Accidental Tube Research Articles

Enteral Nutrition in Critically Ill Children: Are Prescription and Delivery According to Their Energy Requirements?

The purpose of this study was to compare the differences between prescribed and delivered energy among critically ill children and to identify the factors that impede the optimal delivery of enteral nutrition in the first 5 days of nutrition support. In a prospective cohort study, we evaluated 55 critically ill children aged 8.2 +/- 11.4 months (0-162.3 months), who were fed for > or =2 days through a gastric or postpyloric tube. The patients were followed from admission until day 10 of enteral nutrition. Prescribed and delivered energy were recorded daily and compared with each other and with the estimated basal metabolic rate (BMR). The Paediatric Index of Mortality 2 (PIM 2) was used to estimate illness severity. The ratio of delivered:required energy was <90% in 55.7% of the enteral nutrition days. Low prescription was the main reason for not achieving the energy goal in the first 5 days of enteral nutrition. Discrepancies between prescribed and delivered: energy were attributable to interruptions in feeding caused by clinical instability, airway management, radiologic and surgical procedures, and accidental feeding tube removal. The other factors associated with the delivery of less than required energy were PIM 2 > or =15%, gastrointestinal complications, dialysis, and use of alpha-adrenergic vasoactive drugs. The latter was the only variable in multivariate analysis that was associated with not ultimately achieving energy goal. The prescription and delivery of energy were not adequate in >50% of enteral nutrition days. The gap between the effective administration and energy requirements can be explained by both underprescription and underdelivery. Administration of vasoactive drugs was the only variable independently associated with a low energy supply.

Nasal Bridling of Endoscopically Placed Nasojejunal Feeding Tubes

Purpose: Post-ampullary, Nasojejunal feedings have been shown to be an important component in the management of critically ill patients and patients with pancreatitis. However, proximal migration or dislodgement of the tubes can occur, limiting the effectiveness of the feeding in ICU patients. Methods: Intensive care unit (ICU) patients undergoing placement of nasojejunal feeding tubes (NJT) from January 2000 to December 2005 were prospectively identified. The feeding tube was positioned endoscopically into the post ampullary duodenum. After feeding tube placement, the NJT was “bridled” with umbilical tape to the posterior nasal septum. Bridling was performed using an NG tube, advanced to the posterior pharynx and pulled out through the mouth. Umbilical tape was secured to the NG tube which was then pulled back through the nose. The bridle was then created by securing the end of the umbilical tape to the feeding tube, with the nasal septum anchoring the tube in position, limiting displacement of the NJT when pulled. Results: A total of 153 NJT were placed and bridled in 139 patients. Positioning of the feeding tube was performed using snare (32%) and rat-tooth forceps (68%). Feeding tube position was confirmed to be post pyloric endoscopically and with abdominal xray after placement. All included patients had undergone repeat abdominal films from 5–19 days after initial placement, at which time feeding tube position was reassessed. Accidental tube dislodgement or gastric proximal migration occurred in 6 cases (4%) and tube occlusion or malfunction in 3 cases (2%). There was mild nosebleeding in 2 patients (1.5%) and perinasal ulceration in 3 patients (2%). Goal tube feedings were achieved within 72 hrs. in 142 cases (93%). Conclusions: Nasal Bridling of endoscopically placed NJT maintains post pyloric feeding tube position at a high rate (94%), with very few complications. This allows for rapid delivery of optimal nutrition in ICU patients.

Management of established percutaneous gastrostomy tubes in adults-A systematic review

Objective The purpose of this review is to critically appraise and summarise the best available evidence relating to the management of percutaneous gastrostomy (PEG) tubes in adults. Question What are the best methods of preventing and managing complications associated with PEG tubes? These complications include occlusion, site infection, excoriation at the stoma site and accidental removal Inclusion Criteria Types of participants This review will include adult patients (> 18 years of age) with PEG tubes in the acute, aged or community setting. Studies relating to neonates or children will be excluded. Types of interventions This review will include studies that assess the effectiveness of interventions for preventing complications associated with PEG tubes. These may include, but are not limited to, frequency and volume of flushing, use on antibiotics, site dressing regimes, manipulation of the tube to prevent excoriation and techniques to prevent and manage accidental tube removal. Studies examining the appropriateness of techniques of PEG tube insertion and/or the timing of initial feeding post insertion will not be included. Studies involving nasogastric, nasoenteric or jejunal feeding tubes will also be excluded from this review. Types of outcome measures The primary outcomes of interest are objective or subjective measures of the following: 1. Occlusion 2. Site infection ( such as erythema, purulent drainage, positive swabs) 3. Excoriation at stoma site 4. Accidental removal

