Hypercapnic Hyperventilation to Accelerate Emergence from Inhaled Volatile Anesthetics: A Practical Method Using Standard Hospital Equipment

Summary

This protocol demonstrates a practical method to induce controlled hypercapnic hyperventilation using standard anesthesia equipment. The technique facilitates rapid emergence from volatile anesthesia by accelerating anesthetic washout via elevated CO₂ levels and enhanced ventilation, providing a feasible alternative when proprietary commercial systems are unavailable.

Abstract

Hypercapnic hyperventilation is a technique used to support emergence from volatile anesthesia by allowing a controlled elevation of arterial carbon dioxide (CO₂) levels. The resulting hypercapnia increases minute ventilation, enhances the washout of anesthetic gases from the lungs, and increases cerebral blood flow, which may facilitate faster elimination of volatile agents from brain tissue. Commercial devices have been developed to achieve this effect; however, their availability is limited in many regions. This protocol describes a practical alternative approach using standard anesthesia equipment commonly available in European hospitals. By temporarily removing the CO₂ absorber and reducing fresh gas flow, controlled CO₂ rebreathing is facilitated, while an active charcoal filter eliminates residual volatile anesthetics from the circuit. The protocol provides step-by-step guidance to help achieve the desired end-tidal CO₂ levels safely and efficiently. This method offers a practical and low-cost way to induce hypercapnic hyperventilation, which may be associated with faster emergence from anesthesia under appropriate clinical conditions.

Introduction

Recently, there has been an increased focus on approaches aimed at facilitating emergence from general anesthesia¹. Delayed emergence and residual anesthetic effects remain clinically relevant challenges, particularly when rapid neurological assessment and operating room efficiency are desired. One of these approaches is hypercapnic hyperventilation. Hypercapnic hyperventilation is a controlled anesthetic emergence technique in which arterial carbon dioxide (CO₂) levels are deliberately elevated to enhance minute ventilation and is thought to facilitate the washout of volatile anesthetics at the end of surgery^2,3,4,5,6,7. By inducing mild hypercapnia, this approach increases cerebral blood flow^8,9 and is associated with stimulation of the respiratory centers in the brainstem, which may support the return to spontaneous ventilation and consciousness. The overall goal of the method is to shorten the time to support timely awakening and extubation after volatile anesthesia while maintaining patient safety and minimizing residual anesthetic effects.

Conventional emergence strategies rely primarily on high fresh gas flows to eliminate volatile anesthetics. Although effective, this can be time-consuming and may not optimally support cerebral elimination of anesthetic agents. This represents a largely passive elimination strategy that does not actively engage physiological mechanisms known to influence anesthetic clearance. Hypercapnic hyperventilation aims to address these limitations by coupling two physiological mechanisms—CO₂-mediated respiratory drive and increased cerebral perfusion⁹—that are thought to enhance anesthetic clearance from both pulmonary and cerebral compartments. Clinical studies have suggested that this strategy can significantly reduce emergence times and improve recovery quality compared to standard approaches.

A commercial system is available which utilizes an extendable rebreathing loop in combination with an active charcoal filter device⁷. This device integrates rebreathing and anesthetic gas scavenging within a single-use system designed to accelerate anesthetic elimination. However, this device is currently not widely available in Europe and other regions, limiting its clinical adoption. As a result, despite supportive evidence in the literature, the practical application of this technique remains limited in many clinical settings.

The present protocol describes a practical and accessible alternative for inducing hypercapnic hyperventilation using standard anesthesia equipment commonly available in most European hospitals. By removing the CO₂ absorber and reducing the fresh gas flow, controlled rebreathing is facilitated, while an active charcoal filter eliminates residual volatile anesthetics from the breathing loop. This method allows anesthesia providers to replicate the physiological benefits of hypercapnic hyperventilation without specialized commercial devices¹⁰. This protocol, therefore, aims to bridge the gap between the technique as described in the literature and its feasibility in daily clinical practice.

