From Dr. Mark Schreiner on gastric fluid volumes and the risk of aspiration
I haven’t practiced clinical medicine for almost 20 years and I’m not the most current person on the timing of preoperative fluid management. However, the discussions surrounding preoperative liquids seem to have barely changed over the last 30 years so I do have some perspectives based on my experiences as a clinical investigator, a member of the first ASA task force and my training in clinical epidemiology.
The study I conducted with Andy Triebwasser comparing preoperative liquids up to 2 hours prior to induction to usual fasting was one of the first to be performed in children and was the first to place no limits on the volume of fluid.1 This and other similar studies (cardiac patients) that I was involved in, resulted in my being appointed to the first ASA Task Force examining preoperative fasting. What became immediately apparent to the task force members and methodologists was that volume of gastric fluid at the time of induction of anesthesia was a surrogate for risk for aspiration and a bad one at that. “Published evidence is silent on the relationship between fasting times, gastric volume, or gastric acidity and the risk of emesisi/reflux or pulmonary aspiration in humans.”2 That statement made in 1999 remains true today.
I would have thought that the work of Roberts and Shirley would deserve no more than a footnote today. What I wrote in an editorial in 1998 on the 25th anniversary of their paper is more elegant than what I can muster at present. “Because of the rarity of clinical pulmonary aspiration and the difficulties in measuring GFV before the induction of anesthesia, conducting either a RCT or a cohort study is unlikely to prove feasible. Well performed case-control studies and predictive modeling will probably be the most fruitful designs to help to establish and to allow estimation of the magnitude of true risk factors for the development of pulmonary aspiration of gastric contents. It is time to put an end to using the criteria of Roberts and Shirley, a surrogate measure with no proven clinical basis, and to put an end to discussions of risk based on studies whose designs fail to meet basic criteria for adequate evidence. The discussion should be shifted from a focus on the GFV at the time of induction of anesthesia to the patient’s characteristics and comorbid conditions, as well as to the anesthetic practices that place patients at risk of pulmonary aspiration of gastric and intestinal contents.”3 (emphasis added)
And though contrary to what I wrote in 1998, GFV can now be estimated with ultrasound, that still doesn’t avoid the biggest obstacle for conducting a randomized controlled trial; significant aspiration is an very uncommon event. Prior to liberalizing fasting at CHOP (1998 - 2001) the incidence of aspiration was 3/10,000; afterwards (2001 - 2004) it was 3/100,000 (Total N=118,145).4 “The central issue is that pulmonary aspiration of gastric contents is a rare event. Mortality or significant morbidity associated with pulmonary aspiration is exceedingly rare. To carefully measure the impact of various fasting regimens on even uncomplicated pulmonary aspiration, randomized, controlled trials would require sample sizes in excess of 30,000.”4 The estimated sample size of 30,000+ is probably a significant underestimate.
A case-control study assigning those who aspirated as cases vs those who didn’t as controls and then examining preoperative fasting interval as a risk factor would determine if fasting for one hour versus 2+ hours was a risk factor for aspiration. A cohort study would also be possible with patients from institutions where 1 hour fasting is the norm could be compared with those cared for at institutions requiring with longer fasting intervals. Since clear liquids empty exponentially with a half time of 10 – 20 minutes, this all seems like a lot of effort to reduce the incidence of something that is quite rare.
References
1. Schreiner MS, Triebwasser A, Keon TP: Ingestion of liquids compared with preoperative fasting in pediatric outpatients. Anesthesiology 72:593-7, 1990)
2. Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures: a report by the American Society of Anesthesiologist Task Force on Preoperative Fasting. Anesthesiology. 1999 Mar;90(3):896-905. doi: 10.1097/00000542-199903000-00034. PMID: 10078693.
3. Schreiner MS. Gastric fluid volume: is it really a risk factor for pulmonary aspiration? Anesth Analg. 1998 Oct;87(4):754-6. doi: 10.1097/00000539-199810000-00002. PMID: 9768764.
4. Cook-Sather SD, Schreiner MS, Nicolson SC, et al. Proponents of liberalized fasting guidelines. Anesthesiology 102:2365-7, 2005.
