Recurrent respiratory depression after total intravenous anaesthesia with propofol and alfentanil

Since first commented upon by Lamarche in 1984, several cases of recurrent respiratory arrest after alfentanil infusions have been reported. In all these cases the alfentanil infusions have been used to supplement conventional anaesthetic techniques with nitrous oxide and/or inhalational agents and in most cases rather high total alfentanil doses have been administered. We have seen two cases of severe recurrent respiratory depression in healthy patients after relatively minor procedures performed under total intravenous anaesthesia with propofol–alfentanil infusions, air–oxygen ventilation and muscle relaxation, where the alfentanil doses administered were quite small. These cases are presented in detail and compared within a tabulated presentation with the earlier published cases of alfentanil-related recurrent respiratory depression.     

Changes in respiratory pattern after repeated doses of diazepam and midazolam in healthy subjects

Changes in respiratory pattern and arterial PCO2 after three repeated intravenous sedative doses of midazolam 0.05 mg/kg or diazepam 0.15 mg/kg were studied in eight healthy male volunteers in a randomized double-blind crossover design. In order to reduce the influence of the measuring equipment, we utilized a noninvasive computerized technique to measure respiratory variables. Both drugs caused equal changes in breathing pattern with a decrease in tidal volume, an increase in respiratory rate and an unaltered minute ventilation. These alterations in breathing pattern were associated with CO2 retention. Respiratory changes were mainly induced by the first injection of either drug. Despite increased plasma drug concentrations, subsequent doses did not cause further changes in respiratory variables except for an increase in PCO2 after the second dose of midazolam. The clinical significance of these changes in PaCO2 in otherwise healthy individuals is probably limited. The duration of the subjective sensation of sedation was longer after diazepam than after midazolam.     

The effects of multiple small doses of exogenous surfactant on experimental respiratory failure induced by lung lavage in rats

Aim: To test the effect on pulmonary gas exchange and mechanics of multiple small doses of exogenous surfactant as an alternative to bolus delivery in experimental respiratory failure induced by lung lavage.
Methods: After anesthesia, tracheostomy and constant volume ventilation, respiratory failure was induced by lung lavage in 20 rats. Animals were randomly assigned to an untreated control group or two experimental groups. Equal total doses of modified porcine surfactant (200 mg ·kg^-1 body weight,) were given by tracheal instillation, either as a single bolus or in four (50 mg·kg^-1 b.w.) fractional doses at 10-min intervals. Arterial pH and blood gases, and peak inspiratory pressure (PIP) were measured.
Results: After lavage, a rapid decrease in arterial pH and PaO₂, and an increase in PaCO₂ and PIP were observed in all animals. In both surfactant-treated groups, PaO₂ increased after surfactant instillation, and remained significantly higher than controls throughout the experiment. Arterial pH was significantly higher and PaCO₂ significantly lower only in the single bolus group. In the multiple dose group, these levels were similar to those of controls.
Conclusions: In surfactant-depleted rats with respiratory failure, instillation of four fractional surfactant doses did not result in the same enhancement on gas exchange and PIP, in the following 60 min, as same total dose given by a single bolus.     

Propofol or halothane anaesthesia for children with asthma: effects on respiratory mechanics

Propofol may cause histamine release and alter airway tone and reactivity. Although its use has been reported to be safe in asthmatics, there is a lack of information on its effect on lung function in children with asthma. We measured respiratory mechanics after i.v. or inhalation anaesthesia in 60 children, aged 2-12 yr, with or without asthma. Anaesthesia was induced with propofol 3 mg kg-1, fentanyl 1 microgram kg-1 and atracurium 0.5 mg kg-1 and maintained with an infusion of propofol 10 mg kg-1h-1 and 50% nitrous oxide in oxygen. Halothane was administered subsequently at a concentration of 1 MAC. Respiratory mechanics were measured by applying a single- compartment model using multi-linear regression analysis to calculate dynamic compliance (Crs,dyn) and respiratory system resistance (Rrs), based on: Pao = V/Crs,dyn + V Rrs + PA,EE, where Pao = airway opening pressure, PA,EE = alveolar pressure, V = volume and V = flow. The two groups were comparable in age, weight and ventilation variables (tidal volume and peak pressure). Respiratory mechanics during propofol anaesthesia were comparable in normal and asthmatic children (Rrs = 20.5 X 10(-4) (SD 5.2 X 10(-4)) vs 21.5 X 10(-4) (5.7 X 10(-4)) kPa ml- 1 S-1 (ns) and Crs,dyn = 247.5 (76.51 vs 235.1 (63.8) ml kPa-1 (ns)). Halothane produced a minimal decrease in Rrs and a minimal increase in tidal volume in both groups without changes in Crs,dyn. In conclusion, respiratory mechanics were comparable after propofol anaesthesia in both children with and without asthma. Changes in Rrs after halothane administration were not clinically relevant.      

