The imaginary line method is not reliable for identification of prosthetic heart valves on AP chest radiographs

OBJECTIVE

To examine the utility of four criteria for distinguishing aortic from mitral valve prostheses on supine anteroposterior (AP) chest x rays in critically ill patients.

MATERIALS AND METHODS

Two reviewers independently examined the post operative chest X-rays (CXR) of all patients undergoing either an aortic or mitral valve replacement over a 32 month period, in a blinded fashion. They applied four criteria to each film. For each criterion a sensitivity and specificity of differentiating the valve positions correctly was calculated for each reviewer, as well as a kappa statistic for inter-observer agreement between the two reviewers.

RESULTS

Two hundred and twenty seven CXR's were evaluated by each of the reviewers. There were 174 aortic and 53 mitral valve replacements. There was a high level of inter-observer agreement for all four criteria applied (kappa values 0.785 to 0.966). Criterion one (imaginary line method) could be applied by both reviewers to less than 50% of CXR's, and when applied was specific but not sensitive. The other three criteria could be applied by both reviewers to approximately 80% of films. Criterion 2 (orientation method) was sensitive but not specific. Criteria 3 (valve orifice method) and 4 (perceived direction of blood flow method) were both highly sensitive and specific and are therefore the best methods.

CONCLUSIONS

The well known imaginary line method is of limited value when identifying prosthetic valve positions on supine AP CXR's. We advocate the use of the "valve orifice" method or the "perceived direction of blood flow" method to gain valuable information regarding the presence and position of prosthetic heart valves.

Experiences of anticholinesterase pesticide poisonings in an Australian tertiary hospital

There is limited information regarding the management and outcomes of patients presenting with anticholinesterase pesticide poisoning in Australia. Patients presenting to a tertiary referral hospital with anticholinesterase exposures were identified by discharge coding. The medical records of each patient were retrospectively reviewed. Based on clinical outcome, patients were classified as severe or non-severe poisonings. Forty-one presentations were noted between 1990 and 2003. Eight patients (20%) had severe poisoning of which tachycardia, fasciculations with weakness and metabolic acidosis were common manifestations. The diagnosis was delayed in four patients due to the absence of a clear history, which did not influence patient outcomes or put hospital staff at risk of nosocomial poisoning. The median length of hospital stay was prolonged in severe poisonings (20 days) compared to 12 hours in other patients. Two cases of intermediate syndrome were attributed to fenthion and diazinon, and one case of delayed polyneuropathy to trichlorfon. Cholinesterase activities were performed in only 49% of presentations. The overall mortality was 2.4% (1 death) and the mortality in patients with severe poisoning was 12.5%. The incidence of anticholinesterase poisoning in Australia is low. These outcomes were favourable and comparable with other published data. Measures to enhance the knowledge of medical staff supplemented by validated treatment protocols should be developed. For less significant exposures, an emphasis on adequate documentation of cholinergic signs and cholinesterase activities is necessary for rapid triage and may also have potential forensic implications if not performed.

Monitoring cerebral perfusion and oxygenation: an elusive goal

The impetus for cerebral hemodynamic monitoring in neurotrauma first arose from the original "talk and die" studies which described the group of head injured patients "who talk and then subsequently died". At necropsy, hypoxic or ischaemic brain damage was observed in a variable proportion of patients raising the possibility that systemic or cerebral hypoxia post trauma may have contributed to the poor neurological outcome. Improved understanding of the pathophysiology of neurotrauma influenced clinical practice in two ways: a) there was a plethora of monitoring modalities developed for evaluating cerebral hemodynamics and oxygenation and b) squeezing oxygenated blood through a swollen brain became the cornerstone of therapy in patients with head injury. Whilst there appears to be some agreement on the principles of management of neurotrauma, opinion still remains divided on what provides the best assessment of cerebral perfusion and oxygenation. Although initial monitoring was largely confined to global indices of brain oxygenation, refinement in technology has made the measurement of oxygen tensions further down in the oxygen cascade at the level of the tissue possible and applicable by the bedside. Metabolic monitoring of the brain is now possible with the use of a variety of biochemical indices and with the availability of microdialysis. The purpose of this review is to examine the various modes of monitoring cerebral oxygenation, critically review the literature concerning their use in day to day intensive care practice, outline their limitations and define possible indications for their use.

