Comparison of superimposed high-frequency jet ventilation with conventional jet ventilation for laryngeal surgery.

BACKGROUND: New ventilators have simplified the use of supraglottic superimposed high-frequency jet ventilation (SHFJV(SG)), but it has not been systematically compared with other modes of jet ventilation (JV) in humans. We sought to investigate whether SHFJV(SG) would provide more effective ventilation compared with single-frequency JV techniques. METHODS: A total of 16 patients undergoing minor laryngeal surgery under general anaesthesia were included. In each patient, four different JV techniques were applied in random order for 10-min periods: SHFJV(SG), supraglottic normal frequency (NFJV(SG)), supraglottic high frequency (HFJV(SG)), and infraglottic high-frequency jet ventilation (HFJV(IG)). Chest wall volume variations were continuously measured with opto-electronic plethysmography (OEP), intratracheal pressure was recorded and blood gases were measured. RESULTS: Chest wall volumes were normalized to NFJV(SG) end-expiratory level. The increase in end-expiratory chest wall volume (EEV(CW)) was 239 (196) ml during SHFJV(SG) (P<0.05 compared with NFJV(SG)). EEV(CW) was 148 (145) and 44 (106) ml during HFJV(SG) and HFJV(IG), respectively (P<0.05 compared with SHFJV(SG)). Tidal volume (V(T)) during SHFJV(SG) was 269 (149) ml. V(T) was 229 (169) ml (P=1.00 compared with SHFJV(SG)), 145 (50) ml (P<0.05), and 110 (33) ml (P<0.01) during NFJV(SG), HFJV(SG), and HFJV(IG), respectively. Intratracheal pressures corresponded well to changes in both EEV(CW) and V(T). All JV modes resulted in adequate oxygenation. However, was lowest during HFJV(SG) [4.3 (1.3) kPa; P<0.01 compared with SHFJV(SG)]. CONCLUSION: SHFJV(SG) was associated with increased EEV(CW) and V(T) compared with the three other investigated JV modes. All four modes provided adequate ventilation and oxygenation, and thus can be used for uncomplicated laryngeal surgery in healthy patients with limited airway obstruction.

Evaluation of a new fibre-optical monitor for respiratory rate monitoring.

OBJECTIVES: To present further development of a fibre-optical respiratory rate monitor and evaluate the function in the final version. METHODS: Respiration was recorded in 18 healthy volunteers of ages 9-83 years by three different methods simultaneously: fibre-optical monitoring, capnography and manually. The recordings were made-breath by breath in four 3-minute periods in each subject. In total there were 54 observations, corresponding to 648 minutes. The recordings were fed simultaneously into a computer. Two subjects were excluded because of pronounced differences between all three methods. One person was later diagnosed as having a nasal septum deviation. Recordings with any kind of technical problem were also excluded. RESULTS: In total 516 minutes were analysed. Students' paired t-test showed a mean of 0.5 and 0.3 more breaths were recorded by fibre-optical monitor compared with the manual method and capnography respectively. The 95% confidence interval of the differences between the fibre-optical monitor and the other two methods was -0.5 to +1.5 when the mean respiratory frequency was 14 breaths per minute. Analysis of variance revealed that the fibre-optical monitor tended to overestimate the mean respiratory rate (p < 0.001). CONCLUSION: The fibre-optical monitor has sufficient accuracy for clinical monitoring. It is easy to use and inexpensive. Combinations with pulse oximetry seem attractive, to use especially for application outside "high tech areas," for example when respiratory depressant drugs are used or in ambulances.

Use of post-tetanic count in assessment of a repetitive vecuronium-induced neuromuscular block.

