Accuracy of a central mass spectrometer system at high respiratory frequencies

We have shown that in a laboratory setting the long lengths of sampling catheters necessary to access a central mass spectrometer restrict the high-frequency response of the system. Reported here are the results from a clinically operating Perkin-Elmer Advantage system. The sampling catheter was 50 meters long and the sampling flow was 240 ml/min. Rapid changes in carbon dioxide concentration were created by an electronically operated solenoid valve switching between 6.94% CO₂ in 50% O₂ balance N₂ and 100% O₂. The frequency of this simulated brething was varied between 10 and 100 breaths/min with the ratio of inspiration to expiration fixed at 1:2. Data were taken from the terminal in the operating room. Errors greater than 5% of the true value occurred at 35 breaths/min for the indicated inspired concentration and 73 breaths/min for the indicated expired concentration. For critical situations in which respiratory frequencies exceed 40 breaths/min, a centrally located mass spectrometer may not be adequate for measuring CO₂ because of errors introduced by the long sampling catheters.Presented at the annual meeting of the American Society of Anesthesiologists, Las Vegas, NV, October 1986. Published in abstract form in Anesthesiology 1986;65:A136     

Capnometry for continuous postoperative monitoring of nonintubated,spontaneously breathing patients

We continuously monitored spontaneous respiration after extubation by end-tidal CO₂ tension (PetCO₂) in 19 patients aged 20 to 72 years who had undergone major operations. The respiratory gas was sampled from the nasopharynx via a special nasal catheter and analyzed by a side-stream analyzer. In each case, optimal placement of the nasal catheter was determined by CO₂ waveform and the capnograms were recorded for waveform analysis and trend monitoring.PetCO₂ was compared with arterial CO₂ tension (PaCO₂) two to four times during the 2- to 19-hour observation periods by simultaneous measurements. For 65 simultaneous measurements, meanPetCO₂ was 38.9 ± 5.7 mm Hg (range, 26.3 to 48.3 mm Hg) and mean PaCO₂ was 38.9 ± 5.7 mm Hg (range, 26.8 to 46.0 mm Hg;r=0.82;p<0.01). While the mean values forPetCO₂ and PaCO₂ were similar, several patients had large differences for PaCO₂ toPetCO₂. The differences of the individual patients did not differ significantly between the various times of measurement. We conclude that this form of capnometry is well suited for continuous, noninvasive monitoring of respiration in nonintubated, spontaneously breathing patients.     

Evaluation of a regional oxygen saturation catheter for monitoring SJVO2 in head injured patients

Objectives. Monitoring jugular venous oxygen saturation (SjvO₂) has been useful for the early identification and treatment of cerebral ischemia in patients with severe head injury. However, the catheters that have been used for this purpose have not performed optimally. The purpose of this study was to evaluate the performance of a new regional oxygen saturation catheter for monitoring SjvO₂.Methods. Eighteen regional oxygen saturation catheters, 4-Fr in diameter (Baxter Healthcare Corporation, Edward Critical Care), were used in this study. Each catheter was inserted percutaneously into the dominant jugular vein and the catheter's tip position in the jugular bulb was verified by radiograph. The catheter was calibratedin vitro prior to insertion using the optic calibrator provided by the manufacturer. The catheter was recalibrated every 8 to 12 hours by comparing the oxygen saturation value from the catheter with that measured by a cooximeter in a blood sample drawn through the catheter.Results. In vitro calibration using the optic calibrator was not always successful. Five catheters could not be calibrated. The remaining 13 catheters could all be calibrated, but only 9 provided a value that was within 4% of the oxygen saturation derived from the blond sample. After the firstin vivo calibration, the correlation between the catheter and the blond sample values was improved. A total of 196 comparisons were made. The median, 25th, and 75th quartile differences between the catheter and the blond sample measurement of SjvO₂ were 0.00, −1.15, and 1.25%, respectively. Using longitudinal data regression, the overall slope of the regression between the catheter and blood values was 0.997 (p = 0.001).Conclusions. The new regional oxygen saturation catheter provided reliable measurement of SjvO₂ 83% of the time when the signal quality index was ≤3, and may be useful for continuous monitoring of SjvO₂. This work was supported by NIH grant #PO1-NS26716.     

