Use of heliox in critical upper airway obstruction. Physical and physiologic considerations in choosing the optimal helium:oxygen mix

Helium-oxygen mixture: clinical applicability in an intensive care unit

Objective

To evaluate if distress respiratory decreases after using helium-oxygen mixture in pediatric patients diagnosed with bronchospasm.

Methods

This is a retrospective, non-randomized study that included patients diagnosed with bronchospasm, who received a helium-oxygen mixture at three time points (30, 60, and 120 minutes) according to the organization protocol singular, and were admitted to the intensive care unit, from January 2012 to December 2013. This protocol includes patients with bronchospasm who sustained a modified Wood score of moderate to severe, even after one hour of conventional treatment.

Results

Twenty children were included in the study. The mean score of severity of the disease at the initial moment was 5.6 (SD:2.0), and at moment 120 minutes, it was 3.4 (SD: 2.0). The severity score showed a significant improvement as of 30 minutes (p<0.001).

Conclusion

The use of helium-oxygen mixture proved to be effective in diminishing the respiratory distress score for children with airway obstructions; it should be considered a supplementary therapeutic option, together with drug therapy, in specific clinical situations.

Evaluation of lung function and deposition of aerosolized bronchodilators carried by heliox associated with positive expiratory pressure in stable asthmatics: a randomized clinical trial

While administration of medical aerosols with heliox and positive airway pressure are both used clinically to improve aerosol delivery, few studies have differentiated their separate roles in treatment of asthmatics. The aim of this randomized, double blinded study is to differentiate the effect of heliox and oxygen with and without positive expiratory pressure (PEP), on delivery of radiotagged inhaled bronchodilators on pulmonary function and deposition in asthmatics. 32 patients between 18 and 65 years of age diagnosed with stable moderate to severe asthma were randomly assigned into four groups: (1) Heliox + PEP (n = 6), (2) Oxygen + PEP (n = 6), (3) Heliox (n = 11) and (4) Oxygen without PEP (n = 9). Each group received 1 mg of fenoterol and 2 mg of ipratropium bromide combined with 25 mCi (955 Mbq) of Technetium-99m and 0.9% saline to a total dose volume of 3 mL placed in a Venticis II nebulizer attached to a closed, valved mask with PEP of 0 or 10 cm H2O. Both gas type and PEP level were blinded to the investigators. Images were acquired with a single-head scintillation camera with the longitudinal and transverse division of the right lung as regions of interest (ROIs). While all groups responded to bronchodilators, only group 1 showed increase in FEV1%predicted and IC compared to the other groups (p < 0.04). When evaluating the ROI in the vertical gradient we observed higher deposition in the middle and lower third in groups 1 (p = 0.02) and 2 (p = 0.01) compared to group 3. In the horizontal gradient, a higher deposition in the central region in groups 1 (p = 0.03) and 2 (p = 0.02) compared to group 3 and intermediate region of group 2 compared to group 3. We conclude that aerosol deposition was higher in groups with PEP independent of gas used, while bronchodilator response with Heliox + PEP improved FEV1 % and IC compared to administration with Oxygen, Oxygen with PEP and Heliox alone. Trial registration NCT01268462.

Difficult Airway Society Guidelines for the management of tracheal extubation

Tracheal extubation is a high-risk phase of anaesthesia. The majority of problems that occur during extubation and emergence are of a minor nature, but a small and significant number may result in injury or death. The need for a strategy incorporating extubation is mentioned in several international airway management guidelines, but the subject is not discussed in detail, and the emphasis has been on extubation of the patient with a difficult airway. The Difficult Airway Society has developed guidelines for the safe management of tracheal extubation in adult peri-operative practice. The guidelines discuss the problems arising during extubation and recovery and promote a strategic, stepwise approach to extubation. They emphasise the importance of planning and preparation, and include practical techniques for use in clinical practice and recommendations for post-extubation care.

[Heliox-driven bronchodilator nebulization in the treatment of infants with bronchiolitis]

INTRODUCTION

Heliox is a helium-oxygen mixture which improves laminar flow and decreases airway resistance and the work of breathing. The aim of this study was to assess the effects of salbutamol or epinephrine nebulization driven by heliox in infants with moderate-to-severe bronchiolitis.

