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CHANGES IN VENTILATORY PATTERNS DURING HALOTHANE ANAESTHESIA IN CHILDREN
Br.J. Anaesth. (1985), 57, 569-572
CHANGES IN VENTILATORY PATTERNS DURING HALOTHANE ANAESTHESIA IN CHILDREN
Halothane is the most commonly used anaesthetic agent in paediatric anaesthesia (Reynolds, 1962; Krivosic-Horber, Sauvage and Calmes, 1973; Govaerts and Sanders, 1975) and, like all halogenated hydrocarbon anaesthetics, depresses ventilation (Munson, 1972) — an effect dependent on the age of the patient (Lindahl, Olsson and Thomson, 1981) and on the alveolar concentration of the anaesthetic (Munson et al., 1966). However, few studies are available which detail the changes in ventilatory patterns during halothane anaesthesia in children (Wilson and Harrison, 1964). This paper describes measurements of minute ventilation (VE), tidal volume (VT), respiratory frequency (/), mean inspiratory flow (VT/7I), inspiratory timing (T\IVot) and end-tidal carbon dioxide tension (PE'CO ) m 12 children weighing between 10 and 20 kg. The measurements were made at increasing inspired concentrations of halothane.
SUMMARY Changes in ventilatory variables (VE, VE, f, T//T'0' VT/XI, PE'COJ were studied in 12 unpremedicated children, weighing between 10 and 20 kg, during halothane anaesthesia. At an inspired concentration of 0.5% halothane, respiratory rate increased, VT decreased, and VE did not change markedly. When the inspired.; halothane concentration increased further, there was a significant decrease in VE, mainly as a result of a marked decrease in\lT. PE'CO2 increased significantly and inspiratory duty cycle'decreased at high inspired halothane concentrations. On return to baseline (0.5% halothane), there was a significant decrease in inspiratory timing and a significant increase in PE'CO2- The relations between these changes and the effect of halothane on inspiratory muscles are discussed.
anaesthetics apart from halothane and nitrous oxide had been used during the surgical procedure. Anaesthesia was induced with oxygen and nitrous Twelve children, scheduled for elective minor surgical procedures, were studied. Mean (± SD) age was oxide in equal parts (Flo2 0.5) and 2-2.5% 39 ± 17 months (range 20-68 months), weight halothane using an appropriate mask and an open 15 ± 2.9 kg (range 10.5-20 kg) and height circuit with a non-rebreathing valve. Intubation was 96 ± 11.5 cm (range 77-111 cm). All patients were performed without neuromuscular blockade under healthy, were taking no medication and had normal appropriate inspired halothane concentration (uncardiopulmonary function. Parental consent was cuffed endotracheal tube). The total fresh gas flow obtained after full explanation before anaesthesia. was identical for all patients (oxygen 4 litre, nitrous None of the children included in this study was pre- oxide 4 litre) throughout the study, and was suffimedicated. The study was performed either cient to prevent rebreathing (Lindahl, Hulse and immediately before surgery (eight children), or dur- Hatch, 1984). After tracheal intubation, the ing the period after operation (four children) if no inspired concentration of halothane was decreased to 0.5%; the children were breathing spontaneously. Rectal temperature was monitored and mainI. MURAT, M.D.; M. M. DELLEUR, M.D.; K. MACGEE, M.D.; C. tained between 36.5 and 37.5 °C for all children. SAINT-MAURICE, M.D.; Departement d'Anesthesie-Reanimation Chirurgicale, Hopital Saint-Vincent-de-Paul, 74, avenue The ECG was monitored continuously. Denfert-Rochereau, 75674 Paris Cedex 14, France. The tidal volume (VT) was measured by integratPATIENTS AND METHODS
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
I. MURAT, M. M. DELLEUR, K. MACGEE AND C. SAINT-MAURICE
570
BRITISH JOURNAL OF ANAESTHESIA total breathing cycle (Tot) were measured by averaging 10 successive breaths. The following respiratory variables were calculated: minute ventilation VE (ml min"1 kg"1), respiratory frequency (/), mean inspiratory flow (VT/Tl) (ml kg"' min"1), inspiratory duty cycle (Til T101) and end-tidal carbon dioxide partial pressure (PE'Co2)(kPa). Carbon dioxide output (VCO2) was calculated for each period using the following formula: VCO2 (ml min"1) = VE x F E C O 100
is the expired carbon dioxide fraction. VE was corrected to body temperature and pressure saturated (BTPS), Vco2 values to ambient temperature and pressure saturated (ATPS). Statistical evaluation of the data utilized a twoway analysis of variance between the four periods of the study and the two-tailed t test for paired samples. P values < 0.05 were regarded as significant. The values are expressed as mean ± standard error of the mean (SEM). FE C O 2
RESULTS
Values (mean ± SEM) of VE, Vr,f, VT/Tl, 71/7™, PE' C Q 2 VCO2, obtained at various inspired concentrations ol halothane are shown in table I. Values at To were not significantly different between the chil-
TABLE I. Ventilatory variables (mean + SEM) at various inspired concentrations of halothane. Comparisons are made between the initial period T o and the other periods,
T, T2 and T' o . ***P < 0.001; **P <0.01; *P < 0.05
VE (ml kg"' min"') (ml kg"') /
(b.p.m.)
