Changes inPetCO2 and pulmonary blood flow after bronchial occlusion in dogs

The use ofPetCO₂ in detecting accidental bronchial intubation was investigated. ThePetCO₂ was measured in six mongrel dogs after occluding the left mainstem bronchus in three conditions; pentobarbital anaesthesia, 0.8% halothane insufflation together withpentobarbital anaesthesia, and simultaneous left pulmonary artery and bronchial airway occlusion with intravenous pentobarbital anaesthesia. An external flow probe measured left pulmonary artery blood flow. ThePetCO₂ decreased after bronchial occlusion during pentobarbital (35 ± 3 vs 30 ± 5 mmHg) and halothane-pentobarbital (30 ± 6 vs 25 ± 6 mmHg) conditions (P < 0.05). However, within three minutes of bronchial occlusion, the values ofPetCO₂ had returned to their pre-occlusion values. After five minutes of bronchial occlusion pulmonary artery blood flow in the non-ventilated lung decreased (P < 0.05) during pentobarbital (770 ± 533 ml · min^?1 vs 575 ± 306 ml · min^?1) and halothane-pentobarbital (495 ± 127 ml · min^?1 vs 387 ± 178ml · min^?1) conditions. Simultaneous bronchial and pulmonary artery occlusion prevented any changes inPetCO₂. It was concluded that accidental one- lung ventilation results in small and transient decreases inPetCO₂. A redistribution of blood flow from the nonventilated to ventilated lung occurs which restoresPetCO₂ to the original values observed with twolung ventilation.     

Pulmonary resistance in dogs: a comparison of xenon with nitrous oxide

Xenon (Xe) may cause an increase in airway resistance due to its high density and viscosity. The object of this study was to examine the effects of Xe on pulmonary resistance using dog models with normal and methacholine-treated airways. During anaesthesia 22 mongrel dogs’ tracheas were intubated and the lungs were mechanically ventilated with 70% N₂/30% O₂ as a control gas. The gases 70% nitrous oxide (N₂O), 50% N₂O, 70% Xe and 50% Xe were administered in a random order for 25 min. Bronchoconstriction was produced by a continuous infusion of methacholine, 0.22 mg · kg^?1 · hr^?1. Pulmonary resistance (Rl) was calculated by the isovolume method using flow at the airway opening, volume and transpulmonary pressure. In normal dogs,Rl breathing 70% Xe (mean ± SEM, 0.84 ± 0.12 cm H₂O · L^?1 · sec^?1) was greater (P < 0.05) than with 70% N₂O, 50% N₂O or control gas (0.61 ± 0.08, 0.59 ± 0.06 and 0.62 ± 0.06 cm H₂O · L^?1 sec^?1). Breathing 50% Xe theRL (0.77 ± 0.10 cm H₂O · L^?1 · sec^?1) was not different from 50% N₂O or control. Methacholine infusion increasedRL 3.92 ± 1.98 (mean ± SD) times. TheRL breathing 50% Xe (2.55 ± 0.44 cm H₂O · L^?1 · sec^?1) was not greater than during 50% N₂O or control (2.08 ± 0.33 and 2.13 ± 0.33 cm H₂O · L^?1 · sec^?1) in methacholine-treated dogs. The data suggest that inhalation of high concentrations of Xe increases airway resistance, but only to a modest extent in dogs with normal or methacholine-treated airways.     

Arrhythmogenic potential of dopexamine hydrochloride during halothane anaesthesia in dogs

Dopexamine hydrochloride (Dopacard®) is the novel synthetic catecholamine designed for use in the acute management of a low cardiac output status. In addition to dopaminergic receptor stimulation, dopexamine hydrochloride is a potent β₂ adrenoreceptor agonist with negligible direct β₁ and no alpha adrenergic effect. The objective of this study was to compare the arrhythmogenic effects of dopexamine hydrochloride and dopamine in dogs anaesthetized with halothane (1.2 MAC). The starting dose for dopexamine hydrochloride was 3.5 μg · kg^?1 min^?1 and for dopamine was 5 μg · kg^?1 min^?1. Concentrations of the drugs were increased until four or more premature ventricular contractions within 15 seconds were produced. All dogs developed ventricular tachycardia when dopamine was administered in concentrations ranging between 18–20 μg · kg^?1 · min^?1. Unlike dopamine, dopexamine hydrochloride even at concentrations as high as 50 μg · kg^?1· min^?1 did not induce any atrial or ventricular ectopic beats. Lack of β_-1 and alpha adrenergic agonist effects is a likely explanation for low arrhythmogenicity of dopexamine hydrochloride. Both drugs increase cardiac output; dopexamine hydrochloride primarily by a dose-related increase in heart rate and increased aflerload. At the maximal concentration dopexamine hydrochloride increased heart rate from 114 to 150 beat · min^?1, mean arterial pressure decreased from 81 mmHg to 45 mmHg and SVR decreased from 2418 to 962 dyne · sec^?1cm^?5. Myocardial contractility increased only moderately, as evaluated by dP/dt, which increased from 1290 to 1696 mmHg · sec^?1. Dopamine had a more marked inotropic effect: the dP/dt increased, at the maximal concentration, from 1480 to 2570 mmHg · sec^?1. Dopamine also produced vasoconstriction: SVR increased from 2325 to 2683 dyne · sec · cm^?5 and mean arterial pressure from 86 mmHg to 110 mmHg. In conclusion, dopexamine hydrochloride is less arrhythmogenic than dopamine, has less of an inotropic effect, and a greater effect on aflerload.     

