Hypercapnic Hyperventilation Shortens Emergence Time from Isoflurane Anesthesia

Cardiopulmonary effects of apneustic anesthesia ventilation in anesthetized pigs: a new mode of ventilation for anesthetized veterinary species

Objective

To compare the cardiopulmonary effects of apneustic anesthesia ventilation (AAV) and conventional mechanical ventilation (CMV) in anesthetized pigs and to describe a new mode of ventilation for anesthetized veterinary species.

Study design

Randomized, crossover design without washout.

Animals

Twelve healthy, female white Landrace pigs.

Methods

Following ketamine-midazolam premedication and anesthetic induction with propofol, the trachea was intubated, and each pig was positioned in dorsal recumbency. Anesthesia was maintained with propofol and sufentanil infusions. Pigs were instrumented and their lungs were sequentially ventilated with each mode, in random order, for 1 h according to predefined criteria [fraction of inspired oxygen (FiO2) = 0.21, 10 mL kg-1 tidal volume (VT), and arterial carbon dioxide tension (PaCO2) within 40-45 mmHg]. Cardiopulmonary data were collected at baseline, 30 and 60 min. In 8 pigs, thoracic computed tomography (CT) was performed following the 60 min time point for each mode of ventilation and images were analyzed to quantify lung aeration. The effects of ventilation mode, time, and order were analyzed using repeated measures ANOVA. Paired t-tests were used to compare lung aeration between modes. Significance was defined as p < 0.05.

Results

Data from 12 pigs were analyzed. A significant effect of mode was found for heart rate, mean arterial pressure (MAP), pulmonary artery occlusion pressure, cardiac index (CI), stroke volume index, systemic vascular resistance, pulmonary vascular resistance, oxygen delivery index (DO2I), oxygen extraction ratio (O2ER), VT, arterial oxygen tension, arterial hemoglobin saturation, PaCO2, end-tidal carbon dioxide tension, alveolar dead space (VDalv/VTalv), venous admixture (Q . s / Q . t ), mean airway pressure, and dynamic compliance index (CRSI). Order effects were also observed for some cardiovascular and respiratory variables. For the eight pigs that underwent thoracic CT, AAV resulted in significantly larger proportions of normally and hyperaerated lung while CMV resulted in larger proportions of hypoaerated and atelectatic lung.

Conclusions

In dorsally recumbent anesthetized pigs, ventilated with FiO2 = 0.21, both modes of ventilation supported adequate oxygenation while AAV resulted in higher CRSI, and lower VDalv/VTalv andQ . s / Q . t , compared with CMV. AAV was also associated with lower MAP, CI, and DO2I and higher O2ER compared with CMV. Further investigation of AAV in anesthetized animals is warranted.

Comparison of the effects of 5 and 10 L/minute fresh gas flow on emergence from sevoflurane anesthesia: A randomized clinical trial

BACKGROUND

A high fresh gas flow of >5 L/minute is commonly used for emergence from inhalation anesthesia. In addition, a high fresh gas flow may have detrimental effects on climate change. However, no study has determined the optimal fresh gas flow for emergence from inhalation anesthesia. Therefore, we compared the effect of fresh gas flows of 5 L/minute and 10 L/minute on emergence time from sevoflurane anesthesia.

METHODS

Patients who were scheduled for transurethral resection of bladder tumor were randomly assigned to receive fresh gas flows of 5 L/minute (group 5) or 10 L/minute (group 10) during emergence. Emergence time was defined as the time from discontinuation of sevoflurane to tracheal extubation. The primary outcome was the emergence time, and the secondary outcomes were the time to self-movement and the time to eye-opening.

RESULTS

A total of 54 patients were included. In groups 5 and 10, emergence time (12.1 ± 2.9 minutes vs 11.1 ± 2.7 minutes, respectively; P = .232), time to self-movement (9.4 ± 3.8 minutes vs 8.5 ± 4.6 minutes, respectively; P = .435), and time to eye-opening (11.5 ± 3.1 minute vs 10.6 ± 3.0 minutes, respectively; P = .252) were not significantly different.

CONCLUSIONS

Emergence time, time to self-movement, and time to eye opening were not significantly different between fresh gas flow rates of 5 L/minute and 10 L/minute in transurethral resection of bladder tumor, thus suggesting that fresh gas flow of 5 L/minute is sufficient for emergence from sevoflurane anesthesia.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT05376631).

