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INFLUENCE OF AIRWAY RESISTANCE AND VENTILATORY PATTERN ON PaCO2 DURING ENFLURANE ANAESTHESIA
Br.J. Anaesth. (1979), 51, 123
INFLUENCE OF AIRWAY RESISTANCE AND VENTILATORY PATTERN ON PaCOa DURING ENFLURANE ANAESTHESIA W. M. WAHBA SUMMARY
Pa cc , 2 during halothane anaesthesia with spontaneous ventilation is related to the severity of airway obstruction before operation and to tidal volume during anaesthesia (Pietak et al., 1975). There was a significant correlation between Pa C02 and the ratio of tidal volume to surface area ( F T / S A ) and forced expiratory volume standardized for height (FEV^ht). The purpose of the present study was to determine if similar relationships exist for enflurane. Apart from the brief comments by Lebowitz, Blitt and Dillon (1970), no published data could be found on the pattern of breathing during enflurane anaesthesia when premedication, induction and maintenance are standardized. Therefore a pattern was sought from the present data. METHODS
The study was performed on 21 clinically healthy adults undergoing elective operations on the extremities. The study was approved by the Hospital Research and Ethics Committee. The general and lung function data are shown in table I. On the day before operation, FEVX and vital capacity (VC) were determined from three measurements with the patients seated upright. Blood was sampled from a radial artery by direct puncture while the subject was supine and breathing a mixture of 33% oxygen in nitrogen from a venturi-type mask. The blood was withdrawn anaerobically into heparinized syringes, which were packed in ice. The sample was analysed within 10 min for gas tensions and pH by standard electrodes calibrated with nominal 0, 5 and 10% mixtures of carbon dioxide W.
M.
WAHBA, M.B., B.CH., M.SC.(MCGIIX),
F.R.C.P.(C),
McGill University, Montreal, Canada. Correspondence to: Department of Anaesthesia, Queen Elizabeth Hospital of Montreal, 2100 Marlowe Avenue, Montreal, Quebec H4A 3L6, Canada. 0007-0912/79/020123-04 $01.00
(Corning 165). No corrections were made for time, thus introducing a possible error of 0.01-0.07 kPa for Pa cc , 2 (Kelman and Nunn, 1966). Premedication consisted of anileridine and promethazine by i.m. injection 1 h before operation. The doses (based on body weight) ranged from 12.5 to 37.5 mg of the former, and 12.5 to 25 mg of the latter. Anaesthesia was induced with thiopentone 2-3 mg kg" 1 i.v. followed by suxamethonium 1 mg kg" 1 to facilitate orotracheal intubation. Anaesthesia was maintained with enflurane in either 33% or 40% oxygen in nitrous oxide at a fresh gas flow rate of 4.5 or 6.0 litre min" 1 . The breathing system was a semi-closed circle with carbon dioxide absorption and a low-resistance, uni-directional valve. Following endotracheal intubation, the lungs were ventilated manually until spontaneous breathing was deemed adequate. The vaporizer (Cyprane) was adjusted to deliver a concentration of enflurane which abolished the response to surgical stimulation. In 19 patients concentration in the fresh gas was between 1.5 and 3 % ; in two the concentration was greater than 3 % . (These two patients did not exhibit distinct differences in breathing pattern or Pco 2 compared with the others). Twenty to thirty minutes after the start of the operation and when a steady tidal volume and frequency had been present for 5 min, arterial blood was sampled as described above. Expired minute volume (VE) was measured with a Wright respirometer connected to the uni-directional valve without disconnecting the patient from the breathing circuit. The data were analysed using Student's t test and by least squares regression. RESULTS
Pa C02 and ventilation values during anaesthesia are given in table II. Mean Vr during enflurane © Macmillan Journals Ltd 1979
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
Tidal volume, respiratory frequency and P&co, were measured in 21 healthy, premedicated adults during anaesthesia with enflurane and 60 or 66% nitrous oxide in oxygen. The increase in Paco, correlated with the value of FEVi/VC determined before anaesthesia. />aco, during anaesthesia correlated with an index of airway resistance (FEV^height) and was influenced by the pattern of breathing. These correlations are similar to those reported for halothane.