MATERIALS AND METHODS

This prospective, observational, interventional, controlled and randomized study included ninety-six children who came to our pediatric emergency department with first episode of moderate-to-severe bronchiolitis. The patients were randomized to receive salbutamol or epinephrine nebulized with either oxygen (control group) or heliox (70% helium and 30% oxygen) as the driving gas. Heart rate, respiratory rate, pulse oximetry oxygen saturation and clinical score were measured before and after the treatment period. We also reported hospitalization rates and the number of patients who returned to the emergency department in the following seventy two hours.

RESULTS

There were no significant differences between both groups. The only statistically significant difference was that, in the heliox group, patients with severe bronchiolitis needed a lower number of nebulizations than infants in the control group.

CONCLUSIONS

According to our study, heliox-driven salbutamol or epinephrine is not an effective therapy in patients with acute bronchiolitis.

Anesthetic considerations for airway stenting in adult patients

The attributable morbidity from central airway obstruction is significant. Airway stenting provides a therapeutic option to manage these complex lesions. This article focuses on the relevant anesthetic considerations of airway stenting in adult patients.

Clinical review: use of helium-oxygen in critically ill patients

Use of helium-oxygen (He/O₂) mixtures in critically ill patients is supported by a reliable and well understood theoretical rationale and by numerous experimental observations. Breathing He/O₂ can benefit critically ill patients with severe respiratory compromise mainly by reducing airway resistance in obstructive syndromes such as acute asthma and decompensated chronic obstructive pulmonary disease. However, the benefit from He/O₂ in terms of respiratory mechanics diminishes rapidly with increasing oxygen concentration in the gaseous mixture. Safe use of He/O₂ in the intensive care unit requires specific equipment and supervision by adequately experienced personnel. The available clinical data on inhaled He/O₂ mixtures are insufficient to prove that this therapy has benefit with respect to outcome variables. For these reasons, He/O₂ is not currently a standard of care in critically ill patients with acute obstructive syndromes, apart from in some, well defined situations. Its role in critically ill patients must be more precisely defined if we are to identify those patients who could benefit from this therapeutic approach.

Eficacia del tratamiento con heliox en niños con insuficiencia respiratoria

OBJECTIVE

To analyze response to heliox therapy in critically ill infants and children with upper and/or lower airway respiratory insufficiency.

PATIENTS AND METHODS

Sixty-five patients, aged between 12 days and 8 years old, treated with heliox through facial mask, nasal prongs or non-invasive ventilation were studied. Diagnoses were bronchiolitis (25), upper postextubation respiratory insufficiency (19), respiratory insufficiency after airway surgery (14), and croup-laryngotracheomalacia (7). Response to heliox treatment was measured by the change in clinical scores, respiratory rate, heart rate, pulse oximetry, blood gas analysis, and the need for non-invasive and invasive mechanical ventilation.

RESULTS

Fifty-four patients (83.1 %) improved after heliox therapy, with statistically significant differences in clinical score (from 8.7 to 5.5), respiratory rate (from 51.4 to 38.8 rpm), and heart rate (from 161.6 to 145.6 bpm). No changes were observed in saturation or blood gas analysis. After heliox therapy, 29.8 % of patients required non-invasive ventilation and 26.5 % required intubation. Patients with bronchiolitis and those aged less than 1 year had a lesser response to heliox therapy and more frequently required non-invasive ventilation. No significant differences were found in intubation requirements. No adverse effects were observed.

CONCLUSIONS

Heliox therapy improved clinical scores in infants and children with upper and lower airway respiratory insufficiency, but a significant percentage of patients needed non-invasive or invasive mechanical ventilation.

Room air entrainment during beta-agonist delivery with heliox

Studies of the efficacy of heliox in patients with severe asthma have shown mixed results. Among the factors that are responsible for variable outcomes, the failure of heliox delivery systems to prevent room air entrainment (RAE) during beta-agonist delivery is probably the most critical. While keeping the rotameter flow rate (FR) of heliox mixed 70:30 to a nebulizer at 10 L/min, the FR of heliox from a second gas source to a T-connector (TC) was increased during the delivery of the beta-agonist with a conventional T-nebulizer delivery system (TNDS). A negative peak inspiratory flow (pneumotachometer reading) or a helium concentration of < 70% (quadralizer reading) were indicators of RAE. RAE was tested during spontaneous tidal breathing and acute asthma. A rotameter FR of 10 L/m to the nebulizer with no flow from a second gas source to a TC (conventional TNDS) resulted in a significant drop in helium concentration during tidal breathing (46.2%) and acute asthma (27.5%) due to RAE. This degree of helium dilution can negate the beneficial effects of heliox to lung mechanics almost completely. A rotameter FR of 10 L/m each to a nebulizer and a TC resulted in a helium concentration 69.8% during tidal breathing (no RAE), but 49% (significant RAE) during asthma events. A rotameter FR of 15 L/m (pressure regulator setting, 100 lbs per square inch) to a TC, while maintaining a rotameter FR of 10 L/m to a nebulizer prevented RAE during asthma (helium concentration, 69.9%). Conventional TNDS may be used to deliver the beta-agonist with heliox during asthma without RAE.

