Continuous end-tidal CO2 sampling within the proximal endotracheal tube estimates arterial CO2 tension in infants

Carbon dioxide monitoring in children-A narrative review of physiology, value, and pitfalls in clinical practice

Continuous capnography has been recognised as an essential monitoring device in all anesthetized patients, despite which airway device is in use, regardless of their location, as a measure to improve patient safety. Capnography is the non-invasive measurement of a sample of the exhaled carbon dioxide which has multiple clinical uses including as a method to confirm placement of a tracheal tube and/or to assess ventilation, perfusion and metabolism. Notably, capnography is used during routine paediatric anesthesia to assess ventilation and as a surrogate measure for arterial carbon dioxide pressure. The inaccuracies associated with these surrogate measures need to be considered to inform improved ventilation management of infants and children. This review highlights some major principles to understand the carbon dioxide elimination, the physiology of paediatric capnography, the clinical application and the limitations of capnography during anesthesia for neonates, infants and small children.

Correlation of Intraoperative End-Tidal Carbon Dioxide Concentration on Postoperative Hospital Stay in Patients Undergoing Pylorus-Preserving Pancreaticoduodenectomy

Background

Hypocapnia has been traditionally advocated during general anesthesia, even though it may induce deleterious physiological effects that result in unfavorable outcomes in patients. This study investigated the association between intraoperative end-tidal carbon dioxide (EtCO₂) and length of hospital stay (LOS) in patients who underwent pylorus-preserving pancreaticoduodenectomy (PPPD).

Methods

The medical records of 759 patients from 2006 to 2015 were reviewed. The patients were divided into two groups based on the mean EtCO₂ value during general anesthesia: the hypocapnia group (< 35 mmHg) and the normocapnia group (≥ 35 mmHg). The primary outcome was LOS between the groups. Secondary outcomes included the length of intensive care unit (ICU) stay, postoperative 30-day, 1-year, and 2-year mortality, and perioperative factors associated with LOS.

Results

A total of 727 patients were finally analyzed. The median LOS of the hypocapnia group was significantly longer than that of the normocapnia group (22 days vs. 18 days, respectively; p < 0.001). Postoperative mortality did not differ between the groups. Cox regression analysis revealed that hypocapnia was an independent risk factor for longer LOS (hazard ratio [HR], 1.61; 95% confidence interval [CI], 1.37–1.89; p < 0.001). Age and postoperative pancreatic fistula were also risk factors for a longer LOS.

Conclusions

It was concluded that low levels of intraoperative EtCO₂ during general anesthesia were associated with an increased LOS for patients undergoing PPPD.

Application of end-tidal carbon dioxide monitoring via distal gas samples in ventilated neonates

BACKGROUND

Previous research has suggested correlations between the end-tidal partial pressure of carbon dioxide (P_ETCO₂) and the partial pressure of arterial carbon dioxide (PaCO₂) in mechanically ventilated patients, but both the relationship between P_ETCO₂ and PaCO₂ and whether P_ETCO₂ accurately reflects PaCO₂ in neonates and infants are still controversial. This study evaluated remote sampling of P_ETCO₂ via an epidural catheter within an endotracheal tube to determine the procedure's clinical safety and efficacy in the perioperative management of neonates.

METHODS

Abdominal surgery was performed under general anesthesia in 86 full-term newborns (age 1-30 days, weight 2.55-4.0 kg, American Society of Anesthesiologists class I or II). The infants were divided into 2 groups (n = 43 each), and carbon dioxide (CO₂) gas samples were collected either from the conventional position (the proximal end) or a modified position (the distal end) of the epidural catheter.

RESULTS

The P_ETCO₂ measured with the new method was significantly higher than that measured with the traditional method, and the difference between P_ETCO₂ and PaCO₂ was also reduced. The accuracy of P_ETCO₂ measured increased from 78.7% to 91.5% when the modified sampling method was used. The moderate correlation between P_ETCO₂ and PaCO₂ by traditional measurement was 0.596, which significantly increased to 0.960 in the modified sampling group. Thus, the P_ETCO₂ value was closer to that of PaCO₂.

CONCLUSION

P_ETCO₂ detected via modified carbon dioxide monitoring had a better accuracy and correlation with PaCO₂ in neonates.

Arterial and end-tidal carbon dioxide difference in pediatric intensive care

Background and Aim:

Arterial carbon dioxide tension (PaCO₂) is considered the gold standard for scrupulous monitoring in pediatric intensive care unit (PICU), but it is invasive, laborious, expensive, and intermittent. The study aims to explore when we can use end-tidal carbon dioxide tension (P_ETCO₂) as a reliable, continuous, and noninvasive monitor of arterial CO₂

Materials and Methods:

Concurrent P_ETCO₂, fraction of inspired oxygen, PaCO₂, and arterial oxygen tension values of clinically stable children on mechanical ventilation were recorded. Children with extra-pulmonary ventriculoatrial shunts were excluded. The P_ETCO₂ and PaCO₂ difference and its variability and reproducibility were studied.

