Usability testing of a prototype Phone Oximeter with healthcare providers in high- and low-medical resource environments.

To increase the use of pulse oximetry by capitalise on the wide availability of mobile phones, we have designed, developed and evaluated a prototype pulse oximeter interfaced to a mobile phone. Usability of this Phone Oximeter was tested as part of a rapid prototyping process. Phase 1 of the study (20 subjects) was performed in Canada. Users performed 23 tasks, while thinking aloud. Time for completion of tasks and analysis of user response to a mobile phone usability questionnaire were used to evaluate usability. Five interface improvements were made to the prototype before evaluation in Phase 2 (15 subjects) in Uganda. The lack of previous pulse oximetry experience and mobile phone use increased median (IQR [range]) time taken to perform tasks from 219 (160-247 [118-274]) s in Phase 1 to 228 (151-501 [111-2661]) s in Phase 2. User feedback was positive and overall usability high (Phase 1--82%, Phase 2--78%).

The GlideScope Video Laryngoscope: randomized clinical trial in 200 patients.

BACKGROUND: The GlideScope Video Laryngoscope is a new intubating device. It was designed to provide a view of the glottis without alignment of the oral, pharyngeal and tracheal axes. The aim of the study was to describe the use of the GlideScope in comparison with direct laryngoscopy for elective surgical patients requiring tracheal intubation. METHODS: Two hundred patients were randomly assigned to intubation by direct laryngoscopy using a Macintosh size 3 blade (DL, n=100) or intubation using the GlideScope (GS, n=100). Prior to intubation all patients were given a Cormack and Lehane (C&L) grade by a separate anaesthetist using a Macintosh size 3 blade. The patient was then intubated, using direct laryngoscopy or the GlideScope, by a different anaesthetist during which the larynx was inspected and given a laryngoscopy score. Time to intubate was measured. RESULTS: In the GS group, laryngoscopy grade was improved in the majority (28/41) of patients with C&L grade >1 and in all but one of patients who were grade 3 laryngoscopy (P<0.001). The overall mean time to intubate was 30 (95% CI 28-33) s in the DL group and 46 (95% CI 43-49) s in the GS group. The time to intubate for C&L grade 3 was similar in both groups, being 47 s for the DL group and 50 s for the GS group respectively. CONCLUSION: In most patients, the GlideScope provided a laryngoscopic view equal to or better than that of direct laryngoscopy, but it took an additional 16 s (average) for tracheal intubation. It has potential advantages over standard direct laryngoscopy for difficult intubations.

The effects of retroperitoneal carbon dioxide insufflation on hemodynamics and arterial carbon dioxide.

BACKGROUND: Laparoscopic techniques are being increasingly used for retroperitoneal surgery. However, hemodynamic and ventilatory efforts of retroperitoneal carbon dioxide (CO2) insufflation have not been studied. We hypothesized that differences in absorptive surface, anatomy, and compartment compliance could result in different hemodynamic and ventilatory effects between retroperitoneal and intraperitoneal insufflation. METHODS: Pigs (n = 7) were anesthetized and stabilized. The peritoneal cavity was incrementally insufflated with CO2 to a maximum pressure of 25 cm H2O and the gas released. Hemodynamics and arterial blood gas values were recorded initially, at each level of insufflation, and following the pneumoperitoneum release until baseline values were reached. This insufflation protocol was repeated in the retroperitoneum. RESULTS: Mean arterial pressure (111 mm Hg, 95% confidence interval 99 to 156) and cardiac output (3.7 L/min, 2.8 to 5.2) did not change with increasing insufflation pressure of either intraperitoneum or retroperitoneum. PaCO2 was directly related to insufflation pressure in both spaces, increasing from 41.2 mm Hg (37.3 to 43.4) at baseline to 57.7 mm Hg (47.6 to 82.1) at insufflation pressure of 25 cm H2O. After release of the insufflation gas, time to return to baseline PaCO2 was slightly less from the retroperitoneal space (73 minutes, 45 to 105) than the intraperitoneal (107 minutes, 35 to 175). CONCLUSIONS: The effects of CO2 insufflation on hemodynamics and PaCO2 are the same in the retroperitoneal and intraperitoneal spaces.

