubber breathing bag is filled with nitrous oxide and the anesthesia flowmeters are immediately set to deliver: 1,500 e.c. per minute (45 per cent) oxygen Nitrous oxide Cyclopropane

1,000 300

C.C. per w. per

392

minute minute

(45 (10

per per

cent) cent)

Vdurne64

BALANCED

Number 3

MIXTURE

FOR

TERMINAL

ANERTHEXIA

:g,.3

The percentage figures relating to the gases are, of course, approximak and are by no means exactly what exists in the alveoli or in the blood stream. This involves so many variables that exact figures are difficult to obtain. It would appear that t,he 1,500 C.C. of oxygen would be more than 45 per cent since 1,000 cc. of nitrous oxide are also labeled 45 per cent. The reason for this apparent discrepancy is the minute-to-minute utilization of oxygen, whereas the nitrous oxide is inert, reaches an equilibrium with the circulating blood, and Mains a comparatively constant concentration. Since oxygen is constantly consumed an additional 500 C.C. per minute is recluired t,o maintain an apgroximatel: equal percentage with the nitrous ositlc.

OIlen

fully

at all

times

settings c.c., and to permit

for the balanced mixture. Cyclopropane flow8 at 300 cr. nitrous oxide 1,000 cc. per minute. The exhalation valve k the escape of carbon dioxide along with the excess gases.

This large volume flow of gases prevents the accumulation and retentioil of carbon dioxide as seen in closed system anesthesias by permitting a portion of each exhalation to be blown out of the exhalation valve into the operating room. It furt,hermore prevents the accumulat,ion of cyclopropane, thus ohviating a gradual deepening of the anesthesia. Upon inhalation the valve closes and prevents the entrance of room air. Fresh soda lime should be used in the system to eliminate those traces of carbon dioxide which may not be completelyeliminated via the exhalation valve. Within two minutes of breathing t,his mixture the patient is unconscious. Nest patients are anesthetized in less than two minutes. The patient will. rcmain in Plane I anesthesia and will not descend deeper than this plane regardless of how many hours she breathes the gases. As the fetal head is being drlivered, the nitrous oxide and cyclopropane should be temporarily turned off.

continuously at, a the bag flushed out, and 100 per (*+1111oxygen a(lministered high flow of 10 I,. or more per minuf,e uutil the umbilical cord is clamped. The cord, if pulsating, should bc permittccl tu continue to pulsate for a minute or two so that the oxygen which t,hc mother is breathin, v will benefit the child. This step is highly important. After the cord is clamped the breat,hin g bag is again squeezed until ii’ is emptied of oxygen. It is refilled with nitrous oxide and the flowmeters are once more set at 1,000 CC. for nitrous oxide. 1,500 cc. for oxygen, and 300 C.C. for cyclopropane. It is remarkable to observe how smoothly patients drift into consciousness when the 100 per cent oxygen is administered as the he,ad is delivered, and lapse into unconsciousness with the re-establishment of the balanced mixture for repair of episiotomy. The Unsecihted

Patient.-

The parturient entering the delivery room who has received no sedation whatsoever during labor will react to the balanced mixture differently from the sedated patient. She may vomit during the induction stage, she may struggle violently during the excitement stage, or she may remain in the struggling excitement stage and never quite reach Plane I of the surgical stage, or she may It is finally reach Plane I after a prolonged period of breathing the mixture. for these reasons that some intravenous hypnotic should be administered to the unsedated parturient immediately before the mask is placed on her face. We prefer intravenous Nembutal in the amount of 2 C.C. (100 mg. or 11/2 grains) although Evipal, Pentothal, Surital, or intravenous Demerol, 50 to 100 mg., may be used equally effectively. If Evipal, Pentothal, or Surital is used, the dose should not put the patient completely to sleep, but make her only sleepy or amnesic. This small dosage range will of course avoid undue fetal respiratory depression. Comment In this series the Heidbrink machine was used. Most machines, however, may be utilized for this anesthesia. The percentages of both nitrous oxide and cyclopropane used in the balanced mixture are in reality about half of what it would require for complete anesthesia if either of the gases were used alone. Thus, it would require at least 80 per cent or more of nitrous oxide to produce anesthesia if it were used only with oxygen. It requires from 15 to 20 per cent when cyclopropane is used alone. Yet a combination of the two gases at half their anesthesia range will produce and maintain light anesthesia indefinitely, providing the patient has been amnesically sedated or an intravenous barbiturate is used to induce a state of hypnosis, not necessarilv anesthesia. This implies that, regardless of the number of hours the operation progresses, no additional sedation or intermittent doses of barbiturates will be required.* In an attempt to explain this phrnomcnon the work of Barbour may be pertinent. Barbour demonstrated that when barbiturates or morphine are injected into animals a shift occurs in the brain water balance. The cerebral As the effect of the barcortex loses water which is taken up by the medulla. biturate diminishes and a return to normal cerebration supervenes, the medulla gives up the water and the cerebral cortex rehpdrates. Prout3 expressed the view that the inhalation of t.he nitrous oxide and cycloprapane in t.he balanced mixture concentration is perhaps suffieient to maintain the water shift. so that consciousness would not return until the gases were discontinued. This explanation is, of course, thcol*etical, and is offered only as an attempt to explain the consistent,ly prc~dictahlc action of the balanced mixture when abdominal injections

*When

the balanced mixture relaxation is precluded of curare are therefore

is useil for due to the necessary

general surgery the attainment lightness of the anesthesia plane. to produce relaxation.