In addition to its simplicity and low cost, this approach offers an educational advantage by allowing clinicians to explore the physiological interplay between ventilation, CO₂ retention, and anesthetic elimination. The described technique is appropriate for adult patients without contraindications to transient hypercapnia, such as elevated intracranial pressure or pulmonary hypertension. When applied under proper monitoring and within defined safety limits, hypercapnic hyperventilation may represent an additional option in the modern anesthesia emergence repertoire, allowing readers to assess whether this method is suitable for their clinical environment and patient population.

Protocol

This procedure is performed in compliance with institutional human research ethics and anesthesia practice guidelines. Apply this method only to patients in whom transient hypercapnia is not contraindicated, such as those without elevated intracranial pressure or pulmonary hypertension. Continuous monitoring of oxygen saturation, end-tidal CO₂, anesthetic gas concentration, and hemodynamics is required throughout the procedure. The data shown are anonymized monitoring data from a single patient and were used in accordance with institutional policies regarding the educational or scientific use of clinical data. At hospital admission, patients provide broad consent for such use of their anonymized medical data (“consent at admission”); therefore, no study-specific informed consent or separate ethics approval was required.

NOTE: Patient selection criteria: Adult patients undergoing elective surgery under volatile anesthesia with expected standard emergence and stable intraoperative hemodynamics. Exclusion criteria: Do not apply this protocol to patients with intracranial hypertension, severe pulmonary hypertension, or uncompensated cardiac disease. Additional contraindications include any condition in which transient hypercapnia is considered unsafe based on established clinical indications and intraoperative anesthesiologist judgment. The hypercapnic hyperventilation protocol is initiated at the end of the surgical procedure, after cessation of surgical stimulation, when the clinician determines that emergence can be initiated.

CAUTION: Prior to initiating the procedure, verify that the anesthesia workstation allows safe modification of the breathing circuit, including temporary removal or bypass of the CO₂ absorber during ongoing mechanical ventilation. Ensure familiarity with the specific ventilator settings and alarm functions of the device in use. Confirm availability of continuous monitoring of airway pressure, ventilation parameters, and gas exchange throughout the procedure.

1. Preparation of the anesthesia circuit

NOTE: Disposal of used active charcoal filters should follow local institutional protocols for waste management of single-use anesthetic devices and materials potentially contaminated with volatile anesthetic agents.

1. Turn off the volatile anesthetic vaporizer and ensure that no anesthetic agent is being delivered to the circuit.
2. Set the inspired oxygen fraction (FiO₂) to 1.0 by adjusting the anesthesia machine oxygen blender to deliver 100% oxygen.
3. Reduce the fresh gas flow (FGF) to approximately 0.2 L·min⁻¹ using the flow control knobs on the anesthesia machine to promote rebreathing within the circuit.
4. Attach a single active charcoal filter (as listed in Table of Materials) to the inspiratory limb of the anesthesia circuit immediately distal to the Y-piece, ensuring correct directional orientation according to manufacturer instructions as shown in Figure 1A–C.
5. Confirm correct placement by verifying a secure, airtight connection without leaks and ensuring unidirectional gas flow through the filter.
6. Refill the breathing circuit with 100% oxygen in case of unwanted disconnection as advised by the manufacturer (i.e., 1–2 s flush of the O₂ button or temporary increase of fresh gas flow for 3–4 s to 15 L·min⁻¹).
   NOTE: Some institutions permit limited reuse of active charcoal filters under defined conditions; adhere strictly to local policies regarding reuse and disposal.
7. Disconnect the CO₂-absorbing canister (soda lime) from the anesthesia machine to allow CO₂ accumulation within the breathing loop, as shown in Figure 1D–E.
   NOTE: Ensure that the CO₂ absorber is completely bypassed or removed; partial removal may result in unpredictable CO₂ levels. Confirm correct configuration by verifying that the absorber is fully excluded from the breathing circuit (no gas flow through the canister) and by visual inspection of the bypass position before proceeding. Visually check that the bypass lever is in the correct position, and confirm the expected rise in end-tidal CO₂ after initiating rebreathing before proceeding.
8. During initiation of hypercapnic hyperventilation, continuously monitor inspired volatile anesthetic concentration.
   NOTE: Under low fresh gas flow (0.2 L·min⁻¹), a rapid decline of inspired volatile anesthetic concentration to near-zero levels (<0.1 vol%) is expected within approximately 1–2 min. If inspired concentrations remain detectable beyond this period, replace the active charcoal filter immediately before continuing the protocol.
9. Confirm that all circuit connections are airtight and that the anesthesia machine displays normal pressure and flow readings before proceeding.