Oxygen uptake during peritoneal ventilation in a porcine model of hypoxemia.

OBJECTIVES: Peritoneal ventilation (PV) can greatly increase PaO2 in hypoxemic rabbits. We tested the hypothesis that the peritoneum can provide a gas exchange surface for oxygen uptake in larger animals that, like humans, have a smaller relative peritoneal surface area and corresponding blood flow. DESIGN: Prospective, randomized, controlled animal study. SETTING: University research laboratory. INTERVENTIONS: In six anesthetized pigs, a modified endotracheal tube (9.0-inner diameter) was inserted into the peritoneal cavity, and the peritoneal cavity was ventilated with oxygen in helium in gas phase. Measurements of peritoneal oxygen uptake and mixed venous oxygen saturation were made over 30 mins of: a) baseline FiO2 0.20, no PV; b) FiO2 0.20, PV; c) FiO2 0.20, PV, dopamine 5 microg/kg/min; d) baseline FiO2 0.15, no PV; e) FiO2 0.15, PV; and f) FiO2 0.15, PV, dopamine 5 microg/kg/min. MEASUREMENTS AND MAIN RESULTS: Mixed venous oxygen saturation was 61% at the baseline FiO2 of 0.20 and 33% at an FiO2 of 0.15 and did not increase significantly from baseline with PV or with dopamine at either FiO2. Peritoneal oxygen uptake, measured with a waterseal spirometer, was 9.1+/-3.1 (SD) and 11.9+/-3.0 mL/min when lung FiO2 was 0.20 and 0.15, respectively, and 9.7+/-2.8 and 12.2+/-2.7 mL/min when FiO2 was 0.20 and 0.15 and dopamine was infused, respectively. CONCLUSION: Peritoneal ventilation does not result in clinically significant oxygen uptake or alter mixed venous oxygen saturation in a porcine model of hypoxemia.

Prophylactic oral dolasetron mesylate reduces nausea and vomiting after abdominal hysterectomy. The Canadian Dolasetron Study Group.

PURPOSE: The incidence of postoperative nausea and vomiting (PONV) varies from 50% to 75% after gynaecological surgery under general anaesthesia. This study evaluates the dose-response relationships, safety, and efficacy of the new 5-HT3 antagonist, dolasetron mesylate, in the prevention of PONV in women undergoing total abdominal hysterectomy (TAH). METHODS: Three hundred and seventy four women scheduled for TAH under general anaesthesia were studied at 13 Canadian centres. Patients received in a randomized, double-blind manner 25, 50, 100, or 200 mg dolasetron or placebo po one to two hours before induction of anaesthesia. The anesthetic protocol was standardized. Efficacy was evaluated for 24 hr after surgery by comparing the number of emetic episodes, administration of rescue medication, severity of nausea, and patient satisfaction. RESULTS: Analysis of complete response (no emetic episodes and no rescue for 24 hr) revealed a linear dose-response relationship across dolasetron groups (P < 0.002). Dolasetron 100 mg (P < 0.003) and 200 mg (P < 0.01) were superior to placebo. The percentage of patients with no emetic episodes increased from 29.3% (placebo) to 54.1 % (100 mg). Subgroup analysis revealed ASA status (I > II), previous history of PONV, previous history of motion sickness, and total morphine dose (> 55 mg associated with less PONV than < 55 mg) influenced the incidence of emetic symptoms, but did not alter the results of the primary analysis. CONCLUSION: Prophylactic dolasetron (100 mg and 200 mg) reduces the incidence of PONV in patients having total abdominal hysterectomy.

A North American survey of intravenous regional anesthesia.

