Datex Ohmeda Research Articles

Effects of fresh gas flow, tidal volume, and charcoal filters on the washout of sevoflurane from the Datex Ohmeda (GE) Aisys, Aestiva/5, and Excel 210 SE Anesthesia Workstations.

We investigated the effects of tidal volume (VT), fresh gas flow (FGF), and a charcoal filter in the inspiratory limb on the washout of sevoflurane from the following Datex Ohmeda (GE) Anesthesia Workstations (AWSs): Aisys, Aestiva/5, and Excel 210SE. After equilibrating the AWSs with 2% sevoflurane, the anesthetic was discontinued, and the absorbent anesthesia breathing circuit (ABC), reservoir bag, and test lung were changed. The lung was ventilated with 350 or 200 mL·breath(-1), 15 breaths·min(-1), and a FGF of 10 L·min(-1) while the washout of sevoflurane was performed in triplicate using a calibrated Datex Ohmeda Capnomac Ultima™ and a calibrated MIRAN SapphIRe XL ambient air analyzer until the concentration was ≤ 10 parts per million (ppm). The effects of decreasing the FGF to 5 and 2 L·min(-1) after the initial washout and of a charcoal filter in the ABC were recorded separately. The median washout times with the Aisys AWS (14 min, P < 0.01) and the Aestiva/5 (17 min, P < 0.001) with VT 350 mL·breath(-1) were significantly less than that with the Excel 210SE (32 min). The mean (95% confidence interval) washout time with the Aisys increased to 23.5 (21.5 to 25.5) min with VT 200 mL·breath(-1) (P < 0.01). Decreasing the FGF from 10 to 5 and 2 L·min(-1) with the Aisys caused a rebound in sevoflurane concentration to ≥ 50 ppm. Placement of a charcoal filter in the inspiratory limb reduced the sevoflurane concentration to < 2 ppm in the Aisys and Aestiva/5 AWSs within two minutes. The GE AWSs should be purged with large FGFs and VTs ~350 mL·breath(-1) for ~25 min to achieve 10 ppm sevoflurane. The FGF should be maintained to avoid a rebound in anesthetic concentration. Charcoal filters rapidly decrease the anesthetic concentration to < 2 ppm.

Palatal obturator: Perioperative concerns

Sir, A 46-year-old male, weighing 60 kg with diabetes mellitus type II since 10 years was scheduled for debridement of the nasal cavity under general anaesthesia (GA). Patient had undergone surgical procedure for mucormycosis under GA uneventfully one year ago. Systemic examination was unremarkable. The airway examination showed a Mallampati (MMP) class IV [Figure 1a] with mouth opening of 3 cm, thyromental distance of 10 cm and possible anterior mandibular protrusion. Patients blood biochemistry and other routine investigations were acceptable. Patient was kept nil per oral and premedicated with anxiolytics and antacids on the night before and on the morning of surgery while morning dose of insulin was omitted. On the day of surgery blood sugar and electrolytes were within the normal range. In the operating room, a multi parameter monitor (AS5, Datex Ohmeda, Finland) was attached to the patient and after securing intravenous (IV) access, IV glycopyrrolate 0.2 mg and IV fentanyl 120 μg were given. Difficult airway cart was kept ready. GA was induced with IV propofol 120 mg and IV succinylcholine 100 mg was given after confirmation of ability to ventilate the lungs. Oral endotracheal intubation was performed with 8.0 mm cuffed endotracheal tube with Glidescope® (GVL; Verathon Inc., Bothell, WA). During intubation, the posterior end of palatal obturator was visualized. Following correct placement of endotracheal tube, the palatal obturator was removed [Figure 1b]. Rest of the perioperative period was unremarkable.Figure 1: (a) Airway examination of patient shows a mallampati grade IV. (b) The palatal obturator after removalPalatal obturator is a prosthetic device and is indicated in patients with cleft palate, traumatic injuries and tumours of palate.[12] Palatal obturator consists of an acrylic plate and retention clasps of orthodontic wire, which covers a fistula of the palate. It serves to restore speech, mastication, deglutition and aesthetics.[12] Successful obturation depends on the volume of the defect, tissue retention available around the cavity and development of muscular control.[34] It must be as light as possible as its weight may act as a dislocating force.[3] The palatal obturator can cause anaesthetic complications including airway obstruction, inability to pass endotracheal tube due to dislodgement of prosthesis, limitation of the space for a laryngoscope and a traumatic intubation. According to recent practice guidelines for management of the difficult airway, video-assisted laryngoscopy can now be used as an initial approach to intubation in patients in non-emergent pathway with difficult airway.[5] We administered succinylcholine considering uneventful previous anaesthetic exposure of the patient and MMP class IV being the only predictor for difficult airway and rest of the airway examination also being normal.[5] The difficult airway cart with other alternative intubation devices were however kept ready. The absence of symptoms of regurgitation of food or water, MMP class IV on airway examination and observer limitation of not able to differentiate between similar looking palatal obturator with the oral mucosa in room light; all probably contributed to the cause of missed finding in the present case. However, we did not encounter any complication during the anaesthetic procedure. Pre-anaesthesia evaluation is considered as basic element of anaesthesia care and includes a multi-disciplinary approach including patient's medical record, history taking, physical examination and findings from medical tests and evaluations. At the same time, anaesthesiologist should consult other health-care professionals to obtain information relevant to perioperative care to avoid any catastrophe. Assessment performed during pre-anaesthetic evaluation may be used to formulate plans for intraoperative care, post-operative recovery, perioperative pain management and patient education.[6]

Dexmedetomidine decreases requirement of thiopentone sodium and pentazocine followed with improved recovery in patients undergoing laparoscopic cholecystectomy.

