Pain pathways during labour

Pain pathways during labour

1. PAIN PATHWAYS DURING LABOR Presenter- Dr. Suresh Pradhan Moderator- Prof. UC Sharma

2. Pain Pain : Latin - ‘ poena ’ : punishment/ penalty International Association for the Study of Pain (IASP): “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”

3. Nociception Latin: ‘ Noci ’ : Harm/ Injury. Neural response only to the Traumatic / Noxious Stimuli

4. Physiological Effects of Pain Cardiovascular system Gastrointestinal system Respiratory system Genitourinary system

5. Musculoskeletal system Immune system Psychological and cognitive effects Nausea and vomiting Chronic pain

6. PAIN PATHWAY Experience of pain involves: TRANSDUCTION TRANSMISSION MODULATION PAIN PERCEPTION

7. TRANSDUCTION Process by which a noxious stimuli is converted to an electrical impulse in sensory nerve endings

8. TRANSMISSION Process of conduction of the electrical impulse to the CNS, along the dorsal horn of the spinal cord, Thalamus and the Somatosensory cortex.

9. MODULATION Process of altering the pain transmission. Modulation can be inhibitory (suppress the pain) or excitatory (aggravate).

10. PERCEPTION Perceiving pain occurs at the Thalamus with Cortex being the important area for the discrimination of the sensory experiences.

11. TRANSMISSION & PERCEPTION The 3 Neuron Pathway Pain due to noxious stimuli from the periphery is conducted to the Cerebral Cortex along 3 neuron pathways : FIRST – ORDER NEURONS SECOND – ORDER NEURONS THIRD – ORDER NEURONS

12. FIRST ORDER NEURONS Primary afferent neurons – cell bodies in the dorsal root ganglion. Each neuron has a single axon that bifurcates, sending one end to the peripheral tissues it innervates and the other into the dorsal horn of the spinal cord.

13. Entering dorsal horn – synapse with 2 nd order neurons or interneurons / sympathetic neurons/ ventral horn neurons

14. Qualitatively two different types of pain – FAST PAIN Starts when stimulus applied and ends promptly when stimulus is removed. Myelinated A δ neurons with velocity 12-30 m/s SLOW PAIN Due to Unmyelinated C fibres – velocity 0.5 - 2m/s Pain after the removal of stimulus.

15. Axons in the Peripheral Nervous System

16. SECOND ORDER NEURONS Lissauer’s Tract axons of most of the 2 nd order neurons cross the midline and ascend along the spinothalamic tract to Thalamus (VPL nucleus) Reticular formation Periaqueductal grey Nucleus Raphe Magnus

17. Structure of Spinal Cord

18. Spinal cord lamina Spinal cord gray matter was divided by Rexed into 10 lamina Lamina I and II receive afferent fibers of A δ and C

19. THIRD ORDER NEURONS Located in the Thalamus Relay fibres to somatosensory areas I and II in the postcentral gyrus of the parietal cortex Here, Perception and localization of pain occurs Some fibres from the medial nuclei project to the anterior cingulate gyrus which mediate the suffering and emotional aspects of the pain

20. Nerve Supply to the Pelvic Organs Somatic Autonomic SOMATIC Both the motor and sensory part of the somatic supply to the pelvic organs are through: ( i ) Pudendal nerve—S 2 , S 3 , S 4 (ii) Ilio -inguinal nerve—L 1 , L 2 (iii) Genital branch of genitofemoral nerve—L 1 , L 2 (iv) Posterior cutaneous nerve of thigh

21. AUTONOMIC principally from the sympathetic and partly from the parasympathetic systems Sympathetic carries both the sensory and motor fibers motor fibers arise from the segments T5 and T6 sensory fibers from the segments T10 to L1 fibers from the preaortic plexus of the sympathetic system are continuous with those of the superior hypogastric plexus lies in front of 5th lumbar vertebra

22. While passing over the bifurcation of aorta, it divides into right and left hypogastric nerves the hypogastric nerve joins the pelvic parasympathetic nerve of the corresponding side and forms the pelvic plexus (right and left) or inferior hypogastric plexus or Frankenhauser plexus this plexus lies in the loose cellular tissue, posterolateral to the cervix below the uterosacral folds of peritoneum The pelvic plexus then continues along the course of the uterine artery as paracervical plexus

