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ANALYSIS OF COSTS OF ANAESTHETIC BREATHING SYSTEMS
CORRESPONDENCE
389 after each operation, the cost per unit time will depend on the duration of the anaesthetic. The present calculations were based on the latter assumption. In circle systems a smaller fresh-gas flow is usually used, compared with the semi-open systems. If the absorber is changed before each anaesthetic, the circle system will be the cheapest system in prolonged operations, and the semi-open systems will be the cheapest for short operations. The duration of anaesthesia, at which the expenses are equal, is denned as the iso-cost point. This can be expressed in the formula: where Y = iso-cost point; X = fresh-gas flow in the circle system; A = cost of soda-lime per anaesthesia; B = cost per litre of anaesthetic gas mixture; C = fresh-gas flow in the semi-open system. The formula can be changed to: Y =
M. R. C. RODRIGO Hong Kong
B(C-X) This is the formula of the "iso-cost curve", which illustrates the variations of the iso-cost point with different fresh-gas flows in the circle system. The curves will be independent of REFERENCES changes in prices or currencies, provided that the changes are Allonen, H., Ziegler, G., and Klotz, U. (1981). Midazolam proportionate. kinetics. Clin. Pharmacol. Ther., 653, 661. Some examples of iso-cost curves are illustrated. In figure Blanloeil, Y., Bigot, A., and Dixneuf, B. (1982). Anaesthesia 1, from the curve, the iso-cost point can be found using various in Huntington'8 chorea. Anaesthesia, 37, 695. flows in the circle system. For example, if a fresh-gas flow of Davies, D. D. (1966). Abnormal response to anaesthesia in a 5 litre min"1 is used in the circle system (which is common case of Huntington's chorea. Br. J. Anaesth., 38, 490. practice), it is cheaper to use a semi-open system with fresh-gas Dundee, J. W. (1975). New i.v. anaesthetics. Br. J. Anaesth., flow of 10 litre min"1 for procedures lasting less than 50 min. 51,641. If lower fresh-gas flows are used, for example 3 litre min"1 in Farina, J., and Rauscher, L. A. (1977). Anaesthesia and the circle system and 6 litre min"1 in the semi-open system, Huntington's chorea. A report of two cases. Br. J. Anaesth., then the iso-cost point is 83 min. 49, 1167. The calculations in figure 2 are made for various halothane Grell, F. I., Koons, R. A. and Denson, J. S. (1970). Fentanyl concentrations. When increasing halothane concentrations are in anaesthesia: a report of 500 cases. Anesth. Analg., 49,523. used, the expense of the anaesthetic gas mixture increases Gualandi, W., and Bonfanti, G. (1968). Un caso di apnea simultaneously. For example, when a fresh-gas flow at 3 litre prolungata in corea di Huntington. Ada Anaesthesiol. min"1 in the circle system is used with 0.5 % halothane, then (Padova), (Suppl. 6), 235. the iso-cost point is 119 min. If 2% halothane is used, then the Johnson, K. K., and Heggie, N. M. (1985). Huntington's iso-cost point will be 53 min. chorea. A role for the newer anaesthetic agents. Br. J. Anaesth., 57, 235. Lamont, A. M. S. (1979). Anaesthesia and Huntington's chorea. Anaesth. Intern. Care, 8, 189. Wells, D. (1979). Anaesth. Intern. Care, 8, 383. E2O0 Whittaker, M. (1980). Plasma cholinesterase variants and the anaesthetist. Anaesthesia, 35, 174. 150
ANALYSIS OF COSTS OF ANAESTHETIC BREATHING SYSTEMS Sir,—Few studies of the economy of the various anaesthetic breathing systems have been performed (Edsall, 1981). As the semi-open systems are now used widely, we have compared the expense of using the circle system and these systems. The calculations were performed with various fresh-gas flows and halothane concentrations, and with various regimens of utilization of the absorber. Other expenses, such as salaries, i.v. anaesthetics and maintenance of equipment are assumed to be independent of the choice of anaesthetic breathing system. If the carbon dioxide absorber is used for a fixed period of time, the cost of soda-lime depends upon the duration of the anaesthetic procedure. If, however the absorber is changed
a 100 o = 50 1.0
2.0
3.0
4.0
5.0
Circle system (litre min"1)
FIG. 1. Iso-cost curves. Fresh-gas flow to semi-open system: 4, 6, 8, 10 litre min"1. Nitrous oxide in oxygen 2:1; 1% halothane; soda-lime 600 g.
