Supplemental systemic oxygen support using an intestinal intraluminal membrane oxygenator.

An intraluminal membrane oxygenator (IMO) prototype was surgically inserted in the ileum and evaluated as a method of supporting systemic oxygenation in an acutely hypoxemic porcine model. Animals were assigned randomly to the test (n = 12) or the control (n = 8) groups, which underwent identical protocols with the exception of the O2 flow in the IMO device, which was shut off in the control group. In each case, hypoxia was induced by a reduction in the inspired oxygen fraction (FiO2) to 0.14. A highly significant improvement (p < 0.005) in arterial and venous O2 content and lower arteriovenous O2 difference (p < 0.05), cardiac output, and hemoglobin (p < 0.005) were found in the test group during hypoxia. The results show that it is possible to meet a physiologically significant portion of the body's O2 demands via the intestine during respiratory hypoxia and suggests that similar devices may be of significant potential value as a supplemental oxygenation device in cases of respiratory distress.

Gastric tonometry in healthy volunteers: effect of ranitidine on calculated intramural pH.

OBJECTIVE: To determine if intraluminal production of CO2 leads to underestimation of gastric intramural pH (pHi) by tonometry. DESIGN: Nonrandomized controlled study. PATIENTS: Healthy volunteers. INTERVENTIONS: NG tonometers were placed in healthy volunteers. Some of the volunteers (n = 11) were pretreated with ranitidine to prevent secretion of protons into the gastric lumen. Others (n = 13) were untreated (i.e., gastric acid secretion was uninhibited). MEASUREMENTS AND MAIN RESULTS: Gastric pHi was calculated from the arterial (HCO3-) and the tonometrically determined intraluminal PCO2 using the Henderson-Hasselbalch equation. Intraluminal PCO2 was significantly higher in the control group (54 +/- 14 torr [7.2 +/- 1.9 kPa]) than in the ranitidine-treated group (42 +/- 4 torr [5.6 +/- 0.4 kPa], p = .02). Mean gastric luminal pH was 1.9 +/- 0.6 in the control group as compared with 6.7 +/- 0.7 in volunteers treated with ranitidine (p less than .01). Mean calculated gastric pHi was 7.30 +/- 0.11 in the untreated group and 7.39 +/- 0.03 in the ranitidine-treated group (p less than .03). CONCLUSIONS: These data suggest that intraluminal production of CO2 from the titration of gastric HCO3- by secreted H+ can result in the underestimation of gastric pHi by tonometry. This phenomenon can be eliminated by H2-receptor blockade.

Efficacy of large-bore intravenous fluid administration sets designed for rapid volume resuscitation.

We tested the hypothesis that large-bore iv tubing sets provide greater in vitro flow rates than conventional sets currently utilized for the administration of normal saline. The study was conducted in two parts. First, flow rates were measured using a conventional iv tubing set under gravity and 300 mm Hg of pressure, and four large-bore iv tubing sets under gravity. Additional measurements were made after attaching various catheters and sheaths ranging in size from 14 ga to 9 Fr. Five trials were conducted for each combination. Second, we measured the amount of time taken in a mock drill by 28 randomly chosen anesthesiology residents and staff to load a unit of packed RBC into a pressure infusor bag, inflate to 300 mm Hg, and deflate to ambient pressure. Data were analyzed for individual tubing sets as a whole and individual catheter-tubing set combinations, using the Mann-Whitney U test with Bonferroni adjustment. Statistically significant (p less than .03) differences in flow rates were noted between the conventional set under gravity compared with both the pressurized conventional set and the large-bore tubing sets under gravity. There was no statistical difference in flow rates between pressurized conventional iv sets and large-bore iv sets. Mean time necessary for the 28 anesthesiology staff and residents to pressurize and deflate a conventional tubing set was 65 sec/bag of packed RBC. We conclude that a considerable amount of time can be saved by utilizing large-bore iv tubing sets instead of conventional pressurized sets during massive volume resuscitation. Clinical trials are indicated to corroborate these results.

