Haemodynamic effects of methoxyflurane versus fentanyl and placebo in hypovolaemia: a randomised, double-blind crossover study in healthy volunteers

Background

Methoxyflurane is approved for relief of moderate to severe pain in conscious adult trauma patients: it may be self-administrated and is well suited for use in austere environments. Trauma patients may sustain injuries causing occult haemorrhage compromising haemodynamic stability, and it is therefore important to elucidate whether methoxyflurane may adversely affect the haemodynamic response to hypovolaemia.

Methods

In this randomised, double-blinded, placebo-controlled, three-period crossover study, inhaled methoxyflurane 3 ml, i.v. fentanyl 25 μg, and placebo were administered to 15 healthy volunteers exposed to experimental hypovolaemia in the lower body negative pressure model. The primary endpoint was the effect of treatment on changes in cardiac output, while secondary endpoints were changes in stroke volume and mean arterial pressure and time to haemodynamic decompensation during lower body negative pressure.

Results

There were no statistically significant effects of treatment on the changes in cardiac output, stroke volume, or mean arterial pressure during lower body negative pressure. The time to decompensation was longer for methoxyflurane compared with fentanyl (hazard ratio 1.9; 95% confidence interval 0.4-3.4; P=0.010), whereas there was no significant difference to placebo (hazard ratio -1.3; 95% confidence interval -2.8 to 0.23; P=0.117).

Conclusions

The present study does not indicate that methoxyflurane has significant adverse haemodynamic effects in conscious adults experiencing hypovolaemia.

Clinical trial registration

ClinicalTrials.gov (NCT04641949) and EudraCT (2019-004144-29) https://www.clinicaltrialsregister.eu/ctr-search/trial/2019-004144-29/NO.

Sodium appetite and thirst do not require angiotensinogen production in astrocytes or hepatocytes

In addition to its renal and cardiovascular functions, angiotensin signalling is thought to be responsible for the increases in salt and water intake caused by hypovolaemia. However, it remains unclear whether these behaviours require angiotensin production in the brain or liver. Here, we use in situ hybridization to identify tissue-specific expression of the genes required for producing angiotensin peptides, and then use conditional genetic deletion of the angiotensinogen gene (Agt) to test whether production in the brain or liver is necessary for sodium appetite and thirst. In the mouse brain, we identified expression of Agt (the precursor for all angiotensin peptides) in a large subset of astrocytes. We also identified Ren1 and Ace (encoding enzymes required to produce angiotensin II) expression in the choroid plexus, and Ren1 expression in neurons within the nucleus ambiguus compact formation. In the liver, we confirmed that Agt is widely expressed in hepatocytes. We next tested whether thirst and sodium appetite require angiotensinogen production in astrocytes or hepatocytes. Despite virtually eliminating expression in the brain, deleting astrocytic Agt did not reduce thirst or sodium appetite. Despite markedly reducing angiotensinogen in the blood, eliminating Agt from hepatocytes did not reduce thirst or sodium appetite, and in fact, these mice consumed the largest amounts of salt and water after sodium deprivation. Deleting Agt from both astrocytes and hepatocytes also did not prevent thirst or sodium appetite. Our findings suggest that angiotensin signalling is not required for sodium appetite or thirst and highlight the need to identify alternative signalling mechanisms. KEY POINTS: Angiotensin signalling is thought to be responsible for the increased thirst and sodium appetite caused by hypovolaemia, producing elevated water and sodium intake. Specific cells in separate brain regions express the three genes needed to produce angiotensin peptides, but brain-specific deletion of the angiotensinogen gene (Agt), which encodes the lone precursor for all angiotensin peptides, did not reduce thirst or sodium appetite. Double-deletion of Agt from brain and liver also did not reduce thirst or sodium appetite. Liver-specific deletion of Agt reduced circulating angiotensinogen levels without reducing thirst or sodium appetite. Instead, these angiotensin-deficient mice exhibited an enhanced sodium appetite. Because the physiological mechanisms controlling thirst and sodium appetite continued functioning without angiotensin production in the brain and liver, understanding these mechanisms requires a renewed search for the hypovolaemic signals necessary for activating each behaviour.