2. Inducing hypercapnic hyperventilation

1. General approach
   1. Apply the protocol in either mechanically ventilated or spontaneously breathing patients, depending on intraoperative ventilation status at the end of surgery.
2. Mechanically ventilated patients
   1. Set mechanical ventilation to achieve controlled hypercapnia.
   2. Increase tidal volume to 8–10 mL·kg⁻¹ ideal body weight and adjust minute ventilation to 10–12 L·min⁻¹.
   3. NOTE: These adjustments are operator-controlled and are used to regulate CO₂ levels indirectly by modifying alveolar ventilation. Avoid relying solely on respiratory rate adjustments, as tidal volume changes are more effective for controlled CO₂ retention.
3. Reduce fresh gas flow (see 1.3) and remove the CO₂ absorber (see 1.4) to allow controlled CO₂ accumulation. In this setting, rising CO₂ levels stimulate the respiratory drive, resulting in a physiological increase in minute ventilation without external ventilator adjustments.
4. CO₂ monitoring and adjustment of fresh gas flow
   1. Continuously monitor end-tidal CO₂ (EtCO₂) via capnography.
   2. Adjust fresh gas flow (FGF) in a stepwise and titrated manner based on real-time CO₂ trends.
   3. Increase FGF in small increments of approximately 0.1–0.3 L·min⁻¹ when EtCO₂ exceeds the target range (7.0–7.3 kPa; 52.5–55 mmHg).
   4. Reassess EtCO₂ within 1–2 min after each adjustment to evaluate response.
   5. Decrease FGF to a minimum of approximately 0.2 L·min⁻¹ when EtCO₂ is below the target range to facilitate CO₂ accumulation.
   6. Avoid abrupt or large adjustments to prevent overshooting and instability of CO₂ levels.
   7. Maintain FGF within a low-flow range (0.2–1.0 L·min⁻¹) throughout the procedure, titrated according to continuous capnographic feedback.
      NOTE: The induced hypercapnia is intended to be transient and limited to the emergence phase of anesthesia. The target end-tidal CO₂ range (7.0–7.3 kPa; 52.5–55 mmHg) is typically maintained for several minutes during anesthetic washout and is discontinued immediately upon return of adequate spontaneous ventilation and clinical signs of emergence.
5. Stabilization: Increase fresh gas flow slightly (e.g., from 0.2 to 0.5 L·min⁻¹) once the target EtCO₂ range is reached to stabilize CO₂ levels.
   NOTE: Avoid excessive CO₂ accumulation (>8.0–8.5 kPa) to reduce the risk of respiratory acidosis or sympathetic overactivation.

3. Maintenance and monitoring

1. Maintain FiO₂ at 0.7–1.0 during the entire procedure.
2. Continue monitoring of inspiratory and expiratory volatile anesthetic concentrations using a calibrated gas analyzer (see Figure 2 for a representative monitor display).
3. Observe the patient’s hemodynamics, oxygenation, and ventilation parameters until the inspired volatile anesthetic concentration decreases to zero.
4. Assess for the return of spontaneous breathing and clinical signs of emergence (e.g., eye opening, purposeful movement, or response to verbal commands).
5. Once the patient demonstrates adequate conditions, proceed with extubation according to standard institutional criteria.

