![Page 1: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/1.jpg)
The GI Tract: Secretions, Motility & PONV
Dr James F PeerlessOctober 2013
![Page 2: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/2.jpg)
ObjectivesAnnex B• Physiology & Biochemistry: Gastrointestinal
– PB_BK_80 Gastric function; secretions, nausea and vomiting– PB_BK_81 Gut motility, sphincters and reflex control –
neurohumoral integration– PB_BK_82 Digestive functions; composition of secretions;
digestion of carbohydrates, lipids, proteins, vitamins, minerals
Annex C• Applied Physiology & Biochemistry: Gastrointestinal Tract
– PB_IK_30 Nausea and vomiting
![Page 3: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/3.jpg)
Gut Motility
![Page 4: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/4.jpg)
The GI Tract
• Series of organs with specialised functions and characteristic properties
• Digestion of ingested food• Absorption of– Water– Nutrients– Electrolytes– Vitamins
• Excretion of indigestible and waste products
![Page 5: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/5.jpg)
![Page 6: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/6.jpg)
Gut Motility
• Circular and longitudinal muscle• Smooth muscle cells with gap junctions allows
for a functional syncytium– Relaxation: rhythmic depolarisation/repolarisation
with slow-wave activity– Contraction: spike-burst activity as
transmembrane threshold is reached• Frequency and amplitude controlled by nervous and
chemical mediators
![Page 7: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/7.jpg)
Nervous Control
• Intrinsic and extrinsic control• Short and long reflexes
• Somatic NS– Pharynx & anus
• Autonomic NS– PNS
• Vagus – oe prox. colon• S2,3,4 – dist. colon, rectum, anus
– SNS• Sympathetic chain
![Page 8: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/8.jpg)
Nervous Control
• Local enteric NS– Latticework of plexuses and ganglia within the
bowel wall– Auerbach’s (myenteric) plexus• Between long. and circular muscle layers
– Neurones classified:• Cholinergic (stim.)• Adrenergic (inh.)• NANC (inh.)
– NO, VIP
![Page 9: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/9.jpg)
Humoral ControlFactor Gastric
MotilityGastric
EmptyingIntestinal Motility
Gallbladder Emptying
Gastrin -
Cholecystokinin
Secretin (augments CCK)
Gastric Inhibitory Peptide
- -
Motilin -
Somatostatin
![Page 10: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/10.jpg)
Control of the Lower Oe Junction
• Functional zone of high pressure (15-25 mmHg) 2-4 cm of lower oesophagus
• Histologically indistinct• Prevents reflux of gastric contents into Oe• Barrier pressure is the pressure difference
between LOS and intragastric pressure– Any decrease in LOS or increase in intragastric
pressure increased risk of reflux
![Page 11: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/11.jpg)
Factors Affecting Lower Oe ToneIncreased Tone Decreased Tone
Cholinergic Stimulation Cholinergic InhibitionDopaminergic Inhibition Dopaminergic Stimulation
Histamine Oestrogenα-adrenergic Stimulation α-adrenergic Inhibition
β-adrenergic Blockade β-adrenergic StimulationGastrin CholecystokininMotilin Secretin
PGF2 PGE1
![Page 12: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/12.jpg)
Secretions
![Page 13: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/13.jpg)
Secretions
• Main gastrointestinal secretions– mucus and digestive enzymes
• Specialised secretory cells throughout the gastrointestinal tract, plus liver and pancreas as specialised glands
• Secretion stimulated by presence of food in the GI tract, as well as PNS and the intrinsic neuronal control
![Page 14: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/14.jpg)
Summary of Gut SecretionspH Volume (mL day-1)
Saliva 6-7 1000-1500
Gastric 1-3.5 1500-2500
Pancreatic 8 1000-1500
Bile 7-8 700-1200
Small bowel 7-8 1800
Large bowel 7-8 200
![Page 15: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/15.jpg)
Saliva• Multifunctional:
– Salivary amylase digests starch– Salivary lipase– Buffering and diluting irritants– Aids swallowing, speech and lubricant– Antibacterial: lysozymes, IgA
• Serous and mucous mixture: 1000-1500mL day-1
– Parotid - serous– Sublingual and submandibular – both– Buccal – mucus
• Regulation– PNS – superior/inf. salivary nuclei– Triggered by taste and touch sensors– Appetite– Reflex salivation by GI irritation
