Helium-oxygen in treatment of upper airway obstruction

Evaluation of isoflurane and sevoflurane vaporizers over a wide range of oxygen flow rates

OBJECTIVE

To examine the accuracy and precision of isoflurane and sevoflurane anesthetic vaporizers.

SAMPLE POPULATION

5 identical isoflurane and 5 identical sevoflurane vaporizers.

PROCEDURES

Oxygen flow rates from 0.02 to 10 L/min were used with different vaporizer dial settings. Agent concentrations were measured at the common gas outlet by use of a refractometer. Accuracy was defined as the difference between measured agent concentrations, and dial settings were expressed as a percentage of the applied dial settings. Precision was defined as SD of the measured agent concentrations for each combination of dial setting and flow.

RESULTS

Isoflurane values were generally greater than the dial settings. Accuracy of the isoflurane vaporizer was > 20% when 0.6% and 1% was dialed. Accuracy of the sevoflurane vaporizer was always within +/- 20% but decreased at 0.02 L/min flow and at combinations of high flow and high dial settings. Overall precision of the isoflurane vaporizer was better than that of the sevoflurane vaporizer.

CONCLUSIONS AND CLINICAL RELEVANCE

A possible explanation for the inaccuracy of the isoflurane vaporizer may be that it was manufactured to be accurate with air but not oxygen, which must be accounted for when using the vaporizer with oxygen, especially with nonrebreathing systems. The sevoflurane vaporizer may not deliver accurate agent concentrations at high flow and high dial settings. Both vaporizers are suitable for clinical use with a wide range of oxygen flow rates if these precautions are properly addressed.

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.

Heliox administration in the pediatric intensive care unit: an evidence-based review

OBJECTIVE

To provide a comprehensive, evidence-based review of helium-oxygen gas mixtures (heliox) in the management of pediatric respiratory diseases.

DATA SOURCE

A thorough, computerized bibliographic search of the preclinical and clinical literature regarding the properties of helium and its application in pediatric respiratory disease states.

DATA SYNTHESIS

After an overview of the potential benefits and technical aspects of helium-oxygen gas mixtures, the role of heliox is addressed for asthma, aerosolized medication delivery, upper airway obstruction, postextubation stridor, croup, bronchiolitis, and high-frequency ventilation. The available data are objectively classified based on the value of the therapy or intervention as determined by the study design from which the data are obtained.

CONCLUSIONS

Heliox administration is most effective during conditions involving density-dependent increases in airway resistance, especially when used early in an acute disease process. Any beneficial effect of heliox should become evident in a relatively short period of time. The medical literature supports the use of heliox to relieve respiratory distress, decrease the work of breathing, and improve gas exchange. No adverse effects of heliox have been reported. However, heliox must be administered with vigilance and continuous monitoring to avoid technical complications.

Patterns of helium-oxygen (heliox) usage in the critical care environment

The objective of this study was to describe the patterns of heliox use in critical care units of an academic medical center. The design was a prospective case series involving 7 critical care units of an academic medical center. All patients receiving heliox therapy over a 4-year period were studied, with prospective recording of patient demographics and the location, mode, indication for, and duration of heliox use. Use pattern comparisons based on anatomic location (upper vs lower airway) and age group (pediatric vs adult) were performed by alpha(2) analysis and unpaired Student t test. Eighty-nine patients, aged 17.4 +/- 20.9 years, received heliox for 30.5 +/- 44.6 hours on 92 occasions. Pediatric (</= 18 years) applications accounted for 72.8% of heliox use. Use was greater in frequency and scope during the final 2 study years, particularly in adults. Applications were split between upper airway (47%) and lower airway (53%) disorders. Airway manipulation was required in more adults (7/16) than in children (3/27) with upper airway obstruction (P < .05). The use patterns mirrored current literature emphases on postextubation stridor and asthma. This is the first description of heliox use patterns in the tertiary care critical care environment. Heliox use may be as dependent on practitioner experience as on published data. As a benign and relatively inexpensive therapy, heliox use should continue to be attractive, although ongoing study regarding efficacy in a number of settings is indicated.