n/ro1 PEco2 (kPa) Vco2 (ml kg"'min"1) VllT\ (mlkg"'min-')
Inspired halothane concentration (%) 1.5 0.5 0.5 1 Period T2 Period To Period 7"! Period r 0 148.22 129.90*** 113.40*** 140.8* ±6.85 ±6.74 ±5.99 ±7.79 3.34*** 5.06 4.98 4.11*** ±0.25 ±0.29 ±0.34 ±0.36 35.36*** 32.75 31.76 28.76 ±2.66 ±1.94 ±2.45 ±2.52 0.52* 0.52* 0.53 0.55 ±0.01 ±0.02 ±0.02 ±0.02 5.3** 5.2 5.5*** 6.1*** ±0.23 ±0.19 ±0.22 ±0.19 741.5 692 682*** 743 ±26.4 ±22.5 ±20.1 ±23.7 243.4*** 262.5 217.7*** 272.7 ±14.4 ±13 ±11.6 ±12.9
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
ing the flow signal obtained from a Fleish No. 0 pneumotachograph with an internal volume of 4.7 ml connected to a Godart differential pressure transducer. The pneumotachograph was placed between the endotracheal tube and a non-rebreathing valve with a low opening pressure (DighbyLeigh). The fraction of carbon dioxide in the expired gas (FEco) w a s monitored continuously in the tracheal tube by a capnograph with automatic correction for nitrous oxide (Datex). The rate of sampling was 50 ml min"1. The study was divided into four different periods. In the first period, the children were maintained at an inspired concentration of halothane of 0.5% for at least 15 min and a recording of respiratory patterns obtained, breath-by-breath for 1 min (To). Then, the inspired halothane concentration was increased to 1% for 10 min and measurements obtained for 1 min (Tj). The inspired halothane concentration was increased again, to 1.5% for 10 min (7"2). Finally, the inspired halothane concentration was decreased to 0.5% for 15 min. This last period, called T'Q, was studied to determine individual variations and eventual consequences of prolonged anaesthesia. Records of VT and FE C O were made throughout the study, but breath-by-breath recordings were performed only during the 1 min at the end of each period. The children were not stimulated in any way throughout the period of study. At each inspired halothane concentration, the durations of inspiration (TV), expiration (TE) and
HALOTHANE AND VENTILATORY PATTERN IN CHILDREN +30
571
C02
+20. +10.
Inspired Halothane Concentration
a> - i o . u .20.
• 0.5 (control)v. 0.5 .30. -40
VT
n/rtot
FlG. 1. Per cent change in ventilatory variables, expressed as per cent of the initial value (Period 7"o). *P < 0.05; **P < 0.01; ***P < 0.001.
