Duration of safe apnea in patients with morbid obesity during passive oxygenation using high-flow nasal insufflation versus regular flow nasal insufflation,a randomized trial

BackgroundObese patients are at risk for rapid oxygen desaturation during anesthesia induction. Apneic oxygenation with regular flow oxygen insufflation has successfully been used to prolong the duration of safe apnea without desaturation (DAWD) in morbidly obese patients. Using high-flown nasal insufflation of oxygen (HFNI) for apneic oxygenation might further increase the DAWD.ObjectivesTo compare the duration of safe apnea using high-flown nasal insufflation of oxygen or standard flow oxygen insufflation for apneic oxygenation in a simulated difficult intubation scenario in patients with morbid obesity.SettingOperating room, University Hospital, Austria.MethodsIn a prospective, randomized, clinical trial, patients received standardized preoxygenation and anesthesia induction. Apneic oxygenation was performed using standard nasal prongs (10 L/min) or HFNI (120 L/min) during laryngoscopy. A Cormack-Lehane 3° view was maintained until the oxygen saturation on pulse oximetry (SpO₂) dropped ≤95% or for a maximum of 15 minutes. The primary outcome of this study was to compare the duration of safe apnea using HFNI or standard flow oxygen insufflation for apneic oxygenation. In addition, arterial blood gas results, and airway pressures were investigated.ResultsIn 40 patients with morbid obesity (body mass index [BMI] >40 kg/m²) and the American Society of Anesthesiologists physical classification ≤3 who underwent bariatric surgery, the median duration of safe apnea was 601 (268–900) seconds in the standard group and 537 (399–808) seconds in the HFNI group (P = .698). No differences in arterial blood gas results were observed between the groups. The median airway pressure was 0 (0–0) cm H₂O in the standard group and 1 (0–2) cm H₂O in the HFNI group (P = .005).ConclusionCompared with standard nasal apneic oxygenation, HFNI did not increase the duration of safe apnea in patients with morbid obesity. A significant but clinically negligible higher airway pressure was observed when using HFNI.     

About the quality of prehospital emergency ventilation – a prospective study in trauma patients

Introduction: The prehospitaly initiated endotracheal intubation and controlled ventilation, is especially in multi-system-trauma cases, recognized to be the “gold standard”. Thus especially in view of the increasing demands being placed upon the quality of prehospital emergency treatment in general, the quality of such prehospital induced ventilation, is becoming of increasing importance. Thereby we must take into consideration the limited possabilities, which are afflicted with a high degree of uncertainess, which we have at our disposal to effectively evaluate the efficiency of emergency ventilation. The purpose of our study within a collective of severely traumatized patients, was to determine the quality of prehospitaly induced ventilation with regards to the adequacy of oxygenation and ventilation and as a result of our findings, to identify areas for procedural optimization. Results: The prospective study over an one year period involved n = 104 trauma cases (male: 79; female: 25/age: 39,8 ± 20,8 years/ISS: 28,1 ± 15,3) whose prehospital emergency treatment required and included endotracheal intubation and controlled ventilation. All patients were subject to a prehospital pulse oxymetric monitoring, whereas none were subject to an objectivating apparatus monitoring of ventilation: 94,2 % of the patients were upon admission adequately oxygenated (paO₂ > 80 mmHg); only one patient was hypoxemic (paO₂ < 60 mmHg). 46,2 % were adequately ventilated (paCO₂: 35–45 mmHg), 43,2 % however were hyperventilated (paCO₂ < 35 mmHg), and 10,6 % hypoventilated (paCO₂ > 45 mmHg). A statistical significant relation between hyper-/hypoventilation and the degree of severity of trauma as well as to the individual injury pattern was not evident. However with reference to age: The group of > 60 years of age were significantly more frequently hyperventilated (paCO₂ < 30 mmHg: 31,2 %; p < 0,05). A noteworthy accumulation of hypoventilation was experienced amongst the group of patients, who during the prehospital treatment phase were hemodynamic instable (shock index > 1). Conclusion: In summary it is evident, that as a rule, even very severe traumatized patients can prehospitaly be adequately oxygenated and that such oxygenation can with the assistance of pulse oxymetric monitoring be effectively controlled. Remaining problem is the emergency physicians ability to evaluate and control ventilation. The prehospital determination of minute volume (MV) in accordance with the presently valid recommendation: MV = 100–150 ml/kg body weight, in the majority of trauma cases results in inadequate ventilation. The introduction of an objectifying monitoring method is therefore urgently required.      

