An improved bioacoustic method for monitoring of respiration.

Reliable monitoring of respiration plays an important role in a broad spectrum of applications. Today, there are several methods for monitoring respiration, but none of them has proved to be satisfactory in all respects. We have recently developed a bioacoustic method that can accurately time respiration from tracheal sounds. The aim of this study is to tailor this bioacoustic method for monitoring purposes by introducing dedicated signal processing. The method was developed on a material of ten patients and then tested in another ten patients treated in an intensive care unit. By studying the differences in the variation of the spectral content between the different phases of respiration, the described method can distinguish between inspiration and expiration and can extract respiration frequency, and respiration pause periods. The system detected 98% of the inspirations and 99% of the expirations. This method for respiration monitoring has the advantage of being simple, robust and the sensor does not need to be placed closed to the face. A commercial heart microphone was used and we anticipate that further improvement in performance can be achieved trough optimization of sensor design.

Troponin T-values provide long-term prognosis in elderly patients undergoing non-cardiac surgery.

BACKGROUND: The aim of this study was to evaluate the significance of elevated postoperative Troponin T (TnT) levels in an elderly population undergoing non-cardiac surgery. METHODS: Five hundred and forty-six consecutive patients aged 70 years or older undergoing non-cardiac surgery of >30-min duration were enrolled in this prospective, observational study. A postoperative TnT measurement was obtained on the 5th to 7th postoperative day. Troponin T values greater than 0.02 ng ml(-1) were considered positive. Patients were followed over a 1-year period, and mortality and non-fatal cardiac events (acute myocardial infarction and coronary interventions) were recorded. RESULTS: Troponin T concentrations greater than 0.02 ng ml(-1) were detected in 53 of the study subjects (9.7%). Eleven per cent of the patients with elevated TnT had electrocardiographic or clinical signs of myocardial ischemia. One year after surgery, 17 (32%) of the patients with abnormal TnT concentrations had died. In a multivariate Cox regression analysis adjusting for baseline and perioperative data, a TnT value >0.02 ng ml(-1) was an independent correlate of the mortality adjusted hazard ratio (HR): 14.9 (95% CI 3.7-60.3). Other independent predictors of death were tachycardia (HR, 14.9 95% CI 3.45-64.8), ASA 4 (HR, 8.1 95% CI 1.3-50.0), reoperation (HR, 6.4 95% CI 1.1-36.9), and use of diuretics (HR, 4.2 95% CI 1.3-13.8). CONCLUSION: We conclude that elevated TnT levels in the postoperative period confer a 15-fold increase in mortality during the first year after surgery. Our findings also provide evidence that silent myocardial ischemia is common in an elderly population. Routine perioperative surveillance for TnT might therefore be of use in detecting patients at an increased risk of mortality during the first postoperative year.

Moderate hypothermia for 359 operations to clip cerebral aneurysms.

BACKGROUND: Experimental data have suggested that hypothermia (32-34 degrees C) may improve outcome after cerebral ischaemia, but its efficacy has not yet been established conclusively in humans. In this study we examined the feasibility and safety of deliberate moderate perioperative hypothermia during operations for subarachnoid aneurysms. METHODS: A total of 359 operations for intracranial cerebral aneurysms were included in this prospective study. By using cold intravenous infusions (4 degrees C) and convective cooling our aim was to reduce the patient's core temperature to more than 34 degrees C within 1 h before operation. The protocol assessed postoperative complications such as infections, prolonged mechanical ventilation, pulmonary complications and coagulopathies. RESULTS: During surgery, the body temperature was reduced to a mean of 32.5 (SD 0.4) degrees C. Cooling was accomplished at a rate of 4.0 (SD 0.4) degrees C h(-1). All patients were normothermic at 5 (sd 2) h postoperatively. Peri/postoperative complications included circulatory instability (n=36, 10%), arrhythmias (n=17, 5%) coagulation abnormalities and blood transfusion (n=169, 47%), infections (n=29, 8%) and pulmonary complications (infiltrate or oedema while on ventilatory support) (n=97, 27%). Eighteen patients died within 30 days (5%). There was no significant correlation between the extent of hypothermia and any of the complications. However, there was a strong correlation between the occurrence of complications and the severity of the underlying neurological disease as assessed by the Hunt and Hess score. CONCLUSION: Moderate hypothermia accomplished within 1 h of induction of anaesthesia and maintained during surgery for subarachnoid aneurysms appears to be a safe method as far as the risks of peri/postoperative complications such as circulatory instability, coagulation abnormalities and infections are concerned.

The in vitro effects of crystalloids and colloids on coagulation.

