Assessment of intraoperative microaspiration: does a modified cuff shape improve sealing?

BACKGROUND: Intra-operative aspiration of oropharyngeal secretions is associated with post-operative pneumonia. The use of endotracheal tubes (ETTs) with a modified cuff shape could be one preventive action. In this clinical, prospective, randomised controlled trial, we hypothesised that altering the cuff shape to a tapered shape could reduce the aspiration incidence. The primary outcome was aspiration of dye solution into the trachea. METHODS: Patients scheduled for lumbar surgery were intubated with either an ETT with a barrel-shaped polyvinylchloride cuff (control group, n = 30) or tapered-shaped polyvinylchloride cuff (intervention group, n = 30). Subsequently, instillation with methylthioninium chloride was performed. At 10, 30, 60, 90, and 120 min after intubation, bronchoscopy was performed assessing the degree of dye descent along the cuff and digitally stored. Single blind review of the videoclips provided data on incidence of dye aspiration and depth of penetration along the cuff. RESULTS: The traditional cuff showed descent of dye into the trachea in 20% of the patients. Although a tapered-shaped polyvinylchloride cuff leaked up to the second third of the cuff, no dye leakage into the trachea was observed. The use of a tapered-shaped cuff had a protective role against aspiration (T30: OR 3.0, CI 1.57-5.75; P = 0.001). CONCLUSIONS: Short-term use of tapered-shaped polyvinylchloride cuffs in surgical patients results in more effective sealing of the tracheal lumen in comparison with a traditional barrel-shaped polyvinylchloride cuffs. Further evaluation is needed to determine whether a reduction in post-operative pneumonia can be demonstrated when these cuffs are used.

Comparison of the effects of intrathecal administration of levobupivacaine and lidocaine on the prostaglandin E2 and glutamate increases in cerebrospinal fluid: a microdialysis study in freely moving rats.

BACKGROUND: Bupivacaine has a lower incidence of transient neurological symptoms than lidocaine after intrathecal (i.t.) injection. The increased toxic potential of lidocaine does not support its use in the clinical setting and could be related to augmented levels of spinal prostaglandin E(2) (PGE(2)). We tested whether levobupivacaine leads to lower PGE(2) levels than lidocaine. Moreover, we compared the release of PGE(2) and glutamate after i.t. injections of levobupivacaine or lidocaine. METHODS: Rats were anaesthetized for implantation of an i.t. dialysis catheter. This allowed sampling dialysates of cerebrospinal fluid (CSF) for measuring PGE(2) and glutamate levels. The microdialysis setting included baseline sampling and was followed by an i.t. injection of levobupivacaine 250 microg, 100 microg, or saline. PGE(2) and glutamate levels in CSF were analysed for 4 h. In addition, the residual effect of a second i.t. injection on, respectively, of PGE(2) and glutamate changes was compared after injection of either 250 or 100 microg levobupivacaine, 1000 or 400 microg lidocaine, or saline. RESULTS: Prolonged spinal PGE(2) increases lasting 50-120 min were observed after levobupivacaine injection. Higher PGE(2) concentrations were observed after the second lidocaine 1000 microg injection. Glutamate release after the second injection did not vary between the local anaesthetic groups. CONCLUSIONS: Spinal PGE(2) levels are similarly increased after i.t. levobupivacaine injection of 250 and 100 microg. A higher PGE(2) response was observed after a second i.t. injection in the animals receiving 1000 microg lidocaine than those receiving 400 mg lidocaine or either dose of levobupivacaine.

Intrathecal lidocaine elevates prostaglandin E2 levels in cerebrospinal fluid: a microdialysis study in freely moving rats.

BACKGROUND: In this study, we have investigated whether intrathecal (i.t.) lidocaine administration is accompanied with changes of cerebrospinal fluid (CSF) prostaglandin E(2) (PGE(2)) levels. METHODS: Rats were anaesthetized for i.t. implantation of a triple-lumen spinal loop dialysis catheter. CSF changes in PGE(2) after i.t. injection of saline, 400, or 1000 microg of lidocaine were measured. The impact of i.t. pretreatment with 5 microg MK801 (N-methyl-D-aspartate glutamate antagonist) or 10 microg SC76309A (COX-2 inhibitor) was also investigated. CSF dialysates for measurement of PGE(2) were collected for 4 h. During the whole procedure, motor and sensory blocks were evaluated. A separate group receiving i.t. lidocaine 400 microg (without dialysate sampling) was assessed for mechanical (Von Frey) and radiant heat pain. RESULTS: PGE(2) levels increased to 400% of baseline and remained elevated for 90-120 min after i.t. lidocaine at both doses. Pretreatment with SC76309A and MK801 attenuated this increase. A 40 min period of enhanced pain response was observed after Von Frey filament stimulation during and after sensory and motor block recovery. CONCLUSIONS: I.T. lidocaine (400 or 1000 microg) increases PGE(2) levels in the CSF for 90-120 min along with a transient period of mechanical hyperalgesia after sensory and motor block recovery.

