Management of the challenging airway with the Bullard laryngoscope.

The Bullard laryngoscope is a rigid fiber-optic device that offers a new approach to oral laryngoscopy. In this report, I present five cases illustrative of the use of the Bullard laryngoscope in patients with demonstrated or suspected difficult laryngoscopy and intubation.

Extubation after transsternal thymectomy for myasthenia gravis: a prospective analysis.

Recommendations concerning postoperative extubation after thymectomy for myasthenia gravis are presently based upon retrospective chart reviews. We present the results of a prospective investigation of time to extubation after thymectomy for 14 patients over a 12-month period based upon a protocol that included preoperative immunologic therapy, combined epidural and general anesthesia, postoperative epidural narcotic analgesia, and a standardized approach to discontinuation of ventilatory support. After a neurologist took measures to optimize preoperative neuromuscular function, all 14 patients received agents to produce lumbar epidural anesthesia and light general anesthesia. Muscle relaxants were avoided in all but one patient. Postoperative analgesia was initially maintained with epidural hydromorphone, then therapy was switched to patient-controlled intravenous morphine sulfate. Criteria for weaning from mechanical ventilation, first measured at the end of anesthesia, were partial pressure of oxygen (arterial) greater than or equal to 90 mm Hg (fraction of inspired oxygen = 0.40), partial pressure of carbon dioxide (arterial) less than or equal to 50 mm Hg, pH greater than or equal to 7.30, and respiratory rate less than or equal to 30 breaths/min. If these criteria were not met, ventilatory support was continued postoperatively with intermittent mandatory ventilation, and the patient was weaned gradually from this support. Criteria for extubation included meeting the criteria for weaning, vital capacity greater than or equal to 10 mL/kg, and inspiratory pressure better than -30 cm H2O. Criteria for reintubation included tachypnea (respiratory rate greater than 40 breaths/min), respiratory acidosis not due to narcotics, or vital capacity less than or equal to 8 mL/kg. The mean time to extubation was 9 hours (range, 0.75 to 25 hours). Mean preoperative vital capacity was 2.59 +/- 0.64 L (range, 1.90 to 4.20), which decreased approximately 50% to 1.19 +/- 0.39 L (range, 0.70 to 2.0) at the time of extubation. No patient required reintubation. Half of the patients required postoperative anticholinesterase therapy based upon serial neurologic examinations; there were no instances of cholinergic crisis. Thirteen patients returned to the ward on the first postoperative day, and one on the second day. Thirteen patients preferred epidural analgesia to patient-controlled analgesia. The time to extubation and average length of stay in an intensive care setting were markedly reduced compared to those reported in previous retrospective studies. We conclude that a multidisciplinary approach that optimizes neuromuscular function and decreases poststernotomy pulmonary insult will shorten the time to extubation and decrease the length of stay in the intensive care or recovery room after thymectomy.

Clinical responses to ORG 9426 during isoflurane anesthesia.

To determine average dose requirements and pharmacodynamic characteristics before general clinical use, the dose-response curve, onset time, and recovery time for the neuromuscular relaxant ORG 9426 were determined in 72 adult patients given doses of 120, 160, 200, or 240 micrograms/kg after establishment of a steady-state expired isoflurane concentration of approximately 1%. Neuromuscular blockade was continuously recorded using the ulnar evoked electromyogram. Using the log probit method, ED95 was 268 micrograms/kg, ED90 was 251 micrograms/kg, and ED50 was 144 micrograms/kg. The time until 80% blockade was 1.9 min at 240 micrograms/kg, and the average time to peak effect was 4.6 min, which did not vary with dose. The clinical duration (injection until T1 returned to 25%) was 20.5 min, and the recovery index (T1 increased from 25% to 75% of control) was 15.4 min, after a total dose of 300 micrograms/kg. The duration of 75-micrograms/kg and 100-micrograms/kg repeat (maintenance) dose was 14.6 and 17.8 min, respectively, and no cumulative effect was apparent after as many as five maintenance doses. No cardiovascular side effects were seen at doses used in the study. We conclude that ORG 9426 is a nondepolarizing muscle relaxant with a rapid onset and short duration of action that deserves further clinical evaluation.

The relative accuracies of two automated noninvasive arterial pressure measurement devices.

