Continuous Blood Gas Monitoring Research Articles

A comparison of continuous blood gas monitors during cardiopulmonary bypass LivaNova B-Capta, Terumo CDI 500, spectrum medical M4.

Accurate and precise management of blood gas parameters during cardiopulmonary bypass (CPB) is crucial to patient care and outcome. This study compares the data provided by Livanova B-Capta, Terumo CDI500, and Spectrum Medical M4 with the results from a gold standard blood gas analyzer to test accuracy. All three continuous blood gas monitoring (CBGM) devices were used simultaneously during CPB on one dedicated HLM. Arterial and venous blood samples of 40 adult patients who underwent elective cardiac surgery with CPB were taken from the CPB circuit. Pre- and post-alignment deviation in percentages are compared with CLIA guidelines. B-Capta data reveals that the deviation pre-alignment is small and within the CLIA threshold for all parameters. Pre-alignment data for CDI 500 is within CLIA threshold for SvO2 and PaO2. The pre-alignment data for the M4 exceeds the CLIA thresholds for all parameters. Post-alignment data for B-Capta and CDI 500 reveals an accurate agreement for Hb and Hct and strong agreement for PaO2. All values for B-Capta and CDI 500 are within CLIA threshold values except for SvO2. Post-alignment the M4 exceeded the CLIA threshold value only for PaO2. B-Capta is the only CBGM device that operates within the CLIA guidelines and is in agreement with laboratory values prior to alignment.

Continuous Monitoring of pH and Blood Gases Using Ion-Sensitive and Gas-Sensitive Field Effect Transistors Operating in the Amperometric Mode in Presence of Drift.

Accurate and cost-effective integrated sensor systems for continuous monitoring of pH and blood gases continue to be in high demand. The capacity of ion-selective and Gas-sensitive field effect transistors (FETs) to serve as low-power sensors for accurate continuous monitoring of pH and blood gases is evaluated in the amperometric or current mode of operation. A stand-alone current-mode topology is employed in which a constant bias is applied to the gate with the drain current serving as the measuring signal. Compared with voltage-mode operation (e.g., in the feedback mode in ion-selective FETs), current-mode topologies offer the advantages of small size and low power consumption. However, the ion-selective FET (ISFET) and the Gas-sensitive FET (GasFET) exhibit a similar drift behavior, imposing a serious limitation on the accuracy of these sensors for continuous monitoring applications irrespective of the mode of operation. Given the slow temporal variation associated with the drift characteristics in both devices, a common post-processing technique that involves monitoring the variation of the drain current over short intervals of time can potentially allow extraction of the measuring signal in presence of drift in both sensor types. Furthermore, in the amperometric mode the static sensitivity of a FET-based sensor, given by the product of the FET transconductance and the sensitivity of the device threshold voltage to the measurand concentration, can be increased by adjusting the device design parameters. Increasing the sensitivity, while of interest in its own right, also enhances the accuracy of the proposed method. Rigorous analytical validation of the method is presented for GasFET operation in the amperometric mode. Moreover, the correction algorithm is verified experimentally using a Si3N4-gate ISFET operating in the amperometric mode to monitor pH variations ranging from 3.5 to 10.

Changes in Rat Brain MicroRNA Expression Profiles Following Sevoflurane and Propofol Anesthesia.

Background:Sevoflurane and propofol are widely used anesthetics for surgery. Studies on the mechanisms of general anesthesia have focused on changes in protein expression properties and membrane lipid. MicroRNAs (miRNAs) regulate neural function by altering protein expression. We hypothesize that sevoflurane and propofol affect miRNA expression profiles in the brain, expect to understand the mechanism of anesthetic agents.Methods:Rats were randomly assigned to a 2% sevoflurane group, 600 μg·kg−1·min−1 propofol group, and a control group without anesthesia (n = 4, respectively). Treatment group was under anesthesia for 6 h, and all rats breathed spontaneously with continuous monitoring of respiration and blood gases. Changes in rat cortex miRNA expression profiles were analyzed by miRNA microarrays and validated by quantitative real-time polymerase chain reaction (qRT-PCR). Differential expression of miRNA using qRT-PCR among the control, sevoflurane, and propofol groups were compared using one-way analysis of variance (ANOVA).Results:Of 677 preloaded rat miRNAs, the microarray detected the expression of 277 miRNAs in rat cortex (40.9%), of which 9 were regulated by propofol and (or) sevoflurane. Expression levels of three miRNAs (rno-miR-339-3p, rno-miR-448, rno-miR-466b-1*) were significantly increased following sevoflurane and six (rno-miR-339-3p, rno-miR-347, rno-miR-378*, rno-miR-412*, rno-miR-702-3p, and rno-miR-7a-2*) following propofol. Three miRNAs (rno-miR-466b-1*, rno-miR-3584-5p and rno-miR-702-3p) were differentially expressed by the two anesthetic treatment groups.Conclusions:Sevoflurane and propofol anesthesia induced distinct changes in brain miRNA expression patterns, suggesting differential regulation of protein expression. Determining the targets of these differentially expressed miRNAs may help reveal both the common and agent-specific actions of anesthetics on neurological and physiological function.

