Intraoperative end-tidal carbon dioxide values and derived calculations correlated with outcome: prognosis and capnography

Prehospital ETCO2 is predictive of death in intubated and non-intubated patients

BACKGROUND

Prehospital identification of shock in trauma patients lacks accurate markers. Low end tidal carbon dioxide (ETCO2) correlates with mortality in intubated patients. The predictive value of ETCO2 obtained by nasal capnography cannula (NCC) is unknown. We hypothesized that prehospital ETCO2 values obtained by NCC and in-line ventilator circuit (ILVC) would be predictive of mortality.

METHODS

This was a prospective, observational, multicenter study. ETCO2 values were collected by a NCC or through ILVC. AUROCs were compared with prehospital systolic blood pressure (SBP) and shock index (SI). The Youden index defined optimal cutoffs.

RESULTS

Of 550 enrolled patients, 487 (88.5%) had ETCO2 measured through an NCC. Median age was 37 (27-52) years; 76.5% were male; median ISS was 13 (5-22). Mortality was 10.4%. Minimum prehospital ETCO2 significantly predicted mortality with an AUROC of 0.76 (CI 0.69-0.84; Youden index ​= ​22 ​mmHg), outperforming SBP with an AUROC of 0.68; (CI 0.62-0.74, p ​= ​0.04) and shock index with an AUROC of 0.67 (CI 0.59-0.74, p ​= ​0.03).

CONCLUSION

Prehospital ETCO2 measured by non-invasive NCC or ILVC may be predictive of mortality in injured patients.

The difference between arterial pCO2 and etCO2 after cardiac arrest - Outcome predictor or marker of unfavorable resuscitation circumstances?

INTRODUCTION

In former studies, the arterio-alveolar carbon dioxide gradient (ΔCO₂) predicted in-hospital mortality after initially survived cardiac arrest. As early outcome predictors are urgently needed, we evaluated ΔCO₂ as predictor for good neurological outcome in our cohort.

METHODS

We retrospectively analyzed all patients ≥18 years of age after non-traumatic in- and out of hospital cardiac arrest in the year 2018 from our resuscitation database. Patients without advanced airway management, incomplete datasets or without return of spontaneous circulation were excluded. The first arterial pCO₂ after admission and the etCO₂ in mmHg at the time of blood sampling were recorded from patient's charts. We then calculated ΔCO₂ (pCO₂ - etCO₂). For baseline analyses, ΔCO₂ was dichotomized into a low and high group with separation at the median. Good neurological outcome on day 30, expressed as Cerebral Performance Category 1-2, defined our primary endpoint. Survival to 30 days was used as secondary endpoint.

RESULTS

Out of 302 screened patients, 128 remained eligible for analyses. ΔCO₂ was lower in 30-day survivors with good neurological outcome (12.2 mmHg vs. 18.8 mmHg, p = 0.009) and in 30-day survivors (12.5 mmHg vs. 20.0 mmHg, p = 0.001). In patients with high ΔCO₂, a cardiac etiology of arrest was found less often. They had a higher body mass index, longer duration of resuscitation, higher amounts of epinephrine, lower pO₂ levels but both higher pCO2 and blood lactate levels, resulting in lower blood pH and HCO₃^- levels at admission. In a crude binary logistic regression analysis, ΔCO₂ was associated with 30-day neurological outcome (OR = 1.041 per mmHg of ΔCO₂, 95% CI 1.008-1.074, p = 0.014). This association persisted after the adjustment for age, sex, witnessed arrest and shockable first rhythm. However, after addition of the duration of resuscitation or the cumulative epinephrine dosage to the model, ΔCO₂ lost its association.

CONCLUSION

ΔCO₂ at admission after a successfully resuscitated cardiac arrest is associated with 30 days survival with good neurological outcome. However, a higher ΔCO₂ may rather be a surrogate for unfavorable resuscitation circumstances than an independent outcome predictor.

Difference between arterial and end-tidal carbon dioxide and adverse events after non-cardiac surgery: a historical cohort study

Purpose

The difference between arterial and end-tidal partial pressure of carbon dioxide (ΔCO₂) is a measure of alveolar dead space, commonly evaluated intraoperatively. Given its relationship to ventilation and perfusion, ΔCO₂ may provide prognostic information and guide clinical decisions. We hypothesized that higher ΔCO₂ values are associated with occurrence of a composite outcome of re-intubation, postoperative mechanical ventilation, or 30-day mortality in patients undergoing non-cardiac surgery.

Methods

We conducted a historical cohort study of adult patients undergoing non-cardiac surgery with an arterial line at a single tertiary care medical centre. The composite outcome, identified from electronic health records, was re-intubation, postoperative mechanical ventilation, or 30-day mortality. Student’s t test and Chi-squared test were used for univariable analysis. Logistic regression was used for multivariable analysis of the relationship of ΔCO₂ with the composite outcome.

Results

A total of 19,425 patients were included in the final study population. Univariable analysis showed an association between higher mean (standard deviation [SD]) intraoperative ΔCO₂ values and the composite outcome (6.1 [5.3] vs 5.7 [4.5] mm Hg; P = 0.002). After adjusting for baseline subject characteristics, every 5-mm Hg increase in the ΔCO₂ was associated with a nearly 20% increased odds of the composite outcome (odds ratio, 1.20; 95% confidence interval, 1.12 to 1.28; P < 0.001).

Conclusions

In this patient population, increased intraoperative ΔCO₂ was associated with an increased odds of the composite outcome of postoperative mechanical ventilation, re-intubation, or 30-day mortality that was independent of its relationship with pre-existing pulmonary disease. Future studies are needed to determine if ΔCO₂ can be used to guide patient management and improve patient outcomes.

"Low initial pre-hospital end-tidal carbon dioxide predicts inferior clinical outcomes in trauma patients"

INTRODUCTION

Current guidelines continue to lead to under- and over-triage of injured patients in the pre-hospital setting. End-tidal carbon dioxide (ETCO2) has been correlated with mortality and hemorrhagic shock in trauma patients. This study examines the correlation between ETCO2 and in-hospital outcomes among non-intubated patients in the pre-hospital setting.

METHODS

We retrospectively studied a cohort of non-intubated adult trauma patients with initial pre-hospital side-stream capnography-obtained ETCO2 presenting via ground transport from a single North Carolina EMS agency to a level one trauma center from January 2018 to December 2018. Using the Liu method, the optimal threshold for low ETCO2 was ≤ 28.5 mmHg.

