Stability of the intraoperative arterial to end-tidal carbon dioxide partial pressure difference in children with congenital heart disease

Effect of corrective or palliative procedures on arterial to end-tidal carbon dioxide pressure difference in pediatric cardiac surgery

BACKGROUND

The normal small difference (3-5 mmHg) between arterial (partial pressure of carbon dioxide [PaCO₂]) and end-tidal carbon dioxide pressure (ETPCO₂) increases in children with congenital heart disease. The present study was conducted to evaluate the effect of corrective or palliative cardiac surgery on this difference (known as DPCO2).

PATIENTS AND METHODS

In a prospective study, 200 children (aged <12 years old) candidate for corrective or palliative cardiac surgery were studied. Using arterial blood gas measurement and simultaneous capnography, DPCO₂ was calculated at various intra- and postoperative periods. DPCO₂ values were compared within and between corrective or palliative procedures.

RESULTS

Corrective and palliative procedures were carried out on 154 and 46 patients, respectively. Initial DPCO₂ was higher than normal values in corrective or palliative procedures (15.50 ± 13.1 and 10.75 ± 9.1 mmHg, respectively). DPCO₂ was higher in patients who underwent palliative procedure, except early after procedure. The procedure did not have any effect on the final DPCO₂ in palliative group. Although DPCO₂ decrease was significant in the corrective group, it did not return to normal values. Operation time was longer, and the need to inotropic support was higher in corrective procedures; however, longer periods of ventilatory support were needed in the palliative group. Complication rate and Intensive Care Unit stay time were the same in two operation types.

CONCLUSIONS

DPCO₂ did not change after palliative cardiac procedures. DPCO₂ decreased after corrective procedures; however, it did not return to normal values at early postoperative period. Thus, DPCO₂ may not have any clinical value in monitoring the quality of corrective or palliative procedures.

Monitoring of standard hemodynamic parameters: heart rate, systemic blood pressure, atrial pressure, pulse oximetry, and end-tidal CO2

BACKGROUND

Continuous monitoring of various clinical parameters of hemodynamic and respiratory status in pediatric critical care medicine has become routine. The evidence supporting these practices is examined in this review.

METHODOLOGY

A search of MEDLINE, EMBASE, PubMed, and the Cochrane Database was conducted to find controlled trials of heart rate, electrocardiography, noninvasive and invasive blood pressure, atrial pressure, end-tidal carbon dioxide, and pulse oximetry monitoring. Adult and pediatric data were considered. Guidelines published by the Society for Critical Care Medicine, the American Heart Association, the American Academy of Pediatrics, and the International Liaison Committee on Resuscitation were reviewed, including further review of references cited.

RESULTS AND CONCLUSIONS

Use of heart rate, electrocardiography, noninvasive and arterial blood pressure, atrial pressure, pulse oximetry, and end-tidal carbon dioxide monitoring in the pediatric critical care unit is commonplace; this practice, however, is not supported by well-controlled clinical trials. Despite the majority of literature being case series, expert opinion would suggest that use of routine pulse oximetry and end-tidal carbon dioxide is the current standard of care. In addition, literature would suggest that invasive arterial monitoring is the current standard for monitoring in the setting of shock. The use of heart rate, electrocardiography. and atrial pressure monitoring is advantageous in specific clinical scenarios (postoperative cardiac surgery); however, the evidence for this is based on numerous case series only.

Arterial to endtidal carbon dioxide gradient during pediatric laparoscopic fundoplication

BACKGROUND

Discrepancies between arterial carbon dioxide (P(a)CO(2)) and endtidal carbon dioxide (ETCO(2)) measures have been demonstrated in ventilated children with cyanotic congenital heart disease, infants with respiratory failure and during visceral and urological laparoscopic surgery.

OBJECTIVES

Our objective was to assess the extent of the P(a)CO(2) to ETCO(2) gradient in children during laparoscopic fundoplication.

METHODS

We prospectively collected data on patient characteristics, surgical conditions, pH, ETCO(2)and P(a)CO(2) during laparoscopic fundoplication using carbon dioxide insufflation in children age <29 months.

RESULTS

Data were collected on nine cases, four cases aged <1 year. A P(a)-ETCO(2) gradient was present during insufflation. The gradient was larger in children age less than 1 year but statistically significantly different from a value of zero, only at t = 30 min (mean = 8 mmHg, sem = 0.81, P = 0.004) and t = 60 min (mean = 5 mmHg, sem = 1, P = 0.014). Minute ventilation was increased from 20% to 100% to control ETCO(2).

CONCLUSIONS

ETCO(2) may not accurately represent arterial values during laparoscopic fundoplication, especially in the infant when carbon dioxide insufflation is used. Consideration should be given to placing an arterial line for blood gas measurement in some patients.

The value of end-tidal carbon dioxide monitoring during systemic-to-pulmonary artery shunt insertion in cyanotic children

OBJECTIVE

To investigate the relationship between end-tidal carbon dioxide levels and augmentation of pulmonary blood flow achieved by insertion of systemic-pulmonary shunts.

DESIGN

Prospective clinical study.

SETTINGS

University hospital.

PARTICIPANTS

Nineteen cyanotic children with tetralogy of Fallot.

INTERVENTIONS

Modified Blalock-Taussig shunt operations were performed on the left side in 14 patients and on the right side in 5 patients.