UNLABELLED: One thousand questionnaires concerning the techniques and complications of intravenous regional anesthesia (IVRA) were sent to 900 American and 100 Canadian anesthesiologists. Of the 321 respondents, 86% perform IVRA regularly. A wide variation in device-related and clinical aspects was found, ranging from acceptable to falling outside published guidelines. Anesthesiologists perform a median of four upper-limb IVR procedures per month, most often using 50 mL of lidocaine 0.5% at tourniquet pressures of 250 mm Hg or 100 mm Hg greater than the systolic blood pressure. Forearm, thigh, and calf IVRA are occasionally used. Complications, reported infrequently in the literature, were reported by respondents, including mistaken deflation of the cuff; dysphoria, dizziness, or facial tingling; seizures; cardiac arrests; and deaths. Although there was no correlation between complications and deviation from traditional practice, we recommend that IVRA be performed following recognized protocols by anesthesiologists who are familiar with the technique and trained to treat its potential complications. We recommend a protocol for IVRA. IMPLICATIONS: Intravenous regional anesthesia is a widely used anesthetic technique. A survey of 321 American and Canadian anesthesiologists indicates a wide variation in technique. Despite no correlation between complications and technique, the authors recommend that recognized protocols be used for this technique.

The addition of continuous intravenous infusion of ketorolac to a patient-controlled analgetic morphine regime reduced postoperative myocardial ischemia in patients undergoing elective total hip or knee arthroplasty.

This double-blind randomized trial assessed the effect of adding an intravenous continuous infusion of ketorolac to a patient-controlled analgesia (PCA) morphine regimen on analgesia, heart rate, arterial blood pressure, and postoperative myocardial ischemia. Patients having elective total hip or knee replacement were randomized to receive ketorolac 30 mg bolus, followed by an infusion of 5 mg/h for 24 h or placebo. All patients had access to PCA morphine (20 microg/kg bolus, with a lockout of 6 min). Patients were monitored for pain visual analog scale, blood pressure, heart rate, and ST segment depression via a continuous Holter monitor. ST depression of 1 mm 60 ms after the J point was considered significant if it lasted more than 1 min. There was no difference in demographics, risk factors, or cardiac medications between the groups. Ketorolac-treated patients had significantly better pain control at 2, 6, and 24 h. There was significant morphine sparing at all times after 3 h. There was no difference in the number of ischemic events between the groups. The ischemic episodes of the patients who received ketorolac occurred at slower heart rates (97 +/- 15 vs 114 +/- 16 bpm, P = 0.001) than those of patients in the placebo group. The duration of ST depression was shorter in ketorolac-treated patients (24 +/- 35 vs 76 +/- 95 min, P < 0.05). All ST depressions were clinically silent. Logistic regression of factors predicting ischemia included the use of calcium channel blockers and low pain score. These results suggest that analgesia with ketorolac reduces the duration of ischemic episodes in the first 24 h postoperatively.

Myocardial anaerobic metabolism occurs at a critical coronary venous PO2 in pigs.

We tested the hypothesis that the onset of myocardial anaerobic metabolism is fundamentally different from the whole body and other organs, where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio--not at a critical venous PO2. We measured oxygen saturation and PO2 of arterial and coronary venous blood at the onset of global myocardial anaerobic metabolism during progressive hypoxic hypoxia (n = 7) compared with carbon monoxide hypoxia (n = 7), which left-shifted the oxygen-hemoglobin dissociation curve. The onset of global myocardial anaerobic metabolism was defined by decreased myocardial lactate consumption and left ventricular contractility. Coronary venous PO2 was no different during hypoxic hypoxia and carbon monoxide hypoxia at equivalent arterial oxygen saturations, particularly at the onset of myocardial anaerobic metabolism (PO2 17.0 +/- 1.7 torr versus 15.9 +/- 2.2 torr, p = NS). However, the myocardial oxygen extraction ratio was significantly greater during hypoxic hypoxia than during carbon monoxide hypoxia at the onset of myocardial anaerobic metabolism (0.88 +/- 0.02 versus 0.65 +/- 0.04, p < 0.01). Thus, in contrast to the whole body where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio, the onset of myocardial anaerobic metabolism occurs at a critical coronary venous PO2.

Effect of subcutaneous carbon dioxide insufflation on arterial pCO2.

