Cardiotocography

At present, cardiotocography (CTG) is the leading method for assessing the functional state of the fetus. There are indirect (external) and direct (internal) cardiotocography. During pregnancy, only indirect cardiotocography is used. The classical cardiotocogram represents 2 curves, combined in time. One of them displays the heart rate of the fetus, and the other - the uterine activity. The uterine activity curve, in addition to uterine contractions, also fixes the motor activity of the fetus.

Information on the cardiac activity of the fetus is obtained with the help of a special ultrasonic sensor, whose work is based on the Doppler effect.

In childbirth apply the method of direct cardiotocography. The research is based on the registration of the fetal ECG. In this method, after the outflow of amniotic fluid and the opening of the cervix for 3 cm or more, a spiral ECG electrode is placed on the head of the fetus, another electrode is attached to the femur femur. It should be noted that this method allows you to get a better quality curve for the fetal heart rate.

Modern cardiac monitors are also equipped with strain gauges. With the help of such a sensor, in addition to the contractile activity of the uterus, the motor activity of the fetus is recorded.

When examining an ultrasound transducer, a woman is placed on the anterior abdominal wall in the best listening position of the fetal heart and fixed with a special strap. The sensor is installed when the sound, light or graphic indicators available in the instrument begin to show the stable cardiac activity of the fetus. An external strain gage sensor is mounted on the woman's front abdominal wall and is attached with a strap.

There are also antenatal cardiac monitors, where two curves are recorded simultaneously using a single ultrasonic sensor: the heart rate of the fetus and its motor activity. The expediency of creating such devices is due to the fact that when using an ultrasonic sensor, much more fetal movements are registered than with the use of a strain gauge.

Registration of cardiotocography is performed in the position of a woman on her back, side or sitting.

Reliable information on the condition of the fetus using this method can be obtained only in the III trimester of pregnancy (from 32-33 weeks). This is due to the fact that by this time of pregnancy the myocardial reflex and all other kinds of vital activity of the fetus, which exert a significant influence on the character of his cardiac activity, reach maturity. Along with this, it is precisely during this period that the activity-rest (sleep) cycle of the fetus develops. The average duration of the active state of the fetus is 50-60 minutes, calm - 15-40 minutes. Leading to the evaluation of the fetal condition with the use of cardiotocography is the active period, since changes in cardiac activity during rest are almost the same as those observed when the fetus is disturbed. Therefore, taking into account the sonlike state of the fetus, to avoid errors, the recording time should be at least 60 minutes.

When decoding the cardiotocograms, analyze the amplitude of instantaneous oscillations, the amplitude of slow accretions, estimate the basal heart rate, take into account the magnitude of the decelerations.

The decoding of the cardiotocogram is usually started with the analysis of the basal heart rate. By basal rhythm is meant the average heart rate of the fetus, which remains unchanged for 10 min or more. In this case, the accelerations and de -cellations are not taken into account. In the physiological state of the fetus, the heart rate is subject to constant small changes, which is due to the reactivity of the autonomous fetal system.

Variability of the heart rate is judged by the presence of instantaneous oscillations. They represent a fast, short duration of the deviation of the heart rate from the basal level. Calculation of oscillations is performed in 10 min of the survey in areas where there are no slow accelerations. Although the determination of the frequency of oscillations may have a certain practical significance, the calculation of their number with a visual evaluation of the cardiotocogram is practically impossible. Therefore, when analyzing cardiotocograms, it is usually limited to counting only the amplitudes of instantaneous oscillations. There are low oscillations (less than 3 heartbeats per minute), medium (3-6 per minute) and high (more than 6 per minute). The presence of high oscillations usually indicates a good condition of the fetus, and low - about its violation.

Particular attention is paid to the analysis of cardiotocograms for the presence of slow accelerations. Count their number, amplitude and duration. Depending on the amplitude of slow accelerations, the following variants of cardiotocograms are distinguished:

• mute or monotonous with a low amplitude of the accelerations (0-5 cuts per minute);
• slightly undulating (6-10 cuts per minute);
• inducing (11-25 cuts per minute);
• Saltatory or skipping (more than 25 cuts per minute).

The presence of the first two variants of the rhythm usually indicates a violation of the fetus, the latter two - about its good condition.

In addition to oscillations or accelerations, when decoding cardiotocograms, attention is also paid to deceleration (slowing of the heart rate). Deceleration is understood as episodes of slowing the heart rate by 30 contractions and longer than 30 seconds or more. Deceleration usually occurs with contractions of the uterus, but in some cases they can be sporadic, which usually indicates a marked violation of the fetus. There are 3 main types of declerations.