Accuracy of central venous pressure monitoring during simultaneous continuous infusion through the same catheter

Continuous central pressure monitoring and simultaneous continuous infusion via the same central venous catheter are sometimes necessary. Based on theoretical calculations and experimental measurements, we have determined that pressure monitoring is essentially unaffected if the continuous infusion rate is 50 ml.h(-1) or less for an adult and a paediatric central catheter. At rates > 200 ml.h(-1), the central venous pressure is exaggerated by up to 4 mmHg and 8 mmHg for the adult and paediatric catheters, respectively.

New Anesthesia Techniques

Advances in anesthesia involve refinements in understanding, technique, and technology. These refinements have led to better control of the anesthetic state, effective anesthesia for a wider variety of situations, and the ability to bring sicker patients to the operating room. Although the molecular mechanisms underlying the general anesthetic state are unknown, evidence suggests a specific, receptor-based effect. This concept has allowed anesthesiologists to treat anesthetic end points of immobility, lack of awareness, and autonomic control separately. It is likely that anesthesia and naturally occurring sleep interact physiologically. New, processed EEG monitors may allow anesthesiologists to titrate more finely anesthetic dose, with possible benefits in terms of speed of recovery and detection of intraoperative awareness. Since the 1990s, new anesthetic drugs (propofol, desflurane/sevoflurane, cisatracurium) have enhanced greatly control of the anesthetic state. The new intravenous anesthetic agent dexmedetomidine offers sedation with preserved respiration and cognitive function. Although its role has yet to be defined fully, it currently plays a role in ICU sedation and monitored anesthesia care. New anesthesia ventilators have better monitoring and better flow delivery at high airway pressures. These improvements significantly narrow the performance gap between anesthesia and ICU ventilators. In patients with COPD, pulmonary hypertension, or severe hypoxemia, heliox may improve gas flow, and NO may reduce pulmonary vascular resistance and improve oxygenation.

Development of Aerosol Drug Delivery with Helium Oxygen Gas Mixtures

Aerosol drug delivery using helium-oxygen gas mixtures (heliox) is considered in terms of flow physics, atomization, and aerosol mechanics. Theoretical considerations are then related to past studies of the physiological effects of the inhalation of heliox and its potential use as a drug delivery medium. Past clinical trials of heliox investigating this use are reviewed and technical recommendations made for its successful development. It is proposed that improved peripheral lung drug delivery with heliox is highly dependent on proper administration, especially the inclusion of proper reservoir system for the gas.

Total airway obstruction during local anesthesia in a non-sedated patient with a compromised airway

PURPOSE

To report a case of complete upper airway obstruction after topicalization with lidocaine in a completely conscious patient with partial upper airway obstruction.

CLINICAL FEATURES

A 69-yr-old man with a history of neck cancer and radiation presented for resection of recurrent neck tumour. No preoperative sedation was given. He had inspiratory and expiratory stridor but had no history of aspiration or swallowing problem. Phonation was distorted but effective. The surgeon was reluctant to perform an awake tracheostomy under local anesthesia. In preparation for a fibrescope-assisted orotracheal intubation, the non-sedated patient was given topical upper airway lidocaine during which he developed total airway obstruction and hypoxemia. He was immediately intubated with a fibrescope. His vocal cords were not edematous although the supraglottic structures appeared to be. The vocal cords were abducted and their movement was limited and not paradoxical. Tumour resection was uneventful upon successful tracheal intubation and general anesthesia. Tracheostomy at the end of the case was difficult, as expected. The patient tolerated the procedures and regained consciousness with no neurologic sequelae.