A case of atypical vivax malaria with a global review of reports on myriads of morpho-variations in parasitized red blood cells

Plasmodium vivax, one of the major species associated with human malaria, continues to be a major public health problem in many parts of the world. Numerous studies related to vivax malaria have described quantitative haematological findings (level of haemoglobin, thrombocytopaenia, haematocrit values), but diverse morphological changes of parasite forms within infected red blood cells (iRBCs) have been mentioned only in few studies. Here we report a case of a 13-year-old boy who presented with fever, significant low platelet counts and hypovolaemia that created a diagnostic dilemma. Detection of microgametocytes by microscopic examinations, further confirmed by multiplex nested PCR assays and response to anti-malarials, helped to make the diagnosis. We present an atypical case of vivax malaria with a review of morpho-variations of iRBCs and have summarized the characteristics that aid in creating increased awareness among laboratory health professionals and public health workers.

Ultrasonographic assessment of the caudal vena cava diameter in cats during blood donation

OBJECTIVES

Ultrasonography of the caudal vena cava (CVC) has been previously established to assess fluid status in dogs but not in cats. The aim of this study was to determine CVC diameter changes during feline blood donation.

METHODS

Inter- and intra-observer variability were assessed in 11 client-owned cats. Minimal and maximal CVC diameters were assessed longitudinally in the subxiphoid view (SV) and right paralumbar view (PV), and transversely in the right hepatic intercostal view (HV). Eighteen client-owned, healthy, anaesthetised cats were evaluated during 21 blood donation procedures of 10 ml/kg in the same anatomical locations before (T0) and after (T1) blood donation, and after volume resuscitation with 30 ml/kg lactated Ringer's solution (T2). The CVC index was calculated.

RESULTS

Intra-observer variability was acceptable for all probe positions, except for the HV, whereas inter-observer variability was considered unacceptable for all probe positions. Complete measurements were obtained during 21 blood donations at T0, T1 and T2 at the SV, during 18/21 blood donations at the HV and during 16/21 blood donations at the PV. At the SV, the minimal CVC diameter between T1 and T2 (P <0.001), and the maximal CVC diameter between T0 and T1 and between T1 and T2 (P <0.001) were significantly different. At the HV, the minimal vertical diameter, maximal vertical diameter and minimal horizontal diameter were different between all timepoints (P <0.001). The maximal horizontal diameter was different between T1 and T2 (P = 0.002). At the PV, both diameters were different between all timepoints (P <0.001). The CVC index was not different between timepoints.

CONCLUSION AND RELEVANCE

Significant probe position dependent CVC diameter changes with marked overlap were observed before and after blood donation, and after fluid bolus. No absolute CVC diameter could be used to indicate hypovolaemia. Ultrasonographic assessment of the feline CVC is highly operator-dependent. The CVC index is not useful in cats.

Pseudo-pheochromocytoma due to obstructive sleep apnea: a case report

SUMMARY

Obstructive sleep apnea (OSA) is a condition of intermittent nocturnal upper airway obstruction. OSA increases sympathetic drive which may result in clinical and biochemical features suggestive of pheochromocytoma. We present the case of a 65-year-old male with a 2.9-cm left adrenal incidentaloma on CT, hypertension, symptoms of headache, anxiety and diaphoresis, and persistently elevated 24-h urine norepinephrine (initially 818 nmol/day (89-470)) and normetanephrine (initially 11.2 µmol/day (0.6-2.7)). He was started on prazosin and underwent left adrenalectomy. Pathology revealed an adrenal corticoadenoma with no evidence of pheochromocytoma. Over the next 2 years, urine norepinephrine and normetanephrine remained significantly elevated with no MIBG avid disease. Years later, he was diagnosed with severe OSA and treated with continuous positive airway pressure. Urine testing done once OSA was well controlled revealed complete normalization of urine norepinephrine and normetanephrine with substantial symptom improvement. It was concluded that the patient never had a pheochromocytoma but rather an adrenal adenoma with biochemistry and symptoms suggestive of pheochromocytoma due to untreated severe OSA. Pseudo-pheochromocytoma is a rare presentation of OSA and should be considered on the differential of elevated urine catecholamines and metanephrines in the right clinical setting.

