Levon M. Capan

Optimization of Arterial Oxygenation during One-lung Anesthesia

The effects of different respiratory maneuvers on Pao2, Qs/Qt, and cardiac output were studied during one-lung anesthesia in 21 adult patients undergoing pulmonary surgery in lateral position with halothane-oxygen anesthesia using endobronchial intubation. The patients were divided into three groups. In group A (n = 11) seven different respiratory maneuvers were sequentially performed. When both lungs were ventilated (maneuver A) Pao2 and Qs/Qt were 376 ± 28 torr (mean ± SE) and 26 ± 2.33% (mean ± SE), respectively. Corresponding values were 155 ± 25 torr and 38 ± 1.5% when the upper lung was deflated (maneuver B) and 85 ± 11 torr and 44 ± 4% when PEEP (10 cm H2O) was added to the dependent lung with the upper lung remaining deflated (maneuver C). When the collapsed upper lung was insufflated with oxygen (7 L/min) with the lower lung receiving PEEP (maneuver D) Pao2 and Qs/Qt were 127 ± 29 torr and 38 ± 3%, respectively, 177 ± 34 torr and 37 ± 3.5% when the upper lung was insufflated with oxygen and lower lung ventilated without end-expiratory pressure (maneuver E). When the upper lung was insufflated with oxygen at 10 cm H2O pressure with the dependent lung ventilated with PEEP (maneuver F), Pao2 was 248 ± 41 torr and Qs/Qt was 31 ± 2% and finally, during insufflation of the upper lung at 10 cm H2O pressure while the lower lung was ventilated with zero end-expiratory pressure (maneuver G) Pao2 averaged 286 ± 49 torr and Qs/ Qt 28 ± 2.5%. Cardiac output was reduced only when the dependent lung was ventilated with PEEP and the deflated upper lung insufflated with oxygen with or without pressure. In group B (n = 5) the effects of only maneuver F on arterial oxygenation were evaluated 50, 95, and 140 minutes after the start of anesthesia. In group C (n = 5), only maneuver G was studied 50, 95, and 140 minutes after the start of anesthesia. The values for Pao2 and Qs/Qt did not differ from each other at these time intervals and were comparable with the values obtained during corresponding maneuvers in group A patients. It is concluded that arterial oxygenation can be optimized during one-lung anesthesia by oxygen insufflation of the upper deflated lung at 10 cm H2O pressure while the lower lung is ventilated with zero end-expiratory pressure.

Guidelines for the Treatment of Acidaemia with THAM

SummaryTHAM (trometamol; tris-hydroxymethyl aminomethane) is a biologically inert amino alcohol of low toxicity, which buffers carbon dioxide and acids in vitro and in vivo. At 37°C, the pK (the pH at which the weak conjugate acid or base in the solution is 50% ionised) of THAM is 7.8, making it a more effective buffer than bicarbonate in the physiological range of blood pH. THAM is a proton acceptor with a stoichiometric equivalence of titrating 1 proton per molecule. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system, accepting a proton, generating bicarbonate and decreasing the partial pressure of carbon dioxide in arterial blood (paCO2). It rapidly distributes through the extracellular space and slowly penetrates the intracellular space, except for erythrocytes and hepatocytes, and it is excreted by the kidney in its protonated form at a rate that slightly exceeds creatinine clearance. Unlike bicarbonate, which requires an open system for carbon dioxide elimination in order to exert its buffering effect, THAM is effective in a closed or semiclosed system, and maintains its buffering power in the presence of hypothermia.THAM rapidly restores pH and acid-base regulation in acidaemia caused by carbon dioxide retention or metabolic acid accumulation, which have the potential to impair organ function.Tissue irritation and venous thrombosis at the site of administration occurs with THAM base (pH 10.4) administered through a peripheral or umbilical vein; THAM acetate 0.3 mol/L (pH 8.6) is well tolerated, does not cause tissue or venous irritation and is the only formulation available in the US. In large doses, THAM may induce respiratory depression and hypoglycaemia, which will require ventilatory assistance and glucose administration.The initial loading dose of THAM acetate 0.3 mol/L in the treatment of acidaemia may be estimated as follows: THAM (ml of 0.3 mol/L solution) = lean body-weight (kg) × base deficit (mmol/L). The maximum daily dose is 15 mmol/kg for an adult (3.5L of a 0.3 mol/L solution in a 70kg patient).When disturbances result in severe hypercapnic or metabolic acidaemia, which overwhelms the capacity of normal pH homeostatic mechanisms (pH ≤7.20), the use of THAM within a ‘therapeutic window’ is an effective therapy. It may restore the pH of the internal milieu, thus permitting the homeostatic mechanisms of acid-base regulation to assume their normal function. In the treatment of respiratory failure, THAM has been used in conjunction with hypothermia and controlled hypercapnia. Other indications are diabetic or renal acidosis, salicylate or barbiturate intoxication, and increased intracranial pressure associated with cerebral trauma. THAM is also used in cardioplegic solutions, during liver transplantation and for chemolysis of renal calculi.THAM administration must follow established guidelines, along with concurrent monitoring of acid-base status (blood gas analysis), ventilation, and plasma electrolytes and glucose.

