Sean C. Skinner

Comparison of end-tidal PCO2 and average alveolar expired PCO2 during positive end-expiratory pressure

The measurement of average alveolar expired PCO2 (PAECO2) weights each PCO2 value on the alveolar plateau of the CO2 expirogram by the simultaneous change in exhaled volume.PAECO2 can be determined from a modified analysis of the Fowler anatomic dead space (VDANAT). In contrast, end-tidal PCO2 (PETCO2) only measures PCO2 in the last small volume of exhalate. In conditions such as mechanical ventilation with positive end-expiratory pressure (PEEP), where the alveolar plateau can have a significant positive slope, we questioned how much PETCO2 could overestimate PAECO2. Accordingly, in six anesthetized ventilated dogs, we digitally measured and processed tidal PCO2 and flow to determine VD (ANAT). We determined PETCO2 and PAECO before and after the application of 7.6 cm H2 O PEEP. Alveolar dead space to tidal volume fraction (VD/VT) was determined by [arterial PCO2-alveolar PCO2]/arterial PCO2, where alveolar PCO (2) was determined by either PETCO2 or PAECO2. During baseline ventilation, PETCO2 was 3.4 mm Hg (approximately 11%) greater than PAECO2. Because PEEP significantly increased the slope of the alveolar plateau from 28 to 74 mm Hg/L, the difference between PETCO2 and PAECO2 significantly increased to 6.6 mm Hg (approximately 20% difference. The concurrent increase in VDANAT during PEEP decreased alveolar tidal volume and tended to limit the overestimation of PETCO (2) compared to PAECO2. When alveolar PCO2 was estimated by PETCO2, alveolar VD/VT was 18%, compared to an alveolar VD/VT of 26% when alveolar PCO (2) was estimated by PAECO2. This difference was significantly magnified during PEEP ventilation. The overestimation of PAECO2 by PETCO2 can result in a falsely high assessment of overall alveolar PCO2. Moreover, the use of PETCO (2) to estimate alveolar PCO2 in the determination of the alveolar dead space fraction can result in falsely low and even negative values of alveolar dead space. (Anesth Analg 1996;82:368-73)

Improved survival in venovenous vs venoarterial extracorporeal membrane oxygenation for pediatric noncardiac sepsis patients: a study of the Extracorporeal Life Support Organization registry

BACKGROUND/PURPOSE There are few studies comparing venoarterial (VA) and venovenous (VV) extracorporeal membrane oxygenation (ECMO) in pediatric noncardiac sepsis patients. METHODS Following approval, we reviewed the Extracorporeal Life Support Organization registry data from 1990 to 2008 for patients 0 to 18 years with a diagnosis of sepsis and without diagnosis of congenital heart disease. Survival to discharge was compared between VA and VV ECMO using χ(2) analysis and multivariable logistic regression. RESULTS Four thousand three hundred thirty-two ECMO runs were reviewed, 3256 VA (75%) and 1076 VV (25%). A majority of VA modality was noted in each decade studied. Overall survival was 68% and was higher in VV (79%) than in VA ECMO (64%, P < .001). Survival decreased with increasing age (73% in newborns ≤ 1 month, 40% in children 1 month to 12 years, and 32% in adolescents >12 years, P < .001). VA ECMO had increased mortality risk after adjustment for age, use of vasoactive agents, and advanced respiratory support (odds ratio, 2.06; 95% confidence interval, 1.74-2.44; P < .001). CONCLUSIONS These data demonstrate improved survival in VV vs. VA ECMO in select pediatric septic patients without congenital heart disease. When technically feasible, physicians should consider VV ECMO as first therapeutic choice in this patient population.

The abdominal compartment syndrome in patients with burn injury.

Abstract Introduction: Intra-abdominal hypertension (IAH) and subsequent abdominal compartment syndrome (ACS) in burned patients is common. This sequence of events typically occurs in patients with larger burns receiving high volume fluid resuscitation. Methods: A review of the literature was performed. The National Library of Medicine (PUBMED) was queried for “Burn” and “Abdominal Compartment Syndrome”. Twenty-nine articles were retained for study. Results: Abdominal pressure monitoring is appropriate in all patients with burns that require significant volume resuscitation (>30% total burned surface area- TBSA). Prevention of ACS in burns includes limiting fluid resuscitation, burn escharotomy, and percutaneous drainage when abdominal pressures are reaching perilous levels. Treatment includes all of the above and in addition, decompressive laparotomy when needed. However, despite decompressive laparotomy, mortality rates among burn victims with ACS remain unacceptably high. Conclusion: Increasing amounts of volume delivery are associated with an increased risk of IAH. Therefore, intra-abdominal pressure should be monitored in all burn patients requiring massive fluid resuscitation. Escharotomy, paracentesis, and decompressive laparotomy may all be needed to counter the side effects of appropriate fluid resuscitation in the severely burned patient. Nevertheless, the prognosis in burn patients developing ACS is grim.