4. Post-procedure steps

1. Remove the active charcoal filter from the inspiratory limb immediately after completion of the protocol and prior to preparation for the next case.
2. To reduce the risk of human error, verify visually and physically that the filter has been removed and that the standard circuit configuration has been restored.
   CAUTION: Failure to remove the active charcoal filter can result in unintended adsorption of anesthetic gases and intraoperative awareness during subsequent cases¹¹.
3. Reconnect or reinstall the CO₂ absorber (soda lime) before initiating anesthesia for the next case.
4. Confirm correct function by verifying normal CO₂ absorption and stable baseline capnography before induction. To mitigate omission risk, incorporate this step into the standard anesthesia machine checkout procedure between cases.
   CAUTION: Failure to restore the CO₂ absorber can result in unintended rebreathing and intraoperative hypercapnia during subsequent cases. Given the critical nature of circuit modification, explicit post-procedure circuit checks are recommended. A standardized “return-to-baseline” verification of the anesthesia machine configuration should be performed before the next case to ensure that all temporary components are removed and the standard settings are restored.

5. Safety and troubleshooting

1. Immediately terminate hypercapnic hyperventilation by increasing fresh gas flow to 10 L·min⁻¹ if any of the following occur: oxygen desaturation (SpO₂ < 94%), hemodynamic instability (e.g., hypotension requiring intervention or clinically relevant arrhythmia), or excessive hypercapnia (EtCO₂ > 8.5 kPa; 64 mmHg) despite corrective measures.
2. After termination, immediately restore conventional anesthesia conditions by reinstalling the CO₂ absorber, returning fresh gas flow to standard settings, and resuming conventional ventilation parameters appropriate for the patient and anesthetic phase.
   CAUTION: If unexpected resistance, leaks, or abnormal capnography values occur, inspect the breathing circuit, connectors, and the orientation of the active charcoal filter. Verify an airtight assembly and correct unidirectional flow through the filter before continuing the procedure. This protocol should only be performed by anesthesia providers experienced in mechanical ventilation, capnography interpretation, and volatile anesthetic management.

6. Pause points

CAUTION: The procedure can be paused after completion of step 1.6 (circuit setup) before induction of hypercapnic hyperventilation, if necessary. Do not pause the procedure once CO₂ accumulation has started. Continuous patient monitoring is mandatory during active hypercapnia.

Results

This section demonstrates the physiological and clinical effects of the hypercapnic hyperventilation technique in a representative case. As shown in Figure 1, the experimental setup enables controlled bypass of the CO₂ absorber and integration of an active charcoal filter, thereby allowing simultaneous CO₂ rebreathing and volatile anesthetic scavenging. This configuration forms the basis for the observed physiological changes with controlled CO₂ elevation and accelerated anesthetic washout (Figure 2).

Suboptimal results may occur when the CO₂ absorber bypass is incomplete or when the fresh gas flow is insufficiently reduced, leading to inadequate CO₂ accumulation and slower anesthetic elimination. These scenarios highlight the importance of strict adherence to the protocol steps and continuous monitoring of end-tidal CO₂ and anesthetic gas concentrations for optimal performance of the technique. The predefined clinical endpoints of this representative case were time to eye opening, time to extubation, and time to zero inspired and expired volatile anesthetic concentration. Table 1 shows the measured ventilatory and hemodynamic parameters of a representative patient (not the same as in Figure 1) at the onset of hypercapnic hyperventilation (at t = 0 min), following the cessation of sevoflurane, removal of the CO₂ absorber, insertion of the active charcoal filter, and reduction of fresh gas flow to 0.2 L·min⁻¹.

The controlled ventilation of this patient, a middle-aged individual in their mid-50s with an ideal body weight of approximately 60 kg, was adjusted from 12/min with a tidal volume of 425 mL to 14/min with a tidal volume of 575 mL, resulting in an increase in minute ventilation from 5.1 L·min⁻¹ to 8 L·min⁻¹. No further adjustments were required to stabilize end-tidal CO₂. Successful CO₂ rebreathing was confirmed by the increase in end-tidal CO₂ following the start of hypercapnic hyperventilation (Figure 2). The end-tidal CO₂ did not exceed the safety threshold of approximately 8.0–8.5 kPa (60–64 mmHg).

