A comparison of the reinforced and standard laryngeal mask airway: ease of insertion and the influence of head and neck position on oropharyngeal leak pressure and intracuff pressure

Influence of head and neck position on the performance of supraglottic airway devices: A systematic review and meta-analysis

Background

Changes in head and neck position may significantly affect the performance of supraglottic airway devices (SADs) by altering the pharyngeal structure.

Purpose

This systematic review and meta-analysis aimed to elucidate the effect of changes in head and neck position on performance of SADs.

Data source

Bibliographic databases, including PubMed, EMBASE, the Cochrane library, and the Web of Science.

Study eligibility criteria

Prospective studies investigating the effects of head and neck positions on the performance of SADs.

Methods

A random effect model was applied in the all analyses. Subgroup analysis was performed according to the type of device and the age of patient. The oropharyngeal leak pressure was the primary outcome measure. Secondary outcome measures included peak inspiratory pressure, fibreoptic view, and ventilation score (PROSPERO, CRD42017076971).

Results

Seventeen studies met the eligibility criteria. Overall, the oropharyngeal leak pressure significantly increased (mean difference 4.07 cmH₂O; 95% confidence interval 3.30 to 4.84) during neck flexion with adverse effects on ventilation and fibreoptic view. Conversely, the oropharyngeal leak pressure decreased (mean difference −4.05; 95% confidence interval −4.90 to −3.20) during neck extension with no significant effect on ventilation or fibreoptic view. Rotation of the head and neck did not significantly affect SAD performance.

Conclusions

The reduced oropharyngeal leak pressure in the extended neck position was not associated with impaired ventilation except with the air-Q self-pressurizing airway. The flexed neck position significantly worsens ventilation and the alignment between the SAD and glottis despite improving the seal except with the air-Q self-pressurizing airway and LMA Proseal.

Flexion decreases the ventilation quality of the Ambu® AuraGain™ laryngeal mask in paralysed children: A prospective randomised crossover study

BACKGROUND

The influence of different head and neck positions on ventilation with the Ambu® AuraGain™ remains unevaluated in children. This study assessed the influence of different head and neck positions on ventilation with the AuraGain™ in paediatric patients.

METHODS

In this prospective, randomised crossover study, children ≤7 years of age who were scheduled for elective surgery under general anaesthesia were enrolled. An AuraGain™ was placed in all patients; mechanical ventilation was performed using a volume-controlled mode with a tidal volume of 10 mL/kg. Respiratory rate was adjusted to maintain a ETCO2 of 35-40 mm Hg. The oropharyngeal leak pressure, expiratory tidal volume, peak inspiratory pressure, ventilation score and fibreoptic bronchoscopic view score were assessed for the neutral head and neck position, and then for the flexed, extended and rotated head and neck positions in a random order.

RESULTS

Compared with the neutral position, the oropharyngeal leak pressure increased in the flexed position (P < .001), and decreased in the extended (P = .014) and rotated position (P = .002). The expiratory tidal volume and ventilation score were significantly reduced during flexion (all P < .005), and were comparable among the neutral, extended and rotated positions. The fibreoptic score improved in the extended and rotated position (all P < .001). Only the flexion ventilation score was lower compared with the neutral position (P = .014).

CONCLUSIONS

Clinically, the flexed head and neck positions negatively affected ventilation due to obstruction of the airway. Ventilation with AuraGain™ can be effectively performed with the head and neck in the neutral, extended and rotated position in paediatric patients.

Comparison of the ProSeal laryngeal mask airway with the I-Gel™ in the different head-and-neck positions in anaesthetised paralysed children: A randomised controlled trial

Background and Aims:

Head and neck movements alter the shape of the pharynx, resulting in changes in the oropharyngeal leaking pressures and ventilation with supragottic airway devices. We compared the effect of the different head-and-neck positions on the oropharyngeal leak pressures and ventilation with the I-Gel™ and ProSeal™ laryngeal mask airway (PLMA) in anaesthetised paralysed children.

Methods:

A total of 70 children were randomly assigned to receive PLMA (n = 35) or I-Gel™ (n = 35) for airway management. Oropharyngeal leak pressure in maximum flexion, maximum extension and the neutral position was taken as the primary outcome. Peak inspiratory pressures (PIPs), expired tidal volume, ventilation score and fibreoptic grading were also assessed.

Results:

No significant difference was noted in oropharyngeal leak pressures of PLMA and I-Gel™ during neutral (P = 0.34), flexion (P = 0.46) or extension (P = 0.18). PIPs mean (standard deviation [SD]) were significantly higher (17.7 [4.03] vs. 14.6 [2.4] cm H₂O, P = 0.002) and expired tidal volume mean [SD] was significantly lower (5.5 [1.6] vs. 6.9 [2] ml/kg, P = 0.0017) with I-Gel™ compared to PLMA. Fibreoptic grading and ventilation score were comparable in both the groups in all the three head-and-neck positions.

Conclusion:

PLMA and I-Gel™, both recorded similar oropharyngeal leaking pressures in all the three head-and-neck positions. However, higher peak pressures and lower expired tidal volume in maximum flexion of the neck while ventilating with I-Gel may warrant caution and future evaluation.

Comparison of i-gel™ and Laryngeal Mask Airway Supreme™ in Different Head and Neck Positions in Spontaneously Breathing Pediatric Population

BACKGROUND

Although the advantages of ventilation with i-gel™ and laryngeal mask airway Supreme (LMA-Supreme™) has been well documented, they are still under debate for surgeries requiring flexion and extension of neck such as thyroid surgery, tonsillectomy, and neck exploration. Hence, we conducted a study to demonstrate the effect of neck flexion and extension in spontaneously breathing anesthetized pediatric patients utilizing i-gel™ and LMA-Supreme™.

METHODS

A prospective, randomized comparative study was conducted on sixty children, thirty each in i-gel™ and LMA-Supreme™ group. Oropharyngeal leak pressure (OPLP), fiberoptic view of vocal cords, and exhaled tidal volume were evaluated in neutral, flexion, and extension neck positions in spontaneously breathing children.

