A population-based study on epidemiology of intensive care unit treated traumatic brain injury in Iceland.

BACKGROUND: Traumatic brain injury is a worldwide health issue and a significant cause of preventable deaths and disabilities. We aimed to describe population-based data on intensive care treated traumatic brain injury in Iceland over 15 years period. METHODS: Retrospective review of all intensive care unit admissions due to traumatic brain injury at The National University Hospital of Iceland 1999-2013. Data were collected on demographics, mechanism of injury, alcohol consumption, glasgow come scale upon admission, Injury Severity Scoring, acute physiology and chronic health evaluation II score, length of stay, interventions and mortality (defined as glasgow outcome score one). All computerized tomography scans were reviewed for Marshall score classification. RESULTS: Intensive care unit admissions due to traumatic brain injury were 583. The incidence decreased significantly from 14/100.000/year to 12/100.000/year. Males were 72% and the mean age was 41 year. Majority of patients (42%) had severe traumatic brain injury. The most common mechanism of injury was a fall from low heights (36.3%). The mortality was 18.2%. Increasing age, injury severity score, Marshall score and acute physiology and chronic health evaluation II score are all independent risk factors for death. Glasgow coma scale was not an independent prognostic factor for outcome. CONCLUSIONS: Incidence decreased with a shift in injury mechanism from road traffic accidents to falls and an increased rate of traumatic brain injury in older patients following a fall from standing or low heights. Mortality was higher in older patients falling from low heights than in younger patients suffering multiple injuries in road traffic accidents. Age, injury severity score, acute physiology and chronic health evaluation II score and Marshall score are good prognostic factors for outcome. Traumatic brain injury continues to be a considerable problem and the increase in severe traumatic brain injury in the middle age and older age groups after a seemingly innocent accident needs a special attention.

Avoiding bladder catheterisation in total knee arthroplasty: patient selection criteria and low-dose spinal anaesthesia.

BACKGROUND: Bladder catheterisation may be inconvenient for patients, delay mobilisation and risk complications. We hypothesised that by excluding pre-operatively patients at high risk of post-operative urinary retention, the majority of patients could avoid perioperative catheterisation during low-dose spinal anaesthesia. METHODS: Patients undergoing total knee arthroplasty were assigned if fit for spinal anaesthesia and without severe symptoms of lower urinary tract obstruction, gross incontinence, mobilisation difficulties hindering micturition and > 200 ml residual urine volume. Bladder volume was monitored by ultrasound and temporary catheterisation advised if > 400 ml. RESULTS: Fifty-two patients (men 54%, age 65 ± 9 years, body mass index 31 ± 5, 30% with history of urinary tract problems) were included. Intrathecal hyperbaric bupivacaine given was 7.8 ± 1.08 mg and always 7.5 µg sufentanil providing sufficient anaesthesia in all cases. Crystalloid given during surgery was 8.5 ± 4.0 ml/kg. Voluntary micturition was reached by 46 patients (88%, confidence interval (CI) 79-97%), but six (12%, CI 3-21%) needed temporary catheterisation once (four men/two women). Larger bladder volumes were found in those catheterised than those with voluntary micturition on the pre-operative (131 ± 76 ml vs. 68 ± 57 ml, P = 0.03) and first post-operative bladder scan (445 ± 169 ml vs. 271 ± 129 ml, P = 0.004). All but two patients (96%) could be mobilised the same day. No patient suffered bladder dysfunction. CONCLUSION: Low-dose spinal anaesthesia combined with simple selection criteria allowed for early mobilisation (96%) and avoidance of bladder catheterisation in the vast majority (88%) of patients undergoing total knee arthroplasty, and the rest (12%) only needed a single temporary catheterisation.

Severe sepsis and septic shock: a prospective population-based study in Icelandic intensive care units.