RESULTS

Initial pre-hospital ETCO2 was recorded for 324 (22.0%) of 1473 patients with EMS data. Patients with low ETCO2 (N = 98, 30.3% of cohort) were older (median 58y vs 45y), but mechanisms of injury and scene vital signs were similar (p>0.05) between low and normal/high ETCO2 cohorts. Median injury severity score (ISS) did not differ significantly between the low and normal/high ETCO2 groups (5 vs 8, p=0.48). Compared to normal/high ETCO2, low ETCO2 correlated with increased unadjusted odds of mortality (OR 5.06), in-hospital complications (OR 2.06), and blood transfusion requirement (OR 3.05), p<0.05. Low ETCO2 was associated with 7.25 odds of mortality (95% CI 2.19,23.97, p=0.001) and 3.94 odds of blood transfusion (95% CI 1.32-11.78) after adjusting for age, ISS, and scene GCS. All but one of the massive transfusion patients (N = 8/9) had a low pre-hospital ETCO2.

CONCLUSIONS

Low initial pre-hospital ETCO2 associates with poor clinical outcomes despite similar ISS and mechanisms of injury. ETCO2 is a potentially useful pre-hospital point-of-care tool to aid triage of trauma patients as it may identify hemorrhaging patients and predict mortality.

Prehospital end-tidal carbon dioxide predicts massive transfusion and death following trauma

BACKGROUND

The lack of an accurate marker of prehospital hemorrhagic shock limits our ability to triage patients to the correct level of care, delays treatment in the emergency department, and inhibits our ability to perform prehospital interventional research in trauma. End-tidal carbon dioxide (ETCO2) is the measurement of alveolar carbon dioxide concentration at end expiration and is measured noninvasively in the ventilator circuit for intubated patients in continuous manner. Several hospital-based studies have been able to demonstrate that either low or decreasing levels of ETCO2 as well as disparities between ETCO2 and plasma carbon dioxide correlate with increasing mortality in trauma. We hypothesized that prehospital ETCO2 values will be predictive of mortality and need for massive transfusion following injury.

METHODS

This is a single-center retrospective study from an urban level 1 trauma center. We reviewed all intubated adult patients transported for injury who had prehospital ETCO2 values available. Unadjusted comparisons of continuous variables were done with the Wilcoxon two-sample test. The predictive performance of prehospital ETCO2, the prehospital shock index, and prehospital systolic blood pressure were assessed and compared using areas under the receiver operating characteristic curves. Optimal cutoffs were estimated by maximizing the Youden index. Massive transfusion was defined as >10 U of blood or death in 24 hours.

RESULTS

A total of 173 patients were identified with prehospital ETCO2 values during the 2-year study period. Population was 78.5% male with a median age of 37.5 years (interquartile range, 23.5-53.5 years). Injury mechanism was penetrating in 22.8%. This cohort had a median Injury Severity Score of 26 (interquartile range, 17-36), massive transfusion rate of 34.7%, and mortality of 42.1%. In the evaluation of prediction of postinjury mortality and massive transfusion, ETCO2 outperformed systolic blood pressure and shock index, but these differences did not reach statistical significance.

CONCLUSION

End-tidal carbon dioxide is a novel prehospital predictor of mortality and massive transfusion after injury.

LEVEL OF EVIDENCE

Prognostic/Epidemiologic, level III.

End-tidal carbon dioxide underestimates plasma carbon dioxide during emergent trauma laparotomy leading to hypoventilation and misguided resuscitation: A Western Trauma Association Multicenter Study

BACKGROUND

End-tidal carbon dioxide (ETCO2) is routinely used during elective surgery to monitor ventilation. The role of ETCO2 monitoring in emergent trauma operations is poorly understood. We hypothesized that ETCO2 values underestimate plasma carbon dioxide (pCO2) values during resuscitation for hemorrhagic shock.

METHODS

Multicenter trial was performed analyzing the correlation between ETCO2 and pCO2 levels.

RESULTS

Two hundred fifty-six patients resulted in 587 matched pairs of ETCO2 and pCO2. Correlation between these two values was very poor with an R of 0.04. 40.2% of patients presented to the operating room acidotic and hypercarbic with a pH less than 7.30 and a pCO2 greater than 45 mm Hg. Correlation was worse in patients that were either acidotic or hypercarbic. Forty-five percent of patients have a difference greater than 10 mm Hg between ETCO2 and pCO2. A pH less than 7.30 was predictive of an ETCO2 to pCO2 difference greater than 10 mm Hg. A difference greater than 10 mm Hg was predictive of mortality independent of confounders.

CONCLUSION

Nearly one half (45%) of patients were found to have an ETCO2 level greater than 10 mm Hg discordant from their PCO2 level. Reliance on the discordant values may have contributed to the 40% of patients in the operating room that were both acidotic and hypercarbic. Early blood gas analysis is warranted, and a lower early goal of ETCO2 should be considered.

LEVEL OF EVIDENCE

Therapeutic, level IV.

Comparing Quick Sequential Organ Failure Assessment Scores to End-tidal Carbon Dioxide as Mortality Predictors in Prehospital Patients with Suspected Sepsis

Introduction

Early identification of sepsis significantly improves outcomes, suggesting a role for prehospital screening. An end-tidal carbon dioxide (ETCO₂) value ≤ 25 mmHg predicts mortality and severe sepsis when used as part of a prehospital screening tool. Recently, the Quick Sequential Organ Failure Assessment (qSOFA) score was also derived as a tool for predicting poor outcomes in potentially septic patients.

Methods

We conducted a retrospective cohort study among patients transported by emergency medical services to compare the use of ETCO₂ ≤ 25 mmHg with qSOFA score of ≥ 2 as a predictor of mortality or diagnosis of severe sepsis in prehospital patients with suspected sepsis.

Results

By comparison of receiver operator characteristic curves, ETCO₂ had a higher discriminatory power to predict mortality, sepsis, and severe sepsis than qSOFA.

Conclusion

Both non-invasive measures were easily obtainable by prehospital personnel, with ETCO₂ performing slightly better as an outcome predictor.

Prehospital End-tidal Carbon Dioxide Predicts Mortality in Trauma Patients

BACKGROUND

End-tidal carbon dioxide (EtCO₂) measurement has been shown to have prognostic value in acute trauma.

OBJECTIVE

Evaluate the association of prehospital EtCO₂ and in-hospital mortality in trauma patients and to assess its prognostic value when compared to traditional vital signs.

METHODS

Retrospective, cross-sectional study of patients transported by a single EMS agency to a level one trauma center. We evaluated initial out-of-hospital vital signs documented by EMS personnel including EtCO₂, respiratory rate (RR), systolic BP (SBP), diastolic BP (DBP), pulse (P), and oxygen saturation (O₂) and hospital data. The main outcome measure was mortality.