RESULTS

OPLP for i-gel™ was found to be significantly higher in flexion (29.00 ± 1.95 cmH₂O, P < 0.001) and lower in extension (21.07 ± 2.08 cmH₂O, P < 0.001) as compared to neutral (24.67 ± 2.08 cmH₂O). Similar results were observed for LMA-Supreme™ which showed significantly higher OPLP in flexion (24.73 ± 2.26, P < 0.001 respectively) and lower in extension (18.67 ± 1.42 cmH₂O, P < 0.001) as compared to neutral (20.87 ± 1.80 cmH₂O). Worsening of fiberoptic view occurs for i-gel™ and LMA-Supreme™ in flexion (10/12/5/3/0 and 11/14/2/2/1, P < 0.05) as compared to neutral position (17/10/2/1/0 and 15/12/1/1/1), respectively. Significant change did not occur in extension. Ventilation worsening occurred in flexion as compared to neutral position evidenced by significant decrease in exhaled tidal volume (92.90 ± 11.42 and 94.13 ± 7.75 ml, P < 0.05) as compared to neutral (100.23 ± 12.31 and 101.50 ± 8.26 ml) for i-gel™ and LMA-Supreme™, respectively.

CONCLUSION

Neck flexion caused a significant increase in leak pressure in both i-gel™ and LMA-Supreme™. With deterioration of fiberoptic view and ventilation, both devices should be used cautiously in pediatric patients in extreme flexion.

Evaluation of I-Gel™ size 2 airway in different degrees of neck flexion in anesthetized children - a prospective, self-controlled trial

BACKGROUND

A previous study by our group demonstrated an increase in oropharyngeal leak pressures and a deterioration of ventilation in maximum neck flexion with the I-Gel^™ . To ascertain the optimal degree of neck flexion which increases OPLP without compromising ventilation we conducted a prospective self-controlled trial with the I-Gel^™ in different degrees of neck flexion in anesthetized paralyzed children.

METHODOLOGY

The I-gel^™ was inserted in 60 children undergoing inhalation induction with muscle paralysis for routine general anesthesia. Recordings of peak inspiratory pressures (PIP) at flexion of 15°, 30°, and 45° were taken as the primary outcome. Expired tidal volume, ventilation scoring, fiberoptic gradings, and OPLP in different degrees of flexion were recorded as secondary outcomes.

RESULTS

There was a significant increase in mean PIP in cm H₂ O at flexion 30° [13.3 (95% CI 12.8-13.8) cm H₂ O, P < 0.001] and 45° flexion (16.5 [15.9-17.1] cm H₂ O, P < 0.001) compared to neutral. A decrease in the expired tidal volume was seen at flexion of 30° (7.6 [7.3-7.8] cm H₂ O, P = 0.00) and 45° (7.6 [7.3-7.8] cm H₂ O, P = 0.00). There was deterioration of ventilation score, mean [range] at 30° flexion 2[0-3], and 45° flexion 1[0-3] compared to the neutral 3[2-3]. There was a significant increase in OPLP with an increase in degree of flexion.

CONCLUSION

We conclude that 15° neck flexion can safely be applied without compromising ventilation with the I-Gel^™ in anesthetized paralyzed children. However, Flexion of 30° or more warrants caution or the use of alternative devices like an endotracheal tube due to increase in PIP and worsening of ventilation score.

Evaluation of I-gel™ airway in different head and neck positions in anesthetized paralyzed children

BACKGROUND

Studies that have compared and quantified the oropharyngeal leak pressure (OPLP) and adequacy of ventilation with supraglottic airway devices in different head and neck positions have been done in adult populations. The effects of head-neck position changes on the functioning of I-gel(™) in pediatric population still remain unevaluated.

AIM

This study aimed to quantify the influence of different head and neck positions namely neutral, maximum flexion, and maximum extension on OPLP, ventilation scoring, and fiberoptic grading using I-gel(™) in anesthetized, paralyzed children.

METHODS

I-gel(™) was inserted in 30 paralyzed, anesthetized children scheduled for elective urological and orthopedic procedures. Anesthesia was induced with sevoflurane in oxygen. Atracurium was administered intravenously to facilitate neuromuscular relaxation. Recordings of OPLP in neutral, maximum flexion, and maximum extension were taken as primary outcome. Fiberoptic grading, insertion of ryle's tube and ventilation scoring were also measured in different head and neck positions as secondary outcomes.

RESULTS

The OPLP was significantly higher in flexion (27.6 ± 3.3 cm H2 O, P = 0.000) and lower in extension (19.6 ± 3.2 cm H2 O, P = 0.006) in comparison to the neutral position (23.2 ± 3.2 cm H2 O). There was a worsening of the fiberoptic view in flexion compared to neutral position (0/5/19/6 vs 5/21/4/0). The ventilation score was poorer (1 [0-3], P < 0.05) and peak inspiratory pressures higher in flexion (15.2 ± 1.4 cm H2 O, P = 0.000) compared to the neutral position (10.4 ± 1.6 cm H2 O).

CONCLUSION

Caution is warranted in pediatric patients while ventilating with I-gel(™) in extreme flexion of head and neck owing to poor ventilation despite increase in OPLP.

Laryngeal mask placement in a teaching institution: analysis of difficult placements

Background: Laryngeal mask airway (LMA) placement is now considered a common airway management practice. Although there are many studies which focus on various airway techniques, research regarding difficult LMA placement is limited, particularly for anesthesiologist trainees. In our retrospective analysis we tried to identify predictive factors of difficult LMA placement in an academic training program.

Methods: This retrospective analysis was derived from a research airway database, where data were collected prospectively at the Memorial Hermann Hospital, Texas Medical Center, Houston, TX, USA, from 2008 to 2010. All non-obstetric adult patients presenting for elective surgery requiring general anesthesia, were enrolled in this study: anesthesiology residents primarily managed the airways. The level of difficulty, number of attempts, and type of the extraglottic device placement were retrieved.