Pulmonary artery catheter monitoring during single-lung ventilation in dogs

The effect of pulmonary artery (PA) catheter insertion on cardiac output measurements and the effect of singlelung ventilation on data derived from catheters placed in both the right and left pulmonary arteries were examined in 17 anesthetized mongrel dogs. Serial tricarboncyanine dye measurements of cardiac output were taken at baseline and after insertion of each of two PA catheters, one catheter in each lung, to detect possible changes in cardiac output due to instrumentation. In the second part of the study, single-lung ventilation was achieved through a Kottmeier double-lumen tube. Right and left paired values of thermodilution cardiac output, PA systolic pressure, and PA Po₂ were compared during ventilation of both lungs, during right lung ventilation, during return to ventilation of both lungs, and during left lung ventilation. Mean dye-dilution cardiac outputs were not significantly different after one or two catheters were inserted. Paired right and left values were similar for thermodilution cardiac output, PA Po₂, and pulmonary systolic pressure, regardless of ventilation conditions. Even during single-lung ventilation, data obtained from PA catheters in the ipsilateral and contralateral lung were equivalent in supine dogs.This study was supported by a grant from the Department of Anesthesiology of the University of Pittsburgh.     

Evaluation of a regional oxygen saturation catheter for monitoring SJVO2 in head injured patients

Objectives. Monitoring jugular venous oxygen saturation (SjvO₂) has been useful for the early identification and treatment of cerebral ischemia in patients with severe head injury. However, the catheters that have been used for this purpose have not performed optimally. The purpose of this study was to evaluate the performance of a new regional oxygen saturation catheter for monitoring SjvO₂.Methods. Eighteen regional oxygen saturation catheters, 4-Fr in diameter (Baxter Healthcare Corporation, Edward Critical Care), were used in this study. Each catheter was inserted percutaneously into the dominant jugular vein and the catheter's tip position in the jugular bulb was verified by radiograph. The catheter was calibratedin vitro prior to insertion using the optic calibrator provided by the manufacturer. The catheter was recalibrated every 8 to 12 hours by comparing the oxygen saturation value from the catheter with that measured by a cooximeter in a blood sample drawn through the catheter.Results. In vitro calibration using the optic calibrator was not always successful. Five catheters could not be calibrated. The remaining 13 catheters could all be calibrated, but only 9 provided a value that was within 4% of the oxygen saturation derived from the blond sample. After the firstin vivo calibration, the correlation between the catheter and the blond sample values was improved. A total of 196 comparisons were made. The median, 25th, and 75th quartile differences between the catheter and the blond sample measurement of SjvO₂ were 0.00, –1.15, and 1.25%, respectively. Using longitudinal data regression, the overall slope of the regression between the catheter and blood values was 0.997 (p = 0.001).Conclusions. The new regional oxygen saturation catheter provided reliable measurement of SjvO₂ 83% of the time when the signal quality index was 3, and may be useful for continuous monitoring of SjvO₂.This work was supported by NIH grant #PO1-NS26716.     

Pulmonary artery catheter monitoring during single-lung ventilation in dogs

The effect of pulmonary artery (PA) catheter insertion on cardiac output measurements and the effect of singlelung ventilation on data derived from catheters placed in both the right and left pulmonary arteries were examined in 17 anesthetized mongrel dogs. Serial tricarboncyanine dye measurements of cardiac output were taken at baseline and after insertion of each of two PA catheters, one catheter in each lung, to detect possible changes in cardiac output due to instrumentation. In the second part of the study, single-lung ventilation was achieved through a Kottmeier double-lumen tube. Right and left paired values of thermodilution cardiac output, PA systolic pressure, and PA Po₂ were compared during ventilation of both lungs, during right lung ventilation, during return to ventilation of both lungs, and during left lung ventilation. Mean dye-dilution cardiac outputs were not significantly different after one or two catheters were inserted. Paired right and left values were similar for thermodilution cardiac output, PA Po₂, and pulmonary systolic pressure, regardless of ventilation conditions. Even during single-lung ventilation, data obtained from PA catheters in the ipsilateral and contralateral lung were equivalent in supine dogs. This study was supported by a grant from the Department of Anesthesiology of the University of Pittsburgh.     

