The stress responses from tracheal intubation are potentially dangerous in patients with higher cardiovascular risk, such as obese patients. The primary outcome objective of this study was to test whether, in comparison with the endotracheal tube (ETT), the Proseal™ Laryngeal Mask Airway (PLMA™) (Laryngeal Mask Airway Company, Jersey, United Kingdom) reduces blood pressure and norepinephrine responses and the amounts of muscle relaxants needed in obese patients.
We assessed hemodynamic and hormonal stress responses, ventilation, and postoperative recovery in 75 morbidly obese patients randomized to receive standardized anesthesia with either an ETT or the PLMA™ for laparoscopic gastric banding.
In repeated-measures ANOVA, mean arterial blood pressure and plasma norepinephrine were significantly higher in the ETT group than in the PLMA™ group. In individual pairwise comparisons, blood pressure rose higher in ETT than PLMA™ patients after insertion and removal of airway devices, and after recovery. In ETT compared with PLMA™ patients, plasma norepinephrine was higher after induction of carboperitoneum (mean ± SD, 534 ± 198 and 368 ± 147 and pg/ml, P = 0.001), after airway device removal (578 ± 285 and 329 ± 128 pg/ml, P < 0.0001), and after recovery in postanesthesia care unit (380 ± 167 and 262 ± 95 and pg/ml, P = 0.003). Compared with use of the ETT, the PLMA™ reduced cisatracurium requirement, oxygen desaturation, and time to discharge from both the postanesthesia care unit and the hospital.
PLMA™ reduces stress responses and postoperative complaints after laparoscopic gastric banding.
What We Already Know about This Topic
Insertion of a supraglottic airway induces less circulatory responses than tracheal intubation in nonobese patients
No study has assessed advantages of the supraglottic airway for reducing perioperative stress responses in morbidly obese patients in whom use of the device is controversial
What This Article Tells Us That Is New
In morbidly obese patients, use of the Proseal Laryngeal Mask Airway resulted in less hemodynamic and catecholamine responses during and after laparoscopic gastric banding surgery, and better postoperative course compared with tracheal intubation
OBESITY is becoming increasingly prevalent in developed countries and anesthesiologists will face larger numbers of obese patients undergoing bariatric surgery.1Obese body composition alters volumes of distribution and dosage requirements of lipid soluble drugs; regional-specific fat deposition may alter respiratory mechanisms and predispose to difficult airway.2Further, obesity is associated with important comorbidities (i.e. , diabetes mellitus, arterial and pulmonary hypertension, obstructive sleep apnea syndrome), which increase risk of perioperative complications.2,–,4In obese patients, the levels of catecholamines and cortisol are often increased and contribute to metabolic and vascular abnormalities.4Invasive tracheal intubation augments stress hormones with potential detrimental effects on coronary and cerebral circulations in patients at risk.1,3,4Supraglottic devices, such as the Laryngeal Mask AirwayTM(LMATM) (Laryngeal Mask Airway Company, Jersey, United Kingdom), attenuate stress responses and respiratory morbidity and are therefore of interest for the obese patient population.5,–,7
The classic type of LMA (cLMATM) has a proven record of efficacy and safety in lean subjects, but has been seldom used in obese patients.5This is because cLMATMis limited by providing an incomplete protection of upper airways against risk of aspiration and a limited range of positive pressure ventilation.5cLMATMhas been included in the algorithm for difficult intubation by several national societies. In obese patients, cLMATMand other types of LMATMhave been used as a temporary ventilatory device before laryngoscope-guided tracheal intubation, and as an emergency device for unpredicted or predicted difficult intubations.6,–,14The Proseal™ Laryngeal Mask Airway (PLMA™, Laryngeal Mask Airway Company) is a newer type of LMATMfeaturing a gastric drainage tube and higher sealing pressures, which provide an increased protection against aspiration.6,7,15PLMA™ has proven effective in elective urological, gynaecological, and abdominal surgery in obese patients.7,15,–,19Despite its potential advantage, the use of supraglottic devices in obese patients remains controversial and further studies can help to document their efficacy and safety profiles in this patient population.5,18,19Recently, for example, cLMA™ has been shown to improve early postoperative lung function and pulse oximetry saturation without complications in obese patients after minor surgery.19,20Given the potential benefits of PLMA™ over the endotracheal tube (ETT), we designed a double-blind, randomized study to examine whether insertion and ventilation with the PLMA™ compared with an ETT resulted in lesser elevation of arterial blood pressure and norepinephrine levels and lower consumption of muscle relaxant drugs in obese patients undergoing laparoscopic gastric banding (LGB).
