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Anesth Analg 1999;88:1335
© 1999 International Anesthesia Research Society

ECONOMICS AND HEALTH SYSTEMS RESEARCH

The Costs of Intense Neuromuscular Block for Anesthesia During Endolaryngeal Procedures Due to Waiting Time

Arto I. E. Puura, MD*, Michael G. F. Rorarius, MD, PhD{dagger}, Pia Manninen, MD{ddagger}, Sanna Hopput, MD{ddagger}, and Gerhard A. Baer, MD, PhD{dagger}

*Department of Anaesthesia, Municipal Hospital of Valkeakoski; {dagger}Department of Anaesthesia, Tampere University Hospital and Medical School; and {ddagger}Medical School, University of Tampere, Tampere, Finland

Address correspondence and reprint requests to Arto Puura, MD, Katajatie 19 B, FIN-36200 Kangasala, Finland. Address e-mail to puura{at}sci.fi


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
The goal of this double-blinded, prospective study was to compare the costs incurred by waiting time of intense neuromuscular block while posttetanic count (PTC) was maintained at 0–2 during jet ventilation. Fifty patients were randomized into five groups to receive atracurium (ATR), mivacurium (MIV), rocuronium (ROC), vecuronium (VEC), and succinylcholine (SUCC). PTC <=2 was maintained until completion of laryngomicroscopy by administering additional doses of relaxants or by adjusting the speed of the infusion of SUCC. We compared waiting time, i.e., onset time and recovery time, and costs of intense neuromuscular block. The expenses due to waiting time were calculated based on the average costs in the otorhinolaryngological operating room in Tampere University Hospital: FIM 40 (approximately $8) per minute in 1997. MIV and SUCC differ favorably from ATR, ROC, and VEC when waiting time and costs are concerned. The recovery times with MIV and SUCC were considerably shorter than those with ATR, ROC, and VEC (P < 0.001 in all pairwise comparisons). Using the muscle relaxant with the longest waiting time instead of that with the shortest waiting time (difference 21.8 min) cost more than FIM 800 (approximately $160) extra per patient.

Implications: In this randomized, double-blinded, prospective study, we evaluated the costs of intense neuromuscular block due to waiting time. Succinylcholine and mivacurium are the most economical muscle relaxants to use when intense neuromuscular block is mandatory. Using intermediate-acting muscle relaxants results in unduly prolonged recovery time and extra costs.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Microsurgery of the larynx aims at exact excision of the lesion with minimal destruction of normal tissue and maximal preservation of function. Intratracheal jet ventilation provides excellent working conditions for endolaryngeal procedures (ELPs) (1). Intratracheal jet-ventilation for ELPs is safe only when the muscles of the larynx and diaphragm are completely paralyzed (2,3). Intense neuromuscular block (NMB) and absolute immobility are mandatory during ELPs. The choice of a muscle relaxant may cause extra expense because intense NMB is essential until completion of the operation, and the duration of recovery from intense NMB varies considerably with different muscle relaxants (MRs). However, there are no comparative studies regarding intense NMB with new short- and intermediate-acting nondepolarizing MRs. The goal of this prospective, double-blinded study was to compare waiting time, i.e., onset time and total recovery time, and the costs of intense NMB. During ELPs, the target of the intense NMB was to maintain the posttetanic count (PTC) at 0–2, which means that additional doses of MRs were administered if more than two single twitch responses (STW) were detected after a 50-Hz tetanic stimulation.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
We studied 50 healthy (ASA physical status I–III) patients scheduled for ELPs in the Tampere University Hospital after obtaining ethical committee approval and written, informed patient consent. Patients used no drugs and had no disorders known to affect NMB. Patients with body mass index >28 kg/m2 were not enrolled in the study. The patients were allocated randomly (by drawing lots) into five groups to receive atracurium (ATR), mivacurium (MIV), rocuronium (ROC), vecuronium (VEC), or succinylcholine (SUCC).

Except for the head, patients were covered with thermal blankets. The IV infusion of acetated Ringer's solution was warmed by using an infusion warmer. Axillary temperature was recorded at the beginning of anesthesia and at the end of the procedure. Usual monitoring was used. Anesthesia was induced with alfentanil 20 µg/kg, followed after 60 s by propofol 1–2 mg/kg, and was maintained with an infusion of propofol. Additional doses of alfentanil 5 µg/kg were administered if the heart rate increased to >100 bpm or if the arterial systolic blood pressure was >150 mm Hg. The lungs were ventilated with pure oxygen via a face mask until intubation of the trachea with a double-lumen jet catheter. A jet ventilator was used for ventilation, and a special monitor was used to monitor the airway pressure curve (1). The tracheal pressure signal was observed via the monitoring line of the double-lumen jet catheter. The same line was used for end-tidal gas monitoring during expiration (4). Ventilation was adjusted to maintain the end-tidal carbon dioxide level at each patient's baseline level.