The effects of bronchodilator-inhaler aerosol propellants on respiratory gas monitors

Spurious readings from a mass spectrometer have been reported following the administration of aerosol bronchodilators. We quantified the response of various respiratory gas analyzers to the aerosol propellant of albuterol inhalant (Proventil). The mass spectrometer systems tested, two Advantage systems, a SARA system, and a Model 6000 Ohmeda system, all displayed artifactual readings in response to the albuterol propellant. Each metered dose of the Proventil brand of albuterol contains 4 ml of Freon 11 (trichloromonofluoromethane) and 11 ml of Freon 12 (dichlorodifluoromethane). The concentration of propellant was expressed in doses/L, where each liter of gas contains 0.4 vol % of Freon 11 and 1.1 vol % of Freon 12 per dose. In proportion to the concentration of albuterol propellant, the two Advantage systems showed substantial readings of isoflurane (%) when no isoflurane was present (13% and 16% per dose/L) and reduced readings of enflurane (–8% and –10% per dose/L) and carbon dioxide (CO₂) (–3 and +5 mm Hg per dose/L). The SARA system showed substantial CO₂ readings when no CO₂ was present (5 mm Hg per dose/L) and displayed small enflurane readings (0.1% per dose/L) when no enflurane was present. The Model 6000 unit showed CO₂ readings when no CO₂ was present (5 mm Hg per dose/L). Neither the Raman spectrometer, the infrared spectrometers, nor the piezoadsorptive analyzer we tested showed an artifactual effect of albuterol propellant on any of its readings. Simulation and clinical tests demonstrated that a single dose of albuterol propellant into a breathing circuit at the onset of inspiration resulted in concentrations of 0.8 and 0.3 dose/L, respectively. The phenomenon may be clinically useful, by allowing the anesthetist to verify the uptake of an inhalant into a patient.     

The effects of bronchodilator-inhaler aerosol propellants on respiratory gas monitors

Spurious readings from a mass spectrometer have been reported following the administration of aerosol bronchodilators. We quantified the response of various respiratory gas analyzers to the aerosol propellant of albuterol inhalant (Proventil). The mass spectrometer systems tested, two Advantage systems, a SARA system, and a Model 6000 Ohmeda system, all displayed artifactual readings in response to the albuterol propellant. Each metered dose of the Proventil brand of albuterol contains 4 ml of Freon 11 (trichloromonofluoromethane) and 11 ml of Freon 12 (dichlorodifluoromethane). The concentration of propellant was expressed in doses/L, where each liter of gas contains 0.4 vol % of Freon 11 and 1.1 vol % of Freon 12 per dose. In proportion to the concentration of albuterol propellant, the two Advantage systems showed substantial readings of isoflurane (%) when no isoflurane was present (13% and 16% per dose/L) and reduced readings of enflurane (−8% and −10% per dose/L) and carbon dioxide (CO₂) (−3 and +5 mm Hg per dose/L). The SARA system showed substantial CO₂ readings when no CO₂ was present (5 mm Hg per dose/L) and displayed small enflurane readings (0.1% per dose/L) when no enflurane was present. The Model 6000 unit showed CO₂ readings when no CO₂ was present (5 mm Hg per dose/L). Neither the Raman spectrometer, the infrared spectrometers, nor the piezoadsorptive analyzer we tested showed an artifactual effect of albuterol propellant on any of its readings. Simulation and clinical tests demonstrated that a single dose of albuterol propellant into a breathing circuit at the onset of inspiration resulted in concentrations of 0.8 and 0.3 dose/L, respectively. The phenomenon may be clinically useful, by allowing the anesthetist to verify the uptake of an inhalant into a patient.     