dren studied before operation and those studied after operation. Carbon dioxide output was statistically linked to weight (P < 0.001), height (P < 0.001) and age (P < 0.001). The changes in the ventilatory patterns at various depths of halothane anaesthesia are summarized in figure 1. There was a significant decrease in VE when the inspired concentration of halothane increased, mainly as a result of a significant decrease in VT. The increase in respiratory rate was significant between 0.5 and 1.5%, but no increase was found between 0.5 and 1%. Changes in effective respiratory timing were significant between 0.5 and 1.5% halothane. Mean inspiratory flow decreased significantly with increasing depth of halothane anaesthesia. Changes in P E ' C O 2 were also related to changes in inspired halothane concentration, but the increase obtained between 1 and 1.5% was about twice that obtained between 0.5 and 1%. FCO2 decreased significantly only between 0.5 and 1.5% inspired halothane concentration. The control period was marked by a significant decrease in inspiratory timing and an increase in PE'QO > but no significant change in VT, respiratory rate, mean inspiratory flow or KCO2. DISCUSSION
Few data are available on normal ventilatory patterns in children younger than 6 years of age, probably because of difficulties in obtaining real cooperation at this age. In comparison with normal data for awake children (Crone, 1983), the respiratory rate at To was
markedly increased, tidal volume was decreased, but minute ventilation did not change markedly. The end-tidal carbon dioxide tension was at the normal upper range limit for age, and mean values for KCO2 were similar to published data for anaesthetized children (Nightingale and Lambert, 1978; Lindahl, Olsson and Thomson, 1981; Lindahl, Hulse and Hatch, 1984), and not different from those obtained by Lewis, Dural and Iliff (1943) in awake children. The effect on the respiratory patterns, of the use of nitrous oxide in this study, is difficult to delineate. Nitrous oxide has been shown to have either a mild stimulant effect (Eckenhoff and Helrich, 1958) or a ventilatory sparing effect (Hornbein et al., 1969). In children, Salanitre and Rackow (1976) demonstrated a decrease in VE during halothane anaesthesia with 70% nitrous oxide when compared with 3% nitrous oxide. However, a mixture of nitrous oxide, oxygen and halothane is generally used during general anaesthesia to reduce the MAC of halothane, and this study was essentially performed to define the changes in ventilatory patterns under general anaesthesia with halothane in children. An increase in inspired halothane concentration produced significant decreases in VT, VE and VTI Tl, with a significant increase in P E ' C O 2 - Thus, the increase in inspired halothane concentration produced, as previously reported in adults (Devine, Hamilton and Pittinger, 1958; Larson et al., 1969; Munson et al., 1966), a marked decrease in alveolar ventilation. In children, Wilson and Harrison (1964) found, as we did, a marked decrease in VE and VT, but only a mild difference in mean respiratory rate
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
• 1 v. 0.5 W 1.5 v. 0.5
572
BRITISH JOURNAL OF ANAESTHESIA
REFERENCES
Brandstater, B., Eger, E., and Edelist, G. (1965). Constant depth halothane anesthesia in respiratory studies. J. Appl. Physiol., 20, 171. Crone, R. K. (1983). The respiratory system; in Pediatric Anesthesia (Ed. G. A. Gregory), p.35. Edinburgh: Churchill Livingstone.
Devine, J. C , Hamilton, W. K., and Pittinger, C. B. (1958). Respiratory studies in man during fluoihane anesthesia. Anesihesiology, 19, 11. Eckenhoff, J. E., and Helrich, M. (1958). The effect of narcotics, thiopental and nitrous oxide upon respiration and respiratory response to hypercapnia. Anesthesiology, 19, 240. Gautier, H. (1980). Control of the pattern of breathing. Clin. Sci., 58, 343. Govaerts, M. J. M., and Sanders, M. (1975). Induction and recovery with enflurane and halothane in paediatric anaesthesia. Br.J Anaesth., 47, 877. Hornbein, T. F . , Martin, W. E., Bonica, J. J., Freund, F. G., and Parmentier, P. (1969). Nitrous oxide effects on the circulatory and ventilatory responses to halothane. Anesthesiology, 31, 250. Hulse, M. G., Lindahl, S. G. E., and Hatch, D. L. (1984). Comparison of ventilation and gas exchange in anaesthetized infants and children during spontaneous and artificial ventilation. Br. J. Anaesth., 56, 131. Krivosic-Horber, R., Sauvage, M. R., and