Multicenter study on the usefulness of the NasOral system for the denitrogenation and apneic oxygenation in anesthesia

OBJECTIVES: To study the usefulness of the NasOral system for denitrogenation prior to anesthetic induction for improving pulmonary oxygen storage that maintains SpO2 within the normal range during induced apnea and facilitates apneic oxygenation. MATERIAL AND METHODS: To establish the study population of 125, five hospitals of the Valencian Community (Spain) enrolled patients scheduled for elective procedures under general anesthesia. The patients were preoxygenated using the NasOral system (denitrogenation). For two minutes, the patients inhaled oxygen through the nose (FiO2 1) at a flow rate of 8-10 l/min (never less than the patient's own minute volume) and exhaled orally through a unidirectional valve. We measured time of apnea with SpO2 > or = 96% to assess the usefulness of the device for denitrogenation. We also measured PetCO2 after endotracheal intubation and after maximum time of apnea (< or = 10 minutes) to assess use of the device for apneic oxygenation during laryngoscopy. RESULTS: We found no significant differences with regard to age, sex, ASA or Mallampati classification among patient groups enrolled at the participating hospitals. Cox's regression analysis was used to determine relative risk of SpO2 < 96%. At 10 minutes post-apnea, 88.8% of all patients maintained SpO2 > or = 96%. However, SpO2 > 96% was maintained by 94.1% in the Mallampati I group and by 84.1% in the Mallampati II group. SpO2 fell below the cut-off (< 96%) in 33.3% of obese patients and in 7.5% of non-obese patients. Analysis of the likelihood of SpO2 < 96% associated with the variables of obesity, sex, age, ASA and Mallampati classification was significant only for obesity, for which a risk of 1.95 was calculated relative to non-obesity (95% CI 1.14-3.35). The NasOral system allows performance of direct laryngoscopy for oral tracheal intubation, maintaining oxygen flow through the permeable airway to facilitate apneic oxygenation. CONCLUSIONS: The NasOral system facilitates denitrogenation before induction of anesthesia in all patients with permeable nasal fossae as well as apneic oxygenation during laryngoscopy.     

Vital capacity induction with 8% sevoflurane and N2O causes cerebral hyperemia

Purpose. Little is known about the influence of high-dose sevoflurane on cerebral volume. We evaluated induction time and cerebral blood volume with 8% sevoflurane using the “vital capacity induction” technique. Methods. Thirty-four patients were randomly allocated into three groups. Group P received 2.0 mg·kg⁻¹ of propofol i.v. and inhalation of 67% N₂O/O₂, whereas group S5 and group S8 received inhalation of primed 5% and 8% sevoflurane in 67% N₂O/O₂, respectively. Induction time was measured as the time from the start of inhalation, or from the end of injection, until loss of eyelash reflex. Near-infrared spectroscopy and bispectral index (BIS) were monitored continuously until 3 min after tracheal intubation. Results. Induction time was less in group S8 (17.3 ± 6.4 s, mean ± SD) than in groups P (25.7 ± 8.2 s) and S5 (33.0 ± 16.8 s). There was a significant increase in cerebral blood volume after intubation in group S8, as suggested by higher cerebral oxyhemoglobin and total hemoglobin levels. There were no differences in BIS scores among the groups during the study period. Conclusion. Vital capacity inhalation of 8% sevoflurane produces a faster loss of eyelash reflex than does 5% sevoflurane or propofol, but increases cerebral blood volume. Received: May 20, 2002 / Accepted: August 27, 2002 Address correspondence to: K. Iwasaki     

A randomised controlled trial comparing transnasal humidified rapid insufflation ventilatory exchange (THRIVE) pre‐oxygenation with facemask pre‐oxygenation in patients undergoing rapid sequence induction of anaesthesia

Pre‐oxygenation is an essential part of rapid sequence induction of general anaesthesia for emergency surgery, in order to increase the oxygen reservoir in the lungs. We performed a randomised controlled trial of transnasal humidified rapid insufflation ventilatory exchange (THRIVE) pre‐oxygenation or facemask pre‐oxygenation in patients undergoing emergency surgery. Twenty patients were allocated to each group. No patient developed arterial oxygen saturation < 90% during attempted tracheal intubation. Arterial blood gases were sampled from an arterial catheter immediately after intubation. The mean (SD) PaO₂ was 43.7 (15.2) kPa in the THRIVE group vs. 41.9 (16.2) kPa in the facemask group (p = 0.722); PaCO₂ was 5.8 (1.1) kPa in the THRIVE group vs. 5.6 (1.0) kPa in the facemask group (p = 0.631); arterial pH was 7.36 (0.05) in the THRIVE group vs. 7.34 (0.06) in the facemask group (p = 0.447). No airway rescue manoeuvres were needed, and there were no differences in the number of laryngoscopy attempts between the groups. In spite of this, patients in the THRIVE group had a significantly longer apnoea time of 248 (71) s compared with 123 (55) s in the facemask group (p < 0.001). Transnasal humidified rapid insufflation ventilatory exchange is a practicable method for pre‐oxygenating patients during rapid sequence induction of general anaesthesia for emergency surgery; we found that it maintained an equivalent blood gas profile to facemask pre‐oxygenation, in spite of a significantly longer apnoea time.     

