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At least 163 records · Page 9Linked to original sources

PubMed2006

Precystectomy nomogram for prediction of advanced bladder cancer stage.

OBJECTIVE: To evaluate precystectomy prediction of pT and pN stages at cystectomy. METHODS: Multivariate logistic regression analyses modelled variables of 726 evaluable patients treated with radical cystectomy and bilateral pelvic lymphadenectomy. The first set of models predicted pT(3-4) stage at cystectomy, and the second set predicted pN(1-3) stages at cystectomy. Transurethral resection (TUR) predictors consisted of 2002 T stage, 1973 WHO tumour grade, presence of carcinoma in situ, age, gender, and delivery of neo-adjuvant chemotherapy. The area under the ROC curve quantified nomogram accuracy. Two hundred bootstrap resamples were used to reduce overfit bias. RESULTS: At TUR, 11% of patients were staged as pT(3-4) versus 42% at cystectomy. Lymph node metastases were found in 24% of patients at cystectomy (pN(1-3)). The multivariate pT(3-4) nomogram was 75.7% accurate versus 71.4% for TUR T stage. The multivariate pN(1-3) nomogram was 63.1% accurate versus 61.0% for TUR T stage. CONCLUSION: Multivariate nomograms are not perfect, but they do predict more accurately than TUR T stage alone.

Adult↗

PubMed2006

Prognostic nomogram for renal insufficiency after radical or partial nephrectomy.

PURPOSE: We analyzed prognostic factors to predict renal insufficiency after partial or radical nephrectomy. We developed and performed internal validations of a postoperative nomogram for this purpose. We used a prospectively updated renal tumor database of more than 1,500 patients. MATERIALS AND METHODS: From July 1989 to October 2003, 161 partial nephrectomies and 857 radical nephrectomies performed at Memorial Sloan-Kettering Cancer Center for renal cortical tumors were analyzed. Computerized tomography images were reviewed by a single radiologist. Kidney volume was calculated using the ellipsoid formula, V = L1 x L2 x L3 x pi/6, where V represents volume and L represents length. Renal insufficiency was defined by 2 serum creatinine values greater than 2.0 mg/dl at least 1 month postoperatively. Tumor histology was not an exclusion criterion and yet we excluded cases of bilateral synchronous disease. Prognostic variables were preoperative serum creatinine, American Society of Anesthesiologists score, percent change in kidney volume after surgery, and patient age and sex. RESULTS: Renal insufficiency was noted in 105 of the 857 patients with radical nephrectomy (12.3%) and in 6 of the 161 with partial nephrectomy (3.7%) studied. Patients had a median followup of 21.2 months (maximum 157.9). The 7-year probability of freedom from renal insufficiency in the cohort was 79.1% (95% CI 74.6 to 83.6). The nomogram was designed based on a Cox proportional hazards regression model. Following internal statistical validation nomogram predictions appeared accurate and discriminating with a concordance index of 0.835. CONCLUSIONS: A nomogram was developed that can predict the 7-year probability of renal insufficiency in patients undergoing radical or partial nephrectomy.

Adolescent↗

PubMed2006

Defining high risk prostate cancer with risk groups and nomograms: implications for designing clinical trials.

PURPOSE: Death from prostate cancer is usually preceded by metastases and it usually occurs in men with high risk disease who experienced biochemical failure with a short prostate specific antigen doubling time. We developed a model for determining disease specific survival in prostate cancer. MATERIALS AND METHODS: We used the model for defining high risk prostate cancer that was developed by the Radiation Therapy Oncology Group and combined it with the Kattan nomogram for predicting the risk of metastases. We selected 414 Radiation Therapy Oncology Group intermediate and high risk patients who were treated with external beam radiotherapy alone. Excluded were patients with low risk disease. The Kaplan-Meier product limit method was used to estimate the probability of freedom from biochemical failure, overall survival and disease specific survival. RESULTS: A significant difference was observed in freedom from biochemical failure, disease specific survival and overall survival among the 3 tertiles created by the nomogram using the cutoff points less than 8.5%, 8.5% to 15% and greater than 15% (p <0.001, 0.0002 and 0.0003, respectively). Only the risk of metastases using the categorized nomogram score (less than 8.5% and 8.5% to 15% vs greater than 15%), not preradiotherapy prostate specific antigen or Radiation Therapy Oncology Group risk (Radiation Therapy Oncology Group 2 vs 3), was a significant predictor of disease specific and overall survival for intermediate/high risk patients and intermediate/high risk with 15% or less risk for metastases. CONCLUSIONS: We combined a risk group stratification scheme for disease specific survival with a nomogram predicting the risk of metastases and created a model that may be useful for designing phase III trials with metastases and disease specific survival as study end points.