Calmes, M. O. (1973). Notre experience a propos de 6000 anesthesies a l'halothane chez l'enfant. Ann. Chir. Infant., 14, 81. Larson, C. P., Eger, E. I., Muallem, M., Bueche, D. R., Munson, E. S., and Eisele, J. H. (1969). The effects of diethyl ether and methoxyflurane on ventilation: II. A comparative study in man. Anesthesiology, 30, 174. Lewis, R. C , Dural, A. M., and Iliff, A. (1943). Standards for basal metabolism in normal infants. J . Pediatr., 23, 1. Lindahl, S., Olsson, A. K., and Thomson, D. (1981). Carbon dioxide output in spontaneously breathing infants during anaesthesia and surgery. B r . J . Anaesth., 53,647. Lindahl, S. G. E., Hulse, M. G., and Hatch, D. J. (1984). Ventilation and gas exchange during anaesthesia and surgery in spontaneously breathing infants and children. Br.J. Anaesth., 56, 121. Macklem, P. T. (1980). Respiratory muscles: the vital pump. Chest, 78, 753. Milic-Emili, J., and Tyler, J. M. (1963). Relation between work output of respiratory muscles and end-tidal CO 2 tension. J. Appl. Physiol., 18, 497. Munson, E. S. (1972). Modem Inhalation Anesthetics (Ed. M. B. Chenoweth), p.254. Berlin: Springer Verlag. Babad, A. A., Regan, M. J., Buechel, D. R. and Eger, E. I. (1966). The effects of halothane, fluoroxane and cyclopropane on ventilation: a comparative study in man. Anesthesiology, 27, 716. Ngai, S. H., Katz, R. L., and Farhie, S. E. (1965). Respiratory effects of trichlorethylene, halothane and methoxyflurane in the cat. J . Pharmacol. Exp. Ther., 148, 123. Nightingale, D. A., and Lambert, T. F. (1978). Carbon dioxide output in anaesthetised children. Anaesthesia, 33, 594. Nishino, T., Shirahata, M., Yonezawa, T., and Honda, Y. (1984). Comparison of changes in the hypoglossal and the phrenic nerve activity in response to increasing depth of anesthesia in cats. Anesthesiology, 60, 19. Reynolds, R. N . (1962). Halothane in pediatric anesthesia. Int. Anesth. Clin., 1, 209. Salanitre, E., and Rackow, H. (1976). N 2 O volumes absorbed and excreted during N 2 O anesthesia in children. Anesth. Analg., 55,95. Wilson, L. A., and Harrison, G. A. (1964). Pulmonary ventilation in children during halothane anesthesia. Anesthesiology, 25,613.
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
during halothane anaesthesia and recovery from anaesthesia. Decrease in Vco2 at high inspired halothane concentration is most likely the result of a large decrease in effective alveolar ventilation. The decrease in tidal volume seems to result from a central action of halothane, which has a primary direct action on the central regulatory and integratory mechanisms (Ngai, Katz and Farhie, 1965). The significant decrease in mean inspiratory flow reflects a decrease of the rate of increase of the centrally generated inspiratory activity (Gautier, 1980). The effect of halothane on respiratory rate is less well known. In agreement with the results recently reported in cats (Nishino et al., 1984), our study demonstrated a decrease in the timing of the inspiratory drive during halothane anaesthesia. This effect was true essentially for high inspired concentrations and suggests that there was a direct effect of halothane on inspiratory muscles. Using the return to baseline concentration (T'o), individual variations can be assessed and the role of the duration of anaesthesia characterized. We did not find any significant change in VT, VCO2, VT/TI and respiratory rate between To and T'o- However, there was a significant decrease in inspiratory duty cycle and a significant increase in PE'CO2 between the two periods. Changes in inspiratory timing may result from a direct effect of halothane on inspiratory muscles with progressive recovery. Changes in ar PE'CO 2 e also related to work output of inspiratory muscles (Milic-Emili and Tyler, 1963). Indeed, the duration of anaesthesia does not seem to influence carbon dioxide response curves in the dog and the increase in PE'CQ2 cannot be explained by changes in the carbon dioxide sensitivity (Brandstater, Eger and Edelist, 1965). In this study, the duration of anaesthesia did not change VCO2 either, although carbon dioxide production increased with inspiratory muscle fatigue (Macklem, 1980). Thus, the changes in respiratory variables we have observed in this study may be an additional reason for assisting ventilation in children undergoing surgical procedures of long duration (Hulse, Lindahl and Hatch, 1984) to avoid prolonged ventilatory depression and possible alterations in muscle activity.