RESULTS

135 trauma patients were included; 9 (7%) did not survive. The mean age of patients was 40 (SD17) [Range 16-89], 97 (72%) were male, 76 (56%) were admitted to the hospital and 15 (11%) went to the ICU. The mean EtCO2 level was 18 mmHg (95%CI 9-28) [Range 5-41] in non-survivors compared to 34 mmHg (95%CI 32-35) [Range 11-51] in survivors. The area under the ROC curve (AUC) for EtCO₂ in predicting mortality was 0.84 (0.67-1.00) (p = 0.001), RR was 0.82 (0.63-1.00), SBP was 0.72 (0.49-0.96), DBP was 0.72 (0.47-0.97), pulse was 0.51 (0.26-0.76), and O₂ was 0.64 (0.37-0.91). Cut-off values at 30 mmHg yielded sensitivity = 89% (51-99), specificity = 68% (59-76), PPV = 13% (6-24) and NPV = 99% (93-100) for predicting mortality. There was no correlation between RR and EtCO₂ (correlation 0.16; p = 0.06).

CONCLUSION

We found an inverse association between prehospital EtCO₂ and mortality. This has implications for improving triage and assisting EMS in directing patients to an appropriate trauma center.

Current methodological and technical limitations of time and volumetric capnography in newborns

Although capnography is a standard tool in mechanically ventilated adult and pediatric patients, it has physiological and technical limitations in neonates. Gas exchange differs between small and adult lungs due to the greater impact of small airways on gas exchange, the higher impact of the apparatus dead space on measurements due to lower tidal volume and the occurrence of air leaks in intubated patients. The high respiratory rate and low tidal volume in newborns, especially those with stiff lungs, require main-stream sensors with fast response times and minimal dead-space or low suction flow when using side-stream measurements. If these technical requirements are not fulfilled, the measured end-tidal CO2 (P et CO 2 ), which should reflect the alveolar CO2 and the calculated airway dead spaces, can be misleading. The aim of this survey is to highlight the current limitations of capnography in very young patients to avoid pitfalls associated with the interpretation of capnographic parameters, and to describe further developments.

Correlation Between Changes in End-Tidal Carbon Dioxide Concentration and Cardiac Output During Inferior Vena Cava Clamping and Unclamping in Living-donor Liver Transplantation

BACKGROUND

To test the hypothesis that low end-tidal carbon dioxide tension encountered during anhepatic phase in liver transplantation is related to hemodynamic status rather than ventilatory status, and can be used to predict the change in cardiac output during anhepatic phase.

METHODS

We retrospectively analyzed and compared data, included end-tidal carbon dioxide tension (ETCO2), arterial blood pressure, heart rate, central venous pressure, cardiac output, cardiac index, and stroke volume, before and after inferior vena cava clamping, and 0, 5, 10, 30 minutes during the anhepatic, and 5 minutes after the release of IVC cross clamp during the reperfusion phase, with paired Student t test, repeated measurement, and linear regression. P < .05 was regarded as significant.

RESULTS

The cardiac output and ETCO2 decrease significantly after clamping the inferior vena cava and increase concomitantly after unclamping. There is a positive correlation between the changes in % in cardiac output and ETCO2 (Pearson coefficient r = 0.741).

CONCLUSION

The changes in ETCO2 can be used to predict the changes of the cardiac output in % when cardiac output monitoring is not available. Before unclamping of the IVC, mild hyperventilation is suggested to prevent excessive increase in PaCO2.

A prehospital screening tool utilizing end-tidal carbon dioxide predicts sepsis and severe sepsis

OBJECTIVE

To determine the utility of a prehospital sepsis screening protocol utilizing systemic inflammatory response syndrome (SIRS) criteria and end-tidal carbon dioxide (ETCO2).

METHODS

We conducted a prospective cohort study among sepsis alerts activated by emergency medical services during a 12 month period after the initiation of a new sepsis screening protocol utilizing ≥2 SIRS criteria and ETCO2 levels of ≤25 mmHg in patients with suspected infection. The outcomes of those that met all criteria of the protocol were compared to those that did not. The main outcome was the diagnosis of sepsis and severe sepsis. Secondary outcomes included mortality and in-hospital lactate levels.

RESULTS

Of 330 sepsis alerts activated, 183 met all protocol criteria and 147 did not. Sepsis alerts that followed the protocol were more frequently diagnosed with sepsis (78% vs 43%, P < .001) and severe sepsis (47% vs 7%, P < .001), and had a higher mortality (11% vs 5%, P = .036). Low ETCO2 levels were the strongest predictor of sepsis (area under the ROC curve (AUC) of 0.99, 95% CI 0.99-1.00; P < .001), severe sepsis (AUC 0.80, 95% CI 0.73-0.86; P < .001), and mortality (AUC 0.70, 95% CI 0.57-0.83; P = .005) among all prehospital variables. Sepsis alerts that followed the protocol had a sensitivity of 90% (95% CI 81-95%), a specificity of 58% (95% CI 52-65%), and a negative predictive value of 93% (95% CI 87-97%) for severe sepsis. There were significant associations between prehospital ETCO2 and serum bicarbonate levels (r = 0.415, P < .001), anion gap (r = -0.322, P < .001), and lactate (r = -0.394, P < .001).

CONCLUSION

A prehospital screening protocol utilizing SIRS criteria and ETCO2 predicts sepsis and severe sepsis, which could potentially decrease time to therapeutic intervention.

Exhaled CO2 Parameters as a Tool to Assess Ventilation-Perfusion Mismatching during Neonatal Resuscitation in a Swine Model of Neonatal Asphyxia

Background

End-tidal CO₂ (ETCO₂), partial pressure of exhaled CO₂ (PECO₂), and volume of expired CO₂ (VCO₂) can be continuously monitored non-invasively to reflect pulmonary ventilation and perfusion status. Although ETCO₂ ≥14mmHg has been shown to be associated with return of an adequate heart rate in neonatal resuscitation and quantifying the PECO₂ has the potential to serve as an indicator of resuscitation quality, there is little information regarding capnometric measurement of PECO₂ and ETCO₂ in detecting return of spontaneous circulation (ROSC) and survivability in asphyxiated neonates receiving cardiopulmonary resuscitation (CPR).

Methods

Seventeen newborn piglets were anesthetized, intubated, instrumented, and exposed to 45-minute normocapnic hypoxia followed by apnea to induce asphyxia. Protocolized resuscitation was initiated when heart rate decreased to 25% of baseline. Respiratory and hemodynamic parameters including ETCO₂, PECO₂, VCO₂, heart rate, cardiac output, and carotid artery flow were continuously measured and analyzed.

Results

There were no differences in respiratory and hemodynamic parameters between surviving and non-surviving piglets prior to CPR. Surviving piglets had significantly higher ETCO₂, PECO₂, VCO₂, cardiac index, and carotid artery flow values during CPR compared to non-surviving piglets.

Conclusion

Surviving piglets had significantly better respiratory and hemodynamic parameters during resuscitation compared to non-surviving piglets. In addition to optimizing resuscitation efforts, capnometry can assist by predicting outcomes of newborns requiring chest compressions.

