British Journal of Anaesthesia 1991; 66: 200-204
USE OF CONTINUOUS POSITIVE AIRWAY PRESSURE IN PAEDIATRIC DENTAL EXTRACTION UNDER GENERAL ANAESTHESIA
SUMMARY In a controlled prospective study, we studied 150 grade ASA I children undergoing outpatient dental extraction under inhalation anaesthesia with a T-piece system allocated to three equal groups: a control group (0 cm H20 CPAP), and two study groups receiving 2.5 or 5 cm H2O of CPAP via a nasal mask. We found that the incidence and severity of oxygen desaturation were reduced significantly in the 5-cm H2O CPAP group. KEY WORDS Anaesthesia: outpatient, dental Oxygen: pulse oximetry. Ventilation • continuous positive pressure breathing.
PATIENTS AND METHODS
Following approval by the London Hospital Ethics Committee, we studied 150 children of ASA grade I, aged 1-14 yr, undergoing outpatient dental extraction under general anaesthesia. They were allocated to three groups: group A = 0 cm H2O CPAP; group B = 2.5 cm H2O CPAP; group C = 5 cm H2O CPAP. The groups were studied in the sequence C, B and A and involved many anaesthetists, surgeons and trainees of varying grades, to negate the learning curve effect and to conform with our normal clinical practice. The range of ages encountered (group A 2-14 yr, group B 2-14 yr and group C 1-13 yr) reflected the occasional admission of patients at the extremes of this range during the period of study and was limited to the two patients concerned in each group (table I). Measurement of oxygen saturation (5pOj) commenced before anaesthesia using an Ohmeda Biox 111 BOC Health Care pulse oximeter, which has been shown to have an accuracy of ± 2.4 % in the 80-100% range [10]. Oxygen saturation was recorded continuously on a Gould TA 550 threechannel pen chart recorder. All patients were monitored with a Cardiorater ECG. Heart rate was recorded at 30-s intervals and incidence and duration of cardiac arrhythmias noted and recorded. Anaesthesia was induced in patients in the
A decrease in arterial oxygen saturation by more than 10% has been demonstrated in children undergoing dental extraction under general anaesthesia with both inhalation and i.v. techniques of induction [1,2]. This results predominantly from upper airway obstruction at the time of insertion of the dental prop and pack and during extractions. This obstruction may be accentuated in children of this age group by their tendency to rhinitis and hypertrophy of the adenoids and tonsils [3]. Nasal continuous positive airways pressure (CPAP) has been reported to increase oxygen saturation in the presence of measured oxygen desaturation and partial airway obstruction in adults and children, for example in obstructive sleep apnoea syndrome [4-6]. CPAP also exerts a . SURESH, D.A., F.F.A.R.C.S.I., P. J. FLYNN, M.B., F.F.A.R.C.S.I., beneficial effect on the functional residual capacity DD.CH., D.OBST. (Anaesthetics Unit); G. PURDY*, M.B., CH.B., (FRC) [7-9] and the work of breathing [9]. B.A.O., F.F.A.R.C.S.I., M.R.C.P.(U.K.), A. P. WAINWRIGHT, M.B., This study was designed to measure oxygen CH.B., F.c.ANAES. (Department of Anaesthesia); The London saturation in children undergoing outpatient den- Hospital, Whitcchapel, London El. Accepted for Publication: 3, 1990. tal extractions, when 0, 2.5 or 5 cm HjO of CPAP September *Present address: Department of Anaesthesia, Hull Royal was added to a standard technique of inhalation Infirmary, Hull. nasal mask anaesthesia via a T-piece system. Correspondence to A.P.W.
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
D. SURESH, G. PURDY, A. P. WAINWRIGHT AND P. J. FLYNN
CPAP IN PAEDIATRIC DENTAL EXTRACTION CPAP valve
201
Nasal mask
o
Passive \ scavenging system
Boyles machine FGF
Wide bore tubing
CO2 analyser
FIG. 1. Circuit diagram.
supine position via the open end of the T-piece held close to the mouth and nose, using halothane in increasing concentrations up to 5 % and 66 % nitrous oxide in oxygen. When judged appropriate by the anaesthetist, a nasal mask (SEFAM, France) was applied and the halothane concentration decreased to 2 %. The' use of a nasopharyngeal airway was left to the discretion of the anaesthetists who were of varying grades and included supervised dental students and junior trainees in anaesthesia. The grade of the person performing dental extractions (which included supervised dental students) was noted. The T-piece system had a wide-bore inspiratory tube and 4-litre reservoir bag. A CPAP level of 0 cm, 2.5 cm or 5 cm H2O was applied with an adjustable Heidbrink valve. The fresh gas flow used was 9 litre min~x in children aged 1-7 yr and 12 litre min"1 in children older than 7 yr, to ensure that the reservoir bag remained almost fully distended throughout the respiratory cycle [11, 12]. The SEFAM nasal mask has two oxygen portholes which were utilized for pressure monitoring and carbon dioxide sampling (fig. 1). Carbon dioxide was measured with a Datex Normocap carbon dioxide monitor and a pen chart recorder with a sampling rate of 150 ml min"1. A Gould Statham P231D pressure transducer was used to measure CPAP and, consequently, the duration of gas tight seal at the mask during the ventilatory cycle. Both the Datex Normocap and Gould Statham transducer were calibrated according to the manufacturers' instructions before each anaesthetic session. Airway pressure was recorded continuously on a Gould TA 550 three-channel pen chart recorder.
