Nikolaus Gravenstein

Head rotation during internal jugular vein cannulation and the risk of carotid artery puncture.

We undertook a prospective laboratory study to examine the effect of head position on the relative positions of the carotid artery and the internal jugular vein (IJV).Volunteers (n = 12) from departmental staff, 18-60 yr of age, who had never undergone cannulation of the IJV underwent imaging of their IJV and carotid artery. With the subject in a 15 degrees Trendelenburg position, two-dimensional ultrasound images of the IJV and the carotid artery were obtained on the left and right sides of the neck at 2 and 4 cm from the clavicle along the lateral border of the sternal head of the sternocleidomastoid muscle at 0 degrees, 40 degrees, and 80 degrees of head rotation from the midline. The percent overlap of the carotid artery and IJV increased significantly at 40 degrees and 80 degrees head rotation to both the right and left (P < 0.05). Data from 2 and 4 cm above the clavicle did not differ and were pooled. The percent overlap was larger on the left than the right only with 80 degrees of head rotation (P < 0.05). The increased overlap of carotid artery and IJV with head rotation >40 degrees increases the risk of inadvertent puncture of the carotid artery associated with the common occurrence of transfixion of the IJV before it is identified during needle withdrawal. The IJV frequently collapses with needle insertion. This may result in puncture of the posterior wall of the vessel, and thus of the carotid artery when the two vessels overlap. To decrease this risk, the head should be kept in as neutral a position as possible, that is <40 degrees rotation, during IJV cannulation. (Anesth Analg 1996;82:125-8)

In vitro evaluation of relative perforating potential of central venous catheters: Comparison of materials, selected models, number of lumens, and angles of incidence to simulated membrane

Perforation of the vena cava or atrium is a serious complication of monitoring with a central venous catheter. We designed an in vitro model with a pulsating simulated membrane to evaluate a number of variables that could affect relative perforating potential of different types of central venous catheters. To determine the perforating potential of central venous catheters, we studied the effects of (1) the angle of incidence (n=6) between catheter and simulated membrane; (2) catheter material (polyurethane and polyethylene); (3) make (manufacturer and model) (n=6), with 3 catheters of each make tested; (4) design (n=3 each: silicone rubber, open-ended, blunt-ended, and polyurethane pigtail); and (5) number of lumens (single, double, or triple). Each trial was repeated five times with each catheter that was tested. Perforation was significantly more likely when the angle of incidence between catheter and pulsating simulated membrane was greater than 40° than when it was 40° (P<0.05). Perforation was less likely with single-lumen than comparable Frenchsized double- and triple-lumen catheters; among single-lumen catheters, perforation required many more pulsations with a polyurethane than a polyethylene catheter (P<0.001). Perforation potential differed significantly among 6 makes of 7-French triple-lumen catheters (P<0.05). Compared with other materials or designs, silicone rubber or a pigtail tip decreased the perforation potential of catheters (P<0.001). These data offer additional objective information to consider when choosing and positioning central venous catheters.

The effect of body inclination during prone positioning on intraocular pressure in awake volunteers: a comparison of two operating tables.

Visual loss is a rare, but catastrophic, complication of surgery in the prone position. The prone position increases intraocular pressure (IOP), which may lead to visual loss by decreasing perfusion of the anterior optic nerve. We tested whether the reverse Trendelenburg position ameliorates the increase in IOP caused by prone positioning. Furthermore, we compared two prone positioning setups. The IOP of 10 healthy awake volunteers was measured in the prone position at 3 different degrees of inclination (horizontal, 10° reverse Trendelenburg, and 10° Trendelenburg) and in the sitting and supine positions in a randomized crossover study comparing the Jackson table and the Wilson frame. In a given eye, all prone IOP values (median [25th–75th percentile] exceeded those of the sitting (15.0 mm Hg [12.8–16.3 mm Hg]) and supine (16.8mm Hg [14.0–18.3 mm Hg]) positions. IOPs in the reverse Trendelenburg, horizontal, and Trendelenburg positions were 20.3 mm Hg (16.3–22.5 mm Hg), 22.5 mm Hg (19.8–25.3 mm Hg),* and 23.8 mm Hg (21.5–26.3 mm Hg),*† respectively (*P < 0.001 versus reverse Trendelenburg; †P < 0.001 versus horizontal). The reverse Trendelenburg position ameliorated the increase in IOP caused by the prone position. Furthermore, the reverse Trendelenburg position decreased the number of grossly abnormal IOP values (>23 mm Hg) by 50% and 75% compared with the prone horizontal and Trendelenburg positions, respectively. The prone positioning setups did not differ in their effect on IOP. The increase in IOP caused by prone positioning was ameliorated by the reverse Trendelenburg position and was aggravated by the Trendelenburg position. The short time period between changes in position and changes in IOP suggests an important role for ocular venous pressures in determining IOP. Therefore, IOP can be beneficially manipulated by operating table inclination in the prone position.