CHANGES IN VENTILATORY PATTERNS DURING HALOTHANE ANAESTHESIA IN CHILDREN
Halothane is the most commonly used anaesthetic agent in paediatric anaesthesia (Reynolds, 1962; Krivosic-Horber, Sauvage and Calmes, 1973; Govaerts and Sanders, 1975) and, like all halogenated hydrocarbon anaesthetics, depresses ventilation (Munson, 1972) — an effect dependent on the age of the patient (Lindahl, Olsson and Thomson, 1981) and on the alveolar concentration of the anaesthetic (Munson et al., 1966). However, few studies are available which detail the changes in ventilatory patterns during halothane anaesthesia in children (Wilson and Harrison, 1964). This paper describes measurements of minute ventilation (VE), tidal volume (VT), respiratory frequency (/), mean inspiratory flow (VT/7I), inspiratory timing (T\IVot) and end-tidal carbon dioxide tension (PE'CO ) m 12 children weighing between 10 and 20 kg. The measurements were made at increasing inspired concentrations of halothane.
SUMMARY Changes in ventilatory variables (VE, VE, f, T//T'0' VT/XI, PE'COJ were studied in 12 unpremedicated children, weighing between 10 and 20 kg, during halothane anaesthesia. At an inspired concentration of 0.5% halothane, respiratory rate increased, VT decreased, and VE did not change markedly. When the inspired.; halothane concentration increased further, there was a significant decrease in VE, mainly as a result of a marked decrease in\lT. PE'CO2 increased significantly and inspiratory duty cycle'decreased at high inspired halothane concentrations. On return to baseline (0.5% halothane), there was a significant decrease in inspiratory timing and a significant increase in PE'CO2- The relations between these changes and the effect of halothane on inspiratory muscles are discussed.
anaesthetics apart from halothane and nitrous oxide had been used during the surgical procedure. Anaesthesia was induced with oxygen and nitrous Twelve children, scheduled for elective minor surgical procedures, were studied. Mean (± SD) age was oxide in equal parts (Flo2 0.5) and 2-2.5% 39 ± 17 months (range 20-68 months), weight halothane using an appropriate mask and an open 15 ± 2.9 kg (range 10.5-20 kg) and height circuit with a non-rebreathing valve. Intubation was 96 ± 11.5 cm (range 77-111 cm). All patients were performed without neuromuscular blockade under healthy, were taking no medication and had normal appropriate inspired halothane concentration (uncardiopulmonary function. Parental consent was cuffed endotracheal tube). The total fresh gas flow obtained after full explanation before anaesthesia. was identical for all patients (oxygen 4 litre, nitrous None of the children included in this study was pre- oxide 4 litre) throughout the study, and was suffimedicated. The study was performed either cient to prevent rebreathing (Lindahl, Hulse and immediately before surgery (eight children), or dur- Hatch, 1984). After tracheal intubation, the ing the period after operation (four children) if no inspired concentration of halothane was decreased to 0.5%; the children were breathing spontaneously. Rectal temperature was monitored and mainI. MURAT, M.D.; M. M. DELLEUR, M.D.; K. MACGEE, M.D.; C. tained between 36.5 and 37.5 °C for all children. SAINT-MAURICE, M.D.; Departement d'Anesthesie-Reanimation Chirurgicale, Hopital Saint-Vincent-de-Paul, 74, avenue The ECG was monitored continuously. Denfert-Rochereau, 75674 Paris Cedex 14, France. The tidal volume (VT) was measured by integratPATIENTS AND METHODS
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
I. MURAT, M. M. DELLEUR, K. MACGEE AND C. SAINT-MAURICE
570
BRITISH JOURNAL OF ANAESTHESIA total breathing cycle (Tot) were measured by averaging 10 successive breaths. The following respiratory variables were calculated: minute ventilation VE (ml min"1 kg"1), respiratory frequency (/), mean inspiratory flow (VT/Tl) (ml kg"' min"1), inspiratory duty cycle (Til T101) and end-tidal carbon dioxide partial pressure (PE'Co2)(kPa). Carbon dioxide output (VCO2) was calculated for each period using the following formula: VCO2 (ml min"1) = VE x F E C O 100
is the expired carbon dioxide fraction. VE was corrected to body temperature and pressure saturated (BTPS), Vco2 values to ambient temperature and pressure saturated (ATPS). Statistical evaluation of the data utilized a twoway analysis of variance between the four periods of the study and the two-tailed t test for paired samples. P values < 0.05 were regarded as significant. The values are expressed as mean ± standard error of the mean (SEM). FE C O 2
RESULTS
Values (mean ± SEM) of VE, Vr,f, VT/Tl, 71/7™, PE' C Q 2 VCO2, obtained at various inspired concentrations ol halothane are shown in table I. Values at To were not significantly different between the chil-
TABLE I. Ventilatory variables (mean + SEM) at various inspired concentrations of halothane. Comparisons are made between the initial period T o and the other periods,
T, T2 and T' o . ***P < 0.001; **P <0.01; *P < 0.05
VE (ml kg"' min"') (ml kg"') /
(b.p.m.)
