Mohamad F. El-Khatib

Preoxygenation: Comparison of Maximal Breathing and Tidal Volume Breathing Techniques

BACKGROUND Preoxygenation with tidal volume breathing for 3-5 min is recommended by Hamilton and Eastwood. This report compares tidal volume preoxygenation technique with deep breathing techniques for 30-60 s. METHODS The study was conducted in two parts on patients undergoing elective coronary bypass grafting. In the first group (n = 32), each patient underwent all of the following preoxygenation techniques: the traditional technique consisting of 3 min of tidal volume breathing at an oxygen flow of 5 l/min; four deep breaths within 30 s at oxygen flows of 5 l/min, 10 l/min, and 20 l/min; and eight deep breaths within 60 s at an oxygen flow of 10 l/min. The mean arterial oxygen tensions after each technique were measured and compared. In the second group (n = 24), patients underwent one of the following techniques of preoxygenation: the traditional technique (n = 8), four deep breaths (n = 8), and eight deep breaths (n = 8). Apnea was then induced, and the mean times of hemoglobin desaturation from 100 to 99, 98, 97, 96, and 95% were determined. RESULTS In the first group of patients, the mean arterial oxygen tension following the tidal breathing technique was 392+/-72 mm Hg. This was significantly higher (P<0.05) than the values obtained following the four deep breath technique at oxygen flows of 5 l/min (256+/-73 mm Hg), 10 l/min (286+/-69 mm Hg), and 20 l/min (316+/-67 mm Hg). In contrast, the technique of eight deep breaths resulted in a mean arterial oxygen tension of 369+/-69 mm Hg, which was not significantly different from the value achieved by the traditional technique. In the second group of patients, apnea following different techniques of preoxygenation was associated with a slower hemoglobin desaturation in the eight-deep-breaths technique as compared with both the traditional and the four-deep-breaths techniques. CONCLUSION Rapid preoxygenation with the eight deep breaths within 60 s can be used as an alternative to the traditional 3-min technique.

A single dose of propofol at the end of surgery for the prevention of emergence agitation in children undergoing strabismus surgery during sevoflurane anesthesia

Background:Emergence agitation in children after sevoflurane is common. Different drugs have been used to decrease its occurrence with variable efficacy. The authors compared the incidence and severity of emergence agitation in children who received a single dose of propofol at the end of strabismus surgery versus children who received saline. Methods:In this prospective, randomized, double-blind study, the authors enrolled 80 healthy children aged 2–6 yr. The children were randomly allocated to the propofol group (n = 41), which received 1 mg/kg propofol at the end of surgery, or to the saline group (n = 39), which received saline. Results:The mean scores on the Pediatric Anesthesia Emergence Delirium scale were significantly lower in the propofol group compared with the saline group (8.6 ± 3.9 vs. 11.5 ± 4.5; P = 0.004). Also, the incidence of agitation was significantly lower in the propofol group compared with the saline group (19.5% vs. 47.2%; P = 0.01). A threshold score greater than 10 on the Pediatric Anesthesia Emergence Delirium scale was the best discriminator between presence and absence of emergence agitation. Times to removal of the laryngeal mask airway (10.6 ± 1.5 vs. 9.4 ± 1.9 min; P = 0.004) and emergence times (23.4 ± 5.7 vs. 19.7 ± 5 min; P = 0.004) were significantly longer in the propofol group. However, discharge times were similar between the two groups (propofol: 34.1 ± 8.4 min; saline: 34.9 ± 8.6 min). More parents in the propofol group were satisfied. Conclusions:In children undergoing strabismus surgery, 1 mg/kg propofol at the end of surgery after discontinuation of sevoflurane decreases the incidence of agitation and improves parents’ satisfaction without delaying discharge from the postanesthesia care unit.

Intraarticular Tramadol-Bupivacaine Combination Prolongs the Duration of Postoperative Analgesia After Outpatient Arthroscopic Knee Surgery