CONCLUSION

Dynamic airflow limitation associated with local anesthesia of the upper airway may lead to complete upper airway obstruction in a compromised airway. The main cause may be the loss of upper airway muscle tone, exacerbated by deep inspiration during panic.

The upper airway during anaesthesia

Upper airway obstruction is common during both anaesthesia and sleep. Obstruction is caused by loss of muscle tone present in the awake state. The velopharynx, a particularly narrow segment, is especially predisposed to obstruction in both states. Patients with a tendency to upper airway obstruction during sleep are vulnerable during anaesthesia and sedation. Loss of wakefulness is compounded by depression of airway muscle activity by the agents, and depression of the ability to arouse, so they cannot respond adequately to asphyxia. Identifying the patient at risk is vital. Previous anaesthetic history and investigations of the upper airway are helpful, and a history of upper airway compromise during sleep (snoring, obstructive apnoeas) should be sought. Beyond these, risk identification is essentially a search for factors that narrow the airway. These include obesity, maxillary hypoplasia, mandibular retrusion, bulbar muscle weakness and specific obstructive lesions such as nasal obstruction or adenotonsillar hypertrophy. Such abnormalities not only increase vulnerability to upper airway obstruction during sleep or anaesthesia, but also make intubation difficult. While problems with airway maintenance may be obviated during anaesthesia by the use of aids such as the laryngeal mask airway (LMA( dagger )), identification of risk and caution are keys to management, and the airway should be secured before anaesthesia where doubt exists. If tracheal intubation is needed, spontaneous breathing until intubation is an important principle. Every anaesthetist should have in mind a plan for failed intubation or, worse, failed ventilation.

Management of complications of tracheal surgery

Basic principles of tracheal reconstruction, which were introduced in the 1960s and 1970s, served to reduce the prevalence of many complications. These principles include thorough preoperative assessment (endoscopic and radiologic) of the tracheal anatomy and glottic function, avoidance of excessive anastomotic tension, preservation of tracheal blood supply, and meticulous dissection and anastomosis. The tracheal surgeon should have access to expert help in radiology and anesthesiology, experienced nursing units, and the help and advice of consultants, especially otolaryngologists. The surgical approach should be meticulously planned. No irreversible maneuvers should be performed until one establishes certainty to proceed to resection. The surgeon should not attempt to exceed the limits of what appears to be reasonably possible. It must be remembered that a permanent tracheal T-tube might be the best solution for a patient with extensive tracheal damage that would defy reconstruction.

Heliox vs air-oxygen mixtures for the treatment of patients with acute asthma: a systematic overview

OBJECTIVE

To evaluate, by systematic review, the efficacy of heliox on respiratory mechanics and outcomes in patients with acute asthma.

METHODS

The search strategy included searching electronic databases (MEDLINE, EMBASE, and The Cochrane Library) and the references of relevant articles. Study quality was assessed based on allocation concealment. Randomized controlled trials (RCTs) comparing heliox to an air-oxygen mixture (airO(2)) as an adjunct treatment in patients with acute asthmatic attacks were analyzed. For the qualitative portion of the analysis, all reports of the use of heliox in patients with acute asthma were included.

RESULTS

Four RCTs (n = 278) were found to have a common respiratory parameter (peak expiratory flow rate as a percentage of predicted) suitable for meta-analysis. Within the 92% confidence interval (CI), there was a small benefit with the use of heliox compared to airO(2) (weighted mean difference, + 3%; 95% CI, - 2 to + 8%). There was also a slight improvement in the dyspnea index (weighted mean difference, 0.60; 95% CI, 0.04 to 1.16) with the use of heliox over airO(2). Overall, five RCTs, one nonrandomized unblinded parallel trial, one retrospective case-matched control trial, three case series, and one case report had results in favor of heliox; one RCT and one case series showed no improvement with heliox; one RCT showed a possible detrimental effect with heliox; and 1 small RCT was inconclusive. Most investigators did not prevent entrainment of room air during heliox use or compensate for the lower nebulizing efficiency of heliox.

CONCLUSION

Based on surrogate markers, heliox may offer mild-to-moderate benefits in patients with acute asthma within the first hour of use, but its advantages become less apparent beyond 1 h, as most conventionally treated patients improve to similar levels, with or without it. The effect of heliox may be more pronounced in more severe cases. There are insufficient data on whether heliox can avert tracheal intubation, or change intensive care and hospital admission rates and duration, or mortality.