- Email: [email protected]
Insertion of the cuffed oropharyngeal airway (COPA) with propofol or sevoflurane in adults
Original Contributions Insertion of the Cuffed Oropharyngeal Airway (COPA) with Propofol or Sevoflurane in Adults Takahisa Goto, MD,* Yoshinori Nakata, MD, MBA,* Shoichi Uezono, MD,† Yoshinari Niimi, MD, PhD,* Masanori Uchiyama, MD,‡ Shigeho Morita, MD§ Department of Anesthesia, Teikyo University, School of Medicine, Ichihara Hospital, Chiba, Japan
*Associate Professor of Anesthesia, Teikyo University School of Medicine, Ichihara Hospital, Chiba, Japan †Assistant Professor of Anesthesia, Teikyo University, School of Medicine, Ichihara Hospital, Chiba, Japan ‡Associate Professor of Anesthesiology, Nihon University, School of Medicine, Tokyo, Japan §Professor and Chairman, Department of Anesthesia, Teikyo University, School of Medicine, Ichihara Hospital, Chiba, Japan Address correspondence to Dr. Goto at the Department of Anesthesia, Teikyo University School of Medicine, Ichihara Hospital, 3426-3 Anesaki, Ichihara-shi, Chiba 299-0111 Japan. E-mail: [email protected] Received for publication August 24, 1998; revised manuscript accepted for publication March 15, 1999.
Study Objectives: To compare the respiratory depressant effects of propofol and sevoflurane used to facilitate the placement of the cuffed oropharyngeal airway (COPA), and to evaluate the effectiveness of the COPA in supporting positive pressure ventilation during anesthetic-induced apnea. Design: Randomized, single-blinded study. Setting: University hospital. Patients: 60 ASA physical status I and II adult patients scheduled for elective surgery with general anesthesia. Interventions: Patients were induced either with spontaneous inhalation of 5% sevoflurane or with propofol 2.0 mg/kg intravenously (IV) followed by a continuous infusion of 170 g kg⫺1 min⫺1. If the propofol patient had a tight jaw in 90 seconds, additional propofol (0.5 mg/kg) was administered and the infusion rate was increased to 200 g kg⫺1 min⫺1. The COPA was placed as soon as the jaw was sufficiently relaxed to allow its insertion into the mouth. Measurements and Main Results: The median (range) times to the COPA placement were 90 seconds (30 to 150 sec) and 120 seconds (60 to 210 sec) with propofol and sevoflurane, respectively (p ⫽ 0.07, Mann-Whitney U-test). Unacceptable responses to the placement (3 or more coughs, vigorous or persistent [⬎30 sec] movements) occurred in 23% and 17% of those who received propofol and sevoflurane, respectively, (p ⫽ 0.35, Chi-square test). All these responses were easily suppressed by additional doses of the assigned induction drug. After placement of the COPA, 53% (16/30) of the propofol patients had apnea lasting at least 30 seconds. Notably, the positive airway pressure at which a leak occurred in the mouth (pharyngeal leak pressure) was lower during this propofol-induced apnea than after the return of spontaneous breathing [9 (5 to 20) cmH2O vs. 15 (5 to 20) cmH2O, p ⬍ 0.01, Wilcoxon’s signed-rank test]. In contrast, at no time were the sevoflurane patients apneic, and their pharyngeal leak pressure immediately following the placement was 12 (10 to 20) cmH2O. Conclusions: Propofol and sevoflurane are equally effective in facilitating the placement of the COPA. However, propofol often induces apnea, which is complicated by a less effective seal of the airway by the COPA against positive pressures. Because sevoflurane induction allows spontaneous respiration to continue and provides an adequate pharyn-
Journal of Clinical Anesthesia 11:280 –284, 1999 © 1999 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
0952-8180/99/$–see front matter PII S0952-8180(99)00037-9
COPA placement with propofol or sevoflurane: Goto et al.
geal seal immediately following the placement of the COPA, it may be advantageous when apnea is not desired. © 1999 by Elsevier Science Inc. Keywords: Anesthetics, intravenous: propofol; anesthetics, volatile: sevoflurane; Equipment and supplies: cuffed oropharyngeal airway.
Introduction The cuffed oropharyngeal airway (COPA) is a new airway device intended primarily for use during spontaneous respiration. However, the reliability of this device during positive pressure ventilation (PPV) has been questioned by some investigators.1,2 For example, an air leak occurs at a lower positive airway pressure with the COPA than with the laryngeal mask airway (LMA).1 and the tidal volume delivered with a certain positive airway pressure is smaller than that achieved using a face mask.2 These data imply that, when placing the COPA, it may be preferable to minimize respiratory depression with the drugs used for anesthetic induction because PPV through the COPA may not necessarily be effective. The most commonly used anesthetic for the placement of the COPA has been propofol at the full induction dose (2 to 2.5 mg/kg).1,3 However, this regimen almost always produces apnea lasting several minutes.1,3–5 In contrast, inhalational induction using sevoflurane appears devoid of excessive respiratory depression when used to facilitate the placement of the LMA.6 This technique also has been shown to provide a smooth anesthetic induction at a speed that approaches that of the intravenous (IV) agents and with good acceptance by the patient.6,7 Accordingly, we conducted this randomized, singleblinded study to test the hypothesis that inhalation of sevoflurane, when compared with propofol, would be associated with a lower incidence and/or duration of apnea when both drugs are used to produce equally suitable conditions for placement of the COPA. At the same time, we aimed to evaluate the effectiveness of the COPA in supporting PPV during anesthetic-induced apnea.