How does experimental pulmonary embolism decrease CO2 elimination

To test how large pulmonary embolism changes non-steady state CO2 kinetics, the right pulmonary artery (RPA) was occluded in 5 anesthetized, ventilated, thoracotomized dogs. By 1 min after RPA occlusion, CO2 volume exhaled per breath (VCO2,br) decreased from 9.3 +/- 2.8 to 7.0 +/- 2.6 ml and end-tidal PCO2 (PETCO2) decreased from 28.7 +/- 4.2 to 21.8 +/- 3.3 Torr. During the ensuing 70 min, VCO2,br increased back to baseline but PETCO2 was still 13% less than baseline. Both PaCO2 (41.5 +/- 1.7 to 55.1 +/- 8.1 Torr) and PvCO2 (48.2 +/- 1.9 to 62.8 +/- 6.5 Torr) steadily increased and approached equilibrium by 45 min of RPA occlusion. Cardiac output did not significantly change. In summary, RPA occlusion immediately decreased VCO2,br by 25%, due mostly to increased alveolar VD (VDalv). Then, VCO2,br recovered back to baseline as CO2 accumulated in tissues and lung. In contrast, elevated VDalv caused persistent decreased PETCO2, which did not detect recovery of VCO2,br nor increase in PaCO2 during RPA occlusion.

A Middle Fidelity Model Is Effective in Teaching and Retaining Skill Set Needed to Perform a Laparoscopic Pyloromyotomy

INTRODUCTION An inanimate technical skills trainer for laparoscopic pyloromyotomy (LP) has not been described. A middle fidelity model, reproducing the three consistent steps in LP, was developed as a component of a teaching module for surgical residents, and tested on medical students, residents, and pediatric surgeons. MATERIALS AND METHODS In the first phase of the study, a cohort of 29 pediatric surgeons used the LP model and completed questionnaires about the models realism and accuracy. Descriptive statistics were used to analyze questionnaire responses. Chi-square tests were performed to determine if level of experience influenced responses. For the second phase of the study, medical students and surgical residents individually participated in the training of cognitive knowledge about hypertrophic pyloric stenosis and skills acquisition for LP. Subject testing consisted of simulator task performance and multiple-choice quiz administration immediately after training and repeated at 8 weeks after training. Data were analyzed by using paired sample t-tests and one-way analyses of variance (ANOVA). RESULTS The pediatric surgeons agreed that the model accurately simulated essential components of the pyloromyotomy, and that the model would be an excellent tool to introduce surgeons to LP. A total of 26 students and early surgical residents completed the training and testing. Knowledge-based test performance improved from pre- to postinstruction by 17.45 [standard error of the mean (SEM) + 3.5] (P < 0.001) and from preinstruction to 8 weeks by 4.54 (SEM = 3.2) (P = 0.17). Mean improvement in time of simulator task performance was 85.2 +/- 75.4 seconds. Based on a one-way ANOVA, higher level of training was associated with decreased mean times (P = 0.04). CONCLUSIONS Face and content validities of the simulation were demonstrated by the pediatric surgeons. An effective training experience was demonstrated with medical students and residents. At 2 months, simulator task-completion rates and task-performance times showed technical skills were retained, whereas, based on test scores, cognitive knowledge was not as well retained.

Carbon dioxide elimination measures resolution of experimental pulmonary embolus in dogs