Background:Pain relief remains the most fundamental and consequential aspect of surgery for patients throughout perioperative period. Dexmedetomidine has created an interest in α2-adrenoceptor agonists in the management of pain and hence the aim of this study was to evaluate the effectiveness of the drug in hilly population of North India.Materials and Methods:Patients, irrespective of gender, were randomly allocated to two groups, control and test, each having 30 patients. Test group received an infusion of dexmedetomidine at a rate of 0.5 μg/kg/h 30 min before induction and 0.6 μg/kg/h after inducing anesthesia. Control patients received a volume-matched infusion of normal saline as placebo. Approximately 2 min before induction, analgesia was provided in the form of pentazocine, 0.5 mg/kg in control and 0.3 mg/kg in the test group. Induction was performed by 2 mg/kg thiopentone sodium supplemented with intravenous boluses of 25 mg thiopentone sodium every 15 s until loss of eyelid reflex (determined every 15 s). Induction dose of thiopentone sodium and total pentazocine dose were recorded. Recovery was assessed on the clinical recovery score (CRS) scale.Results:Infusion of dexmedetomidine decreased the induction dose of thiopentone approximately by 33% and of pentazocine dose by approximately 39% in patients undergoing laparoscopic cholecystectomy. Moreover, incidence of pain was also decreased significantly. Improved CRS from 4.33 to 6.87 was noticed immediately post-operatively in dexmedetomidine group of patients.Conclusion:Infusion of dexmedetomidine during the laparoscopic cholecystectomy decreases the requirement of thiopentone sodium and pentazocine and leads to early recovery of patients.

Can phrenic stimulation protect the diaphragm from mechanical ventilation-induced damage?

To the Editor: Mechanical ventilation is a prominent lifesaving treatment. It is, however, associated with an array of adverse effects, which include ventilator-associated pneumonias, volume-induced lung injury and, more recently identified, ventilator-induced diaphragm dysfunction (VIDD) [1–3]. VIDD combines diaphragm weakness with muscle fibre atrophy, remodelling and injury. Its mechanisms involve decreased protein synthesis, increased proteolysis, increased oxidative stress and mitochondrial dysfunction [2, 4]. Controlled mechanical ventilation appears to be the main, if not the sole, risk factor for VIDD, which in animal models is attenuated by the maintenance of respiratory efforts (assisted ventilatory modes) [2]. Although the corresponding human evidence is still lacking, this underlies the current notion that “clinicians should encourage persistent diaphragmatic activity” in patients receiving mechanical ventilation [2]. Diaphragm pacing has been proposed as a surrogate for spontaneous respiratory activity when the latter is not compatible with the condition of the patient [2, 5], but this approach has, seemingly, not yet been tested experimentally. Here we report a preliminary description of putative beneficial effects of diaphragm pacing in three mechanically ventilated sheep. Three female adult sheep (41, 32 and 34 kg), were anaesthetised (premedication: acepromazine 1.3 mg·kg−1 i.m. , 30 min before induction; induction: propofol 6 mg·kg−1 i.v. ; maintenance: continuous propofol 1–2 mg·kg−1·h−1, midazolam 0.3–2 mg·kg−1·h−1 and morphine 0.2–0.3 mg·kg−1·h−1; no paralysing agents), tracheotomised and mechanically ventilated with a minute ventilation ensuring normocapnia (Aisys, GE Healthcare, Datex Ohmeda, Madison, WI, USA). Additional oxygen was given to maintain transcutaneous-pulsed oxygen saturation >92%. Adequate fluid and nutritional support was provided and glycaemia controlled. Body temperature, heart rate and arterial pressure were monitored. Intradiaphragmatic phrenic nerve stimulation electrodes were inserted bilaterally in …

Cases of carbon dioxide rebreathing without significant color change in the appearance of the carbon dioxide absorbent canisters