Materials and Methods Following Teikyo University School of Medicine Institutional Review Board approval and informed consent, 60 ASA physical status I and II adult patients who were scheduled for elective surgery with general anesthesia were randomly divided via a computer-generated random number table to receive either propofol or sevoflurane for anesthetic induction (n ⫽ 30 [14 males] each). Exclusion criteria included abnormal airway anatomy, instability of the cervical spine, and an increased risk of aspiration of gastric contents. No premedication was given. Before anesthetic induction, all subjects breathed a 6 L/min flow of oxygen via a face mask-Jackson-Rees system for at least 3 minutes. An IV catheter and routine monitor, including a pulse oximeter, were placed.
In the meantime, if the patient was assigned to receive sevoflurane, the anesthesia circuit was primed with a sevoflurane-oxygen mixture. The opening of the breathing circuit distal to the Y-connector was plugged with a rolled paper pad, and a fresh flow of oxygen was supplied at 6 L/min for 3 minutes from a standard anesthesia machine (Sulla 808V, Dra¨ger, Lu¨beck, Germany) with its pop-off valve open and with a sevoflurane vaporizer (Vapor 19.3, Dra¨ger) set at 5%, the maximum setting in Japan. The 3-L reservoir bag was emptied and allowed to refill several times. The concentration of sevoflurane was measured with an infrared analyzer (Capnomac Ultima, Datex, Helsinki, Finland). Its display screen was visible only from behind the anesthesia machine. Then, the Jackson-Rees system was removed from the patient’s face and the patient started to breathe a sevoflurane-oxygen mixture via the primed anesthesia circuit. The fresh gas supply and the vaporizer setting were maintained at 6 L/min and 5%, respectively. Concomitantly, 10% Intralipid IV was infused. The infused volume was identical to that dictated by the infusion protocol for the propofol patients (see following). This action was done to blind the investigator placing the COPA (who would afterwards enter the room) to the induction drug administered. For the patients assigned to receive propofol, after switching from the Jackson-Rees system to the anesthesia circuit, propofol 2 mg/kg IV was administered at a rate of 200 mg/min, followed immediately by a continuous infusion at 170 g kg⫺1 min⫺1. A fresh flow of oxygen at 6 L/min was supplied to the anesthesia circuit. Patients in both groups were instructed to breathe normally. Their ability to open their eyes on verbal command was checked every 15 seconds by the primary anesthetist until unresponsiveness occurred (loss of consciousness [LOC]). At this time, an investigator who was to place the COPA entered the room and evaluated jaw relaxation every 30 seconds until he could open the patient’s mouth sufficiently wide for insertion of the COPA by placing his thumb on the lower incisors or the gum (i.e., adequate jaw relaxation). The airway was manually supported to allow the patient to breathe spontaneously, but no PPV was given unless oxygen saturation (SpO2) decreased to 95% or lower. If the patients receiving sevoflurane were made apneic for more than 30 seconds before adequate jaw relaxation was obtained, manual ventilation was given to deepen the anesthetic level. In the propofol patients, if their jaws remained tight for the first 90 seconds, additional propofol (0.5 mg/kg) was given and the infusion was increased to 200 g kg⫺1 min⫺1. As soon as adequate relaxation of the jaw was noted, the COPA was placed. The same investigator (YN) placed the COPA in all patients. The size of the COPA was chosen based on the manufacturer’s instruction: its length between the cuffed end and the proximal flange should be approximately 1 cm greater than the anterior-posterior distance between the mandibular angle and the lip of each patient.1,3 Once inserted into the mouth, the COPA was fixed with a rubber strap, the cuff was inflated with the recommended volume of air (30, 35, and 40 ml for the 9-, J. Clin. Anesth., vol. 11, June 1999
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10-, and 11-cm COPAs, respectively), and the breathing circuit was connected. The patient’s head was then moderately extended and rotated to one side to obtain better airway patency. Any occurrence of vigorous movements or airway responses from mouth opening to head positioning was noted. “Unacceptable” responses were defined as vigorous movements requiring restraint or lasting over 30 seconds, 3 or more coughs, laryngospasm, stridors, and breath holding. If these responses occurred, the propofol patients received an additional 0.5 mg/kg dose of propofol and the sevoflurane patients received 5% sevoflurane through the COPA by spontaneous respiration. If these initial treatments failed to suppress the responses within 30 seconds, an additional 0.5 mg/kg dose of propofol was given to both groups of patients. When all of the responses were suppressed or in those patients who demonstrated no responses to the COPA placement, the sevoflurane concentration was decreased to 2%. The infusion of propofol was maintained at either 170 g kg⫺1 min⫺1 or 200 g kg⫺1 min⫺1, whichever dose was used at the time of the COPA placement. Thirty seconds after the completion of the COPA placement (i.e., the end of head positioning in those patients who had no response to the placement of the COPA, or disappearance of all the responses to placement), the leak test was performed by closing the expiratory valve of the circuit at a fixed gas flow of 6 L/min and noting the positive airway pressure (measured in the anesthesia circuit) at which audible leak around the cuff of the COPA occurred into the mouth. This threshold pressure was recorded as the pharyngeal leak pressure. If the patient was apneic at this time, the test was repeated 30 seconds after regular spontaneous respiration was resumed. The airway pressure applied was limited to 20 cmH2O to avoid gastric distention. The time from completion of the COPA placement until resumption of spontaneous respiration was recorded. After all the recordings were completed, anesthesia was conducted at the discretion of the primary anesthetist. Data were expressed as medians (ranges). Both incidences of patients who were smokers and also unacceptable responses to the COPA placement were compared using Chi-square tests. Wilcoxon’s signed-rank tests were used to compare the pharyngeal leak pressures during apnea versus after the return of spontaneous breathing. Other data were analyzed using Mann-Whitney U-tests. A p-value less than 0.05 was considered statistically significant.