Clevidipine compared with nitroglycerin for blood pressure control in coronary artery bypass grafting: a randomized double-blind study

Purpose

We tested the hypothesis that clevidipine, a rapidly acting dihydropyridine calcium channel blocker, is not inferior to nitroglycerin (NTG) in controlling blood pressure before cardiopulmonary bypass (CPB) during coronary artery bypass grafting (CABG).

Methods

In this double-blind study from October 4, 2003 to April 26, 2004, 100 patients undergoing CABG with CPB were randomized at four centres to receive intravenous infusions of clevidipine (0.2-8 μg·kg^?1·min^?1) or NTG (0.4 μg·kg^?1·min^?1 to a clinician-determined maximum dose rate) from induction of anesthesia through 12 hr postoperatively. The study drug was titrated in the pre-CPB period with the aim of maintaining mean arterial pressure (MAP) within ± 5 mmHg of a clinician-predetermined target. The primary endpoint was the area under the curve (AUC) for the total time each patient’s MAP was outside the target range from drug initiation to the start of CPB, normalized per hour (AUC_MAP-D). The predefined non-inferiority criterion for the primary endpoint was a 95% confidence interval (CI) upper limit no greater than 1.50 for the geometric means ratio between clevidipine and NTG.

Results

Total mean [standard deviation (SD)] dose pre-bypass was 4.5 (4.7) mg for clevidipine and 6.9 (5.4) mg for NTG (P < 0.05). The geometric mean AUC_MAP-D for clevidipine was 283 mmHg·min·hr^?1 (n = 45) and for NTG was 292 mmHg·min·hr^?1 (n = 48); the geometric means ratio was 0.97 (95% CI 0.74 to 1.27). The geometric mean AUC_MAP-D during aortic cannulation was 357.7 mmHg·min·hr^?1 for clevidipine compared with 190.5 mmHg·min·hr^?1 for NTG. Mean (SD) heart rate with clevidipine was 76.0 (13.8) beats·min^?1 compared with 81.5 (14.4) beats·min^?1 for NTG. There were no clinically important differences between groups in adverse events.

Conclusion

During CABG, clevidipine was not inferior to NTG for blood pressure control pre-bypass.     

Inhibition of cerebral metabolic and circulatory responses to nitrous oxide by 6-hydroxydopamine in dogs

Purpose

To determine whether cerebral metabolic and circulatory consequences of N₂O result from activation of the sympathoadrenal system. The effects of pretreatment with intracistemal injection of 6-OHDA, which produces chemical sympathectomy, were studied in dogs.

Method

Seven days before measurement dogs were pretreated with intracisternal injection of either saline vehicle (sham-group) or 100 μg· kg^?1 6-hydroxydopamine (6-OHDA group). Cerebral blood flow (CBF) was measured using an electromagnetic flow-meter probe and cerebral metabolic rate for oxygen (CMRO₂) was calculated as the product of CBF and arterial-sagittal sinus blood oxygen content difference [C(a-v)O₂].

Results

In the sham group, N₂O (60%) increased CMRO₂ from 6.11 ± 0.21 ml· 100 g^?1· min^?1 to 7.10 ± 0.39 ml· 100g^?1· min^?1 and CBF from 63 ± 5 ml· 100 g^?1 · min^?1 to 173 ± 26 ml· 100 g^?1· min^?1. In the 6-OHDA group, CMRO₂ did not change during N₂O exposure, whereas CBF increased from 61 ± 3 ml· 100 g^?1· min^?1 to 135 ±19 ml· 100 g^?1· min^?1 but less then in the sham group. The 6-OHDA group displayed a reduction in cortical noradrenaline (NA) concentration from 263.2 ± 35.6 ng·g^?1 to 102.7 ± 16.5 ng· g^?1. Cortical dopamine (DA) concentration was not affected by 6-OHDA administration.

Conclusion

These results suggest that most of the increase in CMRO₂ and, at least a part of, the increase in CBF during N₂O exposure in the sham-group are related to sympathoadrenal-stimulating effects of N₂O.     

Epidural and intravenous bolus morphine for postoperative analgesia in infants

Purpose

To compare two doses of bolus epidural morphine with bolus iv morphine for postoperative pain after abdominal or genitourinary surgery in infants.