To the Editor: Three cases of carbon dioxide rebreathing without a significant color change in the appearance of the canisters were experienced during general anesthesia with the same model anesthesia machines; Aestiva/5 (Datex Ohmeda, Wisconsin, USA) with a fresh gas flow of 1–2 l/min. Carbon dioxide rebreathing was recognized because the inspiratory carbon dioxide baseline of the capnogram trace gradually rose. The inhalational carbon dioxide concentration decreased immediately after increasing the fresh gas flow, and rose again with decreasing the fresh gas flow. This indicates that carbon dioxide rebreathing was due to carbon dioxide accumulation in the semi-closed circuit system of the anesthesia machines. A color change in the appearance of the carbon dioxide absorbent was recognized only in the upper part of the canister (Fig. 1a). The top surface of the canister showed a significant color change limited to the middle part of it (Fig. 1b). The section image of the canister showed a significant columnar color change of the carbon dioxide absorbent along the full length of the center part of it (Fig. 1c). The observation of the canister bottom of Aestiva/5 revealed that only the center part of it had the mesh part for the exhaled gas, and the color change of the carbon dioxide absorbent seemed to accord with the mesh part of the bottom (Fig. 1d). As an experiment, when a transparent plastic partition wall was settled in the canister before filling with carbon dioxide absorbent, the columnar color change was no longer visible. This indicated that the flow of the exhaled gas was influenced by the wall in the canister. Considering these results, it is supposed that the structural characteristic of the canister bottom of the anesthesia machine; Aestiva/5, caused channeling and the inhomogeneity of the current of inhaled gas in the canister led to the columnar color change of the carbon dioxide absorbent. The role of the carbon dioxide absorbent canister becomes more important as the fresh gas flow quantity decreases. A technique of using a fresh gas flow of 1 l/min was reported first in 1952 [1]. The technique with the fresh gas flow less than 1 l/min subsequently became known as ‘‘low-flow anesthesia’’. Afterwards, a technique using a fresh gas flow of 500 ml/min was reported as ‘‘minimal flow anesthesia’’ [2]. These cases of carbon dioxide rebreathing without significant color change in the appearance of the canisters provide very important information not only for anesthesiologists, but also for all persons using anesthesia machines. When carbon dioxide rebreathing is recognized, carbon dioxide accumulation in the circuit system of the anesthesia machines should be suspected and exhaustion of the carbon dioxide absorbent should be immediately T. Yamamoto (&) Department of Pediatric Anesthesiology and Critical Care Medicine, Children’s Hospital Asklepios Klinik Sankt Augustin, Arnold-Janssen-Str. 29, 53757 Sankt Augustin, Germany e-mail: yamatomo270@hotmail.com; t.yamamoto@asklepios.com

ASSA13-08-12 Hyperlactatemia in Children with Congenital Heart Diseasesafter Operations with Cardiopulmonary Bypass

<h3>Background</h3> Hyperlactatemia is a well recognised marker of circulatory failure [1]. Several studies have shown a strong correlation between blood lactate levels and the risk of morbidity and mortality in varying clinical situations such as circulatory shock, septic shock, severe hypoxemia, liver failure, diabetes mellitus, and others [2]. After cardiac surgery, Hyperlactatemia is relatively common and is associated with morbidity and mortality. Hyperlactatemia occurs during cardiopulmonary bypass in patients undergoing operations for congenital cardiac disease and may be an early indicator for postoperative morbidity and mortality. It is a well-known fact that tissue hypoperfusion and inadequate oxygen delivery are associated with lactic acidosis owing to anaerobic metabolism [3]. The aim of the present study is to estimate the frequency and to reveal predictors of heperlactatemia occurrence in children with congenital heart diseases in the early postoperative period. <h3>Methods</h3> This prospective study was spent in our centre between March and September 2007. Seventy two patients with congenital heart diseases operated in artificial blood circulation conditions from 1 till 17 years old were included in to the research. The study design was approved by the centre ethical committee. Written voluntary consent to participation in the scientific programme was signed by children’s parents. The induction to anaesthesia was performed in the presence of parents and includes the following components: Ketamin 7 mg/kg; Relanium 0.25 mg/kg; Atropine 0.015 mg/kg. After an approach of proof sedative effect the child was delivered to the operation room. Myoplegia was carried out by an intravenous injection of pipikuronium bromide 0.1 mg/kg. Artificial lungs ventilation was carried by Datex Ohmeda ADU AS-5 (Finland) (IPPV-mode). <h3>Results</h3> We have obtained the following data: increase in lactate concentration &gt; 5 mmol/l was marked in 2.37% blood samples. Time intervals analysis has shown, that maximal lactate concentration were observed in 7–11 hours after operation. There were no cases of heperlactatemia after 24 hours after operation. Having investigated interrelation between lactate and glucose concentration, we have found statistically authentic differences in glucose level &gt; 9 mmol/l (r = 0.56). This interrelation was traced only in two time intervals: 1–6 and 7–11 hours after operation. <h3>Conclusions</h3> Metabolic infringements in children with congenital heart diseases operated in artificial blood circulation conditions are observed in small percent of cases. Lactate concentration peak is observed in 7–11 hours interval after operation. There is no significant interrelation between artificial circulation time and heperlactatemia intensity in early postoperative period.

Comparison of BIS values in patients under anesthesia with minimum alveolar concentration of sevoflurane and median effective concentration of propofol at loss of consciousness