We compared the accuracies of two types of noninvasive blood pressure devices. Thirty-two patients requiring an intraarterial catheter for anesthetic management underwent simultaneous monitoring with Dinamap 1846SX and Ohmeda Finapres 3700 devices. For the first 10 minutes of recording, new Dinamap determinations were performed every 60 seconds; subsequent recordings were made at 3-minute intervals. Data were obtained at the time of new Dinamap readings, and twice between new readings to approximate the real-time performance of the two monitors. We defined superior accuracy as a statistically significant difference in mean absolute error greater than 5 mm Hg. With these criteria, pooled data from all patients revealed no difference in performance, even in real time. Pooled data can be misleading since there was a significant amount of variation in accuracy for both monitors. Therefore, we used nonparametric analysis to determine how many individual patients were monitored better by either device. When we compared only data from new Dinamap readings, the Finapres monitor showed superior performance for systolic readings in 13 patients, versus 6 patients for the Dinamap (P less than 0.05, chi-square test). Similar analysis for diastolic and mean pressure performance did not reach statistical significance. However, in real time, the Finapres unit monitored more patients more accurately for systolic (14 Finapres versus 3 Dinamap), diastolic (11 Finapres versus 3 Dinamap), and mean (10 Finapres versus 3 Dinamap) pressure determinations. The magnitude of these differences were, however, less dramatic than expected. This was probably due to stabilization of arterial pressure during the anesthetic, which minimized the error due to intermittent sampling. We conclude that continuous Finapres readings and new Dinamap determinations are equally accurate for diastolic and mean arterial pressures. The accuracy of Finapres appears to be slightly superior for systolic pressure. The intermittent sampling of oscillometric devices compromises their performance relative to the Finapres in many, but not all, cases.

The accuracy of rapid oscillometric blood pressure determination.

The Dinamap 1846SX (DIN) offers a "stat mode" (SM) for rapid repetitive blood pressure determinations, but its accuracy has not been reported. Thirty patients who required an intra-arterial catheter (IAC) for management of anesthesia underwent induction with concomitant noninvasive blood pressure measurement provided by a DIN set in SM. Computerized automated data acquisition recorded digital outputs from both monitors at the time of new SM readings. Systolic pressure mean absolute error (MAE) was 13.3 +/- 5.7 mmHg (mean +/- SEM) and the mean error (bias) was -8.7 +/- 9.8 mmHg. Mean pressure MAE was 6.8 +/- 3.4 mmHg and bias was -0.5 +/- 6.3 mmHg. Diastolic pressure MAE was 7.0 +/- 3.3 mmHg and bias was -0.3 +/- 6.5 mmHg. There was a tendency for systolic pressure readings to underestimate IAC pressures at higher pressures. These findings echo results reported previously for DIN operating in its normal mode. Rapid arterial pressure determination by SM does not appear to compromise accuracy.

Gastroesophageal reflux during anesthetic induction with thiopental and succinylcholine.

The effects of patient physiology and the prior administration of a nondepolarizing muscle relaxant on the frequency of gastroesophageal reflux during induction with thiopental sodium and succinylcholine were investigated. Forty patients underwent anesthetic induction during continuous esophageal pH monitoring. Twenty patients had preoperative symptoms of gastroesophageal reflux, and 20 asymptomatic patients served as controls. Half the patients in each group received a small dose of nondepolarizing muscle relaxant prior to induction. Five patients (25%) with gastroesophageal reflux and none of the control patients showed significant decreases in esophageal pH during induction. Two of these patients received prior administration of a nondepolarizing drug. In all five patients, reflux occurred during laryngoscopy and intubation, suggesting the possibility that succinylcholine did not play a role in the generation of reflux. Preoperative gastroesophageal reflux symptomatology is associated with an increased frequency of reflux during induction, and the vulnerable period seems to occur after the achievement of neuromuscular blockade during laryngoscopy. Preinduction administration of a non-depolarizing muscle relaxant prior to succinylcholine use had no demonstrable effect on the frequency of reflux during induction, although the numbers studied were too small to be conclusive.

Problems associated with the determination of pulmonary vascular resistance.

The presence of critical pressures in the pulmonary circulation complicates the traditional use of pulmonary vascular resistance (PVR). The recruitable nature of the pulmonary circulation violates a basic assumption of the PVR formula, that is, that the involved vessels are rigid-walled. Flow through collapsible blood vessels is subject to the influence of critical opening pressures in addition to inflow and outflow pressures. As a result, PVR has a variable relationship to the Poiseuille resistance, approximating it better when zone 3 conditions predominate. In addition to being flow-dependent, PVR cannot easily distinguish among vasodilation, recruitment, and rheologic changes. PVR may be viewed as an index of steady-state power dissipation by the circulation, describing the relationship between power dissipation and flow, but it will still underestimate power dissipation by as much as 50%, since it cannot express oscillatory and kinetic power components. Laboratory data regarding the pulmonary circulation are predicted and explained by positing the existence of critical pressures in the pulmonary circulation and allow estimation of Poiseuille resistance. Unfortunately, clinical application of this approach is difficult owing to the necessity of generating pressure-flow plots under very stringent conditions. The clinical use of both pressure-flow and PVR-flow plots is impaired by shifting to different curves during hemodynamic manipulation. PVR must be interpreted in light of its considerable limitations.

Reinforced endotracheal tube placement: radiographic misdiagnosis.

The position of an armored endotracheal tube was misinterpreted on radiographs. This occurred because no one recognized that there was no radiopaque line extending to the tip of the catheter. Physicians should be aware of this possible pitfall, and manufacturers should remedy the situation by marking such lines on these tubes.