Surgery commenced when the depth of anaesthesia was judged to be adequate and key anaesthetic and surgical events were noted. Whenever desaturation in excess of 10% from baseline values occurred, surgery was interrupted until SpOx had improved to nearer baseline values following restoration of the airway. Statistical analysis Parametric data were analysed using an unpaired Student's t test. Non-parametric 95% confidence intervals for median baseline and median least SpOi(%) were obtained for the three groups and a Mann—Whitney U test used to compare baseline oxygen saturation and peroperative desaturation. The incidence of cardiac arrhythmias was compared using a chi-square test. Three-way analysis of variance was performed to compare the groups and the grades of anaesthetists and surgeons for peroperative desaturation. P < 0.05 was accepted as statistically significant. RESULTS
The three groups were comparable with regard to age and numbers of teeth extracted (table I), and race (table II). TABLE I. Patient characteristics in groups A, B and C (T-piece system: 0, 2.5 and 5 cm HtO of CPAP, respectively) Age (yr) (mean (range)) Group A Group B Group C
6.3 (2-14) 6.5 (2-14) 5.7(1-13)
Number of teeth extracted (mean (SEM))
3.9 (0.3) 3.4(0.3) 3.4 (0.3)
50 50 50
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
Reservoir bag (4-litre)
Pressure transducer
BRITISH JOURNAL OF ANAESTHESIA
202 TABLE
II. Racial distribution of patients in groups A, B and C
Caucasian
Asian
26 30 31
22 18
2 2
16
1
Group A Group B Group C
Negro Negro/Caucasian 0 0 2 c Q.
"S ID
Baseline 5p Ol Group A Group B Group C
98 (97-99) 99 (98-100) 99 (99-100)
Least S p ^
E
96(95-96) 96(96-98) 98.50 (96-99)
TABLE IV. Respiratory data (mean (SEM)). *P < 0.05
0 1-5 6-10 > 10 Maximum decrease in SpO2(%)
Ventilatory frequency End-tidal CO, (b.p.m.) (%) Group A Group B Group C
32(1.7) 34(1.4) 34(1.5)
FIG. 2. Histogram showing oxygen desaturation in groups A ( • = 0 cm H,O CPAP), B ( • = 2.5 cm H,O CPAP) and C (H = 5 cm H,O CPAP).
3.7(1.1) 4.8 (0.07)* 4.6(0.1)*
There was a significant difference between groups with regard to oxygen desaturation, the incidence and severity of which was less in the 5cm HjO study group compared with the control group (fig. 2, table III). Oxygen desaturation occurred mainly during the following events: induction, application of mask, insertion of the prop and pack and during dental extractions. These episodes of hypoxemia resulted predominantly from partial upper airways obstruction during these events.
Ventilatory frequency was similar in the groups, although the end-tidal concentrations of carbon dioxide increased significantly in patients who received CPAP (table IV). There was no significant difference between the two study groups for the percentage of time that CPAP, and hence a gas tight seal, was maintained (72% for group B, 64% for group C). Temporary loss of CPAP occurred, as anticipated, during insertion of the dental prop and pack and jaw manipulation. The mean baseline heart rate in the three groups was similar. In all groups, the majority of patients displayed a mean increase in heart rate
TABLE V. Mean (SEM) heart rate and arrhythmias, and number of ventricular eclopic beats in groups A, B and C. n = No. patients
Heart rate (beat min '')
Group A Group B Group C
Ectopic beats (No. min"1)
Baseline
Increase
Decrease
89 (2.6) (n = 50) 99 (2.6) (n = 48) 101 (2.6) (n = 50)
41 (3.3) (n = 46) 35 (2.5) (n = 43) 33 (2.9) (n = 44)
22(12.2)
1-2
(n = 4)
(n = 6) 0.5-6 (n = 7) 0.5-3 (« = 6)
40(12.2) (n = 5)
39 (6.0) (n = 6)
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
TABLE III. Baseline and median least SpOt (median non-parametric 95 % confidence intervals) in groups A, B and C
CPAP IN PAEDIATRIC DENTAL EXTRACTION
203
TABLE VI. Incidence of hypoxacmia exceeding 10% of baseline Spo for different grades of anaesthetist and surgeon. SHO = Senior House Officer; SR = Senior Registrar; Reg. = Registrar; Cons. = Consultant
Surgeon (Total in each grade)
Anaesthetist (Total in each grade) SHO/Reg.