Objective To compare the BIS values in patients under anesthesia with minimum alveolar concentration (MAC) of sevoflurane and median effective concentration (EC50) of propofol at loss of consciousness.Methods Sixty ASA Ⅰ or Ⅱ patients,aged 18-60 yr,undergoing elective surgery under general anesthesia,were equally and randomly divided into 2 groups:inhalational anesthesia with sevoflurane group (group Sev) and intravenous anesthesia with propofol ( group Pro).The end-tidal concentration of sevoflurane was monitored using Aestiva anesthesia machine (Datex Ohmeda) in group Sev.Anesthesia was induced with intravenous injection of etomidate 0.3 mg/kg,rocuronium 1 mg/kg,and remifentanil 0.2 μg/kg.The patients were mechanically ventilated after tracheal intubafion.Sevoflurane inhalation was started 12.5 min after intubation in group Sev.Propofol was given by target-controlled infusion with the target plasma concentration set at 3.8 μg/ml 12.5 min after intubation in group Pro.When the effect-site concentrations of propofol reached EC50 of propofol at loss of consciousness (2.2 μg/ml),1.3 EC50(2.86 μg/ml) and 1.5 EC50 (3.3μg/ml) and when the end-tidal concentrations of sevoflurane reached 1.0,1.3 and 1.5 MAC,BIS value,MAP and HR were recorded.Results HR was significantly higher at 1.3 MAC or 1.3 EC50,and at 1.5 MAC or 1.5 EC50 in group Pro than in group Sev ( P ＜0.05).BIS value was significantly decreased at 1.3 MAC or 1.3 EC50,and at 1.5 MAC or 1.5 EC50 compared with that at 1.0 MAC or EC50(P ＜0.05).There was no significant difference in MAP and BIS value at each time point between the two groups ( P ＞ 0.05).Conclusion No significant change in BIS values is found in patients under anesthesia with 1.0,1.3 and 1.5 MAC of sevoflurane and with 1.0,1.3 and 1.5 EC50 of propofol. Key words: Anesthetics, inhalation; Propofol; Electroencephalography; Unconsciousness; Doseresponse relationship, drug

Intraoperative fluid management in open gastrointestinal surgery: goal-directed versus restrictive

OBJECTIVE:The optimal strategy for fluid management during gastrointestinal surgery remains unclear. Minimizing the variation in arterial pulse pressure, which is induced by mechanical ventilation, is a potential strategy to improve postoperative outcomes. We tested this hypothesis in a prospective, randomized study with lactated Ringer's solution and 6% hydroxyethyl starch solution.METHOD:A total of 60 patients who were undergoing gastrointestinal surgery were randomized into a restrictive lactated Ringer's group (n = 20), a goal-directed lactated Ringer's group (n = 20) and a goal-directed hydroxyethyl starch group (n = 20). The goal-directed fluid treatment was guided by pulse pressure variation, which was recorded during surgery using a simple manual method with a Datex Ohmeda S/5 Monitor and minimized to 11% or less by volume loading with either lactated Ringer's solution or 6% hydroxyethyl starch solution (130/0.4). The postoperative flatus time, the length of hospital stay and the incidence of complications were recorded as endpoints.RESULTS:The goal-directed lactated Ringer's group received the greatest amount of total operative fluid compared with the two other groups. The flatus time and the length of hospital stay in the goal-directed hydroxyethyl starch group were shorter than those in the goal-directed lactated Ringer's group and the restrictive lactated Ringer's group. No significant differences were found in the postoperative complications among the three groups.CONCLUSION:Monitoring and minimizing pulse pressure variation by 6% hydroxyethyl starch solution (130/0.4) loading during gastrointestinal surgery improves postoperative outcomes and decreases the discharge time of patients who are graded American Society of Anesthesiologists physical status I/II.

An unusual site of an occult air leak in an armoured endotracheal tube in the midst of surgery

Sir, Even after a recommended check of the anaesthesia equipments, we may sometimes face some intriguing problems during the surgical interventions. We describe an unusual site of an air leak in an armoured endotracheal tube (ETT) in the midst of the surgical procedure involving the trachea. A 35-year-old male, ASA class 1 patient with a history of tracheal injury was posted for Montgomery T-tube insertion through the tracheostomy site. After administration of general anaesthesia, the tracheostomy tube was removed and the patient was intubated with a 38FG Rusch® armoured ETT through the tracheostomy site. Before insertion, a recommended check of cuff and cuff inflation assembly was performed, with no leaks detected.[12] Instead of using an adhesive tape for securing the ETT in place, the surgeon insisted on application of a stay suture over the sternal skin and to tie it with the ETT. We noticed the leak pressure alarm displayed on the screen of the anaesthesia machine (GE Datex Ohmeda Aestiva 5®) nearly 20 min after the start of the surgical procedure. The surgeons also noticed the leak around the cuff and immediately alarmed us. The cuff was reinflated and surgery started, but again the same leak pressure alarm was displayed on the monitor after 10 min of the commencement of surgery. We decided to stop the surgery and replace the armoured ETT with fresh armoured ETT. Meanwhile, we carried out an in vitro check for patency of cuff, which showed no air leak, and, therefore, we decided to put whole tube in water to check the leak in the inflation tube assembly. To our surprise, we found a leak from the site where the surgeons had applied the stay suture near the 20 cm mark where the inflation tube was embedded in the ETT [Figure 1].Figure 1: Air leak site from the inflation tube assemblyWe concluded that applying a stay suture might have breached the integrity of the inflation tube that was embedded in the armoured ETT, leading to occult air leak. A similar observation with resterlized armoured ETT had been noted before when these tubes were stretched during the surgical procedure, allowing air to leak if any cuts or holes were present in the ETT, which usually get missed on routine check.[34] We observed that the inflation tube assembly of the armoured ETT is more superficially embedded in the wall of the ETT as compared with the poly vinyl chloride ETT; therefore, the chances of its damage are greater. The surgeons should be discouraged to apply stay suture on these ETTs for securing it in place. In certain situations, if the stay suture is necessary for securing the tube, then certain simple yet effective maneuvers can be done to avoid damage to the inflation tube assembly. The ETT should be placed in such a way that the tangential force of the stay suture should not directly be applied on the wall of the ETT where the inflation tube assembly is embedded. For that, the ETT with the inflation tube assembly should be facing downward and away from the contact point of the suture. If required, we can also apply a sterilized adhesive tape or an aluminium foil circumferentially in that area where the stay suture is tied onto the ETT, which will negate the effects of that tangential force and hence avoiding the breach in the inflation tube assembly.