Assessment of a continuous blood gas monitoring system in animals during circulatory stress.

BackgroundThe study was aimed to determine the measurement accuracy of The CDI™ blood parameter monitoring system 500 (Terumo Cardiovascular Systems Corporation, Ann Arbor MI) in the real-time continuous measurement of arterial blood gases under different cardiocirculatory stress conditionsMethodsInotropic stimulation (Dobutamine 2.5 and 5 μg/kg/min), vasoconstriction (Arginine-vasopressin 4, 8 and 16 IU/h), hemorrhage (-10%, -20%, -35%, and -50% of the theoretical volemia), and volume resuscitation were induced in ten swine (57.4 ± 10.7 Kg).Intermittent blood gas assessments were carried out using a routine gas analyzer at any experimental phase and compared with values obtained at the same time settings during continuous monitoring with CDI™ 500 system. The Bland-Altman analysis was employed.ResultsBias and precision for pO2 were - 0.06 kPa and 0.22 kPa, respectively (r2 = 0.96); pCO2 - 0.02 kPa and 0.15 kPa, respectively; pH -0.001 and 0.01 units, respectively ( r2 = 0.96). The analysis showed very good agreement for SO2 (bias 0.04,precision 0.33, r2 = 0.95), Base excess (bias 0.04,precision 0.28, r2 = 0.98), HCO3 (bias 0.05,precision 0.62, r2 = 0.92),hemoglobin (bias 0.02,precision 0.23, r2 = 0.96) and K+ (bias 0.02, precision 0.27, r2 = 0.93). The sensor was reliable throughout the experiment during hemodynamic variations.ConclusionsContinuous blood gas analysis with the CDI™ 500 system was reliable and it might represent a new useful tool to accurately and timely monitor gas exchange in critically ill patients. Nonetheless, our findings need to be confirmed by larger studies to prove its reliability in the clinical setting.

Improving Cardiopulmonary Bypass: Does Continuous Blood Gas Monitoring Have a Role to Play?

The CDI™500 (Terumo Cardiovascular Systems, Ann Arbor, MI) is an in-line blood gas monitoring device that has been used in clinical practice for over a decade. Few randomized studies have evaluated the value of this device with respect to improved perfusion management. We routinely use automated continuous quality indicator programs to assess perfusion management. The aim of this study is to investigate in a prospective randomized trial the role of in-line blood gas monitoring in the improvement of blood gas management during cardiopulmonary bypass (CPB) utilizing continuous quality indicators. Patients were randomized into two groups (Control, CDI). Patients in the Control group received our standard CPB blood gas management, with intermittent blood gas results. Continuous blood gas measurements from the CDI™500 were recorded at 20-second intervals, with the perfusionist blinded to these measurements. Patients in the CDI group received standard CPB blood gas management, in addition to continuous blood gas measurements visible on the CDI™500, the alarm system activated, and the data recorded. Perfusion management for all cases was guided by institutional protocols. One hundred patients (50 in each group) were included in the study. No significant difference existed between the groups on demographic, surgical, or clinical outcomes. Blood gas levels of patients in the CDI group were able to be maintained in accordance to protocol a greater percentage of the time, e.g., pCO2management was 2% versus 20% (p= .008); this was most notable for differences between the Control and the CDI group for pCO2> 45 mmHg (p= .003). Practice variation determined via statistical control charts improved for both pH and pCO2, represented by a decrease in the variation associated with practice. Continuous blood gas monitoring with the CDI™500 results in significantly improved blood gas management as determined by adherence to institutional protocols.

Improving Cardiac Surgery: Does Continuous Blood Gas Monitoring Have a Role to Play?

Improving Cardiac Surgery: Does Continuous Blood Gas Monitoring Have a Role to Play?