Results The two anesthetic treatment groups showed similar demographics (Table 1). The selection of the COPA size was comparable between the two groups; 9-cm and 10-cm COPAs were generally used for females and males, respectively (Table 1). The initial concentration of sevoflurane in the primed anesthesia circuit was 5.1% (4.9 to 5.3). Loss of consciousness occurred slightly earlier with propofol than with sevoflurane [42.5 (15 to 60) sec vs. 60 (45 to 120) sec, 282
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Table 1. Demographic Data and Selection of Cuffed Oropharyngeal Airway (COPA) Size
Age (yrs) Height (cm) Weight (kg) Smokers COPA size used 9 cm 10 cm 11 cm
Propofol (n ⴝ 30)
Sevoflurane (n ⴝ 30)
42 (22 to 65) 160 (150 to 174) 57 (41 to 82) 12 (40%)
48 (21 to 76) 158 (142 to 177) 59 (39 to 81) 13 (43%)
F;10 M;12, F;6 M;2
F;4 M;12, F;2 M;2
Note: data are reported as medians (range) of numbers of subjects (percentage). F ⫽ female; M ⫽ male.
respectively; p ⬍ 0.01]. The time to the placement of the COPA was retrospectively defined as the time from the start of administration of the anesthetic drug to the first sign of adequate jaw relaxation because, as will be described the condition of the COPA placement at this endpoint was found to be acceptable in approximately 80% of the patients in both anesthetic groups and because the remaining patients could also be easily managed with a modest additional dose of anesthetic. The times to COPA placement were 90 seconds (30 to 150 sec) and 120 seconds (60 to 210 sec) for propofol and sevoflurane, respectively (p ⫽ 0.07). The propofol dose administered until the COPA placement was 2.2 (2.0 to 3.2) mg/kg. The incidence of unacceptable responses to placement of the COPA was approximately 20% and was not different between propofol and sevoflurane groups (Table 2, Chisquare ⫽ 2.09, df ⫽ 2, p ⫽ 0.35). Even when these responses occurred, they were readily suppressed by the initial treatment described previously. In no instance did the COPA need to be removed. Laryngospasm, breath
Table 2. Responses to the Placement of the Cuffed Oropharyngeal Airway
Total acceptable None Movement; mild and lasting ⱕ 30 sec Airway: swallowing Pushing out COPA with tongue 1 or 2 coughs Total unacceptable Movement; vigorous or lasting ⬎ 30 sec Airway: 3 or more coughs
Propofol (n ⴝ 30)
Sevolflurane (n ⴝ 30)
23 (77%) 17 1
25 (83%) 14 3
2 1 2 7 (23%) 3
2 3 3 5 (17%) 0
4
5
Note: The incidence of unacceptable responses to the cuffed oropharyngeal airway (COPA) placement (defined in this table) was not different between the two anesthetic groups (Chi-square test).
COPA placement with propofol or sevoflurane: Goto et al.
Figure 1. Pharyngeal leak pressures during apnea and after return of spontaneous breathing in 16 patients who received propofol and remained apneic for at least 30 seconds following placement of the cuffed oropharyngeal airway. The rectangles and whiskers represent 25th to 75th percentiles (with the central bars representing medians) and 10th and 90th percentiles, respectively, whereas each line depicts the change in each patient. Note that the pharyngeal leak pressure was less than 10 cmH2O in 50% (8/16) of patients during apnea, but in six patients the leak pressures improved to 10 cmH2O or greater after spontaneous breathing was resumed.
holding, stridor, vomiting, or dental injuries were not observed. All the patients who received sevoflurane maintained spontaneous respiration throughout the study period. In contrast, all but three propofol patients were apneic at the time of the COPA placement, and in 16 of them apnea persisted for at least 30 seconds [duration 150 (30 to 330) sec] after the placement was completed. Notably, these 16 patients demonstrated a significantly reduced pharyngeal leak pressure during apnea compared to that recorded after a return of spontaneous respiration [9 (5 to 20) vs. 15 (5 to 20) cmH2O, p ⬍ 0.01, Figure 1]. No patient suffered an SpO2 of 95% or less during apnea. During spontaneous breathing, the pharyngeal leak pressure was similar for the propofol and sevoflurane groups [15 cmH2O (5 to 20) and 12 cmH2O (10 to 20), respectively], and the median pressure was 14.5 cmH2O when the two groups were combined.