Physiological Impact of Pneumoperitoneum on Gastric Mucosal CO2 Pressure During Laparoscopic Versus Open Appendectomy in Children

Funded knowledge about the physiological impact of laparoscopic surgery in children is sparse. Although there are data on hemodynamic compromise after creation of a pneumoperitoneum in children, little is known about microcirculatory changes at the mucosa level. Therefore, the aim of this study was to assess gastric microcirculation by continuous gastric air tonometry in the setting of laparoscopic versus open appendectomy. Twenty children 5-17 years old undergoing laparoscopic and 7 children undergoing open appendectomy were included in the study. Gastric intramucosal CO(2) pressure (pCO(2)i) was measured under standardized flow and intraperitoneal pressure using continuous air tonometry (TONOCAP(®), Datex Ohmeda), and ΔpCO(2) (pCO(2)i - end-expiratory CO(2) pressure [pCO(2)e]) was obtained for the time course of surgery. ΔpCO(2) increased significantly from the baseline value not only in the laparoscopic group but also in the open surgery group. Even though ΔpCO(2) was higher in the laparoscopic group at all time points, the overall increase in ΔpCO(2) for both groups was uniform. The largest differences were observed during the initial 20 minutes of the operation. The changes observed were exclusively due to an increase of pCO(2)i in relation to a constant pCO(2)e. In the setting of a standardized, simple operation in an otherwise healthy child above the age of 5 years, our data suggest that the effect of a pneumoperitoneum on splanchnic perfusion is comparable to the compromise caused by open surgery. Further research must be obtained when evaluating the full impact of laparoscopy in children.

Abstract 196: Measurement of Depth, Thrust and Thoracic Impedance During Mechanical Cardiopulmonary Resuscitation: Is Thoracic Impedance a Potential Indicator of Effective External Cardiac Massage in a Porcine Model of Cardiac Arrest?

Purpose of the Study: The 2010 AHA guidelines currently recommend a depth of at least 2 inches (5cm) during external cardiac massage. The purpose of this study was to determine if the use of an alternative measure to depth could assist in quantifying the effectiveness of CPR in an out-of-hospital setting and to determine how achievable depths of at least 2 inches are in experimental models of cardiac arrest. Materials and Methods: A total of 12 porcine models were used each weighing 30.7±4.2kg. Depth (mm), thrust (kg); End-tidal CO 2 , and Cardiac Output (CO) were measured at 2 minute intervals for each model. The Impedance Cardiogram (ICG)/Thoracic Impedance (non-invasive measure of cardiac output) was recorded via 2 standard defibrillation electrodes, as a method of detecting the presence of effective CPR. Ethical approval was granted by the Northern Ireland Home Office. Models were anaesthetised using Isoflurane and connected to a Datex Ohmeda® for anaesthesia monitoring. Depth and rate of CPR were continuously measured using Q-CPR®, Philips. CPR was administered using the HLR-201®, Michigan Instruments. Recordings from each experiment were acquired using the Datex Ohmeda for statistical analysis using Microsoft Access®. Results: During CPR, cardiac output was maintained at an average of 21% of normal CO levels. At thrusts of 60kg and a rate 112±2 compressions per minute, the average depth (using Q-CPR®, Philips) achieved using a stabilised mechanical CPR system was 37.12mm±3 (1.46±0.12inches). Using the HLR-201®, Michigan Instruments the average depth achieved was 50mm (1.97inches). A strong linear correlation was achieved when comparing depth (mm) using Q-CPR® and the thrust (kg) using the HLR-201®, Michigan Instruments; r=0.856. In addition a strong linear correlation was attained when the Impedance cardiogram (ICG) (ohms) was compared with depth (mm) using Q-CPR®, Philips of; r=0.86. Conclusions: A depth of at least 2 inches was almost unattainable in this porcine model, even at thrusts of 60 kg. An algorithm will incorporate the results from this study, providing feedback to the operator on the quality of CPR by measuring the ICG amplitude which has been strongly correlated with standard measures of depth as well as a number of physiological parameters.

Entropy decreases post-operative morbidity in patients undergoing major gynaecological laparoscopic surgery

We have read with great interest the article written by Soumpasis et al.1 The authors studied the effect of depth of anaesthesia using bispectral index monitoring on post-operative analgesic requirements after major urological procedures. We recently conducted an audit on post-operative morbidity in 100 patients who have undergone major laparoscopic gynaecological surgery with the use of entropy monitoring (Datex Ohmeda, GE Healthcare Chalfont St. Giles, UK). The supreme or flexible laryngeal mask airway was inserted at response entropy and state entropy of 20 and 30, respectively, and maintained at 30 and 40, respectively, during the procedure. The laryngeal mask airway was removed at response entropy and state entropy of 70 and 90, respectively. Nitrous oxide and sevoflurane were used as inhalation agents, along with propofol infusion, fentanyl 200 μg at induction followed by diclofenac suppository for pain relief. Additional analgesia was provided by intravenous tramadol, along with ondansetron. Our audit found that the incidence of post-operative pain was 8%. The incidence of post-operative airway problems was 7%; however, none of these patients required re-intubation and ventilation. The cumulative incidence of post-operative nausea and vomiting during the first 24 h post-operatively was 11%. As observed by Soumpasis et al.,1 we strongly believe that the use of depth of anaesthesia monitoring decreases not only post-operative pain but also airway problems and the incidence of post-operative nausea and vomiting. Acknowledgements This work was supported by the Department of Anaesthesiology, BEAMS Hospital, Mumbai, India. There are no conflicts of interest.

