CRITICALLY APPRAISED TOPIC FERNANDO B. SERRA III June 23, 2010

The Case  29-year old female, ASA 1, with diagnosis of pelvic endometriosis with bilateral endometriotic cyst, for laparoscopic oophorocystectomy  During referral to consultant, premedications were discussed:  Nalbuphine 10mg and Promethazine 25mg IM 1hour PTOR – for sedation  Ranitidine 50mg or Omeprazole 20mg PO HS – to decrease gastric contents and increase gastric pH – to minimize risk of acid aspiration syndrome if ever patient vomits post-operatively

The Case  Postoperative nausea and vomiting are among the most common and distressing symptoms after laparoscopic surgery. This poses risk for Acid Aspiration Syndrome.  Aspiration of acidic gastric contents during vomiting causes chemical pneumonitis characterized initially by diffuse bronchospasm, hypoxemia, and atelectasis.  Morbidity increases directly with volume of aspirate and inversely with the pH of the aspirate.  Aspirates above 0.4–1.0 ml/kg and with pH below 2.0–2.5 are most serious (Acid Aspiration Syndrome)

The Question  Between ranitidine and omeprazole, which is a better premedication in reducing the risk for acid aspiration syndrome among patients for elective surgery?  Reduce Gastric Volume  Increase Gastric pH  Ranitidine – H 2 receptor antagonists  Omeprazole – proton pump antagonist

PIOM  Population - patients for electvive surgery  Intervention - ranitidine vs omeprazole  Outcome - reduced risk for acid aspiration syndrome  Methodology -randomized controlled trial

The Search  Terms:  Ranitidine  Omeprazole  Acid Aspiration Syndrome  Elective surgery  Limits:  Randomized Controlled Trial  Free Full Text Article

The Search 

The Journal  A Comparison of Lansoprazole, Omeprazole, and Ranitidine for Reducing Preoperative Gastric Secretion in Adult Patients Undergoing Elective Surgery  Kahoru Nishina, MD, Katsuya Mikawa, MD, Nobuhiro Maekawa, MD, Yumiko Takao, MD, Makoto Shiga, MD, and Hidefumi Obara, MD

The Journal  A prospective randomized double blinded study of 200 adult patients ASA 1 undergoing elective surgery.  Patients were divided into 8 groups (n=25 each) according to their premedication: Lansoprazole- lansoprazole (Group L-L), lansoprazole-placebo (Group L-P), placebo-lansoprazole (Group P-L), omeprazole- omeprazole (Group O-O), omeprazole-placebo (Group O-P), placebo-omeprazole, (Group P-O), placebo- ranitidine (Group P-R), or placebo-placebo (Group P-P)  Gastric fluid was aspirated via an orogastric tube after intubation, and the volume and pH of the aspirate were measured.

Appraising Validity 1.Were the patients randomly assigned to treatment groups?  Yes.  Sample size of 200 ASA 1 patients for elective surgery were randomly assigned to one of eight groups as follows (n = 25 for each group): L-L, L-P, P-L, O-O, O-P, P-O, P-R, and P-P. where L, 0, R, and P indicate lansoprazole (30 mg per dose), omeprazole (80 mg per dose), ranitidine (150 mg), and placebo, respectively.

Appraising Validity 2.Was allocation concealed?  No mention of concealment

Appraising Validity 3.Were the groups similar at the start of the trial?  Yes.  The overall averages of age, weight, and height of the patients were yr old, kg, and cm, respectively (mean 5 SD, P > 0.05 for all variables among eight groups).

Appraising Validity 4.Were patients treated equally?  Yes.  All patients fasted overnight. Premedications were taken with 20mL of water  For each treatment regimen, the first medication was administered at 9:00 PM on the day preceding surgery and the second at 5:30 AM on the day of surgery.  No other premedicants were administered.

Appraising Validity 4.Were patients treated equally?  Induction of anesthesia in all cases was started at 8:30 AM. with intravenous thiopental and maintained with sevoflurane and nitrous oxide in oxygen.  The lungs were ventilated, with care taken to avoid inflation of the stomach.  Tracheal intubation was facilitated by administration of vecuronium.  All inductions were uneventful and no patients had coughing, laryngospasm, or vomiting during induction.

Appraising Validity 4.Were patients treated equally?  After tracheal intubation, a 16-Fr orogastric tube was inserted into the stomach and verified by auscultation over the epigastrium during introduction of 10 mL air.

Appraising Validity 5.Were patients and caregivers/outcome assessors blinded to treatment assignment?  Yes  Randomized double blinded study  Patients were blinded to treatment received  Gastric fluid samples were obtained by gentle aspiration with a 50-mL syringe by an investigator who was unaware of the patient’s preanesthetic medication

Appraising Validity 6.Were all patients who entered the study accounted for? Were patients analyzed in the groups to which they were originally randomized?  Yes  However, in 15 patients, volume aspirated was very small; the gastric fluid remained in the gastric tube and could not be aspirated into the syringe  These small quantities were recorded as a volume of 0 mL and excluded from pH measurement

Results

Appraising the Results 1.How large was the treatment effect?  Relative Risk (RR) = risk of the outcome in the treatment (ranitidine) group / risk of the outcome in the control group.  RR = 0/0.48 = 0  Since the RR < 1, ranitidine 150mg PO 3 hours PTOR decreases the risk of acid aspiration syndrome

Appraising the Results 1.How large was the treatment effect?  Absolute Risk Reduction (or Difference) (ARR) = risk of the outcome in the control group - risk of the outcome in the ranitidine group  ARR = 0.48 – 0 = 0.48 = 48%  The absolute benefit of ranitidine is a 48% reduction in rate of acid aspiration syndrome

Appraising the Results 1.How large was the treatment effect?  Number Needed to Treat (NNT) = inverse of the ARR and is calculated as 1 / ARR.  NNT = 1/0.48 = 2.08  We would need to treat 2 people in order to prevent 1 event

Appraising the Results 2.How precise was the measurement of the treatment effect?  p < 0.05 = difference is statistically significant

Conclusions  Between ranitidine and omeprazole, which is a better premedication in reducing the risk for acid aspiration syndrome among patients for elective surgery?  Single dose of oral ranitidine 150mg 3 hours PTOR is a better premedication for reducing the risk of acid aspiration syndrome

Appraising Applicability 1.Is my patient similar to those in the study that the results can apply?  Yes

Appraising Applicability 2.Will the results help me in caring for my patient?  Yes

Appraising Applicability 3.Is the treatment feasible in my setting?  Yes

CRITICALLY APPRAISED TOPIC THANK YOU FERNANDO B. SERRA III June 23, 2010

Appraising the Results 1.How large was the treatment effect?  Relative Risk Reduction (RRR) = 1 – RR  RRR = 1 – 0 = 1  Ranitidine reduced the risk of acid aspiration syndrome by 100% relative to that occurring in the control group