Clinical Trials as Topic↗

PubMed2007

Development and external validation of an extended repeat biopsy nomogram.

PURPOSE: We hypothesized that the outcome of repeat biopsy could be accurately predicted. We tested this hypothesis in a contemporary cohort from 3 centers. MATERIALS AND METHODS: The principal cohort of 1,082 men from Hamburg, Germany was used for nomogram development as well as for internal 200 bootstrap validation in 721 and external validation in 361. Two additional external validation cohorts, including 87 men from Milan, Italy and 142 from Seattle, Washington, were also used. Predictors of prostate cancer on repeat biopsy were patient age, digital rectal examination, prostate specific antigen, percent free prostate specific antigen, number of previous negative biopsy sessions and sampling density. Multivariate logistic regression models were used to develop the nomograms. RESULTS: The mean number of previous negative biopsies was 1.5 (range 1 to 6) and the mean number of cores at final repeat biopsy was 11.1 (range 10 to 24). Of the men 370 (30.2%) had prostate cancer. On multivariate analyses all predictors were statistically significant (p < or =0.028). After internal validation the nomogram was 76% accurate. External validation showed 74% (Hamburg), 78% (Milan) and 68% (Seattle) accuracy. CONCLUSIONS: Relative to the previous nomograms (10 predictors or 71% accuracy) our tool relies on fewer variables (6) and shows superior accuracy in European men. Accuracy in American men is substantially lower. Racial, clinical and biochemical differences may explain the observed discrepancy in predictive accuracy.

Adult↗

PubMed2006

Development of a nomogram to predict probability of positive initial prostate biopsy among Japanese patients.

OBJECTIVES: Several nomograms for prostate cancer detection have recently been developed. Because the incidence of prostate cancer is lower among Asian men, nomograms based on Western populations cannot be directly applied to Japanese men. We, therefore, developed a model for predicting the probability of a positive initial prostate biopsy using clinical and laboratory data from a Japanese male population. METHODS: Data were collected from 834 Japanese male referrals who underwent initial prostate biopsies as individual screening. We analyzed age, total prostate-specific antigen (PSA) level, free/total PSA (f/t PSA) ratio, prostate volume, and digital rectal examination findings. Of these data, we randomly reserved 20% for study validation. Logistic regression analysis estimated relative risk, 95% confidence intervals, and P values. RESULTS: Independent predictors of a positive biopsy result included elevated PSA levels, decreased f/T PSA ratio, advanced age, small prostate volume, and abnormal digital rectal examination findings. We developed a predictive nomogram for an initial positive biopsy using these variables. The area under the receiver operating characteristic curve for the model was 81.8%, which was significantly greater than that of the prediction based on PSA alone (area under the receiver operating characteristic curve 67.8%). If externally validated, applying this model could reduce unnecessary biopsy procedures by 32% and reduce the overall need for prostate biopsies by 26%. CONCLUSIONS: In this study of a Japanese population, incorporating clinical and laboratory data into a prebiopsy nomogram significantly improved the prediction of prostate cancer compared with predictions based solely on the individual factors.

Aged↗

PubMed2006

Nomogram predictive of pathological inguinal lymph node involvement in patients with squamous cell carcinoma of the penis.

PURPOSE: In penile cancer the therapeutic benefits of early inguinal lymphadenectomy must be counterbalanced by the high rates of morbidity, postoperative complications and mortality. A relevant aim is optimizing the selection of the patients who could really have the highest survival advantage from inguinal lymphadenectomy, limiting the cases in which this surgery might be considered over treatment with a risk of severe complications. We generated a nomogram estimating the risk of pathological inguinal lymph node involvement according to clinical lymph node stage and pathological findings of the primary tumor. MATERIALS AND METHODS: We retrospectively collected the clinical and pathological data of 175 patients who had undergone surgical therapy for squamous cell carcinoma of the penis from 1980 to 2002 at 11 urological centers in northeastern Italy. A logistic regression model was used to construct the nomogram. RESULTS: The presence of palpable groin lymph nodes and the histological findings of vascular and/or lymphatic embolization were important predictors of metastatic inguinal lymph node involvement. The nomogram predicting the risk of metastatic lymph node involvement showed a good concordance index (0.876) and good calibration. CONCLUSIONS: The clinical stage of groin lymph nodes and pathological findings of penectomy specimens allowed us to generate a nomogram to predict the probability of metastatic lymph node involvement in patients with squamous cell carcinoma of the penis. The statistical model showed an excellent ability to identify the patients with lymph node metastases and good calibration.