Bumetanide Alleviates Epileptogenic and Neurotoxic Effects of Sevoflurane in Neonatal Rat Brain

Background:We tested the hypothesis that in newborn rats, sevoflurane may cause seizures, neurotoxicity, and impairment in synaptic plasticity—effects that may be diminished by the Na+–K+–2Cl− cotransporter 1 inhibitor, bumetanide. Methods:Electroencephalography, activated caspase-3, and hippocampal long-term potentiation were measured in rats exposed to 2.1% sevoflurane for 0.5–6 h at postnatal days 4–17 (P4–P17). Results:Arterial blood gas samples drawn at a sevoflurane concentration of 2.1% showed no evidence of either hypoxia or hypoventilation in spontaneously breathing rats. Higher doses of sevoflurane (e.g., 2.9%) caused respiratory depression. During anesthesia maintenance, the electroencephalography exhibited distinctive episodes of epileptic seizures in 40% of P4–P8 rats. Such seizure-like activity was not detected during anesthesia maintenance in P10–P17 rats. Emergence from 3 h of anesthesia with sevoflurane resulted in tonic/clonic seizures in some P10–P17 rats but not in P4–P8 rats. Bumetanide (5 &mgr;mol/kg, intraperitoneally) significantly decreased seizures in P4–P9 rats but did not affect the emergence seizures in P10–P17 rats. Anesthesia of P4 rats with sevoflurane for 6 h caused a significant increase in activated caspase-3 and impairment of long-term potentiation induction measured at 1 and 14–17 days after exposure to sevoflurane, respectively. Pretreatment of P4 rats with bumetanide nearly abolished the increase in activated caspase-3 but did not alleviate impairment of long-term potentiation. Conclusion:These results support the possibility that excitatory output of sevoflurane-potentiated &ggr;-aminobutyric acid type A/glycine systems may contribute to epileptogenic and neurotoxic effects in early postnatal rats.

Continuous neonatal evaluation in the delivery room by pulse oximetry

The pulse oximeter, a noninvasive and continuous monitor of arterial oxygenation that is reliable in adults, children, and infants, was evaluated for use in neonates in the delivery suite. One hundred newborn infants, weighing 850 to 5,230 g each, delivered vaginally or by cesarean section with general or epidural anesthesia were studied. After delivery, each infant was placed in a radiant warmer, and a pulse oximetry probe was placed on the right hand. Hemoglobin saturation was then recorded for 15 minutes. Initial pulse oximetry values were obtained in less than one minute after cord clamping in 43% of infants, less than two minutes in 81 %, and less than three minutes in 98%. Average arterial oxygen saturation was 59% at 1 minute (43 infants), 68% at 2 minutes (81), 82% at 5 minutes (98), and 90% at 15 minutes (91). Oxygen saturation was less than 30% in 12 neonates and less than 50% in 26 neonates at some time during the 15-minute monitoring period. Oxygen saturation did not differ significantly between neonates delivered vaginally or by cesarean section, regardless of the presence or type of anesthetic used. Arterial oxygen saturation measured by pulse oximetry showed a statistically significant relationship when compared with the traditional Apgar scoring system. Pulse oximetry was found to be very useful in objectively judging the adequacy of resuscitative efforts, as well as in identifying children who had marked arterial desaturation during the early neonatal period.

Cricoid Pressure Results in Compression of the Postcricoid Hypopharynx: The Esophageal Position Is Irrelevant

BACKGROUND: Sellick described cricoid pressure (CP) as pinching the esophagus between the cricoid ring and the cervical spine. A recent report noted that with the application of CP, the esophagus moved laterally more than 90% of the time, questioning the efficacy of this maneuver. We designed this study to accurately define the anatomy of the Sellick maneuver and to investigate its efficacy. METHODS: Twenty-four nonsedated adult volunteers underwent neck magnetic resonance imaging with and without CP. Measurements were made of the postcricoid hypopharynx, airway compression, and lateral displacement of the cricoid ring during the application of CP. The relevant anatomy was reviewed. RESULTS: The hypopharynx, not the esophagus, is what lies behind the cricoid ring and is compressed by CP. The distal hypopharynx, the portion of the alimentary canal at the cricoid level, was fixed with respect to the cricoid ring and not mobile. With CP, the mean anterioposterior diameter of the hypopharynx was reduced by 35% and the lumen likely obliterated, and this compression was maintained even when the cricoid ring was lateral to the vertebral body. CONCLUSIONS: The location and movement of the esophagus is irrelevant to the efficiency of the Sellick’s maneuver (CP) in regard to prevention of gastric regurgitation into the pharynx. The hypopharynx and cricoid ring move together as an anatomic unit. This relationship is essential to the efficacy and reliability of Sellick’s maneuver. The magnetic resonance images show that compression of the alimentary tract occurs with midline and lateral displacement of the cricoid cartilage relative to the underlying vertebral body.

