Vacuum-hypothermic fetal extraction technique

The Vacuum-Hypotherm-Extractor device. The developed device and the method of its application allow for cranio-cerebral hypothermia of the fetus during labor and, at the same time, due to the technical innovations of the device, for the most careful delivery by means of vacuum extraction against the background of fetal hypothermia. The device consists of an elastic cap connected to a vacuum device and a refrigeration unit; sensors from the vacuum-hypotherm-extractor are connected to an encephalograph and a potentiometer. In the thickness of the cap walls, parallel to the base, there are channels in a ring-shaped manner and across the entire surface, connected to a source of coolant under pressure. This design allows the vacuum extractor to be given the function of a hypotherm (hypotherms are special suits, helmets, refrigeration units and other equipment designed for hypothermia), and also to quickly and reliably fix the cap to the fetus's head, due to its automatic opening in the birth canal. Throughout the operation, it is possible to obtain information on the functional state of the fetus (registration of direct ECG, EEG, REG) and the rate of decrease in the temperature of its brain, due to the built-in sensors. The design of the device (due to contact between the cooled cap and the cooled tubes through which the coolant enters, along the walls of the vagina) allows for simultaneous hypothermia of the vagina and thereby affect the increase in contractile activity of the uterus (this issue is not considered in this paper).

The ALG-2 m refrigeration unit, to which a vacuum-hypotherm extractor is connected, allows for rapid cooling of the circulating solution and automatically maintains the solution temperature within the range of - 5 to - 7 C.

Along with the use of an elastic cap, metal cups with a cooling system are used for vacuum extraction with simultaneous cranio-cerebral hypothermia, with the circulation of cooled liquid occurring between the double walls of the cup, with built-in electrodes for recording ECG, EEG, REG and a thermocouple. Preparation of the woman in labor for the operation is no different from other obstetric operations - it is necessary to empty the bladder and intestines, treat the external genitalia and thighs with alcohol and 2% iodine solution, and cover the surgical field with sterile linen.

Often, during vacuum extraction of the fetus with a conventional serial vacuum extractor AVE-1, the cup is torn off from the fetal head - this is often due to insufficient adhesion force between the cup and the head. The traction force that an obstetrician can develop is equal to and opposite in direction to the adhesion force between the cup and the head. This traction force is calculated using the formula proposed by Malmstrom. According to this formula, for a Malmstrom type No. 7 cup, 60 mm in diameter, at a negative pressure of 0.8 kg/cm2 ^, the maximum traction force will be equal to 22.6 kg. An attempt was made to determine the traction force developed by an obstetrician using a dynamometer and expressed it as approximately 25 kg. With such a traction force, there is no guarantee that the cup will not slip off the fetal head.

The traction force can be increased in two ways - by increasing the negative pressure under the cup-cap or by increasing the area of the cup surface in contact with the head (the working surface). It is impossible to increase the negative pressure above 0.7-0.8 atm, as this will lead to deep trauma to the skull and brain of the fetus. Increasing the working surface of metal cups above No. 7 (diameter 60 mm) is also impossible. In the design of a vacuum-hypotherm extractor with an elastic cap, which can be inserted into the birth canal in a folded form, there is an opportunity to increase the working surface - accordingly, the adhesion force increases. The risk of the cap coming off during traction is significantly reduced. According to the Malm-Strohm formula, the maximum traction force, and therefore the adhesion force taking into account the diameter of the elastic cap, equal to 10 cm, at an air vacuum of 0.8 atm will be equal to 62.8 kg.

Consequently, the maximum traction force when using the vacuum-hypotherm extractor proposed by us can be increased almost 3 times, although there is no need for this, but it should still be noted that the risk of the cap tearing off during tractions is also reduced almost 3 times. Snoeck, Dragotesku, Roman conducted a thorough study of the mechanical foundations of the vacuum extraction method and the application of obstetric forceps to the contents of the fetal skull. The authors showed that during traction, the intracranial pressure of the fetus during vacuum extraction reaches 75 g / cm ², and in the case of even the most successful application of obstetric forceps - 1480-1500 g / cm ², i.e. the pressure on the brain during vacuum extraction, even under less favorable conditions, is only 1/2 of the pressure when applying obstetric forceps.

When using the elastic vacuum-hypotherm extractor that we proposed, the area of contact of which with the fetal head increases almost 2 times, the distribution of negative pressure during traction occurs over a twice as large area, therefore the intracranial pressure in the fetus during traction is only 35-40 g/ ^cm2.

We used a vacuum-hypotherm extractor with an elastic cap mainly when the fetal head was located in the cavity or at the outlet of the small pelvis.

Indications for the use of vacuum-hypotherm extractor:

• weakness of labor, threatening fetal asphyxia;
• the onset of intranatal fetal asphyxia;
• toxicosis of the second half of pregnancy, threat of intrapartum fetal asphyxia;
• narrow pelvis, incorrect cephalic presentation, prolonged standing of the head in one plane of the small pelvis;
• extragenital pathology;
• premature detachment of placenta previa;
• prolapse of the umbilical cord (after its repositioning).

Contraindications for the use of vacuum-hypotherm extractor:

• clinically narrow pelvis, excluding the possibility of delivery through the natural birth canal;
• central placenta previa:
• face and frontal presentation;
• hydrocephalus;
• deep prematurity of the fetus.