23. Parasympathetic Known as nervi erigentes derived from the S2, S3, and S4 nerves join the hypogastric nerve of the corresponding side to form pelvic plexus the fibers are mainly sensory to the cervix from the vaginal plexus, the nerve fibers pass on to the uterus, upper-third of vagina, urinary bladder, ureter and rectum

24. Ovarian Plexus derived from the coeliac and renal ganglia fibers accompany the ovarian vessels to supply to ovary, Fallopian tube and the fundus of the uterus the sensory supply of the tube and ovary is from T10 to T12

25. Nerve supply of the internal genital organs

26. Labor is characterized by regular, painful uterine contractions that increase in frequency and intensity are associated with progressive cervical effacement and dilatation labor has been divided into three stages The First Stage occurs from onset of cervical change to 10cms dilatation can be divided into latent and accelerative phases latent phase can last up to 8hrs, without the need of intervention active phase is associated with a faster rate of cervical dilatation and usually begins at 2-4cms dilatation and the duration varies from 2 to 6hrs

27. The Second Stage occurs from full cervical dilatation (10 cm) to delivery of the baby normally lasts for 2 hrs (3 hrs with regional anaesthesia ) in a primipara and 1 hr (2 hrs with regional anaesthesia ) in a multipara The Third Stage occurs from delivery of the baby to separation and expulsion of placenta and the membranes

28. Mechanism of Labor Pain perception of pain during the first stage of labor begins with nociceptive stimuli arising in the mechanical and chemoreceptors in the uterus and cervix high threshold mechanoreceptors get stimulated due to intense pressure generated during contractions of the uterus myocellular injury due to repeated contractions in later stages, release bradykinin, histamine, serotonin, acetylcholine and potassium ions which activate chemical nociceptors

29. Peripheral pathways I stage of labor pain of the first stage of labor is due to uterine contractions and stretching of the cervix cramping and visceral in nature, diffuse and poorly localized sensations are carried through Ad and C primary afferent fibres which pass sequentially through the inferior, middle and superior hypogastric plexus, the lumbar and lower thoracic sympathetic chain and end in rami communicantes associated with T10-L1 spinal nerves

30. Peripheral nerve pathways associated with labor sensation

31. II stage of labor somatic pain predominates, as a result of distension and traction on the pelvic structures, the pelvic floor and the perineum is carried via the pudendal nerve through the anterior rami of S2 through S4 unlike visceral pain of first stage, it is sharp and well localised , due mainly to less arborization and the faster conduction velocity in the sacral pathways It is predominantly carried by the Ad fibres

32. pain originates from the perineum

33. Labor pain: Pathways and mechanisms

34. Central Pathways The pathways labor sensation travels after entry into the central nervous system includes both the ascending and the descending pathways Ascending pathways The first synapse in the pathways occurs in the dorsal grey matter of spinal cord ( Rexed’s Laminae I to V) most of the primary afferent neurons synapse initially in the more superficial laminae I and II (substantia gelatinosa ); locally projecting interneurons in turn synapse on the more deeply located wide dynamic range (WDR: lamina V) neurons The WDR neurons receive synaptic excitatory input from both the large myelinated Aâ and Aä mechanoreceptor afferents and C polymodal nociceptive afferents.

35. projections from the dorsal grey matter cross to the contralateral ventral white matter of the cord and then cephalad via the spinothalamic tract to the thalamus, brain stem, and cerebellum, where spatial and temporal analysis occurs, then to the hypothalamic and limbic systems, where emotional and autonomic responses originate

36. Descending pathways these pathways originate in primary sensory cortex and project to peri-aqueductal grey matter in the midbrain which further project to rostral ventral nuclei in thalamus projections from thalamus enter the spinal cord through dorsilateral funiculus and end in dorsal grey matter of the spinal cord

37. THANK YOU!!!

38. Pain Stimuli PROTOPATHIC Noxious Stimuli High Threshold Receptors Conducted by smaller lightly myelinated A δ fibres and unmyelinated C fibres EPICRITIC Non – noxious stimuli Light touch, pressure, proprioception , temperature. Low threshold receptors Large and myelinated nerve fibres