Discussion The results of this study confirmed our hypothesis that spontaneous inhalation of 5% sevoflurane for 120 seconds produced distinctly less respiratory depression than did
propofol 2.2 mg/kg IV, while both were equally effective in suppressing somatic and airway responses to placement of the COPA. All patients who received sevoflurane maintained spontaneous ventilation whereas propofol produced apnea lasting at least 30 seconds after placement of the COPA in 53% (16/30) of the patients. In addition, during this propofol-induced apnea, an air leak around the cuff of the COPA occurred at a lower positive airway pressure than after the spontaneous respiration was resumed. To our knowledge, this is the first study to directly compare propofol and sevoflurane with respect to their respiratory depressant effects. The high incidence of apnea caused by propofol that we observed is in accordance with other reports.1,3–5 Sevoflurane has not been as thoroughly investigated as propofol in this regard, but our result is consistent with that of Muzi et al.,6 who demonstrated that hyperventilation with 6% to 7% sevoflurane plus 66% nitrous oxide before placing the LMA permits an immediate return of spontaneous ventilation after LMA placement. For a meaningful comparison of two anesthetics, it is important to administer equipotent doses. Because our goal was to compare propofol and sevoflurane with regard to the degree of respiratory depression associated with the placement of the COPA, we wanted to administer both drugs in doses just sufficient to allow smooth placement of the COPA. For this purpose, we titrated these to a common surrogate endpoint, i.e., jaw relaxation, before attempting the COPA placement. The reasons for this action were threefold. First, the anesthetic requirement for placement of the COPA has not been thoroughly investigated, especially in the case of sevoflurane. Second, we predicted that jaw relaxation would be a critical step for the smooth placement of the COPA, because our previous experience with the COPA,7 and those of others with the LMA,5,6 have revealed that poor jaw relaxation due to inadequate anesthesia is the most frequent cause of unsuccessful placement. Finally, estimating the depth of anesthesia based on the degree of jaw relaxation is a common clinical practice when placing airway devices such as LMA and COPA. Both sevoflurane and propofol at the doses we used permitted smooth placement of the COPA in approximately 80% of patients. Therefore, we believe the doses of these anesthetics used in this study are equally and sufficiently close to their respective true requirements for COPA placement. The finding of the reduced pharyngeal leak pressure during propofol-induced apnea was unexpected. If we assume a pharyngeal leak pressure less than 10 cmH2O to be clinically unacceptable, 50% (8/16) of those who were apneic for at least 30 seconds after COPA placement, or 27% (8/30) of all the patients who received propofol, had unacceptable pharyngeal leak pressures while they were apneic. Fortunately, 75% (6/8) of these patients restored their pharyngeal leak pressures to the acceptable range (i.e., 10 cmH2O or higher) with a return of spontaneous respiration (Figure 1). Therefore, it is unlikely that this finding represents a significant risk under normal circumJ. Clin. Anesth., vol. 11, June 1999
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stances, provided the patient has been sufficiently preoxygenated to tolerate several minutes of apnea. Rather, the implication is that an inadequate pharyngeal leak pressure during propofol-induced apnea does not necessarily indicate failed placement or inappropriate size selection. However, this reduction of pharyngeal leak pressure during propofol-induced apnea may warrant consideration if one desires to continuously keep airway and ventilation under one’s control. In such cases, inhalational induction using sevoflurane may be advantageous because it allows placement of the COPA without producing apnea and provides an effective seal of the pharynx against positive airway pressures once the COPA is placed. One example of such a situation is the management of possible difficult airways, because maintaining spontaneous respiration is generally a reasonable strategy. In fact, recent case reports suggest that the COPA may be a useful aid in the management of difficult airways.8 –10 It facilitates fiberoptic intubation by supporting the airway and by allowing spontaneous respiration and inhalational anesthesia to continue.8,9 The mechanism for the reduction of pharyngeal leak pressure during propofol-induced apnea is unclear. We speculate that an overshoot in anesthetic depth from a bolus injection of propofol might have caused excessive relaxation of the pharyngeal structures while producing apnea. Because the COPA is designed to seal the airway within the relatively compliant pharyngeal space, it is conceivable that loss of tissue tone surrounding the cuff significantly compromises the effectiveness of the seal. In contrast, gradual deepening of an anesthetic level achieved by inhalation of sevoflurane probably served to maintain the tone of the pharyngeal tissues, resulting in the more effective pharyngeal seal against positive airway pressures immediately following the placement of the COPA. It remains to be determined whether a slower administration of propofol would similarly prevent apnea and improve the seal of the airway while producing satisfactory conditions for the placement of the COPA. In conclusion, both propofol and sevoflurane are fast
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and effective in facilitating the placement of the COPA. However, propofol-induced apnea persists in more than half of the patients after placement is completed, which is accompanied by a reduced pharyngeal leak pressure. Sevoflurane induction may be advantageous because, as assessed by the leak pressure test, it allows the COPA to seal the pharynx effectively should PPV be required.