Part 4: Advanced Life Support

The topics reviewed by the International Liaison Committee on Resuscitation (ILCOR) Advanced Life Support Task Force are grouped as follows: (1) causes and prevention, (2) airway and ventilation, (3) drugs and fluids given during cardiac arrest, (4) techniques and devices to monitor and assist the circulation, (5) periarrest arrhythmias, (6) cardiac arrest in special circumstances, (7) postresuscitation care, and (8) prognostication. Defibrillation topics are discussed in Part 3. The most important developments in advanced life support (ALS) since the last ILCOR review in 2000 include For many topics there were insufficient data with which to make firm treatment recommendations. The following interventions in particular need further research: Rescuers may be able to identify some noncardiac causes of arrest and tailor the sequence of attempted resuscitation. Most patients sustaining in-hospital cardiac arrest display signs of deterioration for several hours before the arrest. Early identification of these high-risk patients and the immediate arrival of …

Initial presentation and fatal complications of linear IgA bullous dermatosis in the larynx and pharynx

Two cases of linear IgA bullous dermatosis initially presenting as ulcerative lesions in the larynx and pharynx are reported. It was difficult to diagnose and treat the lesions, but they were finally diagnosed from the histopathological findings of accompanying skin lesion specimens. One of the patients required a tracheostomy due to increased airway stenosis by a laryngeal lesion. Despite general corticosteroid administration this could not be completely resolved, although partial opening of the glottis was observed, and the patient died of accidental tracheostomy tube complications during home care. Although there are no reports of this disease in the otolaryngological field, these rare diseases involving the skin and entire body should be considered in the differential diagnosis of laryngeal and pharyngeal ulcerative lesions, including airway stenosis. Furthermore, simple and safe procedures for relieving airway stenosis should be selected for rare and difficult-to-diagnose airway disease, prior to the final diagnosis.

Babies With Tracheostomies

Babies With Tracheostomies

Submental Orotracheal Intubation: An Alternative to Tracheotomy in Transfacial Cranial Base Surgery

This retrospective study evaluated the safety and efficacy of submental intubation not only for trauma treatment but also for oncological cranial base surgery. The medical records of 24 patients who underwent submental intubation from 1996 to 2002 were reviewed. There were 6 procedures for craniofacial trauma, 12 transmaxillary approaches to the clivus for clivus chordomas, and 6 transmaxillary approaches to the cranial base for chondrosarcomas. Time required for intubation, accidental extubation, postoperative complications, and the healing of intraoral and submental scars were evaluated. The submental orotracheal intubation was completed successfully in all patients. No accidental extubations or tube injuries occurred. The mean time required for intubation was 5 minutes. The only complication was one case of superficial infection of the submental wound. The intraoral and submental accesses healed with minimal scarring in all patients. Submental orotracheal intubation is a useful and safe technique for airway management of craniomaxillofacial traumas and during transfacial approaches to the cranial base. It avoids the complications associated with tracheostomy. It also permits considerable downward retraction of the maxilla after a Le Fort I osteotomy and is associated with good clival exposure. Furthermore, it does not interfere with maxillomandibular fixation at the end of the surgery.