Mapping of three translocation breakpoints associated with orofacial clefting within 6p24 and identification of new transcripts within the region

Orofacial clefting (OFC) is a common congenital malformation. Here we report the refinement of three translocation breakpoints of patients exhibiting OFC within the 6p24 region, and the isolation and characterisation of novel genes, one of which is directly disrupted by the translocation breakpoint of a patient. The gene has been characterized and orthologues identified in bovine, murine and pufferfish.

Assessment of adrenocortical function in the critically ill

OBJECTIVE

To review current concepts in the diagnosis of adrenocortical disease in the critically ill patient.

DATA SOURCES

A review of articles reported on adrenocortical insufficiency in the acutely ill patient.

SUMMARY OF REVIEW

The contribution of adrenal insufficiency to the morbidity of critically ill patients is currently under renewed scrutiny. The debate continues about the role of steroids in sepsis and essentially the question remains unanswered. Central to this debate is the issue of whether adrenal insufficiency is common in the critically ill patient. What is incontrovertible is that adrenocortical function is essential for host survival during critical illness, but what constitutes adrenocortical insufficiency in critically ill patients is not clear. Absolute adrenocortical insufficiency (diagnosed by very low plasma cortisol concentrations) is uncommon in the intensive care population. The diagnosis of relative adrenocortical insufficiency (elevated basal plasma cortisol with a subnormal increase in plasma concentrations following an ACTH stimulus) continues to generate debate. The controversy surrounding the role of steroids in sepsis and the confusion over the criteria for diagnosing adrenal insufficiency in the critically ill are reviewed.

CONCLUSIONS

We suggest that the following caveats be borne in mind when diagnosing adrenal insufficiency in the critically ill patient. Firstly, the gold standard for the diagnosis has not been established. Secondly, caution must be exercised when interpreting a single plasma cortisol value. In the event of a single result indicating adrenal hypofunction, we suggest repeating the measurements after a 6 to 12 hour interval. The clinician must also be aware of variations in cortisol concentrations induced by the assay. Thirdly, the clinician must be aware of the potential limitations of the conventional high dose corticotrophin test. We also suggest that plasma free cortisol is more relevant than total plasma cortisol in the assessment of adrenal function in critical illness and that the low dose corticotrophin test is more sensitive than the conventional high dose test. These areas should be the subject of further investigations.

Indices to quantify changes in intracranial and cerebral perfusion pressure by assessing agreement between hourly and semi-continuous recordings

OBJECTIVES

Little published data exists on whether nurse-recorded end-hour values of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are representative of continuous monitoring during the hour. There is also no standard method of quantifying the observed perturbations in cerebral hemodynamics. This study compared the level of agreement between end-hour values and computer downloaded observations of ICP and CPP at 15-min intervals. We also developed the intracranial hypertension index and the cerebral hypoperfusion index to quantify perturbations in cerebral hemodynamics. Each of these indices relates the number of abnormal observations to the total number of observations taken.

METHODS

Prospective, non-interventional study.

RESULTS

The bias and precision between the two methods for ICP and CPP were -0.002+/-2.6 mmHg and -1.1+/-6.2 mmHg, respectively. A strong correlation existed between the hourly mean calculated from the 15-min and the end-hour values for both ICP ( r(2)=0.95, p<0.0001) and CPP ( r(2)=0.78, p<0.001). The intracranial hypertension index was 40% from the 15-min measurements and 41% from the hourly observations ( p= NS). The cerebral hypoperfusion indices were 13.4% and 13.1% with the 15-min and end-hour values, respectively ( p= NS).