Conditions for use of the vacuum-hypotherm extractor.

A necessary condition for using a vacuum-hypotherm extractor is the absence of the amniotic sac, and the opening of the cervix of at least 6 cm, which is sufficient for inserting the cup-cap with the head fixed.

Technique of vacuum extraction surgery with simultaneous craniocerebral hypothermia of the fetus

The woman in labor is placed on the operating table or Rakhmanov's bed in a position generally accepted for vaginal manipulations. After the external genitalia have been appropriately prepared, the vagina is opened with speculums (application of the vacuum-hypotherm-extractor cap is also permissible under finger control), the sterilized cap-cup is applied to the fetal head, closer to the conducting point. Using a manual or electric pump, the air under the cap applied to the fetal head is discharged to 0.1-0.2 atm in order to fix it to the fetal head. After this, the speculums are removed. Then the circulation of the cooled liquid is turned on - the temperature of the hypothermia surface decreases to - 5 ° C and is automatically maintained at this level.

Moderate cranio-cerebral hypothermia of the fetus, in which the skin temperature of the fetal head under the vacuum-hypotherm extractor cap decreases to + 27 - + 28° C (while the temperature at the level of the fetal cerebral cortex is + 29 - + 30° C) is achieved in this mode in 20-30 minutes. After achieving moderate hypothermia, if there are indications for vacuum extraction of the fetus, the air under the cap is pumped out to 0.5-0.7 atm (the air must be pumped out slowly (!) for 3-5 minutes) and tractions are performed along with contractions or pushing. Throughout the operation, dynamic monitoring of the functional state of the fetus is advisable (cardiac monitoring, recording of ECG, EEG, REG of the fetus, etc.).

Due to the therapeutic effect of hypothermia on the fetus in hypoxic conditions, increased resistance of its brain to extreme conditions and stabilization or improvement of its functional state, the time interval for vacuum extraction against the background of craniocerebral hypothermia of the fetus is extended, i.e. the obstetrician gains time, so the operation should not be forced, but, monitoring the functional state of the fetus, carefully, with low-force tractions, vacuum extraction against the background of fetal hypothermia. When the head is cut, the vacuum in the vacuum-hypotherm extractor system is eliminated and the cap is removed from the head. The average time of vacuum extraction with simultaneous craniocerebral hypothermia of the fetus is 30-40 minutes, while the time of conventional vacuum extraction is on average 15-20 minutes. Therefore, the technique of vacuum extraction against the background of craniocerebral hypothermia of the fetus consists of two points.

The first moment we called: “vacuum hypothermia of the fetus”, when only cranio-cerebral hypothermia of the fetus is performed (the cup of the vacuum hypothermia extractor is fixed with a harmless vacuum of 0.1-0.2 atm to the head of the fetus), while traction is not performed.

The second point is the traction itself against the background of fetal hypothermia (the vacuum under the cup of the vacuum-hypotherm extractor is brought to 0.5-0.7 atm).

We gave the name "vacuum-hypotherm-extraction of the fetus" to the whole operation, consisting of the first and second moments. The first moment takes, on average, 20-30 minutes, while the second - 10-20 minutes. The whole operation takes, on average, 30-40 minutes.

In conclusion, the following should be noted:

1. The temperature of the fetal head skin under the cap during a hypothermia session is measured using a thermocouple built into the cap. The set temperature of the head skin (+ 27° - + 28° C) is maintained at this level using a relay by turning the coolant circulation on and off. Since the brain temperature recovers slowly after hypothermia cessation (up to 48 hours), there is practically no need to repeat the vacuum hypothermia session until labor is complete.
2. In case of complicated labor and development of intranatal asphyxia of the fetus, after the first moment of the operation (maximum time of vacuum hypothermia is 1.5 hours), it is necessary to proceed to the completion of labor. If conditions are present, vacuum extraction is performed against the background of fetal hypothermia or completed by applying obstetric forceps, depending on the indications. If the cervix has not opened completely, then labor is accelerated both by medications and by using vacuum stimulation of the fetus.
3. The maximum duration of cranio-cerebral hypothermia of the fetus with subsequent vacuum extraction against its background (i.e. the 1st and 2nd moments of the operation) is 2 hours. The presence of the vacuum-hypotherm extractor cap on the head of the intrauterine fetus, at a cooling liquid temperature and, accordingly, the surface of -5° C, for more than 2 hours may have negative consequences. A vacuum of 0.1-0.2 atm, fixing the cap-cup for a given time, is harmless, but the cooling itself for more than 2 hours can lead to necrosis of skin areas and to the transition of hypothermia from the moderate stage to the deep stage, which is undesirable.
4. In case of deterioration of the functional state of the fetus (usually associated with the underlying pathology) during the operation, the completion of labor is immediately started.
5. The vacuum under the cup-cap should not exceed 0.1-0.2 atm during a vacuum-hypothermia session, i.e. during the 1st moment of the operation, and more than 0.5-0.7 atm during tractions against the background of fetal hypothermia, i.e. during the 2nd, since forced tractions are not performed, the obstetrician, having a reserve of time, removes the fetal head with gentle tractions, causing less trauma to both the fetus’s body and the birth canal of the mother.