The sixth vital sign: prehospital end-tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances

OBJECTIVE

To determine the ability of prehospital end-tidal carbon dioxide (ETCO₂) to predict in-hospital mortality compared to conventional vital signs.

METHODS

We conducted a retrospective cohort study among patients transported by emergency medical services during a 29-month period. Included patients had ETCO₂ recorded in addition to initial vital signs. The main outcome was death at any point during hospitalization. Secondary outcomes included laboratory results and admitting diagnosis.

RESULTS

Of 1328 records reviewed, hospital discharge data, ETCO₂, and all 6 prehospital vital signs were available in 1088 patients. Low ETCO₂ levels were the strongest predictor of mortality in the overall group (area under the receiver operating characteristic curve (AUC of 0.76, 95% confidence interval [CI] 0.66-0.85), as well as subgroup analysis excluding prehospital cardiac arrest (AUC of 0.77, 95% CI 0.67-0.87). The sensitivity of abnormal ETCO₂ for predicting mortality was 93% (95% CI 79%-98%), the specificity was 44% (95% CI 41%-48%), and the negative predictive value was 99% (95% CI 92%-100%). There were significant associations between ETCO₂ and serum bicarbonate levels (r = 0.429, P < .001), anion gap (r = -0.216, P < .001), and lactate (r = -0.376, P < .001).

CONCLUSION

Of all prehospital vital signs, ETCO₂ was the most predictive and consistent for mortality, which may be related to an association with metabolic acidosis.

The use of end-tidal carbon dioxide monitoring in patients with hypotension in the emergency department

Background

The aim of this study was to determine the usefulness of end tidal carbon dioxide (ETCO₂) monitoring in hypotensive shock patients presenting to the ED.

Methods

This was a prospective observational study in a tertiary ED. One hundred three adults in shock with hypotension presenting to the ED were recruited into the study. They were grouped according to different types of shock, hypovolemic, cardiogenic, septic and others. Vital signs and ETCO₂ were measured on presentation and at 30-min intervals up to 120 min. Blood gases and serum lactate levels were obtained on arrival. All patients were managed according to standard protocols and treatment regimes. Patient survival up to hospital admission and at 30 days was recorded.

Results

Mean ETCO₂ for all patients on arrival was 29.07 ± 9.96 mmHg. Average ETCO₂ for patients in hypovolemic, cardiogenic and septic shock was 29.64 ± 11.49, 28.60 ± 9.87 and 27.81 ± 7.39 mmHg, respectively. ETCO₂ on arrival was positively correlated with systolic and diastolic BP, MAP, bicarbonate, base excess and lactate when analyzed in all shock patients. Early ETCO₂ measurements were found to be significantly lower in patients who did not survive to hospital admission (p = 0.005). All patients who had ETCO₂ ≤ 12mmHg died in the ED. However, normal ETCO₂ does not ensure patient survival.

Conclusion

The use of ETCO₂ in the ED has great potential to be used as a method of non-invasive monitoring of patients in shock.

End-tidal CO₂ detection of an audible heart rate during neonatal cardiopulmonary resuscitation after asystole in asphyxiated piglets

Even brief interruption of cardiac compressions significantly reduces critical coronary perfusion pressure during cardiopulmonary resuscitation (CPR). End-tidal CO₂ (ETCO₂) monitoring may provide a continuous noninvasive method of assessing return of spontaneous circulation (ROSC) without stopping to auscultate for heart rate (HR). However, the ETCO₂ value that correlates with an audible HR is unknown. Our objective was to determine the threshold ETCO₂ that is associated with ROSC after asphyxia-induced asystole. Neonatal swine (n = 46) were progressively asphyxiated until asystole occurred. Resuscitation followed current neonatal guidelines with initial ventilation with 100% O₂ followed by cardiac compressions followed by epinephrine for continued asystole. HR was auscultated every 30 s, and ETCO₂ was continuously recorded. A receiver operator curve was generated using the calculated sensitivity and specificity for various ETCO₂ values, where a positive test was defined as the presence of HR >60 bpm by auscultation. An ETCO₂ cut-off value of 14 mm Hg is the most sensitive ETCO₂ value with the least false positives. When using ETCO₂ to guide uninterrupted CPR in this model of asphyxia-induced asystole, auscultative confirmation of return of an adequate HR should be performed when ETCO₂ ≥ 14 mm Hg is achieved. Correlation during human neonatal CPR needs further investigation.

The partial pressure of resting end-tidal carbon dioxide predicts major cardiac events in patients with systolic heart failure

BACKGROUND

The resting partial pressure of end-tidal carbon dioxide (Petco2) has been shown to reflect cardiac performance in acute care settings in patients with heart failure (HF). The purpose of the present study was to compare the prognostic ability of the partial pressure of Petco2 at rest to other commonly collected resting variables in patients with systolic HF.

METHODS

A total of 353 patients (mean age 58.6+/-13.7, 72% male) with systolic HF were included in this study. All patients underwent cardiopulmonary exercise testing where New York Heart Association (NYHA) class, resting Petco2, peak oxygen consumption, and the minute ventilation/carbon dioxide production slope were determined. Subjects were then followed for major cardiac events (mortality, left ventricular assist device implantation implantation, urgent heart transplantation).

RESULTS

There were 104 major cardiac events during the 23.6+/-17.0-month tracking period. Multivariate Cox regression analysis revealed NYHA class (chi2 28.7, P<.001), left ventricular ejection fraction (residual chi2 21.7, P<.001), and resting Petco2 (residual chi2 14.1, P<.001) were all prognostically significant and retained in the regression. In a separate Cox regression analysis, left ventricular ejection fraction (residual chi2 8.8, P=.003), NYHA class (residual chi2 7.7, P=.005), and resting Petco2 (residual chi2 5.7, P=.02) added prognostic value to the minute ventilation/carbon dioxide production slope (chi2 26.0, P<.001).

CONCLUSION

Resting Petco2 can be noninvasively collected from subjects in a short period, at a low cost, and with no risk or discomfort to the patient. Given the prognostic value demonstrated in the present study, the clinical assessment of resting Petco2 in the HF population may be warranted.

Intraoperative gastric tonometric examinations in children and infants with a new probe, combined with measurement of the endtidal PCO2

BACKGROUND

Important progress relating to the early prediction of postoperative complications was recently achieved through the combined use of endtidal PCO(2) (P(ET)CO(2)) and gastric tonometry. The aim of this article was to present results obtained with a new tonometric instrument, proving its feasibility and extending its use to the control of anesthetized infants and children.