CONCLUSIONS

The end-hour values of ICP and CPP are as accurate as more frequent measurements during the hour and are adequate for purposes of epidemiological research and medico-legal audit. The intracranial hypertension and cerebral hypoperfusion indices may be useful in describing cerebral hemodynamics for future interventional studies and for assessing quality in the delivery of neuro-critical care.

Designing 'balanced' crystalloids

OBJECTIVE

To present a rationale for the design of balanced resuscitation and renal replacement crystalloids based on Stewart's physical chemical approach to acid-base.

DATA SOURCES

Articles and published abstracts on acid-base physiology, crystalloid infusions and renal replacement therapy.

SUMMARY OF REVIEW

Although it is uncertain that crystalloid-induced metabolic acidosis causes significant harm, Stewart's approach assists in designing balanced fluids without this side effect. In his analysis, the three independent variables determining acid-base balance are PCO2, the total concentration of non-volatile weak acid (A(TOT)) and the strong ion difference (SID). Raising and lowering A(TOT) while holding SID constant cause a metabolic acidosis and alkalosis respectively. Lowering and raising plasma SID while clamping A(TOT) cause a metabolic acidosis and alkalosis respectively. The SID of a crystalloid is its [HCO3-], or that part of an organic bicarbonate surrogate which is metabolised on infusion. Rapid infusion alters plasma SID towards crystalloid SID, but also lowers A(TOT) by haemodilution. We have shown that the SID of a balanced infusion crystalloid is 24 mEq/L. This generates a fall in plasma SID precisely counteracting the A(TOT) dilutional alkalosis. In contrast, a balanced renal replacement crystalloid must generate a higher plasma SID appropriate for the existing A(TOT), since there is no dilution. If A(TOT) is low, as in hypoalbuminaemia, the balanced dialysis SID falls correspondingly. A further SID reduction is needed to counteract Donnan effects within the filter.

CONCLUSIONS

A crystalloid SID of 24 mEq/L is 'balanced' for rapid intravenous administration. The 'balanced' SID of renal replacement fluids is likely to be significantly higher, although less than the normal plasma SID of 42 mEq/L.

Neurone-specific expression and regulation of the pufferfish isotocin and vasotocin genes in transgenic mice

We used comparative genetics to investigate the location, structure and evolution of the oxytocin and vasopressin gene regulatory regions. The pufferfish, Fugu rubripes, is an attractive vertebrate model for comparison because of its maximal evolutionary distance from mammals and short intergenic regions. To determine whether regulatory DNA is conserved between oxytocin and vasopressin, and their Fugu homologs, isotocin and vasotocin, we generated transgenic mice bearing overlapping Fugu cosmids that contained the isotocin and/or vasotocin genes as well as short isotocin (5 kb) and vasotocin (9 kb) constructs. Our study shows that the Fugu isotocin and vasotocin genes express specifically in the mouse oxytocinergic and vasopressinergic neurones, respectively, and that the cis-regulatory elements which mediate neurone-specific expression are located within the short transgene constructs tested. Thus, the neurone-specific expression of the oxytocin and vasopressin gene families, and the mechanisms mediating the cell-specificity, evolved before the divergence of the fish and mammalian lineages. Salt-loading of transgenic mice induced an increase in abundance of isotocin, but not vasotocin mRNA in the cognate neurones. It appears that either the vasotocin gene does not respond to osmotic perturbations or the vasotocin transgene construct tested lacks osmotic response elements. Comparisons of homologous flanking sequences of the Fugu and mouse genes identified several short matching sequences, which are candidate regulatory elements.

Interpreting CSF lactic acidosis: effect of erythrocytes and air exposure

OBJECTIVE

Elevated cerebrospinal fluid (CSF) lactate concentrations in neurotrauma and sub-arachnoid haemorrhage are associated with a poor prognosis. However, in blood-stained CSF, elevated lactate levels may arise from red cell metabolism, even without ischaemia, potentially reducing specificity. This study was undertaken to quantify the erythrocyte contribution to CSF lactate measurements, with and without, exposure to room air.