Classically haemodilution is regarded as causing coagulopathy. However, haemodilution with saline seems to cause a hypercoagulable state both in vivo and in vitro. The aim of the present study was to measure the effect of mild to severe haemodilution using thrombelastography. Blood samples were taken in 12 healthy volunteers and divided into seven aliquots. One aliquot was undiluted and acted as control. The other six were diluted with normal saline, Ringer Acetate, 4% albumin, Dextran 70, 6% and 10% hydroxyethylstarch to 10%, 20%, 40%, 50% and 60% dilution. The dilution was checked by measuring the haemoglobin concentration. Each aliquot was placed in a temperature-controlled thrombelastography channel. Increased coagulation activity, as measured by thrombelastography changes, was detected at low and medium levels of dilution with all the tested solutions. At more than 40% dilution, coagulation returned to normal while in the case of dextran and hydroxyethylstarch coagulopathy developed. For crystalloids and albumin,dilution had to exceed 50% before coagulation was impaired. If these findings can be reproduced in vivo, they may have implications for transfusion practice and prophylaxis against thrombosis.

Cerebrospinal fluid concentrations of propofol during anaesthesia in humans.

The concentration of propofol in and surrounding the human brain during propofol anaesthesia is unknown. We measured simultaneously the concentration of propofol in cerebrospinal fluid (CSF) from an indwelling intraventricular catheter and the concentration in arterial blood in five neurosurgical patients before, during induction (at 2.5 and 5 min) and during a maintenance propofol infusion (at 15 and 30 min). After induction of anaesthesia with propofol 2 mg kg-1, anaesthesia was maintained with an infusion of 8 mg kg-1 h-1 for 15 min and then reduced to 6 mg kg-1 h-1. The plasma concentration of propofol increased rapidly during induction and reached a plateau concentration of mean 2.24 (SD 0.66) micrograms ml-1 after 5 min. The concentration of propofol in CSF showed a slower increase during induction and remained almost constant at 35.5 (19.6) ng ml-1 at 15-30 min after induction. The CSF concentration of propofol that we measured was 1.6% of the plasma concentration and consistent with the high protein binding of the drug in plasma.

Giving both enoxaparin and dextran increases the need for transfusion in revision hip arthroplasty.

OBJECTIVE: To find out if the need for transfusion was increased by volume substitution with dextran 70 in patients receiving prophylaxis against thrombosis with low molecular weight heparin. DESIGN: Open randomised controlled trial. SETTING: University hospital, Sweden. SUBJECTS: 40 patients undergoing revision hip arthroplasty. INTERVENTIONS: Enoxaparin 40 mg was given daily. Intraoperative normovolaemia was maintained with albumin (n = 20) or dextran 70 (n = 20). Intraoperative autotransfusion was used. Packed cell volume was kept above 0.29, if necessary with homologous blood. MAIN OUTCOME MEASURES: External blood loss, red cell balance. RESULTS: Dextran patients received 0.64 (0.2) g/kg of dextran (mean (SD)) and required more (p < 0.05) homologous blood (3.8 (2.4) units) than those receiving albumin (2.3 (1.6) units). The initial and final packed cell volumes were similar (0.40 and 0.32 compared with 0.41 and 0.32, respectively). The calculated loss of red cells was larger in the dextran group (1401 (511) compared with 1077 (374); p < 0.05). CONCLUSION: The combination of enoxaparin and dextran appreciably increased the need for transfusion compared with enoxaparin alone.

Plasma concentrations and hemodynamic changes after repeated interpleural injections of bupivacaine-epinephrine.

BACKGROUND AND OBJECTIVES: The purpose of this investigation was to study the arterial plasma concentrations of bupivacaine and the hemodynamic changes after interpleural injection of 20 ml 0.5% bupivacaine with epinephrine in patients treated by chest drainage for spontaneous pneumothorax. METHODS: Twenty-two patients with spontaneous pneumothorax planned to be treated by chest drainage were randomly allocated to a bupivacaine group and a control group receiving saline. After introduction of the chest drain and evacuation of the pneumothorax, 10 injections through an interpleural catheter were given at 8-hour intervals in a double-blind fashion. Plasma concentrations were determined at 5, 10, 20, 30, 240, and 480 minutes after the first injection and before and at 15 and 30 minutes after the 4th, 7th, and 10th injections. Heart rate and mean arterial pressure was registered before and at 15 and 30 minutes after each injection. RESULTS: Mean Cmax after the first injection was 1.02 +/- 0.24 microgram/ml at 15 minutes, the highest individual Cmax after 20 minutes being 1.56 micrograms/ml. Mean plasma concentrations increased up to and after the 4th injection but did not rise further after the 7th and 10th injections. The highest individual Cmax was 1.92 micrograms/ml at 15 minutes after the 10th injection. The injections were accompanied by a small but statistically significant reduction in mean arterial blood pressure and a rise in heart rate 15 minutes after injection in the bupivacaine group compared with the control group. CONCLUSIONS: Repeated interpleural bolus injections of 20 ml 0.5% bupivacaine-epinephrine at 8-hour intervals are safe regarding plasma concentrations of bupivacaine. Small but statistically significant hemodynamic changes can be noticed, probably the result of beta- adrenergic stimulation by epinephrine.