BACKGROUND: Intraarticular (IA) local anesthetics are often used for the management and prevention of pain after arthroscopic knee surgery. Recently, IA tramadol was also used for the management of these patients. However, the IA combination of local anesthetic and tramadol has not been evaluated in arthroscopic outpatients. Our primary aim in this study was to evaluate the analgesic effect of an IA combination of bupivacaine and tramadol when compared with each drug alone using visual analog scale (VAS) pain scores in patients undergoing day-care arthroscopic knee surgery. Additionally, we assessed analgesic demand. METHODS: Ninety ASA I/II patients undergoing arthroscopic partial meniscectomy, performed by a single surgeon under general anesthesia, were assigned in a randomized, double-blind manner into three groups: group B (n = 30) received 0.25% bupivacaine, group T (n = 30) received 100 mg tramadol, and group BT (n = 30) received 0.25% bupivacaine and 100 mg tramadol to a total volume of 20 mL by the IA route after surgery. Postoperative pain scores were measured on a VAS, at rest and on mobilization at 0.5, 1, 2, 4, 6, 8, 12, and 24 h. Duration of analgesia, the subsequent 24 h consumption of rescue analgesia, time to ambulation, and time to discharge were evaluated. In addition, the systemic side effects of the IA injected drugs were also assessed. RESULTS: The results showed significantly lower VAS pain scores in group BT (P ≪ 0.1) when compared with groups T and B. Group BT had a later onset of postsurgical pain and longer time to first rescue analgesic than groups B and T. The 24 h consumption of analgesic was significantly less in group BT when compared with the other two groups (26.7% of the patients required rescue analgesia in group BT, whereas this number was 90% in group B and 86.7% in group T). In addition, time in hours to discharge and time to unassisted ambulation were significantly shorter in group BT when compared with groups T and B, and this was not associated with any detectable systemic effects. CONCLUSION: The IA admixture of tramadol 100 mg with bupivacaine 0.25% provides a pronounced prolongation of analgesia compared with either drug alone in patients undergoing day care arthroscopic knee surgery.

A Taxonomy for Mechanical Ventilation: 10 Fundamental Maxims

The American Association for Respiratory Care has declared a benchmark for competency in mechanical ventilation that includes the ability to “apply to practice all ventilation modes currently available on all invasive and noninvasive mechanical ventilators.” This level of competency presupposes the ability to identify, classify, compare, and contrast all modes of ventilation. Unfortunately, current educational paradigms do not supply the tools to achieve such goals. To fill this gap, we expand and refine a previously described taxonomy for classifying modes of ventilation and explain how it can be understood in terms of 10 fundamental constructs of ventilator technology: (1) defining a breath, (2) defining an assisted breath, (3) specifying the means of assisting breaths based on control variables specified by the equation of motion, (4) classifying breaths in terms of how inspiration is started and stopped, (5) identifying ventilator-initiated versus patient-initiated start and stop events, (6) defining spontaneous and mandatory breaths, (7) defining breath sequences (8), combining control variables and breath sequences into ventilatory patterns, (9) describing targeting schemes, and (10) constructing a formal taxonomy for modes of ventilation composed of control variable, breath sequence, and targeting schemes. Having established the theoretical basis of the taxonomy, we demonstrate a step-by-step procedure to classify any mode on any mechanical ventilator.

Noninvasive bilevel positive airway pressure for preoxygenation of the critically ill morbidly obese patient.

PurposeWe describe the use of noninvasive bilevel positive airway pressure (BiPAP) in a critically ill, hypoxemic and morbidly obese patient for preoxygenation prior to rapid sequence induction of anesthesia.Clinical featuresA critically ill morbidly obese patient (body mass index: 49 kg·m-2) was scheduled for urgent laparoscopic cholecystectomy. Preoxygenation with 5 L·min-1 oxygen flow resulted in a moderate increase in oxygen saturation (SPO2) from 79% to 90%. Prior to rapid sequence induction of anesthesia, a trial of noninvasive BiPAP with oxygen delivery at 5 L·min-1 increased his SPO2to 95% initially, with full saturation of 99% achieved when oxygen flow was increased to 10 L·min-1. Bilevel positive airway pressure with an inspiratory and expiratory pressures of 17 cm H2O and 7 cm H2O, respectively, was applied using a full face mask to achieve a tidal volume of 8 mL·kg-1. Rapid sequence induction proceeded uneventfully.ConclusionsPrior to rapid sequence induction of anesthesia in patients with respiratory compromise secondary to factors which reduce FRC, noninvasive BiPAP in combination with supplemental oxygen may be indicated whenever traditional preoxygenation does not provide adequate oxyhemoglobin saturation. Improved oxygenation is most likely attributable to improved ventilation and alveolar recruitment.RésuméObjectifNous décrivons l’utilisation de la ventilation en pression positive non invasive à bi-niveau (BiPAP) chez un patient sévèrement malade, hypoxémique et obèse morbide, pour la préoxygénation précédant l’induction de l’anesthésie en séquence rapide.Éléments cliniquesUn patient sévèrement malade et obèse morbide (indice de masse corporelle: 49 kg·m-2) s’est présenté pour une cholécystectomie laparoscopique urgente. La préoxygénation avec un débit d’oxygène de 5 L·min-1 a eu pour résultat une augmentation modérée de la saturation d’oxygène (SPO2) de 79 % à 90 %. Avant l’induction de l’anesthésie à séquence rapide, un essai de BiPAP non invasive avec un débit d’oxygène à 5 L·min-1 a accru sa SPO2 à 95% initialement, avec une saturation complète achevée à 99 % lorsque le débit d’oxygène a été accru à 10 L·min-1. La ventilation en pression positive bi-niveau avec des pressions inspiratoire et expiratoire de 17 cm H2O et 7 cm H2O respectivement a été appliquée à l’aide d’un masque facial total afin d’obtenir un volume courant de 8 mL·kg-1. L’induction à séquence rapide s’est déroulée sans incident.ConclusionAvant l’induction de l’anesthésie à séquence rapide chez les patients présentant des difficultés respiratoires secondaires à des facteurs réduisant la capacité fonctionnelle résiduelle, la BiPAP non invasive combinée à de l’oxygène supplémentaire pourrait être indiquée lorsque la préoxygénation traditionnelle ne fournit pas une saturation de l’oxyhémoglobine appropriée. Une meilleure oxygénation est sans doute attribuable à une meilleure ventilation et à un meilleur recrutement alvéolaire.

