End-tidal Carbon Dioxide Concentration Research Articles

Do simple ventilation and gas exchange measurements predict early successful weaning from respiratory support in unselected general intensive care patients?

BackgroundThe value of respiratory variables as weaning predictors in the intensive care unit (ICU) is controversial. We evaluated the ability of tidal volume (Vtexp), respiratory rate (f), minute volume (MVexp), rapid shallow breathing index (f/Vt), inspired–expired oxygen concentration difference [(I–E)O2], and end-tidal carbon dioxide concentration (Pe′co2) at the end of a weaning trial to predict early weaning outcomes. MethodsSeventy-three patients who required >24 h of mechanical ventilation were studied. A controlled pressure support weaning trial was undertaken until 5 cm H2O continuous positive airway pressure or predefined criteria were reached. The ability of data from the last 5 min of the trial to predict whether a predefined endpoint indicating discontinuation of ventilator support within the next 24 h was evaluated. ResultsPre-test probability for achieving the outcome was 44% in the cohort (n=32). Non-achievers were older, had higher APACHE II and organ failure scores before the trial, and higher baseline arterial H+ concentrations. The Vt, MV, f, and f/Vt had no predictive power using a range of cut-off values or from receiver operating characteristic (ROC) analysis. The [I–E]O2 and Pe′co2 had weak discriminatory power [area under the ROC curve: [I–E]O2 0.64 (P=0.03); Pe′co2 0.63 (P=0.05)]. Using best cut-off values for [I–E]O2 of 5.6% and Pe′co2 of 5.1 kPa, positive and negative likelihood ratios were 2 and 0.5, respectively, which only changed the pre- to post-test probability by about 20%. ConclusionsIn unselected ICU patients, respiratory variables predict early weaning from mechanical ventilation poorly.

Clinical significance of end-tidal carbon dioxide tension monitoring during mechanical ventilation

End-tidal carbon dioxide tension or concentration monitoring is characterized with noninvasive,convenient and fast reaction,which Can be continuously monitored and dynamically displayed On electrocardiogram monitor.The technique has been extensively applied in the operation room,intensive care unit and emergency room. Key words: Respirator; Respiratory failure; End-tidal carbon dioxide monitoring

The influence of transcutaneous electrical neurostimulation (TENS) on human cerebral blood flow velocities

BackgroundIt has been shown that transcutaneous electrical neurostimulation (TENS) reduces sympathetic tone. Spinal cord stimulation (SCS) has proven qualities to improve coronary, peripheral, and cerebral blood circulation. Therefore, we postulate that TENS and SCS affect the autonomic nervous system in analogous ways. In this line of thought, cervical application of TENS might be a useful and simple adjunct in the treatment of cerebrovascular disease by improving cerebral blood flow. Experiments were performed in order to assess whether cervical TENS is safe and whether an effect on cerebral blood flow velocity (CBFV) can be shown in healthy subjects.MethodA controlled, non-randomized, phase 1 study was performed with 20 healthy volunteers. Cervical TENS was applied in several frequencies, with and without hyperventilation. Continuous registration of blood pressure, pulse, CBFV (estimated by transcranial Doppler sonography) and end-tidal carbon dioxide concentration was performed.FindingsCervical TENS was well-tolerated by all subjects. Despite small effects on heart rate (HR) and mean arterial blood pressure (MAP), a significant effect on middle cerebral artery (MCA) blood flow velocity was not demonstrated. No effect of age, gender, current or session order on MCA, HR, or MAP was found. TENS did not influence the effect of hyperventilation.ConclusionsIn these experiments, application of cervical TENS is proven to be a safe procedure. However, no effects on cerebral blood flow velocity could be detected, perhaps due to the intact cerebral autoregulation in the healthy volunteers.