Results:

A total of 624 concurrent readings were obtained from 105 children (mean age [SD] 5.53 [5.43] years) requiring invasive bi-level positive airway pressure ventilation in the PICU. All had continuous P_ETCO₂ monitoring and an arterial line for blood gas measurement. The mean (SD) number of concurrent readings obtained from each child, 4-6 h apart was 6.0 (4.05). The P_ETCO₂ values were higher than PaCO₂ in 142 observations (22.7%). The PaCO₂–P_ETCO₂ difference was individual admission specific (ANOVA, P < 0.001). The PaCO₂–P_ETCO₂ difference correlated positively with the alveolar-arterial oxygen tension [P(A-a)O₂] difference (ρ = 0.381 P < 0.0001). There was a fixed bias between the P_ETCO₂ and PaCO₂ measuring methods, difference +0.66 KPa (95% confidence interval: +0.57 to +0.76).

Conclusions:

The PaCO₂–P_ETCO₂ difference was individual specific. It was not affected by the primary disorder leading to the ventilation.

The effect of volume loading on systemic oxygenation after bidirectional superior cavopulmonary anastomosis

BACKGROUND

The unique series arrangement of the cerebral and pulmonary circulation in bidirectional superior cavopulmonary anastomosis (BCPA) makes the pulmonary blood flow dependent upon the cerebral blood flow. Until now, several investigators have tried to correct post-BCPA hypoxemia with various methods such as induced hyperventilation, the addition of carbon dioxide, and inhaled nitric oxide with variable success rates.

METHODS

We prospectively studied 25 children with univentricular physiology undergoing BCPA surgery at 5 different time points in the preoperative (1 time point) and postoperative period (4 time points, each separated by at least 3 mm Hg changes in the superior vena cava [SVC] pressure). Intravenous fluids were administered in the postoperative period to raise the SVC pressure.

RESULTS

The systemic arterial oxygen saturation (Sao2) increased significantly (p = 0.000) from a preoperative value of 80% ± 7% to 86% ± 7%, 91% ± 3% and 95% ± 4% at SVC pressures of 9 ± 1.6 mm Hg, 13 ± 1.3 mm Hg, and 16 ± 1.4 mm Hg, respectively, and then decreased to 94% ± 4% at SVC pressure of 20 ± 1.7 mm Hg. Systolic and diastolic blood pressure increased significantly and simultaneously with SVC pressure from 71 ± 8 mm Hg and 42 ± 6 mm Hg to 89 ± 11 mm Hg and 52 ± 7 mm Hg, respectively (p = 0.000).

CONCLUSIONS

Administration of intravenous fluids improves the SVC pressure, possibly due to an increase in the cerebral blood flow and the SVC flow, and thus raises the arterial oxygen tension (Pao2) and Sao2. Each patient has a unique SVC pressure where the Sao2 and the Pao2 are maximum; beyond that limit, the Sao2 does not improve.

End-inspiratory rebreathing reduces the end-tidal to arterial PCO2 gradient in mechanically ventilated pigs

PURPOSE

Noninvasive monitoring of the arterial partial pressures of CO(2) (PaCO(2)) of critically ill patients by measuring their end-tidal partial pressures of CO(2) (PETCO(2)) would be of great clinical value. However, the gradient between PETCO(2) and PaCO(2) (PET-aCO(2)) in such patients typically varies over a wide range. A reduction of the PET-aCO(2) gradient can be achieved in spontaneously breathing healthy humans using an end-inspiratory rebreathing technique. We investigated whether this method would be effective in reducing the PET-aCO(2) gradient in a ventilated animal model.

METHODS

Six anesthetized pigs were ventilated mechanically. End-tidal gases were systematically adjusted over a wide range of PETCO(2) (30-55 mmHg) and PETO(2) (35-500 mmHg) while employing the end-inspiratory rebreathing technique and measuring the PET-aCO(2) gradient. Duplicate arterial blood samples were taken for blood gas analysis at each set of gas tensions.

RESULTS

PETCO(2) and PaCO(2) remained equal within the error of measurement at all gas tension combinations. The mean ± SD PET-aCO(2) gradient (0.13 ± 0.12 mmHg, 95% CI -0.36, 0.10) was the same (p = 0.66) as that between duplicate PaCO(2) measurements at all PETCO(2) and PETO(2) combinations (0.19 ± 0.06, 95% CI -0.32, -0.06).