Oxygenation safety was ensured throughout the protocol by maintaining a stable FiO₂ of around 0.7 and constant oxygen saturation at 100% (ventilation setting at 100% oxygen with a low flow of 0.2 L·min⁻¹ at the start of hypercapnic hyperventilation). No desaturation occurred that would have required aborting the maneuver or increasing the fresh gas flow. Hemodynamic safety was verified by stable heart rate and blood pressure trends from baseline throughout the maneuver, with no signs of hemodynamic instability. After 3.5 min, the patient spontaneously opened their eyes and was extubated without complications. Immediately after extubation, the patient began speaking, although they reported still feeling somewhat sleepy. These values correspond to the predefined clinical endpoints and are summarized within the presented case.

The data presented here originate from a single representative patient case and are intended solely to illustrate the type of output generated by the method, rather than to provide confirmatory evidence of clinical efficacy, safety, or reproducibility. In general, application of the hypercapnic hyperventilation protocol is associated with a controlled, transient elevation of end-tidal CO₂ (EtCO₂) and may influence anesthetic elimination and patient emergence. Representative recordings show that, after reducing the fresh gas flow and removing the CO₂ absorber, EtCO₂ rises progressively from baseline values of 4.5–5.0 kPa (34–38 mmHg) to a target range of 7.0–7.3 kPa (52.5–55 mmHg) within approximately 2–4 min (Figure 3).

During this period, the inspired volatile anesthetic concentration decreases rapidly to 0.0–0.1 within one minute, while the expired volatile anesthetic concentration (measured via gas analyzer) decreases to 0.0–0.1 within 5–7 min, compared to 10–15 min under conventional high-flow washout conditions. Cerebral perfusion monitoring (e.g., via transcranial Doppler ultrasound) may demonstrate a transient increase in middle cerebral artery flow velocity⁹, reflecting enhanced CO₂-mediated vasodilation (Figure 3).

In the representative case, earlier return of eye opening on command and purposeful movements were observed within several minutes after initiating the protocol. An excitation phase, as is often observed after volatile anesthetics, was not observed in this representative case, which may be related to the rapid washout of the volatile anesthetic. Following eye-opening or purposeful movement, the controlled mechanical ventilation was discontinued. Following CO₂ elevation, spontaneous breathing with tidal volume and respiratory rate within a physiological range was observed. In this case, extubation readiness occurred approximately 3–5 min earlier compared with the timing observed under conventional emergence conditions in previous reports.

In the present protocol, suboptimal conditions may occur when the fresh gas flow remains too high (>1.0 L·min⁻¹) or when the CO₂ absorber is incompletely disconnected, potentially preventing adequate CO₂ accumulation. In such cases, EtCO₂ may not exceed 6.0 kPa (45 mmHg), which may be associated with slower anesthetic elimination and delayed awakening. Similarly, failure to monitor or limit CO₂ elevation beyond 8.0 kPa (60 mmHg) may be associated with transient respiratory acidosis or sympathetic activation. Overall, maintenance of the target EtCO₂ range, verification of volatile anesthetic elimination with a gas analyzer, and protocol consistency were used to guide protocol consistency. The observed physiological responses support the feasibility of the described approach under the reported conditions.

Figure 1: Hypercapnic hyperventilation setup. (A) active charcoal filter as listed in the Table of Materials, (B) inspiratory limb and expiratory limb without filter, (C) inspiratory limb with filter, (D) connected soda lime canister, (E) disconnected soda lime filter. The authors created this drawing using freely available software, DALL · E from OpenAI, with a prompt designed by them; no copyright was required to publish it. The authors have declared that they have checked the scientific accuracy of the figure themselves. Please click here to view a larger version of this figure.

Figure 2: Representative monitor screen during hypercapnic hyperventilation. The monitor shows airway pressure (Paw), tidal volume, and CO₂ waveforms during controlled rebreathing. Ventilator settings include volume-controlled ventilation with tidal volume 750 mL, respiratory rate 13/min, and FiO₂ 100%. Fresh gas flow is set at 0.2 L·min⁻¹. A progressive increase in end-tidal CO₂ (EtCO₂ 57 mmHg) and inspired CO₂ (53 mmHg) is displayed over time, consistent with controlled CO₂ accumulation during the protocol. Expired sevoflurane concentration is 0.2% at the time of measurement. Please click here to view a larger version of this figure.