End-tidal carbon dioxide concentration monitoring in obstructive sleep apnea patients

Purpose The objective of this study was to investigate the end-tidal carbon dioxide concentration (ET co 2) monitoring in obstructive sleep apnea (OSA) patients during sleep and to explore whether the ET co 2 value may explain a significant portion of the relationship between ET co 2 value and apnea/hypopnea index (AHI) and nocturnal oxygenation indices. Materials and methods Thirty-eight consecutive patients underwent overnight polysomnography and were synchronously monitored for ET co 2 using an microstream capnometer. Mean and maximum values during wake time and different sleep stages were recorded. We grouped 38 OSA patients into 2 subgroups on the basis of their difference of mean total sleep time and wake time ET co 2 [(T − W) ET co 2]; one group, 20 patients with (T − W) ET co 2 less than 0, and the other group,18 patients with (T − W) ET co 2 greater than 0. Results Group with (T − W) ET co 2 less than 0 patients exhibited higher AHI (mean ± SD, 68.58 ± 22.78 vs. 27.61 ± 19.44 events/h) and lower nocturnal oxygenation indices (minimum Sa o 2, 67.85 ± 10.08 vs. 82.61% ± 6.07%; mean Sa o 2, 91.29 ± 3.31 vs. 95.15% ± 1.88%) compared with the other group. Conclusions In summary, the study provides preliminary data showing that ET co 2 potentially can be used in continuous monitoring of OSA patients. And, (T − W) ET co 2 can indicate the severity of OSA.

In Response

We thank Dr. Sherlock for sharing her experience as part of the Tasmanian ambulance service.1 Learning and excelling at ventilation skills is, in our opinion, just as important (if not more) as obtaining proficiency at intubation. To address her specific question, our study group came from different municipalities, and there were different ways of measuring end-tidal carbon dioxide concentration; yet most of the time, it was measured using a capnometer. Our patients were extremely ill with high Injury Severity Scores and low Glasgow Coma Scale, and the conditions in which these intubations were performed were extremely difficult. We believe that the reported incidence of misplaced endotracheal tubes (ETT) stems from a variety of reasons, an important one being the relatively low frequency that the procedure is performed; it is also important to recognize that detection of end-tidal carbon dioxide concentration in patients in shock is not always possible under all circumstances, adding to the confounding factors that make it difficult to ascertain where the tip of an ETT is positioned. Dr. Shatz expressed concern that our article misrepresented the airway skills of Miami-Dade paramedics.2 The definition of “endotracheal intubation” is simply the passage of an ETT through the vocal cords and that was the definition used in our study. When an airway is not secured by means of an ETT, oxygenation and ventilation must be achieved by other (rescue) methods. These interventions include the use of supraglottic devices (such as a laryngeal mask airway [LMA] or Combitube®) or performing a cricothyroidotomy. Dr. Shatz takes issue with the placement of an LMA by the anesthesiologists in the operating room as an adequate airway. There is, however, a big difference between the use of an LMA in a completely elective and controlled setting, where not only the risks of aspiration are minimal but also the positioning, hemodynamics, and spontaneous ventilation are carefully considered. As anesthesiologists with many combined years in the field of Trauma Anesthesia, we can say that having to resort to an LMA in the chaotic setting of a Trauma Bay, after not being able to secure the airway with an ETT, is a life-saving maneuver but far from ideal, especially in critically ill patients considered at risk for aspiration of gastric contents. Placing a supraglottic airway in such circumstances is only a temporary measure until a definitive airway can be obtained. This is the exact scenario that paramedics face frequently but under even less ideal conditions. Having clarified the above, we found no mortality difference when comparing the groups, which points to the fact that we may be asking the wrong question by only looking at intubation rates instead of assessing transport time or adequacy of oxygenation and ventilation, which may be more important. Of special concern is the statement raised by Dr. Shatz regarding the raw data used in the article. The intent of the study was never to compare the success rates of air versus ground crews. Having found a significant difference, we offered a possible explanation in the context of the area studied and international data, yet we explicitly stated “this study did not correlate intubation skills of individual paramedics.”3 We believe that repeated exposure to airway management in the field should improve intubation skills and that it would be worthwhile to undertake a study comparing the success rates of intubation according to the number of procedures performed. Regarding the insightful comments of Dr. Pouliot,4 limiting the number of paramedics and targeting their response as a way to prevent skill dilution is certainly an interesting concept that worth further study. Finally, we reemphasize that performing tracheal intubation in the field is an extremely difficult task and the paramedics of Miami-Dade should be commended for their extraordinary commitment and dedication. Miguel Cobas, MD Keith Candiotti, MD Albert J. Varon, MD Department of Anesthesiology and Perioperative Medicine Miller School of Medicine University of Miami Miami, Florida [email protected]

The use of propofol and sevoflurane for surgical anaesthesia in New Zealand White rabbits

