A case report describes the improvement of a critically ill patient with H1N1 ‘flu after the administration of N-acetylcysteine in a dose similar to that used to treat paracetamol (acetaminophen) overdose.
Influenza virus induces reactive oxygen species that activate nuclear factor kappa B to produce cytokines. High-dose N-acetylcysteine, an antioxidant, is thought to reduce the production of this cytokine storm which contributes to the lethality of influenza. More studies are clearly needed.
High-Dose N-Acetylcysteine Therapy for Novel H1N1 Influenza Pneumonia
Ann Intern Med. 2010 May 18;152(10):687-8
Tag Archives: critical care
Lung Ultrasound Articles
Here are some sites that explain lung sonography as applied to critical care patients:
Clinical review: Bedside lung ultrasound in critical care practice – Critical Care Full Text
Evaluation of ultrasound lung comets by hand-held echocardiography – Cardiovascular Ultrasound Full Text
ICU Sonography Site – Lung Ultrasound Tutorial
Post cardiac arrest guideline
A patient is resuscitated from an out-of-hospital cardiac arrest and is in your emergency department, comatose, with a pulse.
You know that therapeutic hypothermia is indicated and are happy with the protocol for that. You clinically assess for the underlying cause with history, examination, ECG, and other investigations as indicated.
Someone asks you if you want to give some magnesium “as per the guidelines”. As you are wondering what that’s for someone else asks you how long myocardial stunning lasts for and whether that’s the likely cause of hypotension now.
Luckily you avoid getting annoyed with all these reasonable questions by suddenly remembering that there are international recommendations for the management of ‘Post–Cardiac Arrest Syndrome’. You excuse yourself from the room on the pretext of going to the lavatory and quickly find a quiet area where you scan the following article for help:
Post–Cardiac Arrest Syndrome Epidemiology, Pathophysiology, Treatment, and Prognostication
A Consensus Statement From the International Liaison Committee on Resuscitation (American Heart Association, Australian and New Zealand Council on Resuscitation, European Resuscitation Council, Heart and Stroke Foundation of Canada, InterAmerican Heart Foundation, Resuscitation Council of Asia, and the Resuscitation Council of Southern Africa); the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; and the Stroke Council
Circulation 2008;118;2452-2483 Full Text Article
Crystalloids vs colloids and cardiac output
It is said that when using crystalloids, two to four times more fluid may be required to restore and maintain intravascular fluid volume compared with colloids, although true evidence is scarce. The ratio in the SAFE study comparing albumin with saline resuscitation was 1:1.3, however.
A single-centre, single- blinded, randomized clinical trial was carried out on 24 critically ill sepsis and 24 non-sepsis patients with clinical hypovolaemia, assigned to loading with normal saline, gelatin 4%, hydroxyethyl starch 6% or albumin 5% in a 90-min (delta) central venous pressure (CVP)-guided fluid loading protocol. Haemodynamic monitoring using transpulmonary thermodilution was done each 30 min to measure, among other things, global end-diastolic volume and cardiac indices (GEDVI, CI). The reason sepsis was looked at was because of a suggestion in the SAFE study of benefit from albumin in the pre-defined sepsis subgroup.
Independent of underlying disease, CVP and GEDVI increased more after colloid than saline loading (P = 0.018), so that CI increased by about 2% after saline and 12% after colloid loading (P = 0.029).
Their results agree with the traditional (pre-SAFE) idea of ratios of crystalloid:colloid, since the difference in cardiac output increase multiplied by the difference in volume infused was three for colloids versus saline.
Take home message? Even though an outcome benefit has not yet been conclusively demonstrated, colloids such as albumin increase pre-load and cardiac index more effectively than equivalent volumes of crystalloid in hypovolaemic critically ill patients.
Greater cardiac response of colloid than saline fluid loading in septic and non-septic critically ill patients with clinical hypovolaemia
Intensive Care Med. 2010 Apr;36(4):697-701
The right antibiotic in septic shock makes a massive difference
A retrospective review of appropriate vs inappropriate antimicrobial therapy was undertaken in over four thousand septic shock patients from multiple centres. In terms of definitions, the authors state:
“Appropriate antimicrobial therapy was considered to have been initiated if an antimicrobial with in vitro activity appropriate for the isolated pathogen or pathogens (or in the case of culture-negative septic shock, an antimicrobial or antimicrobial agent concordant with accepted international norms for empiric therapy and modified to local flora) was either the first new antimicrobial agent with which therapy was started after the onset of recurrent or persistent hypotension or was initiated within 6 h of the administration of the first new antimicrobial agent. Otherwise, inappropriate therapy was considered to have been initiated.”
The results are striking: survival rates after appropriate and inappropriate initial therapy were 52.0% and 10.3%, respectively (odds ratio [OR], 9.45; 95% CI, 7.74 to 11.54; p < 0.0001).
A multivariable logistic regression analysis of possible factors that may affect outcome showed the appropriateness of the initial antimicrobial therapy remained most strongly associated with outcome (OR, 8.99; 95% CI, 6.60 to 12.23; p < 0.0001) among all the risk factors assessed.
Initiation of Inappropriate Antimicrobial Therapy Results in a Fivefold Reduction of Survival in Human Septic Shock
Chest. 2009 Nov;136(5):1237-48
N.B. This work was done by the same authors who brought us the study that showed the earlier antibiotics were given to hypotensive septic patients, the better the outcome:
Kumar A, Roberts D, Wood KE, et al. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock. Crit Care Med 2006; 34:1589-1596
Is ETT muck delaying weaning?
