[The measurement of end-tidal carbon dioxide (PETCO2) is not a significant parameter to monitor in patients with severe traumatic brain injury]

Trending Ability of End-Tidal Capnography Monitoring During Mechanical Ventilation to Track Changes in Arterial Partial Pressure of Carbon Dioxide in Critically Ill Patients With Acute Brain Injury: A Monocenter Retrospective Study

BACKGROUND

Changes in arterial partial pressure of carbon dioxide (Pa co2 ) may alter cerebral perfusion in critically ill patients with acute brain injury. Consequently, international guidelines recommend normocapnia in mechanically ventilated patients with acute brain injury. The measurement of end-tidal capnography (Et co2 ) allows its approximation. Our objective was to report the agreement between trends in Et co2 and Pa co2 during mechanical ventilation in patients with acute brain injury.

METHODS

Retrospective monocenter study was conducted for 2 years. Critically ill patients with acute brain injury who required mechanical ventilation with continuous Et co2 monitoring and with 2 or more arterial gas were included. The agreement was evaluated according to the Bland and Altman analysis for repeated measurements with calculation of bias, and upper and lower limits of agreement. The directional concordance rate of changes between Et co2 and Pa co2 was evaluated with a 4-quadrant plot. A polar plot analysis was performed using the Critchley methods.

RESULTS

We analyzed the data of 255 patients with a total of 3923 paired ΔEt co2 and ΔPa co2 (9 values per patient in median). Mean bias by Bland and Altman analysis was -8.1 (95 CI, -7.9 to -8.3) mm Hg. The directional concordance rate between Et co2 and Pa co2 was 55.8%. The mean radial bias by polar plot analysis was -4.4° (95% CI, -5.5 to -3.3) with radial limit of agreement (LOA) of ±62.8° with radial LOA 95% CI of ±1.9°.

CONCLUSIONS

Our results question the performance of trending ability of Et co2 to track changes in Pa co2 in a population of critically ill patients with acute brain injury. Changes in Et co2 largely failed to follow changes in Pa co2 in both direction (ie, low concordance rate) and magnitude (ie, large radial LOA). These results need to be confirmed in prospective studies to minimize the risk of bias.

Evaluating a novel formula for noninvasive estimation of arterial carbon dioxide during post-resuscitation care

BACKGROUND

Controlling arterial carbon dioxide is paramount in mechanically ventilated patients, and an accurate and continuous noninvasive monitoring method would optimize management in dynamic situations. In this study, we validated and further refined formulas for estimating partial pressure of carbon dioxide with respiratory gas and pulse oximetry data in mechanically ventilated cardiac arrest patients.

METHODS

A total of 4741 data sets were collected retrospectively from 233 resuscitated patients undergoing therapeutic hypothermia. The original formula used to analyze the data is PaCO₂ -est1 = PETCO₂  + k[(PIO₂  - PETCO₂ ) - PaO₂ ]. To achieve better accuracy, we further modified the formula to PaCO₂ -est2 = k₁ *PETCO₂  + k₂ *(PIO₂  - PETCO₂ ) + k₃ *(100-SpO₂ ). The coefficients were determined by identifying the minimal difference between the measured and calculated arterial carbon dioxide values in a development set. The accuracy of these two methods was compared with the estimation of the partial pressure of carbon dioxide using end-tidal carbon dioxide.

RESULTS

With PaCO₂ -est1, the mean difference between the partial pressure of carbon dioxide, and the estimated carbon dioxide was 0.08 kPa (SE ±0.003); with PaCO₂ -est2 the difference was 0.036 kPa (SE ±0.009). The mean difference between the partial pressure of carbon dioxide and end-tidal carbon dioxide was 0.72 kPa (SE ±0.01). In a mixed linear model, there was a significant difference between the estimation using end-tidal carbon dioxide and PaCO₂ -est1 (P < .001) and PaCO₂ -est2 (P < .001) respectively.

CONCLUSIONS

This novel formula appears to provide an accurate, continuous, and noninvasive estimation of arterial carbon dioxide.

Postoperative care of the neurosurgical patient

PURPOSE OF REVIEW

Monitoring and therapy of patients in neurocritical care are areas of intensive research and the current evidence needs further confirmation.

RECENT FINDINGS

A consensus statement of the Neurocritical Care Society and the European Society of Intensive Care Medicine provided pragmatic guidance and recommendations for multimodal monitoring in neurocritical care patients. Only a minority of these recommendations have strong evidence. In addition, recent multicenter randomized controlled trials concerning the therapy of subarachnoidal hemorrhage and traumatic brain injury could not show decreased mortality or improved functional neurologic outcome after the interventions. The current evidence for monitoring and medical therapy in patients after traumatic brain injury and aneurysmal subarachnoid hemorrhage is highlighted in this review.

SUMMARY

Although strong evidence is lacking, multimodal monitoring is of great value in neurocritical care patients and may help to provide patients with the optimal therapy based on the individual pathophysiological changes.