New Zealand White (NZW) rabbits (n = 34) received intravenous propofol (16 +/- 5 mg/kg) for induction of anaesthesia followed by maintenance with sevoflurane (4.0 +/- 0.5%) in oxygen. All animals underwent ovariohysterectomy. Heart rate, respiratory rate, haemoglobin oxygen saturation, end-tidal carbon dioxide concentration, end-tidal sevoflurane concentration and oesophageal temperature were monitored every 5 min. Time from induction of anaesthesia to tracheal extubation and sternal recumbency were recorded as was the quality of recovery. Direct arterial blood pressure values (mmHg) were recorded every 5 min from 19 rabbits and 22 arterial blood gases analyses were performed (11 postintubation and 11 at the time of recovery). Propofol produced smooth induction of anaesthesia without production of apnoea. Intubation was successfully performed in all but one rabbit in an average of 4 +/- 3 min from the beginning of propofol administration. No ventilatory support was required during the anaesthetic period. Respiratory rate averaged 51 +/- 8 bpm and end-tidal CO(2) (kPa) was 4.0 +/- 0.5 mmHg during anaesthesia. Blood gas values were maintained within normal limits and average mean arterial blood pressure was 73.4 +/- 7.9 mmHg. Time to regain the swallowing reflex following discontinuation of sevoflurane was 2 +/- 1 min and time to sternal recumbency was 8 +/- 0.3 min. No anaesthetic-related mortality occurred and all animals recovered uneventfully. Propofol-sevoflurane anaesthesia produced a good quality of surgical anaesthesia for ovariohysterectomy and stable cardiopulmonary conditions. Propofol-sevoflurane anaesthesia in young healthy NZW rabbits appears to be an effective and practically useful method of anaesthesia.

A Retrospective Observational Study Examining the Admission Arterial to End-Tidal Carbon Dioxide Gradient in Intubated Major Trauma Patients

Major trauma patients who are intubated and ventilated are exposed to the potential risk of iatrogenic hypercapnic and hypocapnic physiological stress. In the pre-hospital setting, end-tidal capnography is used as a practical means of estimating arterial carbon dioxide concentrations and to guide the adequacy of ventilation. In our study, potentially deleterious hypercapnia (mean 47 mmHg, range 26 to 83 mmHg) due to hypoventilation was demonstrated in 49% of 100 intubated major trauma patients arriving at a major Australian trauma centre. A mean gradient of 15 mmHg arterial to end-tidal carbon dioxide concentration difference was found, highlighting the limitations of capnography in this setting. Moreover, 80% of the patients in the study had a head injury. Physiological deadspace due to hypovolaemia in these patients is commonly thought to contribute to the increased arterial to end-tidal carbon dioxide gradient in trauma patients. However in this study, scene and arrival patient hypoxia was more predictive of hypoventilation and an increased arterial to end-tidal carbon dioxide gradient than physiological markers of shock. Greater vigilance for hypercapnia in intubated trauma patients is required. Additionally, a larger study may confirm that lower end-tidal carbon dioxide levels could be safely targeted in the pre-hospital and emergency department ventilation strategies of the subgroup of major trauma patients with scene hypoxia.

Predicting dead space ventilation in critically ill patients using clinically available data*

To develop and validate an equation to predict dead space to tidal volume ratio (Vd/Vt) from clinically available data in critically ill mechanically ventilated patients. Prospective, observational study using a convenience sample of patients whose arterial blood gas and respiratory gas exchange had been measured with indirect calorimetry. Medical and surgical critical care units of a university medical center. Adult, mechanically ventilated patients at rest with Fio2 < or =0.60 and no air leaks who had recent arterial blood gas recordings and end-tidal carbon dioxide concentration monitoring. Observational only. Indirect calorimetry was used to determine carbon dioxide production and expired minute ventilation in 135 patients. Tidal volume and respiratory rate were recorded from the ventilator. End tidal carbon dioxide concentration, body temperature, arterial carbon dioxide partial pressure (Paco2), and other clinical data were recorded. Vd/Vt was calculated using the Enghoff modification of the Bohr equation (Paco2 - PECO2/Paco2). Regression analysis was then used to construct a predictive equation for Vd/Vt using the clinical data: Vd/Vt = 0.32 + 0.0106 (Paco2 - ETCO2) + 0.003 (RR) + 0.0015 (age) (R = 0.67). A second group of 50 patients was measured using the same protocol and their data were used to validate the equations developed from the original 135 patients. The equation was found to be unbiased and precise. Vd/Vt is predictable from clinically available data. Whether this predicted quantity is valuable clinically must still be determined.

