Agreement between three noninvasive temperature monitoring devices during spinal anaesthesia for caesarean delivery: a prospective observational study

Hypothermia during obstetric spinal anaesthesia is a common and important problem, yet temperature monitoring is often not performed due to the lack of a suitable, cost-effective monitor. This study aimed to compare a noninvasive core temperature monitor with two readily available peripheral temperature monitors during obstetric spinal anaesthesia. We undertook a prospective observational study including elective and emergency caesarean deliveries, to determine the agreement between affordable reusable surface temperature monitors (Welch Allyn SureTemp® Plus oral thermometer and the Braun 3-in-1 No Touch infrared thermometer) and the Dräger T-core© (using dual-sensor heat flux technology), in detecting thermoregulatory changes during obstetric spinal anaesthesia. Predetermined clinically relevant limits of agreement (LOA) were set at ± 0.5 °C. We included 166 patients in our analysis. Hypothermia (heat flux temperature < 36 °C) occurred in 67% (95% CI 49 to 78%). There was poor agreement between devices. In the Bland-Altman analysis, LOA for the heat flux monitor vs. oral thermometer were 1.8 °C (CI 1.7 to 2.0 °C; bias 0.5 °C), for heat flux monitor vs. infrared thermometer LOA were 2.3 °C (CI 2.1 to 2.4 °C; bias 0.4 °C) and for infrared vs. oral thermometer, LOA were 2.0 °C (CI 1.9 to 2.2 °C; bias 0.1 °C). Error grid analysis highlighted a large amount of clinical disagreement between methods. While monitoring of core temperature during obstetric spinal anaesthesia is clinically important, agreement between monitors was below clinically acceptable limits. Future research with gold-standard temperature monitors and exploration of causes of sensor divergence is needed.

Method of Anesthesia and Perioperative Risk Factors, Maternal Anesthesia Complications, and Neonatal Mortality Following Cesarean Delivery in Africa: A Substudy of a 7-Day Prospective Observational Cohort Study

BACKGROUND

The African Surgical Outcomes Study (ASOS) found that maternal mortality following cesarean delivery in Africa is 50 times higher than in high-income countries, and associated with obstetric hemorrhage and anesthesia complications. Mothers who died were more likely to receive general anesthesia (GA). The associations between GA versus spinal anesthesia (SA) and preoperative risk factors, maternal anesthesia complications, and neonatal outcomes following cesarean delivery in Africa are unknown.

METHODS

This is a secondary explanatory analysis of 3792 patients undergoing cesarean delivery in ASOS, a prospective observational cohort study, across 22 African countries. The primary aim was to estimate the association between preoperative risk factors and the outcome of the method of anesthesia delivered. Secondary aims were to estimate the association between the method of anesthesia and the outcomes (1) maternal intraoperative hypotension, (2) severe maternal anesthesia complications, and (3) neonatal mortality. Generalized linear mixed models adjusting for obstetric gravidity and gestation, American Society of Anesthesiologists (ASA) category, urgency of surgery, maternal comorbidities, fetal distress, and level of anesthesia provider were used.

RESULTS

Of 3709 patients, SA was performed in 2968 (80%) and GA in 741 (20%). Preoperative factors independently associated with GA for cesarean delivery were gestational age (adjusted odds ratio [aOR], 1.093; 95% confidence interval [CI], 1.052-1.135), ASA categories III (aOR, 11.84; 95% CI, 2.93-46.31) and IV (aOR, 11.48; 95% CI, 2.93-44.93), eclampsia (aOR, 3.92; 95% CI, 2.18-7.06), placental abruption (aOR, 6.23; 95% CI, 3.36-11.54), and ruptured uterus (aOR, 3.61; 95% CI, 1.36-9.63). SA was administered to 48 of 94 (51.1%) patients with eclampsia, 12 of 28 (42.9%) with cardiac disease, 14 of 19 (73.7%) with preoperative sepsis, 48 of 76 (63.2%) with antepartum hemorrhage, 30 of 55 (54.5%) with placenta previa, 33 of 78 (42.3%) with placental abruption, and 12 of 29 (41.4%) with a ruptured uterus. The composite maternal outcome "all anesthesia complications" was more frequent in GA than SA (9/741 [1.2%] vs 3/2968 [0.1%], P < .001). The unadjusted neonatal mortality was higher with GA than SA (65/662 [9.8%] vs 73/2669 [2.7%], P < .001). The adjusted analyses demonstrated no association between method of anesthesia and (1) intraoperative maternal hypotension and (2) neonatal mortality.