Recovery of postural stability following conscious sedation with midazolam in the elderly

Purpose. To investigate the differences in recovery of postural stability, after obtaining similar intravenous sedation levels with midazolam, in elderly and younger patients undergoing dental surgery. Methods. We studied 15 elderly patients (>65 years) and 15 younger patients (<55 years) after intravenous sedation. Midazolam was carefully titrated over 4–5 min until slow response to verbal commands, ptosis of the eyelid, or slight slurring of speech was obtained. Parameters were postural balance tests and an addition test, as a psychomotor function test. Results. The dose of midazolam in the elderly group (0.045 ± 0.012 mg·kg⁻¹) was 62% of that in the younger group (0.074 ± 0.026 mg·kg⁻¹). In evaluation of the percentile rank of a balance test with a visual feedback system, which contained a dynamic balance element, recovery at 60 min in the elderly group was significantly slower than that in the younger group. However, the recovery times for the balance test and the addition test, at which the significantly changed values were restored to the baseline values, were 120 min and 90 min, respectively, in both groups. Conclusion. In the recovery from sedation, elderly patients had more difficulty in acquiring postural adjustment during movement than in maintaining a standing posture. If the dose is carefully administered, however, even elderly patients might be able to return home 2 h after midazolam administration, as could the younger patients. Received: November 6, 2001 / Accepted: April 22, 2002     

Intra-Operative Monitoring of Brain Tissue O<Subscript>2</Subscript> (PtiO<Subscript>2</Subscript>) During Aneurysm Surgery

Summary.  Background: Regional cerebral blood flow may be compromised during aneurysm surgery. This may occur during vessel occlusion by temporary cliping or result from the malposition of an aneurysm clip. In this report we monitored intra-operatively the brain tissue oxygen concentration (PtiO₂) to visualize regional ischaemic events.  Method: During surgery of 10 intracranial aneurysms, monitoring of PtiO₂ was performed using a polarographic microcatheter (Licox, GMS-Kiel-Germany), which was placed in the vascular territory of the artery harboring the aneurysm.  Findings: No complications were observed after implantation of Licox electrodes. In 6 patients PtiO₂ decreased during transient clipping. In two patients PtiO₂ decreased below 2 mmHg without morphological or clinical signs cerebral ischemia. In four patients, without incidence during surgery, only minor oscillations were observed.  Conclusion: Intra-operative monitoring of PtiO₂ is a complimentary procedure to monitor cerebral perfusion and detect episodes of ischaemia. Given the rapid detection of these events, therapeutic intervention may be initiated before irreversible neuronal damage occurs. Published online September 2, 2002 Acknowledgments  This study was supported by Xunta de Galicia: XUGA 90204B98. The authors thank Mr. Romen Das Gupta for his assistance in the preparation of this paper. Correspondence: Miguel Gelabert-González, Neurosurgical Service, Clinical Hospital, La Choupana, 15706 Santiago de Compostela, Spain.     

Serial transcranial Doppler measurements in traumatic brain injury with special focus on the early posttraumatic period