Materials and Methods
Fifteen healthy subjects were recruited to obtain reference values for catecholamines and cortisol. Seventy morbidly obese patients (body mass index of 40 kg/m2or more) scheduled for elective LGB under general anesthesia were enrolled in the study. Ethical committee approval (Ethics Committee for Clinical Research, Padova Hospital Company, Padova, Italy) and written, informed consent were obtained (ISRCTN 18342801). Preoperativately, eligible patients were assessed with complete physical examination, and with routine blood tests (i.e. , red and leukocyte count, coagulation tests, liver and kidney function tests, blood glucose and creatinine, and urinanalysis), electrocardiogram, chest X-ray, and esophagogastroduodenoscopy. For each patient, the sleep apnea clinical score was calculated and, when available, a polysomnography-based diagnosis of obstructive sleep apnea syndrome was recorded.21At recruitment, exclusion criteria included: age less than 18 yr old; nonfasting; symptoms or endoscopic evidence of gastroesophageal reflux, of gastric ulcer, or oropharyngeal pathology; known or predicted difficult airway; allergy to anesthetic and nonsteroidal antiinflammatory drugs; or inability to provide informed consent. Later, patients were dropped from the study in case of difficult mask ventilation, difficult laryngoscopy (i.e. , max three attempts) or difficult or failed tracheal intubation, and in case of failure of placement of the gastric tube (GT). Patients were randomly allocated into two equal-sized groups: airway management, in one group, was with ETT, and, in the other, with a PLMA™. Randomization was achieved using computer-generated numbers and allocation by opening a sealed opaque envelope immediately before surgery by one investigator (UF). Two individuals with extensive prior experience using the PLMA™ (more than 5,000 uses) randomly performed airway management and anesthesia maintenance. The same bariatric surgeon (MF), blinded to airway device used, performed surgery in all patients. A single investigator was dedicated to store and analyze the blood samples (WG). Postanaesthesia care unit (PACU) nurses were unaware of the airway device used. A second single trained observer, also blind to the airway device used, documented the adverse events until discharge of patient in the surgical ward after the surgery.
All patients were instructed to fast for 8 h before surgery and to continue taking their usual medications, including β-blockers and Ca2+-channel blockers and with the exception of insulin and oral antidiabetic agents, until the time of surgery.2Patients were premedicated with intravenous administration of midazolam 0.05 mg/kg ideal body weight (IBW) and of ranitidine 50 mg. Standard monitoring was employed before premedication. All patients had heart rate and pulse oximetry (SpO2) measured continuously and arterial blood pressure at 5-min intervals with blood pressure cuffs (CritikonTMBlood Pressure Cuffs; General Electric Healthcare, Milano, Italy) with appropriated size (i.e. , adult and large adult with 23–33- and 31–40-cm arm circumference). The patients also had inspiratory and expiratory end-tidal gas concentrations (i.e. , oxygen, air, carbon dioxide and sevoflurane) and the adductor pollicis train-of-four ratio (TOFR) monitored (NeuroMuscular Transmission Module and MechanoSensor; Aisys GE Healthcare, Datex-Ohmeda, Milano, Italy). A self-adhesive entropy sensor was positioned on the forehead as recommended by the manufacturer and connected to E-EntropyTMModule for an AMTManesthesia monitor (GE Healthcare, Datex-Ohmeda). The sampling rate of raw electroencephalogram was 400 Hz. Moving, frequency-related time windows for spectral entropy calculations were 15–60 s for state entropy and 2–5 s for response entropy. Entropy values were automatically recorded at 1-min intervals onto the computer. Rate-pressure product (RPP) was calculated by multiplying systolic blood pressure by heart rate.