Methods

Eighteen infants were randomly assigned to bolus epidural morphine (0.025 mg · kg^?1 or 0.050 mg · kg^?1) or bolus iv morphine (0.050–0.150 mg · kg^?1). Postoperative pain was assessed and analgesia provided, using a modified infant pain scale. Monitoring included continuous ECG, pulse oximetry, impedance and nasal thermistor pneumography. The CO₂ response curves and serum morphine concentrations were measured postoperatively.

Results

Postoperative analgesia was provided within five minutes by all treatment methods. Epidural groups required fewer morphine doses (3.8 ± 0.8 for low dose [LE], 3.5 ± 0.8 for high dose epidural [HE] vs. 6.7 ± 1.6 for iv, P < 0.05) and less total morphine (0.11 ± 0.04 mg · kg^?1 for LE, 0.16 ± 0.04 for HE vs 0.67 ± 0.34 for iv, P < 0.05) on POD1 Dose changes were necessary in all groups for satisfactory pain scores. Pruritus, apnoea, and haemoglobin desaturation occurred in all groups. CO₂ response curve slopes, similar preoperatively (range 36–41 ml · min^?1 · mmHg ETco ₂ ^?1 · kg^?1) were generally depressed (range, 16–27 ml · min^?1 · mmHg ETco ₂ ^?1 · kg^?1) on POD1. Serum morphine concentrations, negligible in LE (<2 ng · ml^?1), were similar in the HE and iv groups (peak 8.5 ± 12.5 and 8.6 ± 2.4 ng · ml^?1, respectively).

Conclusion

Epidural and iv morphine provide infants effective postoperative analgesia, although side effects are common. Epidural morphine gives satisfactory analgesia with fewer doses (less total morphine); epidural morphine 0.025 mg · kg^?1 is appropriate initially. Infants receiving epidural or iv morphine analgesia postoperatively need close observation in hospital with continuous pulse oximetry.     

Effects of tidal volume and PEEP on arterial blood gases and pulmonary mechanics during one-lung ventilation

Purpose

The main problem of one-lung ventilation (OLV) is hypoxemia. The use of a high tidal volume for preventing hypoxemia during OLV is controversial. We compared the effects of a high tidal volume versus a low tidal volume with or without PEEP on arterial oxygen tension (PaO₂) and pulmonary mechanics during OLV.

Methods

Sixty patients (age range, 16–65?years; ASA I, II) who underwent wedge resection with video-assisted thoracostomy during OLV were assigned to three groups: group I received a high tidal volume (10?ml/kg) (n?=?20), group II received a low tidal volume (6?ml/kg) (n?=?20), and group III received a low tidal volume (6?ml/kg) with PEEP (5?cmH₂O) (n?=?20). Patient hemodynamics, pulmonary mechanics, and arterial blood gases were measured before (T₀) OLV and 5 (T₁), 15 (T₂), 30 (T₃), and 45?min (T₄) after OLV.

Results

The PaO₂/FiO₂ ratios of group II and III were significantly decreased and the incidence of hypoxemia was significantly higher in groups II and III than in group I (P?Conclusion During OLV, mechanical ventilation with a low tidal volume with or without PEEP increased hypoxemia as compared to that when performing OLV with a high tidal volume.     

Biocompatible heterogeneous porous gel matrix NeuroGelTM promotes regeneration of rat sciatic nerve within tubular silicone prosthesis (experimental study)

Background

The purpose of this study was to investigate the ability of NeuroGel? to promote and enhance the regeneration of rat sciatic nerve within a 10-mm gap using silicone tubular prosthesis, and to evaluate and compare the regeneration outcomes versus autologous grafting.

Methods

The 10-mm gap of rat sciatic nerve was bridged through silicone tubular prosthesis filled with dehydrated NeuroGel?, and NeuroGel? saturated with rat NGF-B (NG30-NGG60, NGgfB30-NGgfB60). To assess the regeneration of the peripheral nerve we utilized three general and most commonly applied methods: electrophysiologic, hystomorphometric, and functional methods.

Results

The average M-wave amplitude (A_MW index), or the intermediary index of the number of regenerated axons, in animal groups NGG60 and NGgfB60 60 days post-op was: 2.44?±?0.57 mV and 1.87?±?0.48 mV. These indices were statistically lower compared to the indices obtained after autologous grafting. The average impulse conduction velocity along motor fibers (V_MF index), or the intermediary index of myelination rate, was: 13.3 mm/ms and 13.3 mm/ms, respectively, statistically equal to indices obtained after autologous grafting. The average density (D) of regenerated fibers (direct numerical indicator in contrast to intermediary A_MW index) in animal groups NGG60 and NGgfB60 was: 4,920?±?178.88 and 5,340?±?150.33 per mm², respectively. These indices were statistically higher versus indices obtained after autologous grafting. Myelination rates of regenerated fibers in animal groups NGG60 and NGgfB60 were 73 and 86 %, respectively. They were also statistically higher. The average sciatic functional index (SFI) in NGG60 and NGgfB60 was: ?25.57?±?3.05 and ?24.124?±?4.8, respectively, which is statistically equal to indices obtained after autologous grafting.

