Isocapnic Hyperventilation - an Alternative Method

Study Overview
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Brief Summary
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Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia by increasing airway carbon dioxide (CO2) during hyperventilation (HV). In two experimental studies (mechanical lung model and porcine model) and in a pilot study on patients undergoing sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, the investigators evaluated the feasibility of an alternative technique of IHV. By performing a prospective, randomised controlled study, the investigators want to further test this alternative method for IHV.

Detailed Description
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Isocapnic hyperventilation (IHV) provides an alternative method for weaning from inhalation anaesthesia which decreases the time to eye-opening, extubation and time spent in the PACU. The method is well known since at least 40-50 years and involves the maintenance of a stable CO2 level during hyperventilation, which increases the elimination of anaesthetic gas without producing hypocapnia. Studies have declared that the reduction in time to eye-opening is 50-60 % compared to a standard weaning procedure after inhalation anaesthesia. There are several principally different ways to maintain the CO2 level during hyperventilation, where a number of technical solutions that add dead-space to the anaesthesia circuit and thereby produce rebreathing of CO2 during hyperventilation are the most studied methods so far. However, the original method of directly adding CO2 to the breathing circuit during hyperventilation could be considered in need of a re-evaluation, as modern anaesthesia delivery units and monitoring equipment to a great extent can eliminate the risk of hypercapnia, that was described with this procedure in the 1980ies. An alternative IHV method is to directly infuse CO2 to the inspiratory limb of the breathing circuit through a mixing box while using mechanical hyperventilation by a standardised protocol. This technique was recently evaluated by the investigators, in a bench test, and in an in vivo model. Based on these studies, the CO2 dosage needed to achieve isocapnia during HV at various levels of alveolar ventilation, CO2 production and dead space was estimated and a gender- and weight-based nomogram for CO2 delivery during IHV was constructed. Furthermore, the investigators could show, in vivo, that the washout time of sevoflurane anaesthesia was one-third compared to normal ventilation. The feasibility of this IHV method was evaluated in a pilot study in humans, based on the results of our two previous experimental studies. To finalize the project the investigators now conduct a prospective randomized trial to evaluate the efficacy of the method, compared to a standard weaning procedure, after long-term sevoflurane anaesthesia.

Official Title
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Isocapnic Hyperventilation for Enhancing Recovery After Inhalation Anaesthesia - an Alternative Method

Conditions
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Oropharyngeal Neoplasms

Intervention / Treatment
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* Device: Isocapnic hyperventilation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adult patients scheduled for major elective ear-nose-throat (ENT) surgery after informed consent was obtained during the pre-operative evaluation. Exclusion Criteria: Patients with severe pulmonary or circulatory disease

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Sequential Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Isocapnic hyperventilation<br>After end of surgery, hyperventilation and administration of a small, precalculated amount of CO2 into the breathing circuit will be performed. | Device: Isocapnic hyperventilation<br>* Mechanical hyperventilation to enhance elimination of inahalation anesthetics. Administration of a precalculated flow of CO2 according to gender and weight into the inspiratory limb of the breathing circuit in order to avoid hypocapnia.<br>* Other names: Normocapnic hyperventilation;|
| No Intervention: Standard procedure<br>After end of surgery, patients will be subdued to a standard weaning procedure. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Time to extubation |  | 5-20 minutes | 
| Time to eye-opening |  | 10-25 minutes | 
| Time to discharge from OR |  | 15-40 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Postoperative recovery | Postoperative quality of recovery (PQRS) scale | 60 minutes | 
| Time to eligible for discharge from post-anaesthesia care unit (PACU) |  | 1-6 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Inhalation Anaesthetics, Sevoflurane, Carbon Dioxide, Hyperventilation, Anaesthesia Recovery Period, Ventilators