The effect of inhaled nitric oxide and inhaled iloprost on hypoxaemia in a patient with pulmonary hypertension after pulmonary thrombarterectomy

Acute pulmonary hypertension with life-threatening right heart failure may complicate the postoperative course following cardiothoracic surgery. Both inhaled nitric oxide and inhaled iloprost, a stable analogue of prostacyclin, have been used frequently for this purpose in acute pulmonary hypertension of various origins. We present a case of a patient with acute pulmonary hypertension and severely impaired gas exchange following pulmonary thrombo-endarterectomy. Therapy with one inhaled vasodilator alone did not satisfactorily abort a postoperative pulmonary hypertensive crisis and low-output syndrome due to right heart failure. Combined inhaled nitric oxide and inhaled iloprost, however, showed additive effects. Hence, the combination of both drugs may be reasonable in cases where the standard therapy fails. The effect has been demonstrated by means of continuous blood gas monitoring.

Does bradycardia or hypertension enhance gas transfer in rainbow trout ( Oncorhynchus mykiss)?

Experiments were conducted to test the hypothesis that branchial gas transfer is enhanced in rainbow trout during hypoxia or hypercarbia by bradycardia and systemic vasoconstriction. Gas transfer was indirectly assessed by continuous monitoring of arterial blood gases, PaO 2 and PaCO 2. Cardiac frequency was maximally decreased by 34.9 ± 4.3 and 8.6 ± 3.2 bpm in hypoxic and hypercarbic fish, respectively. Pre-treating fish with atropine (1 μmol kg − 1) attenuated or abolished the bradycardia during hypoxia and hypercarbia, respectively. However, there were no significant differences in the arterial blood gases between the control and atropinized fish. Dorsal aortic blood pressure was increased maximally by 11.3 ± 2.8 and 17.7 ± 2.0 mm Hg in the hypoxic and hypercarbic fish. Pre-treatment of fish with prazosin (2.4 μmol kg − 1) prevented these increases in blood pressure. Blood gases were unaltered by prazosin treatment in the hypercarbic fish. However, in the hypoxic fish, gas transfer appeared to be impaired by prazosin on the basis of lowered PaO 2 (by approximately 35 mm Hg compared to control fish) and increased PaCO 2 (by approximately 0.3 mm Hg). Because the normal hyperventilatory response to hypoxia was prevented by prazosin, it is possible that the impairment of gas transfer was related to inadequate ventilation rather than to any differences in the pressor response. The present results provide no evidence that gas transfer in rainbow trout is enhanced by bradycardia nor do they reveal any obvious benefit associated with the increases in blood pressure that accompany hypoxia and hypercarbia.

Continuous noninvasive monitoring of transcutaneous blood gases for a stable and persistent BOLD contrast in fMRI studies in the rat

The physiological status of anesthetized rats greatly influences blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). Monitoring of physiological parameters, particularly partial pressure of carbon dioxide (pCO(2)) levels in the blood, is therefore an important part in the design and performance of reliable fMRI experiments. In this paper, the use of a transcutaneous blood gas analyzing system in rats as a completely noninvasive and MR-compatible method is demonstrated. It was successfully used to monitor continuously pCO(2) values, as an effective alternative to more invasive methods, such as analysis of repetitive arterial blood samples or endtidal capnography. In addition, the transcutaneous pCO(2) of rats anesthetized for long periods was studied using different anesthetic substances and experimental protocols. On-line monitoring of pCO(2) values permitted experimental conditions to be established in which the animals remained normocapnic and during which a robust and consistent BOLD contrast could be observed upon somatosensory forepaw stimulation. A transcutaneous pCO(2) threshold level was defined for the reliable detection of a stimulus-dependent BOLD response.

Anesthesia for Lung Transplantation

Lung transplantation is the only therapeutic option for more than 3,000 individuals in the United States with end-stage lung disease. Innovations in anesthetic and surgical techniques have expanded the indications for lung transplantation. Presently, the major limiting factor in the number of lung transplantations that are performed is the availability of suitable donor organs. Lung transplantation includes a number of surgical procedures, including single-lung, double-lung, bilateral-sequential-single-lung, heart-lung, and lobar transplantation. Patients undergoing lung transplantation present a variety of challenges to the anesthesia team. Critical periods include induction of anesthesia, initiation of positive pressure ventilation, establishment and maintenance of one-lung ventilation, pulmonary artery clamping, pulmonary artery unclamping, and reperfusion of the transplanted lung. Pharmacologic advances have been an important factor in the continued development and success of lung transplantation. Newer immunosuppressive agents have improved the prevention and management of post-transplant rejection. Selective pulmonary vasodilators that are administered via inhalation affect the anesthetic management during the surgical procedure. Technologic advances in monitoring have also been valuable in lung transplantation. Transesophageal echocardiography is commonly used to evaluate intraoperative ventricular function. Continuous cardiac output, mixed venous oxygen saturation, continuous arterial blood gas monitoring, and the bispectral index have also been used to monitor the patient during lung transplantation. Anesthetic management of lung transplantation requires a thorough understanding of end-stage lung disease and pharmacologic and technical considerations that may not be applicable in any other part of anesthetic practice.