The initial doses of MRs averaged 2 times 95% effective doses and were: ATR 0.45 mg/kg, MIV 0.15 mg/kg, ROC 0.6 mg/kg, and VEC 0.11 mg/kg. The anesthesiologist was blinded to the MRs used, which were prepared and administered by a nurse anesthetist. Additional doses were 25% of the initial dose of ATR, ROC, and VEC and 50% of the initial dose for MIV at 3-min intervals until PTC <=2 was reached. The first additional doses were given 4 min after the initial dose of the MR as needed. The initial SUCC bolus 1 mg/kg was followed by a SUCC infusion, which was adjusted to maintain PTC <=2. We doubled the speed of the infusion of SUCC if NMB was inadequate, but we decreased the speed of the infusion at steps of 25% when PTC 0 for >6 min.

We used two identical devices to monitor STW and PTC (Myotest®; Biometer, Copenhagen, Denmark). The ulnar nerve was stimulated at the wrist. The movements were tactilely evaluated from the thumb of the patient by the same person (SH), who was not allowed to order or administer anesthetics. For PTC, the Myotest® delivers 1-Hz single-twitch stimulation, which begins 3 s after a 50-Hz tetanic stimulation of 5 s duration. Tetanic stimulation may disturb the next counts for 6 min (5). Therefore, we monitored PTC from both hands in turn at 3-min intervals. STW stimulation was started immediately after the patients became unconscious. After disappearance of the STW, PTC was monitored from both hands. Thus, PTC was recorded the first time 1 min after disappearance of STW and thereafter at 3-min intervals. The onset time between the administration of a MR and the time to reach intense NMB (PTC <=2) was recorded. The intubation and the ELP were not performed before PTC was in the desired range. Inadequate NMB was noted when the anesthesiologist or the nurse anesthetist observed movements of the vocal cords on the video monitor of the operating microscope; when an alarm was sounded by the airway pressure curve monitor; or when PTC increased to >2. When inadequate NMB was noted via one source, an additional dose of MR was administered.

The end of the ELP was recorded when the otorhinolaryngologist discontinued laryngomicroscopy. After ELP, neostigmine 0.04 mg/kg combined with glycopyrrolate 0.008 mg/kg was administered IV (except in the SUCC group), when NMB had recovered spontaneously to PTC 10, which correlates to train-of-four 1/4. The infusion of propofol continued at 4 mg · kg-1 · h-1 until fade had disappeared in dual burst stimulation (DBS) mode.

Total recovery time includes both the spontaneous recovery time from completion of ELP until administration of the antagonists and the neostigmine-induced reversal time from the administration of the antagonists until no fade was detected in DBS mode. The waiting time caused by the MR includes both the onset time and the total recovery time. Waiting time-related costs were calculated based on the average operating room (OR) costs (FIM 2400 or approximately $480) per hour in the otorhinolaryngology department of Tampere University Hospital (a nonprofit hospital). The minor expense of each drug itself was ignored in this study.

Statistical analysis was based on analysis of variance, and post hoc comparisons were based on the least significant difference method. The gender distribution among the groups was performed by using {chi}2. Differences were considered statistically significant at the P < 0.05 level. Data are presented as mean ± SD.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
There was no difference in demographic data among the groups (Table 1). There were no statistical differences among the groups for the duration of the ELP (17.8 ± 14.3 min), mean PTC during ELP (2.9 ± 3.1), axillary temperature at the start (35.5 ± 0.4°C) and end (35.3 ± 0.4°C) of anesthesia, or for end-tidal carbon dioxide at the start (28.5 ± 6.7 mm Hg) and end (27.8 ± 9.0 mm Hg) of anesthesia.


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  		Table 1. Patient Characteristics
 
In the analysis of variance, we found a significant difference in the onset time among the groups. The post hoc comparisons showed that the onset time to achieve intense NMB (PTC <=2) was 4.6 ± 2.0 min in Group SUCC, which was significantly shorter compared with all the other groups (P = 0.02–0.0002 in pairwise comparisons) (Table 2). The mean onset times to PTC <=2 in Groups ATR, ROC, and VEC were 8.2 ± 3.1, 7.2 ± 2.5, and 6.6 ± 0.3 min, respectively, with no significant differences among groups. In Group MIV, the onset time to PTC <=2 was 9.0 ± 2.2 min, which was significantly longer than that in Groups SUCC (4.6 ± 2.0 min; P = 0.0002) and VEC (6.6 ± 0.3 min; P = 0.003).