CONCLUSIONS

The end-inspiratory rebreathing technique is capable of reducing the PET-aCO(2) gradient sufficiently to make the noninvasive measurement of PETCO(2) a useful clinical surrogate for PaCO(2) over a wide range of PETCO(2) and PETO(2) combinations in mechanically ventilated pigs. Further studies in the presence of severe ventilation-perfusion (V/Q) mismatching will be required to identify the limitations of the method.

Successful management of severe hypoventilation and hypercapnia in an alpaca (Vicugna pacos) with short-term mechanical ventilation

OBJECTIVE

To describe the successful management of an alpaca with severe hypoventilation and hypercapnia, suspected to be secondary to an anesthesia-related event.

CASE SUMMARY

A 3-year-old, female alpaca underwent a routine eye enucleation under general anesthesia after traumatic globe perforation. Severe hypoventilation and associated hypercapnia developed postoperatively resulting in a severe primary respiratory acidosis. The awake alpaca was supported with positive-pressure ventilation for approximately 20 hours before successful weaning. Recovery to hospital discharge occurred over the subsequent 5 days with the alpaca regaining apparently normal respiratory function.

NEW OR UNIQUE INFORMATION PROVIDED

To the knowledge of the authors, this is the first report describing positive-pressure ventilation of an alpaca in the veterinary literature. In this case of severe hypoventilation, ventilatory support was essential to the positive outcome. As South American camelids continue to increase in popularity there may be an increased demand for high-quality and sophisticated veterinary care for these animals. Mechanical ventilation can be used to help restore and maintain normal PO2, PCO2, and respiratory acid-base status in alpacas with ventilatory dysfunction.

The impact of shunt size on lung function in infants with univentricular heart physiology

OBJECTIVES

To assess the relationship that shunt size, blood gases, and radiologic findings has on respiratory function in infants with univentricular heart physiology.

SETTING

Cardiac catheter laboratory at Rikshospitalet University Hospital, Norway.

PATIENTS

Fifteen infants with univentricular heart physiology admitted for cardiac catheterization.

MEASUREMENTS

Lung function was measured by a fixed-orifice differential pressure flow sensor and mainstream volumetric capnography in 15 infants with univentricular heart arrangements during routine invasive assessment before the bidirectional cavopulmonary connection. Blood gases were measured from the indwelling catheters. Chest radiographs were assessed for heart size and pulmonary vasculature. Shunt size was assessed angiographically.

MAIN RESULTS

Respiratory compliance was reduced in patients with a large surgical systemic-pulmonary arterial shunt (r = -0.67, r = 0.45, p = 0.03). Respiratory resistance was higher with increased heart size (r = 0.72, r = 0.52, p = 0.004). There was no association between arterial and end-tidal CO2 values. The arterial to end-tidal CO2 difference had an inverse relationship with the pulmonary to systemic shunt ratio (r = -0.38, r = 0.14, p = 0.015).

CONCLUSION

A large surgical shunt size is related to stiffer lungs and a large heart is associated with a higher respiratory resistance. During mechanical ventilation of patients with univentricular heart physiology the end-tidal CO2 may be an unreliable substitute for arterial CO2 before the bidirectional cavopulmonary connection. We found a relationship between a decreased pulmonary to systemic shunt ratio and an increased arterial to end-tidal CO2 difference. This may indicate that a reason for the unreliability of end-tidal CO2 is an impaired gas exchange partially due to pulmonary hypoperfusion.

Arterial-to-end-tidal carbon dioxide tension difference in children with congenital heart disease

OBJECTIVES

This study estimated the arterial-to-end-tidal carbon dioxide tension difference (deltaPaCO2-PE'CO2) in children with congenital heart disease; evaluated whether hyperventilation can reduce this difference; and analyzed the relationship between the difference and the oxygen saturation (SaO2) and hemoglobin level.

DESIGN

Prospective clinical study.

SETTING

Tertiary health care center.

PARTICIPANTS

One hundred patients scheduled for correction of their underlying cardiac defect with either right-to-left or left-to-right intracardiac shunts were divided into 4 groups (n = 25 each): (1) N1, cyanotic with severe pulmonary artery hypertension; (2) N2, cyanotic with normal or decreased pulmonary artery pressure (PAP); (3) N3, acyanotic with normal or mild increases in PAP and severe increases in pulmonary blood flow (PBF); and (4) N4, acyanotic with normal PAP and normal or mild increase in PBF.

INTERVENTIONS

All the patients received the same anesthetic regimen. The initial settings for tidal volume, respiratory rate, and inspiratory-to-expiratory (I:E) ratio were 10 mL/kg, 15 to 30 breath/min, and inspired time 40% of the total respiratory period with a 10% end-inspiratory pause. After the measurement of oxygen saturation, PO2, Hb, and deltaPaCO2-PE'CO2, all the children were hyperventilated (tidal volume: 14-15 mL/kg, respiratory rate: 5-6 breaths/min more than the initial rate, I:E ratio: same) to observe its effects on the deltaPaCO2-PE'CO2.