SR/Cons.
Student
SHO/Reg.
SR/Cons.
2(20) 0(4) 2(6) 4(30)
3(11) 5(39) 0(25) 8(65)
7(19) K7) 1(19) 9(35)
6(24) 3(23) 0(19) 9(66)
6(25) 3(27) 3(29) 12(81)
0(1) 0(2) 0(3)
13%
12%
25%
14%
15%
—
during operation. In a small number of patients there was a reduction in heart rate, but none required treatment. There was no significant difference between the three groups with regard to the incidence or duration of arrhythmias (table V). Three-way analysis of variance between the groups and grades of anaesthetist and surgeon, showed no significant difference (P = 0.89) for the incidence of desaturation (table VI). DISCUSSION
Hypoxaemia during dental extraction under nasal mask anaesthesia is often rapid in onset, not always obvious clinically [1, 13-15], and reported to be a major contributory factor to death from dental anaesthesia [16]. Pulse oximetry provides an advance in monitoring by detecting small reductions in oxygen saturation and displaying trends [10, 17]. Historically, low inspired oxygen concentrations were used for dental extraction under inhalation general anaesthesia. Increasing the fractional inspired oxygen concentration (FI O J ) to 0.3 reduced the incidence and severity of peroperative desaturation compared with an FI O J of 0.2 or 0.25 [18], but it has been shown that a further increase in FI O J to 0.5 does not improve peroperative oxygen saturation [19]. This led to the investigation of the value of nasal CPAP on peroperative oxygen saturation in this study. In young children, airway closure occurs at lung volumes well above FRC, producing a relatively high intrapulmonary shunt [20,21]. During general anaesthesia, when there is further reduction in FRC, this intrapulmonary shunt is exacerbated [20-22] and, together with the propensity for upper airway obstruction caused by
—
rhinitis and lymphoid hypertrophy in this age group, there is greater tendency to hypoxia. Several studies have suggested two mechanisms whereby CPAP may enhance gas exchange and oxygenation in these children. First, there is an increase in FRC proportional to the CPAP [7, 8]. Second, CPAP may overcome apnoea and partial soft tissue airway obstruction [6]. In addition, the application of CPAP may rectify breathing in children with irregular breathing patterns [23]. In this study the application of 5 cm HjO of CPAP resulted in a significant reduction in the incidence and severity of peroperative oxygen desaturation. The increased ventilatory frequencies recorded during anaesthesia were consistent with similar studies in children receiving inhalation general anaesthesia with halothane [24]. The use of a pressure monitor in the circuit permitted attainment of the correct value of CPAP with a small fluctuation in pressure of ± 1 cm HjO noted throughout the ventilatory cycle. Reductions in pressure within the circuit alerted the anaesthetist to malposition of the pack, whereas a loss of pressure variations suggested airway obstruction or apnoea, and allowed early detection and repositioning of the jaw or mask before significant desaturation occurred. Pressure monitoring is also essential to guard against the potential hazard of inadvertent application of excessive CPAP [25]. One consideration in choosing the most appropriate breathing system for anaesthesia is its effect on the work of breathing. It has been shown that, when airway pressure is kept constant with increasing CPAP, the inspiratory work performed by the subject is decreased [26-29]. The 4-litre reservoir bag, wide bore tubing and high fresh gas flows ensured that marked fluctuations in airway pressure did not occur. The system described in
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
Group A Group B Group C Total (A + B + C)
Student
204
BRITISH JOURNAL OF ANAESTHESIA
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10. Taylor MB, Whitwam JG. Pulse oximetry. Anaesthesia 1988; 43: 229-232. 11. Cox D, Niblett DJ. Studies on continuous positive airway pressure breathing systems. British Journal of Anaesthesia 1984; 56: 905-911. 12. Civetta JM, Brons R, Gabel JC. A simple and effective method of employing spontaneous positive pressure ventilation. Journal of Thoracic and Cardiovascular Surgery 1972; 63: 312-317. 13. Al-Kishali T, Padfield A, Perks ER, Thornton JA. Cardio-respiratory effects of nitrous oxide: oxygen: halothane anaesthesia administered to dental outpatients in the upright position. Anaesthesia 1978; 32: 184-188. 