Aspiration. Aspiration. Disclosure. Aspiration on Induction: When to cancel? Christopher G. Choukalas, MD, MS 9/24/2011

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1 on Induction: When to cancel? Christopher G. Choukalas, MD, MS Department of Anesthesia and Perioperative Care University of California, San Francisco What it is Epidemiology Clinical outcomes Vague recommendations Disclosure I have never aspirated on induction What it is Epidemiology Clinical outcomes Vague recommendations 1

2 A rose by any other name Pulmonary aspiration Bronchopulmonary aspiration Pneumonia Pneumonitis In the beginning Inhalation of oropharyngeal or gastric material into lungs Gastric: Healthy: Sterile, acidic, pneumonitis, Mendelson s syndrome Sick: bacteria, pneumonia Oropharyngeal: colonized, pneumonia If you search PubMed In the beginning Gastric:LES pressure gradient: Higher in hiatal hernia Higher under anesthesia ❿ UES tone Anesthetics, paralytics ❿ Airway reflexes Anesthetics, paralytics Ng, A, Smith, G. Anesth Analg,

3 Then what happens? Reflux and Acid Food particles Early, diffuse chemical injury Inflammation Capillary leak, ALI What it is Epidemiology Clinical outcomes Vague recommendations Bacteria Infection Then what happens? Clinical syndromes of Nothing Pneumonitis Acute aspiration syndrome Pneumonia More a phenomenon of sick patients w/ chronic aspiration syndromes. Or bowel obstruction A rare event Epidemiology Registry data: Mayo/Adults: 1:3000 Pitt /Pedatrics: 1:1000 Scandanavia: :10000 Thailand: 1.4%! Borland, LM, et al., J Clin Anesth, 1998 Olsson, et al., Acta Anesthesiol Scan, 1996 Warner, MA, et al., Anesthesiology,

4 How are events identified? Self-report Searches of medical databases Personal interviews Risk factors Trauma Opiate use Critically ill Emergent case Hiatal hernia Epidemiology When it happens Population Estimate Study All-comers 1:3216 Healthy, elective 1:9229 Warner, et al. Sick, emergent 1:343 Trauma 1:3 Locky, et al, 1999 Obstetric (Mask) 1:200 Ezri, T., et al. Obstetric GA via ETT 0:645 Warner, et al Thailand Mayo Pitt/Peds Induction Maintenance Emergence Post-op 0% 20% 40% 60% 80% 100% 4

5 Parameters What it is Epidemiology Clinical outcomes Vague recommendations Clinical outcomes Contributions Nothing (as many as 2/3!) Pneumonitis Pneumonia Volume ph Particles 5

6 Volume Animal data (cats, rats, monkeys, oh my!) Aspirate volumes > 0.4 ml/kg In rats: increasing mortality from 1 ml/kg to 2 ml/kg Apparent interaction/synergy w/ ph ph Acid solutions cause direct tissue injury Diffuse Solutions of ph > 2.5 previously thought to be safe Clinically meaningless? Although acid suppression ph and gastric volume Knight, PR, et al. Anesth Analg, Ng, A, Smith, G. Anesth Analg, Clinically relevant? Gastric volume aspirate volume Gastric volumes well in excess of this 0.4 ml/kg don t routinely aspirate And many NPO patients have > 0.4 ml/kg gastric volume In Rats ph: 1.25 worse than 5.3 More hypoxemia Higher mortality Ng, A, Smith, G. Anesth Analg, Knight, PR, et al. Anesth Analg,

7 In dogs In Rats Group Saline, ph 5.9 HCl, ph 1.8 Gastric contents, food particles, ph 5.9 Gastric contents, food particles, ph 1.8 Gastric contents, NO particles, ph 5.9 Outcome Pneumonitis, hypoxemia, shunt Pneumonitis, hypoxemia, shunt Pneumonitis, hypoxemia, shunt hypoxemia, shunt Washed food particles worse than inert glass particles More inflammation capillary leak ALI Schwartz, DJ, et al. Am Rev Respir Dis Knight, PR, et al. Anesth Analg, Particulates Food particles cause a second (and third?) inflammatory injury Early neutrophils (6 hrs) Later granulomas (48 hrs) Focal Rats And speaking of particulates Human breast milk is terrible! ph for ph, worse than HCl Even at ph of 3 and 7! But it does empty faster than cow milk Rabbits. Knight, PR, et al. Anesth Analg, Ng, A, Smith, G. Anesth Analg, O Hare, B, et al. Anesthesiology

8 Outcomes: summary Mortality is low: 0-4.6% Pneumonitis vs pneumonia Particles, aspirate volume, and ph Closed claims 3% of 2046 damaging events But 29% of obstetric claims! Nearly all cases associated with risk factors: Hiatal hernias Difficult airways Obstetric/emergent cases GA via mask Cheney, FW, et al. Anesthesiology, 1991 Warner, Warner, and Weber Helpful? Of 66 aspirations: 42 had no sequelae 24 had: Cough or wheeze SpO2 A-a gradient CXR finding 12 were sent home All were admitted 13 ventilated 3 deaths Doesn t distinguish: Cancel vs not Discharge vs not Clinical factors predicting outcomes 8

9 When to discharge? What it is Epidemiology Clinical outcomes Vague recommendations When to cancel? When to cancel? No randomized trials No guidelines 9

10 What are the salient factors? Important case Volume, ph, particles? Any of the signs? A-a gradient, wheeze, hypoxemia Duration of case? Will it drag on into the inflammatory window? Some caveats Does not incorporate medicolegal considerations Closed claims analysis My interpretation of the one study that covered these issues UCSF in 2011 But seriously Emergency? Yes: Proceed No: Consider signs Consider bronchoscopy, bronchodilators, lungprotective strategies Wheezing, hypoxemia, airway obstruction? Yes: Consider canceling No: Consider factors Volume ph Particles Consider whether to extubate In the largest registry, 2/3 (44 of 67) were asymptomatic. 20% went home None developed pulmonary complications Any signs/symptoms Admitted, CPO Duration 10

11 Clinical decision support Future directions? Signs or symptoms? Yes: Admit No: ASA 1 or 2 No: Admit Yes: Particulate or large volume? Yes: admit No: Consider Discharge Does acid suppression decrease pneumonitis? But at the expense of colonization and pneumonia? A rare event Conclusions Complications even more rare in the absence of Co-morbidities Particulate High volumes Some clinical decision support rules 11