References 1. Brimacombe JR, Brimacombe JC, Berry AM, et al: A comparison of the laryngeal mask airway and cuffed oropharyngeal airway in anesthetized adult patients. Anesth Analg 1998;87:147–52. 2. Koga K, Kaku M, Sata T, Shigematsu A: Effective use of the cuffed oropharyngeal airway. Anaesthesia 1998;53:715– 6. 3. Greenberg RS, Brimacombe J, Berry A, Gouze V, Piantadosi S, Dake EM: A randomized controlled trial comparing the cuffed oropharyngeal airway and the laryngeal mask airway in spontaneously breathing anesthetized adults. Anesthesiology 1998;88: 970 –7. 4. McKeating K, Bali IM, Dundee JW: The effects of thiopentone and propofol on upper airway integrity. Anaesthesia 1988;43:638 – 40. 5. Blake DW, Dawson P, Donnan G, Bjorksten A: Propofol induction for laryngeal mask airway insertion: dose requirement and cardiorespiratory effects. Anaesth Intensive Care 1992;20:479 – 83. 6. Muzi M, Robinson BJ, Ebert TJ, O’Brien TJ: Induction of anesthesia and tracheal intubation with sevoflurane in adults. Anesthesiology 1996;85:536 – 43. 7. Nakata Y, Goto T, Saito H, Ichinose F, Uezono S, Morita S: The placement of the cuffed oropharyngeal airway with sevoflurane in adults: a comparison with laryngeal mask airway. Anesth Analg 1998;87:143– 6. 8. Uezono S, Goto T, Nakata Y, Ichinose f, Niimi Y, Morita S: The cuffed oropharyngeal airway: a novel adjunct to the management of difficult airways. Anesthesiology 1998;88:1677–9. 9. Pigott DW, Kay NH, Greenberg RS: The cuffed oropharyngeal airway as an aid to fibreoptic intubation. Anaesthesia 1998;53: 480 –3. 10. Asai T, Koga K, Stacey MR: Use of the cuffed oropharyngeal airway after difficult ventilation through a facemask [Letter]. Anaesthesia 1997;52:1236 –7.
*Associate Professor of Anesthesia, Teikyo University School of Medicine, Ichihara Hospital, Chiba, Japan †Assistant Professor of Anesthesia, Teikyo University, School of Medicine, Ichihara Hospital, Chiba, Japan ‡Associate Professor of Anesthesiology, Nihon University, School of Medicine, Tokyo, Japan §Professor and Chairman, Department of Anesthesia, Teikyo University, School of Medicine, Ichihara Hospital, Chiba, Japan Address correspondence to Dr. Goto at the Department of Anesthesia, Teikyo University School of Medicine, Ichihara Hospital, 3426-3 Anesaki, Ichihara-shi, Chiba 299-0111 Japan. E-mail: [email protected] Received for publication August 24, 1998; revised manuscript accepted for publication March 15, 1999.
Study Objectives: To compare the respiratory depressant effects of propofol and sevoflurane used to facilitate the placement of the cuffed oropharyngeal airway (COPA), and to evaluate the effectiveness of the COPA in supporting positive pressure ventilation during anesthetic-induced apnea. Design: Randomized, single-blinded study. Setting: University hospital. Patients: 60 ASA physical status I and II adult patients scheduled for elective surgery with general anesthesia. Interventions: Patients were induced either with spontaneous inhalation of 5% sevoflurane or with propofol 2.0 mg/kg intravenously (IV) followed by a continuous infusion of 170 g kg⫺1 min⫺1. If the propofol patient had a tight jaw in 90 seconds, additional propofol (0.5 mg/kg) was administered and the infusion rate was increased to 200 g kg⫺1 min⫺1. The COPA was placed as soon as the jaw was sufficiently relaxed to allow its insertion into the mouth. Measurements and Main Results: The median (range) times to the COPA placement were 90 seconds (30 to 150 sec) and 120 seconds (60 to 210 sec) with propofol and sevoflurane, respectively (p ⫽ 0.07, Mann-Whitney U-test). Unacceptable responses to the placement (3 or more coughs, vigorous or persistent [⬎30 sec] movements) occurred in 23% and 17% of those who received propofol and sevoflurane, respectively, (p ⫽ 0.35, Chi-square test). All these responses were easily suppressed by additional doses of the assigned induction drug. After placement of the COPA, 53% (16/30) of the propofol patients had apnea lasting at least 30 seconds. Notably, the positive airway pressure at which a leak occurred in the mouth (pharyngeal leak pressure) was lower during this propofol-induced apnea than after the return of spontaneous breathing [9 (5 to 20) cmH2O vs. 15 (5 to 20) cmH2O, p ⬍ 0.01, Wilcoxon’s signed-rank test]. In contrast, at no time were the sevoflurane patients apneic, and their pharyngeal leak pressure immediately following the placement was 12 (10 to 20) cmH2O. Conclusions: Propofol and sevoflurane are equally effective in facilitating the placement of the COPA. However, propofol often induces apnea, which is complicated by a less effective seal of the airway by the COPA against positive pressures. Because sevoflurane induction allows spontaneous respiration to continue and provides an adequate pharyn-
Journal of Clinical Anesthesia 11:280 –284, 1999 © 1999 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
0952-8180/99/$–see front matter PII S0952-8180(99)00037-9
COPA placement with propofol or sevoflurane: Goto et al.
geal seal immediately following the placement of the COPA, it may be advantageous when apnea is not desired. © 1999 by Elsevier Science Inc. Keywords: Anesthetics, intravenous: propofol; anesthetics, volatile: sevoflurane; Equipment and supplies: cuffed oropharyngeal airway.