In order to evaluate the use of the post-tetanic count (PTC) method during repetitive administration of vecuronium, we studied 20 patients allocated randomly to one of two groups: 10 patients received droperidol-fentanyl anaesthesia (control group); 10 other patients were given droperidol-fentanyl anaesthesia modified subsequently by addition of 0.5% isoflurane (isoflurane group). Before tracheal intubation, a bolus dose of vecuronium 0.08 mg kg-1 was given i.v. followed by repeated doses of 0.03 mg kg-1. The twitch response of adductor pollicis was recorded after supramaximal stimulation of the ulnar nerve at the wrist using a Myograph 2000 neuromuscular transmission analyser. In the control group, a close correlation was found between PTC and time to first reaction to train-of-four (TOF) nerve stimulation. This relationship was unchanged when comparing the bolus dose and each of eight consecutive maintenance doses. Further, the degree and the duration of intense block were unchanged after each of the eight maintenance doses. In the isoflurane group, the relationship between PTC and time to first reaction to TOF stimulation remained unchanged after addition of isoflurane. However, isoflurane caused a significant prolongation of the duration of intense block and a corresponding lower PTC in all patients. We conclude that PTC is a reliable method to evaluate intense neuromuscular block caused by vecuronium, even after repetitive administration of the drug and in combination with 0.5% isoflurane.

The influence of 10 mg and 20 mg of bambuterol on the duration of succinylcholine-induced neuromuscular blockade.

Bambuterol is an inactive prodrug which is enzymatically cleaved by plasma cholinesterase to yield the active compound, terbutaline. This catalytic process is accompanied by a selective inhibition of plasma-cholinesterase, the enzyme also necessary for the break-down of succinylcholine. We therefore studied the possible effect of bambuterol on succinylcholine-induced neuromuscular blockade in a double-blind fashion in patients undergoing surgery under general anaesthesia. Of the 39 patients studied, 13 patients had 10 mg of bambuterol, 12 had 20 mg and 14 were given placebo 10-16 h prior to anaesthesia. Succinylcholine 1 mg.kg-1 bw was administered after induction of anaesthesia. Following supramaximal train-of-four stimulation of the ulnar nerve, the tension developed in the adductor pollicis muscle was measured. Onset time and the durations of action (times to 10%, 25%, 75% and 90% recovery of the first twitch of the train-of four response) were recorded. The mean recovery times were prolonged 30-50% in patients who had received 10 or 20 mg of bambuterol as compared with placebo. It is concluded that a prolonged duration of action of succinylcholine can be expected in patients being treated with bambuterol.

Clinical experience with atracurium during prolonged anaesthesia.

The pharmacodynamic properties of repeated injections of atracurium were studied in twenty-two patients. A control group received narcotic-based anaesthesia while another group received the same narcotic-based anaesthesia subsequently modified by the addition of 0.5% isoflurane. The twitch response of the adductor pollicis muscle was recorded after train-of-four (TOF) stimulation of the ulnar nerve at the wrist. Duration of effect and recovery time were measured. A bolus dose of atracurium (0.5 mg/kg b.w.) was given for tracheal intubation and maintenance doses of 0.2 mg/kg b.w. were given during anaesthesia at a TOF ratio of 0.25. Mean duration of anaesthesia was 7.5 hours (range 3-19). In the control group mean duration of effect and mean recovery time remained unchanged (six doses studied). A noteworthy inter-individual variation was found. In the isoflurane group mean duration of effect increased from 36.1 (SD 6.3) minutes to 42.2 (SD 8.1) minutes (P less than 0.05) following the addition of isoflurane. Corresponding recovery times remained unchanged. We conclude that during repeated administration of atracurium during narcotic-based anaesthesia, each patient shows a constant interval between requirements for maintenance doses of atracurium of 0.2 mg/kg b.w. Addition of 0.5% isoflurane causes a moderate prolongation of the duration of effect, but recovery time remains unchanged.

The influence of 0.5% isoflurane on a vecuronium-induced neuromuscular blockade.