METHODS

Blood was added to CSF to achieve three different red cell concentrations. The CSF was then exposed at 37 degrees C to either room air or 5% CO2 and 95% oxygen. Vancomycin and gentamycin were added to inhibit bacterial growth. Lactate concentrations and red cell concentrations were measured prior to the addition of blood and 10 minutes, 6 hours and 24 hours later. CSF without the addition of blood was used as a control.

RESULTS

In the control specimens there were no increases in CSF lactate concentrations over time, either in air or CO2, whereas all specimens with blood added demonstrated significant increases in lactate at 6 and 24 hours (P < 0.01). The lactate increases in both air and CO2 were correlated directly with red cell counts (R2 = 0.62 to 0.87). At all red cell concentrations, the mean lactate increase was greater in air.

CONCLUSIONS

Red cells in CSF cause significant increases in lactate concentrations, more so when exposed to air. This should be considered when interpreting lactate in blood stained CSF. Blood-stained CSF specimens for lactate assay should be collected directly from an external ventricular drain rather than a reservoir bag.

Monitoring tissue gas tensions in critical illness

OBJECTIVE

To review the technology and the role of monitoring tissue oxygenation in critical illness.

DATA SOURCES

Articles and published peer review abstracts on monitoring tissue oxygenation.

SUMMARY OF REVIEW

Miniaturised optodes and electrode systems are the commonly used technology for measurement of tissue gas tensions. Reductions in tissue perfusion frequently leads to a decrease in tissue PO2 and an increase in tissue PCO2 which has been confirmed in a number of animal and human trials in hypovolaemic shock. Monitoring tissue oxygenation has also enabled the delineation of cytopathic hypoxia, which is one of the important pathophysiological mechanisms of sepsis. Although these devices have improved our understanding of pathophysiological mechanisms of critical illness, at a clinical level titrating oxygen therapy to tissue oxygen tensions has only been shown to be useful in patients with impaired wound healing. A number of questions remain unanswered in relation to the monitoring of tissue oxygenation in critical illness. These include establishing normal values of PO2 and PCO2 in humans at the various tissue beds, establishing dysoxic thresholds for the various tissues, identifying optimal sites for monitoring and improving measurement accuracy. Furthermore, the nature of microcirculatory blood flow and tissue gas exchange in critical illness is complex and incompletely understood, limiting our ability to interpret changes from the baseline. Knowing critical tissue PO2 thresholds will provide the clinician with practical resuscitation endpoints in hypoxia and shock, and may even modify the practice of 'permissive hypoxia' in severe respiratory failure. These questions need answers in the years to come.

CONCLUSIONS

Monitoring of tissue oxygenation is largely a research tool. For its application in the critically ill patient there needs to be a greater understanding of normal values of PO2 and PCO2 at the various tissue beds, dysoxic thresholds for the various tissues and optimal sites for monitoring.

Outcome of stroke patients admitted to intensive care: experience from an Australian teaching hospital

The objective of this study was to determine the mortality rate and the functional outcomes of stroke patients admitted to the intensive care unit (ICU) and to identify predictors of poor outcome in this population. The records of all patients admitted to the ICU with the diagnosis of stroke between January 1994 and December 1999 were reviewed. Patients with subarachnoid haemorrhage were excluded. Data were collected on clinical and biological variables, risk factors for stroke and the presence of comorbidities. Mortality (ICU, in-hospital and three-month) and functional outcome were used as end-points. In the six-year-period, 61 patients were admitted to the ICU with either haemorrhagic or ischaemic stroke. Medical records were available for only 58 patients. There were 23 ischaemic and 35 haemorrhagic strokes. The ICU, in-hospital and three-month mortality rates were 36%, 47% and 52% respectively. There were no significant differences in the prevalence of premorbid risk factors between survivors and non-survivors. The mean Barthel score was significantly different between the independent and dependent survivors (94+/-6 vs 45+/-26, P<0.001). A substantial number of patients with good functional outcomes had lower Rankin scores (92% vs 11%, P<0.001). Only 46% of those who were alive at three months were functionally independent. Intensive care admission was associated with a high mortality rate and a high likelihood of dependent lifestyle after hospital discharge. Haemorrhagic stroke, fixed dilated pupil(s) and GCS <10 during assessment were associated with increased mortality and poor functional outcome.