Patients were preoxygenated for 2 min. Anesthesia was induced intravenously with fentanyl 1 μg/kg (total body weight, TBW) and propofol 2–3 mg/kg (TBW). Succinylcholine 1 mg/kg (TBW) was administered intravenously to facilitate tracheal intubation in the ETT group, and no muscle relaxant was used for placement of PLMA™ in the PLMA™ group. An effective airway was defined as two consecutive breaths with an expired tidal volume of 6 ml/kg or more, a square wave capnography, and normal closed-flow volume loop at monitor display.22The airway devices were used in accordance with their respective manufacturer's recommendation for sizes (i.e. , ID 7.5 or 8 mm for ETT and size 5 for PLMA™) and insertion technique. In the PLMA™ group, PLMA™ was positioned using digital technique. It included neck flexion, head extension, full deflation of the cuff, and the use of the index finger to press and then advance the PLMA™ around the palatopharyngeal curve. A slight lateral approach was used if resistance was felt in the oropharynx. The PLMA™ cuff was inflated to and maintained at 60 cm H2O (Mallinckrodt Medical, Athlone, Ireland). The absence of oropharyngeal air leaks was assessed by listening over the mouth and just lateral to the thyroid cartilage with stethoscope, checking for absence of the lubricant blowing back from drainage tube. In the ETT group, after lidocaine gel was applied in the nose, a 14 G Salem GT was blindly introduced through it with the head in flexion position and, if necessary, applying lateral neck pressure or turning the head of patient in lateral position. In the PLMA™ group, the GT was lubricated and passed through the drainage tube of the PLMA™. Correct GT placement was confirmed by the aspiration of gastric contents and/or by epigastric auscultation with a stethoscope during the insertion of 30 ml air into the GT. If suction of gastric fluid was obtained, the amount was recorded. A flexible fiberoptic bronchoscope (Adult Flexible Bronchoscope; Olympus, Milano, Italy) was introduced through the PLMA™ to check and confirm the adequate positioning of PLMA™. In case of failure of GT insertion through drainage tube of PLMA™ or endoscopic incomplete view of glottis, the plan was to withdraw and replace the PLMA™ with an ETT, and the patient dropped out from the study.
Oropharyngeal leak pressure was determined by closing the expiratory valve of circle system at a fixed gas flow of 3 l/min and noting the airway pressure (i.e. , maximum allowed was 40 cm H2O) in the anesthetic breathing system, at which gas leakage occurred into mouth.23Air leakage was evaluated breath to breath and expressed as leak fraction (LF) calculated as the difference between the inspiratory tidal volume (Vt ins) and expiratory tidal volume (Vt exp) divided by the Vt ins, and expressed as a percentage of the Vt ins. If insertion of PLMA™ failed at the first attempt, a single second attempt was allowed using the introducer technique. Failed insertion was defined by any of the following criteria: failed passage into the pharynx; malposition (air leaks); and ineffective ventilation (maximum expired tidal volume less than 6 ml/kg or if an end-tidal carbon dioxide concentration [ETCO2]< 44 mmHg cannot be achieved before carbon dioxide insufflations). The time between laryngoscopy in ETT group and picking up the prepared PLMATM(i.e. , cuff fully deflated, lubricated) in the PLMA™ group and successful insertion of the airway device was recorded. The number of attempts and the etiology of failed insertion was documented. Fixation was in accordance with the manufacturer's instructions. In case of failure of PLMA™ placement, the plan was to withdraw and replace it with an ETT determining the exclusion of patient from the study.
Lung ventilation (Aisys GE Healthcare, Datex-Ohmeda) was set at the beginning to a 35/65 oxygen/air mixture, positive end-expiratory pressure at 5 cm H2O, and peak inspiratory pressure (PIP) at variable value in order to obtain an Vt expof 10 ml/kg IBW, respiratory rate of 12 breaths/min, and inspiratory:expiratory ratio of 1:1. Then, if necessary, minute ventilation was adjusted to maintain EtCO2of more than 30 mmHg during the maintenance phase. Anesthesia was maintained with sevoflurane starting with an end-tidal concentration of about 1 minimum alveolar concentration (i.e. , 2.2%). Then, sevoflurane was titrated to maintain a state entropy value at a target range of 40 ± 5 and to keep the arterial blood pressure and heart rate within 20% of baseline values. In case of increase of their values, if hemodynamic control could not be achieved within 5 min after 0.5% sequential increases of sevoflurane, fentanyl 0.5 μg/kg (TBW) IV was given. On the contrary, systolic hypotension (i.e. , less than 90 mmHg) was treated with 0.5% sequential decrease of sevoflurane, with crystalloids or colloids, and, when necessary, with IV ethylephrine 2 mg and bradycardia (i.e. , less than 50 beats/min) with IV atropine 0.01 mg/kg IBW.