Evaluation of the Datascope ACCUSAT pulse oximeter in healthy adults.

Arterial hemoglobin oxygen saturation measured with the Datascope ACCUSAT pulse oximeter was compared with simultaneous arterial hemoglobin oxygen saturation measurements in healthy adult volunteers. One hundred thirty-five arterial blood samples ranging in saturation from 63 to 100% were obtained from 15 adults, aged 20 to 43 years. These subjects had different skin pigmentation, hematocrit, and smoking habits. Steady-state hypoxia was achieved by varying the inspired oxygen concentration between 10 and 21%. Readings from the Datascope ACCUSAT pulse oximeter and the Hewlett-Packard 47201A ear oximeter were compared with arterial blood samples analyzed by the Instrumentation Laboratories IL 282 in vitro CO-Oximeter. The equation for the best fitted linear regression line between the ACCUSAT pulse oximeter and the reference IL 282 CO-Oximeter was: ACCUSAT = 1.08(IL) - 6.86. The linear regression analysis revealed a high degree of correlation (r = 0.99), and a small standard error of the estimate (SEE = 1.29%). Simultaneous comparisons between arterial hemoglobin oxygen saturation measured with the ACCUSAT pulse oximeter and the Hewlett-Packard ear oximeter also showed a close correlation (r = 0.99, SEE = 1.47%). A similar comparison between the ACCUSAT and the Ohmeda 3700 pulse oximeter revealed good correlation (r = 0.99, SEE = 1.72%). We found that the ACCUSAT pulse oximeter is an accurate instrument for measuring arterial hemoglobin oxygen saturation noninvasively in the range between 60 and 100%.

Simultaneous comparison of three noninvasive oximeters in healthy volunteers.

Noninvasive monitoring of arterial hemoglobin oxygen saturation (SaO2) from the Nellcor N-100 and the Ohmeda-Biox 3700 pulse oximeters were compared with SaO2 measured simultaneously by the Hewlett-Packard 47201A ear oximeter. A total of 868 pairs of data points ranging in saturation from 55-100% were obtained from 31 healthy adult volunteers of different ages, sex, skin pigmentation, height, weight, hematocrit, and smoking habits. Steady state and rapidly changing hypoxic conditions were achieved by varying the inspired O2 concentration between 10 and 100%. Measurements were analyzed by means of linear regression. The equations for the best fitted linear regression line between the Nellcor and the Ohmeda-Biox pulse oximeters as compared to the reference Hewlett-Packard ear oximeter readings were Y = 0.92X + 7.45 and Y = 1.10X - 10.73, respectively. Our study showed that despite a very close correlation among these three oximeters (r = 0.98), when compared to the Hewlett-Packard ear oximeter, the Nellcor pulse oximeter overestimates SaO2 by 2-4%, whereas the Ohmeda-Biox pulse oximeter underestimates SaO2 by 3-6% for SaO2 levels between 70 and 55%.

Analgesic responses to i.v. lignocaine.

The analgesic effect of i.v. lignocaine was evaluated in five patients with clinical neuralgic pain of varying aetiology. The response was compared with that on concurrently-induced ischaemic pain, initially of the same intensity. Following a high dose infusion of 3 mg kg-1 (lignocaine concentrations greater than 3 microgram ml-1) both pains were decreased, clinical pain to a significantly greater extent. Thereafter, at lower doses and blood concentrations, lignocaine was without effect on ischaemic pain, but almost totally suppressed the same patient's clinical pain. The results suggest a divergence in the specificity of the analgesic action of lignocaine i.v. according to the nature of the pain-inducing process. Disorders manifesting as deafferentation or central neuralgias appear to be affected favourably by lignocaine i.v. whereas pain of peripheral origin is unaffected by lignocaine, except at blood concentrations which approach toxic values.