LEARNING POINTS

Obstructive sleep apnea (OSA) is a common condition among adults. OSA may rarely present as pseudo-pheochromocytoma with symptoms of pallor, palpitations, perspiration, headache, or anxiety. OSA should be considered on the differential of elevated urine catecholamines and metanephrines, especially in patients with negative metaiodobenzylguanidine (MIBG) scan results.

Renin signals renal hypoperfusion during Parkland fluid resuscitation of severe burns - a prospective longitudinal cohort study

INTRODUCTION

Previous investigations have shown that fluid resuscitation of burns using the Parkland formula results in controlled hypovolaemia and that kidney injury is a common complication. Enhancing monitoring of tissue perfusion might reduce complications. Plasma renin has recently been suggested to be a promising marker for tissue hypoperfusion in intensive care patients. The aim of this study was to explore plasma renin levels during the first 48 hours after major burns in patients resuscitated using the Parkland formula.

MATERIALS AND METHODS

Patients 18 years or older of age with 10% or more total body surface area (TBSA) burned, admitted to Linköping Burn Intensive Care Unit, and resuscitated using the Parkland formula were included. Samples for plasma renin were drawn at admission and eight-hourly thereafter for 48 hours.

RESULTS

Fifteen patients were included. Median TBSA burned was 36% and age 53 years. The fluid volumes provided were in accordance with the Parkland formula. Mean arterial pressure, urinary output, and lactate remained within reference ranges during the first 48 hours. At eight hours after burn median plasma renin was elevated to more than 25 times the upper reference value, decreasing to about four times the upper reference at 48 hours. Renin concentration was associated with lactate levels and TBSA burned.

CONCLUSION

During Parkland fluid resuscitation of severe burns, plasma renin levels were extremely elevated. The fact that the traditionally used endpoints for Parkland fluid resuscitation remained within the reference range raises concerns about whether the increased renin concentrations may signal a relative renal hypoperfusion.

Paradoxical pulse

For thousands of years, palpation of the peripheral pulse was the most important source of information for the physicians about their patients' circulation. The rate, amplitude, and pattern of the pulse served as a basis of amazing observations, although several of them have been also confirmed and substantiated by modern medicine. One of the classical signs is "paradoxical pulse" (PP), which signals potentially life-threatening conditions with various mechanisms in certain diseases. In our review, we demonstrate the pathophysiological bases of PP, and show the equivalents of this sign provided by modern medical equipments. Orv Hetil. 2020; 161(38): 1629-1635.

The impact of fluid optimisation before induction of anaesthesia on hypotension after induction