Neuromuscular blockade was produced using a single IV bolus of cisatracurium 0.15 mg/kg IBW administered after tracheal intubation in the ETT group and IV cisatracurium 0.05 mg/kg IBW before carboperitoneum in the PLMA™ group. The dose of cisatracurium was chosen on the basis of drug pharmacokinetics and on the average time of LGB in our Surgical Department.24A single IV bolus of cisatracurium (i.e. , 0.15 mg/kg IBW) administered after ETT insertion was generally sufficient to provide muscle relaxation to the end of carboperitoneum.24Additional IV cisatracurium 2 mg was given in case of TOFR more than 0.5. A low-flow system was used with a fresh gas flow of 2 l/min.
PIP, as first step, and respiratory rate, as second step, were increased with the ETCO2of more than 40 mmHg and reduced with the ETCO2of less than 30 mmHg. In the PLMA™ group, PIP was increased until oropharyngeal leak pressure, then only increase of respiratory rate was adopted to reduce the ETCO2exceeding the threshold value of 40 mmHg. During pressure-controlled ventilation, if the LF was more than 15% or in case of gastric insufflation, the following steps were taken: the cuff pressure of PLMA™ was increased in stepwise fashion; the PIP was reduced until a threshold value of Vt expof 6 ml/kg (IBW); and peritoneal insufflation was reduced below 15 cm H2O, according with surgeon. In the case of a LF more than 15% and unresponsive to the above procedures, in presence of ineffective ventilation (i.e. , maximum Vt expof less than 6 ml/kg or ETCO2more than 44 mmHg), and with interference of surgical procedure, the plan was to replace the PLMA™ with an ETT passed endoscopically through PLMA™ with the help of Aintree Intubation Catheter (Cook Medical Italia, Cinisello Balsamo, Milan, Italy).
At the end of LGB, a methylene blue solution was injected through the GT to allow the surgeon to detect gastric leakage and the anesthesiologist to detect endoscopic stain aspiration in upper airway. After the end of carboperitoneum, metoclopramide 10 mg and ketorolac tromethamine 30 mg were given intravenously to reduce postoperative nausea and vomiting (PONV) and to limit narcotics use in the postoperative pain management. Muscle relaxation was reversed at the end of surgery with IV atropine 0.01 mg/kg IBW and neostigmine methylsulfate 0.04 mg/kg IBW if the TOFR was 0.9 or fewer. At the end of surgery, sevoflurane administration ceased and fresh gas flow was increased to 10 l/min. Mechanical ventilation with ventilator set at a triggering sensitivity of 5 or 6 l/min was maintained until the first spontaneous breath occurred. Then, pressure support ventilation was adopted and level adjusted to ensure a Vt expof 8 ml/kg IBW, positive end-expiratory pressure maintained at 5 cm H2O, and inspiratory:expiratory ratio of 1:1. Just before airway device removal, lung ventilation was manually assisted with continuous positive airway pressure during inspiration maintained at 5 cm H2O by adjusting the adjustable pressure limiting valve. The ETT, or the PLMA™ and GT, were removed when a TOFR more than 0.9 was reached and the patient was awake, able to respond to simple commands, sustain hand grip, and lift arms. The times were recorded.
After removal of ETT or PLMA™, patients were followed until they reached an Aldrete score of 9 or more. The modified Aldrete score is a three-point (i.e. , 0–2) postanesthesia recovery score that assesses five areas: patient's ability to move, respiration, circulation, consciousness, and oxygen saturation. The Aldrete score of 9 or more has been used as a discharge criteria from the PACU.25Patients were assessed for SpO2desaturation while breathing room air without oxygen supplementation for 5 min or until SpO2of less than 92%, and were asked for pain (yes/no) and PONV (yes/no) every 15 min in PACU by a nurse blinded to the airway device used. If answer was yes, the patient was asked to rate pain and PONV by using a visual analog scale (VAS) ranging from 0 (none) to 10 (worst). Fentanyl 0.5 μg/kg TBW and paracetamol 1 g IV were given when needed for moderate-severe (VAS more than 4) or mild (VAS 4 or less) pain respectively, and ondansetron 4 mg IV for PONV (VAS more than 3). Patients were discharged from the PACU when the SpO2was more than 95% while breathing room air, were hemodynamically stable, and had no pain and PONV. While in PACU and later in the ward, the patients were also asked if they had sore throat (i.e. , constant pain, independent of swallowing), dysphonia (i.e. , difficulty speaking and pain on speaking), and dysphagia (i.e. , difficulty or pain provoked by swallowing).