Clinical review: Liberation from mechanical ventilation

Mechanical ventilation is the defining event of intensive care unit (ICU) management. Although it is a life saving intervention in patients with acute respiratory failure and other disease entities, a major goal of critical care clinicians should be to liberate patients from mechanical ventilation as early as possible to avoid the multitude of complications and risks associated with prolonged unnecessary mechanical ventilation, including ventilator induced lung injury, ventilator associated pneumonia, increased length of ICU and hospital stay, and increased cost of care delivery. This review highlights the recent developments in assessing and testing for readiness of liberation from mechanical ventilation, the etiology of weaning failure, the value of weaning protocols, and a simple practical approach for liberation from mechanical ventilation.

Critical Care Clinicians’ Knowledge of Evidence-Based Guidelines for Preventing Ventilator-Associated Pneumonia

BACKGROUND Ventilator-associated pneumonia is the most common hospital-acquired infection among patients receiving mechanical ventilation in an intensive care unit. Different initiatives for the prevention of ventilator-associated pneumonia have been developed and recommended. OBJECTIVE To evaluate knowledge of critical care providers (physicians, nurses, and respiratory therapists in the intensive care unit) about evidence-based guidelines for preventing ventilator-associated pneumonia. METHODS Ten physicians, 41 nurses, and 18 respiratory therapists working in the intensive care unit of a major tertiary care university hospital center completed an anonymous questionnaire on 9 nonpharmacological guidelines for prevention of ventilator-associated pneumonia. RESULTS The mean (SD) total scores of physicians, nurses, and respiratory therapists were 80.2% (11.4%), 78.1% (10.6%), and 80.5% (6%), respectively, with no significant differences between them. Furthermore, within each category of health care professionals, the scores of professionals with less than 5 years of intensive care experience did not differ significantly from the scores of professionals with more than 5 years of intensive care experience. CONCLUSIONS A health care delivery model that includes physicians, nurses, and respiratory therapists in the intensive care unit can result in an adequate level of knowledge on evidence-based nonpharmacological guidelines for the prevention of ventilator-associated pneumonia.

Changes in resistances of endotracheal tubes with reductions in the cross-sectional area.

Background and objectives: Partial obstruction of endotracheal tubes due to accumulation of secretions and mucus plugs can increase the tube resistance and subsequently impose increased resistive load on the patient. This study was performed to determine the changes in the resistance of endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm with different degrees and locations of endotracheal tube narrowing. Methods: Reductions of 10%, 25%, 50% and 75% in the endotracheal tubes cross‐sectional areas were created at different sites along the axes of the tube connected to an artificial lung. While ventilating with a constant inspiratory flow, a 1 s end‐inspiratory occlusion manoeuvre was applied and the resulting plateau pressure was determined. The resistance was calculated as (peak airway pressure ‐ plateau pressure)/peak inspiratory flow. Results: Significant increases in the endotracheal tubes resistances were observed as the tubes cross‐sectional area reduction was increased from 25% to 50% and from 50% to 75% for the 7.5 mm endotracheal tube, from 25% to 50% for the 8.0 mm endotracheal tube, and from 50% to 75% for the 8.5 mm endotracheal tube. Changes of the endotracheal tube resistances were not affected by the site of cross‐sectional area reductions along the axes of the tubes. Conclusions: For endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm, significant changes in the tubes resistances are observed when the partial obstructions of the tubes exceed certain critical values. The location of the partial obstruction did not affect the changes in the endotracheal tube resistances.

mechanical ventilators optimized for pediatric use decrease work of breathing and oxygen consumption during pressure-support ventilation