CONCLUSIONS

Analysis of patients undergoing anesthesia for cesarean delivery in Africa indicated patients more likely to receive GA. Anesthesia complications and neonatal mortality were more frequent following GA. SA was often administered to high-risk patients, including those with eclampsia or obstetric hemorrhage. Training in the principles of selection of method of anesthesia, and the skills of safe GA and neonatal resuscitation, is recommended.

Burn injuries in KwaZulu-Natal Province, South Africa: Quantifying the healthcare burden

BACKGROUND

Most burn injuries occur in low- and middle-income countries (LMICs) and affect those of lower socioeconomic status disproportionally. A multifaceted approach is needed to improve burn outcomes. Healthcare strategies and reform should be data driven, but South Africa (SA) currently lacks sufficient baseline data related to burn injuries. The absence of local data is compounded by a global lack of published data from LMIC settings. The Pietermaritzburg Burn Service Registry (PBSR) is the only established registry for burn injuries in SA.

OBJECTIVES

To use the high-quality, detailed data from the PBSR to estimate the KwaZulu-Natal (KZN) provincial burden of burns in terms of length of stay, need for surgery and mortality. Our broader aim is to quantify the magnitude of the problem to highlight the need for specific burn care strategies in SA.

METHODS

We conducted an observational, retrospective review of burns data from two databases, the District Health Information System (DHIS) between 2013 and 2018, and the more detailed PBSR between 2016 and 2019. We compared the distribution of mild, moderate and severe injuries as well as the distribution of adult and paediatric admissions between the DHIS and PBSR data sets. We then assumed that outcomes for the province would follow similar patterns to the Pietermaritzburg Burn Service and applied the proportions to the DHIS data set to estimate the annual provincial burden.

RESULTS

In the DHIS, there was an annual mean (standard deviation (SD)) of 4 807 (760) children (age ≤12 years) and 3 622 (588) adults (age >12 years) admitted to hospitals in KZN with burn injuries. Annual average injury severity was 76.0% mild (mean (SD) n=5 539 (1 112.4)), 19.8% moderate (n=1 441 (148.8)) and 4.2% severe (n=312 (24.5)). These proportions were similar in the PBSR. Projections estimate that 2 967 patients would need surgery, with 212 500 hospital days required annually in the province. Additionally, provincial mortality would be 586 patients, including 84% with burns of mild and moderate severity. These deaths are potentially preventable.

CONCLUSION

There is a significant, unquantified burden of burn injury in KZN, highlighting the urgent need for development of specialised surgical services for burns. Collection of more robust national data to verify our projections is required to confirm the need and guide required healthcare reform.

Global issues in obstetric anaesthesia: perspectives from South Africa, Japan, China, Latin America and North America

South Africa is classified as a low- and middle-income country, with a complex mixture of resource-rich and resource-limited settings. In the major referral hospitals, the necessary skill level exists for the management of complex challenges. However, this contrasts with the frequently-inadequate skill levels of anaesthesia practitioners in resource-limited environments. In Japan, obstetricians administer anaesthesia for 40% of caesarean deliveries and 80% of labour analgesia. Centralisation of delivery facilities is now occurring and it is expected that obstetric anaesthesiologists will be available 24 h a day in centralised facilities in the future. In China, improvements in women's reproductive, maternal, neonatal, child, and adolescent health are critical government policies. Obstetric anaesthesia, especially labour analgesia, has received unprecedented attention. Chinese obstetric anaesthesiologists are passionate about clinical research, focusing on efficacy, safety, and topical issues. The Latin-American region has different landscapes, people, languages, and cultures, and is one of the world's regions with the most inequality. There are large gaps in research, knowledge, and health services, and the World Federation of Societies of Anaesthesiologists is committed to working with governmental and non-governmental organisations to improve patient care and access to safe anaesthesia. Anaesthesia workforce challenges, exacerbated by coronavirus disease 2019, beset North American healthcare. Pre-existing struggles by governments and decision-makers to improve health care access remain, partly due to unfamiliarity with the role of the anaesthesiologist. In addition to weaknesses in work environments and dated standards of work culture, the work-life balance demanded by new generations of anaesthesiologists must be acknowledged.