of

satisfactory Intermittent

Volume Number

64 2

BALANCED

MIXTURE

FOR

TERMINAL

ANESTHESIA

395

used in conjunction with amnesic sedation or an intravenous barbiturate hypnotic induction, and its bizarre unpredictability when amnesics or hypnotics are not used. Results 1. In the 100 cases upon. which this preliminary report is based there were no maternal deaths. 2. There was one infant death in the series. The mother neglected to report that the membranes had been ruptured for eight days prior to hospital admission, there was doubt about the infant prior to delivery, and at delivery, which was a midforceps application, the child was bathed in and had aspirated meconium, there being no heartbeat detectable at any time from the moment of delivery. 3. There were no patients who vomited during either the induction or maintenance phase of anesthesia. Fifteen per cent of the mothers vomited after they had fully awakened and were in control of their pharyngeal and swallowing reflexes. This observation has been previously reported in the 10,000 case surgical series where over 200 patients with histories of having eaten within 4 hours prior to emergency surgery for fractures, tendon repairs, etc., were anesthetized with the balanced mixture. None of these patients vomited during induction or maintenance. All of them did vomit after they were awake and in full control of their reflexes, thus diminishing the danger of aspiration of vomitus. We felt that the negation of vomiting seen with the balanced mixture was of considerable merit since so many of the obstetrical anesthesias in the IJnited States are administered by inexperienced personnel. This observation is in no way to be construed that vomiting may not occur. It may and no doubt will; and every parturient under a.ny type of general anesthesia should be watched for this reaction, which is the largest single factor in maternal mortality from anesthesia. There were two patients who vomited during the 100 per cent oxygen period prior to the clamping of the cord. This occurred when the patient was awakened because of the oxygen inhalation and in full cont.rol of her swallowing reflexes 4. There were no cases of postpartum hemorrhage which exceeded 500 C.C. The amount of blood loss following the balanced mixture was no more than that seen following other types of general anesthesia. 5. A test analysis of the explosive range of the balanced mixture was made by Dr. George Thomas of the Universitv of Pittsburgh and by Dr. Sylvan E. Foreman of the U. S. Industrial Chemical Corporation in Baltimore. Their findings indicated that the explosion hazard posed by the balanced mixture was no more than that encountered in using ether and cyclopropane or straight cyclopropane in a closed system. They stressed that all the usual precautions against explosions, such as grounding, should be observed. 6. The average breathing, crying, anesthesia, and sedation time factors were as follows: breathing time 15 seconds; crying time 291/ seconds; a.nesthesia time 6 minutes; sedation time 21/, hours; opera.tinp time 20 minutes. Breath+ a?wE Crying Time.-This was based upon a stop watch count which was begun the moment the entire child was out of the vagina. The longest breathing and crying time was 3 minutes in an infant, whose mother had 3 grains (200 mg.) of Nembutal and l/100 grain of scopolamine intravenously 45 minutes before delivery. Of the 100 cases in which a11 but 2 mothers were sedated with a barbiturate, Demerol and scopolamine, 57 infants breathed the very in&ant of delivery and, of these, 38 cried at the same instant. The remainder breathed in an average of 15 seconds and cried in an average of 29$$ seconds. The percentage of spontaneous hreathin g times was therefore 57 ‘per’ cent.

.Arn..J Oh. &Gyllei-. .\llt.il’li 19r2

sl-IA;‘\:P: AN11 1,0x(;

3%

Bnesthesicc l’inze (6 minutes).-- This was calculated from the moment the balanced mixture started until the time it. was stopped and 100 per cent oxygen given prior to clamping the cord. Sad&ion Time.-This average1 21, hours and was based upon the time the last dose of sedation was given until the cord was clamped. Thus, if Demerol and scopolamine were given at 2 P.N. and the cord was clamped at 4:lFi P.M.. the sedation time would be 21/4 hours. Operating Time.-This averaged 20 minutes and was based upon the time the balanced mixture was started until the operation itself (delivery, episiotomy, repair, etc.) was completed and the anesthesia mask permanently removed. The 100 per cent oxygen period was not deducted from this over-all figure.

Summary A synergistic anesthesia combination called the balanced mixture was evaluated for obstetrical use and found to possess encouraging possibilities. The balanced mixture was defined as a synergistic anesthesia combination consisting of approximat,ely half the anesthetic dose of nitrous oxide (45 per cent) and cyclopropane (10 per cent) administered with 45 per cent oxygen in a semiclosed absorption system, in conjunction with amnesic sedation or a single, partially hypnot,ic dose of an intravenous barbiturate. The technique and rationale for its administration were detailed. The results indicated that the balanced mixt,ure was not overly depressing to the fetus, that it was simple and comparatively safe for obstetrical interns and residents to administer, and that maternal vomiting during anesthesia was decidedly diminished, thus helping to obviate one of the major causes of maternal mortality. The authors wish to express their gratitude Silverstein, Jerome Pleet, Francis We-yrens, Esther partment of Obstetrics at the Lutheran Hospit.al, for tive effort.

to Drs. William R. Post, Jr., Daniel Lim, and Irina Lotti, all of the I)etheir valued assistance in this coopera-

References

1. Shane, Sylvan M., and Ashman, Harry: South. 2. Barbour, H. 0.: Science Weekly 75: 346, 1931. University of Maryland, Department 3. Prout, L.:

700 ASHBURTON STREET

M. .T., .Tuly, of Physiology,

1953. Personal

communication.