Results: Sixty-nine unique Laryngeal Mask Airways (uLMAs) were utilized as a primary airway device. Two independent predictors for difficult LMA placement were identified: gender and neck circumference. The sensitivity for one factor is 87.5% with a specificity of 50%. However with two risk factors, the specificity increases to the level of 93% and the sensitivity is 63%.

Conclusion: In a large academic training program, besides uLMA not been used routinely, two risk factors for LMA difficulty were identified, female gender and large neck circumference. Neck circumference is increasingly being recognized as a significant predictor across the spectrum of airway management difficulties while female gender has not been previously reported as a risk factor for difficult LMA placement.

Effects of head-neck extension on abnormality of laryngeal mask airway function resulting from opening the mouth

PURPOSE

This study investigated the effects of head-neck extension on abnormalities of laryngeal mask airway (LMA) function resulting from opening the mouth.

PATIENTS AND METHODS

A single, experienced LMA user inserted the LMA in 15 patients scheduled for elective oral surgery. Oropharyngeal leak pressure and intracuff pressure were sequentially documented in 5 mouth conditions in order (0 minutes, mouth closed plus 0° extension; 3 minutes, mouth open plus 0° extension; 6 minutes, mouth open plus 15° extension; 9 minutes, mouth open plus 30° extension; and 12 minutes, mouth open plus 45° extension).

RESULTS

Oropharyngeal leak pressures with the mouth open plus 0° extension (30.7 ± 5.6 cm H(2)O, P < .001), mouth open plus 15° extension (29.1 ± 6.8 cm H(2)O, P < .001), and mouth open plus 30° extension (25.7 ± 6.1 cm H(2)O, P < .001) were significantly higher than with the mouth closed plus 0° extension (19.7 ± 2.8 cm H(2)O). Compared with the position with the mouth closed plus 0° extension (60.0 ± 0 cm H(2)O), intracuff pressures were also higher with the mouth open plus 0° extension (84.5 ± 14.1 cm H(2)O, P < .001), mouth open plus 15° extension (77.4 ± 11.0 cm H(2)O, P < .001), and mouth open plus 30° extension (73.6 ± 9.6 cm H(2)O, P < .001). Both measurement values returned to control levels when the position with the mouth open plus 45° extension was assumed (oropharyngeal leak pressure, 64.5 ± 6.5 cm H(2)O [P = .212]; intracuff pressure, 20.2 ± 4.9 cm H(2)O [P = .969]).

CONCLUSIONS

In procedures requiring the patient to have an open mouth under general anesthesia using LMA, 45° head-neck extension achieves acceptable airway conditions.

Incidence of sore throat in children following use of flexible laryngeal mask airways - impact of an introducer device

BACKGROUND

Insertion of a flexible laryngeal mask airway (FLMA) is more difficult and therefore might result in a higher risk for trauma to the upper airway. To facilitate the insertion of FLMA, the use of an introducer device (Portex Limited, Hythe, Kent, UK) was promoted. However, the impact of the use of this device on the occurrence of postoperative sore throat is unknown.

METHODS

Four hundred children (3-21 years) undergoing elective ambulatory surgery were consecutively included in this study. In 196 cases, the FLMA was inserted using an introducer device. The FLMA cuff was then inflated and the pressure adjusted to below 60 cmH(2)O (according to manufacturers guidelines) using a calibrated cuff manometer (Portex Limited). Three types of FLMA were available: FLMA classic, FLMA unique (both FLMA PacMed, Richmond, Victoria, Australia) and FLMA ProBreathe (Well Lead Medical Co Ltd., Hualong, Guangzhou, China). Prior to discharge, patients' pain was assessed using an age appropriate scale.

RESULTS

Thirteen children (3.3%) developed sore throat, two (0.5%) sore neck and three (0.75%) sore jaw. Of those that developed sore throat, seven had a FLMA inserted with an introducer, six without an introducer. Using a laryngeal mask airways (LMA) with a polyvinyl chloride (PVC), surface was associated with a higher risk for sore throat compared with an LMA with a silicone surface (P = 0.0002).

CONCLUSION

In this study with controlled low cuff pressures, the incidence of sore throat was low. The use of an introducer device did not affect the rate of sore throat.

Optimal degree of mouth opening for laryngeal mask airway function during oral surgery

PURPOSE

This study was performed to determine the optimal degree of mouth opening in anesthetized patients requiring laryngeal mask airway (LMA) during oral surgery.

PATIENTS AND METHODS

A single, experienced LMA user inserted the LMA in 15 patients who were scheduled for elective oral surgery. Oropharyngeal leak pressure, intracuff pressure, and fiberoptic assessment of the LMA position were sequentially documented in 5 mouth conditions-opening of 1.4 (neutral position), 2, 3, 4, and 5 cm-and any resulting ventilatory difficulties were recorded.

RESULTS

Oropharyngeal leak pressure with the mouth open 4 cm (21.8 ± 3.2 cm H(2)O, P = .025) and 5 cm (27.3 ± 7.2 cm H(2)O, P < .001) was significantly higher than in the neutral position (18.1 ± 1.5 cm H(2)O), as was intracuff pressure (neutral position, 60.0 ± 0 cm H(2)O; 4 cm, 72.6 ± 5.1 cm H(2)O [P < .001]; and 5 cm, 86.9 ± 14.4 cm H(2)O [P < .001]). LMA position, observed by fiberoptic bronchoscopy, was unchanged by mouth opening, being similar in the 5 mouth conditions (P = .999). In addition, ventilation difficulties (abnormal capnograph curves or inadequate tidal volume) occurred in 2 of 15 patients (13%) and 7 of 15 patients (53%) (P < .001) with the mouth opening of 4 and 5 cm, respectively.

CONCLUSIONS

This study showed that a mouth opening over 4 cm led to substantial increases in oropharyngeal leak pressure and intracuff pressure of the LMA, warranting caution, because gastric insufflation, sore throat, and ventilation difficulties may occur. A mouth opening of 3 cm achieves acceptable airway conditions for anesthetized patients requiring LMA.