Tranexamic acid at cesarean delivery: Drug-error deaths

The use of tranexamic acid for postpartum hemorrhage has entered obstetrical practice globally with the evidence-based expectation of saving lives. This improvement in the care of women with postpartum hemorrhage has come at a price. For the anesthetist, having tranexamic acid ampoules close at hand would seem an obvious strategy to facilitate its use during cesarean delivery, an important setting for severe hemorrhage. Tragically, we have identified a number of recent instances of inadvertent intrathecal administration of tranexamic acid instead of local anesthetic for spinal anesthesia. Reported cases of this catastrophic error seem to be increasing. The profound neurotoxicity of tranexamic acid causes rapid-onset convulsions, with mortality of 50%. How can these tragic errors be averted? Drug safety alerts have been issued by the US Food and Drug Administration and the World Health Organization, but that is not enough. We recommend extensive dissemination of information to raise awareness of this potential hazard, and local hospital protocols to ensure that tranexamic acid is stored separately from anesthetic drugs, preferably outside the operating room and with an auxiliary warning label. Implementation of safety strategies on a very large scale will be needed to ensure that the life-saving potential of tranexamic acid is not eclipsed by drug-error mortality.

Tranexamic acid at cesarean delivery: drug‐error deaths

The use of tranexamic acid for postpartum hemorrhage has entered obstetrical practice globally with the evidence-based expectation of saving lives. This improvement in the care of women with postpartum hemorrhage has come at a price. For the anesthetist, having tranexamic acid ampoules close at hand would seem an obvious strategy to facilitate its use during cesarean delivery, an important setting for severe hemorrhage. Tragically, we have identified a number of recent instances of inadvertent intrathecal administration of tranexamic acid instead of local anesthetic for spinal anesthesia. Reported cases of this catastrophic error seem to be increasing. The profound neurotoxicity of tranexamic acid causes rapid-onset convulsions, with mortality of 50%. How can these tragic errors be averted? Drug safety alerts have been issued by the US Food and Drug Administration and the World Health Organization, but that is not enough. We recommend extensive dissemination of information to raise awareness of this potential hazard, and local hospital protocols to ensure that tranexamic acid is stored separately from anesthetic drugs, preferably outside the operating room and with an auxiliary warning label. Implementation of safety strategies on a very large scale will be needed to ensure that the life-saving potential of tranexamic acid is not eclipsed by drug-error mortality.

Troubleshooting obstetric spinal anaesthesia at district hospital level

Obstetric spinal anaesthesia is routinely used in South African district hospitals for caesarean sections, providing better maternal and neonatal outcomes than general anaesthesia in appropriate patients. However, practitioners providing anaesthesia in this context are usually generalists who practise anaesthesia infrequently and may be unfamiliar with dealing with complications of spinal anaesthesia or with conversion from spinal to general anaesthesia. This is compounded by challenges with infrastructure, shortages of equipment and sundries and a lack of context-sensitive guidelines and support from specialised anaesthetic services for district hospitals. This continuous professional development (CPD) article aims to provide guidance with respect to several key areas related to obstetric spinal anaesthesia, and to address common concerns and queries. We stress that good clinical practice is essential to avoid predictable, common complications, and hence a thorough preoperative preparation is essential. We further discuss clinical indications for preoperative blood testing, spinal needle choice, the use of isobaric bupivacaine, spinal hypotension, failed or partial spinal block and pain during the caesarean section. Where possible, relevant local and international guidelines are referenced for further reading and guidance, and a link to a presentation of this topic is provided.

Spinal hypotension in obstetrics: Context-sensitive prevention and management

Spinal hypotension during caesarean section remains a common complication, with important attendant maternal and fetal adverse outcomes. Research elucidating the mechanisms of spinal hypotension has led to the development and refinement of effective management strategies, with a particular emphasis on prophylactic vasopressor administration. This has proved effective in well-resourced settings, with maternal comfort and the elimination of nausea now considered the primary aim of treatment. In resource-limited settings, sophisticated strategies are not feasible due to insufficient equipment, staff, and expertise. Therefore, in these areas spinal hypotension remains an important cause of maternal and fetal morbidity and mortality. Translational, context-sensitive research in resource-limited settings has shown promise in implementing pragmatic strategies based on research from resource-rich environments. We review the current best practice for the prevention and treatment of spinal hypotension, with a special emphasis on effective strategies in resource-limited settings. We further suggest a research agenda to address the knowledge gap in specific contexts.