Downloaded from http://bja.oxfordjournals.org/ at Indiana University Library on July 11, 2015
tetrabenazene. The action of midazolam, similar to that of diazepam, would have facilitated the depleted GABA action. Farina and Rauscher (1977) obtained smooth induction with fentanyl and diazepam. However, midazolam would be a better alternative because its action is shorter, it produces profound amnesia and it is water soluble, with a decreased incidence of thombophlebitis (Dundee, 1975). Halothane was used as the volatile agent. Supplements of volatile agents (trichloroethylene, ether and halothane) have been used previously. In patients who received trichloroethylene, generalized tonic spasms have been seen after operation (Davies, 1966). With ether (Davies, 1966) and halothane (Farina and Rauscher, 1977; Lamont, 1979; Wells, 1979) the recovery was smooth. However, unlike the previous experiences with halothane, our patient initially developed halothane-induced postoperative shivering which precipitated tonic spasms. Thus from this experience it may be advisable to avoid halothane in these patients if an alternative is available.
BRITISH JOURNAL OF ANAESTHESIA
390
The cost of soda-lime is important, when the economy is illustrated by means of the iso-cost curves. The iso-cost curves appear very useful for training and are easily computerized from the formula during other conditions, such as change in prices. Previous publications show a tendency to use fresh-gas flows in circle systems, which are close to the alveolar ventilation in adult patients (5-6 litre min"1). By the use of a Mapleson D system with identical fresh-gas flow, this will always be the cheapest in use and protects the patient against accidental hypocarbia. The use of circle systems for shorter lasting operations thus cannot be justified from an economic point of view. K. N. CHRISTENSEN
Aalborg
1.0
Aarhus
2.0 3.0 4.0 5.0 Circle system (litre mln"1)
S. J0RGBNSEN J. FABRIQUS
FIG. 2. Iso-cost curves. Fresh-gas flow to semi-open system: 6 litre min"1. Nitrous oxide in oxygen 2:1; halothane concentrations 0, 0.5, 1, 2 % ; soda-lime 600 g.
Odense
REFERENCES Figure 3 demonstrates that, with repetitive use of the soda-lime, expenses decrease in the circle system, which will be the cheapest in use for operations exceeding 17 min, if the absorbent is re-used for five patients and the fresh-gas flow to the circle syBtem is 3 litre min"1. The present calculations show that, in procedures lasting less than about 1 h, the semi-open system are more economical than the circle system used with traditional gas flows (about 4 litre min~1)The iso-cost curves are used to illustrate graphically the economic consequences of varying halothane concentrations, gas flows and absorber utilization. In previous studies concerning economy, some authors have considered the cost of soda-lime (Bailey, 1978; Simpson, 1978; Edsall, 1981), while others have not (Briscoe, 1970; Nunn, 1979; Virtue, 1979).
Bailey, P. W. (1978). Pricing of anaesthetic techniques. Anaesthesia, 33, 235. Briscoe, E. E. (1970). Halving the cost of anaesthetic agents. Br. Med. J., 1, 488. Edsall, D . W. (1981). Economy is not a major benefit of closed-system anesthesia. Anesthesiology, 54, 258. Nunn, J. F. (1979). Potential economics of using circuit anaesthesia; in Lota Flow and Closed System Anaesthesia, 1st Edn (eds J. A. Aldrete, J. A. Lowe and R. W. Virtue), p. 109. New York: Grune & Stratton. Simpton, P. M. (1978). The cost of anaesthetic drugs and equipment. Anaesthesia, 33, 53. Virtue, R. W. (1979). Low flow anaesthesia. Advantages in its clinical application, cost and ecology; in Low Flow and Closed System Anaesthesia, 1st Edn (eds J. A. Aldrete, H. J. Lowe and R. W. Virtue), p. 103. New York: Grune & Stratton.