14. Tomlin PJ. Death in out-patient anaesthetic practice. Anaesthesia 1974; 29: 551-570. 15. Walsh JF. Training for day-case dental anaesthesia. Oxygen saturation during genera] anaesthesia administered by dental undergraduates. Anaesthesia 1984; 39: 1124-1127. 16. Coplans MP, Curson I. Deaths associated with dentistry. British Dental Journal 1982; 153: 357-362. 17. Ridley SA. A comparison of two pulse oximeters. Anaesthesia 1988; 43: 136-140. 18. Parbrook GD. Arterial oxygen saturation during general anaesthesia for dental extraction in children. Anaesthesia 1988; 43: 67. 19. Allen NA, Rowbotham DJ, Nimmo WS. Hypoxaemia during outpatient dental anaesthesia. Anaesthesia 1989; 44: 509-511. 20. Fairley HB. Airway closure. Anesthesiology 1972; 36: 529-532. REFERENCES 1. Bone ME, Galler D, Flynn PJ. Arterial oxygen saturation 21. Mansell A, Bryan C, Levison H. Airway closure in children. Journal of Applied Physiology 1972; 33: 711. during general anaesthesia for paediatric dental extrac22. Craig DB, McCarthy DS. Closing capacity during CPAP. tions. Anaesthesia 1987; 42: 879-882. Anesthesiology 1976; 44: 88. 2. Beeby C, Thurlow AC. Pulse oximetry during general 23. Gregory G, Kitterman J, Phibbs RH, Tooley WH, anaesthesia for dental extractions. British Dental Journal Hamilton WK. Treatment of the idiopathic respiratory 1986; 160: 123-125. distress syndrome with continuous positive airway press3. Mackay I (cd.) Rhinitis—Mechanisms and Management. ure. New England Journal of Medicine 1971; 284: 1333London: Royal Society of Medicine Services Limited, 1340. 1989. 24. Lindahl SGE, Yates AP, Hatch DJ. Respiratory de4. Wilhoit SC, McTier RF, Findley LJ, Suratt PM. pression at different end-tidal halothane concentrations. Treatment of obstructive sleep apnoea with continuous Anaesthesia 1987; 42: 1267-1275. nasal airflow. Lung 1985; 163: 233-241. 25. Suter PM, Fairley HB, Isenberg MD. Optimum end5. Saunders MH, Moore SE, Eveslage J. CPAP via nasal expiratory airway pressure in patients with acute pulmask: A treatment for occlusion sleep apnoea. Chest 1983; monary failure. New England Journal of Medicine 1975; 9: 83: 144-145. 284-289. 6. Schmidt-Nowara WW. Continuous positive airway press- 26. Butler J, Arnott WM. The work of pulmonary ventilation ure for long-term treatment of sleep apnoea. American at different respiratory levels. Clinical Science 1955; 14: Journal of Disease in Childhood 1984; 138: 82-84. 703-710. 7. Craig DB, McCarthy DS. Airway closure and lung 27. Milic-Emili J, Petit JM, Deroame R. The effects of volumes during breathing with maintained airway positive respiratory rate on the mechanical work of breathing pressures. Anesthesiology 1972; 6: 540-543. during muscular exercise. Internationale Zeitschrift Fuer 8. Abboud N, Rehder K, Roberts JR, Hyatt RE. Lung Anlewandte Physiologie 1960; 18: 330-340. volume and closing capacity with continuous positive 28. Bader ME, Bader RA. The work of breathing. American airway pressure. Anesthesiology 1975; 42: 138-142. Journal of Medicine 1955; 18: 851-854. 9. Gherini S, Peters RM, Virgilio RW. Mechanical work on 29. Kay B, Beatty PCW, Healy TEJ, Accoush MEA, Calpin the lungs and work of breathing with positive endM. Change in the work of breathing imposed by five expiratory pressure and continuous positive airway pressanaesthetic breathing systems. British Journal of Anure. Chest 1979; 76: 251-257. aesthesia 1983; 55: 1239-1246.
this study for the application of CPAP would not, therefore, theoretically affect adversely the work of breathing, but may indeed reduce it. Random allocation of patients in this study was impractical for several reasons, and the possibility of sequential error remains. Unlike a previous investigation [1], the grade of anaesthetist or surgeon was found to have no significant effect on peroperative oxygenation in either this or another study comparing an FI O J of 0.3 with an FiO( of 0.5 [19]. Surprisingly, the percentage incidence of hypoxaemic episodes for senior anaesthetists was twice that of junior trainees and dental students, while trainee and student dental surgeons seemed to contribute equally to these episodes (table VI). Although, on occasions, oxygen saturation decreased to as little as 80%, obvious cyanosis was not reported by the anaesthetists or detected by the observers in any patient. This may have resulted from the close monitoring used for the purposes of this study, and underlines further the value of such practice in routine anaesthesia.