Summary.  Background: Cerebral ischemia is considered a key factor in the development of secondary damage after Traumatic Brain Injury (TBI). Studies on Cerebral Blood Flow (CBF) have documented decreased flow in over 50% of patients with TBI, studied in the acute phase. Transcranial Doppler (TCD) sonography is a non-invasive technique, permitting frequent or continuous measurements of blood flow velocity in the basal cerebral arteries.  Objectives: To investigate the potential of TCD to detect decreased blood flow velocity in the early phase after TBI;  To investigate whether flow velocity differs between hemispheres in patients with focal lesions versus those with more diffuse injuries;  To investigate if decreased blood flow velocity is indicative of cerebral ischemia, as evidenced by measurements of brain tissue pO₂.  Methods: TCD examinations were performed in 57 patients with severe TBI (GCS≤8) daily over a period of 10 days, with particular attention focused on the first 72 hours, during which period examinations were performed more frequently. A low flow velocity state (LFVS) was defined as a flow velocity≤35 cm/sec in one or both MCA's within 72 hours after trauma. PbrO₂ was measured in 33 patients with an intraparenchymal Clark type electrode (Licox).  Patients were differentiated into those with primarily unilateral pathology on the admission CT scan versus those with primarily more diffuse or bilateral pathology. Outcome was evaluated at six months after injury, according to the Glasgow Outcome Scale (GOS).  Results: A low flow velocity state was observed in 63% of patients studied. Decreased flow was most pronounced during the first eight hours after injury and was accompanied by high pulsatility indices, especially at the side of the lesion. Flow velocity increased significantly after this time period. Initial Vmca values had a strong correlation with ipsilateral measured PbrO₂ values (R=0.73). The occurrence of a LFVS was associated with poorer outcome (odds ratio 3.9).  Conclusions: TCD studies show reduction of cerebral blood flow velocity in the acute phase after traumatic brain injury. Decreased flow velocity is most pronounced ipsilateral to focal pathology. A low flow velocity state is probably due to high peripheral resistance, and is indicative of ischemia, as demonstrated by the association with decreased PbrO₂. A low flow velocity state is of prognostic value and identifies patients at increased risk for ischemia. Early TCD studies are recommended in TBI. Published online October 31, 2002 Correspondence: Andrew I. R. Maas, Department of Neurosurgery, Erasmus MC, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands.     

Minor Head Injuries: One Year Experience According to the New Italian Guideline

Summary  Background. The data concerning a consecutive series of 4,536 adult patients suffering from minor head injuries treated at the Department of Neurosurgery over a period of one year are reported.  Method. The patients' age, sex and the circumstances of the injury have been taken into consideration. The patients, according to the new method, were divided into four groups.  Group 0 (3,864 patients) included all patients with Glasgow Coma Scale (GCS) score 15. They did not present any clinical features such as loss of consciousness (LOC), post-traumatic amnesia (PTA), headache or vomiting. No risk factors (RF) such as coagulopaties, alcoholism, drug abuse, epilepsy, previous neurological treatment or disabled elderly patients were detected.  Group 1 (600 patients) included patients with GCS score 15. The patients presented one or more clinical features (LOC, PTA, headache, vomiting). No RF were presented.  Group 2 (24 patients) included patients with GCS score 14 with or without clinical features (LOC, PTA, headache, vomiting) and with or without RF.  Group 0-1R (48 patients) included patients with GCS score 15 with or without clinical features (LOC, PTA, headache, vomiting). All of them presented RF.  The presence of focal neurological signs, open injury and GCS score≦13 were considered criteria for exclusion.  Findings. All the patients from groups 1, 0-1R, 2 and 187 patients from group 0 underwent CT scan for a total of 859 exams which are analyzed and discussed. 458 patients were admitted and are divided as follows: 216 from group 0, 192 from group 1, 26 from group 0-1R and all the 24 belonging to group 2. Six patients were treated surgically (3 extradural haematomas, 2 lobe contusions, 1 acute subdural haematoma) and one of them (0.02% of the total) died (extradural haematoma). The patients who were not admitted were sent home with an information sheet after at least a six hour observation period.  Interpretation. The authors draw the conclusion that they have evaluated the applicability and efficacy of guidelines, developed by the study group on head injury of the Italian Society of Neurosurgery [19]. A critical part of our guidelines is not only to identify all the intracranial lesions, but to identify patients harbouring relevant intracranial mass before clinical deterioration.     

AN ALTERNATIVE METHOD OF INCREASING PCO2 USING APNOEA AND CONTINUOUS POSITIVE AIRWAY PRESSURE

We have examined the use of continuous positive airway pressure(CPAP) and apnoeic oxygenation for restoration of spontaneousbreathing at the end of anaesthesia after controlled ventilation.We studied 45 adult patients without a history of acute or chronicrespiratory disturbances. Anaesthesia wos inducsd with thiopentoneor prnnnfnl and maintained with nitrous oxide and enfluranein oxygen. The patients were normocapnic during artificial ventilation.At the end of surgery, the lungs were ventilated for 5 min withoxygen and then given a CPAP of 8 cm H₂O. Spontaneous ventilationwas regained after a mean of 5 min and an arterial blood samplewas obtained at the third breath. All patients were well oxygenated(PO₂ mean 43.5 kPa, range 21–76 kPa) when spontaneousventilation started. The pH was close to 7.28 in most cases(mean 7.28, range 7.21–7.32), and PCO2 varied in the range6.6–9.9 kPa (mean 7.9 kPa). It is concluded that the methodis safe with regard to oxygenation and acid-base balance. (Br.J. naesth. 1993; 70: 411–413)     