r»2
f 2O0 3
I 150» 100 o | a 50
1.0
2.0 3.0 4.0 5.0 Circle system (litre mln'1)
FIG. 3. Iso-cost curves. Fresh-gas flow to semi-open system: 6 litre min"1. Nitrous oxide in oxygen 2:1; 1% halothane. Soda-lime 600 g. (Used for 1,2,3 and 5 patients (n •= number of patients).)
SINUS ARREST AFTER ALFENTANIL Sir,—We wish to report two cases of sinus arrest during intubation following administration of alfentanil 30 ug kg"1. Laryngoscopy and trachea] intubation have been shown to produce a marked increase in heart rate (Millar and Dally, 1970). Pretreatment with alfentanil 30 ug kg"1 has been shown not only to abolish this tachycardia, but also to produce a relative bradycardia significantly lower than control values 4 min after the administration of the alfentanil (Black, Kay and Healy, 1984). This suggests that the alfentanil may have attained a higher level of activity at this time, indicating a more appropriate moment to intubate. We had intended to study two groups of 20 patients. Patients were premedicated orally with temazepam 10-20 mg. ECG monitoring was commenced on arrival in the anaesthetic room. Anaesthesia was induced with alfentanil 30 ug kg"1 given over 20 s, followed after 1 min by thiopentone 4 mg kg"1 and suxamethonium 1 mg kg"1. The patient's lungs were ventilated by hand with 50% nitrous oxide in oxygen. Laryngeal spray (lignocaine 3 mg kg"1) and intubation were performed in group 1 after 30 s and in group 2 after 2 min.
Downloaded from http://bja.oxfordjournals.org/ at Indiana University Library on July 11, 2015
A. THOMSEN
389 after each operation, the cost per unit time will depend on the duration of the anaesthetic. The present calculations were based on the latter assumption. In circle systems a smaller fresh-gas flow is usually used, compared with the semi-open systems. If the absorber is changed before each anaesthetic, the circle system will be the cheapest system in prolonged operations, and the semi-open systems will be the cheapest for short operations. The duration of anaesthesia, at which the expenses are equal, is denned as the iso-cost point. This can be expressed in the formula: where Y = iso-cost point; X = fresh-gas flow in the circle system; A = cost of soda-lime per anaesthesia; B = cost per litre of anaesthetic gas mixture; C = fresh-gas flow in the semi-open system. The formula can be changed to: Y =
M. R. C. RODRIGO Hong Kong
B(C-X) This is the formula of the "iso-cost curve", which illustrates the variations of the iso-cost point with different fresh-gas flows in the circle system. The curves will be independent of REFERENCES changes in prices or currencies, provided that the changes are Allonen, H., Ziegler, G., and Klotz, U. (1981). Midazolam proportionate. kinetics. Clin. Pharmacol. Ther., 653, 661. Some examples of iso-cost curves are illustrated. In figure Blanloeil, Y., Bigot, A., and Dixneuf, B. (1982). Anaesthesia 1, from the curve, the iso-cost point can be found using various in Huntington'8 chorea. Anaesthesia, 37, 695. flows in the circle system. For example, if a fresh-gas flow of Davies, D. D. (1966). Abnormal response to anaesthesia in a 5 litre min"1 is used in the circle system (which is common case of Huntington's chorea. Br. J. Anaesth., 38, 490. practice), it is cheaper to use a semi-open system with fresh-gas Dundee, J. W. (1975). New i.v. anaesthetics. Br. J. Anaesth., flow of 10 litre min"1 for procedures lasting less than 50 min. 51,641. If lower fresh-gas flows are used, for example 3 litre min"1 in Farina, J., and Rauscher, L. A. (1977). Anaesthesia and the circle system and 6 litre min"1 in the semi-open system, Huntington's chorea. A report of two cases. Br. J. Anaesth., then the iso-cost point is 83 min. 49, 1167. The calculations in figure 2 are made for various halothane Grell, F. I., Koons, R. A. and Denson, J. S. (1970). Fentanyl concentrations. When increasing halothane concentrations are in anaesthesia: a report of 500 cases. Anesth. Analg., 49,523. used, the expense of the anaesthetic gas mixture increases Gualandi, W., and Bonfanti, G. (1968). Un caso di apnea simultaneously. For example, when a fresh-gas flow at 3 litre prolungata in corea di Huntington. Ada Anaesthesiol. min"1 in the circle system is used with 0.5 % halothane, then (Padova), (Suppl. 