Intraoperative Management of Robotic-Assisted Versus Open Radical Prostatectomy

Minimally invasive surgery has been shown to decrease postoperative morbidity and length of stay for several laparoscopic procedures. We sought to retrospectively compare intraoperative surgical and anesthetic parameters, post-anesthetic care unit (PACU) length of stay, and hospital length of stay of patients who underwent robotic-assisted laparoscopic radical prostatectomy (RAP) versus open radical retropubic prostatectomy (ORP). A retrospective investigation was performed using a urologic surgery database and an anesthesia electronic medical record. We queried information regarding 106 ORP patients from 2002 through 2007 and 575 RAP patients from 2007 through 2008. Patients in the RAP group compared with ORP patients had reductions in surgical time, anesthesia time, estimated blood loss, crystalloid administration, and PACU and hospital length of stays. Compared with ORP procedures, intraoperative respiratory rates, peak inspiratory pressures, and arterial pressures in RAP procedures were higher; tidal volumes and heart rates were decreased; but end-tidal carbon dioxide concentrations were not different. In the RAP group, intraoperative complications included severe bradycardia, corneal abrasions, and 2 patients required reintubation. Surgically, no rectal perforations were noted, and no operative mortalities occurred. Our data demonstrate the safety and efficacy of RAP due to a combination of surgical and anesthetic factors.

Effects of SGB on the ventilatory response of bronchial asthmatic patients to step-wise changes in end-tidal carbon dioxide concentration under low FIO2 level

Effects of SGB on the ventilatory response of bronchial asthmatic patients to step-wise changes in end-tidal carbon dioxide concentration under low FIO2 level

Polymorphism of the μ-Opioid Receptor Gene (OPRM1 118A&gt;G) Affects Fentanyl-Induced Analgesia During Anesthesia and Recovery

There is much variation in the response of both individuals and different ethnic populations to opioids, with genetic differences being responsible for interindividual variation. The micro-opioid receptor single nucleotide polymorphism (rs number 1799971) at nucleotide position 118 (OPRM1 118A>G) affects the analgesic response to opioids. This study aimed to investigate the association between the OPRM1 118A>G polymorphism and the effects of fentanyl-induced analgesia, respiratory depression, and anesthetic recovery responses in a population of Han Chinese patients. The study was a case series in a hospital setting, with 1 year of study and 1 year of follow-up. A total of 189 patients (92 males and 97 females; American Society of Anesthesiologists Physical Status I or II, Glasgow Coma Scale = 15) who were scheduled for laparoscopic abdominal surgery received intravenous midazolam (Versed) 0.08-0.01 mg/kg and fentanyl (Duragesic) 5.0 microg/kg. The main outcome measure was the degree of postoperative pain, as assessed using the Visual Analog Scale (VAS). VAS scores were recorded 5, 15, 30, 45, and 60 minutes after a fentanyl bolus injection in the post-anesthesia care unit (PACU). The minute expiratory volume, end-tidal carbon dioxide concentration (EtCO(2)) and respiratory rate (RR) were measured continuously. The incidence of fentanyl-induced respiratory depression (RR <8/min and EtCO(2) >45 mmHg) was recorded at its appearance and treated with respiratory assistance. Blood gas analysis was done 15, 30, 45, and 60 minutes after extubation. These parameters were correlated with genotyping results of genomic DNA extracted from whole blood. Patients with the OPRM1 118 AG or GG genotypes had significantly higher VAS pain scores 15 and 30 minutes after a fentanyl bolus injection in the PACU than AA genotype patients (p < 0.05). A small but statistically significant difference was observed between the 118 AA and 118 AG/GG genotypes with regard to the carbon dioxide arterial pressure (PaCO(2)) at 15 and 30 minutes from the fentanyl bolus injection after extubation (p < 0.05); however, no clinically significant difference in the frequency of respiratory depression was seen. Homozygous 118 GG genotype patients had a significantly shorter time to awakening (p = 0.018) and extubation (p = 0.024) than patients with the 118 AA genotype. When the 118 GG and 118 AG genotypes were combined for analysis, a significantly shorter time to awakening (p = 0.011) and extubation (p = 0.010), compared with the 118 AA genotype, was also seen. The OPRM1 118A>G polymorphism lessens the analgesic response to fentanyl and the time to awakening and extubation but has no clinically significant effect on the incidence of respiratory depression.