METHODS

The new tonometric probe, which is balloon free, consists basically of silicone rubber tubing. The room air initially inside the tubes of the probe equilibrates with the PCO(2) of the body cavity throughout its full length. The PCO(2) content of the gastric cavity (P(g)CO(2)) and simultaneously P(ET)CO(2) were measured with a microcapnograph. A total of 108 measurements were performed intraoperatively on 25 infants and young children operated on at the Surgical Unit of the Department of Pediatrics. The patients were divided into elective surgery cases <2 years of age, group I; elective surgery cases >2 years of age, group II; and acute surgery cases, independently of age, group III. To examine the degree of agreement between the measurements, Pearson's correlation coefficients were determined and Bland-Altman analysis was performed. A mixed model repeated measurements anova was used to compare the differences between the groups.

RESULTS

P(ET)CO(2) and P(g)CO(2) for groups I and II were nearly identical, and statistically not significantly different (mean difference 0.10 mmHg and 0.85 mmHg, P = 0.96 and 0.45, respectively), whereas the corresponding data for group III differed significantly from those for groups I and II (P = 0.03 and 0.001, respectively). On Bland-Altman analysis, the bias value for groups proved to be statistically significantly different (P = 0.001).

CONCLUSIONS

The tested new probe worked very well in small children. The clinical implications of the large gaps found between P(ET)CO(2) and P(g)CO(2) values in acutely ill children and children undergoing elective operations must be investigated further.

Prehospital End-Tidal Carbon Dioxide Concentration and Outcome in Major Trauma

BACKGROUND

End-tidal carbon dioxide (Petco2) concentration is a marker of the pathophysiologic state because it is a reflection of cardiac output. Petco2 correlates with outcome after prehospital primary cardiac arrest, but association with outcome from prehospital trauma has not been established.

METHODS

Between 1998 and 2001, Petco2 was recorded in 191 blunt trauma patients requiring prehospital intubation. Rapid sequence intubation was performed using suxamethonium (1 mg/kg) and etomidate (0.2-0.3 mg/kg). Initial Petco2 after endotracheal intubation (t0) and Petco2 at 20 minutes after endotracheal intubation (t20) were recorded, together with survival to discharge.

RESULTS

Median Petco2 at t20 was 4.10 kPa in survivors and 3.50 kPa in nonsurvivors (95% confidence interval of difference between medians, 0.40 to 0.90 kPa; p < 0.0001). Petco2 at t20 was a better predictor of outcome than at t0.

CONCLUSION

Only 5% patients with Petco2 < 3.25 kPa survived to discharge. Petco2 at t20 is of value in predicting outcome from major trauma.

Estimating alveolar dead space from the arterial to end-tidal CO(2) gradient: a modeling analysis

Using an original, validated, high-fidelity model of pulmonary physiology, we compared the arterial to end-tidal CO(2) gradient divided by the arterial CO(2) tension (Pa-E'CO(2)/PaCO(2)) with alveolar dead space expressed as a fraction of alveolar tidal volume, calculated in the conventional manner using Fowler's technique and the Bohr equation: (VDalv/VTalv)(Bohr-Fowler). We examined the variability of Pa-E'CO(2)/PaCO(2) and of (VDalv/VTalv)(Bohr-Fowler) in the presence of three ventilation-perfusion defects while varying CO(2) production (Vdot;CO(2)), venous admixture, and anatomical dead space fraction (VDanat). Pa-E'CO(2)/PaCO(2) was approximately 59.5% of (VDalv/VTalv)(Bohr-Fowler). During constant alveolar configuration, the factors examined (Vdot;CO(2), pulmonary shunt fraction, and VDanat) each caused variation in (VDalv/VTalv)(Bohr-Fowler) and in Pa-E'CO(2)/PaCO(2). Induced variation was slightly larger for Pa-E'CO(2)/PaCO(2) during changes in VDanat, but was similar during variation of venous admixture and Vdot;CO(2). Pa-E'CO(2)/PaCO(2) may be a useful serial measurement in the critically ill patient because all the necessary data are easily obtained and calculation is significantly simpler than for (VDalv/VTalv)(Bohr-Fowler).

IMPLICATIONS

Using an original, validated, high-fidelity model of pulmonary physiology, we have demonstrated that the arterial to end-tidal carbon dioxide pressure gradient may be used to robustly and accurately quantify alveolar dead space. After clinical validation, its use could replace that of conventionally calculated alveolar dead space fraction, particularly in the critically ill.

End-tidal CO2-derived values during emergency trauma surgery correlated with outcome: a prospective study

BACKGROUND

The purpose of this study was to determine whether end-tidal carbon dioxide (PETCO) derived variables assist in evaluating the adequacy of resuscitation during emergency surgery for trauma.

METHODS

This was a prospective study of end-tidal derived variables and outcome in 106 trauma patients in an urban Level I trauma center.

RESULTS

The patients who lived (compared with those who died) had higher final end-tidal Pco levels, lower arterial-end tidal CO differences (Pa-ET)CO, and a decreased alveolar dead space ratio (p < 0.001). The best survival rates were with a PETCO > 27 mm Hg, a (Pa-ET)CO < or = 9 mm Hg, and 96% (56 of 58) for an alveolar dead space ratio < or = 0.20 (p < 0.001). An inappropriately high or "excess Paco also correlated with a decreased (Pa-ET)CO and poorer prognosis. If, after the initial resuscitation, the PETCO -derived values did not achieve these "optimal" levels, survival was significantly reduced.

CONCLUSION

During emergency trauma surgery, the PETCO and its derived values help to predict outcome and may be used to identify patients needing more aggressive resuscitation.

Comparison of end-tidal CO2 and Paco2 in children receiving mechanical ventilation

OBJECTIVE: To determine whether end-tidal CO(2) (Petco(2)) measurement provides a reliable estimate of ventilation in critically ill children who are mechanically ventilated. DESIGN: Prospective, nonrandomized, consecutive enrollment study. SETTING: A university-affiliated children's hospital pediatric intensive care unit. PATIENTS: All intubated, mechanically ventilated pediatric patients. INTERVENTIONS: All Petco(2)-Paco(2) pairs were from patients ventilated with a Servo 300 Ventilator (Siemens-Elema AB, Stockholm, Sweden). When a blood gas sample was obtained, Petco(2) as measured by a continuous mainstream Petco(2) capnograph was recorded. Measurements: The results of blood gas measurements and corresponding Petco(2) measurements were recorded. Demographic data and primary diagnosis were noted. Petco(2)-Paco(2) pairs obtained from patients with intracardiac shunts or obtained during high-frequency oscillation or extracorporeal membrane oxygenation at the time of measurement were excluded from analysis. Linear regression was used to analyze Petco(2)-Paco(2) pairs. Repeated measure analysis of variance with the mixed-model algorithm in SAS software (SAS Institute, Carey, NC) was used to analyze the trend in the Petco(2) and Paco(2) relationship. Chi-square was used to analyze categorical data. Statistical significance was considered p <.05. RESULTS: A total of 129 children were enrolled, and 1708 paired Paco(2) and Petco(2) measurements were recorded. The mean age +/- sd was 4.1 +/- 5.6 yrs. Paco(2) positively correlated with Petco(2). The linear equation for the regression analysis was y = 0.71x (95% confidence interval, 0.69-0.73) + 8.93 (95% confidence interval, 7.89-9.97), with r (2) =.716 and p <.001. The Petco(2)-Paco(2) difference was </=5 mm Hg (0.67 kPa) in 54% and </=10 mm Hg (1.33 kPa) in 80% of paired data. Increased lung disease had a negative effect on Petco(2) correlation with Paco(2). A total of 223 of 640 (35%) blood gases (defined by Pao(2)/Fio(2) ratio of <200) had >10 mm Hg (1.33 kPa) difference between the Petco(2) and Paco(2). However, only 111 of 1068 (10%) Petco(2)-Paco(2) pairs had a difference of >10 mm Hg (1.33 kPa) in patients with a Pao(2)/Fio(2) ratio >200. Trend analysis showed the Petco(2)-Paco(2) difference increased with increasing duration of mechanical ventilation. CONCLUSION: In most intubated, mechanically ventilated infants and children, Petco(2) reliably estimates ventilation.