Introduction The cuffed oropharyngeal airway (COPA) is a new airway device intended primarily for use during spontaneous respiration. However, the reliability of this device during positive pressure ventilation (PPV) has been questioned by some investigators.1,2 For example, an air leak occurs at a lower positive airway pressure with the COPA than with the laryngeal mask airway (LMA).1 and the tidal volume delivered with a certain positive airway pressure is smaller than that achieved using a face mask.2 These data imply that, when placing the COPA, it may be preferable to minimize respiratory depression with the drugs used for anesthetic induction because PPV through the COPA may not necessarily be effective. The most commonly used anesthetic for the placement of the COPA has been propofol at the full induction dose (2 to 2.5 mg/kg).1,3 However, this regimen almost always produces apnea lasting several minutes.1,3–5 In contrast, inhalational induction using sevoflurane appears devoid of excessive respiratory depression when used to facilitate the placement of the LMA.6 This technique also has been shown to provide a smooth anesthetic induction at a speed that approaches that of the intravenous (IV) agents and with good acceptance by the patient.6,7 Accordingly, we conducted this randomized, singleblinded study to test the hypothesis that inhalation of sevoflurane, when compared with propofol, would be associated with a lower incidence and/or duration of apnea when both drugs are used to produce equally suitable conditions for placement of the COPA. At the same time, we aimed to evaluate the effectiveness of the COPA in supporting PPV during anesthetic-induced apnea.
Materials and Methods Following Teikyo University School of Medicine Institutional Review Board approval and informed consent, 60 ASA physical status I and II adult patients who were scheduled for elective surgery with general anesthesia were randomly divided via a computer-generated random number table to receive either propofol or sevoflurane for anesthetic induction (n ⫽ 30 [14 males] each). Exclusion criteria included abnormal airway anatomy, instability of the cervical spine, and an increased risk of aspiration of gastric contents. No premedication was given. Before anesthetic induction, all subjects breathed a 6 L/min flow of oxygen via a face mask-Jackson-Rees system for at least 3 minutes. An IV catheter and routine monitor, including a pulse oximeter, were placed.
In the meantime, if the patient was assigned to receive sevoflurane, the anesthesia circuit was primed with a sevoflurane-oxygen mixture. The opening of the breathing circuit distal to the Y-connector was plugged with a rolled paper pad, and a fresh flow of oxygen was supplied at 6 L/min for 3 minutes from a standard anesthesia machine (Sulla 808V, Dra¨ger, Lu¨beck, Germany) with its pop-off valve open and with a sevoflurane vaporizer (Vapor 19.3, Dra¨ger) set at 5%, the maximum setting in Japan. The 3-L reservoir bag was emptied and allowed to refill several times. The concentration of sevoflurane was measured with an infrared analyzer (Capnomac Ultima, Datex, Helsinki, Finland). Its display screen was visible only from behind the anesthesia machine. Then, the Jackson-Rees system was removed from the patient’s face and the patient started to breathe a sevoflurane-oxygen mixture via the primed anesthesia circuit. The fresh gas supply and the vaporizer setting were maintained at 6 L/min and 5%, respectively. Concomitantly, 10% Intralipid IV was infused. The infused volume was identical to that dictated by the infusion protocol for the propofol patients (see following). This action was done to blind the investigator placing the COPA (who would afterwards enter the room) to the induction drug administered. For the patients assigned to receive propofol, after switching from the Jackson-Rees system to the anesthesia circuit, propofol 2 mg/kg IV was administered at a rate of 200 mg/min, followed immediately by a continuous infusion at 170 g kg⫺1 min⫺1. A fresh flow of oxygen at 6 L/min was supplied to the anesthesia circuit. Patients in both groups were instructed to breathe normally. Their ability to open their eyes on verbal command was checked every 15 seconds by the primary anesthetist until unresponsiveness occurred (loss of consciousness [LOC]). At this time, an investigator who was to place the COPA entered the room and evaluated jaw relaxation every 30 seconds until he could open the patient’s mouth sufficiently wide for insertion of the COPA by placing his thumb on the lower incisors or the gum (i.e., adequate jaw relaxation). The airway was manually supported to allow the patient to breathe spontaneously, but no PPV was given unless oxygen saturation (SpO2) decreased to 95% or lower. If the patients receiving sevoflurane were made apneic for more than 30 seconds before adequate jaw relaxation was obtained, manual ventilation was given to deepen the anesthetic level. In the propofol patients, if their jaws remained tight for the first 90 seconds, additional propofol (0.5 mg/kg) was given and the infusion was increased to 200 g kg⫺1 min⫺1. As soon as adequate relaxation of the jaw was noted, the COPA was placed. The same investigator (YN) placed the COPA in all patients. The size of the COPA was chosen based on the manufacturer’s instruction: its length between the cuffed end and the proximal flange should be approximately 1 cm greater than the anterior-posterior distance between the mandibular angle and the lip of each patient.1,3 Once inserted into the mouth, the COPA was fixed with a rubber strap, the cuff was inflated with the recommended volume of air (30, 35, and 40 ml for the 9-, J. Clin. Anesth., vol. 11, June 1999
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10-, and 11-cm COPAs, respectively), and the breathing circuit was connected. The patient’s head was then moderately extended and rotated to one side to obtain better airway patency. Any occurrence of vigorous movements or airway responses from mouth opening to head positioning was noted. “Unacceptable” responses were defined as vigorous movements requiring restraint or lasting over 30 seconds, 3 or more coughs, laryngospasm, stridors, and breath holding. If these responses occurred, the propofol patients received an additional 0.5 mg/kg dose of propofol and the sevoflurane patients received 5% sevoflurane through the COPA by spontaneous respiration. If these initial treatments failed to suppress the responses within 30 seconds, an additional 0.5 mg/kg dose of propofol was given to both groups of patients. When all of the responses were suppressed or in those patients who demonstrated no responses to the COPA placement, the sevoflurane concentration was decreased to 2%. The infusion of propofol was maintained at either 170 g kg⫺1 min⫺1 or 200 g kg⫺1 min⫺1, whichever dose was used at the time of the COPA placement. Thirty seconds after the completion of the COPA placement (i.e., the end of head positioning in those patients who had no response to the placement of the COPA, or disappearance of all the responses to placement), the leak test was performed by closing the expiratory valve of the circuit at a fixed gas flow of 6 L/min and noting the positive airway pressure (measured in the anesthesia circuit) at which audible leak around the cuff of the COPA occurred into the mouth. This threshold pressure was recorded as the pharyngeal leak pressure. If the patient was apneic at this time, the test was repeated 30 seconds after regular spontaneous respiration was resumed. The airway pressure applied was limited to 20 cmH2O to avoid gastric distention. The time from completion of the COPA placement until resumption of spontaneous respiration was recorded. After all the recordings were completed, anesthesia was conducted at the discretion of the primary anesthetist. Data were expressed as medians (ranges). Both incidences of patients who were smokers and also unacceptable responses to the COPA placement were compared using Chi-square tests. Wilcoxon’s signed-rank tests were used to compare the pharyngeal leak pressures during apnea versus after the return of spontaneous breathing. Other data were analyzed using Mann-Whitney U-tests. A p-value less than 0.05 was considered statistically significant.
