Postoperative residual paralysis and respiratory status: a comparative study of pancuronium and vecuronium.

The objective of this prospective double-blind study was to determine whether postoperative residual paralysis (PORP) after pancuronium or vecuronium results in hypoxemia and hypercapnia in the immediate admission period to the recovery ward. Eighty-three consecutive surgical patients received balanced or intravenous anesthesia with pancuronium for operations lasting longer than one hour or vecuronium for those lasting less than 60 min, both combined with neostigmine at the end of anesthesia. Standard clinical criteria assessed neuromuscular function intraoperatively. Postoperatively, we determined neuromuscular function (acceleromyography with supramaximal train-of-four (TOF) stimulation of the ulnar nerve, and a 5-s head lift) and pulmonary function (pulse oximetry: SpO2, and blood gas analysis: SaO2, PaCO2). We defined PORP as a TOF-ratio <70%, hypoxemia as a postoperative SpO2 > or =5% below the pre-anesthestic level together with a postoperative SaO2 <93%, and hypercapnia as a PaCO2 > or =46 mm Hg. Among the 49 pancuronium and 27 vecuronium patients studied, the PORP rates were 20% in the pancuronium group and 7% in the vecuronium group (p>0.05). Hypoxemia and hypercapnia occurred more often in pancuronium patients with PORP than in those without PORP namely 60% vs. 10% (p<0.05) and 30% vs. 8% (p>0.05), respectively. We conclude that PORP after pancuronium is a significant risk factor for hypoxemia.

Influence of volatile and intravenous anesthetics on the threshold of the acoustically evoked stapedius reflex.

The influence of volatile and intravenous anesthetics on the threshold of the acoustically evoked stapedius reflex (SR) was studied prospectively in 45 patients undergoing elective ENT surgical procedures. After premedication with flunitrazepam the patients were randomly assigned to one of nine groups. Group I: 70% nitrous oxide (N2O) in oxygen (O2); Groups II-VII: induction of anesthesia with intravenous thiopental, followed by mask inhalation with 100% O2 and 1.13% halothane (Group II), 2.52% enflurane (Group III) or 1.73% isoflurane (Group IV); or 70% N2O in oxygen, and 0.44% halothane (Group V), 0.86% enflurane (Group VI) or 0.75% isoflurane (Group VII): Group VIII: intravenous midazolam and ketamine; and Group IX: intravenous midazolam and alfentanil. Tympanometry and ipsilateral and contralateral SR measurements were performed when the effects of the anesthetics had achieved a steady state. Flunitrazepam raised the SR threshold only slightly. Substances applied during inhalation anesthesia either markedly increased the threshold contralaterally more than ipsilaterally (thiopental, N2O), or suppressed the reflex completely (thiopental, all volatile anesthetics with or without N2O). Under intravenous anesthesia the reflex was always present. The midazolam-ketamine combination influenced the threshold bilaterally only slightly, while the midazolam-alfentanil combination led to a pronounced, contralaterally significant elevation of the threshold. Based on its minimal influence on the SR threshold, flunitrazepam is especially suitable for sedation and the midazolam-ketamine combination for anesthesia in audiological diagnostic procedures.

[Problematic intubation in the patient with laryngeal-hypopharyngeal carcinoma. Retrograde controlled fiber bronchoscopy technique]. / Die problematische Intubation beim Patienten mit Larynx-Hypopharynx-Karzinom. Retrograd-geführte fiberbronchoskopische Technik.

Retrograde or fiberoptic intubation techniques are recommended for patients in whom intubation is difficult; however, each method has its own limitations. Good results have been reported with a combination of both techniques, i.e. retrograde passage of a guidewire through the cricothyroid membrane to guide a fiberoptic bronchoscope. The practicality, success and complication rates of our retrograde-guided fiberoptic bronchoscopic technique (RGFT) were studied prospectively in 93 patients with obstructing tumors scheduled for laryngectomy. The techniques showed itself to be successful, practical and safe, with negligible complications in 89/93 patients (96%). The ability to insert the bronchoscope by means of a guidewire and to direct the intubation procedure optically was found to be advantageous. Limitations with extreme obesity and in two other patients with advanced obstructive carcinomas of the larynx. Additionally, use of the tracheal puncture allows the RGFT to be integrated into clinical medical education as a preparatory exercise for emergency coniotomy.

Simulation of the onset of neuromuscular block based on the early oscillations in the arterial plasma concentrations.