BACKGROUND: The aims of our study were to describe the nationwide epidemiology of sepsis requiring intensive care during an entire year and to evaluate compliance with treatment guidelines. METHODS: This was a prospective, observational study of all adult patients admitted to Icelandic intensive care units (ICUs), who were screened for the ACCP/SCCM criteria for severe sepsis or septic shock on admission. Data were collected from 1 April 2008 to 31 March 2009. RESULTS: One thousand five hundred and twenty-four patients were admitted to the ICUs during the study year, 115 of them because of severe sepsis or septic shock. The incidence in Iceland was 0.48/1000 inhabitants ≥18 years per year [95% confidence intervals (CI) 0.42-0.55]. The mean APACHE II score was 20.7. Mortality was 24.6% (95% CI 17.5-33.3) at 28 days and 40.4% (95% CI 31.8-49.5) at 1 year. The main sources of infections were pulmonary (37%), abdominal (28%) and urinary tract (8%). Pathogens were gram-positive (39%), gram-negative (30%) and mixed (28%). No patient had sepsis caused by methicillin-resistant Staphylococcus aureus or a monomicrobial fungal infection. Pulmonary infections were an independent predictor of death. Compliance to the resuscitation goals of the Surviving Sepsis Campaign ranged from 60% to 72% and the 6-hour Sepsis Bundle was completed in 35% of patients. CONCLUSIONS: This nationwide study showed an incidence of 0.48/1000 inhabitants for severe sepsis and septic shock requiring intensive care therapy. The 28-day mortality rate of 25 % was in the lower range of previous reports but the compliance to resuscitation goals and sepsis bundles was similar.

Induced hypothermia in comatose survivors of asphyxia: a case series of 14 consecutive cases.

BACKGROUND: Induced hypothermia is widely used for comatose survivors of cardiac arrest. Other causes of hypoxic brain injury carry a poor prognosis when treated using traditional methods. At our hospital, hypothermia has also been used for the management of all comatose survivors of asphyxiation. The aim of the present study was to report the results of the management of these patients. METHODS: Hospital charts of all patients admitted unconscious after asphyxiation during a 7-year period were reviewed. This included patients after hanging, drowning, carbon monoxide intoxication and other gas intoxications. In all patients, hypothermia with a target temperature of 32-34 degrees C was induced with external or intravascular cooling for 24 h. The primary outcome was neurologic function at discharge. RESULTS: Fourteen male patients were treated with hypothermia, eight after hanging, three after drowning, two after carbon monoxide intoxication and one after methane intoxication. All were deeply comatose (Glasgow Coma Score 3-5) on arrival to hospital. Nine had been resuscitated from cardiac arrest. There were nine survivors (65%), all with good neurological recovery (Cerebral Performance Category 1-2). Four out of five non-survivors showed cerebral edema already on arrival computed tomographic (CT) scan while none of the nine survivors did. CONCLUSIONS: The results of this study suggest that an early abnormal CT scan of the brain in patients resuscitated after asphyxiation carries an adverse prognosis. The favorable outcome of the patients in the present study suggests that a randomized clinical trial on the use of induced hypothermia in patients exposed to severe asphyxia might be warranted.

Electrical impedance tomography and heterogeneity of pulmonary perfusion and ventilation in porcine acute lung injury.

BACKGROUND: The heterogeneity of pulmonary ventilation (V), perfusion (Q) and V/Q matching impairs gas exchange in an acute lung injury (ALI). This study investigated the feasibility of electrical impedance tomography (EIT) to assess the V/Q distribution and matching during an endotoxinaemic ALI in pigs. METHODS: Mechanically ventilated, anaesthetised pigs (n=11, weight 30-36 kg) were studied during an infusion of endotoxin for 150 min. Impedance changes related to ventilation (Z(V)) and perfusion (Z(Q)) were monitored globally and bilaterally in four regions of interest (ROIs) of the EIT image. The distribution and ratio of Z(V) and Z(Q) were assessed. The alveolar-arterial oxygen difference, venous admixture, fractional alveolar dead space and functional residual capacity (FRC) were recorded, together with global and regional lung compliances and haemodynamic parameters. Values are mean+/-standard deviation (SD) and regression coefficients. RESULTS: Endotoxinaemia increased the heterogeneity of Z(Q) but not Z(V). Lung compliance progressively decreased with a ventral redistribution of Z(V). A concomitant dorsal redistribution of Z(Q) resulted in mismatch of global (from Z(V)/Z(Q) 1.1+/-0.1 to 0.83+/-0.3) and notably dorsal (from Z(V)/Z(Q) 0.86+/-0.4 to 0.51+/-0.3) V and Q. Changes in global Z(V)/Z(Q) correlated with changes in the alveolar-arterial oxygen difference (r(2)=0.65, P<0.05), venous admixture (r(2)=0.66, P<0.05) and fractional alveolar dead space (r(2)=0.61, P<0.05). Decreased end-expiratory Z(V) correlated with decreased FRC (r(2)=0.74, P<0.05). CONCLUSIONS: EIT can be used to assess the heterogeneity of regional pulmonary ventilation and perfusion and V/Q matching during endotoxinaemic ALI, identifying pivotal pathophysiological changes.

