Michael F. M. James

A balanced view of balanced solutions

The present review of fluid therapy studies using balanced solutions versus isotonic saline fluids (both crystalloids and colloids) aims to address recent controversy in this topic. The change to the acid-base equilibrium based on fluid selection is described. Key terms such as dilutional-hyperchloraemic acidosis (correctly used instead of dilutional acidosis or hyperchloraemic metabolic acidosis to account for both the Henderson-Hasselbalch and Stewart equations), isotonic saline and balanced solutions are defined. The review concludes that dilutional-hyperchloraemic acidosis is a side effect, mainly observed after the administration of large volumes of isotonic saline as a crystalloid. Its effect is moderate and relatively transient, and is minimised by limiting crystalloid administration through the use of colloids (in any carrier). Convincing evidence for clinically relevant adverse effects of dilutional-hyperchloraemic acidosis on renal function, coagulation, blood loss, the need for transfusion, gastrointestinal function or mortality cannot be found. In view of the long-term use of isotonic saline either as a crystalloid or as a colloid carrier, the paucity of data documenting detrimental effects of dilutional-hyperchloraemic acidosis and the limited published information on the effects of balanced solutions on outcome, we cannot currently recommend changing fluid therapy to the use of a balanced colloid preparation.

A Head-to-Head Comparison of the In Vitro Coagulation Effects of Saline-Based and Balanced Electrolyte Crystalloid and Colloid Intravenous Fluids

Both fluid composition (e.g., type of hydroxyethyl starch) and formulation (e.g., saline or balanced salt carrier solution) may alter whole blood coagulation. We therefore enrolled 10 healthy volunteers to test ex vivo, thrombelastograph®-based blood coagulation differences of eight crystalloid and colloid solutions at 20%, 40%, and 60% dilutions. Saline and lactated Ringers solution produced a hypercoagulable state at 20%–40% dilutions. Saline, hetastarch in saline, pentastarch in saline, tetrastarch in saline, and human albumin solutions all produced a hypocoagulable state at 60% dilution. Hetastarch in saline also produced a hypocoagulable state at 40% dilution. The larger molecular weight starches produced more intense coagulation abnormalities than the medium molecular weight compounds formulated similarly (i.e., suspended in saline or balanced salt solution). The balanced salt solutions caused fewer coagulation abnormalities, especially pentastarch in balanced salt solution. This balanced salt pentastarch preparation produced the least derangement of coagulation of the colloid solutions at all dilutions, causing hypercoagulability at the lower dilutions and minimal coagulation derangement at 60% dilution. These data support the theory that smaller molecular weight hydroxyethyl starches and colloids suspended in balanced salt solutions preserve coagulation better than large molecular weight starches and saline-based colloids, as judged by thrombelastography.

Aspiration prevented by the ProSeal™ laryngeal mask airway: a case report

PurposeTo describe a case of intraoperative passive regurgitation where the ProSeal™ laryngeal mask airway (PLMA) successfully protected the airway from the respiratory tract.Clinical featuresA 32-yr-old man was electively scheduled for change of dressings and application of plaster of Paris to both legs. A size 5 PLMA was inserted on the first attempt and the patient allowed to breathe spontaneously. Twenty-five minutes into the procedure brown fluid was noticed in the drainage tube of the mask. There was no change in respiratory pattern nor any evidence of coughing retching or vomiting. Twenty-five millilitres of fluid were suctioned out of the tube which tested positive for acid. The PLMA was left in place and the procedure continued uneventfully. After removal of the mask pH testing showed the dorsum of the mask to have a pH of 7 and the ventrum/bowl of the mask to be dry with a pH of 7. The patient had no respiratory symptoms in the recovery room and the postoperative course was uneventful.ConclusionsThis case illustrates that passive regurgitation can occur unexpectedly intraoperatively and shows that the PLMA can protect the airway during such an event by allowing the regurgitated fluid to pass up the drainage tube without leaking into the glottis.RésuméObjectifDécrire un cas de régurgitation peropératoire passive où le masque laryngé ProSeal™ (MLP) a permis de protéger efficacement les voies aériennes du contenu gastrique.Éléments cliniquesLe changement des pansements et l’application de plâtre de Paris aux deux jambes avaient été planifiés pour un homme de 32 ans. Un MLP 5 a été inséré au premier essai et le patient a pu respirer spontanément. Vingtcinq minutes après le début de l’intervention, un liquide brunâtre a été noté dans le tube de drainage du masque. La respiration n’était pas affectée et aucune évidence de hautle-cœur ou de vomissement n’était observée. Vingtcinq millilitres de liquide ont été aspirés du tube et une analyse en a révélé un contenu acide. Le MLP a été laissé en place et l’intervention s’est poursuivie sans incident. Après le retrait du masque, un test de pH a montré que le bord dorsal du masque présentait un pH de 7 et la partie ventrale/creuse était sèche et avait un pH de 7. À la salle de réveil, le patient n’avait pas de symptômes respiratoires et la récupération s’est déroulée normalement.ConclusionCe cas illustre le fait qu’une régurgitation passive puisse se produire de façon inattendue pendant une intervention et que le MLP peut alors protéger les voies aériennes en permettant au liquide régurgité de passer dans le tube de drainage sans aller dans la glotte.