Intra-operative hypotension is a known predictor of adverse events and poor outcomes following major surgery. Hypotension often occurs on induction of anaesthesia, typically attributed to hypovolaemia and the haemodynamic effects of anaesthetic agents. We assessed the efficacy of fluid optimisation for reducing the incidence of hypotension on induction of anaesthesia. This prospective trial enrolled 283 patients undergoing radical cystectomy and randomly allocated them to goal-directed fluid therapy (n = 142) or standard fluid therapy (n = 141). Goal-directed fluid therapy patients received fluid optimisation based on stroke volume response to passive leg raise before induction; those with positive passive leg raise received intravenous crystalloid fluid boluses until stroke volume was optimised. Baseline mean arterial pressure was measured on the morning of surgery and on arriving in the operating theatre. This post-hoc analysis defined haemodynamic instability as either a > 30% relative drop in mean arterial pressure compared with baseline or absolute mean arterial pressure < 55 mmHg, within 15 min of induction. Forty-two (30%) goal-directed fluid therapy patients underwent fluid optimisation after finding an intravascular fluid deficit via passive leg raise testing; 106 (75%) goal-directed fluid therapy and 112 (79%) standard fluid therapy patients met criteria for haemodynamic instability. There was no significant difference in the incidence of haemodynamic instability between the goal-directed fluid therapy and standard fluid therapy groups using absolute mean arterial pressure drop below 55 mmHg (p = 0.58) or using pre-surgical testing or pre-surgical mean arterial pressure values as baseline (p = 0.21, p = 0.89, respectively); however, the difference in the incidence of haemodynamic instability was significant using the operating theatre baseline mean arterial pressure (p = 0.004). We conclude that fluid optimisation before induction of general anaesthesia did not significantly impact haemodynamic instability.

Pseudohypertrophy of the left ventricle secondary to anaphylaxis: A case report

We report a case of pseudohypertrophy of the left ventricle secondary to hypovolaemia from anaphylaxis. The patient was a healthy young female who developed anaphylaxis during a general anaesthetic. A transthoracic echocardiogram performed during the anaphylaxis crisis demonstrated significant left ventricular hypertrophy. However, when the anaphylaxis had resolved, a follow-up transthoracic echocardiogram demonstrated a normal left ventricular wall thickness. This left ventricular hypertrophy was a pseudohypertrophy as the left ventricular mass was normal and the wall thickness normalised when the hypovolaemia and anaphylaxis had resolved. Pseudohypertrophy of the left ventricle is an echocardiographic finding that suggests hypovolaemia. Furthermore, this echocardiographic finding supports the importance of volume resuscitation in the management of anaphylaxis. This phenomenon may be more frequently reported in the future due to the wider availability of point-of-care ultrasonography along with an increase in the number of physicians trained in echocardiography.

Diagnostic accuracy of a calibrated abdominal compression to predict fluid responsiveness in children

BACKGROUND

Fluid administration to increase stroke volume index (SVi) is a cornerstone of haemodynamic resuscitation. We assessed the accuracy of SVi variation during a calibrated abdominal compression manoeuvre (ΔSVi-CAC) to predict fluid responsiveness in children.

METHODS

Patients younger than 8 yr with acute circulatory failure, regardless of their ventilation status, were selected. SVi, calculated as the average of five velocity-time integrals multiplied by the left ventricular outflow tract surface area, was recorded at four different steps: baseline, after an abdominal compression with a calibrated pressure of 25 mm Hg, after return to baseline, and then after a volume expansion (VE) of 10 ml kg^-1 lactated Ringer solution over 10 min. Patients were classified as responders if SVi variation after volume expansion (ΔSVi-VE) increased by at least 15%.

RESULTS

The 39 children included had a median [inter-quartile range (IQR)] age of 9 [5-31] months. Twenty patients were fluid responders and 19 were non-responders. ΔSVi-CAC correlated with ΔSVi-VE (r=0.829; P<0.001). The area under the receiver operating characteristic curve (ROC_AUC) was 0.94 [95% confidence interval (CI), 0.85-0.99]. The best threshold for ΔSVi-CAC was 11% with a specificity of 95% [95% CI, 84-100] and a sensitivity of 75% [95% CI, 55-95]. ROC_AUC of respiratory variation of IVC diameter (ΔIVC) was 0.53 [95% CI, 0.32-0.72].

CONCLUSION

ΔSVi-CAC during abdominal compression was a reliable method to predict fluid responsiveness in children with acute circulatory failure regardless of their ventilation status.

CLINICAL TRIALS REGISTRATION

CPP Lyon sud est II: n° ANSM 2015-A00388-41 Clinicaltrial.gov: NCT02505646.