End tidal CO(2) is reduced during hypotension and cardiac arrest in a rat model of massive pulmonary embolism

BACKGROUND

We investigated the effect of massive pulmonary embolism (MPE) on end tidal CO(2) (etCO(2)) and tested two hypotheses: (1) that etCO(2) can distinguish massive PE from hemorrhagic shock and (2) that PE with cardiac arrest reduces etCO(2) during resuscitation to a greater extent than arrhythmic cardiac arrest.

METHODS

Anesthetized, mechanically ventilated rats (N=10 per group), were subjected to either graded PE (latex microspheres), or graded hemorrhagic shock to produce a final mean arterial blood pressure, (MAP) of 40 mmHg; a third group was subjected to surgical/anesthetic control conditions. Cardiac arrest was induced by the following methods: intravenous injection of a large bolus of microspheres in the PE group, aortic puncture in the hemorrhage group, and intravenous tetrodotoxin (TTX) to produce arrhythmic cardiac arrest in the control group.

RESULTS

At a MAP of 40 mmHg, etCO(2) was significantly decreased in the PE group (18.3+/-1.9 torr) compared with both the hemorrhage (24.3+/-1.3) and the control group (35.0+/-1.3 torr; ANOVA P<0.001). The decreased etCO(2) occurred coincident with an increase in alveolar dead space fraction in the PE group. In the first minute of ventilation after cardiac arrest, the etCO(2) was significantly decreased in the PE group (6.5+/-0.9) versus both hemorrhage (16.5+/-1.1) and TTX (34.2+/-2.4 torr).

CONCLUSIONS

Massive PE with shock decreases the etCO(2) and increases the dead space fraction to a greater extent than hemorrhagic shock at the same MAP. Cardiac arrest from PE is associated with extremely low etCO(2) readings during CPR.

Monitoring gaseous exchange: implications for nursing care

The purpose of this study is to examine whether a relationship exists between arterial and end-tidal carbon dioxide tension (PaCO2 and PETCO2 respectively) in patients admitted to intensive care units (ICUs), and what the implications it has for nursing care. PaCO2 and PETCO2 are indicators of ventilatory adequacy which is an important aspect of respiratory function. These measures of carbon dioxide tension are obtained via invasive and non-invasive monitoring tools. Measurement of PETCO2 has only recently been introduced into ICUs and its usefulness in these environments is open to debate. A population of 30 intubated patients had 214 simultaneous measurements of PaCO2 and PETCO2 taken over a period of 10 months. The findings indicate that, despite strong significant correlations, PETCO2 cannot be used safely as a substitute for PaCO2 as the arterial/end-tidal carbon dioxide gradient is not constant, nor does capnography provide a consistently reliable indicator of PaCO2.

Monitoring end-tidal carbon dioxide during weaning from cardiopulmonary bypass in patients without significant lung disease

End-tidal carbon dioxide tension (PETCO(2)) changes with fluctuations in cardiac output (CO). We compared PETCO(2) to pulmonary artery blood flow (PAQt) during weaning from cardiopulmonary bypass (CPB) in normothermic patients without significant pulmonary disease. Fifteen consecutive adult cardiac surgical patients were prospectively studied during and shortly after weaning from CPB. Before separation from CPB, PETCO(2) and PAQt were measured, the latter by transesophageal Doppler echocardiography. At the time of measurements patients were normothermic, and ventilated at 6 breaths/min with tidal volumes of 10 mL/kg. After separation from CPB, thermodilution cardiac output (TDCO) was measured in addition to PAQt and PETCO(2). Regression and bias analyses were used to compare PETCO(2), PAQt, and TDCO. Seventy measurements were recorded; 31 before separation from CPB and 39 after separation from CPB. A good correlation was seen between PAQt and PETCO(2) (r = 0.88) and between TDCO and PAQt (r = 0.93; mean bias 0.03 L/min; SD 0.52 L/min). The regression analysis of PAQt on PETCO(2) showed greater variability at PETCO(2) levels > 34 mm Hg (n = 22; r = 0.14). Increases in PETCO(2) plateaued at this level, although PAQt continued to increase. When PETCO(2) was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m(2)). When PETCO(2) exceeded 34 mm Hg, all values of PAQt, and 28/29 values of TDCO were more than 5 L/min (>2.5 L/min/m(2)). One patient had TDCO of 4.69 L/min (2.39 L/min/m(2)). In normothermic patients without significant pulmonary disease, PETCO(2) is a useful index of PAQt during separation from CPB. Under the clinical settings in this study, a PETCO(2) greater than 30 mm Hg was invariably associated with a CO more than 4.0 L/min or a cardiac index >2.0 L/min/m(2).

Effectiveness of end-tidal carbon dioxide tension for monitoring thrombolytic therapy in acute pulmonary embolism

OBJECTIVE

In acute massive pulmonary embolism with hemodynamic instability, monitoring of pulmonary artery pressure can be used to assess the efficacy of thrombolytic therapy. As a noninvasive alternative to pulmonary artery catheterization, we investigated the efficacy of continuous monitoring of end-tidal CO2 tension.

DESIGN

In 12 patients with massive pulmonary embolism who required mechanical ventilation, mean pulmonary arterial pressure (MPAP) and end-tidal carbon dioxide tension (ETCO2) were registered continuously during thrombolytic therapy. PaCO2, cardiac index as estimated by thermodilution catheter and respiratory ratio of arterial oxygen tension and inhaled oxygen concentration (PaO2/FIO2) were determined every 60 mins.