Radial artery cannulation: A comparison of 15.2- and 4.45-cm catheters

Eighty-nine patients were studied prospectively to compare the incidence of postdecannulation arterial thrombosis and ischemic complications associated with percutaneous insertion of two different radial artery catheters. Patients scheduled for peripheral vascular surgery were randomized to receive a 15.2-cm (6 in, Argon Medical Corp.) or 4.45-cm (1.75 in, Arrow International, Inc.) 20-gauge, Teflon catheter. Extremity blood flow was evaluated prior to cannulation and again after decannulation with the modified Allen's test, pulse-volume plethysmography, and Doppler ultrasound. The incidence of postdecannulation radial artery occlusion for 15.2-cm catheters was significantly less than for 4.45-cm catheters (4 of 45 cases versus 11 of 44 cases,p=0.05). No case of temporary or permanent ischemic injury occurred. Radial artery transfixion (16 of 45 cases versus 5 of 44 cases,p=0.01) and hematoma formation (5 of 45 cases versus 0 of 44 cases,p=0.02) occurred more frequently during insertion of 15.2-cm catheters than 4.45-cm catheters. The number of arterial punctures during catheter insertion and the duration of cannulation were similar for both groups. Of the 8 patients with positive modified Allen's test who underwent radial artery cannulation, one suffered arterial occlusion. Radial artery cannulation with a 15.2-cm catheter was associated with a lower incidence of postdecannulation radial artery thrombosis than cannulation with the 4.45-cm catheter. Radial artery cannulation with longer catheters (>5.0 cm) appears to be a safe practice.     

An improved nasal prong apparatus for end-tidal carbon dioxide monitoring in awake,sedated patients

We describe and evaluate a new apparatus that monitors end-tidal carbon dioxide (PetCO₂) and augments the inspired oxygen concentration in awake, sedated patients. The unit was evaluated for its effectiveness as an oxygenation device and its accuracy as a predictor of PaCO₂ through the correlation of PaCO₂ withPetCO₂. Twenty cardiac surgical patients, physical status ASA 2–4, participated in this study. ThePetCO₂ monitoring device consisted of a dual-prong nasal oxygen cannula and a 14-gauge intravenous catheter that was inserted into one limb of the oxygen supply tubing and connected to a Datex gas analyzer (Datex Instrumentation Corp, Helsinki, Finland) to measurePetCO₂. The cross-over passage between the prongs was intentionally blocked with the end of a wooden-core cotton swab. The oxygen flow rates were randomly varied (2, 4, and 6 L/min) every 5 minutes, and values forPetCO₂ as well as arterial blood samples for analysis of PaCO₂ and PaO₂ were obtained at the end of each 5-minute period. The accuracy of the system was assessed by comparing the PaCO₂-PetCO₂ differences (bias) at each oxygen flow rate. The ratios ofPetCO₂ compared with PaCO₂ were 0.98, 0.94, and 0.85, with correlation coefficients ofr=0.81, 0.85, and 0.63, respectively. The PaO₂ values were 114, 154, and 183 mm Hg for the corresponding nasal oxygen flow rates of 2, 4, and 6 L/min, respectively. This study indicates that this modified nasal cannula provides supplemental oxygen adequately and yields a satisfactory reflection of the PaCO₂ depending on the oxygen flow rate delivered.     

Carbon dioxide embolism with severe hypotension as an initial symptom during laparoscopy: a case report

Laparoscopy is widely used because it induces minimal postoperative pain and facilitates rapid recovery. However, carbon dioxide (CO₂) embolism is a rare but potentially fatal complication of laparoscopic surgery. Earlier reports have shown that decreased end-tidal CO₂ (ETCO₂) and increased partial pressure of CO₂ might be useful indicators of CO₂ embolism. We herein report a case of CO₂ embolism after the freed bladder neck was released during laparoscopic radical prostatectomy. Sudden hemodynamic disorder and increased ETCO₂ combined with immediate arterial blood gas analysis led us to suspect CO₂ embolism, which was confirmed by the aspiration of foamy blood from the central venous catheter. The patient was successfully resuscitated and recovered well. This case illustrates that hemodynamic collapse accompanied by increased ETCO₂ can indicate CO₂ embolism.     