Improved Outcomes During Cardiac Surgery: A Multifactorial Enhancement of Cardiopulmonary Bypass Techniques

Patients presenting for cardiac surgery with cardiopulmonary bypass (CPB) are more likely to have pre-existing comorbidities, which has resulted in a steady increase in the risk associated with CPB. The resulting challenge has mandated the optimization of perfusion care. The purpose of this study was to retrospectively evaluate the impact of a number of simultaneous, evidence based perfusion care changes on patient outcome. After Institutional Review Board approval, two groups of patients were compared. The control group (n= 317) included all patients undergoing CPB in a 12-month period preceding a multifaceted change in perfusion techniques. The treatment group (n= 259) included all patients undergoing CPB in the 12-month period after the changes, which included the incorporation of updated continuous blood gas monitoring, biocompatible circuitry, updated centrifugal blood propulsion, continuous autotransfusion technology, new generation myocardial protection instrumentation, plasmapheresis, topical platelet gel application, excluding hetastarch while increasing the use of albumin, viscoelastographic coagulation monitoring, and implementing a quantitative quality improvement program. After univariate analysis, propensity scoring and multiple conditional logistical regression were used to control for demographic, preoperative, operative, and postoperative parameters. Results of the primary endpoints revealed a lower mortality rate in the treatment group (4% vs. 9% [95% confidence interval 1.33, 7.72],p= 0.009), lower transfusion rate (51% vs. 59% [1.00, 2.11],p= 0.048), and lower complication rate (55% vs. 65% [1.06,2.19],p= 0.025) despite having similar predicted mortality (11 [2,22] vs. 11[3,22],p= NS) and other preoperative and operative parameters. The lower mortality rate was concurrent with a trend towards a lower incidence of complications, consistent with the differences in primary outcomes. In conclusion, the patients treated after the implementation of a multifactorial improvement plan using evidence based changes in CPB care had decreased complication and mortality rates.

Significance of continuous blood gas monitoring in cardiac surgery with cardiopulmonary bypass

Significance of continuous blood gas monitoring in cardiac surgery with cardiopulmonary bypass

Significance of continuous blood gas monitoring in cardiac surgery with cardiopulmonary bypass

Significance of continuous blood gas monitoring in cardiac surgery with cardiopulmonary bypass

Accuracy and performance of a modified continuous intravascular blood gas monitoring device during thoracoscopic surgery

Objective: The only commercially available continuous intravascular blood gas monitoring system for adults, the Paratrend (Diametrics Medical Inc, High Wycombe, UK), was modified by the manufacturer to the Paratrend 7+ (PT7+) in 1999. The aim of this study was to evaluate the modified probe over a wide range of blood gas and pH values during thoracoscopic surgery in a similar setup as done with the previous model. Design: Prospective methods comparison study. Setting: University hospital. Participants: Twenty-three patients. Interventions: Elective thoracoscopic surgery. Measurements and main results: One hundred thirteen PT7+ readings and their corresponding arterial blood gas and pH measurements (ABGA) were evaluated. The ranges for ABGA values were 50 to 474 mmHg for PO 2, 29 to 58 mmHg for PCO 2, and 7.28 to 7.49 for pH. Bland and Altman analysis revealed a bias ± 2 standard deviation of −20 ± 86 mmHg for PO 2, 3 ± 9 mmHg for PCO 2, and −0.01 ± 0.06 for pH. No specific complications attributable to the probe were observed. Conclusion: In patients undergoing thoracoscopic surgery with rapidly changing blood gas parameters, the PT7+ device is a valuable trend indicator and hence may be helpful for clinical decision making. However, the underestimation of PO 2 values by 20 mmHg on average and the wide limits of agreement documented in this study must be regarded as limiting factors.