OBJECTIVE: The aim of the study was to describe by simulation the true plasma concentrations of non-depolarizing muscle relaxants (NDMRs) as a continuous function of time. In contrast to standard pharmacokinetic analysis of the time course of action via extrapolated plasma concentrations, the derived curve was to reflect zero plasma concentration initially and one or more cycles of peaks and troughs subsequently. We desired to study the influence of the initial delay and the early oscillations in the plasma concentrations on the time to onset of peak but submaximal neuromuscular block (NMB). Hypothetical NDMRs were postulated to display in humans a pattern of early arterial plasma concentrations similar to the reported pattern of indocyanine green plasma concentrations in dogs (an initial delay period and subsequent peaks and troughs). METHODS: Two hypothetical NDMRs with either a very rapid or a slow decay in plasma concentrations were used for the simulations. A delay and oscillations were imposed on a multiexponential function for the plasma concentrations of the NDMRs by an additional, biexponentially dampened sinusoid function. The time between intravenous bolus administration of the NDMRs and the first rise in plasma concentrations was fixed at 0.2 min. As experimentally observed with indocyanine green in dogs, the oscillations were limited to the first minute after injection. The NDMRs were simulated to diffuse from plasma into and out of the interstitial space of muscles according to a rate constant and the concentration gradient. The NDMRs were postulated to have free access from the interstitial space to the receptors, and the neuromuscular block was calculated using the Hill equation. RESULTS: The delay and the peak and trough plasma concentrations during the first minute after bolus injection of the NDMRs were simulated well by the postulated dampened sinusoidal function. The times to peak submaximal NMB and the equieffective doses were similar whether calculated on the basis of oscillatory or extrapolated multiexponential functions. Both simulations demonstrated that a rapid initial decay of the plasma concentrations is associated with a slightly faster onset of peak NMB and a slightly higher equieffective dose. CONCLUSION: Consideration of early oscillations in the plasma concentrations of a NDMR barely alters the simulated time course of action from that simulated by an extrapolated multiexponential function.

[Intubation conditions following administration of atracurium and vecuronium. Bolus method versus priming technique]. / Intubationsbedingungen nach Gabe von Atracurium und Vecuronium. Bolusmethode vs. Primingtechnik.

Prompted by the ongoing discussion of the pros and cons of using succinylcholine, this study was conducted to compare the responses to bolus injections of atracurium or vecuronium with those after sequential injection of these drugs (priming principle). We evaluated the earliest possible intubation times, intubating conditions, and the onset times (i.e. times from the end of injection to the maximum blockade) under conditions approaching real use as closely as possible. METHODS. The randomized and double-blind study was carried out with 80 ASA risk class 1 and 2 patients. Approval of the institutional ethics committee was obtained, and each patient gave informed consent. Patients were randomly allocated to four study groups of 20 patients each. Isotonic saline was administered to those patients assigned to the atracurium or vecuronium bolus groups, whereas the patients assigned to the other two groups received a priming injection of either atracurium (0.05 mg/kg) or vecuronium (0.01 mg/kg). We observed the patients for signs of incipient muscular weakness before the induction of anaesthesia. Anaesthesia was induced with thiopental 3.5 min after the first injection (5 mg/kg and 50-100 mg before intubation). After a further 1 min during which adequate mask ventilating with oxygen was assured, corresponding to a priming interval of 4.5 min, 0.5 mg/kg of atracurium or 0.1 mg/kg of vecuronium was administered to the patients in the bolus groups and 0.45 mg/kg of atracurium or 0.09 mg/kg of vecuronium as intubating doses to those in the priming groups. Intubation was attempted at 90, 120, 150 and 180 s thereafter. Intubating conditions were evaluated on the basis of laryngoscopy, vocal cord movement and coughing or bucking of the patients. Neuromuscular function was monitored via accelerometry at the adductor pollicis muscle (TOF stimulation of the ulnar nerve every 15 s). RESULTS. The priming doses did not diminish the elicited twitches of the adductor pollicis muscle, but led to heavy eyelids and double vision in 35% of the atracurium patients and 47% of the vecuronium patients; these symptoms were well tolerated by the patients. At the time of intubation the adductor pollicis muscle was relaxed to approximately the same degree in all groups (mean +/- SD for the TOF ratios in the bolus groups was 0.46 +/- 0.37 for atracurium, 0.45 +/- 0.4 for vecuronium; in the priming groups 0.52 +/- 0.39 for atracurium, 0.53 +/- 0.36 for vecuronium). The administration of the relaxants in divided doses significantly shortened the intubating time after atracurium (100 vs 124 s) and improved the intubating conditions of vecuronium (good vs tolerable), but had no effect on the time course of the neuromuscular blockade (onset times in the bolus groups 224 +/- 84 s for atracurium and 209 +/- 64 s for vecuronium; in the priming groups 249 +/- 112 s for atracurium and 205 +/- 52 s for vecuronium). CONCLUSIONS. The priming technique presented here is clinically superior to the bolus method and therefore should be preferred in all elective cases and in those patients in whom succinylcholine is contraindicated.