The influence of adding 0.5% isoflurane to a narcotic-based anaesthesia on the duration of effect and recovery time after repetitive administration of vecuronium was studied in ten healthy patients. The twitch response in the adductor pollicis muscle was recorded after supramaximal train-of-four (TOF) stimulation of the ulnar nerve at the wrist. Prior to endotracheal intubation a bolus dose of vecuronium (0.08 mg/kg b.w.) was given. During surgery repeated injections of vecuronium (0.02 mg/kg b.w.) were administered at a TOF ratio of 0.25. Hand-skin temperature, systolic blood pressure, end-tidal CO2 and isoflurane concentrations were continuously monitored. Before and after 90 min administration of isoflurane, the duration of effect was 21 +/- 4 and 24 +/- 5 min (mean +/- s.d., P less than 0.05) respectively. Corresponding recovery times were 270 +/- 60 and 280 +/- 70 s (n.s.). Skin temperature remained unchanged and systolic blood pressure showed only minor variations. The addition of 0.5% isoflurane to a narcotic-based anaesthesia causes a moderate increase in duration of effect but no change in recovery time from a repetitive vecuronium-induced neuromuscular blockade of 0.02 mg/kg.

Experience with vecuronium during long-lasting surgery.

Our knowledge of the possible cumulative properties of vecuronium is limited. Previous studies have shown a tendency towards an increased duration of effect, a slightly prolonged recovery time, as well as an increased variation in duration of effect. We have studied 15 patients scheduled for middle-ear surgery. During i.v. N2O-O2 anaesthesia the twitch response of the adductor pollicis muscle was recorded after supramaximal stimulation of the ulnar nerve at the wrist. Prior to tracheal intubation a bolus dose of vecuronium was given (0.08 mg/kg body weight). During surgery supplementary doses of 0.02 mg/kg body weight were given at a train-of-four (TOF) ratio of 0.25. The duration of effect (DUR-IT-25) and recovery time from a TOF ratio of 0.10 to 0.25 (Recovery-IT-10-25) were recorded. When comparing 10 iteration doses, the mean DUR-IT-25 in the 15 patients studied showed only minor variations (n.s.). Each patient had a near constant interval between the iteration doses; however, a noteworthy variation between individuals was found. Recovery-IT-10-25 was 250 +/- 80 (mean +/- s.d.) 240 +/- 80 and 260 +/- 80 s comparing the second, sixth and tenth iteration doses, respectively. In conclusion, the duration of effect varied considerably between patients. Each patient showed, however, a near constant iteration interval and a recovery time with only small variations. This indicates that cumulation is unlikely to exist following repetitive administration of vecuronium of 0.02 mg/kg body weight.

Experience of multiple supplementary doses of vecuronium. Case report.

Seventy-one supplementary doses of vecuronium were used for muscle relaxation during a 22-h-long NLA II anaesthesia. For assessment of neuromuscular blockade, train-of-four stimulation was used to measure the twitch force of the adductor pollicis after electrical stimulation of the ulnar nerve. No cumulative effect of vecuronium could be demonstrated, measured under strictly controlled conditions. Adding isoflurane 0.5% (end tidal) only slightly prolonged the neuromuscular blocking effect.

Psychological effect of detailed preanesthetic information.

Eighty-one patients admitted for minor surgery were followed with questionnaires and self-rating scales in the pre- and post-anesthetic period to evaluate the effect of giving either routine or detailed information. The patients were randomly allocated to two groups and received either routinely given information by the anesthetist for about 5 min or more detailed information for at least 20 min. The patients' experience of the effect of the preanesthetic visit was tranquillizing and adequate in both groups. The most significant difference with detailed information was a smaller number of side-effects like slow cerebration, nausea and a general feeling of discomfort compared to the routinely informed patients. Repetitive ratings on Spielberger's State of Anxiety Scale showed that the patients who had had previous anesthetic experience were less influenced by the degree of information given. In view of the considerable numbers of parameters investigated, there were relatively few significant differences between the groups, and it was concluded that there was no convincing benefit from expanding routine to detailed information.