Optimum operating parameters of CO2 sorption in turbulent fluidized bed regime using potassium carbonate supported on gamma alumina solid sorbent

The promising solid sorbent, potassium carbonate (K₂CO₃) supported on gamma alumina (γ-Al₂O₃) was prepared through impregnation by insertion into the sorption turbulent riser to determine the optimum operating parameters. A sorption temperature of 60 °C, superficial gas velocity of 0.22 m s⁻¹, and initial sorbent loading of 5 g were determined to be the optimum conditions so that 93 percent of the actual loaded K₂CO₃ could react with CO₂ to obtain the highest CO₂ sorption capacity at 279.95 mg of CO₂/g of K₂CO₃. 2³ factorial design plus center points were used to analyze the result of the main effect and interaction between the operating parameters. The sorption temperature, superficial gas velocity, and sorbent loading all impacted the response parameter. From the obtained interpretation, interaction between sorption temperature and superficial gas velocity, as well as between sorption temperature and initial sorbent loading, portrayed statistically significant effects on CO₂ capture capacity. Calculations showed that concentration of treated gas was greatly reduced. This distinguished breakthrough behavior provided a step toward designing a continuous reactor to maximize CO₂ capture. However, one major obstacle for this design was the persisting formation of hydrated potassium dawsonite, a side product of conventional heat regeneration.

The promising solid sorbent, potassium carbonate (K₂CO₃) supported on gamma alumina (γ-Al₂O₃) prepared through impregnation was inserted into the sorption turbulent riser to determine the optimum operating parameters.     

Validation of air tonometric measurement of gastric regional concentrations of CO2 in critically ill septic patients

Objective: To evaluate the accuracy of continuous air tonometry (Tonocap, Tonometric Division, Instrumentarium, Helsinki, Finland). Design: The accuracy of air tonometry was tested by comparing it with conventional saline tonometry in mechanically ventilated, critically ill septic patients and in vitro determining the partial pressure of carbon dioxide (PCO₂) of humidified gases with known concentrations of CO₂. Setting: A mixed intensive care unit in a university hospital. Patients: 16 mechanically ventilated patients with sepsis. Measurements and results: Two gastric tonometer catheters (TRIP NGS catheter, Tonometric Division, Instrumentarium, Helsinki, Finland) were introduced into the patients' stomachs. The control catheter was used as a conventional saline tonometer and the other catheter was used with the Tonocap monitoring device. A total of 153 paired measurements was made and analysed according to Bland and Altman. The mean difference between air PCO₂ and saline PCO₂ values (bias), the standard deviation of the differences (precision), and the Pearson correlation coefficient between air PCO₂ and saline PCO₂ were calculated. The data on patients were pooled and calculated for different cycle times. The mean bias (kPa) was ?0.02 with a 10-min cycle time, 0.31 with 15 min, 0.56 with 30 min and 0.21 with 60-min. The precisions were 0.39, 0.54, 0.44 and 0.76, respectively. Pearson correlation coefficients were 0.93, 0.97, 0.95 and 0.82, respectively (p < 0.0001). In vitro tonometry with the Tonocap was performed in a gas chamber fully saturated with known CO₂ concentrations. The clinically important 10-min cycle time was tested with 5 Tonocap monitors. Except for the first 10-min cycle time, PCO₂ values determined by the Tonocap monitoring systems were comparable to known CO₂ concentrations. Conclusions: The accuracy of Tonocap continuous air tonometry is close to that of conventional saline tonometry. Moreover, the clinically important 10-min cycle time with air tonometry correlated very well with saline tonometry and the time response with air tonometry was short.     

Veno-venous extracorporeal CO2 removal for the treatment of severe respiratory acidosis: pathophysiological and technical considerations

Introduction

While non-invasive ventilation aimed at avoiding intubation has become the modality of choice to treat mild to moderate acute respiratory acidosis, many severely acidotic patients (pH <7.20) still need intubation. Extracorporeal veno-venous CO₂ removal (ECCO₂R) could prove to be an alternative. The present animal study tested in a systematic fashion technical requirements for successful ECCO₂R in terms of cannula size, blood and sweep gas flow.

Methods

ECCO₂R with a 0.98 m² surface oxygenator was performed in six acidotic (pH <7.20) pigs using either a 14.5 French (Fr) or a 19Fr catheter, with sweep gas flow rates of 8 and 16 L/minute, respectively. During each experiment the blood flow was incrementally increased to a maximum of 400 mL/minute (14.5Fr catheter) and 1000 mL/minute (19Fr catheter).