Coagulation effects of in vitro serial haemodilution with a balanced electrolyte hetastarch solution compared with a saline-based hetastarch solution and lactated Ringer's solution

The hydroxyethyl starches are a group of compounds that has been associated with impairment of coagulation when large volumes are administered. The thrombelastograph® is commonly used to assess point‐of‐care whole blood coagulation. Little is known about the dose–response relationships of haemodilution, and it is reasonable to assume that a linear association exists. This may not be the case with altered electrolyte compositions of the fluids used for haemodilution. We have therefore conducted an in vitro study of haemodilution of human whole blood using lactated Ringers solution and two high molecular weight hetastarches, one in a balanced salt solution, the other in a 0.9% saline solution. The thrombelastograph®, commonly used for the assessment of the coagulation effects of synthetic colloids, was used as the coagulation assessment device. Serial haemodilution with hetastarch in a balanced salt solution demonstrated a biphasic response (of r‐times and k‐times, as well as alpha angles), with haemodilution in the 20–40% range causing enhanced coagulation, and higher degrees of dilution causing a decrease in overall coagulation performance. A similar picture was observed with lactated Ringers solution, but only significantly so in alpha angles. Hetastarch in saline did not display this initial increased coagulability at mild to moderate dilutions. This biphasic response of lactated Ringers solution and hetastarch in a balanced salt solution reflects the complex interaction of fluids and the coagulation system, and that these effects cannot be attributed to simple haemodilution. On the other hand, there was a linear decrease in maximum amplitude with haemodilution. Maximum amplitude was particularly affected by both starches, which is an expected finding in view of the known interaction between the hydroxyethyl starches and von Willebrands factor.

Use of magnesium sulphate in the anaesthetic management of phaeochromocytoma in pregnancy.

The anaesthetic management of two patients with phaeochromocytoma complicating pregnancy is presented. In one patient, the operative delivery was followed by elective tumour resection at a later stage. Magnesium sulphate was used as an adjunct to all three anaesthetics, with notable success on two occasion. In one of the operative deliveries, it proved impossible to achieve adequate blood levels of magnesium, due to severe pre-existing magnesium deficiency. Hypomagnesaemia is likely to be present in such cases and must be corrected preoperatively, Magnesium sulphate is a useful adjunct to the anaesthetic management of the pregnant patient with a phaeochromocytoma provided that adequate serum levels of magnesium can be established.RésuméLa conduite anesthésique de deux patientes atteintes de phéo-chromocytome compliquant la grossesse est présentée. Chez une patiente ľaccouchement fut suivie plus tard par la résection élective de la tumeur. Le sulphate de magnésie fut utilisée tors des trois anesthésies avec un succès notoire à deux occasions. Lors ďun des ces accouchements il a été impossible ďacquérir un niveau sanguin adéquat de magnésium à cause ďune déficience de magnésium sévère pré-existante. Ľhypomagnésémie est probablement présente dans de tels cas et doit être corrigée dans la période pré-opératoire. Le sulfate de magnésie est un additif utile pour la conduite anesthésique des patientes gravides atteintes de phéochromocytome lorsqu’un taux sérique adéquat de magnésium peut être acquis.