Conclusions

Neurogel? strongly promotes the regeneration of rat sciatic nerve within silicone tubular prosthesis. After bridging a 10-mm gap through silicone prosthesis with Neurogel? or Neurogel? +NGF-B-modified intraluminal space, the myelination rate of regenerated axons of rat sciatic nerve appeared to be higher, and the axon count and functional recovery is similar to results seen with the autografting technique.     

Contemporary anesthesia ventilators incur a significant “oxygen cost”

Purpose

Anesthesia ventilators use oxygen or oxygen/air mixtures to drive the bellows during controlled ventilation. As a practitioner may find himself in a situation that the only available oxygen source is a compressed oxygen cylinder, it is important to know the oxygen consumption of anesthesia ventilators during controlled ventilation.

Methods

We tested the Datex-Ohmeda 7900 ventilator mounted on an Excel 210 anesthesia machine under a variety of conditions. For comparison, we also tested the Ohmeda 7800 and the Dräger AV-2 ventilator under control conditions. All experiments were performed using a test lung.

Results

The oxygen consumption of the AV-2 and the Datex-Ohmeda ventilators averaged 302 ± 17 L·hr^?1 and 564 ± 68 to 599 ± 56 L·hr^?1, respectively (P < 0.01 AV-2vs 7800 and 7900). When using an E-type cylinder, this would result in a mean time to alarm of 93 min and 54 to 57 min, respectively. Decreased lung compliance increased the oxygen consumption to 848 ± 16 L·hr^?1.

Conclusions

Machine-driven mechanical ventilation incurs a significant “oxygen cost.” We show that the amount of oxygen consumed by mechanical ventilation with contemporary anesthesia ventilators is influenced by patient-dependent factors and may greatly exceed the amount of oxygen delivered to the patient.     

Increasedl-arginine transport in a nitric oxide-producing metastatic colon cancer cell line

Background: Little is known about amino acid transport in human neoplastic cells. We previously characterizedl-arginine transport in the primary human colon cancer cell line, SW480, and found it is principally mediated by the sodium-independent system y⁺. In this study, we characterizedl-arginine transport in the metastatic cell line, SW620, and compared it with that in the primary cell line, SW480. Methods: Transport of³H-l-arginine in cell monolayers was analyzed in the presence and absence of sodium. Kinetic studies were performed over a range ofl-arginine concentrations to determine transporter affinity (K_m) and maximal transport velocity (V_max). Transport was further characterized through blockade with known amino acids. In addition, the effect of cell age (i.e., time in culture) on arginine transport was examined at 2 and 9 days after seeding. Cellular proliferation was asssessed by using the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Results: l-Arginine uptake was primarily sodium independent in the SW620 cell line. Kinetic and amino acid-inhibition studies revealed a single high-affinity, sodium-independentl-arginine transporter (V_max=1286.3 ± 158.3 pmol/mg protein/30 s; K_m=46.8 ± 4.2 μM). Sodium-independent transport was blocked by system y⁺ substratesl-homoarginine,l-ornithine andl-lysine. Sodium-dependent uptake occurs through a single transporter with system B^O,+ characteristics (K_m=16.15 ± 2.1 μM; V_max=329.94 ± 29.7 pmol/mg protein/30 s). Arginine transport increased with time in culture with day 2 cells transport velocity =241.7 ± 33.6 pmol/mg protein/30s, whereas day 9 cells transport velocity =377 ± 15.4 pmol/mg protein/30 s (p<0.01). Cellular-proliferation studies revealed a doubling time of 3.2 days for SW620 and 5.4 days for SW480 (p<0.05). Conclusions: l-Arginine transport in these neoplastic cell lines occurs primarily through sodium-independent, high-affinity system y⁺. V_max was increased 180% in the metastatic variant (SW620), suggesting upregulation of the y⁺ transporter. The increased y⁺ activity may be a mechanism to provide continuous substrate for tumor growth.     

Remifentanil-Propofol- Anästhesie bei Bandscheibenoperationen: ein Vergleich mit einer Desfluran-N2O- Inhalationsanästhesie Effekte auf Hämodynamik und Aufwachverhalten