Anaesthesia for ruptured ectopic pregnancy at district level

In South Africa, deaths as a result of ectopic pregnancies are increasing despite the overall improvements in maternal mortality. These deaths occur predominantly in district hospitals, with the final cause of death being hypovolaemic shock in almost all cases. In most cases, no anaesthesia was attempted despite the district hospitals having the clinical skills, equipment and infrastructure to provide a caesarean delivery service. It appears that there is a skills gap between the provision of anaesthesia for caesarean delivery and that of ruptured ectopic pregnancy. There is a growing recognition of the urgent need to prioritise the provision of emergency surgical care in rural settings. This should be viewed not as a luxury but as an absolute necessity. In this study, we aim to discuss the pathophysiology of a patient with a ruptured ectopic pregnancy briefly, outline district hospital requirements for safe surgery and then discuss a simple, safe method for the provision of anaesthesia in patients deemed too unstable to transfer to a referral facility.

Effect of COVID-19 pandemic decisions on tertiary-level surgical services in Pietermaritzburg, KwaZulu-Natal Province, South Africa

BACKGROUND

The COVID-19 pandemic has led to the implementation of restrictive policies on theatre procedures, with profound impacts on service delivery and theatre output.

OBJECTIVES

To quantify these effects at a tertiary hospital in KwaZulu-Natal Province, South Africa.

METHODS

A retrospective review of morbidity and mortality data was conducted. The effects on emergency and elective caseload, intensive care unit (ICU) admissions from theatre, theatre cancellations and regional techniques were noted.

RESULTS

Theatre caseload decreased by 30% from January to April 2020 (p=0.02), ICU admissions remained constant, and theatre cancellations were proportionally reduced, as were the absolute number of regional techniques.

CONCLUSIONS

The resulting theatre case deficit was 1 260 cases. It will take 315 days to clear this deficit if four additional surgeries are performed per day.

Prophylactic phenylephrine and fluid co-administration to reduce spinal hypotension during elective caesarean section in a resource-limited setting: a prospective alternating intervention study

Spinal hypotension is a common and clinically important problem during caesarean section. Current consensus recommendations for resource-rich settings suggest the use of a titrated phenylephrine infusion, in combination with fluid coloading, for prevention of maternal hypotension. In resource-limited settings, where syringe drivers are unavailable, these recommendations advise the addition of 500 μg phenylephrine to the first 1 l of intravenous fluid given after initiation of spinal anaesthesia, with additional vasopressor boluses as required. This prospective, alternating intervention study compared the use of a conventional phenylephrine rescue bolus strategy for prevention of hypotension, defined as systolic arterial pressure < 90 mmHg, with a phenylephrine infusion given according to the consensus recommendation. We studied 300 women having elective caesarean section. There were 77 (51%) women who developed hypotension in the bolus group vs. 55 (37%) in the phenylephrine infusion group (p = 0.011). This represented a 29% reduction in hypotension, with a number needed to treat of 6.8. The six highest systolic arterial pressure readings occurred in the phenylephrine infusion group (range 166-188 mmHg), and there were four instances of bradycardia (heart rate < 50 beats.min^-1 ) with preserved systolic arterial pressure in each group. There were no adverse clinical sequelae, and no differences in neonatal Apgar scores in either group. The consensus recommendation for phenylephrine and fluid co-administration in resource-limited settings appears effective in preventing maternal hypotension, but at the cost of sporadic systolic hypertension.

Post-caesarean delivery analgesia in resource-limited settings: a narrative review

Post-caesarean pain is an important and often neglected outcome. It causes suffering, affects breastfeeding and is associated with postpartum depression and the development of chronic pain syndromes. Pain control is often difficult even in resource-rich environments; it is likely far worse in resource-limited settings, where emphasis is on reducing the high maternal mortality rate. Lack of adequate staffing, education, and postoperative monitoring severely limit the options in resource-limited settings. Resource-limited settings are further compromised by limited access to essential analgesic drugs and equipment for their administration. Solutions using affordable and accessible medications as part of a multimodal analgesic strategy are possible, supplemented by education and training programmes. More research is required, both to establish current practice and to test methods for improving maternal pain control. While government involvement is necessary to improve infrastructure and resources in individual countries, other solutions should also be sought, empowering local institutions and harnessing individual cultural characteristics.