A practice survey on vasopressor and inotropic drug therapy in Scandinavian intensive care units.

BACKGROUND: This practice survey was performed to analyse the indications for use of vasopressor/inotropic drugs, preferred drugs and doses as well as concomitant monitoring and desired haemodynamic target values in Scandinavian ICUs. An internet-based reporting system was implemented. METHODS: A total of 223 ICUs were identified in the Scandinavian countries and invited to participate in a one-day point-prevalence study. An internet-based database was constructed and a practice survey protocol designed to identify haemodynamic monitoring, indications for vasopressor/inotropic drug-therapy, fluids used for volume loading, pretreatment circulatory state, actual and targeted haemodynamic variables. Patients were eligible for the study if on vasopressor/inotropic drug-therapy for more than 4 h. RESULTS: A total of 114 ICUs participated. A total of 114 adult patients matched the inclusion criteria. Sixty-seven per cent of the patients had received vasopressor/inotropic drug-treatment for >24 h and 32% received more than one drug. Arterial hypotension (92%) and oliguria (50%) were most common indications. Fluid loading prior to therapy was reported in 87% of patients. Dopamine (47%) and noradrenaline (44%) were the most commonly used drugs followed by dobutamine (24%). No other drug exceeded 6%. Non-catecholamine drugs were rarely used even in cardiac failure patients. Invasive arterial pressure was monitored in 95% of patients, pulmonary artery catheters were used in 19%. Other cardiac output monitoring techniques were used in 8.5% of the patients. CONCLUSION: Dopamine and noradrenaline seem to be the most commonly used inotropic/vasopressor drugs in Scandinavia. Traditional indications for inotropic/vasopressor support as hypotension and oliguria seem to be most common. Invasive monitoring was used in almost all patients, whereas a limited use of pulmonary artery catheters was noted. The internet-based reporting system proved to be an efficient tool for data collection.

Alveolar pressure monitoring: an evaluation in a lung model and in patients with acute lung injury.

OBJECTIVES: We evaluated an algorithm for continuous on-line monitoring of alveolar pressure over time in a lung model with lower and upper inflection points and variable resistance ratios and in patients with acute lung injury. The algorithm is based on "static" pressure/volume curves obtained from tracheal pressure measurements under dynamic conditions. DESIGN AND SETTING: Experimental and clinical evaluation of algorithm in a university hospital laboratory and intensive care unit. PATIENTS: Ten patients undergoing postoperative respiratory therapy (feasibility of tracheal measurement) and ten patients with acute lung injury undergoing ventilator treatment (evaluation of algorithm). MEASUREMENTS AND RESULTS: Direct tracheal pressure measurements with a catheter inserted through the endotracheal tube. Comparison of measured alveolar and the dynostatic alveolar pressure vs. time in a lung model with changes in five ventilatory parameters. Examples of clinical monitoring are reported. In the model there was excellent agreement between alveolar pressures obtained by the algorithm, the dynostatic alveolar pressure, and measured alveolar pressure at all ventilator settings. For inspiratory/expiratory resistance ratios between 1:2.1-2.1:1, the dynostatic alveolar pressure was within +/-1.5 cm H(2)O of measured alveolar pressure. In patients the technique for direct tracheal pressure measurement using a catheter inserted through the endotracheal tube functioned satisfactorily with intermittent air flushes for cleansing. CONCLUSIONS: Using a thin tracheal pressure catheter inserted through the endotracheal tube alveolar pressure allows continuous bedside monitoring with ease and precision using the dynostatic algorithm. The method is unaffected by tube and connector geometry or by secretions.

Ventilator treatment in the Nordic countries. A multicenter survey.