Systemic and Cerebral Haemodynamics During Craniotomy Under Mild Hypothermia in Patients with Acute Subarachnoid Haemorrhage

Summary ? Background. Mild hypothermia provides cerebral protection against ischaemic insults in various animal models. We compared systemic and cerebral oxygenation between mild hypothermic and normothermic management in 60 patients with acute subarachnoid haemorrhage who underwent clipping of cerebral aneurysms.  Method. The temperature in the pulmonary artery was maintained at 36°C in 28 patients and was reduced to 34°C in 32 patients. Parameters in the systemic and cerebral haemodynamics from pulmonary artery and internal jugular vein catheters were compared between the two groups immediately after the induction of anaesthesia (T1), and just before temporary occlusion or aneurysm clipping (T2).  Findings. Cardiac index, oxygen delivery index, oxygen consumption index, and oxygen saturation of the jugular bulb were significantly lower at T2 in hypothermic group (H) (2.9±0.6 L/min/m², 400.8±106.3 ml/min·m², 87.0±14.8 ml/min·m², 55.2±6.6%, respectively) than in normothermic group (N) (3.7±0.6, 521.0±105.5, 109.9±21.7, 60.9±6.6) (p<0.05). The arterial lactate and arteriojugular difference in oxygen content were significantly higher in H (2.3±1.3 mmol/L, 6.5±1.5 ml/dl, respectively) than in N (1.7±1.0, 5.6±1.2) (p<0.05). Arteriojugular differences in carbon dioxide tension and hydrogen ion content were significantly lower at T2 in H (−10.8±2.1 mm Hg, −6.4±1.3 nmol/L, respectively) than in N (−8.9±2.8, −5.3±1.0) (p<0.05).  Interpretation. The balance between oxygen supply and demand systemically and in the brain may worsen during aneurysm surgery for patients with acute subarachnoid haemorrhage under mild hypothermia. Oxygenation of the brain and the whole body should be monitored closely during this surgery, and adequate circulatory assistance is recommended under mild hypothermia.     

Effects of high inspired oxygen fraction during elective caesarean section under spinal anaesthesia on maternal and fetal oxygenation and lipid peroxidation

Background. Oxygen supplementation is given routinely to parturientsundergoing Caesarean section under regional anaesthesia. Whilethe aim is to improve fetal oxygenation, inspiring a high oxygenfraction (FI_O2) can also increase free radical activity andlipid peroxidation in both the mother and baby. In this prospective,randomized, double-blind study, we investigated the effect ofhigh inspired oxygen fraction (FI_O2) on maternal and fetal oxygenationand oxygen free radical activity in parturients having Caesareansection under spinal anaesthesia. Methods. Forty-four healthy parturients were randomized to breatheeither 21% (air group) or 60% oxygen (oxygen group) intraoperativelyvia a ventimask. Maternal arterial blood was collected at 5-minintervals from baseline until delivery, and umbilical arterialand venous blood was collected at delivery. We measured bloodgases and the products of lipid peroxidation (8-isoprostane,malondialdehyde (MDA), hydroperoxide (OHP)) and purine metabolites. Results. At delivery, the oxygen group had greater maternalarterial PO₂ [mean 30.0 (SD 6.3) vs 14.2 (1.9) kPa; mean difference15.8 kPa, 95% confidence interval 12.9–18.7 kPa, P<0.001]and greater umbilical venous PO₂ [4.8 (1.0) vs 4.0 (1.4) kPa;mean difference 0.8 kPa, 95% confidence interval 0.0–1.5kPa, P=0.04] compared with the air group. Maternal and umbilicalplasma concentrations of lipid peroxides (8-isoprostane, MDA,OHP) were greater in the oxygen group than in the air group(P<0.05). Conclusions. We conclude that breathing high FI_O2modestly increasedfetal oxygenation but caused a concomitant increase in oxygenfree radical activity in both mother and fetus. Br J Anaesth 2002; 88: 18–23     

In vitro therapy with dobutamine, isoprenaline and sodium nitroprusside protects vascular smooth muscle metabolism from subarachnoid haemorrhage induced cerebral vasospasm