124
BRITISH JOURNAL OF ANAESTHESIA TABLE I. Biometric data and pulmonary function tests
Mean SEM
Age (yr)
Weight (kg)
Height (cm)
51.7 3.6
67.2 2.9
168.5 1.8
Surface area (m2) 1.73 0.04
FEV/VC (%) 85 2
Pac0 (kPa)
Pa O (kPa) (Fl 0 , = 0.33)
4.69 0.73
17.45 0.73
TABLE II. Values for expired gas volumes, frequency and P , during anaesthesia f (ml) (b.p.m.) VT
332
SEM
28
16.1 0.4
5.51 1.9
FT/SA
(ml m- 2 ) 190 60
P*COt
(kPa) 7.56 0.37
CO Q_
anaesthesia was 332 ±28 ml (SEM) at a mean frequency of 16.1 ±0.4 b.p.m. The values are different from those noted during halothane anaesthesia. Hickey and colleagues (1973) reported a mean F T of 245 ± 18 ml and FE 7.0 ± 0.5 litre min" 1 . In ^ 15 zs 4.5 their study mean PaCOl! was 6.98 ± 0.29 kPa—less 2 than the mean Pa COa (7.56 ± 0.37 kPa) noted for (liitre rrT ) enflurane in spite of a greater F T . FIG. 1. The influence of F E / S A on Paco, during enflurane Paco 2 was increased during anaesthesia in all the anaesthesia. patients in the present study, from a mean value on the day before operation of 4.69 + 0.73 kPa to 7.56 ±0.37 kPa (P< 0.001). This increase was related inversely to FEV,/FVC%: 10.08-O.OSFEVj/FVC
(r = 0.6, P<0.01)
During anaesthesia mean pH was 7.21 + 0.01 units, denoting respiratory acidaemia since the plasma bicarbonate concentration did not change significantly. Pa C02 during anaesthesia correlated with minute volume and with FEVi: 2
(1) Pa COs = 9.63-0.8 FE/SA (litre m" )
-8
-7
-6
(r = 0.79,
P<0.001)(fig. 1);
-5 1
(2) Pa COa = 9.17- l.MFEVj/ht (litre m" ) (r = 0.65, P<0.001)(fig.2) (where SA = surface area).
-r
• FEV
/ht
DISCUSSION
F I G - 2. The relationship between intraoperative PHQO and
T h e anaesthetic technique used in the present study may b e criticized because narcotic premedication was given a n d because each patient did not receive the same concentration of the inhalation agent. Under
* such conditions, it is impossible to separate the effects of premedication and different concentrations of the agent. Nevertheless, we preferred to give these
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
Mean
Vz (litre min"1)
125
patients the anaesthetic that they would have received normally for their operation. When carbon dioxide production and physiological deadspace are constant, hypercarbia is a result of shallow or slow breathing, or both. The average tidal volume noted during enflurane anaesthesia is definitely larger than that reported by Hickey and his co-workers (1973) during halothane anaesthesia. However, such a relatively large tidal volume was insufficient to maintain normocarbia because of the low frequency. An inverse relationship was found between tidal volume and Pa C0]! similar to that reported for halothane by Pietak and others (1975). The data from the present study are presented in the form of F E / S A because this form takes frequency into account
The other important consideration concerns the expected reduction in functional residual capacity (FRC) during anaesthesia. Resting lung volumes (FRC) decrease during anaesthesia and the reduction is a function of body build and FEV^FVC (Hickey et al., 1973). Airway resistance increases in a hyperbolic fashion as lung volume decreases (Nunn, 1977). Thus, subjects with an initial high airway resistance (low FEVX) have greater reductions in FRC and greater increases in airways resistance, and this would compound the problem of the effect of increased impedance on minute ventilation mentioned above. Consequently, elimination of carbon dioxide would be hampered severely. It is conceivable that reducing airways resistance with a bronchodilator may lower carbon dioxide tensions secondary to decreasing airway resistance. We conclude that hypoventilation during enflurane anaesthesia is not only a result of central respiratory depression, but also a function of awake airways resistance.
