Glenn P. McGuire

Effects of varying levels of positive end-expiratory pressure on intracranial pressure and cerebral perfusion pressure.

OBJECTIVE To determine the influence of positive end-expiratory pressure (PEEP) on intracranial pressure and cerebral perfusion pressure. DESIGN Neurosurgical intensive care patients requiring intracranial pressure monitoring and mechanical ventilation were studied in a randomized, controlled study. SETTING Tertiary care, neurosurgical intensive care unit. PATIENTS Eighteen patients were enrolled in the study. Patients had posttraumatic head injuries (n = 9), subarachnoid hemorrhage (n = 7), obstructive hydrocephalus (n = 1), and intracerebral hemorrhage of unknown cause (n = 1). INTERVENTIONS Patients had PEEP levels of 5, 10, and 15 cm H2O applied to their lungs. MEASUREMENTS AND MAIN RESULTS Changes in intracranial pressure, mean arterial pressure, and cerebral perfusion pressure were measured. The results were analyzed separately for patients with normal and increased intracranial pressure (> 15 mm Hg). PEEP at 5 cm H2O had no effect on intracranial pressure in the group with normal intracranial pressure. However, PEEP at 10 and 15 cm H2O produced a significant (p < .05) increase in intracranial pressure (1.9 and 1.5 mm Hg, respectively). In the group with increased intracranial pressure, no significant change in intracranial pressure occurred at any of the PEEP levels used. In both groups, cerebral perfusion pressure was unchanged throughout. CONCLUSIONS In patients with normal intracranial pressure, PEEP at 5 cm H2O did not significantly alter intracranial pressure. The clinical relevance of the intracranial pressure increase at PEEP levels of 10 and 15 cm H2O is questionable because cerebral perfusion pressure did not change and remained > 60 mm Hg. In patients with increased intracranial pressure, higher levels of PEEP did not significantly change intracranial pressure or cerebral perfusion pressure.

A comparison of percutaneous and operative tracheostomies in intensive care patients

The aim of our study was to compare the complication rate of convenional surgical and percutaneous dilational tracheostomies performed under general anaesthesia in critically ill patients. Fifty-three consecutive patients whose lungs were mechanically ventilated and who required tracheostomy were randomised to undergo either conventional surgical tracheostomy (n = 28) in the operating room or percutaneous dilational tracheostomy (n = 25) in the intensive care unit under general anaesthesia. All of the procedures were successfully completed. No deaths were related to the performance of either tracheostomy technique. Three patients in each group required a dressing change for minor bleeding at the tracheostomy site. There was no major bleeding requiring blood transfusion. One patient in each group developed atelectasis detected on chest x-ray postoperatively. In the surgical tracheostomy group, there were two patients with cuff leaks, one with a stomal infection and one with a pneumothorax. None of these complications occurred after percutaneous, dilational tracheostomy. We conclude that the low incidence of complications in both groups indicates that percutaneous dilational tracheostomy can be performed as safely in the intensive care unit with general anaesthesia as surgical tracheostomy can be performed in the operating room.RésuméNous comparons l’incidence des complications causées par la trachéotomie chirurgicale traditionnelle avec celles de la trachéotomie percutanée par dilatation réalisées sous anesthésie générate chez des grands malades. Cinquante-trois patients consécutifs sous ventilation mécanique dont l’état nécessitait une trachéotomie sous anesthésie générate sont répartis pour subir soit une trachéotomie chirurgicale traditionnelle (n = 28) en salle d’opération, soit une trachéotomie percutanée par dilatation (n = 25) a l’unité des soins intensifs. Toutes les interventions ont été complétées avec succès. Aucun décès en rapport avec une ou l’autre des méihodes n’est survenu. Dans les deux groupes, on a du changer le pansement de trois patients pour un saignement mineur du site de la trachéotomie. Il n’y a pas eu de saignement majeur nécessitant de transfusions. Dans chaque groupe, on a détecté de l’atélectasie à la radiographie postopératoire. Dans le groupe de la trachéotomie chirurgicale, deux patients ont présenté des fuites au niveau du ballonnet de la canule, un patient a présenté une infection du stoma et un autre a présenté un pneumothorax. Ces complications ne sont pas survenue avec la méthode percutanée. L’incidence faible de complications dans les deux groupes montre que la trachéotomie percutanée peut être réalisée aussi bien à l’unité des soins intensifs sous anesthésie générate que la trachéotomie chirurgicale en salle d’opération.

A comparison of the Acute Physiology and Chronic Health Evaluation (APACHE) II score and the Trauma-Injury Severity Score (TRISS) for outcome assessment in intensive care unit trauma patients.