Results The two anesthetic treatment groups showed similar demographics (Table 1). The selection of the COPA size was comparable between the two groups; 9-cm and 10-cm COPAs were generally used for females and males, respectively (Table 1). The initial concentration of sevoflurane in the primed anesthesia circuit was 5.1% (4.9 to 5.3). Loss of consciousness occurred slightly earlier with propofol than with sevoflurane [42.5 (15 to 60) sec vs. 60 (45 to 120) sec, 282
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Table 1. Demographic Data and Selection of Cuffed Oropharyngeal Airway (COPA) Size
Age (yrs) Height (cm) Weight (kg) Smokers COPA size used 9 cm 10 cm 11 cm
Propofol (n ⴝ 30)
Sevoflurane (n ⴝ 30)
42 (22 to 65) 160 (150 to 174) 57 (41 to 82) 12 (40%)
48 (21 to 76) 158 (142 to 177) 59 (39 to 81) 13 (43%)
F;10 M;12, F;6 M;2
F;4 M;12, F;2 M;2
Note: data are reported as medians (range) of numbers of subjects (percentage). F ⫽ female; M ⫽ male.
respectively; p ⬍ 0.01]. The time to the placement of the COPA was retrospectively defined as the time from the start of administration of the anesthetic drug to the first sign of adequate jaw relaxation because, as will be described the condition of the COPA placement at this endpoint was found to be acceptable in approximately 80% of the patients in both anesthetic groups and because the remaining patients could also be easily managed with a modest additional dose of anesthetic. The times to COPA placement were 90 seconds (30 to 150 sec) and 120 seconds (60 to 210 sec) for propofol and sevoflurane, respectively (p ⫽ 0.07). The propofol dose administered until the COPA placement was 2.2 (2.0 to 3.2) mg/kg. The incidence of unacceptable responses to placement of the COPA was approximately 20% and was not different between propofol and sevoflurane groups (Table 2, Chisquare ⫽ 2.09, df ⫽ 2, p ⫽ 0.35). Even when these responses occurred, they were readily suppressed by the initial treatment described previously. In no instance did the COPA need to be removed. Laryngospasm, breath
Table 2. Responses to the Placement of the Cuffed Oropharyngeal Airway
Total acceptable None Movement; mild and lasting ⱕ 30 sec Airway: swallowing Pushing out COPA with tongue 1 or 2 coughs Total unacceptable Movement; vigorous or lasting ⬎ 30 sec Airway: 3 or more coughs
Propofol (n ⴝ 30)
Sevolflurane (n ⴝ 30)
23 (77%) 17 1
25 (83%) 14 3
2 1 2 7 (23%) 3
2 3 3 5 (17%) 0
4
5
Note: The incidence of unacceptable responses to the cuffed oropharyngeal airway (COPA) placement (defined in this table) was not different between the two anesthetic groups (Chi-square test).
COPA placement with propofol or sevoflurane: Goto et al.
Figure 1. Pharyngeal leak pressures during apnea and after return of spontaneous breathing in 16 patients who received propofol and remained apneic for at least 30 seconds following placement of the cuffed oropharyngeal airway. The rectangles and whiskers represent 25th to 75th percentiles (with the central bars representing medians) and 10th and 90th percentiles, respectively, whereas each line depicts the change in each patient. Note that the pharyngeal leak pressure was less than 10 cmH2O in 50% (8/16) of patients during apnea, but in six patients the leak pressures improved to 10 cmH2O or greater after spontaneous breathing was resumed.
holding, stridor, vomiting, or dental injuries were not observed. All the patients who received sevoflurane maintained spontaneous respiration throughout the study period. In contrast, all but three propofol patients were apneic at the time of the COPA placement, and in 16 of them apnea persisted for at least 30 seconds [duration 150 (30 to 330) sec] after the placement was completed. Notably, these 16 patients demonstrated a significantly reduced pharyngeal leak pressure during apnea compared to that recorded after a return of spontaneous respiration [9 (5 to 20) vs. 15 (5 to 20) cmH2O, p ⬍ 0.01, Figure 1]. No patient suffered an SpO2 of 95% or less during apnea. During spontaneous breathing, the pharyngeal leak pressure was similar for the propofol and sevoflurane groups [15 cmH2O (5 to 20) and 12 cmH2O (10 to 20), respectively], and the median pressure was 14.5 cmH2O when the two groups were combined.