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.

Usefulness of helium-oxygen mixtures in the treatment of mechanically ventilated patients

The density of helium is markedly lower than that of air or any of its components, leading to a substantial decrease in airway resistance to flow when it is inhaled. In mechanically ventilated patients with obstructive airway disease, replacing the usual air-oxygen mixture with helium-oxygen has been shown to reduce dynamic hyperinflation and intrinsic positive end-expiratory pressure; to decrease lung inflation pressures, respiratory acidosis, and work of breathing; and to improve arterial blood gases. Aerosol delivery to distal airways is enhanced with helium-oxygen. Preliminary data also suggest that the use of helium-oxygen could be a valuable approach to decrease postextubation respiratory distress. However, interference with ventilator function and added costs are two major disadvantages of helium-oxygen. Hence, before its widespread use in mechanically ventilated patients can be recommended, studies are needed to determine whether these favorable short-term effects can influence patient outcome.

Mechanical ventilation during pregnancy using a helium-oxygen mixture in a patient with respiratory failure due to status asthmaticus

The authors present a 15-year-old with a second trimester intrauterine pregnancy who developed respiratory failure as the result of status asthmaticus and the development of the adult respiratory distress syndrome. Mechanical ventilation was provided with a combination of oxygen and helium to facilitate gas exchange and limit peak inflating pressures. The physiologic basis for helium's potential beneficial effects on gas exchange are reviewed. Previous reports concerning the use of helium during mechanical ventilation as well as the techniques of delivery are discussed.

Safety and efficacy of heliox as a treatment for upper airway obstruction due to radiation-induced laryngeal dysfunction

The mixture of helium and oxygen, called heliox, has been successfully used in the management of different respiratory diseases since 1935. Despite several reports on its usefulness, it is not widely available in acute care facilities and it remains somewhat controversial. In this article we present the case of a 69-year-old woman in whom bilateral vocal cord paralysis developed after radiation therapy and in whom heliox was successfully used to manage her upper airway obstruction. Although heliox offers an additional tool in the treatment of various airway and pulmonary problems, it can be used only as a temporizing agent to allow time for appropriate therapy of the underlying process. Given its beneficial physiologic and clinical effects, it seems that further studies are warranted to define a clear and concise protocol for its use in the emergency setting.

Techniques to avoid intubation: noninvasive positive pressure ventilation and heliox therapy

NPPV is useful in decreasing the intubation rate in carefully selected patients with acute respiratory failure--particularly in patients with COPD. The results of some studies also suggest a survival benefit for use of NPPV with acute respiratory failure associated with COPD. Heliox therapy may be beneficial for selected patients with large airway obstruction or asthma. The use of heliox for other indications is unclear. Heliox may adversely affect the function of respiratory care equipment such as flow meters, ventilators, nebulizers, and pulmonary function monitors.

Ventilatory and cardiovascular responses to inspired He-O2 during exercise in chronic obstructive pulmonary disease

Blunted maximum cardiac output and systemic O2 extraction could constitute primary limits to exercise in severe chronic obstructive pulmonary disease (COPD) or they could simply reflect cessation of exercise because of abnormal pulmonary mechanics. To determine which is the case, eight consecutive patients with severe COPD (FEV1 = 0. 56 +/- 0.04 L, mean +/- SEM), five of whom had alpha1-antiprotease deficiency, performed two incremental cycling tests while breathing N2-O2 or He-O2. Expired gases and V E were measured, and radial and pulmonary arterial blood was simultaneously sampled each minute. Peak exercise V E was higher with He-O2 than with N2-O2 (25.5 +/- 2. 2 versus 19.3 +/- 1.5 L/min, p = 0.002) and PaCO2 was lower (42 +/- 2 versus 46 +/- 2 mm Hg, p = 0.0003). V O2max improved only modestly (594 +/- 75 versus 514 +/- 54 ml/min, p = 0.04), and was accompanied by an increase in peak exercise CaO2 (18.7 +/- 0.9 versus 17.6 +/- 0. 9 ml/dl, p = 0.02). Peak Fick cardiac output was decreased (39 +/- 3% pred) and CvO2 was elevated (130 +/- 10% pred), and neither improved with He-O2 (p > 0.05 for each). Abnormal peak exercise cardiac output and systemic O2 extraction in severe COPD cannot be fully accounted for by limiting pulmonary mechanics and may contribute to exercise intolerance.