The ASOS Surgical Risk Calculator: development and validation of a tool for identifying African surgical patients at risk of severe postoperative complications

BACKGROUND

The African Surgical Outcomes Study (ASOS) showed that surgical patients in Africa have a mortality twice the global average. Existing risk assessment tools are not valid for use in this population because the pattern of risk for poor outcomes differs from high-income countries. The objective of this study was to derive and validate a simple, preoperative risk stratification tool to identify African surgical patients at risk for in-hospital postoperative mortality and severe complications.

METHODS

ASOS was a 7-day prospective cohort study of adult patients undergoing surgery in Africa. The ASOS Surgical Risk Calculator was constructed with a multivariable logistic regression model for the outcome of in-hospital mortality and severe postoperative complications. The following preoperative risk factors were entered into the model; age, sex, smoking status, ASA physical status, preoperative chronic comorbid conditions, indication for surgery, urgency, severity, and type of surgery.

RESULTS

The model was derived from 8799 patients from 168 African hospitals. The composite outcome of severe postoperative complications and death occurred in 423/8799 (4.8%) patients. The ASOS Surgical Risk Calculator includes the following risk factors: age, ASA physical status, indication for surgery, urgency, severity, and type of surgery. The model showed good discrimination with an area under the receiver operating characteristic curve of 0.805 and good calibration with c-statistic corrected for optimism of 0.784.

CONCLUSIONS

This simple preoperative risk calculator could be used to identify high-risk surgical patients in African hospitals and facilitate increased postoperative surveillance.

CLINICAL TRIAL REGISTRATION

NCT03044899.

Prophylactic Phenylephrine Infusions to Reduce Severe Spinal Anesthesia Hypotension During Cesarean Delivery in a Resource-Constrained Environment

Phenylephrine infusions are considered as standard management for obstetric spinal hypotension, but there remains reluctance to implement them in resource-limited contexts. This prospective, alternating intervention study of patients undergoing elective or urgent cesarean delivery under spinal anesthesia compared a vasopressor bolus strategy to fixed-rate, low-dose prophylactic phenylephrine infusion with supplemental boluses. The primary outcome was the incidence of severe hypotension (mean arterial pressure <70% baseline or systolic blood pressure <80 mm Hg). Fewer patients receiving prophylactic phenylephrine infusions had severe hypotension (47.4% [n = 120/253] vs 62.1% [n = 157/253], P = .001, estimated relative risk 0.84, 95% confidence interval, 0.69-1.02), with no significant difference in the rate of hypertension (15% [n = 39/253] vs 11% [n = 27/253], P = .11, estimated relative risk 1.39, confidence interval 0.87-2.20). Guidelines for resource-constrained settings should consider a fixed, low-dose phenylephrine infusion in combination with rescue vasopressor bolus therapy.

Clinical accuracy of continuous hemoglobin oxygen saturation monitoring devices

Three devices used to measure hemoglobin oxygen saturation in the extracorporeal circuit were studied and compared to a control. The Baxter Bentley OxySat, Oximetrix Accusat, and Radiometer ABL4 blood gas monitor were compared to a control, the IL 282 Co-Oximeter. Fifty-one sample points were obtained during all phases of cardiopulmonary bypass with results as follows: table: see text. The Accusat was found to be a statistically more accurate means of monitoring hemoglobin oxygen saturations during cardiopulmonary bypass than the ABL4 and the OxySat. All devices had significant correlation with the control and with each other.

The Fatty Acid composition of phosphatidylglycerol and sulfoquinovosyldiacylglycerol of higher plants in relation to chilling sensitivity

The fatty acid composition of phosphatidylglycerol and sulfoquinovosyldiacylglycerol has been measured in the leaves of 27 species of higher plants from six families whose members differed in their degrees of chilling sensitivity. The content of high melting point fatty acids (represented by the sum of hexadecanoic, trans-3-hexadecenoic and octadecanoic acids) in phosphatidylglycerols varied little between members of the same plant family and was not obviously related to the relative chilling sensitivity of members of that family. The saturated fatty acid content (hexadecanoic + octadecanoic acids) of sulfoquinovosyldiacylglycerols also appeared to be characteristic of a plant family, although some exceptions were found. In one case, (Carica papaya) the content of saturated fatty acids in sulfoquinovosyldiacylglycerol was sufficiently high to suggest that this lipid could undergo phase separations above 0 degrees C. It is concluded that the content of high melting point fatty acids in leaf phosphatidylglycerol is not a direct indication of the chilling sensitivity of a plant, but rather may be a reflection of the genetic origin of that plant.