Figure 3: Time course of end-tidal CO₂ and expired sevoflurane concentration during hypercapnic hyperventilation. End-tidal CO₂ (EtCO₂, blue line; left y-axis, mmHg) and expired sevoflurane concentration (red line; right y-axis, vol%) are shown over time before and during hypercapnic hyperventilation. Baseline values are recorded from t = −3 to 0 min. The start of hypercapnic hyperventilation is indicated at t = 0 min. Following initiation, EtCO₂ progressively increases from 39 to 54 mmHg, while expired sevoflurane concentration decreases from 0.9 vol% to 0 vol% over 3 min, reflecting accelerated washout during low fresh gas flow and controlled rebreathing conditions. Please click here to view a larger version of this figure.

	EtCO2 [mmHg]	etSevo [Vol%]	FiO2	SpO2 [%]	RR [mmHg]	heart rate	BIS
t -3 min	36	0.9	0.63	100		65	32
t -2 min	36	0.9	0.63	100	92/64	66	34
t -1 min	37	0.9	0.66	100		68	36
t 0	39	0.5	0.74	100	97/65	70	32
t + 1 min	44	0.2	0.7	100		69	41
t + 2 min	47	0.2	0.69	100		67	53
t + 3 min	50	0	0.68	100	105/68	66	63
t + 4 min	52	0	0.68	100		67	66
t + 5 min	54	0	0.68	100	109/77	95	82

Table 1: Ventilatory and anesthetic parameters recorded during the maneuver. Anesthesia was maintained with a propofol–sevoflurane combination without nitrous oxide. The end-tidal sevoflurane concentration (~1%) reflects the maintenance technique and not a weaning phase. Sevoflurane had been administered for approximately 2 h before the maneuver.

Discussion

The presented protocol describes a practical approach to inducing hypercapnic hyperventilation using standard anesthesia equipment. The critical steps for implementation include complete removal or bypassing of the CO₂ absorber, reduction of fresh gas flow to approximately 0.2 L·min⁻¹, and continuous monitoring of end-tidal CO₂ (EtCO₂). Accurate control of CO₂ accumulation is important for reaching the target range of 7.0–7.3 kPa (52.5–55 mmHg) without exceeding safe physiological limits. The addition of an active charcoal filter on the inspiratory limb is intended to facilitate scavenging of volatile anesthetics while allowing safe CO₂ rebreathing.

Several points in the protocol require particular attention. First, failure to completely remove the CO₂ absorber or maintaining a too-high fresh gas flow may prevent sufficient CO₂ buildup, leading to suboptimal results and delayed emergence. Second, when inducing hyperventilation by increasing the settings of controlled mechanical ventilation, it is recommended to increase the tidal volume rather than the respiratory rate. Third, once the target CO₂ level is reached, maintaining it, if needed, through small, intermittent (or continuous) fresh-gas adjustments may help prevent overshooting and resultant respiratory acidosis. Proper calibration of gas analyzers and vigilant observation of capnography and hemodynamics are necessary for appropriate application.

This method can be modified according to the patient's ventilation status and institutional resources. For patients under spontaneous breathing, hypercapnia develops gradually, allowing natural stimulation of the respiratory drive. In mechanically ventilated patients, tidal volume and minute ventilation can be adjusted to achieve the desired EtCO₂ trajectory more predictably. The described approach can also be adapted for different anesthesia machines, provided the CO₂ absorber can be easily bypassed, and circuit integrity is maintained.

A key limitation of the method is that it may be unsuitable for patients with conditions contraindicated by hypercapnia, such as intracranial hypertension, severe pulmonary hypertension, or uncompensated cardiac disease. Additionally, this approach requires continuous vigilance to avoid excessive CO₂ retention and to ensure proper reinstallation of the CO₂ absorber before subsequent anesthesia cases. The absence of automated feedback control for CO₂ concentration represents another limitation compared to specialized commercial systems designed for this purpose.