Transcutaneous PTCCO2 measurement in combination with arterial blood gas analysis provides superior accuracy and reliability in ICU patients

Hyper or hypoventilation may have serious clinical consequences in critically ill patients and should be generally avoided, especially in neurosurgical patients. Therefore, monitoring of carbon dioxide partial pressure by intermittent arterial blood gas analysis (PaCO₂) has become standard in intensive care units (ICUs). However, several additional methods are available to determine PCO₂ including end-tidal (PETCO₂) and transcutaneous (PTCCO₂) measurements. The aim of this study was to compare the accuracy and reliability of different methods to determine PCO₂ in mechanically ventilated patients on ICU. After approval of the local ethics committee PCO₂ was determined in n = 32 ICU consecutive patients requiring mechanical ventilation: (1) arterial PaCO₂ blood gas analysis with Radiometer ABL 625 (ABL; gold standard), (2) arterial PaCO₂ analysis with Immediate Response Mobile Analyzer (IRMA), (3) end-tidal PETCO₂ by a Propaq 106 EL monitor and (4) transcutaneous PTCCO₂ determination by a Tina TCM4. Bland-Altman method was used for statistical analysis; p < 0.05 was considered statistically significant. Statistical analysis revealed good correlation between PaCO₂ by IRMA and ABL (R² = 0.766; p < 0.01) as well as between PTCCO₂ and ABL (R² = 0.619; p < 0.01), whereas correlation between PETCO₂ and ABL was weaker (R² = 0.405; p < 0.01). Bland-Altman analysis revealed a bias and precision of 2.0 ± 3.7 mmHg for the IRMA, 2.2 ± 5.7 mmHg for transcutaneous, and -5.5 ± 5.6 mmHg for end-tidal measurement. Arterial CO₂ partial pressure by IRMA (PaCO₂) and PTCCO₂ provided greater accuracy compared to the reference measurement (ABL) than the end-tidal CO₂ measurements in critically ill in mechanically ventilated patients patients.

Prehospital management of traumatic brain injury

The aim of this study was to review the current protocols of prehospital practice and their impact on outcome in the management of traumatic brain injury. A literature review of the National Library of Medicine encompassing the years 1980 to May 2008 was performed. The primary impact of a head injury sets in motion a cascade of secondary events that can worsen neurological injury and outcome. The goals of care during prehospital triage, stabilization, and transport are to recognize life-threatening raised intracranial pressure and to circumvent cerebral herniation. In that process, prevention of secondary injury and secondary insults is a major determinant of both short- and longterm outcome. Management of brain oxygenation, blood pressure, cerebral perfusion pressure, and raised intracranial pressure in the prehospital setting are discussed. Patient outcomes are dependent upon an organized trauma response system. Dispatch and transport timing, field stabilization, modes of transport, and destination levels of care are addressed. In addition, special considerations for mass casualty and disaster planning are outlined and recommendations are made regarding early response efforts and the ethical impact of aggressive prehospital resuscitation. The most sophisticated of emergency, operative, or intensive care units cannot reverse damage that has been set in motion by suboptimal protocols of triage and resuscitation, either at the injury scene or en route to the hospital. The quality of prehospital care is a major determinant of long-term outcome for patients with traumatic brain injury.

Correlation of arterial Pco2 and Petco2 in prehospital controlled ventilation

INTRODUCTION

This study was carried out to estimate the relationship between arterial PCO2 (PaCO2) and end-tidal carbon dioxide (PETCO2) during prehospital controlled ventilation and also to evaluate variation of the gradient between PCO2 and PETCO2 during prehospital transport.

METHODS

Measurements of PETCO2 from capnography values and PaCO2 from arterial blood gases were registered at the beginning (T(0)) and at the end (T(end)) of out-of-hospital management. For all patients requiring invasive ventilation, the gradient between PCO2 and PETCO2 was calculated for T(0) and T(end), the PaCO2-PETCO2 variation between T(end) and T(0) was also calculated.

RESULTS

One hundred patients were included in this study (mean age, 58.4 +/- 16.4 years; 57 were male). There was no variation of the mean gradient (DeltaPaCO2-PETCO2 ) during transport (8.64 +/- 13.5 mm Hg at T(0) and 7.26 +/- 12.94 mm Hg at T(end)). Thirty-six percent of patients (n = 36) had a gradient above +10 mm Hg, and for 6% of patients (n = 4) the gradient was lower than -10 mm Hg. The PaCO2-PETCO2 gradient was not significantly different according to the pathology, but was significantly higher in hypercapnic patients compared with hypocapnic or normocapnic patients. In patients with severe head injury, the capnia was normalized in 80% of patients at the end of the transport according to the last blood gas result. In this subgroup the DeltaPaCO2-PETCO2 (T(end) - T(0)) gradient was stable between T(0) and T(end) except in 20% of the patients for whom the DeltaPaCO2-PETCO2 was lower than -10 mm Hg. Fifty-four percent of critical care physicians had modified the respiratory setting after the first arterial blood gas results.

CONCLUSIONS

The PaCO2 cannot be estimated by the PETCO2 in the prehospital setting. There is wide variation in the gradient between PCO2 and PETCO2 depending on patient condition, and over time, the relationship does not remain constant and thus cannot be useful in prehospital ventilation management.