Discussion The results of this study confirmed our hypothesis that spontaneous inhalation of 5% sevoflurane for 120 seconds produced distinctly less respiratory depression than did
propofol 2.2 mg/kg IV, while both were equally effective in suppressing somatic and airway responses to placement of the COPA. All patients who received sevoflurane maintained spontaneous ventilation whereas propofol produced apnea lasting at least 30 seconds after placement of the COPA in 53% (16/30) of the patients. In addition, during this propofol-induced apnea, an air leak around the cuff of the COPA occurred at a lower positive airway pressure than after the spontaneous respiration was resumed. To our knowledge, this is the first study to directly compare propofol and sevoflurane with respect to their respiratory depressant effects. The high incidence of apnea caused by propofol that we observed is in accordance with other reports.1,3–5 Sevoflurane has not been as thoroughly investigated as propofol in this regard, but our result is consistent with that of Muzi et al.,6 who demonstrated that hyperventilation with 6% to 7% sevoflurane plus 66% nitrous oxide before placing the LMA permits an immediate return of spontaneous ventilation after LMA placement. For a meaningful comparison of two anesthetics, it is important to administer equipotent doses. Because our goal was to compare propofol and sevoflurane with regard to the degree of respiratory depression associated with the placement of the COPA, we wanted to administer both drugs in doses just sufficient to allow smooth placement of the COPA. For this purpose, we titrated these to a common surrogate endpoint, i.e., jaw relaxation, before attempting the COPA placement. The reasons for this action were threefold. First, the anesthetic requirement for placement of the COPA has not been thoroughly investigated, especially in the case of sevoflurane. Second, we predicted that jaw relaxation would be a critical step for the smooth placement of the COPA, because our previous experience with the COPA,7 and those of others with the LMA,5,6 have revealed that poor jaw relaxation due to inadequate anesthesia is the most frequent cause of unsuccessful placement. Finally, estimating the depth of anesthesia based on the degree of jaw relaxation is a common clinical practice when placing airway devices such as LMA and COPA. Both sevoflurane and propofol at the doses we used permitted smooth placement of the COPA in approximately 80% of patients. Therefore, we believe the doses of these anesthetics used in this study are equally and sufficiently close to their respective true requirements for COPA placement. The finding of the reduced pharyngeal leak pressure during propofol-induced apnea was unexpected. If we assume a pharyngeal leak pressure less than 10 cmH2O to be clinically unacceptable, 50% (8/16) of those who were apneic for at least 30 seconds after COPA placement, or 27% (8/30) of all the patients who received propofol, had unacceptable pharyngeal leak pressures while they were apneic. Fortunately, 75% (6/8) of these patients restored their pharyngeal leak pressures to the acceptable range (i.e., 10 cmH2O or higher) with a return of spontaneous respiration (Figure 1). Therefore, it is unlikely that this finding represents a significant risk under normal circumJ. Clin. Anesth., vol. 11, June 1999
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stances, provided the patient has been sufficiently preoxygenated to tolerate several minutes of apnea. Rather, the implication is that an inadequate pharyngeal leak pressure during propofol-induced apnea does not necessarily indicate failed placement or inappropriate size selection. However, this reduction of pharyngeal leak pressure during propofol-induced apnea may warrant consideration if one desires to continuously keep airway and ventilation under one’s control. In such cases, inhalational induction using sevoflurane may be advantageous because it allows placement of the COPA without producing apnea and provides an effective seal of the pharynx against positive airway pressures once the COPA is placed. One example of such a situation is the management of possible difficult airways, because maintaining spontaneous respiration is generally a reasonable strategy. In fact, recent case reports suggest that the COPA may be a useful aid in the management of difficult airways.8 –10 It facilitates fiberoptic intubation by supporting the airway and by allowing spontaneous respiration and inhalational anesthesia to continue.8,9 The mechanism for the reduction of pharyngeal leak pressure during propofol-induced apnea is unclear. We speculate that an overshoot in anesthetic depth from a bolus injection of propofol might have caused excessive relaxation of the pharyngeal structures while producing apnea. Because the COPA is designed to seal the airway within the relatively compliant pharyngeal space, it is conceivable that loss of tissue tone surrounding the cuff significantly compromises the effectiveness of the seal. In contrast, gradual deepening of an anesthetic level achieved by inhalation of sevoflurane probably served to maintain the tone of the pharyngeal tissues, resulting in the more effective pharyngeal seal against positive airway pressures immediately following the placement of the COPA. It remains to be determined whether a slower administration of propofol would similarly prevent apnea and improve the seal of the airway while producing satisfactory conditions for the placement of the COPA. In conclusion, both propofol and sevoflurane are fast
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and effective in facilitating the placement of the COPA. However, propofol-induced apnea persists in more than half of the patients after placement is completed, which is accompanied by a reduced pharyngeal leak pressure. Sevoflurane induction may be advantageous because, as assessed by the leak pressure test, it allows the COPA to seal the pharynx effectively should PPV be required.
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