Biosynthesis of sulfoquinovosyldiacylglycerol in higher plants: the incorporation of 35SO4 by intact chloroplasts

Isolated spinach chloroplasts have been found to incorporate 35SO4 into the plant sulfolipid, sulfoquinovosyldiacylglycerol, at rates of up to 700 pmol mg chlorophyll-1 h-1. The reaction is light-dependent, requires that the chloroplasts be intact, and is slightly stimulated by ATP and UTP. UDP-galactose inhibits the formation of sulfoquinovosyldiacylglycerol, presumably by competing for the diacylglycerol pool. The rates of synthesis observed are sufficient to conclude that the chloroplast is autonomous with respect to the synthesis of sulfoquinovose, the headgroup moiety of sulfoquinovosyldiacylglycerol. No evidence could be obtained to support the concept that the proposed sulfoglycolytic pathway is the biosynthetic route for sulfoquinovose formation.

Biosynthesis of sulfoquinovosyldiacylglycerol in higher plants: the origin of the diacylglycerol moiety

The positional distribution of fatty acids in chloroplast polar lipids and phosphatidylcholine from leaves of four plants has been measured in order to determine the origin of the diacylglycerol (DAG) moieties of each lipid. In spinach and tobacco, the DAG of sulfoquinovosyldiacylglycerol (SQDG), monogalactosyldiacylglycerol (MGDG) and digalactosylglycerol (DGDG) were derived partly from the chloroplast and partly from the cytoplasm. The contribution of the chloroplast pathway differed for each lipid, but in both plants the proportion of a lipid derived from that pathway was in the order SQDG greater than MGDG greater than DGDG. In contrast, all the DAG moieties of the three glycolipids of wheat and cucumber were derived from the cytoplasm. The DAG moiety of chloroplast phosphatidylglycerol was synthesized in the chloroplast in all four plants.

The role of lysophosphatidylcholine in lipid synthesis by developing sunflower (Helianthus annuus L.) seed microsomes

The incorporation of oleate from oleoyl-CoA into lipids by microsomes from developing sunflower (Helianthus annuus L.) seeds has been investigated. Oleate was incorporated mainly into position 2 of phosphatidylcholine or released as free fatty acid. The addition of exogenous 1-acyl-lysophosphatidylcholine increased the incorporation of oleate into position 2 of phosphatidylcholine and decreased the release of free oleate. In the absence of exogenous lysophosphatidylcholine, the incorporation of oleate into phosphatidylcholine was limited by the amount of endogenous acceptor present. DH-990, an inhibitor of acyl-CoA:lysophosphatidylcholine acyltransferase, almost completely inhibited the incorporation of oleate from oleoyl-CoA into phosphatidylcholine at a concentration of 2.5 mM. These results indicate that the incorporation of oleate from oleoyl-CoA into microsomal phosphatidylcholine occurs mainly by the acylation of a 1-acyl-lysophosphatidylcholine acceptor rather than by acyl exchange between oleoyl-CoA and phosphatidylcholine. While the incorporation of oleoyl-CoA was completed within 2 to 5 min, exogenous 1-acyl-lysophosphatidylcholine was incorporated into phosphatidylcholine for up to 30 min. Addition of oleoyl-CoA resulted in an increase in both the rate and magnitude of lysophosphatidylcholine incorporation, which could not be accounted for by a stoichiometric reaction between the two substrates. Evidence is provided that free CoA had an independent stimulatory effect on the incorporation of lysophosphatidylcholine. The implications of this finding are discussed.

