NPO vs. Non NPO for Light Sedation Cases The PRO Argument Howard Palte Bascom Palmer Eye Center University of Miami
Mendelson’s Syndrome • 1946 – Curtis Lester Mendelson • New York obstetrician • Classic paper “ The aspiration of gastric contents into the lungs during obstetric anesthesia” • Aspiration in 66 women (44 016 maternities) – 0.15% • Liquid aspiration – dyspnea cyanosis tachycardia
Mendelson’s Syndrome • Demonstrated that acid was responsible for asthma-like symptoms • Instilled acid and gastric contents into the airways of rabbits • Concluded that “gastric retention of solid and liquid material is delayed during prolonged labor, and that aspiration of vomitus into the lungs can occur while laryngeal reflexes are abolished”
Aspiration Pneumonia
Gastric Emptying • William Beaumont – US military surgeon 1840s • Treated Canadian trapper for gunshot abdomen • Gastric fistula – observed distinction between emptying of gastric solids and liquids • Gastric emptying of liquids is an exponential process – rate proportional to amount left in stomach • T1/2 water – 10 mins; 50% stomach emptied in 1h
Gastric Emptying • Pylorus retards passage particles > 2mm diameter • Rate gastric emptying is constant • Starts 1h after a meal • At 2h 50% meal has reached duodenum
Pulmonary Aspiration • Retrospective Review perioperative course of 172 234 consecutive healthy patients > 18yrs • Pulmonary Aspiration – presence bilious secretions or particulate matter in tracheo-bronchial tree • Overall Incidence 1:3 216 • Breakdown – Emergency surgery 1: 895 Elective surgery 1: 3 886 Note: 64% did NOT develop cough/wheeze or SpO2
ASA Guidelines – Pre-Op Fasting • Clear Liquids – gastric volume and pH in adults given clear fluids 2-4 hour before procedure (Category 1 evidence) However: “ Published clinical evidence is insufficient to address the relationship between fasting times for clear liquids and risk of emesis/reflux or pulmonary aspiration ”
ASA Guidelines – Pre-Op Fasting • Conclusion: • “It is appropriate to fast from intake of clear liquids at LEAST 2 hours before elective procedures requiring general anesthesia, regional anesthesia or sedation/analgesia (MAC)” • “Examples of clear liquids include, but are not limited to, water, fruit juices without pulp, carbonated beverages, clear tea and black coffee”
Supplementary Agents • No Routine Use • GI stimulants – metoclopramide • GI Secretion Blockers – H2 antagonists, PPI • Antacids – sodium citrate, sodium carbonate • Anti-emetics – 5HT3 antagonists, butyrophenones
Supplementary Agents • NO USE • Anticholinergic – atropine, scopolamine, glycopyrrolate • Multiple agents
ASA – Consultant Responses • Pre-Op NPO Status • Healthy adults – fasting clear fluids > 2h • Responses 37: Strongly agree 56.8% Agree 40.5% Disagree 0%
ASA – Consultant Responses • Fasting Post Light Meal 6h (N=36) Strongly Agree 41.7% Agree 44.4% Disagree 13.9% Fasting Post Heavy(Fatty) Meal 8h (N=36) Strongly agree 63.9% Agree 27.8% Disagree 2.8%
Summary of Fasting Guidelines • Ingested Material Minimum Fasting Clear Liquids 2h Breast Milk 4h Infant Formula 6h Nonhuman Milk 6h Light Meal 6h Heavy/Fat Meal 8h
Diabetes and Gastric Emptying • Gastric emptying delayed by 30-50% • Pathogenesis poorly understood • Acute changes in blood glucose have major effect on gastric motor activity and emptying • Diabetics – high incidence upper GI symptoms • Pro-kinetic drugs – effective for symptomatic patients with gastroparesis Ref: Diabetic Medicine. 1996; 13: S16-22 •
Gastric Emptying in Diabetics
Gastric Emptying and Narcotics • Study – 8 healthy adults • - acetaminophen absorption • Meperidine and diamorphine vs. placebo (IV) • Placebo – 50% gastric emptying in 4-22 min (M=12) • Meperidine – mean time 90 min • Diamorphine – mean time > 90 min
Propofol and Gastric Emptying • Study – 10 healthy adults - acetaminophen absorption • Sedated to Grade 2-3 on a 5 Grade scale 2 = drowsy 3 = eyes closed but arousable Infusion rate – 2.5 mg/kg/hr.
Dexmedetomidine and Gastric Emptying • 12 Healthy male subjects • Double-blind randomized study • Given 1mcg/kg ‘Precedex’ IV over 20 min • Then infusion 0.7 mcg/kg/hr. for 190 mins • Comparison groups: 1. Morphine 0.1mg/kg IV over 20 min 2. Placebo (saline)
Dexmedetomidine and Gastric Emptying • Gastric emptying assessed with paracetomol absorption test • Blood samples collected - pre-induction - 10 min intervals until 90 mins - 45 min intervals until 4h Conclusion: Dexmedetomidine markedly inhibits gastric emptying
Laryngeal Mask Airway and Aspiration • Study – 50 patients GA with LMA Group A – spontaneous ventilation Group B – mechanical ventilation Methylene blue capsule ingested 10 min pre-induction Assessment oropharynx for staining at end surgery Akhtar TM, Street MK. Br J Anaes 1994; 72: 447-50
LMA and Aspiration • Incidence silent aspiration 9-20% vs. • Reported incidence 0.01 -0.8% • No statistical difference between spontaneous and controlled ventilation • Duncan & Yip – GI reflux – awake 12.5% • - anesthesia 15.9% • LMA – reported incidence regurgitation 0.08-23%
Cataract Surgery and Fasting
Cataract Surgery and Fasting
Patient Satisfaction Cataract Surgery • 306 patients undergoing cataract surgery under topical anesthesia & sedation • Iowa Satisfaction with Anesthesia Scale (ISAS) • Scale: 1-10 0-3 Unsatisfactory 4-6 Moderate 7-10 High Intra-operative adverse event – Pain Post-operative adverse event - Pain
Normalization of Deviance Diane Vaughan – American Sociologist Theory that misconduct within large organizations is described by “ normalization of deviance ” Effect – altered standards of professionalism • "Social normalization of deviance means that people within the organization become so much accustomed to a deviant behavior that they don't consider it as deviant, despite the fact that they far exceed their own rules for the elementary safety”
Normalization of Deviance • To people outside of the organization, the activities seem deviant; however, people within the organization do not recognize the deviance because it is seen as a normal occurrence. • In hindsight, people within the organization realize that their seemingly normal behavior was deviant.
Summary of Fasting Guidelines • Ingested Material Minimum Fasting Clear Liquids 2h Breast Milk 4h Infant Formula 6h Nonhuman Milk 6h Light Meal 6h Heavy/Fat Meal 8h
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