MEASUREMENTS AND MAIN RESULTS

Before thrombolysis, MPAP (34.5+/-9.8 mm Hg) and the difference between PaCO2 and ETCO2 (10.1+/-4.7 mm Hg) were markedly increased compared with normal values. Continuously monitored MPAP was related to ETCO2 for both all patients (r2 = .42; p < .001) and individually (mean r2 = .92; range, .79-.98; p < .001). In ten survivors, the mean cardiac index and PaO2/FIO2 increased during therapy from 1.7+/-0.4 to 2.8+/-0.6 L/min x m2 and 125+/-27 to 285+/-50 mm Hg (p < .01, respectively). In these patients, the difference between PaCO2 and ETCO2 decreased from 9.8+/-4.5 to 2.8+/-0.9 mm Hg (p < .001). Recurrent embolism was detected in two patients by sudden reduction of ETCO2.

CONCLUSIONS

Analysis of ETCO2 allows monitoring of the efficacy of thrombolysis and may reflect recurrent embolism. Thus, on the basis of this small study, analysis of ETCO2 appears to be useful for noninvasive monitoring in mechanically ventilated patients with massive pulmonary embolism.

Carbon dioxide kinetics and capnography during critical care

Greater understanding of the pathophysiology of carbon dioxide kinetics during steady and nonsteady state should improve, we believe, clinical care during intensive care treatment. Capnography and the measurement of end-tidal partial pressure of carbon dioxide (PETCO2) will gradually be augmented by relatively new measurement methodology, including the volume of carbon dioxide exhaled per breath (VCO2,br) and average alveolar expired PCO2. Future directions include the study of oxygen kinetics.

End-tidal carbon dioxide as a noninvasive indicator of cardiac index during circulatory shock

OBJECTIVE

To document the relationships between cardiac index and end-tidal carbon dioxide tension (PetCO2 during diverse low-flow states of circulatory shock.

DESIGN

Randomized, prospective, controlled studies on animal models of hemorrhagic, septic, and cardiogenic shock.

SETTING

University-affiliated research laboratory.

SUBJECTS

Sixteen anesthetized domestic pigs weighing 35-45 kg.

INTERVENTIONS

Hemorrhagic shock was induced in five pigs by bleeding followed by reinfusion of shed blood. Septic shock was induced in five pigs by infusion of live Escherichia coli. Cardiogenic shock followed an interval of global myocardial ischemia after inducing and reversing ventricular fibrillation in six pigs.

MEASUREMENTS AND MAIN RESULTS

PetCO2 was continuously measured. Cardiac index was measured intermittently by using conventional thermodilution techniques. Cardiac index was correlated with PetCO2 by polynomial regression and Bland-Altman analyses. PetCO2 was highly correlated with cardiac index during hemorrhagic shock (r2 = .69, p < .01), septic shock (r2 = .65, p < .01), and cardiogenic shock (r2 = .81, p < .01). PetCO2 predicted thermodilution cardiac index with bias of -11+/-27 (+/-2 SD) mL/min/kg during hemorrhagic shock, 1.3+/-20.4 (+/- 2 SD) mL/min/kg during septic shock, and -1+/-12 (+/-2 SD) mL/min/kg during cardiogenic shock.

CONCLUSIONS

Cardiac output and PetCO2 were highly related in diverse experimental models of circulatory shock in which cardiac output was reduced by >40% of baseline values. Therefore, measurement of PetCO2 is a noninvasive alternative for continuous assessment of cardiac output during low-flow circulatory shock states of diverse causes.

Alveolar dead space as a predictor of severity of pulmonary embolism

OBJECTIVE

To determine whether the alveolar dead space volume (V(D)alv), expressed as a percentage of the alveolar tidal volume (V(D)alv/V(T)alv), can predict the degree of vascular occlusion caused by pulmonary embolism (PE).

METHODS

Fifty-three subjects with suspected PE were prospectively studied. Pulmonary embolism was diagnosed in 33 by high-probability ventilation/perfusion (V/Q) scan (n = 19) or by pulmonary arteriography (PAG, n = 14). Pulmonary embolism was excluded by PAG in 20 subjects. The V(D)alv/V(T)alv was determined from volumetric capnography and arterial blood gas analysis, which permits measurement of the physiologic dead space, V(D)phys (mL) = [(PaCO2 - PeCO2)/PaCO2]. tidal volume. Airway dead space (V(D)aw) was subtracted to yield the alveolar dead space [(V(D)phys - V(D)aw) = V(D)alv (mL)]; the percentage of alveolar volume occupied by alveolar dead space per breath = V(D)alv/V(T)alv x 100%. Percentage perfusion defect was determined from V/Q scans by a radiologist blinded to other data. Regression analysis was performed to show correlation between V(D)alv/V(T)alv and defect on V/Q scan or systolic pulmonary arterial pressure (SPAP).

RESULTS

For subjects with PE, the mean perfusion defect on lung scan was 38 +/- 22%; the mean V(D)alv = 208 +/- 115 mL, V(T)alv = 452 +/- 251 mL, and V(D)alv/V(T)alv = 43 +/- 18%. Regression of V(D)alv/V(T)alv vs perfusion defect yielded r2 = 0.41. Regression of V(D)alv/V(T)alv vs pulmonary artery pressures yielded r2 = 0.59. For subjects without PE, V(D)alv/V(T)alv = 27 +/- 14% and V(D)alv = 89 +/- 66 mL.

CONCLUSIONS

The V(D)alv/V(T)alv correlates with the lung perfusion defect and the pulmonary artery pressures in subjects with PE. These findings show the potential for V(D)alv/V(T)alv to quantify the embolic burden of PE.

[Vascular loading in the first 24 hours following severe head injuries]

The main goal at the acute phase of head injury is to prevent a decrease in blood pressure, which promotes cerebral ischemia. Volume loading is therefore frequently indicated. A normal or increased plasma osmolarity should be maintained. Thus hypotonic fluids should be avoided. Hyperglycaemia is also a risk factor for brain injury and glucose use has to be restricted in the first hours after trauma. Isotonic saline 0.9% is the first solution to be infused. Lactated Ringer solutions are mildly hypotonic as approximately 114 mL of free water is contained in each litre of the solution. Isotonic colloids are indicated to replace blood losses, but have no advantage over cristalloids, concerning the development of cerebral oedema. Fluid restriction minimally affects cerebral edema. Because of the severe consequences of hypovolaemia and hypotension, fluids should not be restricted until haemodynamic stability is achieved. Hypertonic fluids rapidly restore intravascular volume and decrease intracranial pressure. Although they probably have a place in prehospital intensive therapy, the demonstration of their benefit is still lacking. Monitoring of intravascular volume is essential. Continuous arterial pressure and central venous pressure monitoring are mandatory. New monitoring techniques as the measurement of systolic pressure variations or transoesophageal Doppler echocardiography will probably find a place in the management of trauma patients in the near future.