Remifentanil or sufentanil for coronary surgery: comparison of postoperative respiratory impairment

BACKGROUND AND OBJECTIVE: High-dose opioid anaesthesia contributes to decreasing metabolic and hormonal stress responses in patients undergoing cardiac surgery. However, the increase in context-sensitive half-life of opioids given as a high-dose regimen can affect postoperative respiratory recovery. In contrast, remifentanil can be given in high doses without prolonging context-sensitive half-life due to its rapid metabolism. Therefore, we performed a prospective, randomized trial to compare anaesthesia consisting of propofol/remifentanil or propofol/sufentanil with regard to postoperative respiratory function and outcome. METHODS: Patients undergoing coronary artery bypass grafting were randomized to a propofol/remifentanil (0.5-1.0 microg kg(-1) min(-1)) or propofol/sufentanil (30-40 ng kg(-1) min(-1)) based anaesthetic. Carbon dioxide response, forced expiratory volume in one second, vital capacity, and functional residual capacity were measured 1 day prior to the operation, 1 h before extubation, 1, 24 and 72 h after extubation. In addition, the incidence of atelectasis, pulmonary infiltrates, intensive care unit and postoperative length of stay were compared. Patients and physicians were blinded to the treatment group. RESULTS: Twenty-five patients in each treatment group completed the study. There was no difference between patients of the treatment groups regarding demographics, risk- or pain scores. In all patients, carbon dioxide response, forced expiratory volume in one second, vital capacity and functional residual capacity were decreased postoperatively compared to baseline. Patients randomized to remifentanil had less depression of carbon dioxide response, less atelectasis and shorter postoperative length of stay (12 d vs. 10 d) than after sufentanil (P < 0.05). CONCLUSIONS: Intraoperative use of high-dose remifentanil for coronary artery bypass grafting may be associated with improved recovery of pulmonary function and shorter postoperative hospital length of stay than sufentanil.     

Effects of EDTA- and sulfite-containing formulations of propofol on respiratory system resistance after tracheal intubation in smokers

BACKGROUND: The formulation of sulfite-containing propofol (SCP) has not been thoroughly investigated in patients with the extensive smoking history for the effects on the total respiratory system resistance after tracheal intubation. However adverse effects, including acute asthma and bronchospasm, have been reported with several other parenteral formulations of drugs containing sulfite as preservative. Therefore, the aim of this prospective randomized and double blind study was to investigate the effects of EDTA-containing propofol (ECP) and SCP on total respiratory system resistance (Rrs) in patients with the prolonged smoking history and undergoing propofol-based total intravenous anesthesia with tracheal intubation. METHODS: 40 patients scheduled for general anesthesia were enrolled into the study. Anesthesia was induced with either 2 mg/kg ECP, or 2 mg/kg SCP followed by vecuronium (0.1 mg/kg) to ensure complete neuromuscular relaxation for the time of the study. Maintenance anesthesia was continued with propofol infusion at 0.15 mg/kg/min for the first 15 min after intubation. Total respiratory system resistance (Rrs), was measured continuously for 10 min postintubation. RESULTS: The analysis of repeated Rrs measurements taken every minute for 10 min postintubation revealed trend consisting of higher Rrs in the SCP group when compared to the ECP group. The statistical analysis of the data performed using repeated measures analysis of covariance demonstrated statistically significant effect (P < 0.05) of the treatment group factor (SCP vs. ECP) and the time factor (time after intubation) on the postintubation Rrs. CONCLUSION: The total respiratory system resistance measured repeatedly for 10 min after tracheal intubation in patients with smoking history is significantly elevated after induction with SCP than after induction with ECP. The preservative used for propofol formulation may alter the effects of propofol on the total respiratory system resistance in smokers.     