(fig- 1). Forced expiratory volume/vital capacity is a good index of airways resistance because it takes into account individual variations in absolute lung volume. The increase in i3aCOs which occurred during anaesthesia could be correlated significantly with this index while the absolute value of PaCOa had a significant inverse relationship with FEVx/ht (fig. 2). This relationship has two clinical implications. Awake subjects with high airway resistance can overcome impedance to ventilation by an increase in chemical drive. This response is lessened with anaesthesia, appropriate compensation cannot occur, and minute ventilation tends to decrease. Indeed, we found a direct relationship between KE/SA and F E / S A = 0.62+ 1.47FEV1/ht
(r = 0.76, P<0.001) (fig. 3). - 6
-5
-4
-3
en
REFERENCES
Hickey, R. F., Visick, W. D., Fairley, H. B., and Fourcade, H. E. (1973). Effects of halothane anesthesia on functional residual capacity and alveolar-arterial oxygen tension difference. Anesthesiology, 38,20. Kelman, G. R., and Nunn, J. F. (1966). Nomograms for correction of blood Po 2 , Pco 2 , pH and base excess for time and temperature. J. Appl. Physiol., 21,1484. Lebowitz, M. H., Blitt, C. D., and Dillon, J. B. (1970). Clinical investigation of compound 347 (Ethrane). Anesth. Analg. (Cleve.), 49,1. Nunn, J. F. (1977). Applied Respiratory Physiology, 2nd edn, p. 117. London: Butterworths. Pietak, S., Weenig, C. S., Hickey, R. F., and Fairley, H. B. (1975). Anesthetic effects on ventilation in patients with chronic obstructive pulmonary disease. Anesthesiology, 42, 160. INFLUENCE DE LA RESISTANCE DBS PASSAGES D'AIR ET MODALITES VENTILATOIRES SUR LA Pac 0 PENDANT UNE ANESTHESIE A L'ENFLURANE
-2
UJ
•Ik
ACKNOWLEDGEMENTS
Drs D. M. M. Gillies and G. Drummond gave valuable advice during the preparation of the text. Ohio Chemical Products, Canada, donated a supply of Ethrane and financial support for the purchase of a desk-top calculator for the statistical analysis.
-1
RESUME
FE^/ht FIG. 3. KE/SA as a function of FEV^ht.
On a mesur£ sur 21 temoins adultes en bonne sante ayant subi une premedication, pendant une anesthesie a l'enflurane et 60 ou 66% de protoxyde d'azote dans l'oxygene: le volume courant, la frequence respiratoire et la -Paco,L'augmentation de la -Paco, a €ti en correlation avec la
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
PaCOt DURING ENFLURANE ANAESTHESIA
BRITISH JOURNAL OF ANAESTHESIA
126 valeur de FEV^VC determinee avant Panesthesie. Pendant Panes thesie, la Paco, et£ en correlation avec un indice de la resistance des passages d'air (FEVj/taille) et elle a ete influencee par les modalites de la respiration. Ces correlations sont similaires a celles qui ont ete signalees pour Phalothane. EINWIRKUNG DES ATEMWIDERSTANDES UND DES VENTILATORISCHEN RHYTHMUS AUF WAHREND EINER ENFLURANNARKOSE ZUSAMMENFASSUNG
SUMARIO
Se midi6 el voliimen de marea, frecuencia respiratoria y Paco, en 21 adultos sanos, premedicados, durante anestesia con enflurano y 60 o 66% de oxido nitroso en oxigeno. El aumento en el Paco, s e correlacion6 con el valor de FEVj/ VC, determinado antes de la anestesia. El Paco, durante la anestesia se correlaciono con un indice de resistencia en las vias respiratorias (FEVj/altura) y fue influenciado por el tipo de respiration. Estas correlaciones son semejantes a aquellas presentadas para halotano. Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
StrSmungsvolumen, Atmungsfrequenz und Paco, wurden in 21 gesunden Erwachsenen mit Pramedikation wahrend einer Enflurannarkose mit 60 oder 66% Stickoxyd in Sauerstoff gemessen. Das Anwachsen von Paco, stand in Wechselbeziehung mit den Werten von FEV1/VC, vor der Narkose festgestellt. Paco stand wahrend der Narkose in Wechselbeziehung mit emem Atemwiderstandsindex FEVi/GrOsse) und war vom Atmungsrhythmus beeinflusst. Diese Wechselbeziehungen ahneln denen, die von Halothan berichtet wurden.