USE OF CONTINUOUS POSITIVE AIRWAY PRESSURE IN PAEDIATRIC DENTAL EXTRACTION UNDER GENERAL ANAESTHESIA
SUMMARY In a controlled prospective study, we studied 150 grade ASA I children undergoing outpatient dental extraction under inhalation anaesthesia with a T-piece system allocated to three equal groups: a control group (0 cm H20 CPAP), and two study groups receiving 2.5 or 5 cm H2O of CPAP via a nasal mask. We found that the incidence and severity of oxygen desaturation were reduced significantly in the 5-cm H2O CPAP group. KEY WORDS Anaesthesia: outpatient, dental Oxygen: pulse oximetry. Ventilation • continuous positive pressure breathing.
PATIENTS AND METHODS
Following approval by the London Hospital Ethics Committee, we studied 150 children of ASA grade I, aged 1-14 yr, undergoing outpatient dental extraction under general anaesthesia. They were allocated to three groups: group A = 0 cm H2O CPAP; group B = 2.5 cm H2O CPAP; group C = 5 cm H2O CPAP. The groups were studied in the sequence C, B and A and involved many anaesthetists, surgeons and trainees of varying grades, to negate the learning curve effect and to conform with our normal clinical practice. The range of ages encountered (group A 2-14 yr, group B 2-14 yr and group C 1-13 yr) reflected the occasional admission of patients at the extremes of this range during the period of study and was limited to the two patients concerned in each group (table I). Measurement of oxygen saturation (5pOj) commenced before anaesthesia using an Ohmeda Biox 111 BOC Health Care pulse oximeter, which has been shown to have an accuracy of ± 2.4 % in the 80-100% range [10]. Oxygen saturation was recorded continuously on a Gould TA 550 threechannel pen chart recorder. All patients were monitored with a Cardiorater ECG. Heart rate was recorded at 30-s intervals and incidence and duration of cardiac arrhythmias noted and recorded. Anaesthesia was induced in patients in the
A decrease in arterial oxygen saturation by more than 10% has been demonstrated in children undergoing dental extraction under general anaesthesia with both inhalation and i.v. techniques of induction [1,2]. This results predominantly from upper airway obstruction at the time of insertion of the dental prop and pack and during extractions. This obstruction may be accentuated in children of this age group by their tendency to rhinitis and hypertrophy of the adenoids and tonsils [3]. Nasal continuous positive airways pressure (CPAP) has been reported to increase oxygen saturation in the presence of measured oxygen desaturation and partial airway obstruction in adults and children, for example in obstructive sleep apnoea syndrome [4-6]. CPAP also exerts a . SURESH, D.A., F.F.A.R.C.S.I., P. J. FLYNN, M.B., F.F.A.R.C.S.I., beneficial effect on the functional residual capacity DD.CH., D.OBST. (Anaesthetics Unit); G. PURDY*, M.B., CH.B., (FRC) [7-9] and the work of breathing [9]. B.A.O., F.F.A.R.C.S.I., M.R.C.P.(U.K.), A. P. WAINWRIGHT, M.B., This study was designed to measure oxygen CH.B., F.c.ANAES. (Department of Anaesthesia); The London saturation in children undergoing outpatient den- Hospital, Whitcchapel, London El. Accepted for Publication: 3, 1990. tal extractions, when 0, 2.5 or 5 cm HjO of CPAP September *Present address: Department of Anaesthesia, Hull Royal was added to a standard technique of inhalation Infirmary, Hull. nasal mask anaesthesia via a T-piece system. Correspondence to A.P.W.
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
D. SURESH, G. PURDY, A. P. WAINWRIGHT AND P. J. FLYNN
CPAP IN PAEDIATRIC DENTAL EXTRACTION CPAP valve
201
Nasal mask
o
Passive \ scavenging system
Boyles machine FGF
Wide bore tubing
CO2 analyser
FIG. 1. Circuit diagram.
supine position via the open end of the T-piece held close to the mouth and nose, using halothane in increasing concentrations up to 5 % and 66 % nitrous oxide in oxygen. When judged appropriate by the anaesthetist, a nasal mask (SEFAM, France) was applied and the halothane concentration decreased to 2 %. The' use of a nasopharyngeal airway was left to the discretion of the anaesthetists who were of varying grades and included supervised dental students and junior trainees in anaesthesia. The grade of the person performing dental extractions (which included supervised dental students) was noted. The T-piece system had a wide-bore inspiratory tube and 4-litre reservoir bag. A CPAP level of 0 cm, 2.5 cm or 5 cm H2O was applied with an adjustable Heidbrink valve. The fresh gas flow used was 9 litre min~x in children aged 1-7 yr and 12 litre min"1 in children older than 7 yr, to ensure that the reservoir bag remained almost fully distended throughout the respiratory cycle [11, 12]. The SEFAM nasal mask has two oxygen portholes which were utilized for pressure monitoring and carbon dioxide sampling (fig. 1). Carbon dioxide was measured with a Datex Normocap carbon dioxide monitor and a pen chart recorder with a sampling rate of 150 ml min"1. A Gould Statham P231D pressure transducer was used to measure CPAP and, consequently, the duration of gas tight seal at the mask during the ventilatory cycle. Both the Datex Normocap and Gould Statham transducer were calibrated according to the manufacturers' instructions before each anaesthetic session. Airway pressure was recorded continuously on a Gould TA 550 three-channel pen chart recorder.