MEASUREMENTS AND RESULTS

The deltaPaCO2-PE'CO2, when predicted from the oxygen saturation, hemoglobin concentration, and PaO2, was found to be greater than the observed value in the first 3 groups (p < 0.001); whereas in group N4 these 2 values were comparable. It was also found that the gradient was higher when there was a decrease in SaO2 and an increase in the hemoglobin level. After hyperventilation, in groups N1 and N3, deltaPaCO2-PE'CO2 was decreased when compared with their baseline values; this reduction was not as much as predicted (p = 0.363 and 0.236, respectively). However, in groups N2 and N4 posthyperventilation, the deltaPaCO2-PE'27 CO2 was decreased significantly below their baseline measurements. These decreases were as much predicted.

CONCLUSION

The deltaPaCO2-end-tidal carbon dioxide (PE'CO2) can be increased both in cyanotic and acyanotic children. Increased PAP is as important as increased PBF or right-to-left shunting in producing disorders in carbon dioxide homeostasis. Hyperventilation is of little use in reducing deltaPaCO2-PE'CO2 in children with high PAPs and pulmonary hyperperfusion.

Negative arterial to end-tidal carbon dioxide gradient: an additional sign of malignant hyperthermia during desflurane anesthesia

Widespread use of desflurane anesthesia has changed the clinical presentation of malignant hyperthermia (MH). Delayed onset of MH symptoms has been reported previously. A negative gradient between arterial to end-tidal CO2 ([a-ET]Pco2) was observed during anesthesia in pregnant patients and infants and has been associated with increased CO2 production, increased cardiac output, reduced functional residual capacity, and low lung compliance. The same conditions exist in cases of MH crisis. We describe an unusual case of MH in which a negative value of (a-ET) Pco2 gradient has been used as diagnostic and monitoring tool.

The role of carbon dioxide detectors for confirmation of endotracheal tube position

There is evidence that practitioners who are responsible for airway management at newborn resuscitations may place an endotracheal tube incorrectly with confidence. Moving on to the further stages of resuscitation, without managing the airway adequately, and commencing ventilation has the potential for significant harm to the baby. Because primary confirmation is fallible, there is a need for secondary confirmation of correct endotracheal tube placement and effective airway and breathing before moving on to cardiovascular support. Symmetric chest movement, auscultation, exhaled carbon dioxide (CO(2)), and an increase in heart rate have been suggested as providing secondary confirmation. Measurement of exhaled CO(2) is accepted widely as a standard of care in adult and pediatric intensive care and in anaesthetized patients.

Monitoring of end tidal carbon dioxide and transcutaneous carbon dioxide during neonatal transport

OBJECTIVE

To assess the accuracy of measurements of end tidal carbon dioxide (CO2) during neonatal transport compared with arterial and transcutaneous measurements.

DESIGN

Paired end tidal and transcutaneous CO2 recordings were taken frequently during road transport of 21 ventilated neonates. The first paired CO2 values were compared with an arterial blood gas. The differences between arterial CO2 (Paco2), transcutaneous CO2 (TcPco2), and end tidal CO2 (Petco2) were analysed. The Bland-Altman method was used to assess bias and repeatability.

RESULTS

Petco2 correlated strongly with Paco2 and TcPco2. However, Petco2 underestimated Paco2 at a clinically unacceptable level (mean (SD) 1.1 (0.70) kPa) and did not trend reliably over time within individual subjects. The Petco2 bias was independent of Paco2 and severity of lung disease.

CONCLUSIONS

Petco2 had an unacceptable under-recording bias. TcPco2 should currently be considered the preferred method of non-invasive CO2 monitoring for neonatal transport.

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.

Evaluation of an end-tidal portable ETCO2 colorimetric breath indicator (COLIBRI)

Evaluation of tube position is important after in-hospital and prehospital emergency intubation. Colorimetric breath indicators are devices for immediate control of tube positioning by showing a color change according to end-tidal CO2 (ETCO2) concentrations. We hypothesized that colorimetric breath indicators can yield reliable results for confirmation of tube position. The aim of this study was to evaluate the effectiveness and safety of a new colorimetric breath indicator (Colibri, ICOR AB, Bromma, Sweden) in 147 patients during general anesthesia, in critically ill patients, during transport to in-hospital interventions, and in a study design after insertion of a second tube into the esophagus in long-term ventilated patients. The Colibri was attached between the respective airway and ventilatory tubing. Seventy-three patients were investigated during general anesthesia, 39 patients were observed during long-term ventilation with an average duration of 33 hours, in 15 patients during transport to an intervention for up to 4 hours, and in 20 long-term ventilated patients at the medical intensive-care unit after insertion of a second tube intentionally into the esophagus with the help of a laryngoscope. The Colibri worked well in all groups investigated and showed no false results in the group with tubes inserted into the trachea and esophagus. Data suggest that the Colibri might serve as a valuable tool for evaluating and controlling tube position. This device is independent of power supply or electronic equipment, portable, small, and immediately ready for use.