Variance of cardiorespiratory parameters during gynaecological surgery with CO2-pneumoperitoneum.

Laparoscopic procedures with CO2-pneumoperitoneum are used widely in gynaecology and surgery. The effects of a 15 degrees head-down position, different intra-abdominal pressures (IAP) and CO2-insufflation flows on cardiorespiratory parameters were studied prospectively in 18 gyneacologic patients under general anaesthesia. The 15 degrees head-down position led to significant changes in heart rate (-6%) and in central venous pressure (+53%). Furthermore, significant changes under commonly used conditions for gynaecological laparoscopy (IAP 9mmHg, CO2-insufflation flow 2.41/ min., 15 degrees head-down position) were found in heart rate (+16%), systolic blood pressure (+21%), diastolic blood pressure (+26%), central venous pressure (+57%), peak inspiratory pressure (+26%), end-tidal CO2-concentration (+19%), central venous pCO2 (+21%), and central venous pH (-7%). On examination of variable pressure and insufflation flows (IAP 3, 9, and 15mmHg; CO2-insufflation flows 1.2, 2.4, and 6.0 1/min.), increasing changes in heart rate (7% - 24%), diastolic blood pressure (22% - 33%), central venous pressure (30% - 59%) and peak inspiratory pressure (10% - 43%) correlated with increasing IAP. However, they were independent of CO2-insufflation flows. The results demonstrate that CO2-pneumoperitoneum causes marked changes in cardiorespiratory parameters, but these do not exceed levels commonly regarded as safe in ASA class I and II patients.

[Modified hemoglobin solutions as artificial oxygen carriers]. / Modifizierte Hämoglobinlösungen als künstliche Sauerstoffträger.

At least theoretically, hemoglobin (Hb) solutions are ideal colloidal plasma substitutes because of their unique ability to take up oxygen, transport it in bound form, and release it peripherally. The present study gives an overview of the development and present status of modified Hb preparations. While human and bovine erythrocytes are used for production on the one hand, human Hb variants can also be derived from yeast or bacteria as well as via transgenic animals through recombinant DNA technology. The pronounced limitations of extraerythrocytic Hb, that is its high oxygen affinity and its inadequate intravascular persistence, can be overcome by various modifications. Intravascular half-life of free Hb can be significantly increased by intramolecular stabilization, linking to macromolecules, intermolecular cross-linking (PolyHb solutions) or microencapsulation. Oxygen affinity of human Hb may be lowered by coupling of allosteric modulators to the 2,3-bisphosphoglycerate site, e.g. pyridoxal phosphate, whereas bovine Hb has an intrinsically low oxygen affinity. Human pyridoxylated PolyHb solutions and bovine PolyHb solutions presently fulfill at least 2 of the 3 principal requirements for an oxygen-transporting plasma substitute, i.e. maintenance of the circulating blood volume with provision of additionally utilizable oxygen capacity. Matters of concern with all Hb preparations remain potential vasoconstrictive effects and renal toxicity. Major efforts being undertaken at present by industry and research groups give reason to hope, however, that the concept of modified Hb solutions as oxygen carriers will be realized in the foreseeable future.

[Prolonged neuromuscular blockade. Different antagonistic effects following successive exposure to vecuronium and succinylcholine in a patient with atypical plasma cholinesterase]. / Prolongierte neuromuskuläre Blockade. Unterschiedliche Antagonisierungseffekte nach wiederholter kombinierter Gabe von Vecuronium und Succinylcholin bei einem Patienten mit atypischer Plasmacholinesterase.

An 81-year-old patient had prolonged competitive neuromuscular blockade with train-of-four ratios of 0.1 and 0.5, respectively, after two successive anaesthesia procedures (enflurane-N2O/O2; vecuronium-succinylcholine-sequence) for transurethral prostate resection. Although antagonism with neostigmine was promptly successful after the first, 65-min period of anaesthesia (1.5 mg vecuronium for precurarization, 100 mg succinylcholine for intubation, 3 mg vecuronium), repetitive and chronologically staggered administration of neostigmine after the second, 30-min period of anaesthesia (1 mg vecuronium for precurarization, 100 mg succinylcholine for intubation) had hardly any effect, so that the patient had to be ventilated mechanically for a total of 4.5 h. Laboratory analysis revealed homozygous, atypical, plasma cholinesterase (790 U/l; dibucaine number 23; genotype E1aE1a). This retrospectively confirmed a succinylcholine-induced phase II block in both instances, as had already been suspected following the second anaesthetic procedure. The degree of block transformation, and thus the available time, are decisive in explaining the diverse effects of antagonism here. It must be assumed that a complete phase II block developed after the first succinylcholine exposure owing to the longer duration of anaesthesia; the purely competitive component (train-of-four ratio 0.1) was easily antagonized by neostigmine. At the time of the attempted antagonism after the second, shorter period of anaesthesia, however, block transformation was still incomplete (train-of-four ratio 0.5). The administration of neostigmine therefore rather intensified the depolarization segment of the mixed block, so that repeated attempts at antagonism then inhibited any further block transformation.