Also from Dr. Schreiner on ephedrine dose for hypotension: I needed epi or ephedrine exactly zero times during my career during anesthesia induction. I can’t even get my head around the investigators being able to recruit enough subjects to do this study.
From Dheeraj Nagpal MD on direct vs video laryngoscopy: Read the article in PAAD with interest, surprised that even we are even considering VL as the standard of care. I have worked in both academic and private practice anesthesia care and the immediate availability of VL is always a challenge.
So does the author implies if we can’t get a VL and there is a bad outcome as far as airway is concerned the practitioner will be liable as standard of care is not met. This will create a medicolegal nightmare for at least half of practices in our country and most of the practices around the world.
From Myron: I don’t think we need to see everything, especially changes in practice, through the lens of medicolegal potential liability. Rather we need to adjust our practices based on best evidence and practice. Indeed, the PAAD reviewers made the point that access to VL is the key rather than an either/or. These techniques are not mutually exclusive. Becoming expert in both techniques is crucial for all of us. Perhaps you can use the article to convince your administration for the need for more video laryngoscopes in your operating theaters, which was the recommendation of the article and the PAAD review.
From Dr. Robert (Bob) Spear commenting on determining baseline blood pressure in small, uncooperative children.
In very active, screaming and flailing children, it often takes multiple cycles of the BP cuff to get a reading, any reading. If the reading is even remotely plausibly accurate, it gets recorded and mercifully the child’s arm isn’t further tourniqueted, much to the delight of said child and anyone in the vicinity with even mildly sensitive ears.
Here is how I determined a “baseline” BP that I always trusted more than the BP in holding area of OR or on the ward. For mask induction, I wanted a BP just as the child began to quiet…you know, eyes drooping, very subdued movements, and no more biting/spitting. Start with nitrous oxide and oxygen (70/30) and sevoflorane (any dose for 10-15 seconds at which time the concentration is reduced to maybe 2%) until the child is quieting. Then place the BP cuff and cycle it; 20 seconds later the BP on this 2-yr-old is 84/56, which is my “baseline BP” albeit affected (lowered) by a blend of light anesthesia and affected (upward) by residual catecholamines from intense activity only minutes prior. At this stage, maybe 60 sec after initiating the nitrous/O2/sevo, the BP can quickly be measured without movement artifact and can be measured at frequent intervals as deeper levels of anesthesia are approached.
I was often asked why I would do this. My simple reason is avoiding a worst-case scenario. Maybe a 3-yr-old who had recovered from a viral illness a week earlier had mild, unrealized post-viral myocarditis, enough to depress the ejection fraction from 65% to perhaps 40% (an abnormal level just above where parents and pre-op doctors would perceive illness in the child) where the only life-threatening risk to the child is general anesthesia that coincidentally was scheduled during this unfortunate, subclinical yet serious illness.
Finally, I was a believer in getting IV access early during induction using volatile anesthetics, probably a result of training in the 1980s with the harrowing combo of halothane and a BP cuff using Korotkoff sounds as described by Myron a week ago. In my above scenario, this child is 90% “asleep”, nearly immobilized as the BP cuff is giving you your first, reassuring reading at which time an IV can easily be placed. (For what it’s worth, I don’t think laryngospasm from an IV during Stage 2 is a thing…but I am sure that laryngospasm without an IV is a BIG thing).
Blood pressure in children undergoing induction of inhalational anesthesia is akin to running down a very steep hill. The only benefit of sprinting down is getting where you are going a slight bit faster; however, the risk in going fast is going so fast you can’t stop….and you crash. Any opposing views are more than welcome.
From Dr. Jerry Lerman on preoperative fasting
Myron. very disappointing that u failed to cite my editorial in the Euro J Anesth that ripped this entire “1h fast” movement to shreds. It’s junk science of the highest degree. And furthermore, Pa Lonnqvist has written a letter to the EJA that is in press I which he bashed Anderson’s research from Uppsala pointing out even their own hospital do not follow her results from there after several years. And it has NOTHING to do with children’s thirst after 1 or 2 h fast but primarily to do with prolonged fasts and how to prevent those. The French solved that problem in one of their studies.