Desflurane: a reappraisal.

Desflurane use is associated with carbon monoxide production and sympathetic activation. These side effects can be eliminated taking into account certain recommendations such as closing fresh gas flow at the end of anaesthesia, regular replacement of carbon dioxide absorbents and the use of new absorbents for carbon monoxide production and opioid administration with slow increases of inspiration concentrations during desflurane initiation for sympathetic activation.

Isoflurane, desflurane and sevoflurane for carotid endarterectomy.

After carotid endarterectomy under general anaesthesia, the rapid elimination of desflurane and sevoflurane may allow earlier postoperative neurological assessment than after the use of isoflurane. However, desflurane may be associated with tachycardia and hypertension and may therefore increase cardiovascular risk. We investigated haemodynamic and recovery characteristics in patients scheduled for carotid endarterectomy who were anaesthetised with isoflurane, sevoflurane or desflurane. No significant peri-operative differences were noted in cardiac index or ST segment analysis. The times to extubation, movement on command and consciousness were shorter after desflurane and sevoflurane than after isoflurane anaesthesia. Postoperative pain, nausea, vomiting and shivering were similar in the three study groups.

Pharmaco-economic evaluation of a disposable patient-controlled analgesia device and intramuscular analgesia in surgical patients.

The present study contrasted the pharmaco-economics and analgesic efficacy of intramuscular (i.m.) opioid treatment with a parenteral disposable patient-controlled analgesia (PCA) system in two groups of 20 female patients (ASA I-II, aged 35-69 years) scheduled for abdominal hysterectomy. The PCA group received a continuous infusion of 1.5 mg h-1 piritramide, a mu-opioid receptor agonist, with incremental doses of 1.5 mg (lock-out interval = 15 min). The i.m. group received 0.3 mg kg-1 piritramide i.m. when requested by the patient with a minimum interval of 5 h. Pain intensity, sedation and the functional recovery of the patients were followed for 72 h post-operatively. The sum of pain intensity differences (SPID) was used as a measure of analgesic efficiency. Equipment and drug costs, and the demand on nursing time were recorded over 3 days post-operatively. The costs of PCA and i.m. therapies per patient were used to calculate the cost-benefit (cost of treatment vs. nursing time) and cost-effectiveness (cost of treatment vs. SPID) analyses. Both treatments initially provided comparable analgesia, but PCA was more efficient after 16 h and significantly reduced nursing time for pain treatment (PCA = 61 +/- 4 min, i.m. = 88 +/- 5 min; P < 0.001). Functional recovery was not different for either treatment. Cost analysis indicated a better cost-benefit ratio for the i.m. treatment (0.35 vs. 1.1 for PCA treatment), but a similar cost-effectiveness for both treatments (PCA = 1.9 Belgian Francs (BEF) unit-1 SPID; i.m. = 1.7 BEF unit-1 SPID).

Scintigraphic visualization of intrathecal liposome biodistribution.

BACKGROUND: Liposomes containing local anaesthetics have been administered intrathecally and in the epidural space. Poor attention has been given to the pharmacokinetics of liposomes as drug carriers. Therefore, we observed the biodistribution of liposomes after intrathecal injection in rats by scintigraphic imaging during 24 h. METHODS: We administered 99mTc-labeled multilamellar (MLV) and small unilamellar vesicles (SUV) of defined size and volume dispersities into the cerebrospinal fluid at the lumbar level. Those vesicles were free of contamination by radiolabeled colloids as visualized by light and electron microscopy and of neurotoxic products from phosphatidylcholine hydrolysis and peroxidation, both during the preparation process and after 24 h incubation in cerebrospinal fluid at 37 degrees C in vitro. RESULTS: SUV immediately diffused from the lumbar site of injection to the head and were cleared between 1 and 24 h after injection. MLV were cleared more slowly from the spinal space and appeared in the head region 1 h after injection where they accumulated up to 24 h. These differences were explained in terms of vesicle sizes and volumes. SUV with 0.05 micron diameters were rapidly absorbed into the blood through the arachnoid granulations. In contrast, particles larger than the upper size limit of the arachnoid granulations permeability (+/- 8 microns) could accumulate in the head with a slow elimination rate. CONCLUSION: This difference in clearance from the intrathecal space outlines the importance of defining the size of the liposomes, the distribution of a tracer or a drug inside the liposomal preparation, the chemical stability and the absence of toxic degradation products of liposome formulations before clinical use.

99mTechnetium-stannous oxinate as marker of liposome formulations.

Liposomes associated with tin(II) dioxinate were prepared from egg yolk phosphatidylcholine and cholesterol as sterile and pyrogen-free multilamellar or unilamellar vesicles. Complexing of liposomal tin(II) dioxinate with 99mTc attained 98% of the added radioactivity. Thirty percent 99mTc were released during 24-h incubation in biological fluids. The absence of tin colloids seen by electron microscopy and the stability of liposomal phospholipid and tin(II) dioxinate during 72-h incubation at 37 degrees C in plasma and cerebrospinal fluid would allow safe and reliable scintigraphic liposome pharmacokinetic studies.