Summary  Background. The cerebrospinal fluid (CSF) from subarachnoid haemorrhage (SAH) patients with cerebral vasospasm stimulates vasoconstriction and oxygen consumption in the porcine carotid artery in vitro. Stimulation of oxygen consumption has been used as an in vitro model of vasospasm to assess the relative benefits of nimodipine, isoprenaline, dobutamine, and sodium nitroprusside (SNP).  Method. Samples of human CSF were obtained from SAH patients and applied to de-endothelialised porcine carotid artery. Stimulation of oxygen consumption (as an in vitro marker for a stimulation of the vessels) was monitored and the effects of SNP, isoprenaline, dobutamine or nimodipine were measured.  Findings. The CSF from SAH patients with evidence of vasospasm stimulated oxygen consumption to 0.91±0.17 (μ M O₂/min/g dry wt, ± SD p≤ 0.01) and CSF from SAH patients without vasospasm did not significantly stimulate oxygen consumption 0.27±0.02, with 0.23±0.03 (μ M O₂/min/g dry wt) being an unstimulated rate of respiration for the porcine carotid artery. SNP, isoprenaline or dobutamine significantly (p≤ 0.01) decreased the stimulation of oxygen consumption of the porcine carotid artery whereas nimodipine did not. In a cohort of 41 SAH patients who received nimodipine alone or nimodipine and dobutamine, the in hospital mortality rate of the patients who received only nimodipine was 42% as compared to an in hospital mortality rate of 17% in the nimodipine plus dobutamine group P≤ 0.076).  Interpretation. The in vivo data on the 41 patients is not statistically significant, so further studies are required to determine if the differences are important. SNP, isoprenaline and dobutamine significantly decreased oxygen consumption of the porcine carotid arteries exposed to CSF from SAH patients who had vasospasm whereas nimodipine did not. Our in vitro results suggest that these compounds require further study in patients with SAH who are at risk for vasospasm because they may have a direct benefit for the vasospastic arteries.     

Zur Frage der CO2-Speicherung bei laparoskopischer Cholezystektomie mit CO2-Pneumoperitoneum

Methods. Two groups of 22 patients each were studied in a prospective, randomised fashion during laparoscopic cholecystectomy (LCh) and CO₂ pneumoperitoneum (PP) with regard to end-tidal and arterial PCO₂ and pulmonary elimination of CO₂ (ECO₂, Servoventilator with integrated CO₂-analyser 930, Siemens). In group 1 minute ventilation was kept constant, resulting in moderate hypercapnia during PP. paCO₂ increased by about 10?mmHg during up to 50?min PP. In group 2 paCO₂ was kept constant by a stepwise increase in minute ventilation (Fig.?1, Table?2). Results. Compared to values just before PP, ECO₂ increased in group 1 rather rapidly up to 20?min of PP and more slowly thereafter, reaching a mean value 35% above control at 45?min PP. In group 2 ECO₂ was significantly higher than in group 1 between 15 and 35?min PP. At 45?min PP, however, ECO₂ was identical in both observation groups (Fig.?2). Conclusions. Assuming a stable metabolic CO₂ production rate during the observation period and no differences in CO₂ absorption from the PP between the two study groups, differences in ECO₂ between groups would be a measure of CO₂ stored in group 1 patients during the increase in paCO₂ with PP (Fig.?3, Table?3). CO₂ storage rapidly increased between 0 and 15?min PP, more or less reached a plateau between 15 and 35?min PP, and ceased at 45?min PP. Storing capacity for CO₂ during the first 45?min PP amounted to a mean value of 1.20?ml CO₂/kg body weight and mmHg paCO₂, which agrees favourably with data from the literature and a computer model from Fahri and Rahn published in 1960 (Fig.?4, Table?4). If during LCh with CO₂-PP patients are ventilated with a constant minute ventilation, a moderate increase in paCO₂ of about 10?mm Hg can be expected. In this case, during the first 45?min PP a 70-kg patient will retain about 1000?ml CO₂ in blood and tissues, which must be eliminated after cessation of PP. If the paCO₂ is to be held constant during PP, minute ventilation has to be progressively increased by about 40%.     

Prevalence and Severity of Sleep Apnea in a Group of Morbidly Obese Patients

Background Obesity is the most important risk factor for obstructive sleep apnea. It is estimated that 70% of sleep apnea patients are obese. In the morbidly obese, the prevalence may reach 80% in men and 50% in women. The aim of this study was to determine the prevalence and severity of sleep apnea in a group of morbidly obese patients, leading to bariatric surgery. Methods In a cross-sectional study developed in Bahia, northeastern Brazil. 108 patients (78 women and 30 men) from the Obesity Treatment and Surgery Center - “Núcleo de Tratamento e Cirurgia da Obesidade” underwent standard polysomnography. Patients with an apnea-hypopnea index (AHI) ≥ 5 events/hour were considered apneic. Results Mean ± SD for age and BMI were 37.1 ± 10.2 years and 45.2 ± 5.4 kg/m2, respectively. The calculated AHI ranged widely from 2.5 to 128.9 events/hour. Sleep apnea was detected in 93.6% of the sample, wherein 35.2% had mild, 30.6% moderate and 27.8% severe apnea. Oxyhemoglobin desaturation was directly related to the AHI and was more severe in men. Conclusion There was a high frequency of sleep apnea in this group of morbidly obese patients, for whom it was very important to request polysomnography, thus enabling therapeutic management and prognostication.     