[Flexible laryngeal mask airway use during surgical burn management with head mobilisation: a feasibility study]

OBJECTIVE

To evaluate the feasibility and reliability of the flexible laryngeal mask airway (LMA flexible) use during scalp skin harvesting for surgical reparation of burn sequella.

STUDY DESIGN

Observational prospective descriptive study.

PATIENTS AND METHODS

Following local ethic committee approval, 26 patients were included in the study during their preanaesthesia visit. The general anaesthesia induction of each patient was followed by the insertion of a LMA flexible. The number of attempts required to insert the mask and the procedure were documented. The oropharyngeal leak pressure, expired tidal volume and end tidal CO(2) were recorded in five different head positions (neutral, hyperflexion, hyperextension, right and left rotation) at the start and end of surgical procedure. In all ten study periods of 2-3 min each were evaluated.

RESULTS

The airway device was inserted easily in all patients. While similar in four of the five head positions (neutral: 27.9+/-8.1 cmH(2)O, hyperextension, left and right rotation), the oropharyngeal leak pressure was significantly higher in the hyperflexion position (33.3+/-7.3 cmH(2)O). The end tidal volume was stable in all positions except hyperflexion (419+/-114 ml). While this value was significantly lower than the 471+/-68 ml recorded in the neutral position, it remained greater than 7 ml/kg. No significant change was observed for end tidal CO(2) for the ten study periods.

CONCLUSION

The use of LMA flexible during surgical burn repair procedures, including head mobilisation for the harvesting of scalp skin grafts is feasible.

The influence of mouth opening on oropharyngeal leak pressure, intracuff pressure, and cuff position with the laryngeal mask airway

PURPOSE

The aim of this study was to investigate the influence of mouth opening on oropharyngeal leak pressure, intracuff pressure, and cuff position of the laryngeal mask airway (LMA).

PATIENTS AND METHODS

Fifteen patients who were scheduled for elective oral surgery were recruited into this study. A single, experienced LMA user inserted the LMA according to the manufacturer's recommended technique. Oropharyngeal leak pressure, intracuff pressure, and fiberoptic assessment of the LMA position were documented under 3 mouth conditions: neutral position (1.4-cm distance between upper and lower incisors), mouth open (5- to 6-cm distance between upper and lower incisors), and return to the neutral position. Any ventilation difficulties under the 3 mouth conditions were recorded.

RESULTS

Oropharyngeal leak pressure with the mouth open was higher than in the neutral position (P < .001). Compared with the neutral position, intracuff pressure was also higher with the mouth open (P < .001). Both measurement values returned to control levels when the neutral position was once again assumed. The LMA position observed by fiberoptic bronchoscopy was unchanged by mouth opening and was similar in the 3 mouth conditions (P = .998). Although ventilatory difficulties occurred after mouth opening in 8 of 15 patients (P < .001), it did not occur when the neutral position was reassumed.

CONCLUSIONS

This study showed that mouth opening led to substantial increases in oropharyngeal leak pressure and intracuff pressure of the LMA, warranting caution because gastric insufflation, sore throat, and ventilation difficulties may occur.

Impact of laryngeal mask airway cuff pressures on the incidence of sore throat in children

BACKGROUND

Hyperinflation of laryngeal mask airway cuffs can cause harm to the upper airway mainly by exerting high pressures on pharyngeal and laryngeal structures thus impairing mucosal perfusion. Although cuff manometers can be used to guide the monitoring of cuff pressures, their use is not routine in many institutions. In a prospective audit, we assessed the incidence of sore throat following day-case-surgery in relation to the intracuff pressure within the laryngeal mask airway.

METHODS

Four hundred children (3-21 years) were consecutively included in this study. The laryngeal mask airway was inflated as deemed necessary by the attending anesthetist. Cuff pressures were measured using a calibrated cuff manometer (Portex Limited, Hythe, Kent, UK, 0-120 cm H2O, pressures exceeding the measurement range were set at 140 cm H2O for statistical purposes) at induction of anesthesia.

RESULTS

Forty-five children (11.25%) developed sore throat, 32 (8%) sore neck and 17 (4.25%) sore jaw. Of those that developed sore throat, 56.5% had cuff pressures exceeding >100 cm H2O. In contrast, when cuff pressures were <40 cm H2O, there were no episodes of sore throat, whilst there was only a 4.6% occurrence of sore throat if cuff pressures were between 40-60 cm H2O.

CONCLUSION

We have demonstrated that intra cuff pressure in laryngeal mask airways is closely related to the development of sore throat with higher pressures increasing its likelihood. Hence, cuff pressures should be measured routinely using a manometer to minimize the incidence of sore throat.

The effects of head flexion on airway seal, quality of ventilation and orogastric tube placement using the ProSeal laryngeal mask airway

This prospective self-controlled study was designed to evaluate the influences of head flexion on airway seal, quality of ventilation, and orogastric tube placement through the ProSeal laryngeal mask airway (ProSeal LMA) in 80 anaesthetised, paralysed adult patients. After the ProSeal LMA was inserted and the cuff pressure was set at 5.9 kPa, ventilation quality, airway seal pressure, fibreoptic positions of the cuff and the drainage tube, orogastric tube placement and efficacy of intermittent positive pressure ventilation (IPPV) were assessed in two randomly selected positions: neutral and flexed position. When compared to the neutral head position, the head flexed significantly improved the airway seal pressure and the quality of ventilation of the ProSeal LMA (p < 0.05). Fibreoptic scores of the cuff position did not correlate with either the ability to obtain excellent or adequate ventilation through the ProSeal LMA or the ability to generate an airway seal pressure of >or= 2 kPa. Orogastric tube placement via the drainage tube was successful on the first attempt in all patients in the neutral position compared with seven failures following three attempts in the flexed position (p < 0.05). There were no significant differences between the two head positions in the volume of air required to obtain an intracuff pressure of 5.9 kPa, fibreoptic score of the drainage tube position, and expiratory tidal volume and peak inspiratory pressure during IPPV (p > 0.05). In conclusion, head flexion improves airway seal and ventilation quality of the ProSeal LMA. However, placement of an orogastric tube via the drainage tube is impaired in the flexed position compared to the neutral position. Fibreoptic scoring of the ProSeal cuff position is not an accurate test to assess the airway seal and ventilation function.