Application and Efficiency of Transnasal Humidified Rapid-Insufflation Ventilatory Exchange in Laryngeal Microsurgery

OBJECTIVES/HYPOTHESIS

This study aimed to analyze the feasibility of transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) during laryngeal microsurgery (LMS) and investigated its efficiency and application according to the location of the lesion.

STUDY DESIGN

Retrospective chart review.

METHODS

Patients over 20 years of age who underwent LMS without underlying cardiac, pulmonary, or cerebrovascular disease were retrospectively reviewed. Overall, 54 patients with endotracheal intubation (ETI) and 44 patients with THRIVE were included. The operation and anesthesia time, induction and emergence time, oxygen saturation (SpO₂ ), and transcutaneous carbon dioxide (TcCO₂ ) levels were analyzed and compared between the two ventilation methods according to disease subsite.

RESULTS

Compared with ETI, patients with THRIVE presented reduced operation time (16.3 ± 9.69 min vs. 21.9 ± 12.0 min), anesthesia time (33.6 ± 11.4 min vs. 45.4 ± 13.9 min), emergence time (6.73 ± 2.49 min vs. 8.52 ± 3.17 min), without significant decreases in SpO₂ but with increased TcCO₂ (10.9 ± 6.12% vs. 7.33 ± 3.86%). Comparing THRIVE to ETI for lesions at the glottis yielded similar findings, which were particularly more significant. However, lesions above the glottis presented no significant difference for any parameters between THRIVE and ETI groups. Lesions involving multiple subsites and prolonged operation time were risk factors for the intraoperative conversion of ventilation method.

CONCLUSION

THRIVE is reliable for maintaining oxygenation during LMS and is efficient in reducing the operation and emergence times, leading to shorter anesthesia time, especially for lesions at the glottis. However, caution is required administering THRIVE, when lesion involves multiple subsites, and when operation time is prolonged.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Hypercapnia versus normocapnia for emergence from desflurane anaesthesia: Single-blinded randomised controlled study

BACKGROUND

Rapid emergence from general anaesthesia is desirable only if safety is not sacrificed. Mechanical hyperventilation during hypercapnia produced by carbon dioxide infusion into the inspired gas mixture or by rebreathing was reported to shorten emergence time from inhalation anaesthesia.

OBJECTIVES

To test the hypothesis that hypercapnia produced by hypoventilation before desflurane cessation shortens emergence time from general anaesthesia (primary hypothesis) and reduces undesirable cardiorespiratory events.

DESIGN

A single-blinded randomised controlled study.

SETTING

A single university hospital.

PATIENTS

Fifty adult patients undergoing elective abdominal surgery under general anaesthesia using desflurane inhalation and intra-operative epidural anaesthesia.

INTERVENTION

The patients were randomly assigned to either the normocapnia or hypercapnia group.

MAIN OUTCOME MEASURES

Emergence time from desflurane anaesthesia and comparison of the incidence of 11 predefined undesirable cardiorespiratory events during and after emergence from anaesthesia between the groups.

RESULTS

Forty-six patients were included in the analysis. End-tidal carbon dioxide concentrations at cessation of desflurane were 35 ± 6 mmHg (mean ± SD) and 52 ± 6 mmHg in normocapnia (n = 23) and hypercapnia groups (n = 23), respectively. Emergence time was significantly faster in the hypercapnia group than the normocapnia group: 9.4 ± SD min, hypercapnia: 5.5 ± 2.6 min, (P < 0.001) with a difference of 3.8 min on average (95% CI: 2.4 to 5.3). Spontaneous breathing established before recovery of consciousness was more evident in hypercapnia patients (normocapnia: 13%, hypercapnia: 96%, P < 0.001). Hypercapnia patients had more episodes of bradypnoea and apnoea before emergence of consciousness. In contrast, after tracheal extubation, incidences of bradypnoea and hypopnoea were more common in the normocapnia group. Undesirable cardiovascular events were not common, and no group differences were observed during emergence and postextubation periods.

CONCLUSION

Hypoventilation-induced hypercapnia before desflurane cessation shortens the emergence time without causing additional clinically significant undesirable events.

TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN000020143) https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr.cgi?function=brows&recptno=R000023266&language=E.