Three concentrations of levobupivacaine for ilioinguinal/iliohypogastric nerve block in ambulatory pediatric surgery

Study Objective To compare the postoperative analgesia of three different concentrations of levobupivacaine for ilioinguinal/iliohypogastric (II/IH) block in children undergoing inguinal hernia repair. Design Double-blind, prospective, randomized, controlled trial. Setting Operating room and postoperative recovery area of a university hospital. Patients 73 ASA physical status I and II children, aged one to 6 years, scheduled for outpatient inguinal hernia repair. Interventions Patients were randomized to receive one of three levobupivacaine concentrations: 0.125% (L0.125), 0.25% (L0.25), or 0.375% (L0.375). All patients received standard anesthesia with sevoflurane and II/IH nerve block. Measurements Heart rate (HR), non invasive blood pressure (NIBP), respiratory rate, end-tidal carbon dioxide concentration (ETCO 2), and oxygen saturation via pulse oximetry (SpO 2) were monitored during surgery. Postoperative pain scores with CHEOPS (Children's Hospital of Eastern Ontario Pain Scale) and need for rescue analgesia postoperatively were measured and recorded. Main Results 60 patients entered the postoperative observational period. The number of patients who received rescue analgesia was comparable in the three groups. In Group L0.125, mean CHEOPS score was significantly higher, and time to first administration of rescue analgesia was shorter, than in the other two groups ( P < 0.05). Pain scores and time to first administration of rescue analgesia were comparable between Groups L0.25 and L0.375. Conclusions II/IH nerve block using 0.4 mL kg -1 of 0.25% levobupivacaine provided satisfactory postoperative pain relief after inguinal herniorraphy.

No Supplemental Muscle Relaxants Are Required During Propofol and Remifentanil Total Intravenous Anesthesia for Laparoscopic Pelvic Surgery

No administration of supplemental muscle relaxants may be beneficial to the recovery of the ambulatory laparoscopic surgery. For this study, we compared the cardiorespiratory factors during propofol and remifentanil anesthesia for laparoscopic pelvic surgery (LPS) with or without supplemental muscle relaxants. In total, 56 healthy female patients scheduled to undergo laparoscopic pelvic surgeries were randomly assigned to two groups (A and B). Anesthesia was induced with lidocaine 30 mg, propofol target organ concentration 5.0 microg/mL, remifentanil 3.0 ng/mL, and rocuronium 0.6 mg/kg intravenously (i.v.). After tracheal intubation, anesthesia was maintained with 2.0-5.0 microg/mL of propofol and 1-4 ng/mL of remifentanil i.v. All the patients' lungs were mechanically ventilated in both groups and intermittent bolus doses of rocuronium (0.15 mg/kg i.v.) were administered in group A-however, not in group B. Heart rate (HR) and systolic arterial pressure (SAP), diastolic arterial pressure (DAP), end-tidal carbon-dioxide concentration (EtCO(2)), peak inspiratory pressure (PIP), expired minute ventilation (MV), intra-abdominal pressure (IAP), and temperature were measured during the pneumoperitoneum. There were no group differences in HR, SAP, DAP, EtCO(2), PIP, IAP, MV, PaO(2), PaCO(2), and temperature between groups A and B. No supplemental muscle relaxants are required during propofol and remifentanil total i.v. anesthesia for LPS.

Response of cerebral oximetry to increase in alveolar concentration of desflurane: effect of remifentanil and cerebrovascular CO2 reactivity.