The time of surgery was calculated from skin incision to the placement of the last suture. Emergence times (i.e. , opening eyes in response to a verbal command, obeying simple verbal commands) and time of ETT/PLMA™ removal were registered from cessation of sevoflurane. At the end of each LGB, the surgeon was asked to answer yes/no to two questions (i.e. , “Did gastric distension at entry of the laparoscope interfere with surgery?”; and “Were you satisfied with the surgical conditions resulting from the anesthetic?”).
The occurrence of the following complications was recorded: episodes of hypoxemia (i.e. , SpO2of less than 92%), bradycardia (i.e. , beats per minute less than 40/min), systolic hypotension (i.e. , less than 90 mmHg), VAS of postoperative pain and PONV, and complications related to the airway devices such as insertion failure, blood staining, sore throat, dysphonia, and dysphagia were recorded.
Neuroendocrine Stress Response Evaluation
Neuroendocrine stress responses were assessed by measuring resting plasma concentrations of epinephrine, norepinephrine, dopamine, adrenocorticotrophic hormone (ACTH), and cortisol in blood sample collected peripherally from an antecubital vein of the arm contralateral to the intravenous infusion as follows: 30 min before transferring the patient to operating room at 1 and 5 min after ETT/PLMA™ placement; at 10 min after inducing and at 5 min after ending carboperitoneum; and at 10 and 120 min after removal of airway device with the patient awake in the PACU. In all cases, the patients were in head-up position during and after surgery. For catecholamines, ACTH, and cortisol, the samples were transferred to precooled tubes and soon centrifuged at −4°C, and the plasma was stored at −80°C until analysis. All samples were analyzed together. Catecholamines were measured by high-performance liquid chromatography and quantified by electrochemical–coulommetric method (HPLC System Gold Beckman, ESA C18, ESA AC5011A; Coulochem II, Chelmsford, MA). Concentrations of ACTH and cortisol were measured by commercially available radioimmunoassay kit.
The primary endpoints were mean arterial blood pressure (MAP), plasma norepinephrine concentrations, and cisatracurium dosage requirement (α = 0.05 and power = 0.90). Based on a pilot study on 10 obese patients managed with ETT, it was calculated that 32 and five patients per group were required to detect a significant 30% intergroup difference in, respectively, blood pressure and blood norepinephrine, and nine patients per group to detect a 50% difference in cisatracurium dosage. To account for larger SD and possible dropouts, 38 patients per group were included. Secondary endpoints were times taken for ETT/PLMA™ placement and removal, LF, postoperative complications, VAS for pain and PONV, analgesic and antiemetic requirements, and times to discharge from PACU to surgical ward.
Statistical analysis was performed using Statistica software version 9.0 (StatSoft Italia, Vigonza, Padova, Italy). Dosages of drugs, times of anesthesia, and surgery, and ventilatory, hemodynamic, and hormonal data are expressed as means ± SD. All other data are patient numbers (percentages). The distribution of data were analyzed using the Kolmogorov-Smirnov test. Parametric data were analyzed with independent two-tail Student t test and nonparametric data with chi-square test. Serial data were analyzed with a post hoc Bonferroni-corrected repeated-measures ANOVA for intergroup differences over time and a Bonferroni-corrected Student t test for intergroup differences at individual time-points. The nature of significant testing was two-tailed. A P value < 0.05 was considered to be significant.
Seventy-five patients were recruited in the study during a 16-month period: 37 and 38 patients were allocated to the ETT and the PLMA group, respectively. A total of five patients who underwent LGB were subsequently excluded: two ETT patients because of difficult intubation and prolonged surgery, two PLMA patients because of initial placement failure of PLMA and fiberoptic intubation, and one patient because of laryngospasm after PLMA removal. Usable data were, therefore, from 35 ETT patients and 35 PLMA patients.
Demographic and clinical features (table 1), chronic drug treatments, PONV risk factors and numbers of patients at high risk of PONV, anesthetic drug dosages and mean sevoflurane end tidal, state entropy during maintenance (table 2), and times of surgery and of emergence (table 2) were comparable between groups. Six ETT patients and seven PLMA patients were at high risk of PONV (i.e. , Apfel score more than 3, P = 0.758). Succinylcholine was used in ETT patients only. Cisatracurium was given to ETT patients and, at significantly lower doses, to PLMA patients (table 2).