Objectives: a) To investigate whether the patient work of breathing needed to trigger inspiration is affected by the type of ventilator delivering pressure‐support ventilation for mechanically ventilated pediatric patients. b) To determine whether changes in oxygen consumption (&OV0312;o2) trend with changes in work of breathing and would thus be helpful in tracking work of breathing. Design: Prospective study. Setting: Pediatric intensive care unit at a university hospital. Patients: Nine mechanically ventilated patients (2 to 75 months of age). Interventions: While maintaining a constant pressure‐support ventilation level, patients were alternately supported with the Siemens Servo 900C, the Bird VIP, and the Newport Wave E200 ventilators in random order. Measurements and Main Results: Work of breathing, defined as the integral of the pressure‐volume curve corresponding to negative pressure, was calculated with a pulmonary monitoring system. &OV0312;o2 was measured with a metabolic cart. Patient distress levels were assessed using the COMFORT scale, a behavioral scoring system. Mean values (20 breaths/patient) for measured variables with each ventilator were compared using analysis of variance and Scheffé tests, with p < .05 indicating statistical significance. The lowest &OV0312;o2 (103 ± 35 mL/min/m2) and work of breathing (24 ± 15 g.cm/m2) were achieved with the Bird VIP ventilator and were significantly ( p < .05) lower than those values obtained with either the Siemens Servo 900C (&OV0312;o2 147 ± 33 mL/min/m2; work of breathing 49 ± 18 g.cm/m2) or the Newport Wave E200 (&OV0312;o2 122 ± 33 mL/min/m2; work of breathing 35 ± 15 g.cm/ m2). Also, the values of work of breathing and &OV0312;o2 obtained using the Newport Wave E200 were significantly ( p < .05) lower than those values obtained using the Servo 900C. No change in behavioral distress occurred when the ventilators were changed. In all patients, there was a clear similarity in the trends of &OV0312;o2 and work of breathing. Conclusions: We conclude that &OV0312;o2 and work of breathing may be reduced significantly using the latest generation of mechanical ventilators optimized for infant and pediatric use. Because work of breathing is less with the Bird VIP than the other two ventilators tested, leading to a corresponding decrease in &OV0312;o2, we suggest that the Bird VIP better adapts the patient to the ventilator and may facilitate weaning from ventilatory support. We also suggest that changes in &OV0312;o2 might be helpful in tracking changes in work of breathing. (Crit Care Med 1994; 22:1942–1948)

Intraarticular tramadol-bupivacaine combination prolongs the duration of postoperative analgesia after outpatient arthroscopic knee surgery

BACKGROUND: Intraarticular (IA) local anesthetics are often used for the management and prevention of pain after arthroscopic knee surgery. Recently, IA tramadol was also used for the management of these patients. However, the IA combination of local anesthetic and tramadol has not been evaluated in arthroscopic outpatients. Our primary aim in this study was to evaluate the analgesic effect of an IA combination of bupivacaine and tramadol when compared with each drug alone using visual analog scale (VAS) pain scores in patients undergoing day-care arthroscopic knee surgery. Additionally, we assessed analgesic demand. METHODS: Ninety ASA I/II patients undergoing arthroscopic partial meniscectomy, performed by a single surgeon under general anesthesia, were assigned in a randomized, double-blind manner into three groups: group B (n = 30) received 0.25% bupivacaine, group T (n = 30) received 100 mg tramadol, and group BT (n = 30) received 0.25% bupivacaine and 100 mg tramadol to a total volume of 20 mL by the IA route after surgery. Postoperative pain scores were measured on a VAS, at rest and on mobilization at 0.5, 1, 2, 4, 6, 8, 12, and 24 h. Duration of analgesia, the subsequent 24 h consumption of rescue analgesia, time to ambulation, and time to discharge were evaluated. In addition, the systemic side effects of the IA injected drugs were also assessed. RESULTS: The results showed significantly lower VAS pain scores in group BT (P ≪ 0.1) when compared with groups T and B. Group BT had a later onset of postsurgical pain and longer time to first rescue analgesic than groups B and T. The 24 h consumption of analgesic was significantly less in group BT when compared with the other two groups (26.7% of the patients required rescue analgesia in group BT, whereas this number was 90% in group B and 86.7% in group T). In addition, time in hours to discharge and time to unassisted ambulation were significantly shorter in group BT when compared with groups T and B, and this was not associated with any detectable systemic effects. CONCLUSION: The IA admixture of tramadol 100 mg with bupivacaine 0.25% provides a pronounced prolongation of analgesia compared with either drug alone in patients undergoing day care arthroscopic knee surgery.