PURPOSE: Subcutaneous emphysema following laparoscopy could result in postoperative respiratory acidosis from prolonged CO2 absorption. We studied the magnitude and duration of alterations in PaCO2 coincident with direct CO2 insufflation into the subcutaneous fat of the anterior abdominal wall of 5 anesthetized juvenile pigs. METHODS: First, each pig was insufflated with 6 L of CO2 to produce moderate emphysema over the trunk. Following return to baseline PaCO2, each pig was re-insufflated with 12 L of CO2 to produce severe emphysema over lower limbs, neck, head, and trunk. Measurements of arterial blood gases were performed every 5 or 10 min. Minute ventilation was held constant to represent the worst case scenario. RESULTS: From baseline PaCO2 of 41.8 +/- 2.3 mm Hg, PaCO2 peaked at 68.3 +/- 8.6 (P < 0.02) and 92.9 +/- 10.7 (P < 0.01) mm Hg for the 6- and 12-L volumes, respectively, 20 to 25 minutes following insufflation. From baseline arterial pH of 7.40 +/- 0.02, respective nadirs of pH were 7.21 +/- 0.06 (P < 0.02) and 7.08 +/- 0.05 (P < 0.01). PaCO2 and arterial pH took approximately 100 minutes to return to baseline after insufflation with both 6 and 12 L volumes. CONCLUSIONS: When minute ventilation is fixed, subcutaneous CO2 insufflation causes increased PaCO2 and decreased pH that may persist for a prolonged period of time. Therefore, patients with subcutaneous emphysema after laparoscopy should be observed in postanesthetic recovery until PaCO2 and pH approach baseline.

Continuous intravenous administration of ketorolac reduces pain and morphine consumption after total hip or knee arthroplasty.

The purpose of this study was to determine the analgesic efficacy, opioid-sparing effect, and tolerability of ketorolac administered as an intravenous (i.v.) bolus followed by a continuous infusion after total hip or knee arthroplasty. After general anesthesia, patients received either placebo or ketorolac 30 mg i.v. as a bolus over 15-30 s followed by a continuous i.v. infusion of ketorolac 5 mg/h for 24 h. All patients received patient-controlled i.v. morphine with no background infusion. Patients were assessed at 2, 4, 6, and 24 postoperatively with respect to analgesia, morphine consumption, side effects, and blood loss. Patients receiving ketorolac reported were less sedated and required fewer antiemetics. There was no difference in blood loss. Patients receiving ketorolac reported better analgesia and used less morphine (35% for hips and 44% for knees) than those receiving placebo.

Effect of lung inflation and sternotomy direction on pleural space violation.

Patients often are disconnected temporarily from the ventilator before sternotomy to avoid entering the pleural space with the sternal saw. Although this practice is widespread, it is based on questionable physiologic principles. To evaluate the efficacy of this maneuver in reducing the incidence of pleural space violation with first-time sternotomy, 126 cardiac patients were randomized prospectively to either lungs inflated or deflated during sternotomy with the surgeon blinded to the particular assignment. The incidence of pleural space violation overall was 12%, occurring in 15% of patients with deflated lungs and in 9% of those with inflated lungs (p = 0.455 by chi 2 test). Examining the effect of the direction of sternotomy on pleural space entry revealed a 4% incidence with sternotomy starting at the xiphoid versus a 21% incidence with sternotomy starting at the sternal notch (p = 0.009 by chi 2 test). Preexisting hyperinflation of the lungs as evaluated by chest radiograms did not influence the incidence of pleural space violation. To reduce pleural space violation, sternotomy should be performed from the xiphoid to the sternal notch. More importantly, disconnecting the patient from the ventilator does not reduce pleural space violation with sternotomy and its further use is not indicated. These findings are discussed in the context of relevant heart-lung pathophysiology.

Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure in pigs.

BACKGROUND: Carbon dioxide absorption into the blood during laparoscopic surgery using intraperitoneal carbon dioxide insufflation may lead to respiratory acidosis, increased ventilation requirements, and possible serious cardiovascular compromise. The relationship between increased carbon dioxide excretion (VCO2) and intraperitoneal carbon dioxide insufflation pressure has not been well defined. METHODS: In 12 anesthesized pigs instrumented for laparoscopic surgery, intraperitoneal carbon dioxide (n = 6) or helium (n = 6) insufflation pressure was increased in steps, and VCO2 (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation. RESULTS: VCO2 increases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, VCO2 does not increase much further. PaCO2 increases continuously as intraperitoneal insufflation pressure increases from 0 to 25 mmHg. Hemodynamic parameters remained stable. CONCLUSIONS: By considering Fick's law of diffusion, the initial increase in VCO2 is likely accounted for by increasing peritoneal surface area exposed during insufflation. The continued increase in PaCO2 without a corresponding increase in VCO2 is accounted for by increasing respiratory dead space.