INFLUENCIA EJERCIDA POR LA RESISTENCIA DE LAS VIAS RESPIRATORIAS Y TIPO DE VENTILACION SOBRE EL Paco, DURANTE LA ANESTESIA DE ENFLURANO
INFLUENCE OF AIRWAY RESISTANCE AND VENTILATORY PATTERN ON PaCOa DURING ENFLURANE ANAESTHESIA W. M. WAHBA SUMMARY
Pa cc , 2 during halothane anaesthesia with spontaneous ventilation is related to the severity of airway obstruction before operation and to tidal volume during anaesthesia (Pietak et al., 1975). There was a significant correlation between Pa C02 and the ratio of tidal volume to surface area ( F T / S A ) and forced expiratory volume standardized for height (FEV^ht). The purpose of the present study was to determine if similar relationships exist for enflurane. Apart from the brief comments by Lebowitz, Blitt and Dillon (1970), no published data could be found on the pattern of breathing during enflurane anaesthesia when premedication, induction and maintenance are standardized. Therefore a pattern was sought from the present data. METHODS
The study was performed on 21 clinically healthy adults undergoing elective operations on the extremities. The study was approved by the Hospital Research and Ethics Committee. The general and lung function data are shown in table I. On the day before operation, FEVX and vital capacity (VC) were determined from three measurements with the patients seated upright. Blood was sampled from a radial artery by direct puncture while the subject was supine and breathing a mixture of 33% oxygen in nitrogen from a venturi-type mask. The blood was withdrawn anaerobically into heparinized syringes, which were packed in ice. The sample was analysed within 10 min for gas tensions and pH by standard electrodes calibrated with nominal 0, 5 and 10% mixtures of carbon dioxide W.
M.
WAHBA, M.B., B.CH., M.SC.(MCGIIX),
F.R.C.P.(C),
McGill University, Montreal, Canada. Correspondence to: Department of Anaesthesia, Queen Elizabeth Hospital of Montreal, 2100 Marlowe Avenue, Montreal, Quebec H4A 3L6, Canada. 0007-0912/79/020123-04 $01.00
(Corning 165). No corrections were made for time, thus introducing a possible error of 0.01-0.07 kPa for Pa cc , 2 (Kelman and Nunn, 1966). Premedication consisted of anileridine and promethazine by i.m. injection 1 h before operation. The doses (based on body weight) ranged from 12.5 to 37.5 mg of the former, and 12.5 to 25 mg of the latter. Anaesthesia was induced with thiopentone 2-3 mg kg" 1 i.v. followed by suxamethonium 1 mg kg" 1 to facilitate orotracheal intubation. Anaesthesia was maintained with enflurane in either 33% or 40% oxygen in nitrous oxide at a fresh gas flow rate of 4.5 or 6.0 litre min" 1 . The breathing system was a semi-closed circle with carbon dioxide absorption and a low-resistance, uni-directional valve. Following endotracheal intubation, the lungs were ventilated manually until spontaneous breathing was deemed adequate. The vaporizer (Cyprane) was adjusted to deliver a concentration of enflurane which abolished the response to surgical stimulation. In 19 patients concentration in the fresh gas was between 1.5 and 3 % ; in two the concentration was greater than 3 % . (These two patients did not exhibit distinct differences in breathing pattern or Pco 2 compared with the others). Twenty to thirty minutes after the start of the operation and when a steady tidal volume and frequency had been present for 5 min, arterial blood was sampled as described above. Expired minute volume (VE) was measured with a Wright respirometer connected to the uni-directional valve without disconnecting the patient from the breathing circuit. The data were analysed using Student's t test and by least squares regression. RESULTS
Pa C02 and ventilation values during anaesthesia are given in table II. Mean Vr during enflurane © Macmillan Journals Ltd 1979
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
Tidal volume, respiratory frequency and P&co, were measured in 21 healthy, premedicated adults during anaesthesia with enflurane and 60 or 66% nitrous oxide in oxygen. The increase in Paco, correlated with the value of FEVi/VC determined before anaesthesia. />aco, during anaesthesia correlated with an index of airway resistance (FEV^height) and was influenced by the pattern of breathing. These correlations are similar to those reported for halothane.