BACKGROUND: A 1-day point prevalence study was performed in the Nordic countries to identify ventilator-treatment strategies in the region. MATERIAL AND METHODS: On 30 May 30 2001 all mechanically ventilated patients in 27 intensive care units (ICUs) were registered via the internet. The results are shown as medians (25th, 75th percentile). RESULTS: One hundred and eight patients were included (69% male) with new simplified acute physiology score (SAPS) 48 (37,57) and 4.5 d (2,11) of ventilator treatment. The most frequent indication for ventilator treatment was acute respiratory failure (73%). Airway management was by endotracheal tube (64%), tracheostomy (32%) and facial mask (4%). Pressure regulated ventilator modes were used in 86% of the patients and spontaneous triggering was allowed in 75%. The tidal volume was 7 ml/kg (6,9), peak inspiratory pressure 22 cmH2O (18,26) and positive end-expiratory pressure (PEEP) 6 cmH2O (6,9). FiO2 was 40% (35,50), SaO2 97% (95-98), PaO2 11 kPa (10,13), PaCO2 5.4 kPa (4.7,6.3), pH 7.43 (7.38,7.47) and BE 2.0 mmol/l (- 0.5,5). The PaO2/FiO2 ratio was 220 mmHg (166,283). The peak inspiratory pressure (r=0.37), mean airway pressure (r=0.36), PEEP (r=0.33), tidal volume (r=0.22) and SAPS score (r=0.19) were identified as independent variables in relation to the PaO2/FiO2 ratio. CONCLUSION: The vast majority of patients were ventilated with pressure-regulated modes. Tidal volume was well below what has been considered conventional in recent large trials. Correlations between the parameters of gas exchange, respiratory mechanics, ventilator settings and physiological status of the patients was poor. It appears that blood gas values are the main tool used to steer ventilator treatment. These results may help to design future interventional studies of ventilator treatment.

Dead-space reduction and tracheal pressure measurements using a coaxial inner tube in an endotracheal tube.

OBJECTIVE: To evaluate the effects on CO(2) washout of the coaxial double lumen tube (DLT) as compared to a standard endotracheal tube (ETT) and tracheal gas insufflation (TGI). Precision of tracheal pressure monitoring through the DLT and safety issues, including intrinsic PEEP (PEEPi) formation during DLT ventilation, were also evaluated. DESIGN: Lung model study. SETTING: University research laboratory. MEASUREMENTS AND RESULTS: CO(2) washout was analysed in a lung model by measuring single alveolar CO(2) concentration during DLT ventilation as compared to standard ETT ventilation, at different minute ventilation (6-14 l/min) and different CO(2)-output levels (180 ml/min, 240 ml/min, and 300 ml/min). At a CO(2) output level of 240 ml/min the CO(2) washout was also compared to tidal volume-adjusted continuous TGI and expiratory synchronised TGI. Precision of tracheal pressure monitoring and PEEPi formation during DLT ventilation was evaluated by comparing pressure in each limb above the tube to reference tracheal pressure, varying I:E ratios (1:2, 1:1, and 2:1), tidal volumes (300-700 ml), breathing frequencies (15-25), and compliance (20-50 ml/cmH(2)O). DLT ventilation had the same efficacy in removing CO(2) as continuous and expiratory synchronised TGI, reducing single alveolar CO(2) concentration by 9-21% compared to normal ventilation. Tracheal pressure could be measured through the DLT with high precision. There was only marginal formation of PEEPi at tidal volumes

Monitoring functional residual capacity (FRC) by quantifying oxygen/carbon dioxide fluxes during a short apnea.

BACKGROUND: Clinically applicable methods for measuring FRC are currently lacking. This study presents a new method for FRC monitoring based on quantification of metabolic gas fluxes of O2 and CO2 during a short apnea. METHODS: Base line exchange of oxygen and carbon dioxide was measured with indirect calorimetry. End-tidal ( approximately alveolar) O2 and CO2 concentrations were measured before and after a short apnea, 8-12 s, and FRC was calculated according to standard washin/washout formulas taking into account the increased solubility of CO2 in blood when the tension is increased during the apnea. The method was tested in a lung model with CO2 excretion and O2 consumption achieved by combustion of hydrogen and implemented in six ventilator-treated patients with acute respiratory failure (ARF). RESULTS: In the lung model the method showed excellent correlation (r = 0.98) with minimal bias (34 ml) and a good precision, limits of agreement being 160 and -230 ml, respectively, compared to the reference method. In six ARF patients changes in FRC induced by increase or decrease in PEEP and measured with the O2/CO2 flux FRC method corresponded well with changes in reference values of FRC (r = 0.76-0.94). CONCLUSIONS: A new method has been proposed in which FRC could be monitored from measurements of physiological fluxes of gases during a short apnea with the use of standard ICU equipment and some calculations. We anticipate that with further development, this technique could provide a new tool for monitoring respiratory changes and ventilator management in the ICU.