Preparation and comparison of model bilayer systems from chloroplasts thylakoid membrane lipids for 13C-NMR studies

Model bilayer systems from individual purified chloroplast thylakoid membrane lipids, from reconstituted mixtures of these purified lipids, and from leaf total polar lipid extracts have been prepared in water, and the longitudinal relaxation times (T1's) of the individual carbon atoms of the fatty acyl chains measured by 13C-NMR spectroscopy. The T1's increase with increasing distance of the carbon atoms from the polar headgroups in all cases, and as the results from each of the preparations are similar, all can be used as models of chloroplast membrane bilayers. Relaxation time measurements on intact chloroplast thylakoid membranes indicate the presence of chlorophyll resonances in the 13C-NMR spectrum of the membrane.

13C nuclear magnetic resonance studies of the composition and fluidity of several chloroplast monogalactosyldiacylglycerols

The motional properties of four monogalactosyldiacylglycerols isolated from photosynthetic membranes, and containing different fatty acid chain lengths and degrees of unsaturation, have been determined using 13C nuclear magnetic resonance. These properties have been compared with those of a lipid containing only saturated fatty acids. The 13C longitudinal relaxation times (T1) of the carbon atoms of the acyl chains in [2H4] methanol were measured as an index of the rates of motion of the lipid molecules and used to compare the relative fluidity of the acyl chains. The T1 values of the glyceryl and galactosyl carbon atoms in each monogalactosyldiacylglycerol are essentially constant, when allowance is made for concentration differences and the presence of two hydrogens on a methylene carbon versus one on a methine carbon. These results indicate similar rates of motion for the headgroup carbons in each lipid. However, for the acyl chains, the T1 values increase with the introduction of a double bond and increase further with additional unsaturation. This increase in the rate of motion only occurs at carbon atoms beyond the first double bond in an acyl chain. These results differ to those reported for monolayer experiments where changes in packing characteristics are predominantly dependent on the introduction of the first double bond and then vary little between species.

Studies on chloroplast membranes. IV. 13C chemical shifts and longitudinal relaxation times of 3-sn-phosphatidylglycerol

13C chemical shifts, longitudinal relaxation times and some nuclear Overhauser enhancement factors of individual carbon atoms in the chloroplast lipid, 3-sn-phosphatidylglycerol (pg), have been measured in (D4)methanol and (D)chloroform. Correlation times for individual carbon atoms calculated from these results have been interpreted in terms of different secondary structures: a monomeric structure in (D4)methanol and an inverted micelle in (D)chloroform. Differences in structures between the four major lipid components of the chloroplast membrane are briefly discussed.

Monolayer properties of chloroplast lipids

The properties of seven monogalactosyldiacylglycerols and six digalactosyldiacylglycerols, isolated from photosynthetic membranes and possessing different levels of fatty acid unsaturation, have been studied by the monolayer technique and compared with those of the fully saturated compounds. In addition, the monolayer properties of sulphoquinovosyldiacylglycerols and phosphatidylglycerols from higher plant chloroplasts, and several hexadecenoic acids have been measured. Monogalactosyldiacylglycerols containing saturated fatty acids form a condensed monolayer similar to that of saturated phosphatidylcholines. The naturally occurring monogalactosyldiacylglycerols, of which the double bond index ranged from 0.6 to 3.9, possessed comparable force-area curves suggesting that headgroup interactions play a more important role in packing behaviour than in phosphatidylcholines. Although digalactosyldiacylglycerols containing fully saturated fatty acids form a more expanded monolayer than the corresponding monogalactosyldiacylglycerols, the degree of expansion of the monolayer due to the presence of unsaturated fatty acids in the naturally occurring digalactosyldiacylglycerols is much less than in monogalactosyldiacylglycerols. Monogalactosyldiacylglycerols and digalactosyldiacylglycerols from a single species have very similar monolayer properties, and the presence of sulphoquinovosyldiacylglycerols and phosphatidylglycerols in the proportions in which they occur in higher plant chloroplasts does not have any condensing effect on a monolayer of galactolipids.

Postoperative hypoxaemia: oesophagectomy with gastric replacement

Pre- and postoperative arterial blood samples were analysed for oxygen partial pressure (PaO2) and carbon dioxide partial pressure (PaCO2) in a consecutive series of 21 patients subjected to two- or three-stage oesophagectomy for carcinoma of the oesophagus. The forced vital capacity (FVC) was measured at the same time. On the second postoperative day the PaO2 showed a fall to 65 per cent of the preoperative value followed by a gradual recovery to 78 per cent on the tenth postoperative day. After 13 weeks the PaO2 had recovered to 95 per cent of the preoperative value. The PaCO2 decreased in the early postoperative period but had returned to the preoperative level by the tenth day. The FVC showed a trend similar to the PaO2 with a reduction to 33 per cent of the preoperative value on the second postoperative day, 52 per cent on the tenth day and 85 per cent after 13 weeks.