Procalcitonin in critical illness

OBJECTIVE

To detail the biology and diagnostic usefulness of serum procalcitonin in critical illness.

DATA SOURCES

A review of articles published in peer reviewed journals from 1990 to 2001 and identified through a MEDLINE search on procalcitonin.

SUMMARY OF REVIEW

Procalcitonin (PCT) is a prohormone of calcitonin. Serum levels are elevated during sepsis and have been identified as a potential marker of infection in critical illness. However, its function and precise source of origin during sepsis remain unclear. The value of estimating serum PCT appears to be in the differentiation of infectious from non-infectious forms of systemic inflammatory response syndrome. A number of studies also point to its usefulness in distinguishing between bacterial and viral meningitis. However, there are a number of non-infectious conditions, where elevations in serum PCT occur, reducing its specificity. Its superiority as a marker of sepsis compared with other acute phase reactants continues to be debated.

CONCLUSIONS

The utility of serum procalcitonin as a diagnostic test of sepsis is still under evaluation. Moreover, a number of unanswered questions remain regarding the biological role of PCT during sepsis, its target receptors and its protective value to the patient.

Molecular synapomorphies resolve evolutionary relationships of extant jawed vertebrates

The evolutionary relationships of gnathostomes (jawed vertebrates), which comprise chondrichthyans (cartilaginous fishes), lobe-finned fishes (coelacanths and lungfishes), tetrapods, and actinopterygians (ray-finned fishes), have been debated for almost a century. Phylogenetic analyses based on fossils, morphology, and molecular sequences have generated different models of relationships that remain unresolved. We identified 13 derived shared molecular markers (synapomorphies) that define clades in the vertebrate lineage and used them to resolve the phylogenetic relationships of extant jawed vertebrates. Our markers include the presence or absence of insertions and deletions in coding sequences, nuclear introns, and alternatively spliced transcripts. The synapomorphies identified by us are congruent with each other and give rise to a single phylogenetic tree. This tree confirms that chondrichthyans are basal to all living gnathostomes, that lungfishes (Dipnoi) are the closest living relatives of tetrapods, and that bichirs (Cladistia) are the living members of the most ancient family of ray-finned fishes. Our study also provides molecular evidence to support the monophyly of living tetrapods and teleosts.

Conserved synteny between the Fugu and human PTEN locus and the evolutionary conservation of vertebrate PTEN function

Mutations of PTEN, which encodes a protein-tyrosine and lipid phosphatase, are prevalent in a variety of human cancers. The human genome 'draft' sequence still lacks organization and much of the PTEN and adjacent loci remain undefined. The pufferfish, Fugu rubripes, by virtue of having a compact genome represents an excellent template for rapid vertebrate gene discovery. Sequencing of 56 kb from the Fugu pten (fpten) locus identified four complete genes and one partial gene homologous to human genes. Genes neighboring fpten include a PAPS synthase (fpapss2) differentially expressed between non-metastatic/metastatic human carcinoma cell lines, an inositol phosphatase (fminpp1) and an omega class glutathione-S-transferase (fgsto). We have determined the order of human BAC clones at the hPTEN locus and that the locus contains hPAPSS2 and hMINPP1 genes oriented as are their Fugu orthologs. Although the human genes span 500 kb, the Fugu genes lie within only 22 kb due to the compressed intronic and intergenic regions that typify this genome. Interestingly, and providing striking evidence of regulatory element conservation between widely divergent vertebrate species, the compact 2.1 kb fpten promoter is active in human cells. Also, like hPTEN, fpten has a growth and tumor suppressor activity in human glioblastoma cells, demonstrating conservation of protein function.

Transient mesenteric ischaemic episodes tracked by continuous jejunal PCO2 monitoring during liquid feeding

OBJECTIVE

To test the effect of liquid feeds on the responses to splanchnic ischaemia of a continuous rapid response PCO2 sensor inserted in the jejunum.