Vergleich von zwei Larynxmaskenmodellen zur Atemwegssicherung bei Patienten mit Immobilisation der Halswirbelsäule

BACKGROUND

Reduced cervical spine mobility can impair laryngoscopy and tracheal intubation. Supraglottic airway devices can be important alternatives for oxygenation under these circumstances. The Ambu laryngeal mask (ALM) and the LMA-Classic (LMA) are compared in patients with immobilization of the cervical spine.

METHODS

In 60 patients scheduled for elective ambulatory interventions, ALM or LMA were inserted after cervical immobilization with an extrication collar and assessment of laryngoscopic view. Insertion time (removal of facemask until first tidal volume), number of insertion attempts, airway leak pressure (cuff pressure 60 cm H(2)O), intraoperative complications and postoperative complaints were assessed.

RESULTS

Demographical data, insertion attempts, insertion time (ALM 15.6+/-4.4 s, LMA 15.5+/-4.9 s) and airway leak pressure (ALM 25.6+/-5.2 cm H(2)O, LMA 26.5+/-6.5 cm H(2)O) were comparable. Traces of blood were found in 6 LMAs and 3 ALMs after removal, mild trouble with swallowing (visual analogue scale, VAS 2-4) in the recovery room and after 24 h were complaints by 1 ALM and 2 LMA patients.

CONCLUSIONS

LMA-Classic and Ambu laryngeal masks are suitable for rapid and reliable airway management in patients with cervical immobilization.

A Multicenter Study of the Ambu?? Laryngeal Mask in Nonparalyzed, Anesthetized Patients

We designed this multicenter trial to evaluate the performance and safety of the Ambu laryngeal mask, a new disposable supraglottic airway device, in patients scheduled for elective surgery. One-hundred-eighteen nonparalyzed, anesthetized patients (ASA physical status I-II, age, 18-65 yr, body mass index, 18-30 kg/m(-2)) receiving total IV anesthesia were included in this study. After device insertion, fiberoptic position and oropharyngeal leak pressure were determined at an intracuff pressure of 60 cm H2O. Ease of ventilation was determined by controlling ventilation at 6 mL/kg tidal volume. Any complications were noted and recorded. Device placement was successful in all patients on the first or second attempt (92.4% or 7.6%, respectively) with an insertion time (removal of face mask until first tidal volume) of 44.9 +/- 37.91 s. Adequate ventilation was achieved in all patients and the vocal cords could be visualized by fiberoptic endoscopy in 91.5% of patients. Oropharyngeal leak pressures were 24.1 +/- 5.44 cm H2O. Blood was detected on the device in 8.5% of patients. Complications and patient complaints were minor and quickly resolved. The Ambu laryngeal mask is easy and quick to insert and provides a safe and efficient seal during positive pressure ventilation in nonparalyzed patients scheduled for elective surgery.

Cricoid yoke: the effect of surface area and applied force on discomfort experienced by conscious volunteers

BACKGROUND AND OBJECTIVE

The application of cricoid force is central to techniques that reduce the risk of gastric regurgitation and the subsequent pulmonary aspiration associated with obstetric and emergency anaesthesia. The discomfort associated with cricoid force in awake preoperative patients increases the incidence of coughing, struggling and pain during induction of anaesthesia. This study determined if increasing the surface area of a cricoid yoke reduced the associated discomfort in volunteers.

METHODS

Fifty volunteers participated in a randomized single-blinded study. The cricoid yoke was positioned using standard anatomical landmarks and forces of 10, 20, 30 and 40 N were applied in a random order for 20s, using two different yoke attachments with surface areas of 3 and 10 cm2. A rest of 30s was allowed between the application of forces. Discomfort was graded by volunteers on a scale from 0 to 10 (0: no discomfort; 10: worse discomfort imaginable). A score of 10 was allocated if the volunteers could not tolerate the applied force for 20s.

RESULTS

Median scores for the small yoke were always higher than those for the large yoke at each force. There were significant differences between the scores for the small and large yokes at 10 and 20 N (P < 0.001) and 30 N (P = 0.0233), but there was no significant difference at 40 N.

CONCLUSIONS

The larger yoke was tolerated better by volunteers when clinically relevant cricoid forces were applied.

Tracheal intubation without muscle relaxants: remifentanil or alfentanil in combination with propofol

BACKGROUND AND OBJECTIVE

In some situations, the use of muscle relaxants (neuromuscular blocking drugs) are undesirable or contraindicated. We compared intubating conditions without muscle relaxants in premedicated patients receiving either alfentanil 40 microg kg(-1) or remifentanil 2, 3 or 4 microg kg(-1) followed by propofol 2 mg kg(-1).

METHODS

In a randomized, double-blind study, 80 healthy patients were assigned to one of four groups (n = 20). After intravenous atropine, alfentanil 40 microg kg(-1) or remifentanil 2, 3 or 4 microg kg(-1) were injected over 90 s followed by propofol 2 mg kg(-1). Ninety seconds after administration of the propofol, laryngoscopy and tracheal intubation were attempted. Intubating conditions were assessed as excellent, good or poor on the basis of ease of lung ventilation, jaw relaxation, laryngoscopy, position of the vocal cords, and patient response to intubation and slow inflation of the endotracheal tube cuff.

RESULTS

Seven patients who received remifentanil 2 microg kg(-1) and one patient who received remifentanil 3 microg kg(-1) could not be intubated at the first attempts. Excellent intubating conditions (jaw relaxed, vocal cords open and no movement in response to tracheal intubation and cuff inflation) were observed in those who received either alfentanil 40 microg kg(-1) (45% of patients) or remifentanil in doses of 2 microg kg(-1) (20%), 3 microg kg(-1) (75%) or 4 microg kg(-1) (95%). Overall, intubating conditions were significantly better (P < 0.05), and the number of patients showing excellent conditions were significantly higher (P < 0.05) in patients who received remifentanil 4 microg kg(-1) compared with those who received alfentanil 40 microg kg(-1) or remifentanil 2 microg kg(-1). No patient needed treatment for hypotension or bradycardia.