Comparison of the effects of fentanyl on respiratory mechanics under propofol or thiopental anaesthesia

Twenty patients were randomly anaesthetized with either thiopental 5 mg/kg followed by a 15 mg/kg/h continuous infusion, or propofol 2.5 mg/kg followed by a 9 mg/kg/h continuous infusion, paralysed with vecuronium 0.1 mg/kg, intubated and ventilated with nitrous oxide 50% in oxygen. Fifteen minutes after induction, fentanyl 5 micrograms/kg was injected. Inspiratory tracheal pressure (PT), gas flow (V) and volume (V) were continuously measured while the lungs were inflated with a constant inspiratory flow ventilator. Respiratory compliance (Crs) and resistance (Rrs) were calculated from the regression of PT on V. In both groups Crs decreased following anaesthesia. Fentanyl injection elicited an increase in Rrs (from 1.04 +/- 0.70 to 1.63 +/- 0.92 kPa x l-1 x s) and a further decrease in Crs (from 0.55 +/- 0.30 to 0.42 +/- 0.10 l x kPa-1) in the thiopental group but not in the propofol group (Rrs: 1.26 +/- 0.69 to 1.08 +/- 0.44 kPa x l-1 x s, Crs: 0.49 +/- 0.11 to 0.48 +/- 0.13 l x kPa-1). These results suggest that the dose of propofol administered in this study may prevent fentanyl-induced bronchoconstriction.     

The cardiovascular changes associated with equipotent anaesthesia with either propofol or isoflurane

The differences in effects of anaesthetic agents on right ventricular function have not been studied. We have developed a cross–over study design to compare the effects of propofol and isoflurane on cardiac and specifically right ventricular function. Ten patients were anaesthetised with equivalent MAC of isoflurane to MIR of propofol. After measurements had been taken on the randomly assigned first agent the patients were crossed over to the other agent and measurements were repeated. Cardiac function was assessed using a pulmonary artery catheter with a fast response thermistor. There were no differences in heart rate or blood pressure between the two agents suggesting that equivalent anaesthetic doses had been given. There were significantly ( P < 0.05) higher cardiac output (4.0 to 4.5 1 min^-1), right ventricular ejection fraction (35.1 to 39.4%), stroke volume (35.4 to 39.6 ml) and right ventricular end–diastolic volume index (102 to 110 ml m^2–1) with propofol compared to isoflurane. We conclude that propofol results in improved right ventricular performance compared to isoflurane. We have also shown that anaesthetic agents can be compared using a cross–over study design, and have demonstrated that MAC of isoflurane and MIR of propofol can be directly compared. We suggest that propofol may be a more suitable agent than isoflurane for anaesthesia in patients who may already have impaired right ventricular function and in whom maintaining high cardiac output may be beneficial.     

The effects of thiopental and generic and nongeneric propofol on respiratory resistance during anesthetic induction in patients with reactive airways