Bilateral postoperative brachial plexus palsy and longlasting surgery

A 69-year-old (55 kg, 158 cm) woman was scheduled to have major gynaecological surgery due to an ovarian tumour. Before induction of anaesthesia, an epidural thoracic catheter was inserted at the T8–T9 level in a sitting position without any technical difficulty; it was tested with 4 ml of lidocaine 2% and epinephrine 1/200000 to obtain a bilateral T6-S3 sensory block. General anaesthesia was initiated thereafter with propofol, remifentanil and atracurium and maintained with desflurane and remifentanil and an infusion of atracurium for muscle relaxation under NMT monitoring (NMT Datex Ohmeda, Madison, Wisconsin, USA). The patient was installed in the supine position with both arms on abduction with a hard pillow at a low dorsal level (T10–T11) to increase surgical exposure. The surgery was carried out and lasted 6 h, around 2000 ml of blood loss was estimated and patient had a three units of red cells transfused. No haemodynamic instability was observed; mean arterial pressure was above 65 mmHg during the whole procedure. Trendelenburg position was applied from time to time because of surgical necessity. At skin closure, 20 ml of ropivacaine 0.2% was injected over a 30-min period and at the end of surgery reversal of neuromuscular blockade was performed with atropine and neostigmine under neuromuscular monitoring. The patient was extubated subsequently in the operating room after full recovery of neuromuscular blockade (90% train-of-four recovery) and a core temperature of 36°C. Soon after extubation, bilateral upper limb paraparesis was noticed (C4–C6), in association with lower limb hypoparesis. A total spinal anaesthesia was excluded because of the absence of respiratory and haemodynamic instability; therefore, this partial palsy was initially thought to be due to the spread of epidural analgesia above T4.1 However, as bilateral lower limb hypoparesis was also present, patient-controlled epidural analgesia, which consisted of voluntary boluses associated to an infusion of 3–5 ml per hour of ropivacaine, was not initiated. Two hours later, whereas lower limb paralysis faded, upper limb palsy persisted. An emergency cervical and thoracolumbar MRI was performed to exclude epidural haematoma and/or other cervical lesions. No abnormalities were detected and the following hypothesis was retained: postural bilateral upper limb palsy due to supraclavicular stretching of the brachial plexus. After 12 h, while the patient was fully awake and all vital functions were recovered and stabilised, upper limbs motricity and sensitivity was absent. Neurological consultation at day 1 postoperation confirmed our initial hypothesis; subsequently, very active physiotherapy of the upper limbs was undertaken and the patient started to recover partially both upper limb sensitivity and motricity. After 7 days, the patient could use both arms; however, the prone movement of right forehand was not possible, but she continued to improve until day 15, which she was discharged from the hospital. Neurological follow-up detected full recovery within 1 month. At 1 year, no neurological anomaly was detected. Transitional postoperative upper limb palsy is a postural complication of long surgery under general anaesthesia with muscle relaxation and special care should be given to these patients before the start of surgery by both the anaesthetic and surgical team.2 In this case, our patient had bilateral palsy, which is very uncommon. In addition, the presence of epidural analgesia initially misguided us.1,3 Nevertheless, only MRI can rule out a compression to an epidural haematoma; however, it should be performed as soon as possible (within 6 h) to eventually relieve possible compression. The injuries in our case have been previously described and are mostly due to nerve stretching under general anaesthesia, muscle relaxation and Trendelenburg position and arms on abduction and the whole situation was probably aggravated by the thoracic hard pillow that elevated the trunk. Although the outcome is generally favourable, the situation could become stressful for the patients as total nursing assistance (as in this case) would be needed at least in the early postoperative days. In the case of our patient, the concomitant presence of thoracic epidural anaesthesia was an additional confusing factor. Nevertheless, in addition to this complication, she did not benefit from postoperative epidural analgesia. Anaesthetists and surgeons should be aware of the multifactorial bases of this complication.