Zusammenfassung Fragestellung: Unterscheidet sich eine totale intraven?se An?sthesie mit Propofol (P) und Remifentanil (R) von einer Inhalationsan?sthesie mit Desfluran (D) und Lachgas (L) bei lumbalen Bandscheibenoperationen hinsichtlich der Steuerbarkeit der Narkose, der Beeinflussung h?modynamischer Parameter, des Aufwachverhaltens und des postoperativen Analgetikabedarfs der Patienten? Methodik: 50 Patienten (ASA I–II, 18–65 Jahre) wurden randomisiert entweder einer P/R- oder D/L-Gruppe zugeteilt. Nach standardisierter Narkoseeinleitung (1 μg/kg Remifentanil, 1,5 mg/kg Propofol, 0,1 mg/kg Cisatracurium) wurde die An?sthesie in der D/L-Gruppe bedarfsadaptiert mit Desfluran in 50% N₂O und in der P/R-Gruppe mit 2 mg/kg/h Propofol und 0,5 μg/kg/min Remifentanil aufrechterhalten, wobei die Remifentanildosis nach 15 min halbiert wurde. Am Operationsende unmittelbar vor der Umlagerung in die horizontale Rückenlage wurde die Zufuhr der An?sthetika abrupt unterbrochen und folgende Aufwachzeiten erfa?t: Eintritt Spontanatmung (V_T>4 ml/kg), Extubation, Augen?ffnen, richtiges Benennen von Namen und Geburtsdatum und der Analgetikabedarf der ersten 2 postoperativen Stunden im Aufwachraum. Ergebnisse: Die Patienten der D/L-Gruppe reagierten auf den Intubationsreiz und die Hautinzision mit signifikanten Blutdruckanstiegen und zeigten signifikant h?here Herzfrequenzwerte, w?hrend ansonsten die h?modynamischen Parameter w?hrend des Narkoseverlaufs vergleichbar waren. Die Patienten der P/R-Gruppe erreichten signifikant früher eine stabile Spontanatmung (3,2 vs. 6,4 min), konnten früher extubiert werden (3,8 vs. 9,5 min), ?ffneten früher die Augen (3,0 vs. 11,5 min) und waren eher in der Lage, ihren Namen und Geburtsdatum zu benennen (4,8 vs. 14,3 min), wiesen aber auch signifikant h?ufiger Muskelzittern auf. Keine signifikanten Unterschiede fanden sich im Analgetikabedarf sowie in der Inzidenz von übelkeit und Erbrechen. Schlu?folgerung: Die Patienten erwachen aus der TIVA mit Propofol/Remifentanil schneller als aus der Desfluran/N₂O-Narkose und erreichen schneller ein h?heres Vigilanzniveau, wobei die geringe Intensit?t postoperativer Wundschmerzen nach Bandscheibenoperationen kein aufwendiges Konzept zur postoperativen Analgesie erfordert.      

Smoking as a risk factor for intraoperative hypoxemia during one lung ventilation

Background

Smoking is associated with many intra and postoperative events, especially respiratory complications. Hypoxemia and airway damage are found to aggravate any pre-existing respiratory pathology among smokers. One lung ventilation (OLV) carries a 4–10 % risk of development of hypoxia.

Aim

The purpose of this study was to predict the incidence of hypoxemia for smokers during OLV for patients undergoing video-assisted thoracoscopic surgery (VATS).

Patients and methods

Sixty patients undergoing VATS using OLV by double lumen tube were included in this pilot cross-sectional study. These patients were divided into 2 groups, group S which included 30 heavy smoker patients (smoking more than 20 cigarettes per day for more than 20 years) and group NS which included 30 non-smoker patients. Intra and postoperative arterial oxygen tension (PaO₂), arterial carbon dioxide tension (PaCO₂), and intraoperative peak airway pressure were compared between the 2 groups.

Results

PaO₂ was significantly higher in the non-smoker group than in the smoker group, both at the start and end of OLV. It was 173 ± 68 mmHg for NS compared with 74 ± 10.8 mmHg for S at the start of OLV; at the end of OLV it was 410 ± 78 mmHg for the former and 360 ± 72 mmHg for the latter (P < 0.05).

Conclusion

From this study it can be concluded that for heavy smoker patients there was a significant reduction in arterial oxygen tension (PaO₂) in comparison with non-smokers. However, hypoxemia reported for both groups was comparable.     

Hypocapnia prolongs bradycardia induced by bupivacaine or levobupivacaine in isolated rat hearts