243 Changes in Gas Exchange and Oxygenation During Surfactant Administration Using Continuous Arterial Blood Gas Monitoring

Background: While prophylactic surfactant is an evidence based treatment for infants less than 28 weeks gestation, problems occuring during administration including changes in arterial partial pressure of oxygen and carbondioxide (PaO2 & PaCO2) and drug reflux through endotracheal tube (ETT) have been reported. The volume of a surfactant is relevant to the ease of administration and acceptability to the neonatal lungs. In our experience, surfactants with larger volume can cause hypercarbia and hypoxia associated with ETT obstruction, more frequently with high frequency oscillatory ventilation (HFOV), requiring prolonged intermittent positive pressure ventilation (IPPV) immediately after administration. Curosurf volume (100mg/1.25ml/kg) is considerably smaller than other surfactants (100mg/3–4ml/kg) and administered as a single dose. Larger volumes with fractional doses do not give same enhancement on gas exchange as same total dose given by a single dose. Continuous blood gas monitoring (CBGM) has been proven to provide continuous records of changes in pH, PaO2 & PaCO2 with acceptable precision compared to standard blood gas measurements.Aims: To stydy the changes in pH, PaCO2 & PaO2 during surfactant (Curosurf) administration using CBGM.Methods: Pretrem infants less than 28 weeks with respiratory distress syndrome requiring HFOV who had a multi-parameter intraarterial sensor, placed in an umbilical arterial catheter were studied prospectively. Changes were recorded during and 10 minutes after Curosurf administration. The data together with CBGM record printouts are available for discussion.Results: 5 infants (mean gestation 25.8 weeks) were included in the study. All infants tolerated the administration very well with no significant changes in heart rate. In all infants, there were minimal changes in PaCO2 ( mean + 0.18 kPa) 10 minutes after Curosurf. IPPV was applied only for less than 20 seconds and the change in mode of ventilation was not necessary. FiO2 was lower (mean −0.12) with changes in PaO2 (mean − 0.7 kPa) in 10 minutes after Curosurf.Conclusions: This small but important study provides information on effects of Curosurf while it is being given, proven by CBGM. Minimal changes in PaCO2 and minimal interruption in alveolar recruitment on HFOV while surfactant is administered are important in extremely preterm infants' ventilatory management and cerebral circulation. Further studies in these areas with larger number of infants are indicated.

Evaluation of a new probe for continuous intravascular blood gas monitoring in jugular venous and arterial blood

Evaluation of a new probe for continuous intravascular blood gas monitoring in jugular venous and arterial blood

Continuous Blood Gas Monitoring Using an In-Dwelling Optode Method: Comparison to Intermittent Arterial Blood Gas Sampling in ECMO Patients

The ability to measure postmembrane arterial blood gases is essential in the management of critically ill neonates treated with extracorporeal membrane oxygenation (ECMO). A new technology using, the Paratrend 7 system (Diametrics Medical, High Wycombe,UK) allows for continuous measurement of pH, PCO(2) and PO(2), and calculates oxygen saturation, bicarbonate, and base excess. To evaluate and compare the results of continuous blood gas measurement using the Paratrend 7 system with a standard system of blood gas analysis in our intensive care unit. Prospective, controlled, interventional study. The neonatal intensive care unit of a tertiary referral center. Neonates who required extracorporeal life support and were expected to have frequent postmembrane arterial blood sampling during the testing period. To enable Paratrend 7 sensor access to the ECMO circuit, the postmembrane access port extension set that is routinely used for blood drawn for blood gas analysis was used. The study began with the insertion of the Paratrend 7 sensor. Subjects remained on the study until the ECMO was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Paratrend 7 system were not used in clinical management of the patient. BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Paratrend 7 monitor was recorded for comparison. A total of 242 pairs of blood gas samples were collected from 10 neonates. The mean bias/precision for pH was -0.02/0.04; for PO(2) 68.35/93.44 mm Hg; and for PCO(2) 1.75/4.23 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.89 for pH, 0.96 for PO(2), and 0.73 for PCO(2) (Table 1). The blood gases compared in the two methods had a strong correlation for pH, PCO(2) and PO(2). Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal ECMO patients. Use of the Paratrend 7 should allow reduced health-care provider exposure to blood and decreased patient iatrogenic blood loss.

Continuous blood gas monitoring using an in-dwelling optode method: clinical evaluation of the Neotrend sensor using a luer stub adaptor to access the umbilical artery catheter.