n/ro1 PEco2 (kPa) Vco2 (ml kg"'min"1) VllT\ (mlkg"'min-')
Inspired halothane concentration (%) 1.5 0.5 0.5 1 Period T2 Period To Period 7"! Period r 0 148.22 129.90*** 113.40*** 140.8* ±6.85 ±6.74 ±5.99 ±7.79 3.34*** 5.06 4.98 4.11*** ±0.25 ±0.29 ±0.34 ±0.36 35.36*** 32.75 31.76 28.76 ±2.66 ±1.94 ±2.45 ±2.52 0.52* 0.52* 0.53 0.55 ±0.01 ±0.02 ±0.02 ±0.02 5.3** 5.2 5.5*** 6.1*** ±0.23 ±0.19 ±0.22 ±0.19 741.5 692 682*** 743 ±26.4 ±22.5 ±20.1 ±23.7 243.4*** 262.5 217.7*** 272.7 ±14.4 ±13 ±11.6 ±12.9
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
ing the flow signal obtained from a Fleish No. 0 pneumotachograph with an internal volume of 4.7 ml connected to a Godart differential pressure transducer. The pneumotachograph was placed between the endotracheal tube and a non-rebreathing valve with a low opening pressure (DighbyLeigh). The fraction of carbon dioxide in the expired gas (FEco) w a s monitored continuously in the tracheal tube by a capnograph with automatic correction for nitrous oxide (Datex). The rate of sampling was 50 ml min"1. The study was divided into four different periods. In the first period, the children were maintained at an inspired concentration of halothane of 0.5% for at least 15 min and a recording of respiratory patterns obtained, breath-by-breath for 1 min (To). Then, the inspired halothane concentration was increased to 1% for 10 min and measurements obtained for 1 min (Tj). The inspired halothane concentration was increased again, to 1.5% for 10 min (7"2). Finally, the inspired halothane concentration was decreased to 0.5% for 15 min. This last period, called T'Q, was studied to determine individual variations and eventual consequences of prolonged anaesthesia. Records of VT and FE C O were made throughout the study, but breath-by-breath recordings were performed only during the 1 min at the end of each period. The children were not stimulated in any way throughout the period of study. At each inspired halothane concentration, the durations of inspiration (TV), expiration (TE) and
HALOTHANE AND VENTILATORY PATTERN IN CHILDREN +30
571
C02
+20. +10.
Inspired Halothane Concentration
a> - i o . u .20.
• 0.5 (control)v. 0.5 .30. -40
VT
n/rtot
FlG. 1. Per cent change in ventilatory variables, expressed as per cent of the initial value (Period 7"o). *P < 0.05; **P < 0.01; ***P < 0.001.