STUDY OBJECTIVE: To demonstrate a favorable effect of propofol on respiratory system resistance during anesthetic induction, and to determine if generic propofol causes adverse effects on respiratory resistance. DESIGN: Randomized pilot study. SETTING: Anesthetic induction for elective surgery. PATIENTS: 27 consenting ASA physical status II and III patients with reactive airways (positive smoking history or chronic obstructive pulmonary disease), but not receiving bronchodilator therapy. INTERVENTIONS: Patients were randomized equally to one of three anesthetic induction (and maintenance) drugs: sodium thiopental, 5 mg/kg (25 microg/kg/min), generic or nongeneric propofol, 1.25 mg/kg (50 microg/kg/min). They received preinduction midazolam and fentanyl (2 mg and 150 microg) and intravenous lidocaine (0.5 mg/kg). After anesthetic induction, tracheal intubation was established, and predetermined settings for mechanical ventilation were initiated. MEASUREMENTS: Immediately after intubation, a sensor was placed on the 8-mm endotracheal tube to detect baseline airway pressure and flow. During maintenance, repeat measurements of pressure and flow were obtained at 2.5-minute intervals for 10 minutes. Respiratory system resistance was derived off-line using the isovolumetric technique. MAIN RESULTS: Patients were similar across groups. The respiratory resistance measured after anesthetic induction did not differ among groups. During the maintenance infusion of thiopental or propofol, respiratory resistance increased gradually across all groups. There was no difference in the response of respiratory resistance either at induction or during the 10-minute maintenance between the generic and the nongeneric propofol groups. CONCLUSIONS: In contrast to earlier reports, this pilot study was unable to document a difference in the respiratory resistance in patients induced with thiopental or propofol. In addition, we were unable to demonstrate any different respiratory responses between generic propofol, containing sodium metabisulfite preservative, and nongeneric propofol.     

Interaction between sufentanil and U-50488H with respect to antinociception and respiratory depression in rats

Background: Opiate receptors have been argued to differentially regulate analgesia and respiratory depression. In order to validate possible interactions between the opiate mu- and kappa-receptors, interactions between sufentanil and U-50488H were studied in rats.
Methods: Rats equipped with an arterial catheter were tested in the tail flick latency (TFL) test after intravenous treatment with sufentanil (a mu-agonist), U-50488H a kappa-agonist) or fixed ratio combinations of both drugs. Simultaneously, respiratory changes were monitored by blood gas analysis.
Results: The ED₅₀s of sufentanil for a TFL >6.0 and <10.0 s were 0.0002 and 0.00059 mg/kg. For U-50488H the corresponding values were 1.53 and 8.11 mg/kg. Using a fixed dose ratio of 1/10000, an additivity was demonstrated between sufentanil and U-50488H in terms of antinociception. With regard to respiratory parameters, PaCO₂ significantly increased after all doses of sufentanil early after treatment. At the higher doses tested, there was also a decrease in PaO₂ and O₂ saturation. For U-50488H only the highest doses resulted in an early and small shift in PaCO₂. The combination of sufentanil/U-50488H resulted in only a small increase in PaCO₂ at the highest dose regimen tested.
Conclusion: The results presented here demonstrate that drug mixtures of sufentanil and U-50488H can be additive with respect to antinociception with additionally less risk for respiratory side-effects, as compared with sufentanil alone. Therefore, a combination of mu- and kappa-opiate receptor agonists might be more beneficial than each agent alone.     

Liquid ventilation: an adjunct for respiratory management

Although significant advances in respiratory care have reduced mortality of patients with respiratory failure, morbidity persists, often resulting from iatrogenic mechanisms. Mechanical ventilation with gas has been shown to initiate as well as exacerbate underlying lung injury, resulting in progressive structural damage and release of inflammatory mediators within the lung. Alternative means to support pulmonary gas exchange while preserving lung structure and function are therefore required. Perfluorochemical (PFC) liquids are currently used clinically in a number of ways, such as intravascular PFC emulsions for volume expansion/oxygen carrying/angiography and intracavitary neat PFC liquid for image contrast enhancement or vitreous fluid replacement. As a novel approach to replace gas as the respiratory medium, liquid assisted ventilation (LAV) with PFC liquids has been investigated as an alternative respiratory modality for over 30 years. Currently, there are several theoretical and practical applications of LAV in the immature or mature lung at risk for acute respiratory distress and injury associated with mechanical ventilation.     