6), 235. the iso-cost point is 119 min. If 2% halothane is used, then the Johnson, K. K., and Heggie, N. M. (1985). Huntington's iso-cost point will be 53 min. chorea. A role for the newer anaesthetic agents. Br. J. Anaesth., 57, 235. Lamont, A. M. S. (1979). Anaesthesia and Huntington's chorea. Anaesth. Intern. Care, 8, 189. Wells, D. (1979). Anaesth. Intern. Care, 8, 383. E2O0 Whittaker, M. (1980). Plasma cholinesterase variants and the anaesthetist. Anaesthesia, 35, 174. 150
ANALYSIS OF COSTS OF ANAESTHETIC BREATHING SYSTEMS Sir,—Few studies of the economy of the various anaesthetic breathing systems have been performed (Edsall, 1981). As the semi-open systems are now used widely, we have compared the expense of using the circle system and these systems. The calculations were performed with various fresh-gas flows and halothane concentrations, and with various regimens of utilization of the absorber. Other expenses, such as salaries, i.v. anaesthetics and maintenance of equipment are assumed to be independent of the choice of anaesthetic breathing system. If the carbon dioxide absorber is used for a fixed period of time, the cost of soda-lime depends upon the duration of the anaesthetic procedure. If, however the absorber is changed
a 100 o = 50 1.0
2.0
3.0
4.0
5.0
Circle system (litre min"1)
FIG. 1. Iso-cost curves. Fresh-gas flow to semi-open system: 4, 6, 8, 10 litre min"1. Nitrous oxide in oxygen 2:1; 1% halothane; soda-lime 600 g.
Downloaded from http://bja.oxfordjournals.org/ at Indiana University Library on July 11, 2015
tetrabenazene. The action of midazolam, similar to that of diazepam, would have facilitated the depleted GABA action. Farina and Rauscher (1977) obtained smooth induction with fentanyl and diazepam. However, midazolam would be a better alternative because its action is shorter, it produces profound amnesia and it is water soluble, with a decreased incidence of thombophlebitis (Dundee, 1975). Halothane was used as the volatile agent. Supplements of volatile agents (trichloroethylene, ether and halothane) have been used previously. In patients who received trichloroethylene, generalized tonic spasms have been seen after operation (Davies, 1966). With ether (Davies, 1966) and halothane (Farina and Rauscher, 1977; Lamont, 1979; Wells, 1979) the recovery was smooth. However, unlike the previous experiences with halothane, our patient initially developed halothane-induced postoperative shivering which precipitated tonic spasms. Thus from this experience it may be advisable to avoid halothane in these patients if an alternative is available.
BRITISH JOURNAL OF ANAESTHESIA
390
The cost of soda-lime is important, when the economy is illustrated by means of the iso-cost curves. The iso-cost curves appear very useful for training and are easily computerized from the formula during other conditions, such as change in prices. Previous publications show a tendency to use fresh-gas flows in circle systems, which are close to the alveolar ventilation in adult patients (5-6 litre min"1). By the use of a Mapleson D system with identical fresh-gas flow, this will always be the cheapest in use and protects the patient against accidental hypocarbia. The use of circle systems for shorter lasting operations thus cannot be justified from an economic point of view. K. N. CHRISTENSEN
Aalborg
1.0
Aarhus
2.0 3.0 4.0 5.0 Circle system (litre mln"1)
S. J0RGBNSEN J. FABRIQUS
FIG. 2. Iso-cost curves. Fresh-gas flow to semi-open system: 6 litre min"1. Nitrous oxide in oxygen 2:1; halothane concentrations 0, 0.5, 1, 2 % ; soda-lime 600 g.