A better landmark for positioning a central venous catheter.

Background.Improper positioning of central venous catheters (CVCs) can lead to erosion through the superior vena cava (SVC) or right atrium (RA) and pericardial tamponade. It is widely recommended that the tip of CVCs be placed above the heart or the pericardial reflection. The purpose of this study was to identify an easily recognized landmark to allow identification of the proximal extent of the pericardial reflection on a routine chest radiograph (CXR). Methods.We analyzed the computerized tomograms of the chest from 97 adults to evaluate the relationship between the pericardial reflection, SVC, carina, and right mainstem bronchus. Correlations between demographic data and length of SVC or pericardial reflection were sought. Results.The mean length of the SVC was 6.5 cm. The pericardial reflection covered an average of 3.6 cm of the distal SVC. The carina was a mean of 1.3 cm below the mid-point of the SVC and 0.7 cm below the pericardial reflection. There was no significant correlation between SVC or pericardial length and either age, height, or weight. Conclusions.The distal half of the SVC lies within the pericardial reflection, and the upper limit of the pericardial reflection is slightly above the level of the carina. These landmarks are useful for determining proper position of the tip of a CVC on CXR.

Effects of elevating the head of bed on interface pressure in volunteers.

Objective:Intensive care unit patients are at particular risk for pressure ulcers and ventilator-associated pneumonia. Current guidelines recommend that mechanically ventilated patients be kept in a semirecumbent position with the head of bed elevated 30°–45° to prevent aspiration and ventilator-associated pneumonia. We tested the effects of elevating the head of bed on the interface pressure between the skin of the sacral area and the bed with healthy volunteers. Interventions:Interface pressure profiles of the sacral area were obtained for the 0°, 10°, 20°, 30°, 45°, 60°, and 75° head of bed elevated positions from 15 subjects (14 men, one woman). Measurements and Main Results:Peak sacral interface pressures increased with large increases in head of bed elevation. The 30°, 45°, 60°, and 75° head of bed positions all had peak interface pressures that were significantly (p < 0.02) greater than the supine measurement and also were different from all other head of bed positions. Affected areas, defined as areas over which an interface pressure ≥32 mm Hg was obtained, increased with large elevation of the head of bed. The affected areas of the 45°, 60°, and 75° head of bed positions were significantly greater than the supine position and were also significantly different from all other head of bed positions. Conclusions:Raising the head of bed to 30° or higher on a intensive care unit bed increases the peak interface pressure between the skin at the sacral area and support surface in healthy volunteers. At 45° head of bed elevation or higher, the affected area attributed to a skin–intensive care unit bed interface pressure ≥32 mm Hg increased as well. Further study is needed to determine whether the increased peak interface pressures and affected areas that result from raising the head of bed actually increase the incidence of pressure ulcer formation.

Postoperative sore throat: effect of oropharyngeal airway in orotracheally intubated patients.

The incidence of postoperative sore throat was evaluated prospectively in 203 orotracheally intubated patients undergoing general anesthesia for surgical procedures. Patients were randomly assigned to have either a plastic oropharyngeal airway or a gauze bite-block in place during the operation and were evaluated for the occurrence of postoperative sore throat by questionnaire the day after surgery. The incidence of postoperative sore throat was 35.2% in the oropharyngeal airway group and 42.5% in the gauze bite-block group, not a statistically significant difference (P > 0.05). The incidence of postoperative sore throat was significantly higher when blood was noted on the airway instruments (64.5%) than when it was not (30.9%) (P < 0.01). There was an association, although not statistically significant, between the incidence of postoperative sore throat and intubation by an anesthesia resident with <<1 yr experience (P = 0.064). The data from this study indicate that the intraoperative use of hard plastic oropharyngeal airways, compared with the use of soft gauze bite-blocks, does not increase the incidence of postoperative sore throat. These data also suggest that pharyngeal trauma may contribute significantly to the development of postoperative sore throat. We suggest that aggressive oropharyngeal suctioning may contribute to this pharyngeal trauma.

Endobronchial rupture from endotracheal reintubation with an endotracheal tube guide

Endotracheal tube guides are often used to facilitate endotracheal tube exchange in patients whose airways are difficult to intubate. The absence of reported complications with this technique suggests it is a safe technique; however, we report a case of endobronchial rupture associated with such a guide. Diagnosis and management of tracheobronchial tears and alternative approaches to difficult reintubation are described.