dren studied before operation and those studied after operation. Carbon dioxide output was statistically linked to weight (P < 0.001), height (P < 0.001) and age (P < 0.001). The changes in the ventilatory patterns at various depths of halothane anaesthesia are summarized in figure 1. There was a significant decrease in VE when the inspired concentration of halothane increased, mainly as a result of a significant decrease in VT. The increase in respiratory rate was significant between 0.5 and 1.5%, but no increase was found between 0.5 and 1%. Changes in effective respiratory timing were significant between 0.5 and 1.5% halothane. Mean inspiratory flow decreased significantly with increasing depth of halothane anaesthesia. Changes in P E ' C O 2 were also related to changes in inspired halothane concentration, but the increase obtained between 1 and 1.5% was about twice that obtained between 0.5 and 1%. FCO2 decreased significantly only between 0.5 and 1.5% inspired halothane concentration. The control period was marked by a significant decrease in inspiratory timing and an increase in PE'QO > but no significant change in VT, respiratory rate, mean inspiratory flow or KCO2. DISCUSSION
Few data are available on normal ventilatory patterns in children younger than 6 years of age, probably because of difficulties in obtaining real cooperation at this age. In comparison with normal data for awake children (Crone, 1983), the respiratory rate at To was
markedly increased, tidal volume was decreased, but minute ventilation did not change markedly. The end-tidal carbon dioxide tension was at the normal upper range limit for age, and mean values for KCO2 were similar to published data for anaesthetized children (Nightingale and Lambert, 1978; Lindahl, Olsson and Thomson, 1981; Lindahl, Hulse and Hatch, 1984), and not different from those obtained by Lewis, Dural and Iliff (1943) in awake children. The effect on the respiratory patterns, of the use of nitrous oxide in this study, is difficult to delineate. Nitrous oxide has been shown to have either a mild stimulant effect (Eckenhoff and Helrich, 1958) or a ventilatory sparing effect (Hornbein et al., 1969). In children, Salanitre and Rackow (1976) demonstrated a decrease in VE during halothane anaesthesia with 70% nitrous oxide when compared with 3% nitrous oxide. However, a mixture of nitrous oxide, oxygen and halothane is generally used during general anaesthesia to reduce the MAC of halothane, and this study was essentially performed to define the changes in ventilatory patterns under general anaesthesia with halothane in children. An increase in inspired halothane concentration produced significant decreases in VT, VE and VTI Tl, with a significant increase in P E ' C O 2 - Thus, the increase in inspired halothane concentration produced, as previously reported in adults (Devine, Hamilton and Pittinger, 1958; Larson et al., 1969; Munson et al., 1966), a marked decrease in alveolar ventilation. In children, Wilson and Harrison (1964) found, as we did, a marked decrease in VE and VT, but only a mild difference in mean respiratory rate
Downloaded from http://bja.oxfordjournals.org/ at University of California, Santa Barbara on July 4, 2015
• 1 v. 0.5 W 1.5 v. 0.5
572
BRITISH JOURNAL OF ANAESTHESIA
REFERENCES
Brandstater, B., Eger, E., and Edelist, G. (1965). Constant depth halothane anesthesia in respiratory studies. J. Appl. Physiol., 20, 171. Crone, R. K. (1983). The respiratory system; in Pediatric Anesthesia (Ed. G. A. Gregory), p.35. Edinburgh: Churchill Livingstone.
Devine, J. C , Hamilton, W. K., and Pittinger, C. B. (1958). Respiratory studies in man during fluoihane anesthesia. Anesihesiology, 19, 11. Eckenhoff, J. E., and Helrich, M. (1958). The effect of narcotics, thiopental and nitrous oxide upon respiration and respiratory response to hypercapnia. Anesthesiology, 19, 240. Gautier, H. (1980). Control of the pattern of breathing. Clin. Sci., 58, 343. Govaerts, M. J. M., and Sanders, M. (1975). Induction and recovery with enflurane and halothane in paediatric anaesthesia. Br.J Anaesth., 47, 877. Hornbein, T. F . , Martin, W. E., Bonica, J. J., Freund, F. G., and Parmentier, P. (1969). Nitrous oxide effects on the circulatory and ventilatory responses to halothane. Anesthesiology, 31, 250. Hulse, M. G., Lindahl, S. G. E., and Hatch, D. L. (1984). Comparison of ventilation and gas exchange in anaesthetized infants and children during spontaneous and artificial ventilation. Br. J. Anaesth., 56, 