Pre-Treatment with Ten-Minute Carbon Dioxide Inhalation Prevents Lipopolysaccharide-Induced Lung Injury in Mice via Down-Regulation of Toll-Like Receptor 4 Expression

Various animal studies have shown beneficial effects of hypercapnia in lung injury. However, in patients with acute respiratory distress syndrome (ARDS), there is controversial information regarding the effect of hypercapnia on outcomes. The duration of carbon dioxide inhalation may be the key to the protective effect of hypercapnia. We investigated the effect of pre-treatment with inhaled carbon dioxide on lipopolysaccharide (LPS)-induced lung injury in mice. C57BL/6 mice were randomly divided into a control group or an LPS group. Each LPS group received intratracheal LPS (2 mg/kg); the LPS groups were exposed to hypercapnia (5% carbon dioxide) for 10 min or 60 min before LPS. Bronchoalveolar lavage fluid (BALF) and lung tissues were collected to evaluate the degree of lung injury. LPS significantly increased the ratio of lung weight to body weight; concentrations of BALF protein, tumor necrosis factor-α, and CXCL2; protein carbonyls; neutrophil infiltration; and lung injury score. LPS induced the degradation of the inhibitor of nuclear factor-κB-α (IκB-α) and nuclear translocation of NF-κB. LPS increased the surface protein expression of toll-like receptor 4 (TLR4). Pre-treatment with inhaled carbon dioxide for 10 min, but not for 60 min, inhibited LPS-induced pulmonary edema, inflammation, oxidative stress, lung injury, and TLR4 surface expression, and, accordingly, reduced NF-κB signaling. In summary, our data demonstrated that pre-treatment with 10-min carbon dioxide inhalation can ameliorate LPS-induced lung injury. The protective effect may be associated with down-regulation of the surface expression of TLR4 in the lungs.

The effect of isocapnic hyperventilation on early recovery after remifentanil/sevoflurane anesthesia in O2 /air: A randomized trial

BACKGROUND

Isocapnic hyperventilation (ICHV) may hasten emergence from general anesthesia but remains inadequately studied. We prospectively determined emergence time after sevoflurane anesthesia of variable duration with and without ICHV.

METHODS

In 25 ASA I-II patients, general anesthesia was maintained with one age-adjusted MAC sevoflurane in O₂ /air and target-controlled remifentanil delivery. At the start of skin closure, the remifentanil effect-site concentration was reduced to 1.5 ng/mL, any residual neuromuscular block reversed, and once the remifentanil effect-site concentration had decreased to 1.5 ng/mL, remifentanil and sevoflurane administration was stopped, and the fresh gas flow increased above minute ventilation. Patients randomly received either normoventilation (n = 13) or ICHV (doubling minute ventilation while titrating CO₂ into the inspiratory limb to maintain isocapnia [n = 12]). Three early recovery end points were determined: time to proper response to verbal command; time to extubation; and time to stating one's name.

RESULTS

Demographics were the same in both groups. Recovery end points were reached faster in the ICHV group compared to the normoventilation group: time to proper response to verbal command was 7.6 ± 2.2 vs 9.9 ± 2.9 min (P = 0.03); time to extubation was 7.6 ± 2.6 vs 11.0 ± 2.4 min (P = 0.002); and time to stating one's name was 8.9 ± 2.8 vs 12.5 ± 2.6 min (P = 0.003). Within each group, duration of anesthesia only marginally affected the times to reach these recovery end points.

CONCLUSION

Isocapnic hyperventilation only had a small effect on emergence times after anesthesia, suggesting that isocapnic hyperventilation may have limited clinical benefits with modern potent inhaled anesthetics.

Isocapnic hyperventilation provides early extubation after head and neck surgery: A prospective randomized trial

BACKGROUND

Isocapnic hyperventilation (IHV) shortens recovery time after inhalation anaesthesia by increasing ventilation while maintaining a normal airway carbon dioxide (CO2)-level. One way of performing IHV is to infuse CO2 to the inspiratory limb of a breathing circuit during mechanical hyperventilation (HV). In a prospective randomized study, we compared this IHV technique to a standard emergence procedure (control).

METHODS

Thirty-one adult ASA I-III patients undergoing long-duration (>3 hours) sevoflurane anaesthesia for major head and neck surgery were included and randomized to IHV-treatment (n = 16) or control (n = 15). IHV was performed at minute ventilation 13.6 ± 4.3 L/min and CO2 delivery, dosed according to a nomogram tested in a pilot study. Time to extubation and eye-opening was recorded. Inspired (FICO2) and expired (FETCO2) CO2 and arterial CO2 levels (PaCO2) were monitored. Cognition was tested preoperatively and at 20, 40 and 60 minutes after surgery.