Odense
REFERENCES Figure 3 demonstrates that, with repetitive use of the soda-lime, expenses decrease in the circle system, which will be the cheapest in use for operations exceeding 17 min, if the absorbent is re-used for five patients and the fresh-gas flow to the circle syBtem is 3 litre min"1. The present calculations show that, in procedures lasting less than about 1 h, the semi-open system are more economical than the circle system used with traditional gas flows (about 4 litre min~1)The iso-cost curves are used to illustrate graphically the economic consequences of varying halothane concentrations, gas flows and absorber utilization. In previous studies concerning economy, some authors have considered the cost of soda-lime (Bailey, 1978; Simpson, 1978; Edsall, 1981), while others have not (Briscoe, 1970; Nunn, 1979; Virtue, 1979).
Bailey, P. W. (1978). Pricing of anaesthetic techniques. Anaesthesia, 33, 235. Briscoe, E. E. (1970). Halving the cost of anaesthetic agents. Br. Med. J., 1, 488. Edsall, D . W. (1981). Economy is not a major benefit of closed-system anesthesia. Anesthesiology, 54, 258. Nunn, J. F. (1979). Potential economics of using circuit anaesthesia; in Lota Flow and Closed System Anaesthesia, 1st Edn (eds J. A. Aldrete, J. A. Lowe and R. W. Virtue), p. 109. New York: Grune & Stratton. Simpton, P. M. (1978). The cost of anaesthetic drugs and equipment. Anaesthesia, 33, 53. Virtue, R. W. (1979). Low flow anaesthesia. Advantages in its clinical application, cost and ecology; in Low Flow and Closed System Anaesthesia, 1st Edn (eds J. A. Aldrete, H. J. Lowe and R. W. Virtue), p. 103. New York: Grune & Stratton.
r»2
f 2O0 3
I 150» 100 o | a 50
1.0
2.0 3.0 4.0 5.0 Circle system (litre mln'1)
FIG. 3. Iso-cost curves. Fresh-gas flow to semi-open system: 6 litre min"1. Nitrous oxide in oxygen 2:1; 1% halothane. Soda-lime 600 g. (Used for 1,2,3 and 5 patients (n •= number of patients).)
SINUS ARREST AFTER ALFENTANIL Sir,—We wish to report two cases of sinus arrest during intubation following administration of alfentanil 30 ug kg"1. Laryngoscopy and trachea] intubation have been shown to produce a marked increase in heart rate (Millar and Dally, 1970). Pretreatment with alfentanil 30 ug kg"1 has been shown not only to abolish this tachycardia, but also to produce a relative bradycardia significantly lower than control values 4 min after the administration of the alfentanil (Black, Kay and Healy, 1984). This suggests that the alfentanil may have attained a higher level of activity at this time, indicating a more appropriate moment to intubate. We had intended to study two groups of 20 patients. Patients were premedicated orally with temazepam 10-20 mg. ECG monitoring was commenced on arrival in the anaesthetic room. Anaesthesia was induced with alfentanil 30 ug kg"1 given over 20 s, followed after 1 min by thiopentone 4 mg kg"1 and suxamethonium 1 mg kg"1. The patient's lungs were ventilated by hand with 50% nitrous oxide in oxygen. Laryngeal spray (lignocaine 3 mg kg"1) and intubation were performed in group 1 after 30 s and in group 2 after 2 min.
Downloaded from http://bja.oxfordjournals.org/ at Indiana University Library on July 11, 2015
A. THOMSEN