Aged↗

PubMed2006

Preoperative nomogram predicting the 10-year probability of prostate cancer recurrence after radical prostatectomy.

An existing preoperative nomogram predicts the probability of prostate cancer recurrence, defined by prostate-specific antigen (PSA), at 5 years after radical prostatectomy based on clinical stage, serum PSA, and biopsy Gleason grade. In an updated and enhanced nomogram, we have extended the predictions to 10 years, added the prognostic information of systematic biopsy results, and enabled the predictions to be adjusted for the year of surgery. Cox regression analysis was used to model the clinical information for 1978 patients treated by two high-volume surgeons from our institution. The nomogram was externally validated on an independent cohort of 1545 patients with a concordance index of 0.79 and was well calibrated with respect to observed outcome. The inclusion of the number of positive and negative biopsy cores enhanced the predictive accuracy of the model. Thus, a new preoperative nomogram provides robust predictions of prostate cancer recurrence up to 10 years after radical prostatectomy.

Aged↗

PubMedDate not supplied

A nomogram to select the optimal treadmill ramp protocol in subjects with high exercise capacity: validation and comparison with the Bruce protocol.

PURPOSE: Guidelines suggest that individualized ramp protocols with treadmill times targeted between 8 and 12 minutes are most suitable to estimate exercise capacity. However, previous methods to determine individualized ramp rates and comparisons between ramp and standardized protocols have been limited to clinically referred populations. METHODS: Forty-three healthy volunteers [median (interquartile range), age 36 (30-41) years; 10 women] performed an individualized ramp and a Bruce treadmill exercise protocol in random order. The Veterans Specific Activity Questionnaire [VSAQ, resulting in metabolic equivalents (METs)VSAQ] combined with a modified variant of the VSAQ nomogram (resulting in METs(NOMOGRAM)) was used to individualize the ramp protocol. Exercise capacity estimated from speed and grade of the treadmill (METs(ESTIMATED)) and that derived from directly measured peak oxygen uptake (VO2) [METs(MEASURED)] were compared with the pretest estimates of exercise capacity. RESULTS: Median values for METs(VSAQ), METs(NOMOGRAM), METs(ESTIMATED), and METs(MEASURED) for the ramp protocol were 12.0 (10-12), 15.0 (14-16.5), 16.7 (15.9-17.8), and 15.2 (13.5-16.7), respectively. For the ramp protocol, all 43 participants achieved a treadmill time between 8 and 12 minutes, whereas with the Bruce protocol only 6 (14%) participants fell within this range (P < .0001). Peak VO2 [ramp: 53.1 (47.4-58.3) versus Bruce: 53.5 (48.7-58.3) mL/kg/min; P = .008] was slightly lower using the ramp protocol. CONCLUSIONS: The modified variant of the VSAQ nomogram is a useful tool to estimate an individual's exercise capacity and to select a treadmill ramp protocol to yield the recommended exercise duration for moderately to highly fit, healthy individuals. The individualized ramp and the Bruce protocols are similar with regard to directly measured peak VO2 achieved.

Adult↗

PubMed2006

Validation of a nomogram predicting the probability of lymph node invasion based on the extent of pelvic lymphadenectomy in patients with clinically localized prostate cancer.