MEASUREMENTS AND MAIN RESULTS

End-tidal carbon dioxide tension was recorded, and an arterial blood gas sample was obtained simultaneously after thoracotomy (T0) and after completion of systemic-pulmonary shunt (T1). End-tidal carbon dioxide tension was significantly higher ( p < 0.01), and arterial to end-tidal carbon dioxide tension difference was significantly lower (p < 0.01) at T1 when compared with T0. The increase in end-tidal carbon dioxide showed a statistically significant correlation with the response of arterial oxygen saturation (r = 0.61, p < 0.01). The fall in arterial to end-tidal carbon dioxide tension difference correlated inversely with the change of oxygen saturation (r = -0.81, p < 0.0001).

CONCLUSION

It is concluded that end-tidal carbon dioxide tension alterations offer an alternative intraoperative tool to monitor pulmonary blood flow during modified Blalock-Taussig shunt procedures.

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.

The arterial to end-tidal carbon dioxide gradient increases with uncorrected but not with temperature-corrected PaCO2 determination during mild to moderate hypothermia

End-tidal carbon dioxide (PETCO2) monitoring is recommended as a basic standard of care and is helpful in adjusting mechanical ventilation. Gas solubility changes with temperature, which might affect the PaCO2 and thereby the gradient between PaCO2 and PETCO2 (PA-ETCO2) under hypothermic conditions. We investigated whether the PA-ETCO2 changes during mild to moderate hypothermia (36 degrees C-32 degrees C) using PaCO2 measured at 37 degrees C (uncorrected PaCO2) and PaCO2 corrected to actual body temperature. We preoperatively investigated 19 patients. After anesthesia had been induced, controlled ventilation was established to maintain normocarbia using constant uncorrected PaCO2 to adjust ventilation (alpha-stat acid-base regimen). Body core temperature was reduced without surgical intervention to 32 degrees C by surface cooling. Continuous PETCO2 was monitored with a mainstream PETCO2 module. The PA-ETCO2 was calculated using the uncorrected and corrected PaCO2 values. During body temperature reduction from 36 degrees C to 32 degrees C, the gradient between PETCO2 and uncorrected PaCO2 increased 2.5-fold, from 4.1 +/- 3.7 to 10.4 +/- 3.8 mm Hg (P < 0.002). The PA-ETCO2 remained unchanged when the corrected PaCO2 was used for the calculation. We conclude that when the alpha-stat acid-base regimen is used to adjust ventilation, the PA-ETCO2 calculated with the uncorrected PaCO2 increases and should be added to the differential diagnosis of widened PA-ETCO2. In contrast, when the corrected PaCO2 is used for the calculation of the PA-ETCO2, the PA-ETCO2 remains unaltered during hypothermia.

IMPLICATIONS

We investigated the impact of induced hypothermia (36 degrees C-32 degrees C) on the gradient between PaCO2 and PETCO2 (PA-ETCO2). The PA-ETCO2 increased 2.5-fold when CO2 determinations were not temperature-corrected. Hypothermia should be added to the differential diagnosis of an increased PA-ETCO2 when the alpha-stat acid-base regimen is used.

Stability of the arterial to end-tidal carbon dioxide difference during anaesthesia for prolonged neurosurgical procedures

This study was undertaken to examine the variation of the arterial to end-tidal PCO2 (Pa-PETCO2) difference during prolonged neurosurgical anaesthesia. Hyperventilation is often used to reduce intracranial pressure in neurosurgical patients. Continuous end-tidal CO2 monitoring is used as a guide between arterial CO2 measurements. We examined the stability of the Pa-PETCO2 difference in 21 patients undergoing elective craniotomies lasting greater than four hours. A balanced neuroanaesthetic technique was used with the ventilation variables at the discretion of the attending anaesthetist. Once patients were positioned for surgery, simultaneous samples of arterial PCO2 through an arterial catheter, and end-tidal PCO2 via a mass spectrometer were obtained. The Pa-PETCO2 differences of each patient were plotted against time and a slope was derived with simple linear regression. The mean slope for all patients was then computed. There were no changes in the Pa-PETCO2 difference with time (P > 0.05) suggesting a constant relationship between the arterial and end-tidal PCO2 measurements over time. We conclude that end-tidal PCO2 can be used as a reliable guide to estimate arterial PCO2 during neurosurgical procedures of greater than four hours duration once the Pa-PETCO2 difference has been established.

Monitoring during paediatric cardiac anaesthesia

Monitoring of paediatric anaesthesia has become increasingly more complex in recent years and this is particularly true of cardiac anaesthesia. The purpose of this review is to give a comprehensive update of published material related to both routine and specialized cardiac monitoring. Routine monitoring can be particularly affected by the alterations of cardiac rhythm, blood flow, cardiac output and oxygenation which result from the congenital heart abnormalities themselves, the type of surgery undertaken and the effects of cardiopulmonary bypass. The use of specialized monitoring is becoming more widespread, particularly in the areas of cerebral function, mixed venous oxygenation, cardiac output measurement and coagulation. In the last five years, with the development of smaller probes, a great deal has been published on transoesophageal echocardiography. The use of the current monitors of cerebral function still remains controversial despite the need for a monitor of adequate brain perfusion, reflecting the need for a great deal of further research in this area. This review will concentrate on particular areas which have seen the most profound changes and on monitoring that may form the standards of tomorrow. Finally, amongst all the technology, it should not be forgotten that the most important clinical monitor is the bedside clinical monitoring of the physicians themselves.