Late‐Onset Complications of Percutaneous Endoscopic Gastrostomy in Children

ABSTRACTPurposeThe aim of this study was to report the late morbidity of percutaneous endoscopic gastrostomy (PEG) in a pediatric population and to identify possible risk factors for complications developing after PEG insertion.MethodsA PEG was placed in 110 children between 1 May 1990 and 1 January 1997 using the pull technique. A retrospective study of late‐onset complications was performed, with a follow‐up period ranging from 1 to 8 years. All the complications occurring more than 6 days after PEG insertion were recorded, except for gastrostomy tube obstruction and accidental tube dislodgement.ResultsThe prevalence of late‐onset complications related to PEG in our patients varied from 3.8 to 4.4 per 10 5 days. The overall rate of late‐onset complications was 44% (48 complications observed in 29 patients [26%]). Seventy‐five percent of the complications appeared during the first 2 years after PEG insertion. Nine different types of complication have been identified: intragastric buried or extruded gastrostomy (n = 24), gastric metaplasia granulation tissue around the site of gastrostomy (n = 8), intragastric pseudotumoral proliferative gastric mucosa (n = 4), intragastric mucosal ulceration (n = 3), cutaneous necrosis (n = 3), cologastric fistula (n = 2), gastrostomy closure delay after tube removal (n = 2), subcostal neuralgia (n = 1), and peritonitis (n = 1). Wilcoxon and chi‐square tests were used to compare the clinical characteristics of the patients and the type of material used in the two populations, with and without complications. No clinical risk factor for the development of complications could be identified. Intragastric buried or extruded gastrostomy appeared more frequently with the use of one type of button than with the use of tubes.ConclusionsThe authors' experience suggests that PEG is associated with significant late morbidity, which is mainly observed within the first 2 years after PEG insertion. However, no risk factor for the development of such complications could be identified.

Late-onset complications of percutaneous endoscopic gastrostomy in children.

The aim of this study was to report the late morbidity of percutaneous endoscopic gastrostomy (PEG) in a pediatric population and to identify possible risk factors for complications developing after PEG insertion. A PEG was placed in 110 children between 1 May 1990 and 1 January 1997 using the pull technique. A retrospective study of late-onset complications was performed, with a follow-up period ranging from 1 to 8 years. All the complications occurring more than 6 days after PEG insertion were recorded, except for gastrostomy tube obstruction and accidental tube dislodgement. The prevalence of late-onset complications related to PEG in our patients varied from 3.8 to 4.4 per 10 5 days. The overall rate of late-onset complications was 44% (48 complications observed in 29 patients [26%]). Seventy-five percent of the complications appeared during the first 2 years after PEG insertion. Nine different types of complication have been identified: intragastric buried or extruded gastrostomy (n = 24), gastric metaplasia granulation tissue around the site of gastrostomy (n = 8), intragastric pseudotumoral proliferative gastric mucosa (n = 4), intragastric mucosal ulceration (n = 3), cutaneous necrosis (n = 3), cologastric fistula (n = 2), gastrostomy closure delay after tube removal (n = 2), subcostal neuralgia (n = 1), and peritonitis (n = 1). Wilcoxon and chi-square tests were used to compare the clinical characteristics of the patients and the type of material used in the two populations, with and without complications. No clinical risk factor for the development of complications could be identified. Intragastric buried or extruded gastrostomy appeared more frequently with the use of one type of button than with the use of tubes. The authors' experience suggests that PEG is associated with significant late morbidity, which is mainly observed within the first 2 years after PEG insertion. However, no risk factor for the development of such complications could be identified.

Capnography alone is imperfect for endotracheal tube placement confirmation during emergency intubation

This analysis primarily sought to determine the effectiveness of end-tidal capnography for tube placement confirmation during emergency airway management. Secondary objectives were validation of the rate of unanticipated esophageal placement during emergency intubation and quantification of the portion of intubations performed in patients with cardiac arrest where capnography is not recommended. The study was performed in two phases. For the primary objective, a meta-analysis was performed on all experimental capnography trials enrolling emergency populations. For the secondary objectives, inadvertent esophageal intubation and cardiac arrest rates were calculated from a large prospective multicenter observational study of emergency intubation cases. Data analysis included calculation of descriptive statistics, sensitivity, specificity, and confidence intervals (CI). Based on 2,192 intubations, a meta-analysis of previous capnography trials resulted in an aggregate sensitivity of 93% (95% CI 92–94%) and an aggregate specificity of 97% (CI 93–99%) for emergency tube placement confirmation. Thus, for emergency capnography use, the false-negative failure rate (tube in trachea but capnography reports esophagus) was 7% and the false-positive rate (tube in esophagus but capnography reports trachea) was 3%. This translates to potential harm for one patient in every 10 treated with capnographic confirmation alone (number needed to harm: 14 for false-negative, 33 for false-positive, and 10 for both). A further literature review demonstrated no sole method of tube placement confirmation is completely foolproof. Of 4,602 consecutive intubations reported to the National Emergency Airway Registry, 4% of emergency intubation attempts resulted in accidental esophageal intubation, and 10% occurred in nontraumatic cardiac arrest patients. During tracheal intubation of critically ill patients, it is concluded that the rate of accidental esophageal tube placement warrants continued improvement in emergency airway techniques. Misidentification of esophageal placement in the emergency setting may occur with capnography. Multiple methods of tube placement confirmation are superior to any single method because no single method has perfect accuracy.