Humidity and the anesthetized patient.

Damage to the ciliated cells of the tracheobronchial tree and incidence of postoperative pulmonary complications were measured ured by point-scoring systems in 202 patients who breathed dry and humidified anesthetic gases for 225±78 min. The incidence of postoperative pulmonary complications decreas

Sonographically guided infraclavicular brachial plexus block in adults: a retrospective analysis of 1146 cases.

Objective. The aim of this study was to analyze our experience in 1146 cases of sonographically guided infraclavicular brachial plexus block (ICBPB) performed over 32 months. Methods. Anesthetic records of 1146 cases of sonographically guided ICBPB performed by our staff were studied retrospectively with the use of a database created by an automated anesthesia record‐keeping system. The rates of successful blocks, failed blocks necessitating conversion to general anesthesia or requiring supplementation with local anesthetics, those requiring larger‐than‐usual doses of sedation, and complications were determined. Analysis included an attempt to determine the possible causes of inadequate blocks and complications. Results. In 1138 patients (99.3%), the block was successful. Six patients had incomplete blocks requiring general anesthesia, and another 2 patients needed local anesthetic supplementation by the surgeons. Ninety‐seven percent of the blocks were performed by residents directly supervised by an attending anesthesiologist who held the ultrasound probe. The mean age ± SD of the patients was 39 ± 15 years; the mean duration of surgery was 165 ± 114 minutes; and the male‐female ratio was 4:1. More than 50% of patients were obese. There were no reported cases of nerve injury, pneumothorax, or local anesthetic toxicity. Arterial punctures occurred in 8 (0.7%) patients, but all were inconsequential. Conclusions. The data from this retrospective study suggest that sonographic guidance provides a high success rate (99.3%) and improved safety for ICBPB. The increased operator team experience virtually eliminates failure and complications.

Feasibility of an Infraclavicular Block With a Reduced Volume of Lidocaine With Sonographic Guidance

Objective. A successful brachial plexus block requires a large volume of a local anesthetic. Sonography allows reliable deposition of the anesthetic around the cords of the brachial plexus, potentially lowering the anesthetic requirement. Methods. Fifteen sonographically guided infraclavicular blocks were performed in 14 patients with 2% carbonated lidocaine with epinephrine through a 17‐gauge Tuohy needle. The amount of lidocaine injected at several points around each cord was based on satisfactory spread observed sonographically. A 19‐gauge catheter was then placed with its tip between the posterior cord and axillary artery, and tip position was confirmed by observing the spread of 1 to 2 mL of injected air. Lidocaine was injected through the catheter if necessary to prolong the blocks. Results. Surgery was performed in all patients without general anesthesia, rescue blocks, or infiltration. A heroin user was given an additional 50 μg of fentanyl before the block. One patient required 5 mL of lidocaine through the catheter for an incomplete radial nerve block 5 minutes after initial injection. Seven patients received additional midazolam (mean, 2.5 mg) for alleviation of anxiety despite excellent blocks. The mean ± SD volume of lidocaine for the initial block was 16.1 ± 1.9 mL (4.2 ± 0.9 mg/kg). In 4 patients, additional lidocaine 1 hour after an initial successful block increased the total volume to 19.5 ± 7.1 mL (5 ± 1.9 mg/kg). The mean times to perform the block, onset of the block, and achieving surgical anesthesia and the duration of surgery were 10.8 ± 3.3, 2 ± 1.3, 5.9 ± 2.6, and 92.7 ± 54.4 minutes, respectively. Conclusions. A successful infraclavicular block in adults with 14 mL of lidocaine is feasible with the use of sonography. The reduced volume does not seem to affect the onset but shortens the duration of the block.

Acute biceps compartment syndrome associated with the use of a noninvasive blood pressure monitor.