The difficult airway: cardiopulmonary bypass--the ultimate solution

BACKGROUND

Large, compressive thyroid masses are usually removed as an elective procedure. Rarely is a patient's condition allowed to progress to severe respiratory distress before surgical intervention is recommended. When allowed to progress, management of the airway can be problematic.

METHODS

A case report of a patient with a neglected thyroid lymphoma is presented.

RESULTS

The natural progression of the disease, leading to impending airway collapse, necessitated emergency management of the airway. Due to supraglottic edema and a large neck mass, traditional methods of securing the airway were not feasible. Initiation of femoral-femoral cardiopulmonary bypass, under local anesthesia, ensured adequate oxygenation and allowed a controlled tracheotomy to be performed.

CONCLUSIONS

The result obtained suggests that this approach provides a safe solution for airway control when intubation or a surgically created airway is either unsuccessful or too hazardous.

Helium-oxygen therapy in the emergency department

Helium is an inert gas with unique physical properties that allow it to be used for various respiratory emergencies. Because of its low specific gravity and low viscosity, the passage of helium through the respiratory tract is smoother, more laminar, and less turbulent than either air or oxygen. These properties have prompted the use of helium and oxygen in patients with airway obstructions due to tumor, foreign body, edema, or bronchoconstriction. Helium-oxygen has been used to facilitate bronchoscopy through small diameter endotracheal tubes and to increase the effectiveness of high-frequency jet ventilation. Helium has been successful in the treatment of spinal cord decompression sickness seen in divers. Helium-oxygen mixtures are commercially available and may be useful in the emergency department to treat patients with airway obstruction. This article reviews literature concerning the use of helium-oxygen gas mixtures in the emergency department. Additional research conducted in the future may further define the use of this unique gas mixture in the emergency department.

Upper airway obstruction

The airways in infants and children are anatomically different from adults, thus predisposing them to more acute upper airway obstruction. The causes of upper airway obstruction may be infective or non-infective. The presence of dysphonia, dysphagia, abnormal respiratory pattern, cough and abnormal posture suggests upper airway obstruction. The general management consist of supportive care with minimal invasive procedures. The specific treatment depends on the causes and is discussed in text.

Heliox therapy in acute severe asthma

STUDY OBJECTIVE

To assess how patients with respiratory acidosis from acute severe asthma respond to helium-oxygen (heliox) mixtures.

DESIGN

Consecutive case series.

SETTING

Urban community teaching hospital.

PATIENTS

Over a 2-year period, 12 asthmatics (mean age, 33.8 +/- 11.3 years) presented to the emergency department with acute respiratory acidosis (pH < 7.35 and PaCO2 > or = 45 mm Hg). All 12 patients were treated with heliox (60 to 70% helium/30 to 40% oxygen). Five patients received heliox through a ventilator and seven received heliox via face mask.

RESULTS

Arterial blood gases (ABGs) were drawn immediately before and at a mean of 49.2 +/- 25.2 min after beginning heliox therapy. No therapeutic interventions were made between ABGs. For the entire group, the mean PaCO2 decreased from 57.9 to 47.5 mm Hg (p < 0.005) and the arterial pH increased from 7.23 to 7.32 (p < 0.001). In an attempt to find characteristics that might predict the response to heliox, a clinically significant response to heliox was defined as a drop in PaCO2 (to normal or by > or = 15%) coupled with a rise in pH by > or = 0.05. Using this definition, there were eight responders (67%) and four nonresponders (33%). The responders had a shorter duration of symptoms (17.8 vs 78.0 h, p < 0.05) and a lower preheliox pH (7.20 vs 7.30, p < 0.05). All of the responders presented within 24 h of symptom onset. Three of the four nonresponders reported prolonged (> or = 96 h) duration of symptoms, and two eventually required intubation.

