Relieving pain during labor is the basis of obstetric anesthesia. Pain is both a sensory and emotional pathological condition. This fact led clinical practitioners to see that a formal administration of analgesic drugs in response to a woman's complaint is unacceptable as analgesia implies more than mere administration of drugs. The obstetrician should understand the cause of pain and explain it to the patient as lack of mutual understanding can result in failed anesthesia.
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9.1. CAUSES OF PAIN IN LABOR
Immediate causes of pain during delivery are as follows:
• cervical dilation;
• contraction of the uterus and tension of round ligaments of the uterus, parietal peritoneum which is an especially sensitive reflexogenic area;
• excitation of periosteum on the inner sacral surface due to the tension of sacrouterine ligaments and mechanical compression of this area while the fetus is passing through it;
• excessive contraction of the uterus as a sex organ when there are relative obstacles to its evacuation, resistance of pelvic floor muscles;
• vascular constriction and expansion during uterine contractions; the vessels form an extensive network, and their baromechanoreceptors are highly sensitive;
• changes in the chemical activity of tissues: accumulation of underoxidized products of tissue metabolism (lactate, pyruvate) that occurs during a prolonged contraction; temporary ischemia of the uterus due to repeated contractions (Fig. 9.1).
At present all methods of labor anesthesia are conditionally divided into two groups.
• Group one: non-pharmaceutical methods of pain relief
• Group two: pharmaceutical methods of pain relief.
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Fig. 9.1. Causes of labor pain