RESULTS

Time from turning off the vapourizer to extubation was 13.7 ± 2.5 minutes in the IHV group and 27.4 ± 6.5 minutes in controls (P < .001). Two minutes after extubation, PaCO2 was 6.2 ± 0.5 and 6.2 ± 0.6 kPa in the IHV and control group respectively. In 69% (IHV) vs 53% (controls), post-operative cognition returned to pre-operative values within 40 minutes after surgery (NS). Incidences of pain and nausea/vomiting did not differ between groups.

CONCLUSIONS

In this randomized trial comparing an IHV method with a standard weaning procedure, time to extubation was reduced with 50% in the IHV group. The described IHV method can be used to decrease emergence time from inhalation anaesthesia.

Hypercapnia does not shorten emergence time from propofol anesthesia: a pilot randomized clinical study

Background

The elimination of anesthetic agents is a decisive factor in the emergence from general anesthesia. In this pilot study, we hypothesized that hypercapnia would decrease the emergence time from propofol anesthesia by increasing cardiac output and cerebral blood flow.

Methods

A total of 32 patients were randomly divided into two groups based on the end-tidal carbon dioxide values: 30 mmHg (the hypocapnia group) and 50 mmHg (the hypercapnia group). Propofol and remifentanil were infused to maintain a bispectral index of 40–50. Remifentanil infusion was stopped 10 min before the discontinuation of propofol. After cessation of propofol infusion, ventilation settings in the hypocapnia group were maintained constant; a rebreathing tube was connected to the respiratory circuit in the hypercapnia group. The time to spontaneous respiration, eye opening (primary endpoint), mouth opening, and tracheal extubation was recorded and analyzed.

Results

Time to eye opening was 9.7 (1.3) min in the hypocapnia group and 9.0 (1.0) min in the hypercapnia group. The difference in the mean times to eye opening between groups was −0.7 min (95% CI, −4.0 to 2.7, P = 0.688). On multiple regression analysis, there was a significant difference in the mean time to eye opening between males and females. Females recovered about 3.6 min faster than males (95% CI, −6.1 to −1.1, P = 0.009).

Conclusions

We could not detect a beneficial effect of hypercapnia on propofol emergence time. Irrespective of hypercapnia, females seemed to recover faster than males.

Evaluation of a method for isocapnic hyperventilation: a clinical pilot trial

BACKGROUND

Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia using hyperventilation (HV) without lowering airway CO₂ . In a clinical trial on patients undergoing long-duration sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, we evaluated the utility of a technique for CO₂ delivery (DCO₂ ) to the inspiratory limb of a closed breathing circuit, during HV, to achieve isocapnia.

METHODS

Fifteen adult ASA 1-3 patients were included. After end of surgery, mechanical HV was started by doubling baseline minute ventilation. Simultaneously, CO₂ was delivered and dosed using a nomogram developed in a previous experimental study. Time to extubation and eye opening was recorded. Inspired (FICO₂ ) and expired (FETCO₂ ) CO₂ and arterial CO₂ levels were monitored during IHV. Cognition was tested pre-operatively and at 20, 40 and 60 min after surgery.

RESULTS

A DCO₂ of 285 ± 45 ml/min provided stable isocapnia during HV (13.5 ± 4.1 l/min). The corresponding FICO₂ level was 3.0 ± 0.3%. Time from turning off the vaporizer (1.3 ± 0.1 MACage) to extubation (0.2 ± 0.1 MACage) was 11.3 ± 1.8 min after 342 ± 131 min of anaesthesia. PaCO₂ and FETCO₂ remained at normal levels during and after IHV. In 85% of the patients, post-operative cognition returned to pre-operative values within 60 min.

CONCLUSIONS

In this cohort of patients, a DCO₂ nomogram for IHV was validated. The patients were safely extubated shortly after discontinuing long-term sevoflurane anaesthesia. Perioperatively, there were no adverse effects on arterial blood gases or post-operative cognition. This technique for IHV can potentially be used to decrease emergence time from inhalation anaesthesia.

Isocapnic hyperventilation shortens washout time for sevoflurane - an experimental in vivo study

BACKGROUND

Isocapnic hyperventilation (IHV) is a method that fastens weaning from inhalation anaesthesia by increasing airway concentration of carbon dioxide (CO2 ) during hyperventilation (HV). In an animal model, we evaluated a technique of adding CO2 directly to the breathing circuit of a standard anaesthesia apparatus.