In addition, several practical considerations in circuit management should be taken into account when applying this technique in clinical practice. Insufficient CO₂ accumulation may occur if the CO₂ absorber is not fully bypassed or removed, if fresh gas flow is higher than intended, or if unintended leaks are present in the breathing circuit. In such cases, circuit integrity should be verified and low-flow conditions re-established. Conversely, excessive CO₂ accumulation may be managed by small, titrated increases in fresh gas flow and by verifying the correct circuit configuration and capnography function. If inspired volatile anesthetic concentrations do not decrease as expected during low-flow conditions, correct placement and orientation of the active charcoal filter should be confirmed, and the filter replaced if necessary.

The applicability of this technique may depend on anesthesia workstation design and the ability to safely modify the breathing circuit, including temporarily removing or bypassing the CO₂ absorber during ongoing ventilation. Operators should be familiar with the specific functionality and safety features of the anesthesia machine in use, as ventilation performance and alarm behavior may vary between platforms. Close monitoring of ventilatory parameters, airway pressures, and gas exchange is essential whenever modifications to the standard breathing circuit are performed.

Despite these constraints, the presented technique may offer several advantages over alternative methods. It provides an accessible, low-cost means of achieving controlled hypercapnic hyperventilation in institutions where proprietary devices are unavailable. Compared with conventional high-flow washout, this approach has been associated with reduced anesthetic elimination time in previous studies, may enhance cerebral clearance of volatile agents, and may promote faster recovery of spontaneous breathing. Its simplicity also makes it valuable as an educational tool for anesthesia trainees to understand the physiological interplay between ventilation, CO₂ regulation, and anesthetic emergence. Mechanistically, the observed acceleration of emergence is consistent with prior studies suggesting that mild hypercapnia enhances cerebral blood flow and increases minute ventilation, thereby facilitating faster elimination of volatile anesthetic agents from both pulmonary and cerebral compartments^8,9. These physiological effects provide a potential explanation for the reduced time to awakening observed in hypercapnic hyperventilation protocols.

Previous experimental and clinical studies have reported shortened emergence times using hypercapnic or hyperventilation-based strategies compared to conventional anesthetic washout techniques^2,3,4,5,6,7. A study reported accelerated recovery from isoflurane and sevoflurane anesthesia under hypercapnic conditions^2,3, while another study indicated similar effects in animal models⁴. In clinical settings, a group of researchers reported improved recovery profiles in patients receiving postoperative hypercapnia-induced hyperventilation⁵, supporting the translational relevance of this physiological approach.

Future applications of the described hypercapnic hyperventilation technique may include its integration into routine emergency protocols for volatile anesthesia in adult surgical populations. In particular, its use may be explored in fast-track anesthesia pathways, ambulatory surgery, and enhanced recovery after surgery (ERAS) programs, where rapid emergence and early neurological assessment are clinically relevant. Additionally, adaptation of this technique for use in high-risk populations, such as elderly patients or those undergoing prolonged inhalational anesthesia, may be of interest, provided that appropriate safety thresholds for hypercapnia are strictly maintained. Future studies, including larger patient cohorts, are required to formally assess reproducibility and clinical outcomes.

In conclusion, this protocol extends the applicability of hypercapnic hyperventilation by using equipment already available in most operating rooms. It enables clinicians to achieve the physiological effects of controlled hypercapnia safely and reproducibly, which may lead to faster recovery from volatile anesthesia. Future research should focus on quantifying cerebral anesthetic elimination kinetics under controlled hypercapnia and establishing standardized safety thresholds for broader clinical use.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Disposable CO2 absorber, IS Can™, Spherasorb™	Intersurgical, Workingham, United Kingdom	2196000	Disposable CO2 absorber canister, removed during the procedure
Dräger Atlan A350	Drägerwerk, Lübeck, Germany	8621500	Standard mechanical ventilator with circle breathing system, capnography and anesthetic gas analysis
IntelliVue X3 patient monitor	Philips, Eindhoven, The Netherlands	X3 867030	Standard patient monitoring module (ECG, SpO2, NIBP)
Vapor-Clean filter	Dynasthetics, Salt Lake City, USA	SKU 101	www.dynasthetics.com/Vapor-Clean/