Endotracheal tube stability in the resuscitation environment

Evidence presented in the anaesthetic and emergency medical services literature warns of the possibility of accidental or insidious displacement of endotracheal tubes in intubated patients. In particular, there is evidence that head movement in intubated patients can lead to displacement of the distal tip of an endotracheal tube in the trachea while its depth markings remain fixed in relation to the patient's lips or teeth. Immobilisation of the heads of all intubated patients should be considered, to prevent the possibility of accidental endotracheal tube displacement. In addition, all intubated patients must be clinically assessed for proper endotracheal tube placement and maintenance of adequate ventilation after every movement during resuscitation and diagnostic measures.

Endoscopic placement of nasojejunal feeding tubes in ICU patients.

Enteral nutrition is an important component in the management of critically ill patients, but it may be limited by gastric ileus and unreliable positioning of standard feeding tubes. The purpose of this study was to determine the risk, utility, and outcome of endoscopically placed nasojejunal feeding tubes (NJT) in intensive care unit (ICU) patients. We reviewed the records of all ICU patients who underwent endoscopic NJT placement from May 1995 to May 1997. A through-the-scope method was used with placement of either an 8-Fr or 10-Fr 240-cm tube. Comparison was made between tubes secured to a nasopharyngeal bridle and tubes secured without bridling. A total of 66 NJT were placed in 56 patients. Previous gastric feeds had been attempted in 39 patients (70%) an average of 8.4 days prior to placing the NJT. Fifty tubes (76%) were placed in the ICU and 16 (34%) in the OR at the time of additional procedures. Procedure time ranged from 7 to 28 mins (mean, 15.2), and bridling was used in 24 of 66 placements (36%). Full caloric goal rates were achieved via 56 of 66 tubes (85%) at an average of 26.1 h after placement (range, 1-144). Goal rates were not achieved in 10 cases due to inadequate tube positioning in six, ileus in three, and early dislodgement in one. A procedure complication, consisting of aspiration, occurred in one case (1.5%). Length of tube use averaged 18.5 days (range, 1-74). Accidental tube dislodgement or migration occurred in 16 of 42 (38%) nonbridled tubes vs one of 24 (4%) bridled tubes (p <.05). Endoscopic placement of nasojejunal feeding tubes in critically ill patients is a safe, quick, and reliable option for enteral nutrition. Full caloric goal rates can be achieved rapidly in a high percentage of patients, even in cases where previous gastric feeds have not been tolerated. Use of a nasopharyngeal bridling system for tube security significantly decreases the risk of migration or accidental tube dislodgement.

Microsurgical endonasal dacryocystorhinostomy with long-term insertion of bicanalicular silicone tubes.

To assess the results of microsurgical endonasal dacryocystorhinostomy with long-term insertion of single or double bicanalicular silicone tubes in canalicular (presaccal) and ductal (postsaccal) stenosis of the nasolacrimal duct system. Retrospective follow-up of case series between 1992 and 1996. Thirty-eight patients were included in the study: 19 with ductal stenosis; 28 with canalicular stenosis; and 1 (a 6-month-old girl) with congenital agenesis of the lacrimal duct system. Forty-seven endonasal microscopic dacryocystorhinostomies were performed on 38 patients. Bicanalicular silicone tubes were inserted, fixed in the nasal cavity, and left in place as long-term space holders. In patients with canalicular stenosis, a specially designed double bicanalicular tube was inserted for maximal dilatation of the lacrimal canals. The tubes are left in place as long as possible, ie, for months to several years. In cases in which there was recurrent obstruction following accidental tube extrusion, we simply inserted new tubes using a short-acting anesthesia. With 1 procedure, 17 (91%) of the eyes that were surgically treated for ductal stenosis became symptom free. The success rate in the cases of canalicular stenosis was 72%. In the remaining 28% of patients with recurrent obstruction, endonasal revision surgery was performed with new insertion of bicanalicular tubes. With the new tubes in place, these remaining patients have also stayed largely symptom free (length of follow-up, 8 months to 5 years [average, 3 years]). The routine insertion of bicanalicular tubes as long-term spacers has proved effective and has been tolerated without problems. A new aspect of our study is that in cases of canalicular stenosis or congenital agenesis of the lacrimal duct, which generally have a poor prognosis, the patients also benefit when our specially designed long-term double bicanalicular tubes are inserted in the lacrimal ducts.