METHODS

Eight anaesthetised pigs weighing 28 ± 2 kg were intubated and mechanically ventilated. From a baseline ventilation of 5 l/min, HV was achieved by doubling minute volume and fresh gas flow. Respiratory rate was increased from 15 to 22/min. The CO2 absorber was disconnected and CO2 was delivered (DCO2 ) to the inspiratory limb of a standard breathing circuit via a mixing box. Time required to decrease end-tidal sevoflurane concentration from 2.7% to 0.2% was defined as washout time. Respiration and haemodynamics were monitored by blood gas analysis, spirometry, electric impedance tomography and pulse contour analysis.

RESULTS

A DCO2 of 261 ± 19 ml/min was necessary to achieve isocapnia during HV. The corresponding FICO2 -level remained stable at 3.1 ± 0.3%. During IHV, washout of sevoflurane was three times faster, 433 ± 135 s vs. 1387 ± 204 s (P < 0.001). Arterial CO2 tension and end-tidal CO2 , was 5.2 ± 0.4 kPa and 5.6 ± 0.4%, respectively, before IHV and 5.1 ± 0.3 kPa and 5.7 ± 0.3%, respectively, during IHV.

CONCLUSIONS

In this experimental in vivo model of isocapnic hyperventilation, the washout time of sevoflurane anaesthesia was one-third compared to normal ventilation. The method for isocapnic hyperventilation described can potentially be transferred to a clinical setting with the intention to decrease emergence time from inhalation anaesthesia.

A simple method for isocapnic hyperventilation evaluated in a lung model

BACKGROUND

Isocapnic hyperventilation (IHV) has the potential to increase the elimination rate of anaesthetic gases and has been shown to shorten time to wake-up and post-operative recovery time after inhalation anaesthesia. In this bench test, we describe a technique to achieve isocapnia during hyperventilation (HV) by adding carbon dioxide (CO2) directly to the breathing circuit of a standard anaesthesia apparatus with standard monitoring equipment.

METHODS

Into a mechanical lung model, carbon dioxide was added to simulate a CO2 production (V(CO2)) of 175, 200 and 225 ml/min. Dead space (V(D)) volume could be set at 44, 92 and 134 ml. From baseline ventilation (BLV), HV was achieved by doubling the minute ventilation and fresh gas flow for each level of V(CO2), and dead space. During HV, CO2 was delivered (D(CO2)) by a precision flow meter via a mixing box to the inspiratory limb of the anaesthesia circuit to achieve isocapnia.

RESULTS

During HV, the alveolar ventilation increased by 113 ± 6%. Tidal volume increased by 20 ± 0.1% during IHV irrespective of V(D) and V(CO2) level. D(CO2) varied between 147 ± 8 and 325 ± 13 ml/min. Low V(CO2) and large V(D) demanded a greater D(CO2) administration to achieve isocapnia. The FICO2 level during IHV varied between 2.3% and 3.3%.

CONCLUSION

It is possible to maintain isocapnia during HV by delivering carbon dioxide through a standard anaesthesia circuit equipped with modern monitoring capacities. From alveolar ventilation, CO2 production and dead space, the amount of carbon dioxide that is needed to achieve IHV can be estimated.

Effect of Acute Hypercapnia on Outcomes and Predictive Risk Factors for Complications among Patients Receiving Bronchoscopic Interventions under General Anesthesia

Background

The aim of this study is to investigate the effect of acute hypercapnia on surgery outcomes among patients receiving bronchoscopic interventions under general anesthesia. Furthermore, independent predictive factors for surgery complications were analyzed.

Method

A total of 323 patients with airway stenosis were enrolled in this retrospective study. Each patient underwent interventional rigid bronchoscopy under general anesthesia. Arterial blood gas (ABG) was measured intraoperatively. In light of PaCO₂ levels in ABG, patients were divided into three groups: Group C (control) (PaCO₂:≤ 60 mmHg), Group M (moderate) (PaCO₂:61–100 mmHg), and Group S (severe) (PaCO₂: >100 mmHg). Parameters, including PaO₂ levels and recovery delays, were compared across three groups. Complications among patients receiving bronchoscopic interventions were evaluated as well. Independent predictive factors for surgery related complications were analyzed by multivariable regression method.