Hypotension associated with systemic aggregated anaphylaxis is not attenuated by a selective endothelin-A receptor antagonist,BQ 610, in rabbits in vivo

Purpose. The present study was done to investigate the role of endothelin-1 (ET-1) in hypotension and bronchospasm provoked by anaphylaxis in rabbits in vivo. Methods. Forty-five rabbits sensitized to horse serum were randomly allocated to five groups: Group 1 (n = 10) received 0.5 nmol·kg⁻¹ of ET-1; Group 2 (n = 10) received 0.5 nmol·kg⁻¹ of ET-1 and 200 nmol·kg⁻¹ of a selective ET_A receptor antagonist, BQ 610, without anaphylaxis; Group 3 (n = 5) received 200 nmol·kg⁻¹ of BQ 610 alone without anaphylaxis; Group 4 (n = 10) received normal saline alone before being antigen challenged to induce anaphylaxis; Group 5 (n = 10) received 200 nmol·kg⁻¹ of BQ 610 before antigen challenge. Results. Mean arterial pressure (MAP) values were significantly different between Groups 1 and 2. Heart rate (HR), central venous pressure (CVP), dynamic pulmonary compliance (C_dyn), and pulmonary airway resistance (R_L) did not differ significantly between Groups 1 and 2. MAP values were significantly decreased compared with baseline in both Groups 4 and 5; however, the values were not significantly different between two groups. CVP values were significantly different between Groups 4 and 5 only at the 15-min time point following antigen challenge. HR, R_L, and C_dyn values were not significantly different between Groups 4 and 5, nor were the survival rates. Conclusion. BQ 610 does not improve hypotension or survival rates in systemic aggregated anaphylactic rabbits in vivo, implying that circulating ET-1 may not play an important role in anaphylaxis, although direct proof of production of circulating ET-1 or activation of ET_A receptors is lacking in this study. Received: October 15, 2001 / Accepted: August 20, 2002 Address correspondence to: T. Kawakami     

Exploring the limits of prolonged apnoea with high-flow nasal oxygen: an observational study

High-flow nasal oxygen is increasingly used for oxygenation during apnoea. Extending apnoea duration using this technique has mainly been investigated during minor laryngeal surgery, but it is unclear how long it can be administered for before it should be discontinued due to acidosis. We aimed to describe the dynamics of arterial blood gases during apnoeic oxygenation with high-flow nasal oxygen with jaw thrust only, to explore the limits of this technique. We included adult orthopaedic patients scheduled for general anaesthesia. After pre-oxygenation, anaesthesia with neuromuscular blockade was induced and high-flow nasal oxygen (70 l.min⁻¹) was continued with jaw thrust as the only means of airway management, with monitoring of vital signs and arterial blood gas sampling every 5 minutes. Apnoeic oxygenation with high-flow nasal oxygen was discontinued when arterial carbon dioxide tension (PaCO₂) exceeded 12 kPa or pH fell to 7.15. This technique was used in 35 patients and median (IQR [range]) apnoea time was 25 (20–30 [20–45]) min and was discontinued in all patients when pH fell to 7.15. The mean (SD) PaCO₂ increase was 0.25 (0.06) kPa.min⁻¹ but it varied substantially (range 0.13–0.35 kPa.min⁻¹). Mean (SD) arterial oxygen tension was 48.6 (11.8) kPa when high-flow nasal oxygen was stopped. Patients with apnoea time > 25 minutes were significantly older (p = 0.025). We conclude that apnoeic oxygenation with high-flow nasal oxygen resulted in a significant respiratory acidosis that varies substantially on the individual level, but oxygenation was maintained.     