124
BRITISH JOURNAL OF ANAESTHESIA TABLE I. Biometric data and pulmonary function tests
Mean SEM
Age (yr)
Weight (kg)
Height (cm)
51.7 3.6
67.2 2.9
168.5 1.8
Surface area (m2) 1.73 0.04
FEV/VC (%) 85 2
Pac0 (kPa)
Pa O (kPa) (Fl 0 , = 0.33)
4.69 0.73
17.45 0.73
TABLE II. Values for expired gas volumes, frequency and P , during anaesthesia f (ml) (b.p.m.) VT
332
SEM
28
16.1 0.4
5.51 1.9
FT/SA
(ml m- 2 ) 190 60
P*COt
(kPa) 7.56 0.37
CO Q_
anaesthesia was 332 ±28 ml (SEM) at a mean frequency of 16.1 ±0.4 b.p.m. The values are different from those noted during halothane anaesthesia. Hickey and colleagues (1973) reported a mean F T of 245 ± 18 ml and FE 7.0 ± 0.5 litre min" 1 . In ^ 15 zs 4.5 their study mean PaCOl! was 6.98 ± 0.29 kPa—less 2 than the mean Pa COa (7.56 ± 0.37 kPa) noted for (liitre rrT ) enflurane in spite of a greater F T . FIG. 1. The influence of F E / S A on Paco, during enflurane Paco 2 was increased during anaesthesia in all the anaesthesia. patients in the present study, from a mean value on the day before operation of 4.69 + 0.73 kPa to 7.56 ±0.37 kPa (P< 0.001). This increase was related inversely to FEV,/FVC%: 10.08-O.OSFEVj/FVC
(r = 0.6, P<0.01)
During anaesthesia mean pH was 7.21 + 0.01 units, denoting respiratory acidaemia since the plasma bicarbonate concentration did not change significantly. Pa C02 during anaesthesia correlated with minute volume and with FEVi: 2
(1) Pa COs = 9.63-0.8 FE/SA (litre m" )
-8
-7
-6
(r = 0.79,
P<0.001)(fig. 1);
-5 1
(2) Pa COa = 9.17- l.MFEVj/ht (litre m" ) (r = 0.65, P<0.001)(fig.2) (where SA = surface area).
-r
• FEV
/ht
DISCUSSION
F I G - 2. The relationship between intraoperative PHQO and
T h e anaesthetic technique used in the present study may b e criticized because narcotic premedication was given a n d because each patient did not receive the same concentration of the inhalation agent. Under
* such conditions, it is impossible to separate the effects of premedication and different concentrations of the agent. Nevertheless, we preferred to give these
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
Mean
Vz (litre min"1)
125
patients the anaesthetic that they would have received normally for their operation. When carbon dioxide production and physiological deadspace are constant, hypercarbia is a result of shallow or slow breathing, or both. The average tidal volume noted during enflurane anaesthesia is definitely larger than that reported by Hickey and his co-workers (1973) during halothane anaesthesia. However, such a relatively large tidal volume was insufficient to maintain normocarbia because of the low frequency. An inverse relationship was found between tidal volume and Pa C0]! similar to that reported for halothane by Pietak and others (1975). The data from the present study are presented in the form of F E / S A because this form takes frequency into account
The other important consideration concerns the expected reduction in functional residual capacity (FRC) during anaesthesia. Resting lung volumes (FRC) decrease during anaesthesia and the reduction is a function of body build and FEV^FVC (Hickey et al., 1973). Airway resistance increases in a hyperbolic fashion as lung volume decreases (Nunn, 1977). Thus, subjects with an initial high airway resistance (low FEVX) have greater reductions in FRC and greater increases in airways resistance, and this would compound the problem of the effect of increased impedance on minute ventilation mentioned above. Consequently, elimination of carbon dioxide would be hampered severely. It is conceivable that reducing airways resistance with a bronchodilator may lower carbon dioxide tensions secondary to decreasing airway resistance. We conclude that hypoventilation during enflurane anaesthesia is not only a result of central respiratory depression, but also a function of awake airways resistance.