A 29-yr-old man sustained a tibia-fibula fracture with extensive bone loss after a motorcycle accident. He had no past medical history and his vital signs were normal. He was mesomorphic, 168 cm tall, weighed 70 kg, and his physical examination was unremarkable. The patient underwent a microvascular free fibular bone transfer of the left fibula to the right tibia. Prior to surgery, a 125-mm wide NIBP cuff was wrapped firmly around the upper left arm. Cuff size was determined by visual inspection to be approximately 40% of the midarm circumference. The NIBP was cycled every 5 min (Hewlett Packard Component Monitoring System NIBP module 1008-B; Hewlett-Packard, Palo Alto, CA). A right arm vein was cannulated with a 16-gauge catheter. General anesthesia was induced with intravenous midazolam, droperidol, fentanyl, d-tubocurarine, thiopental, and pancuronium and the trachea was intubated via direct laryngoscopy. Sixty minutes after induction of anesthesia, a 20-gauge right radial arterial catheter was inserted, and the NIBP was cycled every 30 min. He was placed in the left lateral decubitus position where he remained for 9 h. The nondependent left arm was supported by a chest roll in a 60” semiflexed position. The NIBP tubing was unobstructed. Anesthesia was maintained with 0,, N,O, isoflurane, fentanyl, and pancuronium. The blood pressure (BP) varied between 110/60 and 120170 mm Hg, except for 10 min when it reached a minimum of 80/60 mm Hg. He received 8800 mL of crystalloid, 7 U of packed red blood cells, and 1000 mL of 5% albumin; blood loss was 2000 mL; urine output 1740 mL. The initial hematocrit was 40%, reached a minimum of 24%, and was 30% at the end of surgery. Arterial blood gases and electrolytes were normal. Muscle

Monitoring for suspected pulmonary embolism

It is fortunate that serious embolic phenomena are uncommon because, with the exception of neurosurgery in the sitting position and cardiac surgery, thoracic echocardiography and the precordial Doppler device, the most sensitive indicators of embolism, are seldom used. Vigilance is required of the anesthesiologist to recognize the rapid fall in end-tidal PCO2, the usual first indicator of a clinically significant PE. Any sudden deterioration in the patients vital signs should include embolism in the differential diagnosis, particularly during procedures that carry a high risk of the complication.

Prolongation of lidocaine spinal anesthesia with phenylephrine.

The effect of added phenylephrine on the duration of sensory analgesia during lidocaine spinal anesthesia was determined in 65 ASA class I-III patients randomly divided into three groups. Group 1 (n = 25) received 62.5 mg lidocaine in 7.5% glucose; group 2 (n = 21) received lidocaine with 2 mg phenylephrine; and group 3 (n = 19) received lidocaine with 5 mg phenylephrine. The level of analgesia to pin prick was assessed by an anesthesiologist unaware of the drug combination used. The mean ± SD cephalad level of analgesia did not differ among the groups. In group 1, the times for two- and for four-segment regression of the level of analgesia, and the time for regresson of analgesia to the T-12 dermatome, were 77 ± 19 (1 SD), 99 ± 24, and 109 ± 26 min, respectively. The corresponding values were 98 ± 25, 118 ± 27, and 130 ± 36 min in group 2 and 124 ± 32, 142 ± 31, and 162 ± 35 min in group 3. All the regression times in group 2 were significantly longer than those in group 1 (P < 0.05). All the regression times in group 3 were significantly longer than those in group 2 (P < 0.02). It is concluded that clinically useful prolongation of sensory analgesia may be obtained by addition of phenylephrine to lidocaine during spinal anesthesia.

Anesthetic considerations in McCune-Albright syndrome: case report with literature review.

M cCune-Albright Syndrome is an uncommon chromosomal endocrine disorder characterized by polyostotic fibrous dysplasia, cafe au lait spots, and sexual precocity (1). Hyperthyroidism, growth hormone excess, hyperparathyroidism, hyperprolactinemia, and/or hypercortisolism may be present in any combination (1). Although the literature states that this syndrome occurs sporadically, we could not find any information about its exact incidence (2,3). Patients with this syndrome often present to the anesthesiologist for repair of bone lesionrelated fractures. The scarcity of information about the anesthetic management of this disorder stimulated the preparation of this case report that describes expected and unexpected aspects of this syndrome.

Arterial to end-tidal CO2 gradients during spontaneous breathing, intermittent positive-pressure ventilation and jet ventilation

Arterial to end-tidal CO2 tension gradients were measured in 18 dogs during spontaneous breathing (SB), intermittent positive-pressure ventilation (IPPV), and both low-frequency and high-frequency jet ventilation (LFJV and HFJV). The dogs were anesthetized with nembutal and permitted to breathe spontaneously through an 8-mm internal diameter endotracheal tube; blood gas tensions, cardiac output, and end-tidal CO2 partial pressure (Petco2) were measured. IPPV, LFJV, and HFJV were then instituted in a random sequence and measurements repeated. Pao2, Paco2 and cardiac output were similar during all four ventilatory modes. The mean Paco2 differed significantly (p< .001) from Petco2 during IPPV, LFJV, and HFJV but not during SB. The mean Paco2-Petco2 gradient was 3.7 ± 1 (sd), 12.6 ± 5.0, and 24.3 ± 8 torr during IPPV, LFJV and HFJV, respectively. The large gradients during LFJV and HFJV were not produced by dilution of tracheal CO2 by entrained air or by oxygen delivered by the jet. These results suggest that both LFJV and HFJV may be associated with a large Paco2-Petco2 gradient.