The relationship between the respiratory parameters under spontaneous breathing and effect site propofol concentrations

BACKGROUND: The prediction of the hypnotic states is useful to maintain the adequate anesthesia. During propofol anesthesia, the respiratory depression has been documented in a dose-dependent manner. Therefore, we investigated whether the respiratory depression under the spontaneous breathing reflected the estimated effect site propofol concentrations (Cp) in a dose-dependent fashion. METHODS: We enrolled 12 patients for elective lower limb surgery under combined subarachnoid anesthesia and propofol sedation. The respiratory parameters and BIS were measured at the Cp of 5 microg x ml(-1) followed by the 0.5 microg x ml(-1) decrements until the patients' movement. Effective indices to predict patients' movement were determined by receiver-operator characteristics. RESULTS: The significant correlations within a particular patient between the respiratory parameters and Cp were observed, although those were not between the patients. An EtCO2 of 53 mmHg or greater represents a clinically determinant condition for non-movement of the patients. CONCLUSIONS: We concluded that the respiratory parameters during spontaneous breathing were useful indices to predict the changes in the effect site propofol concentrations and to maintain the adequate anesthetic levels.     

Effect of tidal volume and respiratory rate on the power of breathing calculation

BACKGROUND: The power of breathing (PoB) is used to estimate the mechanical workload of the respiratory system. Aim of this study was to investigate the effect of different tidal volume-respiratory rate combinations on the PoB when the elastic load is constant. In order to assure strict control of the experimental conditions, the PoB was calculated on an airway pressure-volume curve in mechanically ventilated patients. METHODS: Ten patients received three different tidal volume-respiratory rate combinations while minute ventilation was constant. Respiratory mechanics, PoB and its elastic and resistive components were calculated. Alternative methods to estimate the elastic workload were assessed: elastic work of breathing per litre per minute, elastic workload index (the square root of elastic work of breathing multiplied by respiratory rate) and elastic double product of the respiratory system (the elastic pressure multiplied by respiratory rate). RESULTS: Despite constant elastance and minute ventilation, the elastic PoB showed an increment greater than 200% from the lower to the greater tidal volume, accounting for approximately 80% of the whole PoB increment. On the contrary, elastic work of breathing per litre per minute, elastic workload index and elastic double product did not change. CONCLUSION: Changes in breathing pattern markedly affect the PoB despite constant mechanical load. Other indexes could assess the elastic workload without tidal volume dependence. Power of breathing use should be avoided to compare different mechanical loads or efficiencies of the respiratory muscles when tidal volume is variable.     

Effects of sevoflurane on respiratory activities in the phrenic nerve of decerebrate cats

Although the depressive effect of sevoflurane on ventilation has been reported, its potency and mode of action on the neural respiratory activity is still unclear. Therefore, the effects of sevoflurane on the phrenic nerve discharge and the respiratory timing were compared with those of halothane.
The efferent activity of the phrenic nerve was recorded from decerebrate, un-anesthetized and artificially ventilated cats, and its power spectrum was calculated. The inspiratory and expiratory periods were measured. Sevoflurane and halothane of the doses of 0.5–1.5 MAC were inhaled for 15 min.
With 0.5 MAC, sevoflurane decreased the total power and two dominant spectral components of the high-frequency oscillation and medium-frequency oscillation in the power spectrum. With the same MAC dose, halothane had a greater depressive effect in a normocapnic condition with the vagus nerves being intact. In a state of hypercapnia or after vagotomy, the effect of halothane was considerably attenuated whereas that of sevoflurane remained unaltered. Halothane increased the neural respiratory rate much more than sevoflurane in both normocapme and hypercapnic states. Vagotomy significantly weakened the effect of halothane to increase the respiratory rate but did not modify the effect of sevoflurane. With 1.0–1.5 MAC, both anesthetics severely decreased the phrenic power spectra and the potency difference became indistinct.
The present findings demonstrate that sevoflurane has a weaker depressive effect on the respiratory nerve discharge and a smaller effect on the neural respiratory rate than halothane when the effects of 0.5 MAC were compared. This may be due to the lesser effect of sevoflurane on the vagal mediated and CO₂-related mechanisms which modulate the global outputs of the central respiratory control system.     