Compared with PLMA, ETT required shorter times to achieve an effective airway (table 2). The GT was inserted with difficulty in seven ETT patients and in no PLMA patients. Residual gastric volume was 43 ± 44 and 41 ± 53 ml in the ETT and PLMA groups, respectively. Among ETT patients, laryngoscopy and tracheal intubation were successful at the first attempt in 32 (91%) and at a second attempt in three patients (9%). In the PLMA group, PLMA placement was successful at the first attempt in 33 patients (94%) and at a second attempt in two patients (6%). Mean oropharyngeal leak pressure was 29.6 ± 4.2 cm H2O and positive pressure ventilation with VTexp of 10 ml/kg was possible without audible air leaks in 31 patients (88.5%).
Tidal volumes, SpO2, and EtCO2were not statistically different between the ETT and PLMATMgroup (table 3). Compared with the ETT group, in the PLMA group PIP was higher at the end of surgery and LF after insertion of devices and after induction of carboperitoneum (table 3), but in all cases it did not affect gas exchange. The surgeon reported a significant gastric dilatation in two ETT and three PLMA™ patients, leak of methylene blue in no patients, and high rate of satisfaction with the anesthesia (more than 90%) in ETT patients and PLMA™ patients (table 2). At the end of carboperitoneum, the anesthesiologist reported methylene blue in the upper airways in no patients.
The assumption of a normal distribution for the hemodynamic and hormonal values at each of the time-points was supported by the Kolmogorov-Smirnov test. Repeated-measures ANOVA showed significant group × time interaction with ETT patients having, compared with PLMA patients, higher values of heart rate (F[6,408] 4,37; P = 0.009), MAP (F[6,408] 5,683; P = 0.009), and RPP (F[6,408] 8,783; P = 0.0003). The post hoc comparisons with Bonferroni correction showed similar hemodynamic values at baseline and larger hemodynamic values in ETT than in PLMA after airway device insertion and removal and after recovery in PACU (table 4). Seven ETT and six PLMA patients were on chronic β-blocker therapy (table 1). The same pattern of hemodynamic changes was observed when data were analyzed separately for patients who were receiving β-blockers or patients who were not treated with β-blockers (data not shown).
Plasma concentrations of norepinephrine were a primary outcome in our study. Plasma concentrations of stress hormones in 15 healthy, comparison subjects were: norepinephrine 176 ± 35 pg/ml; epinephrine 66 ± 32 pg/ml; and dopamine 15 ± 17 pg/ml. At baseline, plasma concentrations of catecholamines and cortisol were within reference ranges in 10 ETT and 11 PLMA patients (table 5). Repeated-measures ANOVA revealed a significant group × time interaction with 5–40% higher hormone levels in ETT than in PLMA patients: norepinephrine (F[6,408] = 12,25; P = 0.0005), epinephrine (F[6,408] = 5,49; P = 0.001), dopamine (F[6,408] = 5,26; P = 0.0015), cortisol (F[6,408] = 3,07; P = 0.015) and ACTH (F[6,408] = 3,80; P = 0.005). The post hoc analyses showed similar hormonal levels at baseline and higher levels of catecholamines and of cortisol in ETT than in PLMA patients after induction of carboperitoneum, after insertion and removal of airway devices, and after recovery in PACU. The same pattern of plasma catecholamines, cortisol, and ACTH was observed when data were analyzed separately for patients who were receiving or patients who were not receiving β-blockers (data not shown).
In comparison with ETT patients, PLMA-managed patients presented fewer episodes of postoperative cough, hypoxemia, and PONV (tables 6and 7), and were judged dischargeable from the PACU on average 17 min earlier and from the hospital 111 min earlier (table 7).
This is, to the best of our knowledge, the first study examining influences of airway devices used for LGB surgery in morbidly obese patients on stress responses and immediate postoperative complications. Compared with airway management with an ETT, use of PLMA™ resulted in less hemodynamic and hormonal activation and less hypoxemic and PONV episodes during the postoperative period.