Early Accidental Dislodgement of PEG Tubes

Newer percutaneous endoscopy gastrostomy (PEG) tubes with soft internal bolsters may be prone to accidental dislodgement or removal by patients. When this occurs after a mature gastrocutaneous fistula has formed, it is of little consequence as long as a replacement tube is promptly reinserted before the track closes. Blind reinsertion of a replacement tube before the track is adequately mature may have serious consequences, as exemplified by a patient who developed peritonitis as a result of inadvertent insertion into the peritoneal cavity. We managed two other patients with early accidental PEG tube removal by a period of nasogastric (NG) suction, intravenous antibiotic drugs, and observation, with a new tube placed endoscopically 7-9 days later. We review the management of early, inadvertent dislodgement of PEG tubes.

Gastrostomy conversion to transgastric jejunostomy: technical problems, causes of failure, and proposed solutions in 63 patients.

Sixty-three radiologically guided conversions of gastrostomy to transgastric jejunostomy performed over a 4-year period were reviewed. Conversions succeeded in 31 of 38 surgically placed gastrostomies (82%), in 14 of 18 endoscopically placed gastrostomies (78%), and in seven of seven radiologically placed gastrostomies, for an overall success rate of 83%. Almost all failures (10 of 11 gastrostomies) were primarily the result of unfavorable fundal angulation of the surgical or endoscopic tract; unfavorable angulation was also the most common technical problem encountered in the successful conversions. Of the 52 successful conversions, 23 (44%) necessitated tube replacement: eight for spontaneous proximal migration of the tube, 11 for accidental tube dislodgment, and four for tube blockage. While most gastrostomy to transgastric jejunostomy conversions are simple to perform, in many cases the unfavorable angle of the original transcutaneous tract precludes jejunal intubation and may be a cause for early recoil of a successfully placed jejunal catheter back into the stomach. With early recognition of an unfavorable tract, a fresh transgastric jejunostomy through a new, properly angled puncture may be the preferred approach.

Complications of Nasotracheal Intubation in Neonates, Infants and Children

A computerized database was set up to study the incidence and outcome of complications of nasotracheal intubation in a paediatric hospital. We studied 2953 intensive care admissions over a 4-yr period. The overall complication rate was 8%. Accidental extubation and tube blockage were the most frequent events, accounting for a mean of 3.5% and 2.6% of the complications per year, respectively. Complications were more common in smaller children and there were differences between fields of intensive care. None of the complications was fatal or resulted in serious sequelae. None of the children in the study showed clinical symptoms of acquired subglottic stenosis before discharge from hospital, and none has been readmitted for this condition subsequently.

End-Tidal CO2 Measurement in the Detection of Esophageal Intubation During Cardiac Arrest

Measurement of end-tidal carbon dioxide (ETco 2 ) has been used to detect accidental esophageal tube placement in noncardiac arrest situations. The purpose of our study was to determine whether ETco 2 measurement could distinguish tracheal from esophageal tube placement during closed-chest massage (CCM). Twelve large dogs were anesthetized, and endotracheal tubes were placed in both the trachea and the esophagus. Placement was verified by fiberoptic endoscopy. Ventricular fibrillation was induced by a 60-Hz discharge through a right ventricular pacemaker. After four minutes of cardiac arrest, CCM was initiated and continued for 20 minutes. The dogs were divided into two groups: Group A was ventilated through the tracheal tube, and group B was ventilated through the esophageal tube. Unused tubes were removed. ETco 2 was recorded continuously beginning two minutes before arrest until the end of the experiment. There were no significant between-group differences in mean arterial pressure, weight, blood loss, IV fluid volume administered, or prearrest arterial blood gases. ETco 2 differed significantly between the two groups throughout CCM ( P = .001). In group A, ETco 2 ranged from 13 to 34 mm Hg (median, 20 mm Hg). In group B, ETco 2 ranged from 2 to 11 mm Hg (median, 3 mm Hg). In this experimental model, measurement of ETco 2 reliably distinguished esophageal from tracheal intubation during cardiac arrest and CCM. If confirmed in human beings, this may prove to be a quick, reliable method of detecting esophageal intubation during cardiac arrest.