Surgery commenced when the depth of anaesthesia was judged to be adequate and key anaesthetic and surgical events were noted. Whenever desaturation in excess of 10% from baseline values occurred, surgery was interrupted until SpOx had improved to nearer baseline values following restoration of the airway. Statistical analysis Parametric data were analysed using an unpaired Student's t test. Non-parametric 95% confidence intervals for median baseline and median least SpOi(%) were obtained for the three groups and a Mann—Whitney U test used to compare baseline oxygen saturation and peroperative desaturation. The incidence of cardiac arrhythmias was compared using a chi-square test. Three-way analysis of variance was performed to compare the groups and the grades of anaesthetists and surgeons for peroperative desaturation. P < 0.05 was accepted as statistically significant. RESULTS
The three groups were comparable with regard to age and numbers of teeth extracted (table I), and race (table II). TABLE I. Patient characteristics in groups A, B and C (T-piece system: 0, 2.5 and 5 cm HtO of CPAP, respectively) Age (yr) (mean (range)) Group A Group B Group C
6.3 (2-14) 6.5 (2-14) 5.7(1-13)
Number of teeth extracted (mean (SEM))
3.9 (0.3) 3.4(0.3) 3.4 (0.3)
50 50 50
Downloaded from http://bja.oxfordjournals.org/ at University of California, San Francisco on March 10, 2015
Reservoir bag (4-litre)
Pressure transducer
BRITISH JOURNAL OF ANAESTHESIA
202 TABLE
II. Racial distribution of patients in groups A, B and C
Caucasian
Asian
26 30 31
22 18
2 2
16
1
Group A Group B Group C
Negro Negro/Caucasian 0 0 2 c Q.
"S ID
Baseline 5p Ol Group A Group B Group C
98 (97-99) 99 (98-100) 99 (99-100)
Least S p ^
E
96(95-96) 96(96-98) 98.50 (96-99)
TABLE IV. Respiratory data (mean (SEM)). *P < 0.05
0 1-5 6-10 > 10 Maximum decrease in SpO2(%)
Ventilatory frequency End-tidal CO, (b.p.m.) (%) Group A Group B Group C
32(1.7) 34(1.4) 34(1.5)
FIG. 2. Histogram showing oxygen desaturation in groups A ( • = 0 cm H,O CPAP), B ( • = 2.5 cm H,O CPAP) and C (H = 5 cm H,O CPAP).
3.7(1.1) 4.8 (0.07)* 4.6(0.1)*
There was a significant difference between groups with regard to oxygen desaturation, the incidence and severity of which was less in the 5cm HjO study group compared with the control group (fig. 2, table III). Oxygen desaturation occurred mainly during the following events: induction, application of mask, insertion of the prop and pack and during dental extractions. These episodes of hypoxemia resulted predominantly from partial upper airways obstruction during these events.
Ventilatory frequency was similar in the groups, although the end-tidal concentrations of carbon dioxide increased significantly in patients who received CPAP (table IV). There was no significant difference between the two study groups for the percentage of time that CPAP, and hence a gas tight seal, was maintained (72% for group B, 64% for group C). Temporary loss of CPAP occurred, as anticipated, during insertion of the dental prop and pack and jaw manipulation. The mean baseline heart rate in the three groups was similar. In all groups, the majority of patients displayed a mean increase in heart rate
TABLE V. Mean (SEM) heart rate and arrhythmias, and number of ventricular eclopic beats in groups A, B and C. n = No. patients
Heart rate (beat min '')
Group A Group B Group C
Ectopic beats (No. min"1)
Baseline
Increase
Decrease
89 (2.6) (n = 50) 99 (2.6) (n = 48) 101 (2.6) (n = 50)
41 (3.3) (n = 46) 35 (2.5) (n = 43) 33 (2.9) (n = 44)
22(12.2)
1-2
(n = 4)
(n = 6) 0.5-6 (n = 7) 0.5-3 (« = 6)
40(12.2) (n = 5)
39 (6.0) (n = 6)
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TABLE III. Baseline and median least SpOt (median non-parametric 95 % confidence intervals) in groups A, B and C
CPAP IN PAEDIATRIC DENTAL EXTRACTION
203
TABLE VI. Incidence of hypoxacmia exceeding 10% of baseline Spo for different grades of anaesthetist and surgeon. SHO = Senior House Officer; SR = Senior Registrar; Reg. = Registrar; Cons. = Consultant
Surgeon (Total in each grade)
Anaesthetist (Total in each grade) SHO/Reg.