Purpose: Systemic alkalinization is recommended for resuscitation from local anesthetic-induced cardiotoxicity. It has been suggested that inducing hypocapnic alkalosis, prior to exposure to toxic concentrations of local anesthetics, may minimize cardiotoxicity. However, it remains unclear whether inducing severe hypocapnic alkalosis after administration of local anesthetics will minimize the duration of bradycardia. We used isolated rat hearts to investigate the effects of hypocapnic alkalosis on heart rate (HR) recovery from bupivacaine or levobupivacaine-induced bradycardia. Methods: We measured the time required for the HR in 24 isolated rat hearts, respectively, to attain 90% of the baseline HR (recovery time) following bradycardia induced by 1µg·mL^?1 and 10µg·mL^?1 concentrations of either bupivacaine or levobupivacaine. Normal pH perfusate (bupivacaine or levobupivacaine with normal pH washout groups) or severe hypocapnic alkalosis perfusate (bupivacaine or levobupivacaine with hypocapnic alkalosis washout groups) were reperfused after exposure to the local anesthetics. Results: Severe hypocapnic alkalosis prolonged the recovery time from 273 ± 122 sec, at the 1µg·mL^?1 bupivacaine concentration with normal pH washout, to 1203 ± 540 sec, in the bupivacaine with hypocapnic alkalosis washout (P=0.029). Severe hypocapnic alkalosis also prolonged the recovery time from 1 153 ± 644 sec, at a 10µg·mL^?1 bupivacaine concentration in the normal pH washout group, to 2065 ±617 sec, in the bupivacaine with hypocapnic alkalosis washout group (P=0.032). With levobupivacaine 10µg·mL^?1 in the normal pH washout group, HR recovery time increased from 863 ± 186 sec to 1565 ± 567 sec, compared to the hypocapnic alkalosis washout group (P=0.045). Conclusions: Severe hypocapnic alkalosis prolonged the recovery time from bupivacaine or levobupivacaine-induced bradycardia in isolated rat hearts. When bradycardia occurs after intravascular bupivacaine or levobupivacaine administration, maintenance of normocapnia may minimize the duration of bradycardia.     

Pressure-controlled versus volume-controlled ventilation during one-lung ventilation in the prone position for robot-assisted esophagectomy

Background

The prone position during robotic esophageal mobilization for minimally invasive esophagectomy (MIE) provides several advantages with regards to operative times, surgeon ergonomics, and surgical view; however, this technique requires one-lung ventilation (OLV). There are no guidelines about ventilatory modes during OLV in the prone position. We investigated the effects of volume-controlled (VCV) and pressure-controlled ventilation (PCV) on oxygenation and intrapulmonary shunt during OLV in the prone position in patients who underwent robot-assisted esophagectomy.

Methods

Eighteen patients, no major obstructive or restrictive pulmonary disease, were allocated randomly to one of two groups. In the first group (n = 9), OLV was started by VCV and the ventilator was switched to PCV after 30 minutes. In the second group (n = 9), the modes of ventilation were performed in the opposite order in the prone position. Hemodynamic and respiratory variables were obtained during OLV at the end of each ventilatory mode.

Results

There were no significant differences in arterial oxygen tension (PaO₂), airway pressures, dynamic lung compliance, or physiologic dead space (Vd/Vt) during OLV between PCV and VCV in the prone position. Intrapulmonary shunt (Qs/Qt) was significantly lower with VCV than with PCV during OLV in the prone position (p = 0.044).

Conclusion

PCV provides no advantages compared with VCV with regard to respiratory and hemodynamic variables during OLV in the prone position. Either ventilatory mode can be safely used for patients who undergo robot-assisted esophagectomy and who have normal body mass index and preserved pulmonary function.     

Ventilatory requirements during laparoscopic cholecystectomy

The purpose of this clinical study was to determine: (1) the increase in minute ventilation required to maintain preinsufflation arterial carbon dioxide tension (PaCO₂) during laparoscopic cholecystectomy, and (2) whether end-tidal PCO₂ (PetCO ₂) can be used as an index of PaCO₂ and, therefore, of the adequacy of minute ventilation during the pneumoperitoneum. We measured PaCO₂,PetCO ₂, expired minute volume (V_exp) standardized for body surface area (SA), airway and intra-abdominal pressure (Paw, Pabd) during general anaesthesia for laparoscopic cholecystectomy just before and 30 min after the creation of a CO₂ pneumoperitoneum in 28 healthy (ASA class 1 and 2) consenting adults. They were in the reverse Trendlenburg position (20°) with a 5° lateral tilt. Expired minute volume was increased from 3.75 (SEM ± 0.12) to 4.19 (0.15) L·min^?1·m^?2 to maintain PaCO₂ close to control levels: 38.9 (0.8) vs 40.1 (0.6) mmHg 5.19 (0.1) vs 5.35 (0.08) kPa). In most of the patients (23/28),PetCO ₂ was less than 41 mmHg with a correlation between PaCO₂ andPetCO ₂. In ten of these patients, (Pa-Pet)CO₂ was greater than the normal range. In 5/28, (Pa-Pet)CO₂ was negative. The “driving pressure” (Paw-Pabd) increased from 8.7 (1.0) to 10.4 (1.1) cm H₂O, without any correlation between the increase in Paw-Pabd and that in \(\dot Vexp\) . The results indicate the need for extra ventilatory requirement during laparoscopy and thatPetCO ₂ is an imperfect index of PaCO₂ under these circumstances.     

Bradycardia produced by pyridostigmine and physostigmine

Purpose

The bradycardia produced by pyridostigmine and physostigmine in an animal model of acute cardiac denervation was examined according to its relation to cholinesterase inhibition and sensitivity to block by cholinergic receptor antagonists.