Estimation of alveolar deadspace fraction using arterial and end-tidal CO2: a factor analysis using a physiological simulation

The alveolar deadspace as a fraction of alveolar ventilation (VDalv/VTalv), while technically difficult to measure, is an objective monitor of pulmonary disease progression and a predictor of successful weaning from mechanical ventilation. The aim of the study was to examine the relationship between the arterial to end-tidal PCO2 gradient (Pa-E'CO2) and VDalv/VTalv and between (Pa-E'CO2)/PaCO2 and VDalv/VTalv using the Nottingham Physiology Simulator, an original, validated physiology simulation. The relationships were observed while pulmonary shunt, anatomical deadspace, ventilatory minute volume and metabolic rate were varied. The relationship between Pa-E'CO2 and VDalv/VTalv was non-linear and was affected significantly by all the factors except anatomical deadspace. The relationship between (Pa-E'CO2)/PaCO2 and VDalv/VTalv (best fit: VDalv VTalv = 1.135 x (Pa-E'CO2)/PaCO2-0.005) during normal physiological conditions was approximately linear and less influenced by physiological variation. Shunt and anatomical deadspace caused some inaccuracy, although they are unlikely to prevent the clinical usefulness of this formula.

Pulmonary gas exchange during intramedullary fixation of femoral shaft fractures

BACKGROUND

This study was undertaken to determine if the alveolar dead space fraction (Vd/Vt) or the alveolar-arterial oxygen gradient (A-a DO2) increased during intramedullary fixation of femoral shaft fractures.

METHODS

Fifty hemodynamically stable patients with femur fractures were prospectively enrolled. Three serial measurements of Vd/Vt and A-a DO2 were obtained immediately before femoral nailing (Pre), 30 minutes after nailing (+30), and 120 minutes after nailing (+120). Vd/Vt was determined by simultaneously measuring PaCO2 and the steady-state end-tidal CO2 (PetCO2), where Vd/Vt = (1 - PetCO2/PaCO2).

RESULTS

Vd/Vt before nailing was 0.09 +/- 0.09 (mean +/- SD); at +30 and +120, Vd/Vt was 0.10 +/- 0.06 and 0.08 +/- 0.07, respectively (p > 0.2; paired t test, both time points). A-a DO2 before nailing was 84 +/- 85 mm Hg, and it did not change significantly at +30 (89 +/- 69 mm Hg; p = 0.51 vs. Pre; paired t-test) or at +120 (51 +/- 45 mm Hg). No difference in data was found with analysis by fracture classification or number of reamer passes. Vd/Vt and A-a DO2, however, were both significantly increased in patients with lung contusion (n = 6) before nailing, but neither measurement increased after nailing. One patient developed fat embolism (Vd/Vt of 0.35 at Pre and 0.31 at +120), and another patient experienced postoperative pulmonary thromboembolism (Vd/Vt increased from 0.06 at Pre to 0.17 at +120).

CONCLUSION

The process of femoral nailing does not cause enough pulmonary embolization to alter pulmonary gas exchange as measured by Vd/Vt and A-a DO2. If Vd/Vt is increased preoperatively, the likelihood of subsequent pulmonary dysfunction secondary to either preoperative lung injury or fat embolism is increased.

Intraoperative end-tidal carbon dioxide levels and derived calculations correlated with outcome in trauma patients

BACKGROUND

To determine the relationship between the prognosis of seriously injured patients requiring emergency surgery and intraoperative end-tidal CO2 variables and "excess Pco2."

METHOD

Retrospective chart review of 100 seriously injured patients admitted to Detroit Receiving Hospital and requiring major surgery (mortality rate of 40%). Standard intraoperative monitoring, including continuous capnography, plus arterial blood analyses every 15 to 30 minutes during surgery.

RESULTS

After resuscitation for 45 to 90 minutes, 11 patients had a systolic blood pressure < 100 mm Hg and, of these patients, 10 (91%) died. Of the remaining 89 patients, mortality rates were 53% (16/30), with an end-tidal CO2 of 22 mm Hg or less, versus 24% (14/59) with an end-tidal CO2 of 23 mm Hg or more (p = 0.011). An arterial to end-tidal Pco2 difference of 13 mm Hg or more after resuscitation was associated with an increased mortality rate (50% (20/34 vs. 18% (20/55)) (p < 0.005). The mortality rate was particularly high, with a final arterial to end-tidal Pco2 difference of 12 mm Hg or more (73% (30/41) versus 17% (10/59) (p < 0.001). A final Paco2 excess (i.e., the amount by which the Paco2 was higher than expected from the bicarbonate) > 1.0 mm Hg was also associated with an increased mortality rate ((62% (33/53) vs. 15% (7/47)) (p < 0.001).

CONCLUSION

Values derived from the end-tidal CO2 and the excess Pco2 should be monitored intraoperatively in critically injured patients. Efforts should be made to improve cardiac output and adjust ventilation to maintain an end-tidal Pco2 of 25 mm Hg or more, an arterial to end-tidal CO2 difference of 12 mm Hg or less, and an excess Paco2 of 1.0 mm Hg or less.

Relationship between arterial carbon dioxide and end-tidal carbon dioxide in mechanically ventilated adults with severe head trauma

OBJECTIVE

To examine the agreement and association of a noninvasive method of measuring CO2 (using end-tidal PCO2) with PaCO2 in mechanically ventilated adults with severe head trauma.

DESIGN

A prospective, quasi-experimental, repeated-measures study was used to compare end-tidal PCO2 and PaCO2 at two time points: before and after a standardized endotracheal suctioning procedure.

INTERVENTIONS

Controlled intervention of endotracheal suctioning.

SETTING

The study was conducted at two intensive care units designated as Level 1 trauma centers.

PATIENTS

A consecutive sample of 35 severe head-injured patients with a Glasgow Coma Scale score of < or = 8.

MEASUREMENTS AND MAIN RESULTS

End-tidal PCO2 and PaC02 values were simultaneously obtained and compared. End-tidal PCO2 was measured, using a sidestream sensor placed in line of the ventilator circuit's deadspace. Arterial gases were drawn from an indwelling arterial catheter. No relationship was found between arterial and end-tidal measures (range r2 = .09 to r2 = .11). Using the Bland-Altman technique, agreement decreased as the amount of positive end-expiratory pressure increased. When a subset of patients (mechanically ventilated, with positive end-expiratory pressures of < 5 cm H2O, paralyzed, and sedated) were examined (n = 12), the correlation between the CO2 measures improved (r2 = .77).

CONCLUSIONS

This study indicated that end-tidal PCO2 monitoring correlated well with PaCO2 in patients without respiratory complications or without spontaneous breathing, resulting in rebreathing of gases. However, its clinical validity is questionable in patients who have the greatest need for end-tidal PCO2 monitoring (i.e., patients who have respiratory distress or who are breathing spontaneously and overriding the ventilator.