It is known that sympathetic stimulation and increase in cerebral blood flow velocity can be induced by desflurane. Cerebral oxygen balance could be disturbed during desflurane induction. Aim of this study was to elucidate that cerebral oxygen imbalance induced by desflurane mask induction can be reduced by combination of remifentanil and hypocapnia. Twenty ASA 1-2 subjects were allocated randomly into 5 groups divided by concentration of remifentanil (0.0, 0.5, 1.0, 1.5, and 2.0 ng/ml). After confirmation of attaining proposed concentration of remifentanil, propofol and vecuronium were administered and mechanical ventilation was done with 8% desflurane with facial mask. Subsequently, changes in regional cerebral oxygen saturation (DeltarSO2), arterial blood pressure, heart rate, cardiac index, estimated alveolar concentration of desflurane (PDESF), and end-tidal concentration of carbon dioxide (PETCO2) were recorded for the following 10 minutes. According to concentration of desflurane and remifentanil, DeltarSO2 and hemodynamic factors were checked. During desflurane induction, changes in cerebral oximetry reached up to +10% (6 [first quartile], 13 [third quartile]). Arterial blood pressure, heart rate, and cardiac index were changed within clinical ranges. The DeltarSO2 showed S-shaped increasing pattern according to increasing PDESF. Hypocapnia and concentration of remifentanil reduced the maximum DeltarSO2 (P = 0.0046, P = 0.0060). Hypocapnia also shifted the curve to left (P = 0.0001). During 8% desflurane induction, regional cerebral oxygen saturation (rSO2) increases maximum +25%. Hypocapnia and use of remifentanil can reduce the increase in regional cerebral oxygen saturation.

Obesity Modestly Affects Inhaled Anesthetic Kinetics in Humans

Few studies have determined the effect of obesity on inhaled anesthetic pharmacokinetics. We hypothesized that the solubility of potent inhaled anesthetics in fat and increased body mass index (BMI) in obese patients interact to increase anesthetic uptake and decrease the rate at which the delivered (FD) and inspired (FI) concentrations of an inhaled anesthetic approach a constantly maintained alveolar concentration (end-tidal or FA). This hypothesis implies that the effect of obesity would be greater with a more soluble anesthetic such as isoflurane versus desflurane. In 107 ASA physical status I-III patients, anesthesia was induced with propofol, tracheal intubation facilitated with neuromuscular blockade, and ventilation controlled with 50% nitrous oxide in oxygen to maintain end-tidal carbon dioxide concentrations between 35 and 45 mm Hg. Isoflurane or desflurane was administered in a 1 L/min inflow rate at FD concentrations sufficient to maintain FA at 0.6 minimum alveolar anesthetic concentration (0.7% or 3.7%, respectively). FD, FI, and FA were measured 5, 10, 20, 40, 60, 90, 120,150, and 180 min after starting potent inhaled anesthetic delivery. Fifty-nine patients received isoflurane and 48 received desflurane. BMI ranged between 18 and 63 kg/m(2) and demographic variables did not differ between anesthetic groups. For isoflurane, FD/FA or FI/FA weakly (but significantly) correlated with BMI at 9/18 time points whereas for desflurane FD/FA or FI/FA correlated significantly with BMI at only one time point (P < 0.01). After dividing each group into nonobese (BMI < 30) and obese (BMI > or = 30) patients, with isoflurane, FD/FA or FI/FA was higher in obese patients at four time points whereas there was no difference between nonobese and obese patients for desflurane. Patients receiving isoflurane took longer to respond to command after discontinuing anesthesia but obesity did not increase or decrease awakening time for either isoflurane or desflurane. When BMI was used to normalize FI/FA and FD/FA the median values for isoflurane consistently exceeded the median value for desflurane by factors ranging from 3 to 5, values comparable to the ratios of their blood/gas (3.1), muscle/gas (4.6), and fat/gas (5.4) partition coefficients. BMI modestly affects FD/FA and FI/FA, and this effect is most apparent for an anesthetic having a greater solubility in all tissues. An increased BMI increases anesthetic uptake and, thus, the need for delivered anesthetic to sustain a constant alveolar anesthetic concentration, particularly with a more soluble anesthetic. However, the increase with an increased body mass is small.

Differential Effect of Morphine and Morphine-6-glucuronide on the Control of Breathing in the Anesthetized Cat