Changes in respiratory mechanics and gas exchange during the acute respiratory distress syndrome

BACKGROUND: The time course of impairment of respiratory mechanics and gas exchange in the acute respiratory distress syndrome (ARDS) remains poorly defined. We assessed the changes in respiratory mechanics and gas exchange during ARDS. We hypothesized that due to the changes in respiratory mechanics over time, ventilatory strategies based on rigid volume or pressure limits might fail to prevent overdistension throughout the disease process. METHODS: Seventeen severe ARDS patients {PaO2/FiO2 10.1 (9.2-14.3) kPa; 76 (69-107) mmHg [median (25th-75th percentiles)] and bilateral infiltrates} were studied during the acute, intermediate, and late stages of ARDS (at 1-3, 4-6 and 7 days after diagnosis). Severity of lung injury, gas exchange, and hemodynamics were assessed. Pressure-volume (PV) curves of the respiratory system were obtained, and upper and lower inflection points (UIP, LIP) and recruitment were estimated. RESULTS: (1) UIP decreased from early to established (intermediate and late) ARDS [30 (28-30) cmH2O, 27 (25-30) cmH2O and 25 (23-28) cmH2O (P=0.014)]; (2) oxygenation improved in survivors and in patients with non-pulmonary etiology in late ARDS, whereas all patients developed hypercapnia from early to established ARDS; and (3) dead-space ventilation and pulmonary shunt were larger in patients with pulmonary etiology during late ARDS. CONCLUSION: We found a decrease in UIP from acute to established ARDS. If applied to our data, the inspiratory pressure limit advocated by the ARDSnet (30 cmH2O) would produce ventilation over the UIP, with a consequent increased risk of overdistension in 12%, 43% and 65% of our patients during the acute, intermediate and late phases of ARDS, respectively. Lung protective strategies based on fixed tidal volume or pressure limits may thus not fully avoid the risk of lung overdistension throughout ARDS.     

异丙酚用于人工流产手术麻醉的临床观察

３０例人工流产手术患者接受异丙酚静脉全麻。诱导剂量为２．５ｍｇ／ｋｇ，术中必要时分次追加２０～５０ｍｇ以维持适当麻醉深度。结果表明，异丙酚诱导起效快而平稳，术后恢复迅速而完全，无明显不良反应。麻醉时间及用药量的增加对术后恢复无明显影响。异丙酚对循环及呼吸有轻度抑制作用。我们认为异丙酚是一种安全有效的静脉麻醉药，能提供高质量的诱导及术后恢复。     

Anesthesia for a patient with mitochondrial respiratory chain complex III deficiency

Mitochondrial myopathies make up a group of rare disorders whose onset is in childhood or adolescence. Muscle and central nervous system involvement is variable. Mitochondrial respiratory chain complex III deficiency (coenzyme Q - cytochrome C reductase) can manifest as exercise intolerance, myopathy, encephalopathy, and myocardial disease. Approximately 38 patients with complex III deficiency have been described since 1966, yet only a single anesthetic experience (epidural analgesia for cesarean delivery) has been reported. We describe the case of an 11-year-old boy with mitochondrial respiratory chain complex III deficiency, severe myopathy, and moderate encephalopathy who underwent surgery to improve right ischiotibial muscle spasticity. Monitoring included electrocardiography, noninvasive blood pressure, oxygen saturation by pulse oximetry, end-tidal carbon dioxide pressure, esophageal temperature, spirometry, and neuromuscular block (Relaxograph Datex). Midazolam, fentanyl, and propofol were used for anesthetic induction; mivacurium was used during intubation. Anesthetic maintenance was with propofol in continuous infusion and fractionated doses of fentanyl and mivacurium on demand in a mixture of oxygen and air. The boy's response to mivacurium was abnormal but he could nevertheless be extubated in the operating room at a train-of-four ratio of 75% and with no need to reverse the neuromuscular blockade. There were no problems during the anesthetic procedure, so it could be a good technique for these patients, despite of considering individually every case and extension of syntomatology, due to the little experience in anesthesia with deficiency of Complex III.     