Patients with severe pulmonary embolism can suffer progressive hypercapnia refractory to supramaximal mechanical ventilation, and may require open-thoracic or transvenous emergency embolectomy in addition to anticoagulation and/or thrombolysis. The functional recovery of gas exchange would be signaled by an increase in pulmonary CO2 elimination and decrease in CO2 retention; such data could guide the course of operative embolectomy. Accordingly, we studied five chloralose-urethane anesthetized, mechanically ventilated dogs with open thoraces in which the right pulmonary arteries (RPAs) were reversibly occluded with cloth snares. After waiting for steady state, we abruptly released the snare to restore RPA perfusion and experimentally simulate resolution of pulmonary embolism. For 70 min we serially measure the CO (2) volume exhaled per breath (VCO2,br), arterial, mixed venous, and end-tidal PCO2 (PaCO2, PVCO2, PETCO2), cardiac output (QT), and the alveolar dead space fraction (VDalv/VTalv = [PaCO2 - PETCO2]/PaCO2). RPA reperfusion caused VCO2,br to significantly and abruptly increase from 8.9 +/- 2.7 to 11.6 +/- 3.6 mL; 70 min later VCO2,br had returned to baseline. PaCO2 and PVCO2 steadily decreased during 70 min of RPA reperfusion. PETCO (2) increased from 25 +/- 5 to 33 +/- 5 mm Hg immediately after RPA reperfusion, as VDalv/VTalv decreased from 54% +/- 10% to 32% +/- 12%, but PETCO2 was still significantly greater than baseline at 70 min of RPA reperfusion. QT did not significantly change. We conclude that intraoperative measurement of VCO (2),br should immediately detect and follow the resolution of CO2 retention in the lung and peripheral tissues after RPA reperfusion. PETCO2 could not detect the decrease of VCO2,br back to baseline because PETCO2 does not measure exhaled volume or the PCO2 waveform. (Anesth Analg 1996;83:247-53)

Measurement of blood CO2 concentration with a conventional PCO2 analyzer

OBJECTIVES CO2 content can be determined from the Pco2 in an acidified (forces all CO2 into solution) and diluted blood sample. However, Pco2 concentrations measured in conventional blood gas analyzers are only correct for samples with a significant buffer capacity (such as whole blood), so that mixing with the Pco2 in the rinse solution and tubing walls does not significantly change the sample Pco2. This study describes a calibration method and validation data for the Radiometer Medical ABL2 CO2 electrode system to accurately measure unbuffered blood samples used in the determination of blood CO2 content (or other aqueous fluids). DESIGN Prospective, criterion standard. SETTING Laboratory. MEASUREMENTS AND MAIN RESULTS Blood samples (0.4 mL) were acidified and diluted with 0.2 M lactic acid. After measuring Pco2, CO2 content was calculated using the CO2 solubility coefficient and the dilution factor of 20. CO2 content was determined in a series of sodium carbonate (Na2CO3) solutions spanning the physiologic range of CO2 content. Regression of the measured vs. the actual CO2 content data generated a straight line with a slope of 0.796 and y-intercept of 12.5 (r2 = .99; n = 48). These coefficients were successfully used to correct CO2 content determined in blood samples into which graduated amounts of sodium carbonate were added. CONCLUSIONS This calibration procedure allows accurate measurement of Pco2 in aqueous samples using the Radiometer ABL2 electrode system, and should be applicable to other blood gas analyzers. Necessary syringes and chemicals are readily available, the method is fast and simple, and the sample volume is small. In the practice of critical care medicine, accurate Pco2 measurement in aqueous acidified and diluted blood provides direct determination of blood CO2 content (useful in calculations of modified Fick cardiac output or tissue CO2 production). Determinations of absolute CO2 content in blood requiring complex methodology are not necessary. In addition, accurate measurement of aqueous gastric Pco2 can help determine gastric pH, which is an important marker of tissue perfusion.

Epithelioid hemangioendothelioma encasing the left brachiocephalic vein

Epithelioid hemangioendotheliomas are rare vascular tumors, often arising from medium to large veins in the extremities. Symptoms of these tumors vary depending upon location. Rarely, tumors may arise in chest and involve large vessels in the mediastinum. We present a case of a 17-year-old male presenting with compressive symptoms of the left upper extremity who was found to have a large epithelioid hemangioendothelioma encasing the left brachiocephalic vein.

Laparoscopic imaging of pancreatic agenesis with congenital absence of the gallbladder.

FIGURE 2. Laparoscopic image shows the expected location of the tail of the pancreas bound by the splenic vein (black arrow), spleen (white arrow), inferior mesenteric vein (#), and the stomach ( ). FIGURE 3. Laparoscopic image shows congenital absence of the gall bladder. Porta hepatis (black arrow), first portion of the duodenum (white arrow), and hepatic flexure of colon ( ). FIGURE 1. Laparoscopic image shows the expected location of the head of the pancreas bounded by the left gastric artery (white arrow), stomach (black arrow), C-loop of duodenum ( ), and periaortic lymph nodes (#).