Accuracy of a new low-flow sidestream capnography technology in newborns: a pilot study

OBJECTIVE

To evaluate the accuracy of a new low-flow sidestream capnography technology and analyze components of the capnogram in mechanically ventilated newborns with and without pulmonary disease.

METHODS

Twenty patients were prospectively identified. Eligible infants were mechanically ventilated and had an indwelling arterial catheter. Two groups were identified: newborns who were receiving mechanical ventilation for pulmonary diseases, and newborns who were receiving postoperative mechanical ventilation for nonpulmonary conditions. End-tidal CO(2) (PetCO(2)) was measured for 1-minute pre- and post-arterial blood sampling, and PetCO(2) and PaCO(2) were compared for each patient. Eight quantitative waveform parameters were also measured on all patients.

RESULTS

Newborns in the pulmonary group (n=13) (persistent pulmonary hypertension of the newborn/meconium aspiration syndrome, respiratory distress syndrome, pneumonia) and newborns in the control group (n=7) were matched for birth weight, gestational age, and postnatal age. PetCO(2)-PaCO2 Gradient values were higher in the pulmonary group (7.4+/-3.3 mm Hg) than controls (3.4+/-2.4 mm Hg). Four waveform parameters (ascending slope, alveolar angle, alpha angle, descending angle) were identified, which independently differentiated patients with pulmonary disease from controls.

CONCLUSIONS

Low-flow capnography with Microstream technology accurately measured alveolar CO(2) in newborns without pulmonary disease, as demonstrated by normal PetCO(2)-PaCO(2) gradients. The measured PetCO(2)-PaCO(2) gradient, as expected, was significantly higher in newborns with pulmonary disease. We also identified four quantitative waveform parameters that may be useful in differentiating between mechanically ventilated newborn patients with and without lung disease.

Arterial to end-tidal carbon dioxide tension difference in children with congenital heart disease

In children with congenital cyanotic heart disease, right-to-left intracardiac shunting causes an obligatory difference between arterial and end-tidal carbon dioxide tension (PaCO2-PE'CO2) as venous blood, rich in carbon dioxide, is added to the arterial circulation. This obligatory PaCO2-PE'CO2 difference, which can be predicted from knowledge of oxygen saturation, haemoglobin concentration and PaCO2, increases as oxygen saturation decreases, most markedly when the haemoglobin concentration is high. A second possible cause of the PaCO2-PE'CO2 difference is the effect of pulmonary hypoperfusion caused by the shunt. We studied 60 children undergoing cardiac surgery and compared the predicted the PaCO2-PE'CO2 difference with measured values to investigate the extent to which additional factors influence the clinically observed PaCO2-PE'CO2. In many children, observed values were much greater than predicted, which is compatible with some degree of pulmonary hypoperfusion. However, this was not felt to represent the complete picture in all patients. Another cause of ventilation-perfusion mismatch was suspected in those children who showed a considerable improvement in oxygen saturation during ventilation with an increased FIO2. We believe that pulmonary congestion caused by large left-to-right shunts may further increase the PaCO2-PE'CO2 difference.

Intermittent capnography during high-frequency jet ventilation for prolonged rigid bronchoscopy

BACKGROUND

Gas exchange during high-frequency jet ventilation (HFJV) for prolonged rigid bronchoscopy (RBS) is usually monitored by arterial blood gas analysis. Capnography of expired gases during brief HFJV discontinuation may be a reliable and noninvasive supplemental method. Capnography can be performed either for single breaths or with respiratory rate (RR) reduced to 10 x min(-1). The aim of this study was to demonstrate that capnography during short periods of HFJV discontinuation represents a reliable measure of PaCO2 during prolonged RBS.

METHODS

We prospectively investigated 100 consecutive patients (75 male and 25 female) undergoing HFJV for RBS. HFJV was delivered through the rigid bronchoscope at the following settings: working pressure 1.2 bar, rate 100 x min(-1), FIO2 0.99, t(i)/t(tot)0.6. The light guiding channel ending at the distal tip of the rigid bronchoscope was used for gas sampling. Capnograms were assessed at 5 min intervals and compared to PaCO2 from arterial blood samples drawn simultaneously. The accuracy of single breath CO2 sampling was compared with sampling at RR=10 x min(-1).