CONCLUSIONS

Remifentanil 4 microg kg(-1) and propofol 2 mg kg(-1) administered in sequence intravenously provided good or excellent conditions for tracheal intubation in all patients without the use of muscle relaxants.

Stability of the LMA-ProSeal and standard laryngeal mask airway in different head and neck positions: a randomized crossover study

BACKGROUND AND OBJECTIVE

The LMA-ProSeal laryngeal mask airway is a new laryngeal mask airway with a modified cuff and drainage tube. We compared oropharyngeal leak pressure, intracuff pressure and anatomical position (assessed fibreoptically) for the Size 5 LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway in different head-neck positions and using different intracuff inflation volumes.

METHODS

Thirty paralysed anaesthetized adult male patients were studied. The LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway were inserted into each patient in random order. The oropharyngeal leak pressure, intracuff pressure, and anatomical position of the airway tube and drainage tube (LMA-ProSeal laryngeal mask airway only) were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order), and at 0-40 mL cuff volumes in the neutral position in 10 mL increments.

RESULTS

Compared with the neutral position, the oropharyngeal leak pressure for both the LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway was higher in flexion and rotation (all P < or = 0.02), but lower in extension (all P < or = 0.01). Changes in head-neck position did not alter the anatomical position of the airway tube or the drainage tube. The oropharyngeal leak pressure was always higher for the LMA-ProSeal laryngeal mask airway (all P < or = 0.005) and anatomical position better for the classic laryngeal mask airway (all P < or = 0.04).

CONCLUSIONS

The anatomical position of the LMA-ProSeal and the classic laryngeal mask airway is stable in different head-neck positions, but head-neck flexion and rotation are associated with an increase, and head-neck extension a decrease, in oropharyngeal leak pressure and intracuff pressure. The Size 5 LMA-ProSeal laryngeal mask airway is capable of forming a more effective seal than the Size 5 classic laryngeal mask airway in males.

Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

BACKGROUND AND OBJECTIVE

Automatic tube compensation has been designed as a new ventilatory mode to compensate for the non-linear resistance of the endotracheal tube. The study investigated the effects of automatic tube compensation compared with breathing through a T-piece or pressure support during a trial of spontaneous breathing used for weaning patients from mechanical ventilation of the lungs.

METHODS

Twelve patients were studied who were ready for weaning after prolonged mechanical ventilation (10.2 +/- 8.4 days) due to acute respiratory failure. Patients with chronic obstructive pulmonary disease were excluded. Thirty minutes of automatic tube compensation were compared with 30 min periods of 7 cmH2O pressure support and T-piece breathing. Breathing patterns and workload indices were measured at the end of each study period.

RESULTS

During T-piece breathing, the peak inspiratory flow rate (0.65 +/- 0.20 L s(-1)) and minute ventilation (8.9 +/- 2.7L min(-1)) were lower than during either pressure support (peak inspiratory flow rate 0.81 +/- 0.25 L s(-1) minute ventilation 10.2 +/- 2.3 L min(-1), respectively) or automatic tube compensation (peak inspiratory flow rate 0.75 +/- 0.26L s(-1); minute ventilation 10.8 +/- 2.7 L min(-1)). The pressure-time product as well as patients' work of breathing were comparable during automatic tube compensation (pressure-time product 214.5 +/- 104.6 cmH2O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L(-1)) and T-piece breathing (pressure-time product 208.3 +/- 121.6 cmH2O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L(-1)), whereas pressure support resulted in a significant decrease in workload indices (pressure-time product 121.2 +/- 64.1 cmH2O s(-1) min(-1), patient work of breathing 0.7 +/- 0.4 J L(-1)).

CONCLUSIONS

In weaning from mechanical lung ventilation, patients' work of breathing during spontaneous breathing trials is clearly reduced by the application of pressure support 7 cmH2O, whereas the workload during automatic tube compensation corresponded closely to the values during trials of breathing through a T-piece.

Anaesthetic agents in adult day case surgery

This study reports a review of all comparative published studies of adult day case anaesthesia in the English language up to December 2000. Ten databases were searched using appropriate keywords and data were extracted in a standardized fashion. One hundred-and-one published studies were examined. Recovery measurements were grouped as early, intermediate, late, psychomotor and adverse effects. With respect to induction of anaesthesia, propofol was superior to methohexital, etomidate and thiopental, but equal to sevoflurane and desflurane. Desflurane and sevoflurane were both superior to thiopental. There was no detectable difference between sevoflurane and isoflurane. With respect to the maintenance of anaesthesia, isoflurane and halothane were the worst. There were no significant differences between propofol, desflurane, sevoflurane and enflurane. Propofol is the induction agent of choice in day case patients. The use of a propofol infusion and avoidance of nitrous oxide may help to reduce postoperative nausea and vomiting.

Prediction of difficult tracheal intubation

BACKGROUND AND OBJECTIVE

Preoperative bedside screening tests for difficult tracheal intubation may be neither sensitive nor specific enough for clinical use. The aim was to investigate if a combination of the Mallampati classification of the oropharyngeal view with either the thyromental or sternomental distance measurement improved the predictive value.

METHODS

A total of 212 (109 male, 103 female) non-obstetric surgical patients, aged >18 yr, undergoing elective surgical procedures requiring tracheal intubation were assessed preoperatively with respect to the oropharyngeal (modified Mallampati) classification, thyromental and sternomental distances. An experienced anaesthetist, blinded to the preoperative airway assessment, performed laryngoscopy and graded the view according to Cormack and Lehane's classification.

RESULTS

Twenty tracheal intubations (9%) were difficult as defined by a Cormack and Lehane Grade 3 or 4, or the requirement for a bougie in patients with Cormack and Lehane Grade 2. Used alone, the Mallampati oropharyngeal view, and thyromental and sternomental distances were associated with poor sensitivity, specificity and positive predictive values. Combining the Mallampati Class III or IV with either a thyromental distance <6.5cm or a sternomental distance <12.5cm decreased the sensitivity (from 40 to 25 and 20%, respectively), but maintained a negative predictive value of 93%. The specificity and positive predictive values increased from 89 and 27% respectively for Mallampati alone to 100%.