OBJECTIVE: To develop a multivariate nomogram to predict the rate of lymph node invasion (LNI) in patients with clinically localized prostate cancer according to the extent of extended pelvic lymphadenectomy (PLND), which is associated with significantly higher rate of LNI. PATIENTS AND METHODS: The study comprised 781 consecutive patients (median age 66.6 years, range 45-85) treated with PLND and radical retropubic prostatectomy (RRP) for clinically localized prostate cancer. Their median (range) prostate-specific antigen (PSA) level was 7 (1.03-49.91) ng/mL, and their clinical stages were T1c in 433 (55.4%), T2 in 328 (42%) and T3 in 20 (2.6%). Biopsy Gleason sums were <or= 6 in 514 (65.8%), 7 in 204 (26.1%) and 8-10 in 63 (8.1%). Multivariate logistic regression models were used to test the association between predictors including PSA level, biopsy Gleason sum, clinical stage, number of nodes removed and the rate of LNI. Finally, regression coefficients were used to develop a nomogram, which was internally validated with 200 bootstrap re-samples. RESULTS: The median (range) number of lymph nodes removed was 14 (2-40); LNI was detected in 71 patients (9.1%). The univariate predictive accuracy for total PSA level, clinical stage, biopsy Gleason sum and number of total nodes removed and examined was 64.2%, 59.8%, 74% and 62.9%, respectively. Except for PSA (P = 0.2), all variables were statistically significant multivariate predictors of LNI at RRP (P <or= 0.001). A nomogram based on clinical stage, PSA level, biopsy Gleason sum and the number of total lymph nodes removed was 78.6% accurate, and 1.8% more accurate than a nomogram without the number of removed lymph nodes. CONCLUSIONS: The extent of PLND is directly related to the probability of LNI. The risk of LNI increases linearly, and is proportional to the number of nodes removed and examined. The effect of the increased probability of LNI is weighted more heavily in men with more advanced clinical stage and grade.

Aged↗

PubMed2005

Simple nomograms to calculate sample size in diagnostic studies.

OBJECTIVES: To produce an easily understood and accessible tool for use by researchers in diagnostic studies. Diagnostic studies should have sample size calculations performed, but in practice, they are performed infrequently. This may be due to a reluctance on the part of researchers to use mathematical formulae. METHODS: Using a spreadsheet, we derived nomograms for calculating the number of patients required to determine the precision of a test's sensitivity or specificity. RESULTS: The nomograms could be easily used to determine the sensitivity and specificity of a test. CONCLUSIONS: In addition to being easy to use, the nomogram allows deduction of a missing parameter (number of patients, confidence intervals, prevalence, or sensitivity/specificity) if the other three are known. The nomogram can also be used retrospectively by the reader of published research as a rough estimating tool for sample size calculations.

Diagnostic Techniques and Procedures↗

PubMed2005

Prediction of organ-confined prostate cancer: incremental value of MR imaging and MR spectroscopic imaging to staging nomograms.

PURPOSE: To assess retrospectively the incremental value of endorectal coil magnetic resonance (MR) imaging and combined endorectal MR imaging-MR spectroscopic imaging to the staging nomograms for predicting organ-confined prostate cancer (OCPC). MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study and issued a waiver of informed consent for review of the MR reports and clinical data. Between November 1, 1999, and November 1, 2004, 229 patients underwent endorectal MR imaging and 383 underwent combined endorectal MR imaging-MR spectroscopic imaging before radical prostatectomy. Mean patient age was 58 years (range, 32-74 years). MR studies were interpreted prospectively by 12 radiologists who were informed of patients' clinical data. On the basis of the MR reports, the risks of extracapsular extension, seminal vesicle invasion, and lymph node metastasis were scored retrospectively from 1 to 5; the highest score was subtracted from 6 to determine a score (from 1 to 5) for the likelihood of OCPC on MR studies. The staging nomograms were used to calculate the likelihood of OCPC on the basis of serum prostate-specific antigen level, Gleason grade at biopsy, and clinical stage. Histopathologic findings constituted the reference standard. Logistic regression was used to estimate the multivariable relations between OCPC and MR findings. The area under the receiver operator characteristic curve was calculated for each model. The jackknife method was used for bias correction. RESULTS: MR findings contributed significant incremental value (P </= .02) to the nomograms in the overall study population. The contribution of MR findings was significant in all risk groups but was greatest in the intermediate- and high-risk groups (P < .01 for both). Accuracy in the prediction of OCPC with MR was higher when MR spectroscopic imaging was used, but the difference was not significant. CONCLUSION: Endorectal MR imaging and combined endorectal MR imaging-MR spectroscopic imaging contribute significant incremental value to the staging nomograms in predicting OCPC.

Adult↗

PubMed2006

Nomograms provide improved accuracy for predicting survival after radical cystectomy.