RESULTS

Mean duration of RBS was 30+/-21 min. A significant correlation between capnography (PetCO2) and arterial blood gas analysis (PaCO2) was observed, being r=0.90 for the RR= 10 x min(-1) method and r=0.91 for the single breath method. Mean difference between PaCO2 and PetCO2 was 0.37+/-0.2 kPa throughout the entire study period. No significant differences between single breath sampling or sampling at RR=10 x min(-1) were observed.

CONCLUSION

Capnography performed during short periods of HFJV discontinuation reliably and noninvasively reflects PaCO2 during prolonged endoscopic procedures. Capnography during HFJV for RBS may reduce the frequency of arterial blood gas sampling, the duration of unmonitored intervals and costs.

An advisory statement from the Pediatric Working Group of the International Liaison Committee on Resuscitation

The International Liaison Committee on Resuscitation (ILCOR), with representation from North America, Europe, Australia, New Zealand, Africa, and South America, was formed in 1992 to provide a forum for liaison between resuscitation organizations in the developed world. This consensus document on resuscitation extends previously published ILCOR advisory statements on resuscitation to address the unique and changing physiology of the newly born infant within the first few hours after birth and the techniques for providing advanced life support. After careful review of the international resuscitation literature and after discussion of key and controversial issues, consensus was reached on almost all aspects of neonatal resuscitation, and areas of controversy and high priority for additional research were delineated. Consensus on resuscitation for the newly born infant included the following principles: Common or controversial medications (epinephrine, volume expansion, naloxone, bicarbonate), special resuscitation circumstances affecting care of the newly born, continuing care of the newly born after resuscitation, and ethical considerations for initiation and discontinuation of resuscitation are discussed. There was agreement that insufficient data exist to recommend changes to current guidelines regarding the use of 21% versus 100% oxygen, neuroprotective interventions such as cerebral hypothermia, use of a laryngeal mask versus endotracheal tube, and use of high-dose epinephrine. Areas of controversy are identified, as is the need for additional research to improve the scientific justification of each component of current and future resuscitation guidelines.

Resuscitation of the newly born infant: an advisory statement from the Pediatric Working Group of the International Liaison Committee on Resuscitation

The International Liaison Committee on Resuscitation (ILCOR), with representation from North America, Europe, Australia, New Zealand, Africa, and South America, was formed in 1992 to provide a forum for liaison between resuscitation organizations in the developed world. This consensus document on resuscitation extends previously published ILCOR advisory statements on resuscitation to address the unique and changing physiology of the newly born infant within the first few hours following birth and the techniques for providing advanced life support. After careful review of the international resuscitation literature and after discussion of key and controversial issues, consensus was reached on almost all aspects of neonatal resuscitation, and areas of controversy and high priority for additional research were delineated. Consensus on resuscitation for the newly. born infant included the following principles. (i) Personnel trained in the basic skills of resuscitation should be in attendance at every delivery. A minority (fewer than 10%) of newly born infants require active resuscitative interventions to establish a vigorous cry and regular respirations, maintain a heart rate greater than 100 beats per minute (bpm), and maintain good color and tone. (ii) When meconium is present in the amniotic fluid, it should be suctioned from the hypopharynx on delivery of the head. If the meconium-stained newly born infant has absent or depressed respirations, heart rate, or muscle tone, residual meconium should be suctioned from the trachea. (ii) Attention to ventilation should be of primary concern. Assisted ventilation with attention to oxygen delivery, inspiratory time, and effectiveness judged by chest rise should be provided if stimulation does not achieve prompt onset of spontaneous respirations and/or the heart rate is less than 100 bpm. (iv) Chest compressions should be provided if the heart rate is absent or remains less than 60 bpm despite adequate assisted ventilation for 30 s. Chest compressions should be coordinated with ventilations at a ratio of 3:1 and a rate of 120 'events' per minute to achieve approximately 90 compressions and 30 rescue breaths per minute. (v) Epinephrine should be administered intravenously or intratracheally if the heart rate remains less than 60 bpm despite 30 s of effective assisted ventilation and chest compression circulation. Common or controversial medications (epinephrine, volume expansion, naloxone, bicarbonate), special resuscitation circumstances affecting care of the newly born, continuing care of the newly born after resuscitation, and ethical considerations for initiation and discontinuation of resuscitation are discussed. There was agreement that insufficient data exist to recommend changes to current guidelines regarding the use of 21% versus 100% oxygen, neuroprotective interventions such as cerebral hypothermia, use of a laryngeal mask versus endotracheal tube, and use of high-dose epinephrine. Areas of controversy are identified, as is the need for additional research to improve the scientific justification of each component of current and future resuscitation guidelines.

