Andrew Triebwasser Department of Anesthesiology October, 2014

 pulmonary aspiration of gastric contents a longstanding & central concern in anesthesia  may have been causative in first anesthetic mortality (Hannah Greener 1848)  tri-modal clinical scenarios ◦ (near) drowning ◦ airway obstruction ◦ pneumonitis w/variable severity

 Winternitz - acid pneumonitis (1920)  Hall (JAMA) 15 cases in parturients (1940)  Mendelson: pneumonitis in rabbits worsened w/lower pH, higher volume, solid particles * Mendelson’s syndrome: aspiration ≥ 25 ml (0.4 ml/kg) with pH ≤ 2.5 ** *Am J Obst Gynec 1946;52:191 ** Shirley (unpublished) 1954 (rhesus)

gastric contents capable of damage regurgitation of these gastric contents significant pulmonary aspiration

gastric contents capable of damage regurgitation of these gastric contents significant pulmonary aspiration 1960’s →“modern techniques” please refer to the archived PowerPoint on Sellick and RSI forced emesis balloon tipped esophageal blockers

“nulla per os” after midnight (or 8º fast) had become accepted standard by 1950’s

problems associated with prolonged fasting need for an empty stomach “while it is desirable that there be no solid matter in the stomach when chloroform is administered, it will be found very salutary to give a cup of tea or beef-tea about 2 hours previously” (1883) Joseph Lister as late as 1948, Digby Leigh recommended 1º fast after clears

SALIVARY ∼ 1 ml/kg/hr GASTRIC ACID ∼ 0.6 ml/kg/hr Nordgren. Acta Physiol Scand 1963;58:10

 intense and rigorous fasting protocols  $$$$ invested in the pharmacological manipulation of gastric volume and pH  aspiration risk too low* to provide meaningful endpoints, so we are left with surrogate endpoints to assess risk Narberth, Pa 1987 * Warner MA. Anesthesiology 1999;90:66 ( Mayo Clinic): ~ 2:10,000 elective anesthetics with virtually no morbidity (↑↑ emergent)

 quantification based on direct instillation  “at-risk” parameters under question *  no evidence from RCT, cohort or case- control studies that link GFV & aspiration  30-60% of pts “at-risk” yet very rare event Schreiner MS. Anesth Analg 1998; * James (1984): critical pH 1.8 (rats) Raidoo (1988): 0.4 ml/kg & pH 1.0 minimal effect (rhesus monkeys)

I cannot forecast to you the action of Russia. It is a riddle wrapped in a mystery inside an enigma. -Winston Churchill radio broadcast October, 1939 (widely misquoted) gastric contents

 hypovolemia/hypotension  hypoglycemia (or need for IV dextrose)  irritability (for adults → lack of caffeine)  difficult compliance / dissatisfaction  delays or cancellations IS THE PREOPERATIVE FAST BENIGN?

this would be bad DOES FASTING LEAD TO REDUCED GASTRIC VOLUME?

what about this?? CANCEL? DOES FASTING LEAD TO REDUCED GASTRIC VOLUME?

 historical (why did we stop?)  physiological  benefit to patient  RCT’s

William Beaumont gastric physiologist who determined that liquids emptied from stomach in under an hour and also demonstrated the effects of emotion on gastric emptying

GOOD REFERENCE Splinter et al. Anes Analg 1999:89:80 protein > CHO > lipids simple liquids < 1º, longer if ↑ osm, ↑ cal, non-neutral pH complex meals may take 9º, simple ones under 3º

liquid in stomach liquid and solid (curds) phases in stomach

 historical (why did we stop?)  physiological  benefit to patient  RCT’s

 the only way to “liberalize” fasting guidelines which have unknown morbidity and unclear benefit is to at least “prove” that this would not adversely affect “aspiration risk” through surrogate endpoints of gastric volume and pH another paradox

 slew of RCT’s in 1980’s some w/multiple variables & Mendelson still central endpoint STUDYNPO (hr)VOLUMEGFV (ml/kg) * Maltby Anesth Analg 1986;65:1112 (had ranitidine group) 2.5 study 14.4 control 150 ml water17.6 ml (adults) 26.7 ml Splinter Can J Anaesth 1989;36: control 2.5 study3 ml/kg AJ 0.43± ±0.31 ** Sandhar Anesthesiology : control 2-3 study 5 ml/kg Meakin Br J Anaesth 1987;59:678 (had multiple variables) 2-4 study fasted orange drink drink + biscuit ** significantly different from control * gastric fluid pH consistently < 2.5 in both groups

 “wild” - revised instructions for study group without any confounding interventions  measurement of usual surrogate endpoints  power sufficient for “no difference”  linear analog scoring of several experience-based parameters