AIMS: To develop multivariate nomograms that determine the probabilities of all-cause and bladder cancer-specific survival after radical cystectomy and to compare their predictive accuracy to that of American Joint Committee on Cancer (AJCC) staging. METHODS: We used Cox proportional hazards regression analyses to model variables of 731 consecutive patients treated with radical cystectomy and bilateral pelvic lymphadenectomy for bladder transitional cell carcinoma. Variables included age of patient, gender, pathologic stage (pT), pathologic grade, carcinoma in situ, lymphovascular invasion (LVI), lymph node status (pN), neoadjuvant chemotherapy (NACH), adjuvant chemotherapy (ACH), and adjuvant external beam radiotherapy (AXRT). Two hundred bootstrap resamples were used to reduce overfit bias and for internal validation. RESULTS: During a mean follow-up of 36.4 months, 290 of 731 (39.7%) patients died; 196 of 290 patients (67.6%) died of bladder cancer. Actuarial all-cause survival estimates were 56.3% [95% confidence interval (95% CI), 51.8-60.6%] and 42.9% (95% CI, 37.3-48.4%) at 5 and 8 years after cystectomy, respectively. Actuarial cancer-specific survival estimates were 67.3% (62.9-71.3%) and 58.7% (52.7-64.2%) at 5 and 8 years, respectively. The accuracy of a nomogram for prediction of all-cause survival (0.732) that included patient age, pT, pN, LVI, NACH, ACH, and AXRT was significantly superior (P=0.001) to that of AJCC staging-based risk grouping (0.615). Similarly, the accuracy of a nomogram for prediction of cancer-specific survival that included pT, pN, LVI, NACH, and AXRT (0.791) was significantly superior (P=0.001) to that of AJCC staging-based risk grouping (0.663). CONCLUSIONS: Multivariate nomograms provide a more accurate and relevant individualized prediction of survival after cystectomy compared with conventional prediction models, thereby allowing for improved patient counseling and treatment selection.

Adult↗

PubMed2006

Prostate cancer nomograms are superior to neural networks.

INTRODUCTION: Several nomograms have been developed to predict PCa related outcomes. Neural networks represent an alternative. METHODS: We provide a descriptive and an analytic comparison of nomograms and neural networks, with focus on PCa detection. RESULTS: Our results indicate that nomograms have several advantages that distinguish them from neural networks. These are both quantitative and qualitative. CONCLUSION: In the field of PCa detection, nomograms appear to outweigh the benefits of neural networks. However, the neural network methodology represents a valid alternative, which should not be underestimated.

Forecasting↗

PubMed1995

Astigmatism reduction clinical trial: a multicenter prospective evaluation of the predictability of arcuate keratotomy. Evaluation of surgical nomogram predictability. ARC-T Study Group.

OBJECTIVE: To determine the accuracy of the Lindstrom surgical nomogram for astigmatism. DESIGN: A prospective multicenter study. PATIENTS: One hundred sixty eyes of 95 patients underwent astigmatic keratotomy in eight centers by nine surgeons. Inclusion criteria for the study included age of at least 18 years with 1 to 6 diopters (D) of naturally occurring corneal astigmatism and less than 1 D of lenticular astigmatism. INTERVENTIONS: A standardized astigmatic keratotomy surgical technique was performed on each eye. Surgical measurements were determined using the Lindstrom surgical nomogram for astigmatism. MAIN OUTCOME MEASURE: The Holladay, Cravy, Koch vector analysis method was used to determine the change in refractive cylinder results. Refractive changes also are presented without vector analysis merely using the absolute change in refractive cylinder and axis. RESULTS: Multiple regression analysis was used to develop a mathematical model determining the factors predictive of the change in refractive cylinder. The significant predictors for the amount of astigmatic correction achieved were, in order of decreasing importance, the following: number of incisions (R2 = 30%), incision length (R2 = 16%), age (R2 = 8%), and gender (R2 = 2%). CONCLUSIONS: Astigmatism is a two-dimensional measurement of both quantity and direction that is most appropriately analyzed with vector analysis. The original Lindstrom surgical nomogram for arcuate keratotomy used in this study is still quite useful although it tended to underpredict results for many patients, especially those having two incisional surgeries. Some older subjects having minimal surgery achieved greater correction than predicted by the original nomogram. The most important factors predictive of greater astigmatic keratotomy surgical effect are incision number, incision length, older age, and male gender.

Adult↗

PubMed2003

A competing-risks nomogram for sarcoma-specific death following local recurrence.