[Monitoring neuromuscular function: capnography versus relaxometry]. / Uberwachung der neuromuskulären Funktion: Kapnographie versus Relaxometrie.

OBJECTIVE: A notch ("curare cleft") in the plateau phase of the capnogram of the ventilated patient has been presumed to be a typical early sign of the fading effect of muscle relaxants on the diaphragm. For that reason a prospective study was done to investigate whether capnography can be used diagnostically to indicate the fading effect of vecuronium confirmed by peripheral relaxometry. METHODS: Twenty-five consecutive patients who received inhalation anaesthesia with isoflurane, N2O/O2, and vecuronium during elective neurosurgical procedures were studied. Whenever intraoperative "curare clefts" appeared in the capnogram, diaphragm activity was measured and a simultaneous relaxogram of the adductor pollicis muscle was recorded. After every such event, vecuronium was readministered for complete relaxation. RESULTS: A deformation of the capnogram was registered in 17/25 patients and in all instances (51/51) was caused by diaphragm activity. The deformation disappeared after renewed relaxation and was therefore a reliable indicator of spontaneous breathing. However, it did not correlate with the degree of relaxation of peripheral muscles, because diaphragm activity was present during all degrees of peripheral relaxation, but could also be absent even after complete recovery of neuromuscular transmission. CONCLUSION: Capnography is therefore not a reliable method to indicate the fading effect of muscle relaxants.

Oxygen transport by pyridoxylated polyhemoglobin solution.

Pyrodoxylated Polyhemoglobin (PolyHb-PPa) with physiological oxygen affinity (P50 27 mm Hg) was used in vitro and in vivo. The oxygen binding coefficient was 1.1 ml O2/dl/g Hb, the oxygen capacity of 8.5% PolyHb-PPa solution 9.3 ml O2/dl, Hill coefficient 1.7, Met-Hb content below 2%. Exchange transfusion of whole blood with PolyHb-PPa results in a significant, linear increase in total oxygen capacity, in contrast to exchange transfusion with asanguineous solutions. In vitro analysis of oxygen equilibrium curves of mixtures of whole blood with PolyHb-PPa, however, shows a nonlinear release of the additional blood oxygen capacity. Significant amounts of PolyHb-PPa-bound oxygen are made available only when hemodilution exceeds 25%; only at 75% hemodilution does oxygen delivery by PolyHb-PPa account for 50% of the unloaded oxygen. In vivo results after therapy for hemorrhagic shock in minipigs clearly shows the efficacy of oxygen transport by PolyHb-PPa. At 70% hemodilution, PolyHb-PPa bound oxygen was twice that of erythrocytic oxygen. Availability of this additional oxygen capacity was demonstrated by an oxygen extraction ratio of 0.40%. The utility of PolyHb-PPa solution with "normal" P50 in the therapy of moderate anemia, however, remains to be proved.

Unrecognized endobronchial intubation of emergency patients.

Although intubation of emergency patients in the field is a routine measure, endotracheal tube misplacement remains a serious problem. Using radiologic criteria, the frequency of undetected endobronchial intubation by physicians was determined retrospectively in 100 (78 traumatized) field-intubated adult patients (72 men and 28 women; age, 18 to 90 years; mean age, 39.1 years) consecutively admitted to the University Hospital of Tuebingen, Tuebingen, Federal Republic of Germany, between January 1987 and February 1988. Position of tube tip relative to carina was evaluated on anteroposterior chest radiographs made on admission. Inadvertent endobronchial intubation was not recognized by the physician and the admitting anesthesiologist in 7% of the reviewed cases, and endotracheal positioning of the tube tip near the carina (2 or less cm) occurred in another 13%. While unilateral intubation is not immediately catastrophic, the resulting systemic hypoxemia and hypercapnia are aggravated by potential accompanying injury (eg, lung contusion, hematothorax, pneumothorax, shock, or cerebrocranial trauma), which can lead to secondary damage (eg, acute respiratory insufficiency, ischemic brain damage). Evaluation of the depth of tube insertion with the aid of common clinical techniques is particularly unreliable in the case of thoracic trauma, aspiration, or previously existing pulmonary disease. Suggested measures for prevention of endobronchial intubation are improved and intensified training of emergency staff to increase awareness of and prevent the catastrophic effects of endobronchial malposition of the tube tip, tube shortening before intubation, assessment of insertion depth by checking length scale on the tube, and avoidance of patient head and neck movement.