Results

Amelioration of severe respiratory acidosis was only feasible when blood flow rates of 750 to 1000 mL/minute (19Fr catheter) were used. Maximal CO₂-elimination was 146.1 ± 22.6 mL/minute, while pH increased from 7.13 ± 0.08 to 7.41 ± 0.07 (blood flow of 1000 mL/minute; sweep gas flow 16 L/minute). Accordingly, a sweep gas flow of 8 L/minute resulted in a maximal CO₂-elimination rate of 138.0 ± 16.9 mL/minute. The 14.5Fr catheter allowed a maximum CO₂ elimination rate of 77.9 mL/minute, which did not result in the normalization of pH.

Conclusions

Veno-venous ECCO₂R may serve as a treatment option for severe respiratory acidosis. In this porcine model, ECCO₂R was most effective when using blood flow rates ranging between 750 and 1000 mL/minute, while an increase in sweep gas flow from 8 to 16 L/minute had less impact on ECCO₂R in this setting.     

Radial artery cannulation: A comparison of 15.2- and 4.45-cm catheters

Eighty-nine patients were studied prospectively to compare the incidence of postdecannulation arterial thrombosis and ischemic complications associated with percutaneous insertion of two different radial artery catheters. Patients scheduled for peripheral vascular surgery were randomized to receive a 15.2-cm (6 in, Argon Medical Corp.) or 4.45-cm (1.75 in, Arrow International, Inc.) 20-gauge, Teflon catheter. Extremity blood flow was evaluated prior to cannulation and again after decannulation with the modified Allen's test, pulse-volume plethysmography, and Doppler ultrasound. The incidence of postdecannulation radial artery occlusion for 15.2-cm catheters was significantly less than for 4.45-cm catheters (4 of 45 cases versus 11 of 44 cases,p=0.05). No case of temporary or permanent ischemic injury occurred. Radial artery transfixion (16 of 45 cases versus 5 of 44 cases,p=0.01) and hematoma formation (5 of 45 cases versus 0 of 44 cases,p=0.02) occurred more frequently during insertion of 15.2-cm catheters than 4.45-cm catheters. The number of arterial punctures during catheter insertion and the duration of cannulation were similar for both groups. Of the 8 patients with positive modified Allen's test who underwent radial artery cannulation, one suffered arterial occlusion. Radial artery cannulation with a 15.2-cm catheter was associated with a lower incidence of postdecannulation radial artery thrombosis than cannulation with the 4.45-cm catheter. Radial artery cannulation with longer catheters (>5.0 cm) appears to be a safe practice.     

Monitoring of right ventricular function using a conventional slow response thermistor catheter

Objective To investigate whether determination of right ventricular end-diastolic volume (RVEDV) and right ventricular ejection fraction (RVEF) can be performed with reasonable accuracy and reproducibility using a conventional slow response thermistor pulmonary artery catheter (CPAC) applying an adaptive algorithm.Design To study RVEDV and RVEF simultaneously with pulmonary artery catheters equipped with slow and fast response thermistors (FRPAC) under a broad range of cardiac output.Setting Laboratory of Institute of Experimental Surgery, Technical University.Animals 11 anaesthetised piglets.Interventions Hypovolemia (V–) was induced by withdrawal of blood up to 50 ml/kg, hypervolemia (V+) was produced by retransfusing blood and adding up to 30 ml/kg hydroxyethyl starch. In 5 animals in phases V–and V+ beta-adrenergic stimulation was achieved with dobutamine. Finally pulmonary artery hypertension was induced by infusion of small air bubbles.Measurements and results Cardiac output (CO), RVEDV and RVEF were determined simultaneously with FRPAC and CPAC placed in the same pulmonary artery branch. Measurements were repeated 8 times sequentially in steady state normovolemia. A total of 130 measurements could be analysed. The coefficient of variation was 6.7±4.2 for CO_(FRPAC) and 4.6±1.7% for CO_(CPAC); for RVEF it was 9.7±6.2% (FRPAC) and 9.9±3.9% (CPAC); for RVEDV it was 11.6±4.8% (FRPAC) and 8.54±3.2 (CPAC). Mean difference (bias) was 0.06±0.39 l/min for CO measured with both methods, 19±35 ml for RVEDV and –3.3±6.5% for RVEF. CO_(CPAC) displayed a strong correlation to CO_(FRPAC) (R=0.97,p=0.001) as well as RVEF (R for RVEF_(CPAC) versus RVEF_(FRPAC)=0.90,p=0.001). R for RVEDV_(CPAC) versus RVEDV_(FRPAC) was 0.67,p=0.001. We conclude that this animal study demonstrates good agreement between RVEF and RVEDV obtained with catheters equipped with a fast response thermistor or with a conventional slow response thermistor allowing accurate monitoring of right ventricular function with a conventional pulmonary artery catheter.Supported in part by grants from BMFT (grant number 0706908)     