The majority of staging systems focus on the definition of stage, and, therefore, prediction of prognosis. In the current era of clinical trial research, it has become apparent that the clinical stage alone is not sufficient to assess patient risk of treatment failure. As the number of biological markers increases, our ability to partition the traditional disease classification system improves, and our ability to predict patient success continues to increase. One approach to quantifying individual patient risk is through the nomogram. Nomograms are graphical representations of statistical models, which provide the probability of treatment outcome based on patient-specific covariates. We will focus on the use of the nomogram when the response variable is time to failure and there are multiple, possibly dependent, competing causes of failure. In this setting, estimation of the failure probability through direct application of the Cox proportional hazards model provides the probability of failure (for example, death from cancer) assuming failure from a dependent competing cause will not occur. In many clinical settings this is an unrealistic assumption. The purpose of this study is to illustrate the use of the conditional cumulative incidence function for providing a patient-specific prediction of the probability of failure in the setting of competing risks. A competing risks nomogram is produced to estimate the probability of death due to sarcoma for patients who have already developed a local recurrence of their initially treated soft-tissue sarcoma.

Adolescent↗

PubMed1985

Nomograms of the Goldman equation.

Solutions of the Goldman equations for sodium and potassium ions are displayed in nomograms which allow one to determine which values of the variables in the equation (including the activity of the Na/K pump) are compatible with possible steady states of a cell. The nomograms are particularly suited for the study of relative changes of the cell parameters when one or more of them are altered and the cell undergoes a transition from one steady state to another. Special diagrams are presented for finding the changes of the slope conductance (determined at a clamp potential of -80 mV) associated with such transitions. Separate diagrams are given for the cationic component conductance, (gNa + gK), and the anionic component conductance, gCl. The application of the nomograms is illustrated by the exemplary solution of a problem taken from muscle physiology. Further applications of the nomograms are indicated and the limitations of the method are described. The effects of differing activity coefficients in the intra- and extracellular spaces, as well as the contribution of the electrogenic Na/K pump current to the resting potential are discussed.

Cell Physiological Phenomena↗

PubMed1995

Nomograms for determining the probability of axillary node involvement in women with breast cancer.

We have previously reported that a history of pregnancy is independently associated with axillary node involvement in breast cancer patients. We have now studied additional women with breast cancer and have used our data and the logistic model to produce nomograms for determining the risk of axillary node involvement, based on tumor size, age, and number of pregnancies. There was an increase in the incidence of axillary node involvement in women with a history of pregnancy. To exclude the confounding effect that tumor size or age might have on node involvement, logistic regression was performed. Pregnancy, tumor size, and age were the three independent variables. History of pregnancy had a significant effect on node involvement (P = 0.036) that was independent of tumor size and age. Nomograms were constructed from these data. Surgeons do not perform an axillary dissection in every breast cancer patient. If the axilla is clinically negative and the tumor small, the surgeon, medical oncologist, and radiation oncologist may decide that a dissection need not be done. The nomograms in this article may allow for a more methodical choice of patients for axillary dissection. Moreover, a radiation oncologist might use the nomograms to help decide whether to irradiate an undissected axilla.

Adult↗

PubMed1976

A nomogram to obtain pulmonary shuntflow (Qs/Qt).

A nomogram to simplify the determination of pulmonary shunt is presented. It is based on Leigh's et al. shunt-equation (1969). The nomogram aggregates the factors which contribute most to the pulmonary shunt in acute respiratory failure. Arterial and venous oxygen saturation, Hb content, arterial oxygen tension and barometric pressure do influence strongly the result of calculated shuntflow. For the factors with little importance in the calculation (vapor pressure, mixed venous oxygen tension, alveolar-CO2 tension), international mean values are used. The shunt determined with the nomogram deviates less than 1% from the calculated values, if the range of PCO2 is between 32 and 52 mm Hg and the error does not exceed 1,5% with a PCO2 up to 82 mm Hg unless it is combined with a very low Hb and a high mixed venous saturation. By the nomogram the effect of the different parameters on the shunt can be very well illustrated. Especially mistakes in determination of the mixed venous saturation and of arterial O2 tension result in errors. Too high saturation values in mixed venous blood occur in distally located catheters due to pulmonary capillary admixtures. This contamination can be easily detected if the relationship between PVO2 and PACO2 is examined. The other source of error lies in the technical problems of PO2 determination in high ranges and is caused by escape of O2 into the PO2-electrode and O2-consumption of the blood. The end effect which the factors of O2 escape have on the accuracy of PO2 determination in high ranges is demonstrated with blood samples which have been equilibrated with different gas mixtures at different temperatures and had their PO2 measured at regular intervals. The error in PaO2 measurement can be reduced if blood-gas analyses are performed immediately or on cooled samples.

Carbon Dioxide↗