SR/Cons.
Student
SHO/Reg.
SR/Cons.
2(20) 0(4) 2(6) 4(30)
3(11) 5(39) 0(25) 8(65)
7(19) K7) 1(19) 9(35)
6(24) 3(23) 0(19) 9(66)
6(25) 3(27) 3(29) 12(81)
0(1) 0(2) 0(3)
13%
12%
25%
14%
15%
—
during operation. In a small number of patients there was a reduction in heart rate, but none required treatment. There was no significant difference between the three groups with regard to the incidence or duration of arrhythmias (table V). Three-way analysis of variance between the groups and grades of anaesthetist and surgeon, showed no significant difference (P = 0.89) for the incidence of desaturation (table VI). DISCUSSION
Hypoxaemia during dental extraction under nasal mask anaesthesia is often rapid in onset, not always obvious clinically [1, 13-15], and reported to be a major contributory factor to death from dental anaesthesia [16]. Pulse oximetry provides an advance in monitoring by detecting small reductions in oxygen saturation and displaying trends [10, 17]. Historically, low inspired oxygen concentrations were used for dental extraction under inhalation general anaesthesia. Increasing the fractional inspired oxygen concentration (FI O J ) to 0.3 reduced the incidence and severity of peroperative desaturation compared with an FI O J of 0.2 or 0.25 [18], but it has been shown that a further increase in FI O J to 0.5 does not improve peroperative oxygen saturation [19]. This led to the investigation of the value of nasal CPAP on peroperative oxygen saturation in this study. In young children, airway closure occurs at lung volumes well above FRC, producing a relatively high intrapulmonary shunt [20,21]. During general anaesthesia, when there is further reduction in FRC, this intrapulmonary shunt is exacerbated [20-22] and, together with the propensity for upper airway obstruction caused by
—
rhinitis and lymphoid hypertrophy in this age group, there is greater tendency to hypoxia. Several studies have suggested two mechanisms whereby CPAP may enhance gas exchange and oxygenation in these children. First, there is an increase in FRC proportional to the CPAP [7, 8]. Second, CPAP may overcome apnoea and partial soft tissue airway obstruction [6]. In addition, the application of CPAP may rectify breathing in children with irregular breathing patterns [23]. In this study the application of 5 cm HjO of CPAP resulted in a significant reduction in the incidence and severity of peroperative oxygen desaturation. The increased ventilatory frequencies recorded during anaesthesia were consistent with similar studies in children receiving inhalation general anaesthesia with halothane [24]. The use of a pressure monitor in the circuit permitted attainment of the correct value of CPAP with a small fluctuation in pressure of ± 1 cm HjO noted throughout the ventilatory cycle. Reductions in pressure within the circuit alerted the anaesthetist to malposition of the pack, whereas a loss of pressure variations suggested airway obstruction or apnoea, and allowed early detection and repositioning of the jaw or mask before significant desaturation occurred. Pressure monitoring is also essential to guard against the potential hazard of inadvertent application of excessive CPAP [25]. One consideration in choosing the most appropriate breathing system for anaesthesia is its effect on the work of breathing. It has been shown that, when airway pressure is kept constant with increasing CPAP, the inspiratory work performed by the subject is decreased [26-29]. The 4-litre reservoir bag, wide bore tubing and high fresh gas flows ensured that marked fluctuations in airway pressure did not occur. The system described in
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10. Taylor MB, Whitwam JG. Pulse oximetry. Anaesthesia 1988; 43: 229-232. 11. Cox D, Niblett DJ. Studies on continuous positive airway pressure breathing systems. British Journal of Anaesthesia 1984; 56: 905-911. 12. Civetta JM, Brons R, Gabel JC. A simple and effective method of employing spontaneous positive pressure ventilation. Journal of Thoracic and Cardiovascular Surgery 1972; 63: 312-317. 13. Al-Kishali T, Padfield A, Perks ER, Thornton JA. Cardio-respiratory effects of nitrous oxide: oxygen: halothane anaesthesia administered to dental outpatients in the upright position. Anaesthesia 1978; 32: 184-188. 14. Tomlin PJ. Death in out-patient anaesthetic practice. Anaesthesia 1974; 29: 551-570. 