CONCLUSION

Heliox can rapidly improve ventilation in patients presenting to an emergency department with acute severe asthma with respiratory acidosis and a short duration of symptoms.

The output of four modern vaporizers in the presence of helium

It has been previously demonstrated that the output of calibrated vaporizers is influenced by the concentration of nitrous oxide in the carrier gas. This study was performed to determine whether helium in the carrier gas affects the output of modern calibrated vaporizers. A factorial design was used to determine the influence of carrier-gas helium concentration, carrier-gas flow rate and vaporizer dial setting on the output of four vaporizers: Ohio Calibrated Enflurane, Ohio Calibrated Isoflurane, Ohmeda Isotec 4, and Dräger Vapor 19.1 Isoflurane. Three vaporizers of each model were tested. Output was converted to % of baseline so that different dial settings could be compared. For a given dial setting, baseline was defined as the output at a carrier-gas flow rate of 3 L.min-1 and helium concentration of zero. The data were analyzed using multiple linear regression. There was an effect of helium concentration on vaporizer output in all models. None of these changes was clinically important, since vaporizer output did not vary by more than +/- 10%, except at high flows and at high helium concentrations with the Ohmeda Isotec 4. It is concluded that these vaporizers can be used safely with helium.

Effect of helium concentration on experimental upper airway obstruction

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p less than .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p less than .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

Helium-oxygen gas therapy. Use and availability for the emergency treatment of inoperable airway obstruction

Inoperable obstruction of the upper airway due to extrinsic malignancy may present as respiratory failure. We treated such a patient for 48 hours with 80 percent: 20 percent helium-oxygen delivered by a nonrebreathing mask while chemotherapy and radiation therapy reduced the tumor size. The need for intubation, mechanical ventilation, and high risk surgical intervention was avoided through the use of this gas therapy. We then surveyed San Francisco Bay area hospitals and found that fewer than one half could provide this potentially lifesaving gas therapy in an emergency situation. Physiologic basis of helium-oxygen gas therapy is reviewed and recommendations made for its use and availability.

Helium-oxygen mixtures in airway obstruction due to thyroid carcinoma

The management of a patient with severe airway obstruction secondary to a thyroid mass is reported. When breathing room air the patient appeared in severe respiratory distress but when inspiring 22 per cent oxygen in helium she reported almost instantaneous relief and there was a marked decrease in respiratory rate, and increase in tidal volume and arterial oxygen tension. This improvement was to be expected because in situations where turbulent flow predominates a decrease in the density of inspired gases will result in an increase in flow rates. Contrary to established dogma a marked improvement was sustained when the patient was breathing 50 per cent oxygen in helium. The concentration of oxygen in helium was adjusted to obtain subjective relief for the patient in conjunction with adequate oxygenation.

Quantitative effects of respired helium and oxygen mixtures on gas flow using conventional oxygen masks

A model lung system with a variable artificial constriction was used to quantify the changes in flow produced by the addition of helium to the gas mixture in the system. The tracheal concentration of helium obtained when administering 79% helium/21% oxygen to the system via conventional, disposable face masks was determined using a resuscitation dummy. The greatest proportion of the increase in flow through the orifice occurred at concentrations of helium up to 40%. A tracheal concentration of 40% helium could be obtained with all oxygen masks at fresh gas flow rates greater than 8 litres/minute. These findings will help to rationalise the administration of 79% helium/21% oxygen to patients with upper respiratory tract obstruction.

Efficacy of helium--oxygen mixtures in the management of severe viral and post-intubation croup

An appreciable number of children with viral or post-intubation croup progress to respiratory failure necessitating an artificial airway. We report seven such patients with critical airway narrowing in whom we reduced the work of breathing by developing helium rather than air as a carrier gas for oxygen. Assessment of patients by a croup-scoring system and blood gas analysis suggests helium-oxygen mixtures to be a useful alternative to intervention with tracheostomy or tracheal intubation. The rationale and limitations of this treatment are discussed.