STUDY (clears) (53)CONTROL (NPO) (68)p Gastric fluid volume (GFV) (ml/kg) 0.44 ± ± GFV > 0.4 ml/kg (%) H + mean (pH)0.015±.008 (1.81)0.017±.01 (1.77)0.47 Gastric pH ≤ 2.5 (%) Gastric pH ≤ 2.5 and GFV 0.4 ml/kg (%) Schreiner et al. Anesthesiology 1990;72:593

A ease of compliance B temperament C overall experience p < p < 0.01 Schreiner et al. Anesthesiology 1990;72:593

 revised NPO 2.6 ± 0.7º vs ± 3.1º  clears do not ↑ Mendelson risk factors and with appropriate power might show ↓  clears associated with ↑ satisfaction a major institution well known for conservatism

 what about infants?  what about (others) excluded from study * * ASA III-IV known risk factors that ↓ gastric emptying known risk factors ↑ acid production

INGESTED MATERIALMINIMUM FASTING PERIOD clear liquids2 hours breast milk4 hours infant formula/non-human milk6 hours light meal (toast & clears)6 hours prophylactic pharmacologic agents to reduce aspiration risk NOT recommended

PROBABLY ENOUGH TIME : breast milk complete emptying by 3º * * Sethi AK. Anaesthesia 1999;54:51

PURPOSE  enhance quality efficiency anesthetic care  stimulate evaluation individual practices  reduce severity complications related to pulmonary aspiration of gastric contents Anesthesiology 1999;90:896

10 years well spent  cost effective use peri-op preventive medication  increased patient satisfaction  avoidance delays and cancellations  ↓ risk dehydration/hypoglycemia prolonged fast  minimize perioperative morbidity Anesthesiology 1999;90:896 enhance quality and efficiency of care …..

 meta-analysis of RCT with clears 2-4 hours ◦ adults: highly supportive (A) ↑ pH and ↓ GFV ◦ peds: highly supportive (A) for pH; equivocal GFV (C) ◦ no evidence (D) supporting risk emesis/aspiration  consultants strongly agree on clears 2-4 hours and agree on all other aspects of guidelines Anesthesiology 2011;114:495 no change NPO guidelines

 category B2 evidence that co-morbidities may be associated with ↑ risk pulmonary aspiration ◦ GERD ◦ dysphagia or other disorders GI motility ◦ potential difficult airway ◦ metabolic disorders such as diabetes Anesthesiology 2011;114:495 preoperative assessment – experts strongly agree it should be performed, but only class D evidence it changes outcome

NPO guidelines are only a part of the continuum of patient evaluation and preparation….aspiration risk factors need to be assessed on an individualized basis and anesthetic plan proceed accordingly

 14 yo arrives in HU chewing gum your plan???

Poulton TJ. Pediatric Anesthesia 2012;22:288 overall, may transiently ↑ volume, but not acidity both gastric emptying and LES sphincter relaxation may be ↑, but probably not clinically so SALIVARY may increase 4-5 fold over first 15 minutes

 if it is prohibited, exercise your right to cancel or delay the full 6 hours  compromise and wait 2 hours  no delay but make sure it gets spit out QUESTION: if chewed gum is swallowed, is cancellation indicated? equally reasonable options?

 6 yo fell off monkey bars 4º ago while eating ice cream cone. Supracondylar fracture with possible vascular compromise. If surgeon amenable, any benefit in delaying 2º?  what if the patient was scheduled for the next AM with appropriate NPO time? LMA OK?  what if at that time the patient showed up in the HU without an IV? how proceed?

 GI motility and emptying may be adversely affected by stress (SNS), pain, opioids  affected by severity injury (femur > wrist) *  ↑ gastric aspirates if injury w/in 2º eating ** ◦ hunger not reliable indicator adequate emptying  future directions – US measurement ?? ◦ (residual volume, liquid vs. solid) *** *Olsson GL. Acta Anaesthesiol Scand 1982;26:417 **Bricker SRW. Anaesthesia 1989;44:721 *** Van de Putte. Br J Anaesth 2014;10:1093

 14 month old hypospadias scheduled for 2 PM arrives – has had nothing by mouth since 7 PM the previous evening – it is now 1 PM and OR is on schedule (child is cranky) DO YOU : do nothing? insist on clear fluids w/delay? clear fluids w/out delay? start IV in HU and hydrate?

 concept of “enhanced recovery after surgery”  oral CHO solution 2º pre-op ↓ anxiety/hunger, post-op improved pain scores, ↓ complications  clear advantages to pre-op oral hydration w/ optimal solutions needing further study * future direction? Anesth Analg 2014;118:1163 * Nakamura.Anesth Analg 2014;118:1268