Methods

Cats were anaesthetised, vagotomised and propranolol-treated. Heart rate was continuously recorded. Erythrocyte cholinesterase activity of arterial blood was measured using a radiometric technique. Nicotinic and muscarinic M₁ receptors were blocked with hexamethonium and pirenzepine, respectively. M₂ receptors were blocked with gallamine, pancuronium and AFDX-116.

Results

With pyridostigmine and physostigmine, the dose-response relationship for the decrease in heart rate (ED₅₀ 1.05 ± 0.25 and 0.198 ± 0.03 mg·kg^?1, respectively) was shifted to the right of that for the inhibition of cholinesterase activity (ED₅₀ 0.094 ± 0.03 and 0.032 ± 0.01 mg·kg^?1, respectively). The decrease in cholinesterase activity reached a plateau at a cumulative dose of 0.56 ± 0.08 and 0.32 ± 0.08 mg·kg^?1, respectively. In contrast, there did not appear to be a plateau in the bradycardic effect. The bradycardia produced by pyndostigmine and physostigmine was blocked by hexamethonium (ED₅₀ 10 ± 1.3 and 15.3 ± 2.4 mg·kg^?1, respectively), pirenzepine (ED₅₀ 68 ± 16 and 138 ± 32 μg·kg^?1. respectively), gallamine (56 ± 11 and 67 ± 17 μg·kg^?1, respectively ), pancuronium (32 ± 10 and 30 ± 4 μg·kg^?1, respectively), and AFDX-116 (31 ± 4 and 28 ± 4 μg·kg^?1, respectively).

Conclusion

The bradycardia produced by reversible anticholinesterase drugs containing a carbamyl group is not dearly related to the degree of cholinesterase activity, and has a low sensitivity to nicotinic and muscannic M₁ and a high sensitivity to muscarinic M₂ receptor antagonists.     

Influence of dopexamine hydrochloride on haemodynamics and regulators of circulation in patients undergoing major abdominal surgery

Background: Catecholaminergic support is often used to improve haemodynamics in patients undergoing major abdominal surgery. Dopexamine is a synthetic vasoactive catecholamine with beneficial microcirculatory properties. Methods: The influence of perioperative administration of dopexamine on cardiorespiratory data and important regulators of macro- and microcirculation were studied in 30 patients undergoing Whipple pancreaticduodenectomy. The patients received randomized and blinded either 2 μg · kg^?1 · min^?1 of dopexamine (n=15) or placebo (n=15, control group). The infusion was started after induction of anaesthesia and continued until the morning of the first postoperative day. Endothelin-1 (ET-1), vasopressin, atrial natriuretic peptide (ANP), and catecholamine plasma levels were measured from arterial blood samples. Measurements were carried out after induction of anaesthesia, 2 h after onset of surgery, at the end of surgery, 2 h after surgery, and on the morning of the first postoperative day. Results: Cardiac index (CI) increased significantly in the dopexamine group (from 2.61±0.41 to 4.57±0.78 1 · min^?1 · m^?2) and remained elevated until the morning of the first postoperative day. Oxygen delivery index (DO₂I) and oxygen consumption index (VO₂I) were also significantly increased in the dopexamine group (DO₂I: from 416±91 to 717±110 ml/m² · m²; VO₂I: from 98±25 to 157±22 ml/m² · m²), being significantly higher than in the control group. pHi remained stable only in the dopexamine patients, indicating adequate splanchnic perfusion. Vasopressive regulators of circulation increased significantly only in the untreated control patients (vasopressin: from 4.37±1.1 to 35.9±12.1 pg/ml; ET-1: from 2.88±0.91 to 6.91±1.20 pg/ml). Conclusion: Patients undergoing major abdominal surgery may profit from prophylactic perioperative administration of dopexamine hydrochloride in the form of improved haemodynamics and oxygenation as well as beneficial influence on important regulators of organ blood flow.     