CONCLUSIONS

The findings suggest that the Mallampati classification, in conjunction with measurement of the thyromental and sternomental distances, may be a useful routine screening test for preoperative prediction of difficult tracheal intubation.

Remifentanil versus alfentanil in total intravenous anaesthesia for day case surgery

BACKGROUND AND OBJECTIVE

We assessed the intraoperative haemodynamic responses and recovery profiles of total intravenous anaesthesia with remifentanil and alfentanil for outpatient surgery.

METHODS

Patients in Group 1 (n = 20) received alfentanil 20 microg kg(-1) followed by 2 microg kg(-1) min(-1) intravenously; patients in Group 2 (n = 20) received remifentanil 1 microg kg(-1) followed by 0.5 microg kg(-1) min(-1) intravenously. Both groups then received propofol 2 mg kg(-1) followed by 9 mg kg(-1) h(-1) intravenously. Five minutes after skin incision, infusion rates were decreased, and at the end of surgery, all infusions were discontinued. Early recovery was assessed by the Aldrete score, whereas intermediate recovery was assessed with the postanaesthetic discharge scoring system (PADS).

RESULTS

Perioperative arterial pressure was similar in both groups; heart rate was lower in Group 2 (P < 0.05). The times to spontaneous and adequate respiration, response to verbal commands, extubation and times for Aldrete score > or = 9 were shorter in Group 2 patients (P < 0.05). Pain scores were higher in Group 2 patients (P < 0.05). Overall times for postanaesthetic discharge scores > or = 9 were similar.

CONCLUSIONS

Early recovery of patients after day surgery is significantly shorter after total intravenous anaesthesia with remifentanil compared with that with alfentanil but postoperative pain management must be planned ahead.

Effects of different doses of oral ketamine for premedication of children

BACKGROUND AND OBJECTIVE

A need exists for a safe and effective oral preanaesthetic medication for use in children undergoing elective surgery. The study sought to define the dose of oral ketamine that would facilitate induction of anaesthesia without causing significant side-effects.

METHODS

We studied 80 children undergoing elective surgery under general anaesthesia who received oral ketamine 4, 6 or 8 mg kg(-1) in a prospective, randomized, double-blind placebo controlled study. We compared the reaction to separation from parents, transport to the operating room, the response to intravenous cannula insertion and application of an anaesthetic facemask, the induction of anaesthesia and recovery from anaesthesia.

RESULTS

In the group receiving ketamine 8 mg kg(-1), the children were significantly calmer than those of the other groups, and anaesthesia induction was more comfortable. Recovery from anaesthesia was longer in the group receiving ketamine 8 mg kg(-1) compared with the other groups, but no differences between the groups were observed after 2 h in the recovery room.

CONCLUSIONS

It is concluded that oral ketamine 8 mg kg(-1) is an effective oral premedication in inpatient children undergoing elective surgery.

Trendelenburg positioning after cardiac surgery: effects on intrathoracic blood volume index and cardiac performance

BACKGROUND AND OBJECTIVE

The efficacy of the Trendelenburg position, a common first step to treat suspected hypovolaemia, remains controversial. We evaluated its haemodynamic effects on cardiac preload and performance in patients after cardiac surgery.

METHODS

Twelve patients undergoing mechanical ventilation of the lungs who demonstrated left ventricular 'kissing papillary muscles' by transoesophageal echocardiography, thus suggesting hypovolaemia, were positioned 30 degrees head down for 15 min immediately after cardiac surgery. Cardiac output by thermodilution, central venous pressure, pulmonary artery occlusion pressure, left ventricular end-diastolic area by transoesophageal echocardiography and intrathoracic blood volume by thermo- and dye dilution were determined before, during and after this Trendelenburg manoeuvre.

RESULTS

Trendelenburg's manoeuvre was associated with increases in central venous pressure (9 +/- 2 to 12 +/- 3 mmHg) and pulmonary artery occlusion pressure (8 +/- 2 to 11 +/- 3 mmHg). The intrathoracic blood volume index increased slightly (dye dilution from 836 +/- 129 to 872 +/- 112 mL m(-2); thermodilution from 823 +/- 129 to 850 +/- 131 mL m(-2)) as did the left ventricular end-diastolic area index (7.5 +/- 2.1 to 8.1 +/- 1.7 cm2 m(-2)), whereas mean arterial pressure and the cardiac index did not change significantly. After supine repositioning, the cardiac index decreased significantly below baseline (3.0 +/- 0.6 versus 3.5 +/- 0.8 L min(-1) m(-2)) as did mean arterial pressure (76 +/- 12 versus 85 +/- 11 mmHg), central venous pressure (8 +/- 2 mmHg) and pulmonary artery occlusion pressure (6 +/- 4 mmHg). The intrathoracic blood volume index and left ventricular end-diastolic area index did not differ significantly from baseline.

CONCLUSIONS

Trendelenburg's manoeuvre caused only a slight increase of preload volume, despite marked increases in cardiac-filling pressures, without significantly improving cardiac performance.

Anaesthetic and haemodynamic effects of continuous spinal versus continuous epidural anaesthesia with prilocaine

BACKGROUND AND OBJECTIVE

To compare, using prilocaine, the effects of continuous spinal anaesthesia (CSA) and continuous epidural anaesthesia (CEA) on haemodynamic stability as well as the quality of anaesthesia and recovery in patients undergoing transurethral resection of the prostate gland.

METHODS

Thirty patients (>60 yr) were randomized into two groups. Prilocaine, 2% 40 mg, was given to patients in the CSA group, and prilocaine 1% 150mg was given to patients in the CEA group. Incremental doses were given if the level of sensory block was lower than T10 or if needed during surgery.