131. Krivosic-Horber, R., Sauvage, M. R., and Calmes, M. O. (1973). Notre experience a propos de 6000 anesthesies a l'halothane chez l'enfant. Ann. Chir. Infant., 14, 81. Larson, C. P., Eger, E. I., Muallem, M., Bueche, D. R., Munson, E. S., and Eisele, J. H. (1969). The effects of diethyl ether and methoxyflurane on ventilation: II. A comparative study in man. Anesthesiology, 30, 174. Lewis, R. C , Dural, A. M., and Iliff, A. (1943). Standards for basal metabolism in normal infants. J . Pediatr., 23, 1. Lindahl, S., Olsson, A. K., and Thomson, D. (1981). Carbon dioxide output in spontaneously breathing infants during anaesthesia and surgery. B r . J . Anaesth., 53,647. Lindahl, S. G. E., Hulse, M. G., and Hatch, D. J. (1984). Ventilation and gas exchange during anaesthesia and surgery in spontaneously breathing infants and children. Br.J. Anaesth., 56, 121. Macklem, P. T. (1980). Respiratory muscles: the vital pump. Chest, 78, 753. Milic-Emili, J., and Tyler, J. M. (1963). Relation between work output of respiratory muscles and end-tidal CO 2 tension. J. Appl. Physiol., 18, 497. Munson, E. S. (1972). Modem Inhalation Anesthetics (Ed. M. B. Chenoweth), p.254. Berlin: Springer Verlag. Babad, A. A., Regan, M. J., Buechel, D. R. and Eger, E. I. (1966). The effects of halothane, fluoroxane and cyclopropane on ventilation: a comparative study in man. Anesthesiology, 27, 716. Ngai, S. H., Katz, R. L., and Farhie, S. E. (1965). Respiratory effects of trichlorethylene, halothane and methoxyflurane in the cat. J . Pharmacol. Exp. Ther., 148, 123. Nightingale, D. A., and Lambert, T. F. (1978). Carbon dioxide output in anaesthetised children. Anaesthesia, 33, 594. Nishino, T., Shirahata, M., Yonezawa, T., and Honda, Y. (1984). Comparison of changes in the hypoglossal and the phrenic nerve activity in response to increasing depth of anesthesia in cats. Anesthesiology, 60, 19. Reynolds, R. N . (1962). Halothane in pediatric anesthesia. Int. Anesth. Clin., 1, 209. Salanitre, E., and Rackow, H. (1976). N 2 O volumes absorbed and excreted during N 2 O anesthesia in children. Anesth. Analg., 55,95. Wilson, L. A., and Harrison, G. A. (1964). Pulmonary ventilation in children during halothane anesthesia. Anesthesiology, 25,613.
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during halothane anaesthesia and recovery from anaesthesia. Decrease in Vco2 at high inspired halothane concentration is most likely the result of a large decrease in effective alveolar ventilation. The decrease in tidal volume seems to result from a central action of halothane, which has a primary direct action on the central regulatory and integratory mechanisms (Ngai, Katz and Farhie, 1965). The significant decrease in mean inspiratory flow reflects a decrease of the rate of increase of the centrally generated inspiratory activity (Gautier, 1980). The effect of halothane on respiratory rate is less well known. In agreement with the results recently reported in cats (Nishino et al., 1984), our study demonstrated a decrease in the timing of the inspiratory drive during halothane anaesthesia. This effect was true essentially for high inspired concentrations and suggests that there was a direct effect of halothane on inspiratory muscles. Using the return to baseline concentration (T'o), individual variations can be assessed and the role of the duration of anaesthesia characterized. We did not find any significant change in VT, VCO2, VT/TI and respiratory rate between To and T'o- However, there was a significant decrease in inspiratory duty cycle and a significant increase in PE'CO2 between the two periods. Changes in inspiratory timing may result from a direct effect of halothane on inspiratory muscles with progressive recovery. Changes in ar PE'CO 2 e also related to work output of inspiratory muscles (Milic-Emili and Tyler, 1963). Indeed, the duration of anaesthesia does not seem to influence carbon dioxide response curves in the dog and the increase in PE'CQ2 cannot be explained by changes in the carbon dioxide sensitivity (Brandstater, Eger and Edelist, 1965). In this study, the duration of anaesthesia did not change VCO2 either, although carbon dioxide production increased with inspiratory muscle fatigue (Macklem, 1980). Thus, the changes in respiratory variables we have observed in this study may be an additional reason for assisting ventilation in children undergoing surgical procedures of long duration (Hulse, Lindahl and Hatch, 1984) to avoid prolonged ventilatory depression and possible alterations in muscle activity.