Continuous on-line measurements of respiratory system, lung and chest wall mechanics during mechanic ventilation.

OBJECTIVE: We present a concept of on-line, manoeuvre-free monitoring of respiratory mechanics during dynamic conditions, displaying calculated alveolar pressure/volume curves continuously and separating lung and chest wall mechanics. DESIGN: Prospective observational study. SETTING: Intensive care unit of a university hospital. PATIENTS: Ten ventilator-treated patients with acute lung injury. INTERVENTIONS: Different positive end-expiratory pressure (PEEP) and tidal volumes, low flow inflation. MEASUREMENTS AND RESULTS: Previously validated methods were used to present a single-value dynostatic compliance for the whole breath and a dynostatic volume-dependent initial, middle and final compliance within the breath. A high individual variation of respiratory mechanics was observed. Reproducibility of repeated measurements was satisfactory (coefficients of variations for dynostatic volume-dependent compliance: < or =9.2% for total respiratory system, < or =18% for lung). Volume-dependent compliance showed a statistically significant pattern of successively decreasing compliance from the initial segment through the middle and final parts within each breath at all respiratory settings. This pattern became more prominent with increasing PEEP and tidal volume, indicating a greater distension of alveoli. No lower inflection point (LIP) was seen in patients with respiratory rate 20/min and PEEP at 4 cmH2O. A trial with low flow inflation in four of the patients showed formation of a LIP in three of them and an upper inflection in one. CONCLUSIONS: The monitoring concept revealed a constant pattern of successively decreasing compliance within each breath, which became more prominent with increasing PEEP and tidal volume. The monitoring concept offers a simple and reliable method of monitoring respiratory mechanics during ongoing ventilator treatment.

Warning! Suctioning. A lung model evaluation of closed suctioning systems.

BACKGROUND: Closed system suctioning, CSS, has been advocated to avoid alveolar collapse. However, ventilator manufacturers indicate that extreme negative pressure levels can be obtained during closed system suctioning, impeding the performance of the ventilator. METHODS: Suctioning with a 12 or 14 Fr catheter with a vacuum level of -50 kPa was either performed with an open technology or a CSS, where the catheter is introduced through a tight-fitting connection through the endotracheal tube, EYT. The lung model was ventilated with a Servo 900C or 300 ventilator with an I:E ratio of 1:2, 1:1 and 2:1 and extrinsic positive end-expiratory pressure (PEEP) at 0 or 10 cm H20. Respiratory volumes and alveolar pressure were measured at the lung model alveolus. RESULTS: The initial suctioning flow was >40 l/min with a 14 Fr catheter. When inserting the catheter through a no. 7 ETT, PEEP rose from 11 to 23 cm H2O during volume control ventilation with an I:E ratio 1:1. During suctioning the alveolar pressure fell to 10 cm H2O below the set PEEP level. CSS during pressure control ventilation had fewer effects. Low tidal volumes, inverse I:E ratio and secretions in the tube resulted in pressures down to -92 cm H2O. CONCLUSION: CSS should not be used in volume control ventilation due to risk of high intrinsic PEEP levels at insertion of the catheter and extreme negative pressures during suctioning. Pressure control ventilation produces less intrinsic PEEP effect. The continuous positive airway pressure (CPAP) mode offers the least intrinsic PEEP during insertion of the catheter and least sub-atmospheric pressure during suctioning.

Direct tracheal airway pressure measurements are essential for safe and accurate dynamic monitoring of respiratory mechanics. A laboratory study.

BACKGROUND: All monitoring of respiratory mechanics should depend on tracheal pressures (Trach-P) as endotracheal tube resistance (ETT-Res) will otherwise distort them. The aim of this study was to investigate factors that may vary ETT-Res, causing difficulties in ETT-Res estimation clinically, and to evaluate a method for direct Trach-P measurements to obviate these problems. METHODS: In a model we studied: 1) The influence on ETT-Res caused by different connectors and secretions; 2) Direct Trach-P measurements with a catheter (o.d. 2 mm, i.d. 0.9 mm) with either end or side hole, filled with either air or liquid, introduced through the ETT lumen and evaluated regarding response time and position. RESULTS: The pressure drop between trachea and Y-piece increased by 15% when respectively a swivel connector and a humidification device were connected to the ETT. When injecting 1 ml and 2 ml gel into the ETT lumen the inspiratory resistance increased 100% and 600% respectively. The response time of all catheters was < or = 12 ms. During constant flow in inspiratory and expiratory directions the pressure difference between an end hole catheter positioned from 2 cm above the ETT tip to 4 cm below and a reference pressure in the artificial trachea was less than 1.5 cmH2O. CONCLUSIONS: ETT connections and secretions cause a variance in resistance. Tracheal pressure can be measured with high precision with an air- or liquid-filled catheter. An end hole catheter placed within 2 cm above or below the ETT tip will give sufficiently precise measurements for clinical purposes.