A monolayer study of the reaction of trinitrobenzene sulphonic acid with amino phospholipids

The reaction of trinitrobenzene sulphonic acid with amino phospholipids, and in particular phosphatidylethanolamine has been studied by the monolayer technique. Injection of trinitrobenzene sulphonic acid under a monolayer of amino phospholipid results in an increase in surface pressure. The rate and extent of the pressure change is greatly affected by the initial surface pressure, the fatty acid composition of the lipid, and the presence of other non-reactive lipids, especially negatively charged phospholipids. The extent of the reaction was measured with 32P-labelled phospholipids isolated from Bacillus subtilis. Only about 80% of the phosphatidylethanolamine in the monolayer could be converted to its trinitrophenyl derivative. In the presence of negatively charged phospholipids such as cardiolipin or phosphatidylglycerol, a further 20% decrease in the trinitrophenylation of phosphatidylethanolamine was found. The pressure increase occurring during trinitrophenylation could also be correlated with the extent of the reaction by comparison of the force-area curves of pure phosphatidylethanolamine, its trinitrophenyl derivative and mixtures of both compounds. The data may offer an explanation for the observation that incomplete labelling of amino phospholipids frequently occurs in natural membranes and furthermore indicate that the use of chemical labelling techniques in the study of lipid asymmetry in biological membranes must be approached with great caution.

Changes in the lipid composition of ripening banana fruits and evidence for an associated increase in cell membrane permeability

The content of total lipid in banana fruit pulp tissue remained constant during the climacteric rise induced by applied ethylene. The relative proportions of neutral lipid, glycolipid and phospholipid did not change. However, the fatty acid composition of the lipid did change during ripening. This change was confined largely to the phospholipid fraction, in which there was an increase in the proportion of linolenic acid and a decrease in the proportion of linoleic acid. The net result was an increase in total unsaturation of the fatty acids in the phospholipid fraction. Measurements of spin label motion in liposomes prepared from banana phospholipids showed that the motion and fluidity of bilayer lipids increased during ripening of the fruit from which the liposomes were prepared, probably as a result of increased lipid unsaturation during ripening. Since increases in membrane fluidity are accompanied by increases in the passive permeability to small molecules in a number of membrane systems, it is suggested that the increased leakage which has been previously demonstrated in ripening banana fruit tissue is due to increases in the permeability of at least some cell membranes.

Studies on chloroplast membranes. III. 13C chemical shifts and longitudinal relaxation times of 1,2-Diacyl-3-(6-sulpho-α-quinovosyl)-sn-glycerol

13C Chemical shifts, longitudinal relaxation times and some nuclear Overhauser enhancement factors of the individual carbon atoms in the chloroplast lipid, 1,2-diacyl-3-(6-sulpho-α-quinovosyl)-sn-glycerol (sl), have been measured in the three solvents: methanol[D4], chloroform[D] and water[D2]. Correlation times for the individual carbon atoms calculated from these results have been interpreted in terms of different secondary structures: a monomeric structure in methanol[D4], an inverted micellar structure in chloroform[D] and a bilayer vesicular structure in water[D2]. Substituent shift parameters have been determined for the sulphonic acid group from a series of alkanesulphonic acids and these have been used in the 13C chemical shift assignments in sl and a series of model compounds.

Lipid Composition of Slender Tuna (Allothunnus fallai) as Related to Lipid Composition of Their Feed (Nyctiphanes australis)

The depot lipids of specimens of slender tuna (Allothunnus fallai) were characteristic of the zooplankton (Nyctiphanes australis) on which each was feeding. The lipids of the "krill" and of the depot fats were unusually rich in eicosaenoic and docosahexaenoic acids, although the fatty acid composition of samples of "krill" from individual tuna stomachs varied markedly and this variation was reflected in the fatty acid composition of the tuna depot lipids.Because of the nature of their diet, the composition of the depot lipids of the slender tuna varied significantly from those of other tuna species. However, the liver lipids of the slender tuna were more characteristic of all fish liver oils.