Results

Significant differences in weight (p=0.04), ASA IV (p=0.008), dyspnea index (p=0.003),COPD (p=0.02), dynamic airway collapse (p=0.002), severe stenosis severity (p=0.02), and stenosis locations among three groups were observed. Mild (PaCO₂:~60 mmHg) to moderate (PaCO₂:60–100 mmHg) hypercapnia was not associated with delayed recovery, whereas severe hypercapnia (PaCO₂:>100 mmHg) was associated with delayed recovery, as well as declined PaO₂ (p=0.00) and elevated blood glucose levels (p=0.00). The complications of bronchoscopic interventions included postoperative congestive heart failure (14 cases, 4.3%), tracheorrhagia (8 cases, 2.5%), delayed recovery (19 cases, 5.9%), and transfers to ICU after surgery (10 cases, 3.1%). The multivariable regression analysis showed that procedure duration (p=0.003), lobectomy (p=0.007), dynamic airway collapse (p=0.01), severe bronchial stenosis (p=0.01) and hypercapnia (p=0.02) were independent predictive factors for surgery related complications.

Conclusions

Acute hypercapnia lower than 100 mmHg was not associated with detrimental consequences, whereas severe hypercapnia (PaCO₂: >100 mmHg) was associated with lower levels of PaO₂. Hypercapnia was an independent predictive factor for bronchoscopic intervention complication, which may help physicians to optimize the therapeutic choices.

Hypercapnic hyperventilation shortens emergence time from Propofol and Isoflurane anesthesia

Objective:

The aim of this study is to compare the effects of hypercapnic hyperventilation and normocapnic normoventilation on emergence time from propofol and isoflurane anesthesia.

Methods:

In this clinical trial, the differences in emergence time were evaluated in 80 patients undergoing elective abdominal surgery in Alzahra University hospital, Isfahan, Iran, in 2011-2012. Patients were randomly divided into four groups (groups 1-4) receiving isoflurane hypercapnic hyperventilation, isoflurane normocapnic normoventilation, propofol hypercapnic hyperventilation, and propofol normocapnic normoventilation, respectively. Hypercapnia was maintained by adding CO₂ to the patient's inspired gas during hyperventilation. The emergence time and the duration of stay in recovery room in the four groups were measured and compared by one-way analysis of variance (ANOVA) and least significant difference tests.

Findings:

The average emergence time in groups 1, 2, 3, and 4 were (11.3 ± 3.2), (15.2 ± 3.8), (9 ± 4.2) and (11.8 ± 5.3) min, respectively. These differences were significant (P = 0.001). In patients receiving propofol hypercapnic hyperventilation, the emergence time was faster than in other groups. There was also a significant difference in duration of stay in recovery room between the groups (P = 0.004). Patients who received isoflurane hypercapnic hyperventilation had a shortest length of stay in the recovery room.

Conclusion:

The emergence time after intravenous anesthesia with propofol can be shortened significantly by using hyperventilation and hypercapnia, without any side effects.

Post-operative hypercapnia-induced hyperpnoea accelerates recovery from sevoflurane anaesthesia: a prospective randomised controlled trial

BACKGROUND

The time to recovery from vapour anaesthesia is shortened by an increase in ventilation while maintaining normocapnia. Hypercapnia during emergence from anaesthesia in spontaneously breathing patients also increases anaesthetic clearance from the brain by increasing cerebral blood flow. We hypothesised that hypercapnia-induced hyperpnoea accelerates emergence from sevoflurane anaesthesia compared to the standard anaesthesia protocol.

METHODS

After Ethics Review Board approval, 44 ASA I-III patients undergoing elective gynaecological surgery were randomised after surgery to either hypercapnic hyperpnoea or control groups. In the hypercapnic hyperpnoea group, the end-tidal CO2 was adjusted to a range of 6.0-7.3 kPa to maintain a minute ventilation of 10-15 l/min. Recovery indices were compared using unpaired t-tests and ANOVA.

RESULTS

Prior to extubation, minute ventilation and end-tidal CO2 in hypercapnic hyperpnoea and control groups were 10.3 ± 1.7 l/min vs. 5.4 ± 1.2 l/min (P < 0.001) and 6.6 ± 0.6 kPa and 5.2 ± 0.5 kPa (P < 0.001), respectively. Compared to control, the study group had shorter time to extubation [4.4 ± 1.3 (SD) vs. 9.8 ± 4.4 min, P < 0.01], BIS recovery to > 75 (2.4 ± 0.9 vs. 6.1 ± 3.1 min, P < 0.01), eye opening (3.9 ± 1.6 vs. 9.8 ± 6.2 min, P < 0.01), eligibility for leaving operating room (5.1 ± 1.2 vs. 11.1 ± 4.6 min, P < 0.01), and post-anaesthesia care unit (73.9 ± 14.2 vs. 89.4 ± 22.6)

CONCLUSION

Hypercapnic hyperpnoea in spontaneously breathing patients halves the time of recovery from sevoflurane-induced anaesthesia in the operating room.