PLMA™ was associated with less stress activation than ETT at insertion and at removal of airway devices, and at induction of carboperitoneum. β-blockers attenuate responses to stress when given just before anesthesia. In our study, a repeated-measures ANOVA did not find a significant effect of β-blockers taken chronically on the patterns of hemodynamic and hormonal activation. The findings are probably due to underdosing or low efficacy of specific β-blocking agents and indicate that chronic use of β-blockers does not explain reduced stress response in PLMA™ patients.26Also, depth of anesthesia and doses of anesthetic drugs administered are comparable between groups, suggesting these factors are not involved in lower stress responses to PLMA™. Finally, cisatracurium was given in higher doses to ETT than in PLMA™ patients, and succinylcholine to ETT patients only. However, cisatracurium has no effect on catecholamines, and succinylcholine has a brief, catecholamine-releasing effect that may contribute, at most, to catecholamine increase at the time of intubation but not at later time-points.27,28Hence, smaller stress responses in PLMA™ patients do not appear to be accounted for by chronic therapies or anesthesia drugs. Rather, we believe they result from features of airway devices. In ETT patients, in fact, laryngoscopy and tracheal intubation are strong noxious stimuli on laryngopharyngeal and tracheal mucosa that elicit arterial hypertension, tachycardia, and catecholamine release.7,29,–,32In contrast, PLMA™ may elicit a smaller stress response than ETT because it is less traumatic on upper airway in a fashion similar to other supraglottic devices.7,29,–,32In our study, the maximal stress activation occurred after removal of ETT but not of PLMA™. These findings suggest that, in comparison with PLMA™, manipulation of the upper airway, either for insertion or removal of ETT, is more stimulating and causes larger sympathetic activation.
By reducing stress responses, PLMA™ may be advantageous over ETT in obese patients. Although transitory hypertension and tachycardia are probably of little clinical consequence in healthy individuals, they may be matter of concern in patients with known, or at risk of, cardiovascular diseases such as obese patients.33,–,35In fact, catecholamines promote platelet aggregation and thrombus formation, as well as heart rate and myocardial oxygen consumption, increasing the risk of arrhythmia and ischemia.33–34Myocardial oxygen consumption is a reliable indicator of the load on the heart but is difficult to measure. RPP is a strong correlator of myocardial oxygen consumption and is a risk factor of serious cardiovascular events, and is easier to determine.35In our study, RPP values exceeding 15,000 and 20,000 (i.e. , levels of safety and myocardial ischemia) were found more frequently or solely in the ETT patient group. We had no clinical cardiovascular event. As we did not determine markers of ischemic brain and myocardial injury, we could have not detected subclinical events.35Nevertheless, the PLMA™ capability of reducing RPP may reflect a lesser impact of PLMA™ on cardiovascular functions.
PLMA™ is as effective as ETT for pressure-controlled ventilation for LGB. These findings are of interest because the use of supraglottic devices in morbidly obese patients undergoing laparoscopic surgery is still controversial. In comparison with ETT, in fact, supraglottic devices have the disadvantage of risk of pulmonary aspiration and of delivering positive pressure over a limited range.6,7,16,17,19Among different types of devices available to us, we chose to investigate PLMA™ because of its favorable features such as high rate of and short time for successful insertion, efficacy of ventilation, and capability of gastric drainage.6,7,16,36In this study, compared with ETT, PLMA™ produces similar tidal volumes, lower PIP values, and higher LF, all of which are similar to those previously found in lean subjects.7,16Finally, there was no clinical or endoscopic sign of aspiration in either group, although patients with higher risk were excluded. These are findings consistent with the advantage of PLMA™ over other supraglottic devices of having higher airway seal pressure and lower airflow resistance.7,37,–,39They are also consistent with experimental and clinical evidences supporting the view that when the PLMA™ is properly positioned, the risk of pulmonary aspiration is very low.7,37,40–41Interestingly, i-gel, a supraglottic device by Intersurgical (Wokingham, Berkshire, United Kingdom) has recently demonstrated airway-sealing properties higher than cLMA™ in moderately obese subjects and similar to those of PLMA™ in lean subjects.42,43