Rebreathing and end-tidal CO2 during spontaneous breathing with the Bain circuit

In order to examine the relationship between end-tidal CO₂ (Fet_{co 2}) and inspired CO₂ (Fi_{co 2}) in anaesthetized patients breathing spontaneously with a Bain breathing circuit and afresh gasvolume ( \(\dot VF\) ) of 100 ml · kg^-1 · min^-1, the respiratory rate (f) and minute ventilation ( \(\dot VE\) ) was changed in two groups of six patients each by the induction or reversal of narcotic respiratory depression. During light nitrous oxide-halothane anaesthesia (Group I), the intravenous injection of 0.1 mg · kg^-1 of alphaprodine caused arapid fall in F_{co 2} from 2.3 ± 0.5 per cent to 0.7 ± 0.1 per cent concomitant with the reduction inf(37 ± 5 to 16 ± 4) breath -min^-1 and \(\dot VE\) (137 ± 29 to 55 ± 13 ml · kg^-1 · min^-1), while the Fet_{co 2} rose gradually from 5.2 ± 0.9 percent to 6.4 ± 0.9 per cent over a ten-minute period. During light nitrous oxide-halothane anaesthesia supplemented by alphaprodine (Group II), 0.2 mg of naloxone intravenously caused a rise in Fi_{co 2} from 0.5 ± 0.3 per cent to 2.9 ± 0.6 per cent simultaneous with arise in f (11 ± 2 to 25 ± 7 breath · min^-1) and \(\dot VE\) (70 ± 25 to 133 ± 34 ml · kg^-1 · min^-1), while the FET_{co 2} declined gradually over a ten-minute period from 7.6 ± 0.7 per cent to 6.4 ± 0.4 per cent. The change in Fl_{co 2} always occurred exactly at the same time as the drug-induced change in respiration. It was associated with acorresponding change in the degree of mixing of fresh gas and expired gas within the breathing system and appeared to correlate with the change in the ratio \(\dot VE/\dot VF\) . There was no indication that the Fl_{co 2} or the distribution of CO₂ within the system had any effect onFet _{co 2} or CO₂ elimination. Under these conditions theFl _{co 2} and the volume of rebreatked CO₂ can not be the cause but must be regarded as apassive change consequent to the altered pattern of breathing.     

Intraoperative infusion of lidocaine reduces postoperative fentanyl requirements in patients undergoing laparoscopic cholecystectomy

Background: Lidocaine has been shown to inhibit neural conduction and to have anti-inflammatory properties. The purpose of this study was to determine whether intraoperative lidocaine infusion reduces opioid consumption in the postanesthesia care unit (PACU). Methods: Fifty patients were enrolled in this prospective, randomized and observer-blinded study. At induction of anesthesia the control group (n=25) received fentanyl 3 µg·kg^?1 while the lidocaine group received fentanyl 1.5 µg·kg^?1 and a bolus of lidocaine 1.5 mg·kg^?1 followed by a continuous infusion of lidocaine 2 mg·kg^?1·hr^?1. General anesthesia included propofol, rocuronium, and desflurane titrated to maintain blood pressure and heart rate within set parameters, and the bispectral index between 35 and 50. No supplemental opioids were given during surgery. All patients received acetaminophen, ketorolac, dexamethasone, droperidol and local anesthetics in the skin incision. Patients received fentanyl and ondansetron in the PACU. The primary outcome variable was the amount of fentanyl required in the PACU to establish and to maintain visual analogue scale pain scores<3. Results: Most patients received fentanyl for pain relief in the PACU, but the cumulative mean dose was lower in the lidocaine group compared to the control group (98±54 µg,vs154±3 99 µg, respectively,P=0.018). Lidocaine infusion reduced by 10% the amount of desflurane required (P=0.012). White-Song scoresτ;12 were attained by all patients in both groups within 30 min of their arrival in the PACU. Median time from arrival to the PACU to discharge home was similar in both groups, 167.5 min in the control groupvs 180 min in the lidocaine group (P=0.649). Conclusion: Intraoperative lidocaine infusion reduces opioid consumption in the PACU and intraoperative requirements of desflurane.     

Hemodynamic effects of medical antishock trousers during mechanical ventilation

Purpose

To compare the hemodynamic effects of medical antishock trousers (MAST) inflation in mechanically ventilated patients with normal and poor left ventricular function.

Methods

Twelve patients requiring respiratory support were divided into two groups according to baseline transesophageal echocardiography (TEE) measurements: normal left ventricular dimensions and fractional area of contraction (FAC=61 ± 5%) (n=7) and dilated cardiomyopathy with reduced FAC (21 ± 1%) (n=5). All patients were studied when two successive levels of load (mild load by inflation of the leg compartment of MAST at 50 cmH₂O and high load by adding the abdominal compartment of MAST inflated at 30 cmH₂O) were applied. Global left ventricular systolic function was assessed on the TEE transgastric short-axis view. End-systolic wall stress (ESWS) was used as an indicator of left ventricular afterload.

Results

Total respiratory, lung and chest wall compliances were reduced by 48%, 51% and 27% respectively at the high load level (P < 0.05). Whereas no hemodynamic changes occurred at mild load, the high load level produced an increase in left ventricular afterload as evidenced by concomitant increases in diastolic arterial blood pressure (66 ± 6 to 79 ± 6 mmHg,P < 0.05) and ESWS (69 ± 12 to 74 ± 12 Kdyn·cm^?2·m^?2,P < 0.05). In patients with dilated cardiomyopathy, this increase in afterload impaired the left ventricular systolic function and end-systolic area increased (19.0 ± 2.5 to 21.4 ± 2.9 cm²·m^?2,P < 0.05) while FAC decreased (22 ± 2 to 16 ± 2%,P < 0.05). Left ventricular end-diastolic area remained unchanged during the study in both groups.

Conclusion

MAST inflation impairs respiratory mechanics and global left ventricular systolic function in cardiac patients without changes in left ventricular preload.