A comparison of spinal and epidural anaesthesia for hip arthroplasty

Spinal and epidural anaesthesia were compared in 65 patients undergoing hip arthroplasty, with regard to the degree of sensory and motor blockade, cardiovascular effects, operating conditions, the dose of propofol required to produce satisfactory hypnosis, and complications. Epidural anaesthesia was successful in 30 patients using an initial dose of 15 ml of 0.5% bupivicaine, and spinal anaesthesia in 32 patients, using 4 ml 0.5% isobaric bupivicaine. The two techniques were similar with regard to the level of sensory blockade (T8), degree of hypotension and perioperative haemorrhage. Differences occurred in the degree of motor blockade (mean Bromage score of 1 in the spinal group vs 3.86 in the epidural group) (P < 0.05), time to achieve maximal cephalad spread (13 min in the spinal group vs 21 min in the epidural group) (P < 0.05) and the dose of propofol required to produce adequate hypnosis (1.95 mg · kg−1 · hr−1 in the spinal group vs 2.89 mg -kg−1· hr−1 in the epidural group) (P < 0.05). Only seven patients required urethral catheterization in this spinal group compared with 14 in the epidural group (P < 0.05). Spinal anaesthesia also proved advantageous by providing better operating conditions for the surgeon, with a lower incidence of patient movement.RésuméCette étude compare la rachi-anesthésie et l’anesthésie péridurale chez 65 patients subissant une arthroplastie de la hanche. Les paramètres évalués sont le niveau du bloc de conduction sensitif, la qualité du bloc moteur, les effets cardiovasculaires, la facilité d’accés chirurgical, les complications et la quantité de propofol nécessaire pour maintenir une hypnose au cours de l’intervention. L’anesthésie péridurale est réalisée avec succès chez 30 patients en utilisant une dose initiale de 15 ml de bupivacaine 0,5%. La rachi-anesthésie est faite avec succès chez 32 patients en utilisant 4 ml de bupivacaine 0,5% isobare. Les deux techniques sont associées à un bloc de conduction sensitif de niveau T8. La chute de pression et les saignements périopératoires sont comparables avec une technique ou l’autre. Le bloc moteur moyen est de 1 a l’échelle de Bromage avec la rachi-anesthésie comparativement à 3,86 avec l’anesthésie péridurale (P < 0,05). La migration céphalade maximale de l’agent anesthésique est plus rapide avec la rachi-anesthésie (13 min versus 21 min; P < 0,05). La dose de propofol nécessaire pour maintenir l’hypnose est de 1,95 mg · kg−1 · h−1 chez les patients du groupe rachi-anesthésie comparativement a 2,89 mg · kg−1 · h−1 chez les patients du groupe péridurale (P < 0,05). Sept patients du groupe rachianesthésie versus 14 patients du groupe péridurale ont besoin de cathétérisme vésical (P < 0,05). La rachi-anesthésie est associée à moins de mouvements des patients durant la chirurgie, et de ce fait elle permet un meilleur accés chirurgical.

Magnesium in obstetrics

Magnesium is a critical physiological ion, and magnesium deficiency might contribute to the development of pre-eclampsia, to impaired neonatal development and to metabolic problems extending into adult life. Pharmacologically, magnesium is a calcium antagonist with substantial vasodilator properties but without myocardial depression. Cardiac output usually increases following magnesium administration, compensating for the vasodilatation and minimising hypotension. Neurologically, the inhibition of calcium channels and antagonism of the N-methyl-d-aspartic acid (NMDA) receptor raises the possibility of neuronal protection, and magnesium administration to women with premature labour may decrease the incidence of cerebral palsy. It is the first-line anticonvulsant for the management of pre-eclampsia and eclampsia, and it should be administered to all patients with severe pre-eclampsia or eclampsia. Magnesium is a moderate tocolytic but the evidence for its effectiveness remains disputed. The side effects of magnesium therapy are generally mild but the major hazard of magnesium therapy is neuromuscular weakness.