Capnography monitoring during neurosurgery: reliability in relation to various intraoperative positions

In neurosurgery, estimation of PaCO2 from PETCO2 has been questioned. The aim of this study was to reevaluate the accuracy of PETCO2 in estimating PaCO2 during neurosurgical procedures lasting >3 h and to measure the effect of surgical positioning on arterial to end-tidal CO2 gradient (P[a-ET]CO2) over time. One hundred four neurosurgical patients classified into four groups (supine [SP], lateral [LT], prone [PR], sitting [ST]) were included in a prospective study. PaCO2, PETCO2, and P(a-ET)CO2 were measured after induction of anesthesia (T0), after positioning (T1), each following hour (T2, T3, T4), and at the end of the procedure after return to the SP position (T5). Data are expressed as the mean +/- SD, and statistical analysis used linear regression, the Bland-Altman method, and analysis of variance. The mean durations of positioning and surgery were 4.1+/-1 h and 3.7+/-1.3 h, respectively. We performed 624 simultaneous measurements of PaCO2 (33+/-5 mm Hg) and PETCO2 (27+/-4 mm Hg), leading to a mean P(a-ET)CO2 of 6+/-4 mm Hg. P(a-ET)CO2 of the LT group (7+/-3 mm Hg) was larger (compared with the SP, PR, and ST groups) because of a lower PETCO2 (26+/-4 mm Hg). Negative P(a-ET)CO2 (PETCO2 > PaCO2) occurred 22 times, only in the SP (n = 9) and ST groups (n = 13). Changes in opposite directions of PETCO2 and PaCO2 between two successive measurements were found in 26% of the cases. Correlation coefficients in the four groups (PaCO2 versus PETCO2) were not in good agreement (0.46 to 0.62; P < 0.001). The mean bias was between 5 and 7 mm Hg. The superior (13-15 mm Hg) and inferior (-5 to 0 mm Hg) limits of agreement were too large to expect PETCO2 to replace PaCO2. In conclusion, during neurosurgical procedures of >3 h, capnography should be performed with regular analysis of arterial blood gases for optimal ventilator adjustment.

IMPLICATIONS

This study, which aimed to reevaluate the ability of PETCO2 to estimate PaCO2 during neurosurgical procedures according to surgical position, indicates that PETCO2 cannot replace PaCO2 for the following reasons: scattering of individual values; occurrence of negative arterial to end-tidal CO2 gradient (P[a-ET]CO2; PaCO2 and PETCO2 variations in opposite directions; large changes in P(a-ET)CO2 between two samples; and instability of P(a-ET)CO2 over time.

Difference between arterial and end-tidal carbon dioxide pressures during laparoscopy in paediatric patients

PURPOSE

To assess the effect of pneumoperitoneum on P(a-ET)CO2 gradient in children.

METHODS

Sixty one ASA I and II children (10.7 +/- 3.0 yr, 38.4 +/- 14.2 kg, mean +/- SD), scheduled for visceral or urological laparoscopic procedures, were studied. They were anaesthetized, intubated, paralysed and their lungs ventilated with constant ventilator settings to obtain PETCO2 values between 4.3 and 4.8 kPa. Intra-abdominal pressure was maintained between 8 and 14 mmHg. The following measurements were performed at steady state, before the pneumoperitoneum (T1) and 15 min later (T2): heart rate, systolic and diastolic arterial pressure; peak airway and intra-abdominal pressure; PaCO2 corrected for the patient's temperature; PETCO2 drawn between the micropore filter and the ventilator tubes, corrected for BTPS conditions; P(a-ET)CO2. Values between -1.0 and +1.0 mmHg were considered nil; patient position (horizontal or head-down tilt): all patients were horizontal at T1.

RESULTS

Arterial pressure, heart rate and peak airway pressure increased at T2: PaCO2 and PETCO2 increased by 14%. The incidence of negative gradients increased from 54 to 67% although mean P(a-ET)CO2 remained clinically unchanged. No difference was found in P(a-ET)CO2 gradient, whatever the position and intra-abdominal pressure. The 95% confidence intervals for P(a-ET)CO2 were [-5.6; +3.2] at T1 and [-8.8; +4.8] at T2.

CONCLUSION

PETCO2 often overestimates PaCO2 during laparoscopy in children, by up to 8.8 mmHg. Arterial blood gas analysis should be performed during long procedures to avoid hyperventilation.

Mainstream end-tidal carbon dioxide monitoring in the neonatal intensive care unit

BACKGROUND

Continuous noninvasive monitoring of arterial carbon dioxide (CO2) in neonatal intensive care unit (NICU) patients would help clinicians avoid complications of hypocarbia and hypercarbia. End-tidal CO2 monitoring has not been used in this population to date, but recent technical advances and the introduction of surfactant therapy, which improves ventilation-perfusion matching, might improve the clinical utility of end-tidal monitoring.