Review of intracoronary Doppler catheters

During the last 20 years several types of Doppler catheters have been developed and applied to the measurement of coronary blood flow velocity in man. Validation studies in the laboratory and in animals have shown that these catheters can accurately measure velocity from a small sample volume beside or ahead of the catheter tip. The Doppler transducers have been miniaturized enough (<1 mm dia) to be mounted on subselective coronary catheters or balloon angioplasty catheters without compromising any of the normal catheter functions. Good quality, high fidelity velocity signals have been recorded from many sites within the coronary circulation of patients during coronary arteriography and balloon angioplasty. Coronary flow reserve measured with Doppler catheters is a physiologic index of the severity of a stenosis which, when carefully measured, can be used for assessing lesions, planning treatment, and evaluating the success of interventions.     

Pressure-guided positioning of bicaval dual-lumen catheters for venovenous extracorporeal gas exchange

Purpose

Bicaval dual-lumen catheters allow for single-site cannulation venovenous extracorporeal gas exchange and facilitate early mobilization of patients. Using these catheters blood is drained from the superior and inferior venae cavae, pumped through a respiratory membrane, and returned into the right atrium. The insertion of these catheters is challenging as their correct positioning is fundamental to reduce recirculation and avoid severe complications. We describe here a new technique for the positioning of bicaval dual-lumen catheters.

Materials and methods

The right internal jugular vein was percutaneously cannulated in nine sheep. The distance between skin and tricuspid valve was measured from the point of pressure change in the waveform of a Swan–Ganz catheter being retracted from the right ventricle into the right atrium. The atrium-tricuspid valve-ventricle axis was determined by observing the fluctuations of the tip of the Swan–Ganz entering the ventricle during fluoroscopy. A bicaval dual-lumen catheter was placed on the basis of these evaluations and connected to an extracorporeal respiratory support system.

Results

The position of the catheter was verified at necropsy approximately 18 h after insertion. In all cases the catheter was correctly placed, with the central port situated in front of the tricuspid valve.

Conclusions

The described technique may help to position bicaval dual-lumen catheters for venovenous extracorporeal gas exchange without the use of transesophageal echocardiography or contrast media during fluoroscopy.     

Low-flow CO2 removal integrated into a renal-replacement circuit can reduce acidosis and decrease vasopressor requirements

Introduction

Lung-protective ventilation in patients with ARDS and multiorgan failure, including renal failure, is often paralleled with a combined respiratory and metabolic acidosis. We assessed the effectiveness of a hollow-fiber gas exchanger integrated into a conventional renal-replacement circuit on CO₂ removal, acidosis, and hemodynamics.

Methods

In ten ventilated critically ill patients with ARDS and AKI undergoing renal- and respiratory-replacement therapy, effects of low-flow CO₂ removal on respiratory acidosis compensation were tested by using a hollow-fiber gas exchanger added to the renal-replacement circuit. This was an observational study on safety, CO₂-removal capacity, effects on pH, ventilator settings, and hemodynamics.

Results

CO₂ elimination in the low-flow circuit was safe and was well tolerated by all patients. After 4 hours of treatment, a mean reduction of 17.3 mm Hg (−28.1%) pCO₂ was observed, in line with an increase in pH. In hemodynamically instable patients, low-flow CO₂ elimination was paralleled by hemodynamic improvement, with an average reduction of vasopressors of 65% in five of six catecholamine-dependent patients during the first 24 hours.

Conclusions

Because no further catheters are needed, besides those for renal replacement, the implementation of a hollow-fiber gas exchanger in a renal circuit could be an attractive therapeutic tool with only a little additional trauma for patients with mild to moderate ARDS undergoing invasive ventilation with concomitant respiratory acidosis, as long as no severe oxygenation defects indicate ECMO therapy.