Obstetric anaesthesia in low-resource settings

Close co-operation between obstetricians and obstetric anaesthesia providers is crucial for the safety and comfort of parturients, particularly in low-resource environments. Maternal and foetal mortality is unacceptably high, and the practice of obstetric anaesthesia has an important influence on outcome. Well-conducted national audits have identified the contributing factors to anaesthesia-related deaths. Spinal anaesthesia for caesarean section is the method of choice in the absence of contraindications, but is associated with significant morbidity and mortality. Minimum requirements for safe practice are adequate skills, anaesthesia monitors, disposables and drugs and relevant management protocols for each level of care. The importance of current outreach initiatives is emphasised, and educational resources and the available financial sources discussed. The difficulties of efficient procurement of equipment and drugs are outlined. Guiding principles for the practice of analgesia for labour, anaesthesia for caesarean section and the management of obstetric emergencies, where the anaesthetist also has a central role, are suggested.

Citrated blood does not reliably reflect fresh whole blood coagulability in trials of in vitro hemodilution

IMPLICATIONS Citration and storage of whole blood markedly alter the Thrombelastograph effects of hemodilution on coagulation. The results of hemodilution studies in which citrated blood has been used to study coagulation may not be reliable.

Neutrophils from patients undergoing hip surgery exhibit enhanced movement under spinal anaesthesia compared with general anaesthesia

The purpose of this research was to investigate whether the effects of regional anaesthesia on neutrophil migration differ from those due to general anaesthesia during major orthopaedic surgery in human patients. Eighteen patients underwent spinal or general anaesthesia (halothane or isoflurane) for surgery (six patients in each group). Blood samples were taken prior to induction of anaesthesia and after surgery was in progress for one hour. The movement of isolated neutrophils was measured in both samples in the chemotactic chamber toward lipopolysaccharide activated pooled serum. In addition plasma concentrations of catecholamines were determined in the blood samples. Neutrophils extracted from peripheral blood during spinal anaesthesia and surgery moved further towards a complementderived attractant than neurtrophils obtained from patients undergoing surgery under general anaesthesia with halothane or isoflurane and surgery (156.4 ± 7.6 μm vs 114.3 ± 6.1 μm or 119 ± 8.4 μm respectively, P < 0.05). Increased concentrations of adrenaline were present in both general anaesthetic groups whereas the spinal group had lower concentrations than those prior to anaesthesia and surgery. It is considered unlikely that these differences in neutrophil reactivity are due to the direct effects of anaesthetic agents employed. The effects are likely to be the result of differing effects of spinal anaesthesia on the stress response or immunological mediators.RésuméCette recherche avait pour but d’étudier les effets de l’anesthésie régionale et générale sur la migration des neutrophiles durant la chirurgie orthopédique majeure. Dix-huit patients furent soumis à une anesthésie rachidienne (R) ou générale à l’halothane (H) ou à l’isoflurane (I) (six patients dans chaque groupe). Des échantillons de sang périphérique furent prélevés avant l’induction de l’anesthésie et une heure après le début de la chirurgie afin d’étudier le mouvement des neutrophiles isolés et de mesurer la concentration sérique des catécholamines. Le mouvement des neutrophiles isolés fut mesuré dans une chambre chimiotactique à l’aide de sérums mélangés activés par des lipopolysaccharides. Le déplacement des neutrophiles vers l’activateur dérivé du complément fut plus important dans le groupe R (156,4 ± 7.6 μm) que dans les groupes H (114,3 ±6,1 μm) ou I (119 ± 8,4 μm) (P < 0.05). La concentration d’adrénaline s’est élevée en per-opératoire dans les groupes H et I alors qu ’elle s’est abaissée dans le groupe R (par comparaison avec le prélèvement pré-induction). On considère peu probable que les différences observées sur la réactivité des neutrophiles découlent de l’action directe des agents anesthesiques employes. Ces différences résultent plus vraisemblablement de l’action de l’anesthésie rachidienne sur la réponse au stress ou sur des médiateurs immunologiques.