DESIGN

Prospective experimental animal study in a university research laboratory.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

Adult male Wistar rats (285-425 g) were anaesthetised with sodium pentobarbitone 60 mg/kg i.p. and ventilated with 100% oxygen and isoflurane via tracheostomy to a PaCO2 of 30-40 mmHg. A sensor was inserted into the mid-jejunum to record PCO2 every second. Distal aortic pressure was transduced. Four control rats received no feeds whilst in another four rats liquid feed was infused into the proximal jejunum at 3 ml/h. In each rat five episodes of splanchnic ischaemia were induced by 2-min elevations of an aortic sling to a mean distal aortic pressure of 30 mmHg.

MEASUREMENTS AND MAIN RESULTS

PCO2 elevations were always detectable, usually less than a minute from the onset of splanchnic ischaemia in both fed and unfed rats, with no difference in mean times to detectable response. In the fed rats there was a small but significant increase in the time to peak sensor response (196+/-16 vs. 180+/-12 s) and a trend towards an elevated mean baseline luminal PCO2 (67+/-9 vs. 55+/-4 mmHg).

CONCLUSIONS

Brief episodes of splanchnic ischaemia were tracked successfully by a rapid response jejunal continuous PCO2 sensor during the infusion of a proprietary liquid feed preparation despite minor changes in PCO2 response characteristics and a possible elevation in baseline luminal PCO2.

Acute myocardial ischaemia in the presence of thrombotic thrombocytopenic purpura: what are the treatment options?

We describe a case of severe myocardial ischaemia in the setting of thrombotic thrombocytopoenic purpura (TTP). In this report, we discuss the potential difficulties in the diagnosis and management of acute myocardial ischaemia with TTP, particularly relating to the use of antiplatelet agents. We also highlight the importance of careful monitoring during plasma exchange for TTP when acute myocardial ischaemia is present. The potential role for novel therapies in the management of TTP related myocardial ischaemia is also discussed.

Monitoring tissue oxygenation during resuscitation of major burns

BACKGROUND

Because subcutaneous and splanchnic oxygenation indices are sensitive indicators of evolving hemorrhagic shock and adequacy of resuscitation, we postulated that these indices might have an equivalent role in the monitoring of severely burned patients. This observational study was undertaken to examine changes in tissue oxygenation indices during burn resuscitation.

METHODS

Seven patients with major burns (54 +/- 21% total body surface area) were studied during the first 36 hours of fluid resuscitation. Silastic tubing was placed in the subcutaneous tissue just beneath both normal skin and deep partial thickness burn. Fiberoptic sensors inserted into the tubing measured subcutaneous oxygen and carbon dioxide tensions in the burnt skin (PO2scb and PCO2scb) and normal skin (PO2scn and PCO2scn) continuously. Gastric intramucosal pH (pHi) and the mucosal CO2 (PCO2m) gap were calculated using gastric tonometers. Mean arterial pressure, arterial pH, lactate, and pHi measurements were obtained for 36 hours.

RESULTS

There were no significant differences in mean arterial pressure, arterial pH, or lactate concentrations throughout the study period, whereas indices of tissue oxygenation showed deterioration: pHi decreased from 7.2 +/- 0.1 to 6.7 +/- 0.3 (p = 0.06), the PCO2m gap increased from 12 +/- 17 to 108 +/- 123 mm Hg (p < 0.01), PO2scn decreased from 112 +/- 18 to 50 +/- 11 mm Hg (p < 0.01), PO2scb decreased from 62 +/- 23 to 29 +/- 16 mm Hg (p < 0.01), PCO2scn increased from 42 +/- 4 to 46 +/- 10 mm Hg (p = 0.2), and PCO2scb increased from 42 +/- 10 to 52 +/- 5 mm Hg (p = 0.05).

CONCLUSION

Despite adequate global indices of tissue perfusion after 36 hours of resuscitation, tissue monitoring indicated significant deterioration in the splanchnic circulation and in the normal and burnt skin.