Management of Diarrhoeal Dehydration in Childhood: A Review for Clinicians in Developing Countries

The survival of a child with severe volume depletion at the emergency department depends on the competency of the first responder to recognize and promptly treat hypovolemic shock. Although the basic principles on fluid and electrolytes therapy have been investigated for decades, the topic remains a challenge, as consensus on clinical management protocol is difficult to reach, and more adverse events are reported from fluid administration than for any other drug. While the old principles proposed by Holliday and Segar, and Finberg have stood the test of time, recent systematic reviews and meta-analyses have highlighted the risk of hyponatraemia, and hyponatraemic encephalopathy in some children treated with hypotonic fluids. In the midst of conflicting literature on fluid and electrolytes therapy, it would appear that isotonic fluids are best suitable for the correction of hypotonic, isonatraemic, and hypernatraemic dehydration. Although oral rehydration therapy is adequate to correct mild to moderate isonatraemic dehydration, parenteral fluid therapy is safer for the child with severe dehydration and those with changes in serum sodium. The article reviews the pathophysiology of water and sodium metabolism and, it uses the clinical case examples to illustrate the bed-side approach to the management of three different types of dehydration using a pre-mixed isotonic fluid solution (with 20 or 40 mmol/L of potassium chloride added depending on the absence or presence of hypokalemia, respectively). When 3% sodium chloride is unavailable to treat hyponatraemic encephalopathy, 0.9% sodium chloride becomes inevitable, albeit, a closer monitoring of serum sodium is required. The importance of a keen and regular clinical and laboratory monitoring of a child being rehydrated is emphasized. The article would be valuable to clinicians in less-developed countries, who must use pre-mixed fluids, and who often cannot get some suitable rehydrating solutions.

Assessment of hypovolaemia in the critically ill

Assessment of the intravascular volume status of patients is one of the most challenging tasks for the intensive care clinician. It is also one of the most important skills in intensive care management as both hypervolaemia and hypovolaemia lead to increased morbidity and mortality. The assessment of hypovolaemic patients is aided by several clinical signs, laboratory investigations, and a multitude of haemodynamic monitoring systems. This review aims to outline the definitions, pathophysiology, and various assessment techniques (both old and new) employed by intensivists on the critically ill patient.

Epigenetic Control of the Vasopressin Promoter Explains Physiological Ability to Regulate Vasopressin Transcription in Dehydration and Salt Loading States in the Rat

The synthesis of arginine vasopressin (AVP) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus is sensitive to increased plasma osmolality and a decreased blood volume, and thus is robustly increased by both dehydration (increased plasma osmolality and decreased blood volume) and salt loading (increased plasma osmolality). Both stimuli result in functional remodelling of the SON and PVN, a process referred to as functional-related plasticity. Such plastic changes in the brain have recently been associated with altered patterns of DNA methylation at CpG (cytosine-phosphate-guanine) residues, a process considered to be important for the regulation of gene transcription. In this regard, the proximal Avp promoter contains a number of CpG sites and is recognised as one of four CpG islands for the Avp gene, suggesting that methylation may be regulating Avp transcription. In the present study, we show that, in an immortalised hypothalamic cell line 4B, the proximal Avp promoter is highly methylated, and treatment of these cells with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine to demethylate DNA dramatically increases basal and stimulated Avp biosynthesis. We report no changes in the expression of DNA methyltransferases, Dnmt1 and Dnmt3a, whereas there is decreased expression of the demethylating enzyme ten-eleven-translocation 2, Tet2, in the SON by dehydration and salt loading. We found higher methylation of the SON Avp promoter in dehydrated but not salt-loaded rats. By analysis of individual CpG sites, we observed hypomethylation, hypermethylation and no change in methylation of specific CpGs in the SON Avp promoter of the dehydrated rat. Using reporter gene assays, we show that mutation of individual CpGs can result in altered Avp promoter activity. We propose that methylation of the SON Avp promoter is necessary to co-ordinate the duel inputs of increased plasma osmolality and decreased blood volume on Avp transcription in the chronically dehydrated rat.