COMPLICATIONS OF NASOTRACHEAL INTUBATION IN NEONATES, INFANTS AND CHILDREN: A REVIEW OF 4 YEARS' EXPERIENCE IN A CHILDREN'S HOSPITAL

A computerized database was set up to study the incidence and outcome of complications of nasotracheal intubation in a paediatric hospital. We studied 2953 intensive care admissions over a 4-yr period. The overall complication rate was 8%. Accidental extubation and tube blockage were the most frequent events, accounting for a mean of 3.5% and 2.6% of the complications per year, respectively. Complications were more common in smaller children and there were differences between fields of intensive care. None of the complications was fatal or resulted in serious sequelae. None of the children in the study showed clinical symptoms of acquired subglottic stenosis before discharge from hospital, and none has been readmitted for this condition subsequently.

End-tidal CO 2 measurement in the detection of esophageal intubation during cardiac arrest

Measurement of end-tidal carbon dioxide (ETCO2) has been used to detect accidental esophageal tube placement in noncardiac arrest situations. The purpose of our study was to determine whether ETCO2 measurement could distinguish tracheal from esophageal tube placement during closed-chest massage (CCM). Twelve large dogs were anesthetized, and endotracheal tubes were placed in both the trachea and the esophagus. Placement was verified by fiberoptic endoscopy. Ventricular fibrillation was induced by a 60-Hz discharge through a right ventricular pacemaker. After four minutes of cardiac arrest, CCM was initiated and continued for 20 minutes. The dogs were divided into two groups: Group A was ventilated through the tracheal tube, and group B was ventilated through the esophageal tube. Unused tubes were removed. ETCO2 was recorded continuously beginning two minutes before arrest until the end of the experiment. There were no significant between-group differences in mean arterial pressure, weight, blood loss, IV fluid volume administered, or prearrest arterial blood gases. ETCO2 differed significantly between the two groups throughout CCM (P = .001). In group A, ETCO2 ranged from 13 to 34 mm Hg (median, 20 mm Hg). In group B, ETCO2 ranged from 2 to 11 mm Hg (median, 3 mm Hg). In this experimental model, measurement of ETCO2 reliably distinguished esophageal from tracheal intubation during cardiac arrest and CCM. If confirmed in human beings, this may prove to be a quick, reliable method of detecting esophageal intubation during cardiac arrest.

Early detection of inadvertent oesophageal intubation: pulse oximetry vs. capnography

The aim of our retrospective study was to evaluate the efficacy of routine pulse oximetry and capnometry for detection of oesophageal tube misplacement. Patients undergoing ENT interventions at our hospital are routinely monitored by ECG, arterial blood pressure by cuff, capnography, and pulse oximetry. Beat-to-beat values of Sao2 and CO2 waveform were recorded by a graphic printer connected to a microcomputer, ASA I patients were routinely preventilated with FIO2 = 0.3, and ASA II-III patients with FIO2 = 1.0. Anaesthesia was performed by junior anaesthesiologists under the close supervision of a resident. During a 16-month period, 1372 patients were anaesthetized. The records of 21 patients with accidental oesophageal tube misplacement were available for retrospective evaluation. Nine patients were preventilated with FIO2 = 0.3 (ASA I), 12 patients with FIO2 = 1.0 (ASA II-III). Rapid detection of oesophageal tube position as early as the first ventilation is possible by capnometry, because of the highly significant difference in end-tidal CO2 (0.2 +/- 0.2 vol%; tracheal intubation: 3.7 +/- 0.9 vol.%; P less than 0.0001). The present advanced pulse oximetry method does not permit differentiation between oesophageal and tracheal tube position within 30 s in patients preventilated with FIO2 = 1.0. Oesophageal misplacement was detectable within 7.5 +/- 0.9 s in patients preventilated with FIO2 = 0.3 due to a 2.1 +/- 0.8% decrease in Sao2 (P less than 0.001). Our results underscore the significance of capnometry for rapid detection of inadvertent oesophageal intubation. High-resolution pulse oximetry is a valuable supplement but not a substitute for capnometry.