Effects of carbon dioxide embolism with nitrous oxide in the inspired gas in piglets.

We have compared cardiorespiratory variables in anaesthetized piglets whose lungs were ventilated with oxygen in nitrous oxide (N2O group) or nitrogen (N group) after right ventricular carbon dioxide boluses (0.5 or 1 ml kg-1; n = 12) or slow graded injections (n = 6). Boluses affected all variables studied significantly (P < 0.05) except mean systolic arterial pressure. Significant changes in PE'CO2 (P = 0.012) and PaO2 (P = 0.048) values were observed in the N2O group. Changes in PaCO2 were related to volumes of injected carbon dioxide (P = 0.044). Boluses of 1.0 ml kg-1 induced severe circulatory collapse in two piglets in the N2O group. Slow embolization altered respiratory variables significantly (P < 0.001)). PaO2 decreased significantly in the N2O group (P < 0.0001). Mean pulmonary arterial pressure increased significantly over time (P = 0.001) and lasted longer in the N2O group (P < 0.05). Volumes and time required to induce a 50% increase in mean pulmonary arterial pressure differed significantly between groups (P < 0.05). We conclude that nitrous oxide worsened the effects of rapid and slow carbon dioxide emboli on cardiopulmonary variables. Rapid carbon dioxide embolism altered respiratory and haemodynamic variables, while slow carbon dioxide embolism changed only respiratory variables.

Biodistribution of liposomes after extradural administration in rodents.

We have mapped over 24 h the biodistribution of 99mTc-labelled multilamellar and small unilamellar liposomes in rabbits and rats by scintigraphic imaging after extradural injection. Multilamellar vesicles formed a depot at the site of injection; small unilamellar vesicles spread immediately along the extradural space and entered the systemic compartment 30 min after injection. Well-delineated liver and kidney labellings were seen after 24 h. The use of 3H-cholesterol-labelled small unilamellar vesicles suggested hepatic capture of intact liposomes with sizes averaging 0.05 microns drained unmodified into the systemic circulation through the extradural lymphatics. These results have led to the selection of multilamellar vesicles (0.1-15 microns size range) for clinical trials using liposome-associated local anaesthetics.

Dynamic training of skeletal muscle ventricles. A method to increase muscular power for cardiac assistance.

BACKGROUND: Skeletal muscle can be used for cardiac assistance after electrical stimulation over a period of several weeks. This will adapt it to do chronic work with no resulting fatigue. The result of this procedure, however, is a reduction of 80% in muscle power, > 60% in muscle mass, and approximately 85% in contractile speed. To minimize these disadvantages, the following study was done to develop and test a method to dynamically train skeletal muscle ventricles (SMVs). METHODS AND RESULTS: Barrel-shaped SMVs were tested in 15 Jersey calves. They were made from the latissimus dorsi muscle, which was wrapped around an elastic silicone training device. Six SMVs were used extrathoracically in a single layer and nine intrathoracically in a double layer. With dynamic training preserving contractile speed, the output increased to approximately 5 L/min, the systolic pressure increased to > 200 mm Hg, and power developed to approximately 10 W after 3 months of dynamic training. The contractile speed of dynamically trained SMVs was between 250 and 700 mm/s. The diameter of the latissimus dorsi muscle increased to three times that of the corresponding contralateral muscle. CONCLUSIONS: The combination of electrical conditioning with dynamic training of the SMVs resulted in a strong muscle pump that did not develop fatigue. Dynamic training for skeletal muscle represents a new and promising method for providing powerful autologous cardiac assist.

Acute pulmonary edema after laryngospasm.

Pulmonary edema may develop in healthy patients after anesthesia. Even in adult patients it is important to ascertain the depth of anesthesia before extubation. Too early extubation can result in laryngospasm, followed by increased inspiratory effort and significant rises in pulmonary capillary pressure, which may create fluid movements in the lung resulting in pulmonary edema.

Method-dependent differences in apparent sodium concentrations in plasma after exchange transfusions with citrated blood.

Shortly after exchange transfusions (n = 7) with citrate-dextrose-phosphate (CDP)-treated blood, but not after regular transfusions (n = 9), sodium concentrations in plasma were significantly and paradoxically lower (3-10 mmol/L) by Ektachem 700 XR determination [with use of electrolyte reference fluid (ERF) generation 00] than by flame photometry. Similar between-method differences could also be generated by in vitro supplementation of plasma pools with CDP solution, with trisodium citrate, or to a lesser extent with Na2HPO4. For four potentiometric methods the analytical recovery of sodium added as CDP was significantly lower than by flame photometry. Within each potentiometric method the recovery was also less than the value for sodium added as NaCl. A significant association of sodium ions with citrate3- ions and, to a lesser extent, HPO4(2-) ions could theoretically account for at least part of the observations, conferring greater medical relevance to potentiometric measurements in this particular clinical situation.