PLMA™ depresses postanesthetic respiratory functions less than ETT. Consistently with features of supraglottic devices, in this study PLMA™ requires lower doses of muscle relaxant drugs than ETT.5In ETT-managed patients, succinylcholine creates superior intubation conditions to neuromuscular nondepolarizing agents and the benefits of succinylcholine in the morbidly obese patients outweigh any reason not to use it.44In PLMA™ patients, succinylcholine has not been necessary for the placement of PLMA™.7Nondepolarizing muscle relaxants are used to maintain optimal conditions of tracheal intubation and of carboperitoneum for laparoscopic surgery in ETT patients. In PLMA™ patients, nondepolarizing agents are required only to maintain carboperitoneum. Our preference goes to cisatracurium that has been suggested as the neuromuscular blocking drug of choice for obese patients because it lacks histamine releasing and long half-life effects.24Indeed, upper airway muscles are very sensitive to neuromuscular blocking agents and, in volunteers, even minimal neuromuscular blockade as reflected by a TOFR less than 1.0 puts the upper airway at the risk of collapse.45Increased airway collapsibility was observed at a TOFR ratio of 0.8 (and potentially even 0.9) and it can persist for some minutes even after recovery of the TOFR ratio to unity. Therefore, smaller requirements of muscle relaxants can improve postanesthetic respiratory recovery in PLMA™ patients.45
PLMA™ causes less postoperative cough and PONV than ETT, which is consistent with advantages PLMA™ demonstrated in lean subjects.16,17,37,38,46Although PLMA™ causes less upper airway complications than ETT probably by being less irritating on the laryngotracheal mucosa, the way PLMA™ induces less PONV is less clear. PONV can be predicted by several, quantifiable factors that do not include obesity.47Emetogenic drugs (i.e. , sevoflurane, neostigmine, opioid analgesics) were given in similar doses to ETT and PLMA™ patients, suggesting that other mechanisms may come into play.38,47The PLMA™ cuff in the pharynx is less stimulating than ETT cuff in the trachea and has been postulated by Hohlrieder to actually increase PONV threshold, by a preemptive type of mechanism.38Whatever the reason, at emergence PLMA™ reduces PONV and coughing, which both can result in sympathetic activation, bronchospasm, and desaturation.48,49
The study has a few limitations. First, using different doses of muscle relaxant drugs in ETT and PLMA™ patients may affect stress responses. However, cisatracurium is devoid of effect and succinylcholine has a very short effect on circulating catecholamines.28Second, although we did not observe any symptom or sign of aspiration in the study patients, the sample size was too small to address the critical question of PLMA™ safety against pulmonary aspiration.7,17,18The incidence of pulmonary complications is 1–4/11,000 for cLMA™ to an estimate of 1/200,000–300,000 patients for PLMA™.7Dr. Tim Cook, F.R.C.A. (Department of Anaesthesia, Royal United Hospital, Combe Park, Bath, United Kingdom), calculated that approximately 2,600,000 subjects would be required to have a 80% probability to demonstrate a 50% reduction in pulmonary aspiration with PLMA™, which makes our study underpowered and the issue of respiratory safety of PLMATMdefinitely difficult to assess in obese patients anyway.7Third, reducing stress is beneficial to patients with a high cardiovascular risk. As we did not have any clinical cardiovascular event or marker of subclinical event, we cannot positively determine the potential benefit of stress reduction in terms of risk reduction. Protection against cardiac damage is an exciting topic in clinical anesthesiology research we intend to pursue. Fourth, the anesthesiologists involved in this study were experienced in abdominal and thoracic anesthesia and difficult airway. Adverse events increase with inexperience and the amount of training necessary for a resident to become competent, for example, with obese patients is matter of discussion.37,50,51In our department, senior supervision is mandated when residents anesthetize obese patients. It is possible that the positive outcome with PLMA™ for LGB observed in this study would not generalize to our setting with less experienced users.
With this work, we do not intend to recommend PLMA™ as an alternative to ETT for LGB. Our findings suggest that in the case of obese patients without evidence of gastroesophageal reflux and in whom stress activation could be dangerous, PLMA™ can be considered as a suitable alternative to ETT. At the moment, on the basis of the available information, PLMA™ should be contemplated for LGB only by anesthesiology personnel very experienced with PLMA™. Larger safety studies will be necessary before PLMA™ can be recommended for routine LGB. In future, such studies should be feasible, at least as metanalyses, given the increasing numbers of obese patients undergoing surgery with supraglottic devices and of evidences of their effectiveness.
The authors thank Chiara Bilato, M.D., Resident in Anesthesiology, University of Padova, Padova, Italy, and Federica Pastorelli, M.D., Resident in Anesthesiology, University of Padova, for help with patient assessment and blood sampling; Mario Ermani, M.D., Ph.D., Assistant Professor in Biostatistics, Department of Neuroscience, University of Padova, for suggestions for the statistical analyses; Marco Agostini, Ph.D., Technician, Tumor Tissue Biobank, Department of Surgical and Oncological Sciences, University of Padova, for preprocessing and storing of the blood samples; and Ben Vitiello, M.D., Chief, Child and Adolescent Treatment and Preventive Intervention Research Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, for reviewing the manuscript.