• Type I - the emergence of deceleration with the beginning of the bout, it has a smooth start and finish. The duration of this deceleration in time either coincides with the duration of the bout, or is somewhat shorter. Often occurs with umbilical cord compression.
• Type II - late deceleration, occurs after 30 seconds or more after the onset of uterine contraction. Deceleration often has a steep beginning and a more flat alignment. Its duration is often longer than the duration of the bout. It mainly occurs with fetoplacental insufficiency.
• Type III - variable de -cellations, characterized by a different in time appearance relative to the beginning of the bout and have a different (V-, U-, W-shaped) form. At the apex of the deceleration, additional fluctuations in the heart rate are determined. On the basis of numerous studies it was established that for the normal cardiacogram during pregnancy, the following symptoms are characteristic: the amplitude of instantaneous oscillations is 5 cuts per minute or more; the amplitude of slow accelerations exceeds 16 cuts per minute, and their number should be at least 5 per 1 hour of research; decellations are either absent or are the only ones with a deceleration amplitude of less than 50 cuts per minute.

At a meeting in Zurich (Switzerland) in 1985, the perinatal committee of FIGO suggested evaluating antenatal cardiotocograms as normal, suspicious and pathological.

The criteria for a normal cardiacogram are the following:

• basal rhythm not less than 110-115 per minute;
• amplitude of variability of basal rhythm of 5-25 per minute;
• decelerations are absent or sporadic, shallow and very short;
• two accelerations are registered and more for 10 minutes of recording.

If this type of cardiotocogram is detected even in a short period of study, then the record can not be continued. For a suspicious cardiotocogram are characteristic:

• basal rhythm within the range of 100-110 and 150-170 per minute;
• amplitude of basal rhythm variability between 5 and 10 per minute or more than 25 per minute in more than 40 minutes of the study;
• no more than 40 minutes of recording;
• sporadic declerations of any type except heavy.

If such a type of cardiotocogram is detected, other methods of research should be used to obtain additional information on the fetal condition.

Pathological cardiotocograms are characterized by:

• basal rhythm is less than 100 or more than 170 per minute;
• variability of basal rhythm of less than 5 per minute is observed in more than 40 minutes of recording;
• pronounced variable decelerations or pronounced recurring early de-icerations;
• late declerations of any type;
• prolonged decelerations;
• sinusoidal rhythm lasting 20 minutes or more.

The accuracy of establishing a healthy fetus or a violation of his condition with such a visual assessment of the cardiotocogram is 68%.

In order to improve the accuracy of cardiotocograms, scoring systems for evaluation of the fetal condition were proposed. The most widespread among them was the system developed by Fisher in the Krebs modification.

The score of 8-10 points indicates the normal state of the fetus, 5-7 points - about the initial violations, 4 points or less - about the expressed intrauterine fetal suffering.

The accuracy of a correct evaluation of the fetal state when using this equation was 84%. However, significant subjectivity in the manual processing of the monitor curve and the inability to calculate all the required cardiotocogram parameters to some extent reduced the value of this method.

In connection with this, a completely automated monitor was created ("Fetal Condition Analyzer"). During the study, two curves are displayed on the display screen: the heart rate and the motor activity of the fetus. Registration of the indicated parameters of the fetal life as well as in other devices is carried out using a sensor based on the Doppler effect. After the end of the study, the screen displays all the basic necessary indicators, as well as the index of the fetus.

The main advantages of an automated monitor are compared with other similar devices.

• A higher (by 15-20%) information in comparison with the traditional methods of cardiotocogram analysis.
• Full automation of the information received.
• Unification of the results and the absence of subjectivity in the analysis of cardiotocograms.
• Practically complete elimination of the effect of the fetal sleep on the final result.
• In doubtful cases, automatic extension of the study time.
• Allowance for motor activity of the fetus.
• Unlimited storage of information and its reproduction at any time.
• Significant cost savings due to the absence of the need for expensive thermal paper.
• The possibility of using in any maternity hospital, as well as at home without the direct involvement of medical personnel.

The accuracy of a correct evaluation of the fetal status when using this device was the highest and amounted to 89%.

Analysis of the impact of the use of an automated monitor on perinatal mortality showed that in those institutions where this device was used, it was 15-30% lower compared to the initial one.

Thus, the data presented indicate that cardiotocography is a valuable method, the use of which can contribute to a significant reduction in perinatal mortality.

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