(fig- 1). Forced expiratory volume/vital capacity is a good index of airways resistance because it takes into account individual variations in absolute lung volume. The increase in i3aCOs which occurred during anaesthesia could be correlated significantly with this index while the absolute value of PaCOa had a significant inverse relationship with FEVx/ht (fig. 2). This relationship has two clinical implications. Awake subjects with high airway resistance can overcome impedance to ventilation by an increase in chemical drive. This response is lessened with anaesthesia, appropriate compensation cannot occur, and minute ventilation tends to decrease. Indeed, we found a direct relationship between KE/SA and F E / S A = 0.62+ 1.47FEV1/ht
(r = 0.76, P<0.001) (fig. 3). - 6
-5
-4
-3
en
REFERENCES
Hickey, R. F., Visick, W. D., Fairley, H. B., and Fourcade, H. E. (1973). Effects of halothane anesthesia on functional residual capacity and alveolar-arterial oxygen tension difference. Anesthesiology, 38,20. Kelman, G. R., and Nunn, J. F. (1966). Nomograms for correction of blood Po 2 , Pco 2 , pH and base excess for time and temperature. J. Appl. Physiol., 21,1484. Lebowitz, M. H., Blitt, C. D., and Dillon, J. B. (1970). Clinical investigation of compound 347 (Ethrane). Anesth. Analg. (Cleve.), 49,1. Nunn, J. F. (1977). Applied Respiratory Physiology, 2nd edn, p. 117. London: Butterworths. Pietak, S., Weenig, C. S., Hickey, R. F., and Fairley, H. B. (1975). Anesthetic effects on ventilation in patients with chronic obstructive pulmonary disease. Anesthesiology, 42, 160. INFLUENCE DE LA RESISTANCE DBS PASSAGES D'AIR ET MODALITES VENTILATOIRES SUR LA Pac 0 PENDANT UNE ANESTHESIE A L'ENFLURANE
-2
UJ
•Ik
ACKNOWLEDGEMENTS
Drs D. M. M. Gillies and G. Drummond gave valuable advice during the preparation of the text. Ohio Chemical Products, Canada, donated a supply of Ethrane and financial support for the purchase of a desk-top calculator for the statistical analysis.
-1
RESUME
FE^/ht FIG. 3. KE/SA as a function of FEV^ht.
On a mesur£ sur 21 temoins adultes en bonne sante ayant subi une premedication, pendant une anesthesie a l'enflurane et 60 ou 66% de protoxyde d'azote dans l'oxygene: le volume courant, la frequence respiratoire et la -Paco,L'augmentation de la -Paco, a €ti en correlation avec la
Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
PaCOt DURING ENFLURANE ANAESTHESIA
BRITISH JOURNAL OF ANAESTHESIA
126 valeur de FEV^VC determinee avant Panesthesie. Pendant Panes thesie, la Paco, et£ en correlation avec un indice de la resistance des passages d'air (FEVj/taille) et elle a ete influencee par les modalites de la respiration. Ces correlations sont similaires a celles qui ont ete signalees pour Phalothane. EINWIRKUNG DES ATEMWIDERSTANDES UND DES VENTILATORISCHEN RHYTHMUS AUF WAHREND EINER ENFLURANNARKOSE ZUSAMMENFASSUNG
SUMARIO
Se midi6 el voliimen de marea, frecuencia respiratoria y Paco, en 21 adultos sanos, premedicados, durante anestesia con enflurano y 60 o 66% de oxido nitroso en oxigeno. El aumento en el Paco, s e correlacion6 con el valor de FEVj/ VC, determinado antes de la anestesia. El Paco, durante la anestesia se correlaciono con un indice de resistencia en las vias respiratorias (FEVj/altura) y fue influenciado por el tipo de respiration. Estas correlaciones son semejantes a aquellas presentadas para halotano. Downloaded from http://bja.oxfordjournals.org/ at University of Arizona on July 14, 2015
StrSmungsvolumen, Atmungsfrequenz und Paco, wurden in 21 gesunden Erwachsenen mit Pramedikation wahrend einer Enflurannarkose mit 60 oder 66% Stickoxyd in Sauerstoff gemessen. Das Anwachsen von Paco, stand in Wechselbeziehung mit den Werten von FEV1/VC, vor der Narkose festgestellt. Paco stand wahrend der Narkose in Wechselbeziehung mit emem Atemwiderstandsindex FEVi/GrOsse) und war vom Atmungsrhythmus beeinflusst. Diese Wechselbeziehungen ahneln denen, die von Halothan berichtet wurden.
INFLUENCIA EJERCIDA POR LA RESISTENCIA DE LAS VIAS RESPIRATORIAS Y TIPO DE VENTILACION SOBRE EL Paco, DURANTE LA ANESTESIA DE ENFLURANO