Assessment of cure and recurrence after pituitary surgery for Cushing's disease

Summary  Background. The treatment of choice in Cushing's disease is transsphenoidal adenomectomy with a recurrence rate ranging 9–23%. We investigated whether abnormal hormonal responses may predict the relapse in “operated” patients followed-up for a long period.  Method. Sixty-eight surgically treated patients with Cushing's disease were followed-up for 12–252 months. Forty-eight patients underwent selective adenomectomy, 17 enlarged adenomectomy and 3 underwent total hypophysectomy. After surgery ACTH and cortisol levels were measured after stimulatory (desmopressin and CRH) and inhibitory tests (dexamethasone and loperamide).  Findings. After operation 46 patients were cured (group A), 15 patients only normalized cortisol levels (group B), 7 patients were surgical failures. During the follow-up, a disease-free condition was maintained in 48 of 61 cases (79%), while a recurrence occurred in 13 patients (21%, 5 of group A and 8 of group B).  In 5/13 patients who relapsed an absent inhibition after dexamethasone and an exaggerated response to CRH test preceded the recurrence. In 5 other patients the relapse was suspected by loperamide test. In the 3 remaining cases, positive responses to desmopressin preceded the recurrence. In 7/13 patients who relapsed the pituitary tumour was visualized by MRI/CT imaging.  Interpretation. During the follow-up a careful assessment of ACTH dynamics is needed. Although no single test can reliably predict the late outcome, individual patients at risk for relapse may be identified by abnormal responses to desmopressin, CRH and loperamide tests; particularly, the persistent responsiveness to desmopressin may be a criterion of risk for recurrence in patients who only normalized cortisol levels after surgery.     

Rectal luminal PrCO 2, measured by automated air tonometry, does not reflect gastric luminal PrCO 2 in children

Rectal luminal regional P_{CO 2} (Pr_{CO 2}) was compared with gastric luminal Pr_{CO 2} measured by automated air tonometry at intervals of 10 min in 20 children aged 6–16 years scheduled for elective surgery under general anesthesia. In 5 patients, measurement of rectal Pr_{CO 2} failed because of catheter-related problems. In the remaining 15 children, aged 10.6 ± 2.5 years, 19 ± 7 paired rectal and gastric Pr_{CO 2} values (n total, 241) were measured. Bias and precision for gastric compared to rectal Pr_{CO 2} was −1.79 kPa and 2.89 kPa. In patients with obvious feces in the rectum, bias (precision) for gastric compared to rectal Pr_{CO 2} was −2.7 kPa (2.6 kPa) and in those with empty rectum, −0.75 kPa (1.42 kPa; t-test; P < 0.001). Based on our in vivo data, rectal luminal Pr_{CO 2}, measured by automated air tonometry, does not reflect gastric luminal Pr_{CO 2} in children. Enteral luminal gas production within feces in the rectum seems to be a major source of this disagreement.     

Contractile responses to reactive oxygen species in the canine basilar artery in vitro: selective inhibitory effect of MCI-186, a new hydroxyl radical scavenger

Summary.  Background: Cerebral vasospasm is one of the important pathological phenomena which influence morbidity and mortality following subarachnoid haemorrhage. Reactive oxygen species (ROSs) generated by the autoxidation of oxyhemoglobin to methemoglobin may be one of the essential factors in the pathogenesis of cerebral vasospasm. The direct vasocontractile effects of hydrogen peroxide (H₂O₂), superoxide anion (O₂ ⁻), and hydroxyl radical (^*OH) on the canine basilar artery and the inhibitory effects of MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one), a new ^*OH scavenger, were investigated.  Method: Isometric tension was recorded in basilar artery rings from dogs in vitro. H₂O₂, pyrogallol (O₂ ⁻ donor), and vitamin C (VitC)/Fe²⁺ (^*OH-generating system) were used to generate the ROSs.  Findings: H₂O₂ (10 μmol/L), pyrogallol (10 μmol/L), and VitC/Fe²⁺ (100 μmol/L each) induced fast onset and transient, slow onset and transient, and sustained contraction, respectively, in the canine basilar artery. Contractions induced by H₂O₂ were almost completely inhibited by pre-incubation with catalase (800 U/mL) and those by pyrogallol with superoxide dismutase (150 U/mL), but neither with MCI-186 (10 μmol/L). The contraction induced by VitC/Fe²⁺ was clearly inhibited by pre-incubation with MCI-186, but not with catalase or superoxide dismutase.  Interpretation: ROSs have direct vasocontractile effects on the canine basilar artery in vitro, but different ROSs have different contractile characteristics. Such contractions might be related to the pathophysiology of cerebral vasospasm. MCI-186 had a clear and selective inhibitory effect against ^*OH-induced contraction in vitro. Comparison of different radical scavengers may be important in pharmacological assessment, especially targeted on cerebral vasospasm. Published online December 5, 2002 Acknowledgments  This study was partly supported by grants from the Ministry of Education, Science, Sports and Culture. We thank Ms. Umemura for technical assistance.  Correspondence: Masahiko Tosaka, M.D., Department of Neurosurgery, Gunma University School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma 371-8511, Japan.