15. Walsh JF. Training for day-case dental anaesthesia. Oxygen saturation during genera] anaesthesia administered by dental undergraduates. Anaesthesia 1984; 39: 1124-1127. 16. Coplans MP, Curson I. Deaths associated with dentistry. British Dental Journal 1982; 153: 357-362. 17. Ridley SA. A comparison of two pulse oximeters. Anaesthesia 1988; 43: 136-140. 18. Parbrook GD. Arterial oxygen saturation during general anaesthesia for dental extraction in children. Anaesthesia 1988; 43: 67. 19. Allen NA, Rowbotham DJ, Nimmo WS. Hypoxaemia during outpatient dental anaesthesia. Anaesthesia 1989; 44: 509-511. 20. Fairley HB. Airway closure. Anesthesiology 1972; 36: 529-532. REFERENCES 1. Bone ME, Galler D, Flynn PJ. Arterial oxygen saturation 21. Mansell A, Bryan C, Levison H. Airway closure in children. Journal of Applied Physiology 1972; 33: 711. during general anaesthesia for paediatric dental extrac22. Craig DB, McCarthy DS. Closing capacity during CPAP. tions. Anaesthesia 1987; 42: 879-882. Anesthesiology 1976; 44: 88. 2. Beeby C, Thurlow AC. Pulse oximetry during general 23. Gregory G, Kitterman J, Phibbs RH, Tooley WH, anaesthesia for dental extractions. British Dental Journal Hamilton WK. Treatment of the idiopathic respiratory 1986; 160: 123-125. distress syndrome with continuous positive airway press3. Mackay I (cd.) Rhinitis—Mechanisms and Management. ure. New England Journal of Medicine 1971; 284: 1333London: Royal Society of Medicine Services Limited, 1340. 1989. 24. Lindahl SGE, Yates AP, Hatch DJ. Respiratory de4. Wilhoit SC, McTier RF, Findley LJ, Suratt PM. pression at different end-tidal halothane concentrations. Treatment of obstructive sleep apnoea with continuous Anaesthesia 1987; 42: 1267-1275. nasal airflow. Lung 1985; 163: 233-241. 25. Suter PM, Fairley HB, Isenberg MD. Optimum end5. Saunders MH, Moore SE, Eveslage J. CPAP via nasal expiratory airway pressure in patients with acute pulmask: A treatment for occlusion sleep apnoea. Chest 1983; monary failure. New England Journal of Medicine 1975; 9: 83: 144-145. 284-289. 6. Schmidt-Nowara WW. Continuous positive airway press- 26. Butler J, Arnott WM. The work of pulmonary ventilation ure for long-term treatment of sleep apnoea. American at different respiratory levels. Clinical Science 1955; 14: Journal of Disease in Childhood 1984; 138: 82-84. 703-710. 7. Craig DB, McCarthy DS. Airway closure and lung 27. Milic-Emili J, Petit JM, Deroame R. The effects of volumes during breathing with maintained airway positive respiratory rate on the mechanical work of breathing pressures. Anesthesiology 1972; 6: 540-543. during muscular exercise. Internationale Zeitschrift Fuer 8. Abboud N, Rehder K, Roberts JR, Hyatt RE. Lung Anlewandte Physiologie 1960; 18: 330-340. volume and closing capacity with continuous positive 28. Bader ME, Bader RA. The work of breathing. American airway pressure. Anesthesiology 1975; 42: 138-142. Journal of Medicine 1955; 18: 851-854. 9. Gherini S, Peters RM, Virgilio RW. Mechanical work on 29. Kay B, Beatty PCW, Healy TEJ, Accoush MEA, Calpin the lungs and work of breathing with positive endM. Change in the work of breathing imposed by five expiratory pressure and continuous positive airway pressanaesthetic breathing systems. British Journal of Anure. Chest 1979; 76: 251-257. aesthesia 1983; 55: 1239-1246.
this study for the application of CPAP would not, therefore, theoretically affect adversely the work of breathing, but may indeed reduce it. Random allocation of patients in this study was impractical for several reasons, and the possibility of sequential error remains. Unlike a previous investigation [1], the grade of anaesthetist or surgeon was found to have no significant effect on peroperative oxygenation in either this or another study comparing an FI O J of 0.3 with an FiO( of 0.5 [19]. Surprisingly, the percentage incidence of hypoxaemic episodes for senior anaesthetists was twice that of junior trainees and dental students, while trainee and student dental surgeons seemed to contribute equally to these episodes (table VI). Although, on occasions, oxygen saturation decreased to as little as 80%, obvious cyanosis was not reported by the anaesthetists or detected by the observers in any patient. This may have resulted from the close monitoring used for the purposes of this study, and underlines further the value of such practice in routine anaesthesia.