Theoretical effect of hyperventilation on speed of recovery and risk of rehypnotization following recovery - a GasMan® simulation

Background

Hyperventilation may be used to hasten recovery from general anesthesia with potent inhaled anesthetics. However, its effect may be less pronounced with the newer, less soluble agents, and it may result in rehypnotization if subsequent hypoventilation occurs because more residual anesthetic will be available in the body for redistribution to the central nervous system. We used GasMan^® simulations to examine these issues.

Methods

One MAC of isoflurane, sevoflurane, or desflurane was administered to a fictitious 70 kg patient for 8 h with normoventilation (alveolar minute ventilation [V_A] 5 L.min^-1), resulting in full saturation of the vessel rich group (VRG) and >95% saturation of the muscle group. After 8 h, agent administration was stopped, and fresh gas flow was increased to 10 L.min^-1 to avoid rebreathing. At that same time, we continued with one simulation where normoventilation was maintained, while in a second simulation hyperventilation was instituted (10 L.min^-1). We determined the time needed for the partial pressure in the VRG (F_VRG; representing the central nervous system) to reach 0.3 MAC (MACawake). After reaching MACawake in the VRG, several degrees of hypoventilation were instituted (V_A of 2.5, 1.5, 1, and 0.5 L.min^-1) to determine whether F_VRG would increase above 0.3 MAC(= rehypnotization).

Results

Time to reach 0.3 MAC in the VRG with normoventilation was 14 min 42 s with isoflurane, 9 min 12 s with sevoflurane, and 6 min 12 s with desflurane. Hyperventilation reduced these recovery times by 30, 18, and 13% for isoflurane, sevoflurane, and desflurane, respectively. Rehypnotization was observed with V_A of 0.5 L.min^-1 with desflurane, 0.5 and 1 L.min^-1 with sevoflurane, and 0.5, 1, 1.5, and 2.5 L.min^-1 with isoflurane. Only with isoflurane did initial hyperventilation slightly increase the risk of rehypnotization.

Conclusions

These GasMan^® simulations confirm that the use of hyperventilation to hasten recovery is marginally beneficial with the newer, less soluble agents. In addition, subsequent hypoventilation results in rehypnotization only with more soluble agents, unless hypoventilation is severe. Also, initial hyperventilation does not increase the risk of rehypnotization with less soluble agents when subsequent hypoventilation occurs. Well-controlled clinical studies are required to validate these simulations.

Effects of hypercapnic hyperpnea on recovery from isoflurane or sevoflurane anesthesia in horses

OBJECTIVE

To test the hypothesis that hypercapnic hyperpnea produced using endotracheal insufflation with 5-10% CO(2) in oxygen could be used to shorten anesthetic recovery time in horses, and that recovery from sevoflurane would be faster than from isoflurane.

STUDY DESIGN

Randomized crossover study design.

ANIMALS

Eight healthy adult horses.

METHODS

After 2 hours' administration of constant 1.2 times MAC isoflurane or sevoflurane, horses were disconnected from the anesthetic circuit and administered 0, 5, or 10% CO(2) in balance O(2) via endotracheal tube insufflation. End-tidal gas samples were collected to measure anesthetic washout kinetics, and arterial and venous blood samples were collected to measure respiratory gas partial pressures. Horses recovered in padded stalls without assistance, and each recovery was videotaped and evaluated by reviewers who were blinded to the anesthetic agent and insufflation treatment used.

RESULTS

Compared to isoflurane, sevoflurane caused greater hypoventilation and was associated with longer times until standing recovery. CO(2) insufflation significantly decreased anesthetic recovery time compared to insufflation with O(2) alone without significantly increasing PaCO(2) . Pharmacokinetic parameters during recovery from isoflurane with CO(2) insufflation were statistically indistinguishable from sevoflurane recovery without CO(2). Neither anesthetic agent nor insufflation treatment affected recovery quality from anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypercapnic hyperpnea decreases time to standing without influencing anesthetic recovery quality. Although the lower blood gas solubility of sevoflurane should favor a shorter recovery time compared to isoflurane, this advantage is negated by the greater respiratory depression from sevoflurane in horses.