Postanesthetic respiratory depression in humans: A comparison of sevoflurane,isoflurane and halothane

The postanesthetic respiratory depression with sevoflurane, isoflurane and halothane was studied in twenty-one patients. They were divided into three groups of seven patients each. One group underwent sevoflurane anesthesia, another group isoflurane and the third group halothane. Following extubation, the decrease in blood concentration of the anesthetic agent was most rapid with sevoflurane and slowest with halothane. Twenty minutes following extubation, resting ventilation and ventilatory response to carbon dioxide returned to the preanesthetic state with sevoflurane and isoflurane anesthesia. With halothane anesthesia, however, the depressive respiratory effects of halothane remained; depressed ventilatory response to carbon dioxide, decreased tidal volume and increased respiratory frequency. Although halothane has been reported to have the least depressive respiratory effect of the three, its elimination was slowest. Thus the respiratory effects of halothane persisted up to and past the twenty minute mark, far longer than with sevoflurane or isoflurane.(Doi M, Ideda K: Postanesthetic respiratory depression in humans: A comparison of sevoflurane, isoflurane and halothane. J Anesth 1: 137–142, 1987)     

Upper Airway Reflexes during a Combination of Propofol and Fentanyl Anesthesia

Background: The effects of intravenous anesthetics on airway protective reflexes have not been fully explored. The purpose of the present study was to characterize respiratory and laryngeal responses to laryngeal irritation during increasing doses of fentanyl under propofol anesthesia.

Methods: Twenty-two female patients anesthetized with propofol and breathing through the laryngeal mask airway were randomly allocated to three groups: (1) eight patients who received cumulative total doses of 200 [micro sign]g fentanyl given in the form of two doses of 50 [micro sign]g and one dose of 100 [micro sign]g spaced 6 min under mechanical controlled ventilation while end-tidal carbon dioxide tension (PCO2) was maintained at 38 mmHg (fentanyl-controlled ventilation group), (2) eight patients who received cumulative total doses of 200 [micro sign]g fentanyl while breathing spontaneously while end-tidal PCO2 was allowed to increase spontaneously (fentanyl-spontaneous ventilation group), and (3) six spontaneously breathing patients who were anesthetized with propofol alone (propofol group). The laryngeal mucosa of each patient was stimulated by spraying the cord with distilled water, and the evoked responses were assessed by analyzing the respiratory variables and endoscopic images.

Results: Before administration of fentanyl, laryngeal stimulation caused vigorous reflex responses, such as expiration reflex spasmodic panting, cough reflex, and apnea with laryngospasm. Increasing doses of fentanyl reduced the incidences of all these responses, except for apnea with laryngospasm, in a dose-related manner in both the fentanyl-controlled ventilation and the fentanyl-spontaneous ventilation groups. Detailed analysis of endoscopic images revealed several characteristics of laryngeal behavior during the airway reflex responses.     

Effects of sevoflurane, propofol and position changes on respiratory mechanics

This study was designed to investigate the effects of propofol, sevoflurane and position changes on respiratory mechanics. Forty patients scheduled for thyroid surgery were divided randomly into two groups; those receiving sevoflurane (group S) (n=20), and those receiving TIVA propofol (group P) (n=22). Dynamic compliance (Cdyn), peak inspiratory pressure (PIP), and respiratory resistance (Rr) values were recorded with a VenTrak respiratory monitor (Novometrix Inc. USA) at three time instances. The first measurement was done immediately after the beginning of ventilation and before the inhalation agent was initiated (Induction). Second measurement was done after 5 minutes of thyroid position (Thyroid) (ventilation with 1 MAC sevoflurane concentration or propofol infusion at the rate of 6 mg/kg/h). The third measurement was performed 5 minutes after end of surgery in the supine position (Supine) Blood gases were measured at the three time instances. Respiratory mechanics did not change in the P group (51 +/- 13, 46 +/- 11, 48 +/- 10 mL/cmH2O) at Induction, Thyroid and Supine positions). In the S group, dynamic compliance measurements showed changes statistically significant in the supine position (52 +/- 6 mL/cmH2O)) when compared to Induction (47 +/- 9 mL/cmH2O) and Thyroid position (47 +/- 6 mL/cmH2O) measurements (p<0.05). When the groups were compared with each other, there was no significant difference whatsoever at all periods (p>0.05). His concluded that sevoflurane, propofol and position changes exhibit similar effects on respiratory mechanics and blood gases at described dose and concentration.