Pulse oximetry during intraaortic balloon pump application

Pulse oximeters are multiple used devices in anaesthesiology and intensive care medicine and must provide reliable data during various conditions of signal interference, including light, motion and reduced perfusion. The aim of this study was to evaluate the reliability of different new-generation pulse oximeters during intraaortic balloon pump (IABP) therapy. In the experimental setting, the validity of three pulse oximetry technologies (Masimo Radical 7, Nellcor N-600 and Datex Ohmeda TruSat) was evaluated in patients with IABP treatment. Arterial blood gas analysis (BGA-SaO2) data were compared with the pulse oximetric values (SpO2) during 1:1, 1:2 and 1:3 support ratio. The mean differences (bias) during 1:1, 1:2 and 1:3 IABP support between BGA-SaO2 and Datex-SpO2 were 3.38% [95% confidence intervals (CI):±1.39%], 1.41% (95% CI 1.14%) and 2.10% (95% CI:±0.94%), respectively. Between BGA-SaO2 and Nellcor-SpO2, a bias of 0.77% (95% CI:±0.46%), 0.85% (95% CI:±0.40%) and 0.59% (95% CI:±0.38%) was found. In the comparison of BGA-SaO2 and Masimo-SpO2, a bias of 0.58% (95% CI:±0.56%), 0.19% (95% CI:±0.40%) and -0.01% (95% CI:±0.43%) was found, respectively. In patients with IABP support, the pulse oximetric values of the Masimo Radical 7 are accurate in 1:2 and 1:3 support ratio compared with blood gas analysis. In these support ratios, the Masimo Radical 7 is superior to the Nellcor N-600. The Datex Ohmeda TruSat showed a significant difference between the measured pulse oximetric values and blood gas analysis in all support ratios.

Comparison of oscillometric blood pressure measurement by two clinical monitors: Datex Ohmeda GE S/5 and Criticare 8100E nGenuity

Comparison of oscillometric blood pressure measurement by two clinical monitors: Datex Ohmeda GE S/5 and Criticare 8100E nGenuity

End-tidal CO2 and invasive cardiac output measurements versus thoracic impedance measurements during mechanical CPR as an indicator of effective CPR in a porcine model of cardiac arrest

Purpose of the study: A number of physiological indicators were explored to determine if ICG amplitude could be used as a determinant of effective CPR to guide lay responders in administering optimized cardiac massage thereby improving survival rates from out of hospital cardiac arrest.Materials and methods: A total of seven porcine models around 52.8 ± 9 kg were used. End-tidal CO2 (ETCO2), Cardiac Output (CO), Carotid Flow and the Impedance Cardiogram (non-invasive measure of cardiac output) were utilized as a basis for detecting the presence of effective CPR. Ethical approval was granted by the Northern Ireland Home Office. Models were anaesthetised using Propofol and Isoflurane and connected to a Datex Ohmeda® monitor. Carotid flow and coronary perfusion pressure were measured via the carotid and thermodilution via the jugular. Recordings from each experiment were acquired using HEM® Notocord software for analysis.Results: ETCO2 levels averaged 23.3 mmHg during CPR compared to the models who did not receive CPR producing values close to of 3 ± 1 mmHg. Cardiac Output values of >22% of the normal CO were achieved which, reported as adequate for ROSC. Carotid Flow increased with depth of CPR. ICG amplitude increased with CO as did ETCO2. The results show that the physiological parameters used were good indicators of CPR efficacy.Conclusions: These findings are potentially significant in the field of resuscitation. An algorithm will incorporate the results from this study, providing feedback to the operator on the quality of CPR by measuring the ICG amplitude which can be correlated to the basic physiological parameters recorded during this study. Purpose of the study: A number of physiological indicators were explored to determine if ICG amplitude could be used as a determinant of effective CPR to guide lay responders in administering optimized cardiac massage thereby improving survival rates from out of hospital cardiac arrest. Materials and methods: A total of seven porcine models around 52.8 ± 9 kg were used. End-tidal CO2 (ETCO2), Cardiac Output (CO), Carotid Flow and the Impedance Cardiogram (non-invasive measure of cardiac output) were utilized as a basis for detecting the presence of effective CPR. Ethical approval was granted by the Northern Ireland Home Office. Models were anaesthetised using Propofol and Isoflurane and connected to a Datex Ohmeda® monitor. Carotid flow and coronary perfusion pressure were measured via the carotid and thermodilution via the jugular. Recordings from each experiment were acquired using HEM® Notocord software for analysis. Results: ETCO2 levels averaged 23.3 mmHg during CPR compared to the models who did not receive CPR producing values close to of 3 ± 1 mmHg. Cardiac Output values of >22% of the normal CO were achieved which, reported as adequate for ROSC. Carotid Flow increased with depth of CPR. ICG amplitude increased with CO as did ETCO2. The results show that the physiological parameters used were good indicators of CPR efficacy. Conclusions: These findings are potentially significant in the field of resuscitation. An algorithm will incorporate the results from this study, providing feedback to the operator on the quality of CPR by measuring the ICG amplitude which can be correlated to the basic physiological parameters recorded during this study.

Validity of Pulse Pressure and Systolic Blood Pressure Variation Data Obtained From a Datex Ohmeda S/5 Monitor for Predicting Fluid Responsiveness During Surgery

A simple, inexpensive method is needed for predicting fluid responsiveness in patients during surgery. A previously described method using the Datex Ohmeda S/5 monitor to record arterial and pulse pressure might be accurate enough to use for this purpose. In this study, 26 patients undergoing scheduled craniotomy surgery, we compared measurement of systolic pressure variation (SPV) (measured as both mm Hg and %) and pulse pressure variation (PPV%) using the Ohmeda monitor method to simultaneously measurement of a reference standard, stroke volume variation (SVV) determined with an Edwards FloTrac/Vigileo monitor, during volume loading. Variation in systolic pressure, pulse pressure, and stroke volume all decreased proportionally as fluid volume increased. The 3 test parameters, SPV (%), SPV (mm Hg), and PPV (%) were highly correlated to SVV, the reference standard. Bland-Altman plots comparing SPV (%) and PPV with SVV showed agreement with this standard. Receiver operating characteristic curves showed no significant difference between the 3 test parameters for predicting the vascular response to fluid infusion. There were no significant differences between SPV and PPV estimation using the Ohmeda monitor method and the reference SVV measurement for predicting vascular changes in response to fluid loading. The Ohmeda monitor method requires less sophisticated technology and is much less expensive than other methods.

