Joseph I. Simpson

Flammability of endotracheal tubes in oxygen and nitrous oxide enriched atmosphere.

Endotracheal tube (ETT) fire has been reported secondary to laser and electrocautery ignition. The flammability of polyvinylchloride (PVC), silicone (Si), and red rubber (RR) ETTs in oxygen (O2) and/or nitrous oxide (N2O) in nitrogen was determined and compared by means of the O2 and N2O indices of flammability. The O2 index of flammability is the minimum O2 fraction in nitrogen that will support candle-like flame using a standard ignition source. The O2 index of flammability for PVC ETTs is 0.263, for Si 0.189, and for RR 0.176. The N2O index of flammability is the minimum N2O fraction in N2 that will support candle-like flame using a standard ignition source. The N2O index of flammability for PVC ETTs is 0.456, for Si ETTs 0.414, and for RR ETTs 0.374. The indices are additive. Flammability is a valid method of comparing safety of various endotracheal tube materials. There is a need for new endotracheal tube material with a higher index of flammability. The significance of these findings and the clinical applications are discussed.

Isoflurane versus sodium nitroprusside for the control of proximal hypertension during thoracic aortic cross-clamping: Effects on spinal cord ischemia

Objective: This study was designed to compare the effects of isoflurane and nitroprusside on spinal cord ischemia when they are used to control proximal hypertension during thoracic aortic cross-clamping (TACC). Design: Prospective, randomized, blinded experimental study. Setting: Laboratory and animal research facility. Participants: Adult mongrel dogs. Interventions: Two groups of eight dogs had TACC for 45 minutes. Proximal aortic, distal aortic, and cerebrospinal fluid (CSF) pressures were monitored. Spinal cord perfusion pressure was calculated as the distal mean pressure minus the CSF pressure. Group 1 received nitroprusside and group 2 received isoflurane to control proximal hypertension during cross-clamping. The dogs were neurologically evaluated 24 and 48 hours later by an observer blinded as to the study group. Spinal cord segments were obtained for histopathologic examination. Measurements and Main Results: Distal perfusion pressure and spinal cord perfusion pressure were significantly higher in the isoflurane group (p Conclusions: Isoflurane, when used to control proximal hypertension during TACC, produces a higher spinal cord perfusion pressure and is associated with a lower incidence of neurologic injury than nitroprusside in this canine model.

The effect of helium on endotracheal tube flammability.

The effect on endotracheal tube flammability of helium (He)-diluted oxygen and He-diluted nitrous oxide was determined with the oxidant O2 (He) and oxidant N2O (He) indices of flammability. These values then were compared with the corresponding values for nitrogen dilution, i.e., oxidant O2 (N2) and oxidant N2O (N2) indices of flammability. Four different types of endotracheal tubes were studied: polyvinylchloride (PVC), red rubber (RR), silicone (Si), and the Xomed (Xo) Lasershield tube. The oxidant O2 (He) indices are: PVC 0.274 +/- 0.0055, RR 0.194 +/- 0.0089, Si 0.194 +/- 0.0055, and Xo 0.256 +/- 0.0055. The oxidant N2O (He) indices are: PVC 0.526 +/- 0.0055, RR 0.434 +/- 0.0114, Si 0.416 +/- 0.0055, and Xo 0.456 +/- 0.0154. The oxidant O2 (N2) indices are: PVC 0.254 +/- 0.0055, RR 0.182 +/- 0.0045, Si 0.200 +/- 0, and Xo 0.230 +/- 0. The oxidant N2O (N2) indices are: PVC 0.472 +/- 0.0084, RR 0.356 +/- 0.0055, Si 0.392 +/- 0.0045, and Xo 0.444 +/- 0.0114. These differences, although statistically significant, are modest and demonstrate only a small, and probably clinically not significant, preference of He over N2 in decreasing flammability.

Flammability of esophageal stethoscopes, nasogastric tubes, feeding tubes, and nasopharyngeal airways in oxygen- and nitrous oxide-enriched atmospheres

&NA; SIMPSON JL, WOLF GL. Flammability of esophageal stethoscopes, nasogastric tubes, feeding tubes, and nasopharyngeal airways in oxygen‐ and nitrous oxide‐enriched atmospheres. Anesth Analg 1988;67:1093‐5. This study determines the flammability of materials in the oral cavity and pharynx during anesthesia in an environment of potentially high oxygen (O2) and nitrous oxide (N2O) concentrations where an ignition source (cautery, laser) may be in close proximity. The materials tested included esophageal stethoscopes, Salem sump nasogastric tubes, enteric feeding tubes, and plastic and rubber nasopharyngeal airways. Flammability was determined using oxidant O2 and oxidant N2O indices of flammability. The oxidant O2 and oxidant N2O indices of flammability are defined as the minimum fraction of oxidant (O2 or N2O) in nitrogen diluent that supports a candle‐like flame for a given fuel source. The oxidant O2 index of flammability for esophageal stethoscopes is 0.218, for Salem sump nasogastric tubes 0.229, for enteric feeding tubes 0.192, for plastic nasopharyngeal airways 0.196, and for rubber nasopharyngeal airways 0.172. The oxidant N2O index of flammability for esophageal stethoscopes is 0.430, for Salem sump nasogastric tubes 0.430, for enteric feeding tubes 0.375, for plastic nasopharyngeal airways 0.415, and for rubber nasopharyngeal airways 0.366. These indices are linearly additive.