OBJECTIVE To assess the ability of the Acute Physiology and Chronic Health Evaluation (APACHE II) system and Trauma-Injury Severity Scoring (TRISS) system in predicting group mortality in intensive care unit (ICU) trauma patients. DESIGN Prospective study. SETTING A Canadian adult trauma tertiary referral hospital. PATIENTS Consecutive trauma patients admitted to the medical-surgical ICU or the neurosurgical ICU. INTERVENTION None. MEASUREMENTS AND MAIN RESULTS For each patient, demographic data, mechanism of injury, and surgical status were collected. Revised Trauma Scores and Injury Severity Scores were calculated from emergency room and operative data. The APACHE II score was calculated based on the data from the first 24 hrs of ICU admission. The probability of death was calculated for each patient based on the APACHE II and TRISS equations. The ability to predict group mortality for APACHE II and TRISS was assessed by receiver operating characteristic curve analysis, two by two decision matrices, and calibration curve analysis. Four hundred seventy trauma patients were admitted to the ICU. Sixty-three (13%) patients died and 407 (87%) survived. There were significant differences between survivors and nonsurvivors in age, Glasgow Coma Scale, Revised Trauma Score, Injury Severity Score, and APACHE II score. By receiver operating characteristic curve analysis, the areas under the curves (+/- SEM) of APACHE II and TRISS were 0.92 +/- 0.02 and 0.89 +/- 0.02, respectively. Using two by two decision matrices with a decision criterion of 0.5, the sensitivities, specificities, and percentages correctly classified were 50.8%, 97.3%, and 91.1%, respectively, for APACHE II, and 50.8%, 97.1%, and 90.9%, respectively, for TRISS. From the calibration curves, the r2 value was .93 (p = .0001) for APACHE II and .67 (p = .004) for TRISS. CONCLUSIONS Both APACHE II and TRISS scores were shown to accurately predict group mortality in ICU trauma patients. APACHE II and TRISS may be utilized for quality assurance in ICU trauma patients. However, neither APACHE II nor TRISS provides sufficient confidence for prediction of outcome of individual patients.

Venous air embolism during awake craniotomy in a supine patient.

PurposeTo report a non-fatal case of intraoperative venous air embolism (VAE) during an awake craniotomy. VAE presented with unusual clinical features.Clinical featuresVAE during an awake craniotomy has not been reported frequently. The patient we describe presented with persistent coughing followed by tachypnea, hypoxia and reduction in end-tidal CO2 during dural opening while undergoing an awake craniotomy in the supine position. Cardiovascular variables were stable during the episode except for transient hypertension. Having ruled out airway obstruction and low cardiac output, we concluded that air embolism was the cause. The patient responded immediately to the standard treatment of air embolism and recovered without any complication.ConclusionThis case illustrates a VAE during an awake craniotomy and emphasizes the importance of early diagnosis in the management.RésuméObjectifPrésenter un cas non mortel d’aéroembolie veineuse peropératoire (AEV) survenue pendant une craniotomie vigile. L’AEV présentait des caractéristiques cliniques inhabituelles.Éléments cliniquesL’AEV qui survient pendant la craniotomie vigile n’a pas été souvent rapportée. Le patient que nous décrivons a présenté une toux persistante suivie de tachypnée, d’hypoxie et d’une baisse du CO2 télé-expiratoire pendant l’ouverture durale pour une craniotomie vigile en décubitus dorsal. Les variables hémodynamiques ont été stables pendant l’épisode, sauf pour l’hypertension transitoire. Nous avons d’abord écarté la possibilité d’une obstruction des voies aériennes et un faible débit cardiaque pour en arriver au diagnostic d’embolie gazeuse. Le patient a immédiatement réagi au traitement standard de l’embolie gazeuse et il s’est remis sans complication.ConclusionCe cas illustre un AEV pendant une craniotomie vigile et souligne l’importance d’un diagnostic précoce pour le traitement.