Morphine's metabolite, morphine-6-glucuronide (M6G), activates the mu-opioid receptor. Previous data suggest that M6G activates a unique M6G receptor that is selectively antagonized by 3-methoxynaltrexome (3mNTX). The authors compared the effects of M6G and morphine on breathing in the anesthetized cat and assessed whether 3mNTX reversal was selective for M6G. Step changes in end-tidal carbon dioxide concentration were applied in cats anesthetized with alpha-chloralose-urethane. In study 1, the effect of the 0.15 mg/kg morphine followed by 0.2 mg/kg 3mNTX and next 0.8 mg/kg M6G was assessed in six cats. In study 2, the effect of 0.8 mg/kg M6G followed by 0.2 mg/kg 3mNTX and 0.15 mg/kg morphine was tested in another six cats. The ventilatory carbon dioxide responses were analyzed with a two-compartment model of the ventilatory controller, which consists of a fast peripheral and a slow central component. Both opioids shifted the ventilatory carbon dioxide responses to higher end-tidal carbon dioxide levels. Morphine had a preferential depressant effect within the central chemoreflex loop. In contrast, M6G had a preferential depressant effect within the peripheral chemoreflex loop. Irrespective of the opioid, 3mNTX caused full reversal of and prevented respiratory depression. In anesthetized cats, the mu-opioids morphine and M6G induce respiratory depression at different sites within the ventilatory control system. Because 3mNTX caused full reversal of the respiratory depressant effects of both opioids, it is unlikely that a 3mNTX-sensitive unique M6G receptor is the cause of the differential respiratory behavior of morphine and M6G.

Comparison of sevoflurane and isoflurane in dogs anaesthetised for clinical surgical or diagnostic procedures

To assess attributes of sevoflurane for routine clinical anaesthesia in dogs by comparison with the established volatile anaesthetic isoflurane. One hundred and eight dogs requiring anaesthesia for elective surgery or diagnostic procedures were studied. The majority was premedicated with 0.03 mg/kg of acepromazine and 0.01 mg/kg of buprenorphine or 0.3 mg/kg of methadone before induction of anaesthesia with 2 to 4 mg/kg of propofol and 0.5 mg/kg of diazepam. They were randomly assigned to receive either sevoflurane (group S, n=50) or isoflurane (group I, n=58) in oxygen and nitrous oxide for maintenance of anaesthesia. Heart rate, respiratory rate, indirect arterial blood pressure, haemoglobin saturation, vaporiser settings, end-tidal carbon dioxide and anaesthetic concentration and oesophageal temperature were measured. Recovery was timed. Data were analysed using analysis of variance and non-parametric tests. Heart rate (85 to 140/minute), respiratory rate (six to 27/minute) and systolic arterial blood pressure (80 to 150 mmHg) were similar in the two groups. End-tidal carbon dioxide between 30 and 60 minutes (group S 6.4 to 6.6 and group I 5.8 to 5.9 per cent) and vaporiser settings throughout (group S 2.1 to 2.9 and group I 1.5 to 1.5 per cent) were higher in group S. There was no difference in time to head lift (18+/-16 minutes), sternal recumbency (28+/-22 minutes) or standing (48+/-32 minutes). No adverse events occurred. Sevoflurane appeared to be a suitable volatile anaesthetic for maintenance of routine clinical anaesthesia in dogs.

Effect of Patient Weight and Anesthetic Technique on CO2 Excretion During Thoracoscopy in Children Assessed by End-Tidal CO2

The aim of this study was to review the changes in CO(2) excretion and anesthetic management during thoracoscopy in children. We analyzed end-tidal carbon dioxide concentration (EtCO(2); kPa) during CO(2) pneumothorax. EtCO(2) was measured on a continuous basis by using a positive sampling system and recorded every 10 minutes. Baseline and highest EtCO(2) were used to derive the maximum change in the intraoperative period. EtCO(2) was also analyzed in three time periods: (1) preinsufflation, (2) during insufflation of CO(2) into the chest, and (3) after desufflation. Core temperature was also recorded as an index of thermoregulation. Data are presented as the mean +/- standard error of the mean. Differences within time periods were compared by using paired t tests or repeated measures analysis of variance. Correlation between changes in EtCO(2) and patient demographics was performed by using linear regression. The pattern of change was compared to children undergoing laparoscopy. Median age was 1.9 years (range, 1 day to 15 years). EtCO(2) increased significantly from preinsufflation 5.1 +/- 0.2 to 6.4 +/- 0.3 during insufflation (P < 0.01); values were still significantly elevated after desufflation 6.4 +/- 0.4 (P < 0.01). Single-lung ventilation was associated with higher EtCO(2) levels during insufflation than with two-lung ventilation (P = 0.02). Maximum change in the EtCO(2) in the group undergoing one-lung ventilation negatively correlated to patient weight (r(2) = 0.25, P = 0.02); this correlation was not present with two-lung ventilation (r(2) = 0.02, P = 0.84). Laparoscopy increased EtCO(2) from 4.7 +/- 0.2 preinsufflation to 5.3 +/- 0.2 (P < 0.001) during and decreased to 4.8 +/- 0.2 postdesufflation (P = 0.60). There was a significant increase in core temperature from 35.9 +/- 0.3 to 36.9 +/- 0.2 postoperatively (P = 0.007). There is a significant increase in EtCO(2) in children undergoing thoracoscopy, which is higher than during laparoscopy. Changes in EtCO(2) are larger in smaller children undergoing single-lung ventilation. Thoracoscopy may preserve intraoperative thermoregulation.