Pulse pressure variation does not reflect stroke volume variation in mechanically ventilated rats with lipopolysaccharide-induced pneumonia

1. The present study examined the relationship between centrally measured stroke volume variation (SVV) and peripherally derived pulse pressure variation (PPV) in the setting of increased total arterial compliance (CA rt ). 2. Ten male Wistar rats were anaesthetized, paralysed and mechanically ventilated before being randomized to receive intrapulmonary lipopolysaccharide (LPS) or no LPS. Pulse pressure (PP) was derived from the left carotid artery, whereas stroke volume (SV) was measured directly in the left ventricle. Values of SVV and PPV were calculated over three breaths. Balloon inflation of a catheter positioned in the inferior vena cava was used, for a maximum of 30 s, to decrease preload while the SVV and PPV measurements were repeated. Values of CA rt were calculated as SV/PP. 3. Intrapulmonary LPS increased CA rt and SV. Values of SVV and PPV increased in both LPS-treated and untreated rats during balloon inflation. There was a correlation between SVV and PPV in untreated rats before (r = 0.55; P = 0.005) and during (r = 0.69; P < 0.001) occlusion of the vena cava. There was no such correlation in LPS-treated rats either before (r = -0.08; P = 0.70) or during (r = 0.36; P = 0.08) vena cava occlusion. 4. In conclusion, under normovolaemic and hypovolaemic conditions, PPV does not reflect SVV during an increase in CA rt following LPS-induced pneumonia in mechanically ventilated rats. Our data caution against their interchangeability in human sepsis.

Evolution of fluid therapy

The human organism consists of evolutionary conserved mechanisms to prevent death from hypovolaemia. Intravenous fluid therapy to support these mechanisms had first been published about 180 years ago. The present review depicts the evolution of fluid therapy from early, not well-defined solutions up to modern balanced fluids. Notably, evidence accumulates that the most commonly used fluid (i.e. 0.9% saline) has no advantage over balanced solutions, increases the risk of acute kidney injury and should therefore be abandoned. Notably, in published trials, the prognostically important 'golden hours' of shock, where fluid therapy may be essential, have not been adequately addressed. It is therefore unclear whether negative data on colloids in some trials reflect real harm or rather inadequate use. Future studies should focus on optimal protocols for initiation, dosing and discontinuation of fluid therapy in specific disease entities. Moreover, the practice of de-resuscitation after fluid-based haemodynamic stabilization should be further investigated.

Cardiac arrhythmias associated with acute major haemorrhage during craniectomy in a dog

An estimated 43% of total blood volume was lost during craniectomy in a 32-kg Labrador retriever. One episode of bradycardia, followed by ventricular tachycardia occurred during surgery when the rate of haemorrhage exceeded fluid replacement. Sinus rhythm was re-established with intravenous lidocaine (1.25 mg kg^-1). Twenty-four hours later, premature ventricular complexes appeared followed by episodes of ventricular tachycardia, some requiring lidocaine treatment. Myocardial hypoxia resulting either from hypovolaemia and/or air embolism (the right transverse venous sinus was damaged during surgery) may have caused the arrhythmias. Mild intracranial hypertension may have aggravated the problem.

Debate: Albumin administration should not be avoided

The recent Cochrane report on albumin administration is analysed and criticised on the grounds of clinical methodology, content and interpretation. Although it is naïve and illogical to treat hypoalbuminaemia with albumin infusions, a more balanced view on the use of albumin for resuscitation in acute hypovolaemia is necessary. Once the acute phase of critical illness is past, interstitial volume is often expanded causing oedema, with a low plasma volume. We argue for the use of salt-poor albumin solutions in this situation and conclude that, on current evidence, the assertion that albumin should be avoided in all situations is irrational and untenable.