A reply

Barema welcomes the opportunity to respond to this letter from Drs Campbell and Sellers on behalf of all suppliers of anaesthetic machines, and not just GE Healthcare (formally Datex–Ohmeda). Putting aside the question of checking equipment prior to the starting a case, this letter raises a number points, including the application of standards and regulations on: Hypoxic guards on the anaesthetic machines, Oxygen alarm level on the respiratory gas monitors, Manufacturer responsibility under the provisions of the European Union Medical Devices Directive (93/42/EEC, 2007/47 EEC). The latest revision of BS EN ISO 60601-2.13 states that ‘The anaesthetic gas delivery system shall be provided with a protection device to prevent the unintentional selection of a mixture of oxygen and other gases having an oxygen concentration below 19%.’ This hypoxic protection device is mandated as an integral part of the anaesthetic machine, and not just an alarm. The rationale is to further reduce the risk for accidental error, such as turning off the oxygen delivery valve instead of the nitrous oxide valve. The latest revision contained in EN ISO CD 80601-2.55 allows the user to set the oxygen level. The wording is ‘For each gas reading alarm condition with which the RGM is equipped, the alarm limit(s) shall be operator adjustable. The high gas level for inspired nitrous oxide shall be exempt from this requirement. Deliberate action shall be required on the part of the user to adjust the alarm limits. It shall not be possible to set the low alarm of the inspired oxygen gas reading below 18% without an additional deliberate action’. All medical device manufacturers must comply with the Essential Requirements of the European Union Medical Devices Directive in order to be able to affix the CE Mark to the device. A means of achieving this compliance is by the use of published standards, the standards listed above are two such examples. All suppliers of anaesthetic machines in United Kingdom meet these requirements, with the intention that users will give a safe anaesthetic to patients whatever the circumstances. At the same time, suppliers recognise it is essential to allow users to make adjustments to equipment to meet particular needs. If users believe the default settings on equipment should be revised, then Barema is of the opinion this should be raised with the Safety Committee of the Association of Anaesthetists of Great Britain and Ireland in the first instance.

Application of entropy of EEG in monitoring anesthetic depth

Entropy of EEG is the quantified parameter of irregularity or unpredictability of EEG.Entropy of EEG(ap-proximate entropy.Shannon entropy,spectral entropy)is a good measurement for anesthetic depth.The Datex Ohmeda En-tropyTM module is a commercial available device called-time requency balanced spectral entropy,including two entropy indica-tors:state entropy (SE) and response entropy (RE).State entropy is computed over the frequency range from 0.8 Hz to 32Hz.It includes the EEG.dominant part of the spectrum,and therefore primarily reflects the cortical state of the patient.Re-sponse entropy is computed over a frequency range from 0.8 Hz to 47 Hz.It includes both the EEG-dominant and EMG-dom-inant part of the spectrum.EntropyTM module has similar ability in hypnosis monitoring with BIS monitor.However,response entropy may be useful to identify inadequate anesthesia and patient arousal during painful stimuli.Entropy of EEG is derived from electroencephalogram like other qEEG.The differences are their own algorithms.Therefore,new predictors of anesthetic depth are called in clinical practice. Key words: Electroencephalogram; Entropy; Bispeetral index

Measurement of Systolic Pressure Variation During Graded Volume Loss Using Simple Tools on Datex Ohmeda S/5 Monitor

Direct invasive arterial monitoring is performed routinely for all major neurosurgical procedures. Systolic pressure variation (SPV) used, independently or in combination with central venous pressure (CVP) allows optimal fluid management in hypovolemia and hemorrhage. This study aims to quantify SPV during graded hypovolemia using the simple technique described by Gouvea and Gouvea using Datex Ohmeda S/5, and to compare its reliability relative to other hemodynamic indicators of hypovolemia. Twenty anesthetized neurosurgical patients of ASA grade I and II patients were administered furosemide 0.5 mg/kg intravenously to obtain graded volume loss in the form of urine output. Invasive arterial pressure from radial artery and CVP were monitored using Datex OhmedaS/5 (Finland). Invasive arterial pressure label was changed to pulmonary artery label with the scale appropriate for arterial pressure. The trace was frozen in the wedge mode to reduce the sweep speed and the cursor was used to measure SPV and pulse pressure variation (PPV). Heart rate, systolic blood pressure, diastolic blood pressure, CVP at zero end-expiratory pressure, SPV and PPV are measured at baseline, and after a urine output of 200 and 500 mL. There was a significant correlation between volume loss and CVP, SPV, and PPV. The area under the curve of receiver operating characteristic analysis was >0.75 for CVP, SPV, and PPV. SPV of 7.5 mm Hg and a change of SPV by 4.5 mm Hg, a PPV of 4.5 and change in PPV by 2.5 mm Hg were the best cut-off values that corresponded to a volume change of 500 mL. This simple method enabled calculation of SPV without the computerized modules, and detected volume loss comparable to CVP.