A new method for non-invasive, manoeuvre-free determination of "static" pressure-volume curves during dynamic/therapeutic mechanical ventilation.

BACKGROUND: Lung mechanics are usually measured using static or quasistatic methods, abandoning normal ventilatory treatment. We have developed a method to calculate the alveolar pressure during dynamic/therapeutic conditions, "the dynostatic pressure" (P(dyn)), using airway pressure (P) measured in the trachea and volume (V) and flow (V) at the Y-piece. METHODS: P(dyn) is calculated according to the formula P(dyn)= (P(insp) x V(exp)-P(exp) x V(insp))/(V(exp)-V(insp)), making the assumption that inspiratory and expiratory resistances are equal at isovolume. The method was evaluated in a lung model during dynamic conditions comparing measured alveolar pressure (P(alv)) and P(dyn) at equal and unequal inspiratory and expiratory resistances and P/V-curves obtained during static and dynamic conditions. The algorithm was then applied in patients with acute lung injury (ALI). RESULTS: When inspiratory and expiratory resistances were equal there was an excellent agreement between the P(dyn) and the P(alv), irrespective of ventilator settings, r(2)=0.995 (range 0.981-0.999). P(dyn) derived compliance was equal to static values. When the ratio between inspiratory and expiratory resistance was varied between 2.3:1 and 1:2.3 the r(2) was above 0.95 (range 0.952-0.996). Development of intrinsic PEEP and overdistension was easily revealed in patients, as shown by the dynostatic P/V-curve. CONCLUSION: The dynostatic method gives a breath-by-breath reflection of the interaction between ventilatory settings and lung mechanics in patients during ordinary ventilator treatment. It is only marginally affected by the moderate differences in inspiratory versus expiratory resistances present in patients with ALI.

Evaluation of pressure/volume loops based on intratracheal pressure measurements during dynamic conditions.

BACKGROUND: The aim of this study was to evaluate and compare information about lung mechanics obtained by dynamic pressure/volume loops based on Y-piece and intratracheal airway pressure. METHODS: Airway pressure was measured simultaneously at the Y-piece and trachea. Flow/tidal volume was measured by sidestream spirometry at the Y-piece. The effect of an intraluminal catheter in the tube was evaluated in a lung model. Ten adults with acute lung injury and mechanical ventilation were studied. Measurements were performed during volume-(VC) and pressure-controlled (PC) ventilation at different ventilator settings. RESULTS: Lung model: There was a statistically significant difference (P<0.001) between trachea and Y-piece pressure/volume loop areas during both VC and PC ventilation. The ratio trachea area/Y-piece area decreased with increased endotracheal tube resistance (r=0.96). PATIENTS: The difference between trachea and Y-piece P/V-loops was statistically significant at all 21 ventilatory settings (P<0.05-0.001). The tracheal loop revealed clearly intrinsic PEEP and lowered compliance during overinflation, which was difficult or impossible to see in the Y-piece pressure/volume loop. CONCLUSION: By measuring airway pressure at the trachea the effect of endotracheal tube resistance during inspiration is excluded while it is included during expiration, yielding correct end-points of inspiration and expiration. This makes it possible to calculate accurately total compliance of the respiratory system during dynamic conditions. By monitoring of airway pressure in the trachea, respiratory mechanics can be assessed more accurately and ventilatory settings adjusted to attenuate ventilator induced lung injury.

A simplified method for separate measurements of lung and chest wall mechanics in ventilator-treated patients.