A comparison of regularly dosed oral morphine and on-demand intramuscular morphine in the treatment of postsurgical pain.

A randomized, placebo-controlled, double-blind clinical trial was conducted to compare the use of regularly dosed po morphine and on-demand in morphine in 47 patients undergoing total hip arthroplasty. Patients were randomized to receive either 20 mg (initial dose) of regularly dosed morphine (every four hours po) plus breakthrough pain medication on-demand consisting of both 10 mg morphine po and placebo im, or an equivalent regularly dosed oral placebo (every four hours) with breakthrough pain medication consisting of oral placebo and 5-10 mg morphine im. Subsequent to each request for breakthrough pain medication, the next regularly dosed oral solution was increased by 5 mg (or equivalent volume of placebo) to a maximum of 40 mg po Q4H. Time-averaged pain scores were lower on both postoperative day 1 and 2 in the group receiving regularly dosed morphine po (P < 0.05). Fewer patients requested breakthrough pain medication on both days in the oral morphine group. The incidence of nausea and vomiting, and of decreased respiratory rates were similar in both groups. Regularly dosed oral morphine is inexpensive and should be compared to other methods of opioid delivery.

Reconstituted thiopentone retains its alkalinity without bacterial contamination for up to four weeks.

The manufacturers of thiopentone recommend that after reconstitution, it should be kept only for 24 hr to reduce the risk of contamination. However, there are no studies to support this practice and compliance with this recommendation has economic implications. The reasons for discarding a reconstituted bottle of thiopentone are related to concerns about chemical and physical (pH) stability, contamination with infectious agents, and contamination with cellular material. We studied the incidence of bacterial contamination and pH stability of thiopentone in clinical use, as well as the pH stability of thiopentone not in clinical use, and surveyed the eight hospitals affiliated with the University of British Columbia to determine their protocols for thiopental preparation and storage. Cost comparisons were made between our current practice of discarding thiopentone when depleted and the practice of routinely discarding it 24 hr after reconstitution. Samples of thiopentone in clinical use were cultured daily and the pH was measured. The bottles had been in clinical use from 1 to 25 days (mean 4.23 +/- 4.32 SD). Of 106 samples there were no positive bacteriological cultures and there were only minor changes in pH. The telephone survey of the eight hospitals revealed that only one had a policy to discard thiopentone after 24 hr. Cost comparisons indicate that discarding thiopentone 24 hr after reconstitution would result in increased cost. In conclusion, reconstituted thiopentone retains its alkalinity for up to four weeks, and has an acceptably low risk of bacterial contamination for periods beyond 24 hr, therefore thiopentone need not be discarded after 24 hr.

The effect of inhalation of nebulized steroid on the acid aspiration syndrome.

The effects of acid aspiration on lung mechanics, gas exchange, haemodynamics and lung water, and their modification by nebulized dexamethasone were studied in 10 dogs. Each dog received 0.1 N HCl pH of 1.0 (15 ml/l vital capacity), instilled down the tracheal tube. PEEP 0.98 kPa (10 cm H2O) was introduced 20 minutes after aspiration and was continued until the completion of experiment. Treated animals (N = 5) received dexamethasone 5 mg . kg-1 by continuous nebulization over a two hour period starting 20 minutes after aspiration. Untreated (N = 5) animals received nebulized saline. Measurements were taken before aspiration and at 20 minutes 2.5 and 5.0 hours after aspiration. Red blood cells labelled with 51Cr were injected before sacrifice. After sacrifice multiple lung samples were taken for measurement of pulmonary extravascular water (PEW) by the gravimetric technique. Acid aspiration caused significant changes in lung volumes, PaO2, and intrapulmonary shunt. Pulmonary extravascular water was 6.16 +/- 0.93 ml/g dry tissue in treated and 6.47 +/- 0.60 ml/g dry tissue in untreated animals. These results indicate the presence of severe pulmonary oedema. There were no significant differences in any measured parameter between treated and untreated animals. We conclude that nebulized dexamethasone is of no value in treatment of the acute changes induced by acid aspiration.