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  		Table 2. Onset Time Between Administration of a Muscle Relaxant and the Time to Reach Intense Neuromuscular Block (Posttetanic Count <=2)
 
The post hoc comparisons showed that the total recovery times in Groups MIV and SUCC were 7.6 ± 2.8 and 7.9 ± 4.1 min, respectively, which were significantly shorter than those in Groups ATR, ROC, and VEC (26.0 ± 8.2, 18.6 ± 6.9, and 17.2 ± 5.3 min, respectively; P < 0.001 in all pairwise comparisons) (Table 3). In Group ATR, the total recovery lasted longer (26.0 ± 8.2 min) than that in any other group (Table 3).


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  		Table 3. Total Recovery Time from Completion of Surgery Until no Fade Was Detected in Dual Burst Stimulation
 
The total waiting time due to intense NMB varied from 12.4 ± 6.1 to 34.2 ± 11.3 min (Table 4). The longest difference among the group means (21.8 min) in MR waiting time caused extra OR costs of FIM 800 (approximately $160) per patient in our hospital.


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  		Table 4. Total Waiting Timea Due to Intense Neuromuscular Block (Posttetanic Count <=2)
 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
The main finding of our study is that SUCC is economically superior to all the other MRs to use during short operations when intense NMB is mandatory. Of the nondepolarizing MRs, MIV is the most economical alternative. Using ATR instead of SUCC caused a 21.8-min delay, which cost FIM 800 ($160) extra per patient in our hospital. Recovery times after intense NMB during ELP are considerably longer with ATR, ROC, and VEC than with SUCC and MIV. The differences in onset times are less impressive.

Anesthetic drug expenditures have been a focus of cost-containment efforts, and earlier studies have shown that concerted educational efforts can decrease the per-case expenditures for both volatile anesthetics and MRs (6,7). However, the largest hospital cost category is the OR (33%), whereas anesthesia comprises only 5.6% of perioperative costs (8). In our department, costs of anesthesia drugs are <2% of the total costs of the OR per time unit. The differences in the purchasing price of different MRs are less than the cost of 1 min of OR time and are therefore negligible. Of the OR costs, 84.2% arises during working hours even if there is no patient in the theater. A patient being kept in the theater to recover from anesthesia and MR delays the operation of the next patient.

However, when trying to decrease costs by shortening waiting time, the saved time must be long enough to enable the performance of at least one additional procedure during the same shift. Dexter et al. (9) stated that anesthesia time would have to be decreased by >100% to permit one additional short operation (each lasting >45 min) to be performed in an OR during an 8-h workday. In the present study, the mean duration of ELP was 17.8 ± 14.3 min, and the difference between the shortest (SUCC) and the longest (ATR) waiting time caused by NMB was 21.8 min (Table 4). In the same 3 h that would be needed to complete three ELPs using the MR with the longest waiting time, five could be performed using the MR with the shortest waiting time. Thus, the price of a drug is less important than the impact of the drug on the duration of surgery/anesthesia. Only improvement of this relationship may provide time for additional procedures during one shift.

Much larger doses of MRs are required to achieve surgeon-satisfactory NMB in the muscles of the larynx than in the muscles of the hand (3). Train-of-four recording is not possible during intense NMB, but recording PTC at the muscles of the hand enables one to estimate the level of very intense NMB (10). Twenty percent of patients react mildly to a stimulation of the carina at PTC 1, but total paralysis of the diaphragm muscles is achieved at PTC 0 (11). We developed an airway pressure curve monitoring device to monitor laryngeal and diaphragm muscle activity during intratracheal jet ventilation, in which the stimulus is provided by the blow of the jet on the carina of the trachea (1). In the present study, we accepted PTC <=2 values to avoid unnecessarily intense block and to avoid very long recovery times. There were monitor alarms of insufficient NMB at PTC <=2 with every MR, but the reactions were mild and not potentially hazardous for the patient or the surgery. During ELPs, single airway pressure alarms may be caused by surgery, but surgically induced alarms were not recorded and did not cause alterations in treatment.