OBJECTIVE

To determine the accuracy and precision of end-tidal CO2 monitoring in NICU patients.

DESIGN

Nonrandomized recording of simultaneous end-tidal and arterial CO2 pairs.

SETTING

Two university NICUs.

PATIENTS

Forty-five newborn infants receiving mechanical ventilation who had indwelling arterial access, and a predefined subsample of infants who were <1000 g birth weight, <8 days of age, and who received surfactant therapy (extremely low birth weight -ELBW- <8).

OUTCOME MEASURES

The correlation coefficient, degree of bias, and 95% confidence interval were determined for both the overall population and the ELBW <8 subgroup. Those factors which significantly influenced the bias were identified. The ability of the end-tidal monitor to alert the clinician to instances of hypocarbia or hypercarbia was determined.

RESULTS

There were 411 end-tidal/arterial pairs analyzed from 45 patients. The correlation coefficient was 0.833 and the bias was -6. 9 mm Hg (95% confidence interval, +/-11.5 mm Hg). The results did not differ markedly in the ELBW <8 infants. Measures of the degree of lung disease, the ventilation index and the oxygenation index, had small influences on the degree of bias. This type of capnometry identified 91% of the instances when the arterial CO2 pressure was between 34 and 54 mm Hg using an end-tidal range of 29 to 45 mm Hg. End-tidal values outside this range had a 63% accuracy in predicting hypocarbia or hypercarbia.

CONCLUSION

End-tidal CO2 monitoring in NICU patients is as accurate as capillary or transcutaneous monitoring but less precise than the latter. It may be useful for trending or for screening patients for abnormal arterial CO2 values.

End-tidal carbon dioxide measurement in infants and children during and after general anaesthesia

We have examined the reliability of end-tidal carbon dioxide (PetCO2) monitoring as an estimate of arterial carbon dioxide tension (PaCO2) in spontaneously breathing infants and children. Forty patients were studied in the post-anaesthetic care unit; 20 < 12 kg and 20 > or = 12 kg. The PetCO2 was sampled via a 5 cm 16 gauge catheter taped below an external naris and this measurement was compared with the PaCO2 of a sample drawn from an indwelling arterial line. Twenty additional patients were studied during inhalational anaesthesia. The PetCO2 was measured both from the proximal end of the elbow connector and from a 5 cm cannula inserted through the elbow. An arterial blood gas sample was obtained simultaneously. The arterial to end-tidal (Pa-et) differences were compared between the two sites. Patients studied in the post-anaesthetic care unit showed good correlation between PetCO2 and PaCO2 regardless of weight: Pa-etCO2 of -0.6 +/- 3.6 (< 12 kg) and -1.1 +/- 2.8 mmHg (> or = 12 kg). Patients studied during mask anaesthesia showed better correlation between PetCO2 and PaCO2 when PetCO2 was sampled from the cannula: Pa-etCO2 of 3.5 +/- 4.8 mmHg (cannula), 8.6 +/- 4.5 (elbow) (P < 0.05). These results suggest that end-tidal CO2 monitoring is a useful and reliable method for assessing adequacy of ventilation in spontaneously breathing children weighing between 5.2 and 35 kg.

Capnometry and anaesthesia

In the last decade, capnography has developed from a research instrument into a monitoring device considered to be essential during anaesthesia to ensure patient safety. Hence, a comprehensive understanding of capnography has become mandatory for the anaesthetist in charge of patients in the operating room and in the intensive care unit. This review of capnography includes the methods available to determine carbon dioxide in expired air, and an analysis of the physiology of capnograms, which are followed by a description of the applications of capnography in clinical practice. The theoretical backgrounds of the effect of barometric pressure, water vapour, nitrous oxide and other factors introducing errors in the accuracy of CO2 determination by the infra-red technique, currently the most popular method in use, are detailed. Physiological factors leading to changes in end-tidal carbon dioxide are discussed together with the clinical uses of this measurement to assess pulmonary blood flow indirectly, carbon dioxide production and adequacy of alveolar ventilation. The importance of understanding the shape of the capnogram as well as end-tidal carbon dioxide measurements is emphasized and its use in the early diagnosis of adverse events such as circuit disconnections, oesophageal intubation, defective breathing systems and hypoventilation is highlighted. Finally, the precautions required in the use and interpretation of capnography are presented with the caveat that although no instrument will replace the continuous presence of the attentive physician, end-tidal carbon dioxide monitoring can be effective in the early detection of anaesthesia-related intraoperative accidents.