RESULTS

There was a significant decrease in mean arterial pressure in Group CEA compared with Group CSA (P < 0.01). The decrease in heart rate in Group CSA occurred 10 min after the first local anaesthetic administration and continued through the operation (P < 0.05). The level of sensory anaesthesia was similar in both groups. The times to reach the level of T10 and the upper level of sensory blockade (Tmax) were 18.0 +/- 4.7 and 25.3 +/- 7.0 min in Groups CSA and CEA, respectively, and were significantly longer in Group CEA. The duration of anaesthesia was 76.8 +/- 4min and was shorter in Group CSA (P < 0.01).

CONCLUSIONS

Spinal or epidural anaesthesia administered continuously was reliable in elderly patients undergoing transurethral resection of the prostate. Continuous spinal anaesthesia had a more rapid onset of action, produced more effective sensory and motor blockade and had a shorter recovery period. Prilocaine appeared to be a safe local anaesthetic for use with either continuous spinal anaesthesia or continuous epidural anaesthesia.

Cortical activity assessed by Narcotrend in relation to haemodynamic responses to tracheal intubation at different stages of cortical suppression and reflex control

BACKGROUND AND OBJECTIVE

Many anaesthesiologists still interpret haemodynamic responses as signs of insufficient cortical suppression. The aim was to illustrate how haemodynamics may only poorly reflect the level of cortical suppression and that electroencephalographic monitoring could indicate different relationships between cortical effects and haemodynamics.

METHODS

Anaesthesia was induced with thiopental (7 mg kg(-1)), and fentanyl (2 microg kg(-1)) with succinylcholine (1.5 mg kg(-1)) for neuromuscular blockade in the 11 patients of Group 1. In Group 2 (n = 15), thiopental (7 mg kg(-1)) and succinylcholine (1.5 mg kg(-1)) were given. In Group 3, the patients (n = 13) received thiopental (7 mg kg(-1)), fentanyl (2 microg kg(-1)) and cisatracurium (0.1 mg kg(-1)), and they were intubated 3 min later than the patients in Groups 1 and 2. We determined conventional electroencephalographic (EEG) variables and classified 14 EEG stages in real-time ranging from A (= 1), indicating full wakefulness, to F1 (= 14), at profound cortical suppression.

RESULTS

All groups had profound cortical suppression 45 s after thiopental administration, which rapidly decreased (EEG stage, 11 (6-13) versus 7 (2-13) at 4 min, P < 0.0001). Decreasing EEG stages were associated with increasing SEF 95, relative alpha and beta power and decreasing relative delta power. During tracheal intubation, profound cortical suppression remained unchanged in Groups 1 and 2. In Group 3, cortical suppression had decreased before laryngoscopy (P < 0.005). In Group 2, 11 patients had heart rate responses to tracheal intubation, whereas only two responded in Group 1 (P = 0.015) and three in Group 3 (P = 0.02). Thirteen patients in Group 2 had arterial pressure responses, and five in Group 1 (P = 0.038). Circulatory responses did not differ between Groups 1 and 3.

CONCLUSIONS

Electroencephalographic monitoring was suitable to indicate in real-time that haemodynamics only poorly reflect rapidly changing levels of cortical suppression, and how haemodynamics and cortical activity depend on the applied combination of hypnotic and analgesic drugs during anaesthesia induction with thiopental.

Increasing the injection volume by dilution improves the onset of motor blockade, but not sensory blockade of ropivacaine for brachial plexus block

BACKGROUND AND OBJECTIVE

Ropivacaine used for axillary plexus block provides effective motor and sensory blockade. Varying clinical dosage recommendations exist. Increasing the dosage by increasing the concentration showed no improvement in onset. We compared the behaviour of a constant dose of ropivacaine 150 mg diluted in a 30, 40 or 60 mL injection volume for axillary (brachial) plexus block.

METHODS

A prospective, randomized, observer-blinded study on patients undergoing elective hand surgery was conducted in a community hospital. Three groups of patients with a constant dose of ropivacaine 150 mg, diluted in 30,40 or 60 mL NaCl 0.9%, for axillary plexus blockade were compared for onset times of motor and sensory block onset by assessing muscle strength, two-point discrimination and constant-touch sensation.

RESULTS

Increasing the injection volume of ropivacaine 150 mg to 60 mL led to a faster onset of motor block, but not of sensory block, in axillary plexus block, compared with 30 or 40 mL volumes of injection.

CONCLUSIONS

The data show that the onset of motor, but not of sensory block, is accelerated by increasing the injection volume to 60 mL using ropivacaine 150 mg for axillary plexus block. This may be useful for a more rapid determination of whether the brachial plexus block is effective. However, when performing surgery in the area of the block, sensory block onset seems more important.

Laryngeal mask vs intubating laryngeal mask: insertion and ventilation by inexperienced resuscitators

The laryngeal mask airway (LMA) has been shown to be useful in airway maintenance during resuscitation. The intubating laryngeal mask (ILM) is a modified LMA permitting both ventilation and rapid endotracheal intubation. We aimed to compare the LMA and the ILM with regard to ease of insertion and successful ventilation by inexperienced personnel. We have used anaesthetized, apnoeic, non-paralysed patients as a model to simulate resuscitation. Following standardized training, non-anaesthetic medical staff with no previous experience in laryngeal mask airway insertion (novices) inserted either the LMA or ILM in 55 patients following induction of anaesthesia. There were no differences between the two patient groups included in our study with regard to mean age and body mass index (BMI). The success rate for inserting the airway device and achieving a significant end-tidal CO2 recording within two minutes was 23/28 for the LMA (82.1%) and 22/27 for the ILM (81.5%). Reasons for failure included inability to insert the ILM past the teeth and insertion of the LMA upside down. There were no clinically relevant differences in the mean time to airway insertion and successful ventilation (62.6 vs 62 seconds) or expired tidal volume (781 vs 767 ml) for the LMA and ILM respectively. We conclude that the ILM is as easily inserted and effectively used as an LMA by novices and, because it allows the option offacilitating endotracheal intubation, may be the preferred device for maintaining an airway during resuscitation.