Arterial blood gases are essential in the management of critically ill neonates. A new technology using the Neotrend system (Diametrics Medical) allows for continuous measurement of pH, PaCO(2), and PaO(2), and calculates oxygen saturation, bicarbonate, and base excess. To evaluate and compare the results of continuous blood gas measurement using the Neotrend system with a standard system of blood gas analysis in our intensive care unit. Prospective, controlled, interventional study. The neonatal intensive care unit of a tertiary referral center. Neonates with respiratory distress who required respiratory support and frequent arterial blood gas sampling and had a UAC. To enable Neotrend sensor access to an existing Argyle umbilical artery catheter (UAC) the catheter was cut at the 25-cm mark and connected to an 18-gauge blunt needle luer stub adaptor (Vygon 95440). The study began with the insertion of the Neotrend sensor. Subjects remained on the study until the UAC was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Neotrend system were not used in clinical management of the patient. BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Neotrend monitor was recorded for comparison. A total of 217 pairs of blood gas samples were collected from seven neonates. The mean bias/precision for pH was 0.01/0.04; for PaO(2) 0.72/18.5 mm Hg; and for PaCO(2) 3.96/2.63 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.85 for pH, 0.96 for PaO(2), and 0.92 for PaCO(2). The blood gases compared in the two methods had a strong correlation for pH, PaCO(2), PaO(2), and oxygen saturation. Although the bicarbonate and base excess values showed suboptimal statistical correlation, the difference was not clinically relevant. Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal patients. It also allows reduced healthcare provider exposure to blood and decreased patient iatrogenic blood loss.

The impact of morbid obesity, pneumoperitoneum, and posture on respiratory system mechanics and oxygenation during laparoscopy.

We studied the effect of morbid obesity, 20 mm Hg pneumoperitoneum, and body posture (30 degrees head down and 30 degrees head up) on respiratory system mechanics, oxygenation, and ventilation during laparoscopy. We hypothesized that insufflation of the abdomen with CO(2) during laparoscopy would produce more impairment of respiratory system mechanics and gas exchange in the morbidly obese than in patients of normal weight. The static respiratory system compliance and inspiratory resistance were computed by using a Servo Screen pulmonary monitor. A continuous blood gas monitor was used to monitor real-time PaCO(2) and PaO(2), and the ETCO(2) was recorded by mass spectrometry. Static compliance was 30% lower and inspiratory resistance 68% higher in morbidly obese supine anesthetized patients compared with normal-weight patients. Whereas body posture (head down and head up) did not induce additional large alterations in respiratory mechanics, pneumoperitoneum caused a significant decrease in static respiratory system compliance and an increase in inspiratory resistance. These changes in the mechanics of breathing were not associated with changes in the alveolar-to-arterial oxygen tension difference, which was larger in morbidly obese patients. Before pneumoperitoneum, morbidly obese patients had a larger ventilatory requirement than the normal-weight patients to maintain normocapnia (6.3 +/- 1.4 L/min versus 5.4 +/- 1.9 L/min, respectively; P = 0.02). During pneumoperitoneum, morbidly obese, supine, anesthetized patients had less efficient ventilation: a 100-mL increase of tidal volume reduced PaCO(2) on average by 5.3 mm Hg in normal-weight patients and by 3.6 mm Hg in morbidly obese patients (P = 0.02). In conclusion, respiratory mechanics during laparoscopy are affected by obesity and pneumoperitoneum but vary little with body position. The PaO(2) was adversely affected only by increased body weight. Morbid obesity significantly decreases respiratory system compliance and increases inspiratory resistance. Increased body weight, and not altered mechanics of breathing, was associated with worse PaO(2) during laparoscopy.

Microvascular Assessment of Burn Depth Conversion during Varying Resuscitation Conditions

Conversion of partial- to full-thickness injuries, even after the burning has stopped, remains a significant clinical problem. We developed a rat model with a wide range of burn depths to study this phenomenon by microvascular assessment. Fifty-four male Sprague-Dawley rats weighing 460 g on average were studied. Real-time tissue monitoring of pH, paCO2, and paO2 was achieved by placement of a continuous blood gas monitor transducer in the aorta. Ten, 2-cm x 2-cm burns were created on each animal with milled aluminum templates (100 degrees C) with varying contact times. Conversion of burn depth in these wounds was documented by serial laser Doppler imager scanning over a 5-hour period. Animals received Ringer's lactate resuscitation at 0, 2, 4, 6, and 8 ml/kg/%burn. Serial laser Doppler scanning directly demonstrated progressive loss of perfusion to partial-thickness burns dependent upon the amount of fluid resuscitation. Conversion of partial- to full-thickness burns in this rat model (documented by laser Doppler microvascular assessment) was dependent upon how the animals were resuscitated.