Influence of inspired oxygen concentration on deadspace, respiratory drive, and Paco2 in intubated patients with chronic obstructive pulmonary disease

OBJECTIVES To investigate the response of CO2-retaining chronic obstructive pulmonary disease (COPD) patients to an increase in FIO2 following a period of mechanical ventilation with PaO2 in the normal range. The administration of a high FIO2 to chronic obstructive pulmonary disease (COPD) patients may result in hypercapnia. Recent evidence indicates that the hypercapnia may be due to reversal of preexisting regional hypoxic pulmonary vasoconstriction resulting in a greater deadspace. This effect would be more pronounced in patients whose initial PaO2 was < 60 torr (< 7.9 kPa). DESIGN Single blinded, prospective study. SETTING A medical surgical intensive care until in a tertiary care, teaching hospital. PATIENTS COPD CO2-retaining patients. INTERVENTIONS FIO2 increased to 0.7. MEASUREMENTS AND MAIN RESULTS Twelve intubated COPD patients weaned from mechanical ventilation were studied both at their baseline FIO2 (0.3 to 0.4), and following a 20-min period of exposure to an FIO2 of 0.7. Mean baseline values were: PaO2 of 85 torr (11.3 kPa), PCO2 of 56 torr (7.5 kPa), deadspace of 73%, and respiratory drive normal, as measured by P0.1. Statistical analysis using the paired Students t-test showed that the PaO2 increased significantly when the FIO2 was increased to 0.7, but there was no significant change in PaCO2, deadspace, or respiratory drive. CONCLUSION These results show that following a period of mechanical ventilation with an FIO2 sufficient to maintain a normal PaO2, a further increase in FIO2 does not result in an increased PaCO2 in this group of CO2-retaining COPD patients.

Vital capacity and patient controlled sevoflurane inhalation result in similar induction characteristics

PurposeTo compare patient controlled inhalational induction (PCI) with the most commonly used sevoflurane induction technique, vital capacity inhalational induction (VCI).MethodsFollowing approval of the Research Ethics Board, 124 outpatients undergoing knee arthroscopy were randomly assigned to receive either PCI or VCI sevoflurane followed by laryngeal mask airway (LMA) insertion and sevoflurane maintenance. In the PCI group, the circle circuit was not primed. The patients were asked to hold the facemask themselves and breathe normally with sevoflurane 8% in oxygen at a flow rate of 4 L·min−1. In the VCI group, the circle circuit was primed and patients were asked to take vital capacity breaths with sevoflurane 8% at an oxygen flow rate of 8 L·min−1. The LMA was inserted as soon as the patient’s jaw was relaxed. Time from induction to LMA insertion was recorded and insertion conditions rated. The amount of sevoflurane used for LMA insertion was calculated. Vital signs were monitored at oneminute intervals until ten minutes after LMA insertion.ResultsDemographic data were comparable. There were no differences with respect to LMA insertion time (PCI — 3.4 minvs VCI — 3.3 min), laryngospasm (PCI — 7%vs VCI — 5%), mean arterial pressure, heart rate, SaO2 as well as patient’s overall satisfaction.ConclusionPCI was comparable to VCI in sevoflurane induction with respect to the speed of induction, side effects during induction and patient satisfaction. However, PCI requires no special training and is widely applicable to all patient populations.RésuméObjectifComparer l’induction par inhalation autocontrôlée (IAC) avec l’induction par inhalation à capacité vitale (ICV), technique la plus utilisée.MéthodeAvec l’accord du Comité d’éthique en recherche, 124 patients répartis au hasard pour une arthroscopie du genou en chirurgie ambulatoire ont reçu une IAC ou une ICV au sévoflurane, suivie de l’insertion d’un masque laryngé (ML) et du maintien de l’anesthésie avec du sévoflurane. Le circuit cercle n’a pas été instauré pour l’IAC. Les patients devaient tenir euxmêmes le masque et respirer normalement un mélange d’oxygène et de sévoflurane à 8% selon un débit de 4 L·min−1. Pour l’ICV, le circuit cercle a été amorcé et les patients inspiraient à capacité vitale un mélange identique de gaz à 8 L·min−1. Le ML a été inséré aussitôt la mâchoire relâchée. Le temps écoulé entre l’induction et l’insertion du masque a été noté et les conditions d’insertion cotées. Le sévoflurane utilisé pour l’insertion du ML a été quantifié. Les signes vitaux ont été enregistrés à une minute d’intervalle jusqu’à dix minutes après l’insertion du ML.RésultatsLes caractéristiques des patients étaient comparables. Il n’y a pas eu de différence intergroupe quant au temps précédant l’insertion du ML (IAC — 3,4 min vs ICV — 3,3 min), la présence de laryngospasme (IAC — 7 % vs ICV — 5 %), la tension artérielle moyenne, la fréquence cardiaque, la SaO2 et la satisfaction des patients.ConclusionL’IAC a été comparable à l’ICV pour l’induction au sévoflurane quant à la rapidité de l’induction, aux effets secondaires pendant l’induction et à la satisfaction du patient. Toutefois, l’IAC n’exige pas de formation spéciale et convient à tous les patients.