We decided to use bolus dosing with all nondepolarizing MRs to ensure a uniform study design. However, an infusion of MIV would be preferable for maintenance of NMB because of the short spontaneous recovery time from MIV. A pilot study showed that, in a MIV group, the additional doses had to be larger in relation to the initial dose than those in the other nondepolarizing MR groups to control PTC properly. Mean PTC averaged 2.9 ± 3.1 during ELPs, with no statistical differences among the groups despite the differences in dosing.

In a previous study, the recovery index (T25-75) was similar in patients who received an infusion of MIV or SUCC (12). Our study confirms the similarity of recovery times from intense NMB (from PTC <=2 to DBS recovery) induced by MIV and SUCC. However, in our study, MIV was antagonized with neostigmine 0.04 mg/kg when NMB had recovered spontaneously to PTC 10. In Group SUCC, the fasciculations made some patients' group assignment clear, but we assume that the mistake in the study design did not affect the results because the NMB was always evaluated by the same blinded person (SH), who was not allowed to order or administer anesthetics.

Unfortunately, the shortest possible observation interval with the monitoring equipment we used was 3 min. Intervals <6 min between PTC recordings may produce antagonism of NMB in the stimulated muscles (5). We shortened the interval by using the patient's left and right hands in turn, and there was no statistical difference in the PTC values between the dominant and nondominant hands. Despite our wide-meshed time scale in PTC monitoring, the differences in onset time and recovery time were large enough to exceed the 3-min interval.

In summary, using the MR with the longest waiting time instead of the MR with the shortest waiting time would cause considerable extra costs with every patient undergoing ELP. If intense NMB is mandatory for a short operation, SUCC has both a short onset time and a rapid recovery. However, SUCC is associated with harmful and potentially dangerous complications. MIV is economically the best nondepolarizing alternative, because of its short recovery time, but using intermediate-acting muscle relaxants results in unduly prolonged recovery time and extra costs.


   Acknowledgments
 
This work was supported by the Medical Research Fund of Tampere University Hospital.

We thank nurse anesthetist Anneli Innanmaa for her cooperation.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Baer GA. Intratracheal jet ventilation for endolaryngeal procedures [thesis]. Acta Universitatis Tamperensis, 1985.
  2. Schumacher P, Stotz G, Schneider M, Urwyler A. Laryngospasm during transtracheal high frequency jet ventilation. Anaesthesia 1992;47:855–6.[Medline]
  3. Baer GA. Laryngeal muscle recovery after suxamethonium: detection during intratracheal jet ventilation by pressure curve monitoring. Anaesthesia 1984;39:143–6.[Web of Science][Medline]
  4. Baer GA, Paloheimo M, Rahnasto J, Pukander J. End-tidal oxygen concentration and pulse oximetry for monitoring oxygenation during intratracheal jet ventilation. J Clin Monit 1995;11:373–80.[Web of Science][Medline]
  5. Howardy-Hansen P, Viby-Mogensen J. Tactile evaluation of the posttetanic count (PTC). Anesthesiology 1984;60:372–4.[Web of Science][Medline]
  6. Szocik JF, Learned DW. Impact of a cost containment program on the use of volatile anesthetics and neuromuscular blocking drugs. J Clin Anesth 1994;6:378–82.[Web of Science][Medline]
  7. Freund PR, Bowdle TA, Posner KL, et al. Cost-effective reduction of neuromuscular-blocking drug expenditures. Anesthesiology 1997;87:1044–9.[Medline]
  8. Macario A, Vitez TS, Dunn B, McDonald T. Where are the costs in perioperative care? Anesthesiology 1995;83:1138–44.[Web of Science][Medline]
  9. Dexter F, Coffin S, Tinker JH. Decreases in anesthesia-controlled time cannot permit one additional surgical operation to be reliably scheduled during the workday. Anesth Analg 1995;81:1263–8.[Abstract]
  10. Viby-Mogensen J, Howardy-Hansen P, Chraemmer-Jörgensen B. Post tetanic count (PTC): a new method of evaluating an intense nondepolarizing neuromuscular blockade. Anesthesiology 1981;55:458–61.[Web of Science][Medline]
  11. Fernando PUE, Viby-Mogensen J, Bonsu AK. Relationship between post tetanic count and response to carinal stimulation during vecuronium-induced neuromuscular blockade. Acta Anaesthesiol Scand 1987;31:593–6.[Web of Science][Medline]
  12. Brandom BW, Woelfel SK, Cook DR, et al. Comparison of mivacurium and suxamethonium administered by bolus and infusion. Anaesth 1989;62:488–93.
Accepted for publication February 25, 1999.





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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 1999 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press