![Page 16: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/16.jpg)
Gastric Secretion
![Page 17: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/17.jpg)
Phases of Gastric Secretion• Cephalic Phase
– Thought, sight, smell of food– Vagal stimulation of oxyntic glands and G-cells
• Gastric Phase– Vago-vagal reflexes and local enteric reflexes upon food entering the stomach– Release of gastrin– Secretion of acid to pH 2
• Intestinal Phase– Chyme enters small intestine and gastric secretion declines
• Lack of stimulation• Inhibitory factors:
– Duodenal distension, presence of acid in the duodenum– CCK release
![Page 18: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/18.jpg)
Acid Production in Parietal Cells
![Page 19: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/19.jpg)
Modulation of Gastric Acid Production
![Page 20: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/20.jpg)
Post-operative Nausea & Vomiting
![Page 21: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/21.jpg)
Definitions
Nausea is the sensation of the need to vomit
Vomiting is the involuntary, forceful expulsion of gastric contents through the mouth
Postoperative nausea and vomiting (PONV) is any nausea, retching, or vomiting occurring during the first 24 – 48h after surgery.
![Page 22: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/22.jpg)
PONV
• one of the most common causes of patient dissatisfaction after anaesthesia– reported incidences of 30% in all post-surgical
patients– up to 80% in high-risk patients
• regularly rated in preoperative surveys as the anaesthesia outcome the patient would most like to avoid.
![Page 23: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/23.jpg)
Physiology of Vomiting
![Page 24: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/24.jpg)
Physiology of Vomiting
• Vomiting centre in medulla• CTZ – area postrema (floor of fourth ventricle)
– Outside BBB– Multiple receptors (e.g. H1, D2, 5-HT3)
• Labyrinth (CN VIII)• Higher cortical centres (fear, sight, smell, memory)• Baroreceptors (CN X)• Pain pathways• GIT chemo- and mechanoreceptors (CN X)• Limbic
![Page 25: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/25.jpg)
Physiology of Vomiting
![Page 26: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/26.jpg)
Process of Vomiting
Pre-ejection Phase Ejection Phase
![Page 27: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/27.jpg)
Process of Vomiting
• Pre-ejection Phase– Nausea– SNS stimulation: HR, RR, sweating– PNS stimulation: salivation, relaxation of upper &
lower oesophageal sphincters– Retrograde contraction
![Page 28: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/28.jpg)
Process of Vomiting
• Ejection Phase– Respiratory pause mid-inspiration– Hyoid and larynx raised to open crico-oesophageal
sphincter– Glottis closes– Soft palate elevates to close nasopharynx– abdominal pressure
• diaphragm and abdominal muscles contract
– Gastro-oesophageal sphincter opens– Ejection of contents
![Page 29: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/29.jpg)
PONV is multifactorial
![Page 30: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/30.jpg)
Risk Factors - Patient
• Female• Non-smoker• Previous PONV• Hx motion sickness
![Page 31: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/31.jpg)
Risk Factors - Anaesthetic
• N2O• Opioids• Etomidate• Neostigmine• Hypotension– both regional and GA
![Page 32: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/32.jpg)
Risk Factors - Surgical
• Middle ear surgery• Ophthalmic surgery (esp. strabismus)• Gynaecological procedures
![Page 33: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/33.jpg)
Complications
• Unpleasant• Delayed discharge from POCU• Increased length of stay
• Suture dehiscence• Aspiration of gastric contents• Oesophageal rupture• Raised intraocular & intracranial pressure• Electrolyte imbalance• Dehydration
![Page 34: The GI Tract: Secretions, Motility & PONV Dr James F Peerless October 2013](https://reader038.vdocuments.us/reader038/viewer/2022110116/551b5c3f550346d41a8b65cd/html5/thumbnails/34.jpg)
Management
• Predict the at-risk patient• Multimodal approach– Anaesthetic technique, e.g. TIVA– Local/regional technique– Minimise baseline risk factors, where possible
• Minimise peri-operative opioid use• Combine antiemetic use for additive effects