The oxygen and nitrous oxide indices of flammability of endotracheal tubes determined by laser ignition

This study determines the flammability of polyvinylchloride (PVC), red rubber (RR), and silicone (Si) endotracheal tubes in oxygen‐ and nitrous‐oxide‐enriched atmospheres. Flammability is measured by using the oxygen and nitrous oxide indices of flammability with laser ignition. The laser‐ignited oxygen (O2) index of flammability of the endotracheal tubes is: PVC, 0.25; RR, 0.19; Si, 0.20. The laser‐ignited nitrous oxide (N2O) index of flammability of the endotracheal tubes is: PVC, 0.45; RR, 0.37; and Si, 0.41. These results are similar to the previously reported O2 and N2O indices of flammability with propane‐torch ignition. This study validates the concept that the indices of flammability are useful measures of endotracheal tube flammability and are independent of the ignition source.

ISOFLURANE VERSUS SODIUM NITROPRUSSIDE FOR THE CONTROL OF PROXIMAL HYPERTENSION DURING THORACIC AORTIC CROSS CLAMPING

OBJECTIVE This study was designed to compare the effects of isoflurane and nitroprusside on spinal cord ischemia when they are used to control proximal hypertension during thoracic aortic cross-clamping (TACC). DESIGN Prospective, randomized, blinded experimental study. SETTING Laboratory and animal research facility. PARTICIPANTS Adult mongrel dogs. INTERVENTIONS Two groups of eight dogs had TACC for 45 minutes. Proximal aortic, distal aortic, and cerebrospinal pressure was calculated as the distal mean pressure minus the CSF pressure. Group 1 received nitroprusside and group 2 received isoflurane to control proximal hypertension during cross-clamping. The dogs were neurologically evaluated 24 and 48 hours later by an observer blinded as to the study group. Spinal cord segments were obtained for histopathologic examination. MEASUREMENTS AND MAIN RESULTS Distal perfusion pressure and spinal cord perfusion pressure were significantly higher in the isoflurane group (p < .005). At 24 hours, seven of eight dogs in group 1 had severe neurologic injury (ie, paraplegia), with the eight having mild neurologic injury. This is in contrast to group 2, where 6 of 8 dogs had either minimal or no injury, one had mild injury, and one had severe injury. Similar results were observed at 48 hours (p < .005). CONCLUSIONS Isoflurane, when used to control proximal hypertension during TACC, produces a higher spinal cord perfusion pressure and is associated with a lower incidence of neurologic injury than nitroprusside in this canine model.

The Oxidant O 2 (Helium) Index of Flammability of Endotracheal Tubes

The effect on flammability of endotracheal tubes exposed to helium diluted oxygen was measured by the Oxidant O 2 (He) index of flammability and compared to the corresponding oxidant O 2 (N 2 ) Indices of flammability. Theoxidant O 2 (He) index of flammability for PVC (Portex) ETT is 0.274, for RR ETT 0.194, and for Si ETT 0.194. The differences between helium dilution values and the corresponding nitrogen dilution values are statistically significant, the greatest difference being a factor of 1.2. However the common clinical practice of adding helium as a diluent for oxygen in situations with a potential for flammability may not increase patient safety.

A glycopyrrolateritodrine drug-drag interaction

This is a case report of a 39-year-old patient who developed supraventricular tachycardia secondary to a ritodrine-glycopyrroíate interaction. The cardiovascular effects of ritodrine as well as the possible mechanism for this interaction are discussed. Suggested treatment for ritodrine-induced tachycardia in the parturient are presented.RésuméOn rapporte le cas clinique ďun patient de 39 ans qui a développé une tachycardie supraventriculaire secondaire à une interaction entre la ritodrine et le glycopyrrotate. Les effets cardiovasculares de la ritodrine ainsi que le mécanisme probable de cette interaction sont discutés. On suggère des traitements pour la tachycardie induite par la ritodrine.

Oxidant O 2 and Oxidant N 2 O Indices of Flammability and Their Additive Effect

The oxygen (oxidant O 2 ) index of flammability is accepted as a useful, easily reproducible, and inexpensive method of assigning relative flammability ratings to various materials. There have been reports of the ignition of plastic and rubber endotracheal tubes during anesthesia for surgery when an ignition source is in close proximity. Ignition sources include lasers for laryngeal surgery and pharyngeal electrocautery. Such procedures are often performed in oxygen- (O 2 ) and nitrous-oxide- (N 2 O) enriched atmospheres. This study determines and compares the oxidant O 2 index of flammability for three materials commonly used in endotracheal tubes: polyvinylchloride, red rubber, and silicone. Since nitrous oxide also supports combustion, we introduce the oxidant nitrous oxide (N 2 O) index of flammability for the same three materials. Indices were determined using a technique similar to the one previously described for the oxygen index of flammability. The oxidant O 2 index of flammability for polyvinylchloride endotracheal tubes is 0.263, for silicone endotracheal tubes, 0.189, and for red rubber endotracheal tubes, 0.176. The oxidant N 2 O index of flammability for polyvinylchloride endotracheal tubes is 0.456, for silicone endotracheal tubes, 0.414, and for red rubber endotracheal tubes, 0.374. The indices are linearly additive when O 2 and N 2 O are combined. This study suggests the possibility of developing other indices of flammability using other oxidants and predicting the effect of combining oxidants.