Effect of butorphanol administration on cardiovascular parameters in isoflurane-anesthetized horses – a retrospective clinical evaluation

ObjectiveTo determine cardiovascular responses to administration of butorphanol in isoflurane-anesthetized horses. Study designRetrospective evaluation of anesthetic records. AnimalsSeventy-six horses anesthetized for a variety of clinical surgical procedures. MethodsAnesthetic records of clinical equine patients anesthetized between January 1999 and December 2003 were searched. The records were reviewed for horses in which anesthesia was induced with ketamine and a benzodiazepine and maintained with isoflurane, and horses that received butorphanol intraoperatively. Exclusion criteria included horses in which the rate of infusion of an inotrope or end-tidal isoflurane concentration was changed 10 minutes before or after the butorphanol bolus. The horses were separated into two groups: group 1 horses received butorphanol at intervals as part of a balanced protocol, group 2 horses had ≥10% increase in heart rate (HR) or blood pressure within 10 minutes prior to butorphanol administration. ResultsEighty-nine butorphanol administration events matched the criteria for inclusion, 49 in group 1 and 40 in group 2. There were no significant changes after butorphanol administration in systolic arterial pressure (SAP), mean arterial pressure (MAP), diastolic arterial pressure (DAP), and heart rate (HR) in group 1, or in end-tidal carbon dioxide concentration or hemoglobin oxygen saturation in either group. There were significant decreases in SAP (p < 0.0001), MAP (p < 0.0005), and DAP (p < 0.0008) after butorphanol administration in group 2. Conclusions and clinical relevanceThe results presented here confirm that butorphanol can be administered to horses during isoflurane anesthesia without adverse effects on HR and arterial blood pressure. The results imply that butorphanol can deepen the plane of anesthesia and obtund sympathetic stimulation from a surgical procedure.

Cardiopulmonary effects of administration of a combination solution of xylazine, guaifenesin, and ketamine or inhaled isoflurane in mechanically ventilated calves

To compare the cardiopulmonary effects of administration of a solution of xylazine, guaifenesin, and ketamine (XGK) or inhaled isoflurane in mechanically ventilated calves undergoing surgery. 13 male calves 2 to 26 days of age. Procedures-In calves in the XGK group, anesthesia was induced (0.5 mL/kg) and maintained (2.5 mL/kg/h) with a combination solution of xylazine (0.1 mg/mL), guaifenesin (50 mg/mL), and ketamine (1.0 mg/mL). For calves in the isoflurane group, anesthesia was induced and maintained with isoflurane in oxygen. The rates of XGK infusion and isoflurane administration were adjusted to achieve suitable anesthetic depth. All calves received 100% oxygen and were mechanically ventilated to maintain end-tidal carbon dioxide concentrations from 35 to 40 mm Hg and underwent laparoscopic bladder surgery through an abdominal approach. Cardiopulmonary variables were measured before induction and at intervals up to 90 minutes after anesthetic induction. The quality of induction was excellent in all calves. The XGK requirements were 0.57 +/- 0.18 mL/kg and 2.70 +/- 0.40 mL/kg/h to induce and maintain anesthesia, respectively. Heart rate was significantly lower than baseline throughout the anesthetic period in the XGK group. Systolic arterial blood pressure was significantly higher in the XGK group, compared with the isoflurane group, from 5 to 90 minutes. Cardiac index was lower than baseline in both groups. Differences between groups in cardiac index and arterial blood gas values were not significant. Administration of XGK resulted in excellent anesthetic induction and maintenance with cardiopulmonary alterations similar to those associated with isoflurane in mechanically ventilated calves.