Loss of the airway during tracheostomy: rescue oxygenation and re-establishment of the airway.

PurposeTo describe loss of the airway during tracheostomy and suggest a method for re-establishment of the airway and providing rescue oxygenation.Clinical featuresA 22-yr-old female diagnosed with encephalomyelopathy was admitted to the intensive care unit with a progressively deteriorating level of consciousness and respiratory failure requiring intubation and ventilation. Several weeks later, an elective tracheostomy was performed under anesthesia. The surgeon made an anterior tracheal wall incision and inserted a cuffed #6 Shiley tracheostomy tube. No end-tidal CO2 was detected and the patient could not be ventilated. After another failed attempt at insertion of a second tracheostomy tube, the diagnosis was made of a false passage within the trachea. The Shiley tracheostomy tube was removed and a #6 regular endotracheal tube was introduced in the trachea through the tracheostomy incision. The patient now could be ventilated with difficulty and low readings of end-tidal CO2 were noted. Despite all efforts to further ventilate the patient, the arterial oxygen saturation never recovered, resulting in cardiac arrest.ConclusionTo restore a lost airway during tracheostomy, we recommend that a jet ventilation airway exchange catheter (JVAE) be inserted in the endotracheal tube through a bronchoscope port attachment prior to surgical entry into the trachea. The JVAE will also ensure continued ability to oxygenate the patient.RésuméObjectifDécrire la perte du contrôle des voies aériennes pendant une trachéotomie et suggérer une méthode pour le rétablissement de la ventilation et l’apport d’oxygène de secours.Éléments cliniquesUne femme de 22 ans, atteinte d’encéphalomyélopathie, a été admise à l’unité des soins intensifs. Son état présentait une détérioration progressive du niveau de conscience et une insuffisance respiratoire nécessitant l’intubation et la ventilation. Quelques semaines plus tard, une trachéotomie non urgente a été réalisée sous anesthésie. Le chirurgien a pratiqué une incision à la paroi antérieure de la trachée et inséré une canule de trachéotomie à ballonnet no 6 de Shiley. Le CO2 de fin d’expiration n’a pas été détecté et la ventilation était impossible. L’essai d’une seconde canule de trachéotomie ayant échoué, on a conclu à une insertion paratrachéale de la canule. On a remplacé la canule de Shiley par une canule endotrachéale régulière no 6, introduite dans l’incision trachéale. On pouvait maintenant ventiler, mais avec peine et on a enregistré de faibles relevés de CO2 de fin d’expiration. Malgré tous les efforts supplémentaires fournis pour restaurer la ventilation, la saturation en oxygène du sang artériel n’est jamais revenue à la normale, le tout amenant à un arrêt cardiaque.ConclusionPour rétablir le contrôle des voies aériennes, nous recommandons l’utilisation d’une sonde d’échange permettant la ventilation en jet à haute fréquence (VJHF). Cette sonde devrait glisser par l’ouverture d’un connecteur (utilisé pour les bronchoscopies flexibles) dans une canule endotrachéale et serait mise ne place avant l’introduction chirurgicale dans la trachée. La sonde d’échange (VJHF) maintiendra la capacité d’oxygéner le patient en tout temps.

Fractured laryngeal mask airway (LMA).

To the Editor: In a 65-yr-old man undergoing elective cystolithopaxy anesthesia was induced and a size 4 LMA (Intavent, Oxon, UK) inserted. At emergence, the patient bit on the LMA shaft, shearing it into two pieces (Figure). The proximal shaft outside his clenched teeth was severed. The distal shaft and the inflated LMA remaining inside the patient’s mouth. A facemask with oxygen was applied. He maintained spontaneous breathing but did not open his mouth. One minute later, his mouth opened and the LMA was removed using McGill forceps after cuff deflation. Examination of the LMA showed a spiral fracture of the distal shaft and marked yellowish discoloration of the shaft. The manufacturing date was the second quarter of 1991. Autoclaving (steam, 134°C) at our hospital conforms to the manufacturer’s recommendations.1 We estimate that this LMA had been autoclaved over 400 times. The Canadian supplier (Vitaid, Toronto) recommended the following to ensure safety:1,2 first, record each autoclaving and discard after 40 uses; second, before each use, check colour of shaft, aperture bars, competency of pilot balloon valve, competency of LMA cuff, 15 mm connector fit; third, flex the shaft 180° and observe for kinking; fourth, use a bite block. This case illustrates the potential risk of a fractured LMA due to excessive re-use. Although dramatic in presentation, the patient had no sequlae. It is important to retrieve all pieces of the fractured LMA and that none is aspirated into the lungs.