Interpleural bupivacaine for analgesia during chest drainage treatment for pneumothorax. A randomized double-blind study.

The ability of interpleural analgesia to reduce the pain caused by an indwelling chest drain was evaluated in 22 patients treated for spontaneous pneumothorax. Intermittent 8-hourly bolus injections of 20 ml bupivacaine 0.5% with epinephrine were compared with placebo in a randomized double-blind fashion. Visual analogue pain scale (VAS) scores were registered after the 1st, 2nd, 4th, 7th and 10th injections. The scores were significantly lower in the bupivacaine group at 5, 15, 30 and 60 min after the first injection. No significant differences in pain scores were found after 4 or 8 h. Pain scores in the bupivacaine group were also reduced after the 2nd, 4th, 7th and 10th injections, but compared with placebo the differences were significant only after the 2nd and 7th injections. Parenteral morphine consumption was not significantly lower in the bupivacaine group. Arterial blood gases were unaffected by the treatment in both groups. It is concluded that interpleural analgesia using bupivacaine given as bolus injections at 8-h intervals significantly reduces the pain caused by a chest drain within 5 min of injection, but the duration of pain relief is less than 4 h.

Chest radiograph--a poor method for determining the size of a pneumothorax.

The ability of chest radiographs to determine the size of a pneumothorax was tested in 16 patients using computed tomographic (CT) scan as a reference method. To determine if CT with a slice thickness of 12 mm could be used, its accuracy was assessed in a lung model experiment. The lung model consisted of a water-filled plastic bag (lung) fitted into a plastic chamber (hemithorax), both of approximately the same size and shape as in man. Water was drawn off in incremental steps and a CT was done after each step. The area of the pneumothorax was calculated by computer and when multiplied by slice thickness and number of slices, the total volume of the pneumothorax could be compared with the extracted amount of water. A good correlation (r = 0.99), with the line of regression close to the line of identity, was found between the CT investigation and the artificial pneumothorax. In the patients, the size of the pneumothorax, judged by radiograph using two different methods of calculation, was correlated to the size obtained by CT. The correlation was poor (r = 0.71) irrespective of method of calculation. The size of the pneumothorax estimated by CT showed a good correlation (r = 0.99) to the initial aspirated air volumes in 12 of the 16 patients treated with drainage. A cautious attitude toward the use of chest radiographs for calculations of the degree of lung collapse in patients with pneumothorax is recommended.

Quantification of aspirated air volume reduces treatment time in pneumothorax.

In 62 consecutive cases of pneumothorax, suction treatment was applied by a new method using a recently-developed vacuum pump (Pleupump) allowing the quantification of the volume of air through the chest drain. The previous 62 cases of pneumothorax treated with standard suction equipment were used as a control group. The new technique resulted in a statistically significant reduction in the mean suction treatment time from 8.1 to 4.8 days in patients with spontaneous pneumothorax. The mean total number of days in hospital was reduced from 10.0 to 6.5. This was accomplished without an increase in the number of complications or recurrences of the pneumothorax.

Portable emergency ventilators. Sensitivity to environment.

The function in various types of climate of three ventilators which are commercially available in Sweden: Motivus, Pneupac 2 and Logic 07, was tested as well as their sensitivity to vibration. The ventilators functioned in subzero temperatures only if the driving gas had a low humidity content. They also required an increased driving gas pressure. Only Logic 07 would function below -20 degrees C. In a hot climate there were no functional disturbances. Motivus and Pneupac 2 had few resonance frequencies during the vibration tests. Logic 07 had a very marked resonance frequency at 60 Hz, as well as in other ranges, which disturbed the ventilatory function since the vibration affected the ventilatory frequency regulator. All three ventilators functioned without any complaints after being subjected to vibration tests for at least 15 min at the observed resonance frequencies, or to shock tests. The results suggest that a through scrutiny should be carried out of the function of compact ventilators in various environments.