BACKGROUND: Airway pressure measurements above the endotracheal tube will be distorted because of endotracheal tube resistance. To separate lung and chest wall compliance, esophageal pressure is conventionally measured with an air-filled balloon catheter, which is difficult to insert in unconscious patients. We have developed a methodology with fluid-filled catheters for intratracheal and esophageal pressure measurements. METHODS: Twelve anesthetized patients were studied. Tidal volumes were measured by side-stream spirometry. Airway pressures were measured at the Y-piece and in the trachea with fluid-filled pressure lines. Esophageal pressure was measured via the narrow lumen in a fluid-filled Salem double-lumen stomach tube, which was slowly retracted from the stomach up through the esophagus until maximal respiratory pressure readings and minimal cardiac artifacts were obtained. Lung mechanics were measured at different tidal volumes (TV) and positive end-expiratory pressure (PEEP). RESULTS: There was a significant difference between airway pressures at the Y-piece and in the trachea. Total compliance significantly increased with increasing TV and decreased with increasing PEEP. Chest wall compliance increased significantly with increasing TV, while lung compliance did not change significantly. Two patients showed repeatedly marked increase in lung compliance at one specific ventilatory setting, an increase the proportion of which was not reflected by changes in total compliance. CONCLUSIONS: Y-piece pressures are not representative of intratracheal pressures, which can be measured by inserting a fluid-filled pressure line through the tube. Esophageal pressure is easily recorded with a fluid-filled Salem double-lumen catheter. Large changes in lung compliance may pass unnoticed when only total compliance is monitored. Monitoring of lung compliance may offer an improved basis for decisions about ventilator settings.

Evaluation of a Pitot type spirometer in helium/oxygen mixtures.

OBJECTIVE: Mixtures of helium and oxygen are regaining a place in the treatment of obstruction of the upper and lower respiratory tract. The parenchymal changes during the course of IRDS or ARDS may also benefit from the reintroduction of helium/oxygen. In order to monitor and document the effect of low-density gas mixtures, we evaluated the Datex AS/3 Side Stream Spirometry module with D-lite (Datex-Engstrom Instrumentarium Corporation, Finland) against two golden standards. METHODS: Under conditions simulating controlled and spontaneous ventilation with gas mixtures of He (approx. 80, 50, and 20%)/O2 or N2(approx. 21 and 79%)/02, simultaneous measurements using Biotek Ventilator Tester (Bio-Tek Instr., Vermont, USA) or body plethysmograph (SensorMedics System, Anaheim, USA) were correlated with data from the spirometry module. Data were analyzed according to a statistical regression model resulting in a best-fit equation based on density, voltage, and volume measurements. RESULTS: As expected, the D-lite (a modified Pitot tube) showed density-dependent behaviour. Regression equations and percentage deviation of estimated versus measured values were calculated. CONCLUSION: Measurements with the D-lite using low-density gases are satisfactorily contained in best-fit equations with a standard deviation of less than 5% during all ventilatory modes and mixtures.

[Postoperative restcurarization.].

OBJECTIVE: Muscle relaxants have been used during anesthesia for the past 50 years but in the last decades it has been realised that their use can lead to complications. Studies have shown 20-40% incidence of restcurarization in postanesthesia care units (PACU) even if neuromuscular monitors are used during anesthesia. The purpose of this study was to estimate the frequency of postoperative muscle weakness at the Reykjavik Hospital in Iceland. MATERIAL AND METHODS: Sixty patients, operated for laparoscopic cholecystectomy or lumbal disc prolapse, given muscle relaxants (vecuronium or pancu notronium) during anesthesia were studied in the PACU. The 5-sec headlift test has been shown to be the best clinical sign of recovery and this sign was used to find patients with muscle weakness. Glasgow coma score (GCS) was used to evaluate if patients were too drowsy to co-operate and patients with GCS <12 were excluded. Measurements were made after arrival to the PACU and every 30 minutes thereafter until headlift was at least five seconds. RESULTS: Incidence of restcurarization was 17% on arrival to the PACU and these patients were significantly lower in oxygen saturation before oxygen supplementation was started. Thirty minutes after arrival 6% were still restcurarized and 3% after 60 minutes. All patients had recovered after 90 minutes. No difference was found between patients given vecuronium or pancuronium in the first two measurements but those with longest duration of muscle weakness had received pancuronium. CONCLUSION: The study shows that the incidence of muscle weakness is too high, which might increase the risk for complications such as hypoxia or respiratory failure. To increase patient safety, shorter acting drugs are recommended and the use of new nervestimulators giving the train-of-four(TOF)-ratio during muscle blockade could possibly improve the situation.