Determining gastric contents during general anaesthesia: evaluation of two methods

0 From the Departments of Anaesthesiz, Biochemistry and Surgery, Maisonneuve-Rosemont Hospital, University of Montreal , Montreal , Quebec. Presented in part at the Canadian Anaesthetists" Society annual meeting in Montreal, June 1986. Malsonneuve-Rosemon~Hospital , 5415 I'Assomption Blvd., Montreal , PQ.. HIT 2M4. This work was suppoaed by a gr~mtfrom the University of Montreal 1 Jean-Francois Hardy rap ~ c e c , Gilles Plourde MDrRcec, Michel Lebrun r,l~~, Christiane C6t6 n s c INF, Serge Dub~ MD FRCSC,Yves Lepage Pn n Two methods used to measure the vohtme of gastric contenta were evaluatedin 24 supine anaesthetized adults. Methods come , red were: (1) aspiration of stomach contents through a large, vented, multi-orificed gastric tube, and (2) indirect determination by a dye diluaon method using polyethylene glycol (PEGj as the marker. The volumes determined by these methods (V,~p and Ve~~ respeclively) were compared to the total volume (V,or) present in the stomach, delermined by direct inspection of the gastric pouch by the surgeon at the beginning of surgery. The resuhs show that the volume of aspirated gastricfluid, using this type of tube, is a very good estimate of the total volume of gostrie residue. The PEG dihttion method yields similar re. stdts. However, eorrelalion between Ve~~ and Vro, was not oz close-fitting as the correlation between Vusp and V~o~. PEG dih~aon is more complicated, time-consuming and offers no advam rage over aspiration. - Methods The study was approved by the Ethics Committee and informed consent was obtained for all patients. Twentyfour ASA physical status I-III adult patients undergoing elective laparotomy, excluding surgery of the oesophagus and stomach, were studied. The anaesthetics were standardized. Induction consisted of a defasciculating dose of d-tuboeurarine (DTC 501~g'kg-I), fentanyl 6 p.g.kg-', pro-oxygenation with 100 per cent oxygen by face mask for three minutes, followed by thiopentone 4 m g ' k g - ' and succinylcholine 1.5mg.kg-I. Mask ventilation was avoided to prevent gastric insufllation. The trachea was Hardy etal,: GASTRIC VOLUME MEASUREMENT intubated with a cuffed endotracheal tube. Anaesthesia was maintained with nitrous oxide 60 per cent and isoflurane as needed, in oxygen. Patients were paralysed with pancuronium IV. After the skin incision, but before exploration of the abdominal cavity, an 18 Fr Salem Sump tube (Argyle, St Louis, Mo.) was passed orally into the stomach. Gastric contents were aspirated as completely as possible (aspirated volume: Vasp), using a 50-ml syringe. The surgeon was then asked to inspect the stomach and ascertain complete gastric emptying. This direct inspection could lead to aspiration of additional gastric fluid' upon mobilisation of the gastric pouch (additional volume: Va,~,~).The stomach was then returned to its original position in the abdominal cavity. In 15 patients, the tt~tal volume (Vt,,t = V~p + V~dd) less a 2-ml sample used for later determination of gastric pH was re-injected into the stomach and then diluted with 100rid of a 0.4 per cent polyethylene glycol (PEG) solution. PEG is an indicator currently used in gastroentcrology to measure the rate of gastric emptying. Mixing of the dye with gastric fluid was achieved by withdrawing the gastric contents into a 50mr syringe and then reinjecting the fluid. This was repeated five times. The m i x t u r e was then re-aspirated as c o m p l c t c l T as p o s s i b l e (Vr~_,,p). PEG concentlations were determined by turbidimetry, in two 3 ml samples. Knowledge of PEG concentration enabled calculation of the volume diluting the indicator (VP~G; Figure l). The biochemist in charge of determining V p E O was blinded to Viot, In the first nine patients studied, dilution of gastric fluid with only 30m] of indicator solution led to completely erratic determinations of VpEC, which were excluded (see Discussion). After consultation with a gastroenterologist, the method described above was used to determine VpEc in the remaining 15 patients. Statistical analysis was performed by the Department of Mathematics and Statistics. Student's t tests for paired data and linear regression analysis were used. A p < 0.05 was considered significant. Results Aspiration of gastric contents was performed in all 2~ patients. The volume of fluid retrieved from the stomach on initial aspiration (V~so) was 31.1 -+-28.8 ml (mean SD) TABLE Summary of results (mean Z SD) FIGURE t Fh'incipleof the dye dilutiontechnique. VI (or VpE~) is volumeof fluidinitiallypresentin stomach.V2 is volumeof indicator dye. C1i,~initialconcentrationof indicatc~rdye. C2 is final concentrationof marker, and ranged from 0 to l l O m l . The additional volume (Vadd) aspirated following direct inspection by the surgeon was 4.4_+ 3.9ml (range: 0 to 13ml). The total volume (Vtar) present in the stomach at the beginning of surgery was 35.5 -+ 29.1 ml (range: 1.5 to 118ml). Vtot was significantly larger than V,sr,, (p < 0.0001). The volume determined by indicator dilution (Vrmo) in 15 patients was 26.2 --+28.8 ml. In these 15 patients who had both determinations of gastric contents, VpEG was not statistically different (p = 0.157) from Vasp (31.2 --- 27.7 nil). Complete results are presented in the Table. The volume re-injected into the stomach (Vto, - 2 ml for pH determination + 100ml PEG solution) was 134.1 --- 28.2 ml. This volume was significantly different from Vr~_,~p(122.1 --- 34.3 ml; p < 0.02). There was a statistically significant (p < 0.001) correlation between Vasp and Vto t (r = 0.99; Figure 2). VpEo was significantly (p < 0.00l) correlated to Vtot (R = 0.89, Figure 3). V~ ~spalso significantly (p < 0.001 ) correlated with the volume re-injected in the stomach ( r = 0.87). Discussion This study compared two methods of measuring the residual gastric fluid volume in anaesthetized adult patients and validated these methods in relation to actual volumes measured following direct stomach manipulation during laparotomy. The results indicate that volumes determined by both the aspiration and dye dilution methods are satisfactory estimates of the volume of fluid 9Firstninedeterminationsof VpEo wereexcluded(see text). FIGURE 2 CorrelationbetweenV,sPand V,ot.Vt~ = V.,p + 4 3 m] by linearregressionanalysis(24 datapoints;r = 0.99). present in the stomach. The correlation with Vtot determined by aspiration (r = 0.99) is slightly better than that determined by PEG dilution (r = 0.89). These data are important since significant medical recommendations have been based un such measurements despite the lack of prior validation. The principal disadvantages of the aspiration method are that it requires meticulous attention to detail and that there is always a small residue (about 4 ml) left in the stomach after aspiration. This should not be o f major clinical significance. V,.e-asp was significantly smaller than the volume re-injected into the stomach to determine VpEC- Thi (...truncated)