Isocapnic hyperpnoea shortens postanesthetic care unit stay after isoflurane anesthesia

BACKGROUND

We conducted a prospective controlled clinical trial of the effect of isocapnic hyperpnoea (IH) on the times-to-recovery milestones in the operating room (OR) and postanesthetic care unit (PACU) after 1.5 to 3 hours of isoflurane anesthesia.

METHODS

Thirty ASA grade I-III patients undergoing elective gynecological surgery were randomized at the end of surgery to either IH or the conventional recovery (control). Six patients with duration of anesthesia of <90 minutes were excluded from the analysis. The anesthesia protocol included propofol, fentanyl, morphine, rocuronium, and isoflurane in air/O(2). Unpaired t tests and analyses of variance were used to test for differences in times-to-recovery indicators between the two groups.

RESULTS

The durations of anesthesia in IH and control groups were 140.8 + or - 32.7 and 142 + or - 55.6 minutes, respectively (P = 0.99). The time to extubation was much shorter in the IH group than in the control group (6.6 + or - 1.6 (SD) vs. 13. 6 + or - 3.9 minutes, respectively; P < 0.01). The IH group also had shorter times to eye opening (5.8 + or - 1.3 vs. 13.7 + or - 4.5 minutes; P < 0.01), eligibility for leaving the OR (8.0 + or - 1.7 vs. 17.4 + or - 6.1 minutes; P < 0.01), and eligibility for PACU discharge (74.0 + or - 16.5 vs. 94.5 + or - 14.7 minutes; P < 0.01). There were no differences in other indicators of recovery.

CONCLUSION

IH accelerates recovery after 1.5 to 3 hours of isoflurane anesthesia and shortens OR and PACU stay.

An evaluation of remifentanil-sevoflurane response surface models in patients emerging from anesthesia: model improvement using effect-site sevoflurane concentrations

INTRODUCTION

We previously reported models that characterized the synergistic interaction between remifentanil and sevoflurane in blunting responses to verbal and painful stimuli. This preliminary study evaluated the ability of these models to predict a return of responsiveness during emergence from anesthesia and a response to tibial pressure when patients required analgesics in the recovery room. We hypothesized that model predictions would be consistent with observed responses. We also hypothesized that under non-steady-state conditions, accounting for the lag time between sevoflurane effect-site concentration (Ce) and end-tidal (ET) concentration would improve predictions.

METHODS

Twenty patients received a sevoflurane, remifentanil, and fentanyl anesthetic. Two model predictions of responsiveness were recorded at emergence: an ET-based and a Ce-based prediction. Similarly, 2 predictions of a response to noxious stimuli were recorded when patients first required analgesics in the recovery room. Model predictions were compared with observations with graphical and temporal analyses.

RESULTS

While patients were anesthetized, model predictions indicated a high likelihood that patients would be unresponsive (> or = 99%). However, after termination of the anesthetic, models exhibited a wide range of predictions at emergence (1%-97%). Although wide, the Ce-based predictions of responsiveness were better distributed over a percentage ranking of observations than the ET-based predictions. For the ET-based model, 45% of the patients awoke within 2 min of the 50% model predicted probability of unresponsiveness and 65% awoke within 4 min. For the Ce-based model, 45% of the patients awoke within 1 min of the 50% model predicted probability of unresponsiveness and 85% awoke within 3.2 min. Predictions of a response to a painful stimulus in the recovery room were similar for the Ce- and ET-based models.

DISCUSSION

Results confirmed, in part, our study hypothesis; accounting for the lag time between Ce and ET sevoflurane concentrations improved model predictions of responsiveness but had no effect on predicting a response to a noxious stimulus in the recovery room. These models may be useful in predicting events of clinical interest but large-scale evaluations with numerous patients are needed to better characterize model performance.

Rapid Recovery from Sevoflurane and Desflurane with Hypercapnia and Hyperventilation

BACKGROUND

Hypercapnia with hyperventilation shortens the time between turning off the vaporizer (1 MAC) and when patients open their eyes after isoflurane anesthesia by 62%.

METHODS

In the present study we tested whether a proportional shortening occurs with sevoflurane and desflurane.

RESULTS

Consistent with a proportional shortening, we found that hypercapnia with hyperventilation decreased recovery times by 52% for sevoflurane and 64% for desflurane (when compared with normal ventilation with normocapnia).

CONCLUSION

Concurrent hyperventilation to rapidly remove the anesthetic from the lungs and rebreathing to induce hypercapnia can significantly shorten recovery times and produce the same proportionate decrease for anesthetics that differ in solubility.