Organised secretions can build up in a tracheal tube. This increases airway resistance so during a spontaneous breathing trial in a patient being considered for extubation the patient may have increased work of breathing and unfairly fail the trial, delaying extubation.
How can you spot it? Increased airways resistance can increase peak airway pressure. However inspiratory plateau pressure will not be affected (obtained by performing an inspiratory hold). Identifying a big difference between peak and plateau pressures should prompt a search for increased airway resistance, which includes a narrowed tracheal tube lumen. The amount of accumulated secretion is not necessarily related to the duration of intubation.
Increases in endotracheal tube resistance are unpredictable relative to duration of intubation
Chest 2009; 136:1006-1013
CT cervical spine in obtunded trauma patients
Prolonged collar use and spinal immobilisation in ICU patients can contribute to pressure sores, increased intracranial pressure, venous obstruction, difficulties with airway management, difficulties with central venous access, respiratory complications, and DVT, so a reliable investigation to rule out unstable cervical spine injury is required. Several studies demonstrate the high sensitivity of CT, and now a prospective study from Canada attempts to lend further support to this.
Comparing against their chosen gold standard of dynamic radiography, ie. flexion/extension views (F/E) in 402 patients who received both tests, there was one case of injury detected by F/E but not by CT, leading to quoted sensitivity of 99.75%. However this negative CT turned out to be a reporting error – the scan, which the authors include in their article, was clearly abnormal.
One weakness of this study is that they excluded patients who died on ICU. More worrying are the stats quoted. The authors stat ‘four hundred one patients (99.75%) had normal CT and F-E images facilitating clinical clearance of their C-spine and discontinuation of spinal precautions‘. So in other words, there was only one patient in their series of 402 with an injury (according to the gold standard), and this was missed. The sensitivity is therefore zero percent, not 99.75%. What seems to be a further error is the reporting in a table of 401 patients who had ‘Positive CT and Negative F-E’, which if true, would give a specificty of zero too!
This paper covers an important topic for intensivists but it seems to me to be too flawed to add meaningfully to the existing evidence that necks can be ‘cleared’ by CT in patients without signs of cervical spine injury, in whom it has been said that the risks of prolonged collar use and immobilisation may outweigh the risks of missed cervical injury.
Cervical spine clearance in obtunded blunt trauma patients: a prospective study
J Trauma. 2010 Mar;68(3):576-82
EGDT sepsis bundle challenged
An article in American Journal of Emergency Medicine by two intensivists challenges the science behind Rivers’ early goal-directed therapy (EGDT) protocol for severe sepsis / septic shock. In a nutshell:
- Rivers’ study was small (n = 263), nonblinded, industry-supported and single-center
- early fluids and antibiotics are a sound idea, but other components of EGDT are flawed
- targeting a CVP is meaningless and could result in hypovolaemia or pulmonary oedema; dynamic markers of preload responsiveness such as pulse pressure variation or IVC diameter variation are better guides to fluid resuscitation
- ScvO2 may be normal or elevated in septic shock patients; the low average ScvO2 in Rivers’ study has not been reproduced in subsequent studies.
- packed cells have significant side effects and their non-deformability, pro-inflammatory and pro-thrombotic effects may impair microvascular perfusion and paradoxically worsen tissue oxygen delivery
- dobutamine can potentially further worsen the haemodynamic status of patients with hypovolaemia, vasodilation, or a hyperdynamic circulation, which cannot be differentiated using CVP and ScvO2
Early goal-directed therapy: on terminal life support?
Am J Emerg Med. 2010 Feb;28(2):243-5
I like this paper, mainly because I have been uncomfortable with the chasing of arbitrary targets for some time. My own practice is to try to improve markers of organ hypoperfusion (such as lactate, urine output, mental status, and skin perfusion as well as blood pressure) by early antibiotics, fluid resuscitation guided by clinical and sonographic (IVC) signs, and vasoactive drugs guided by clinical and sonographic (basic echo) findings. I place a central venous catheter for access for the vasoactive drugs, rather than to get a CVP reading. I do measure ScvO2 with a central venous blood gas, but have rarely seen one below 70% even in severely shocked patients – I’m far more interested in clearing the lactate, as are these guys.
Preventing AKI on the ICU
A multinational European working group produced the following evidence-based recommendations for preventing acute kidney injury (AKI). Read the full guideline before criticising – some are just suggestions, some recommendations; I have not included the strength of recommendation or grade of evidence in my summary below.
Volume expansion
Diuretics
- Do not use loop diuretics to prevent or ameliorate AKI
Vasopressors and inotropes
- Maintain mean arterial pressure (MAP) at least 60–65 mmHg, however, target pressure should be individualized where possible, especially if knowledge of the premorbid blood pressure is available.
- In case of vasoplegic hypotension as a result of sepsis or SIRS use either norepinephrine or dopamine (along with fluid resuscitation) as the first-choice vasopressor agent to correct hypotension.
- Do not use low-dose dopamine for protection against AKI.
Vasodilators
- Use vasodilators for renal protection when volume status is corrected and the patient is closely hemodynamically monitored with particular regard to the development of hypotension.
- Prophylactic use of fenoldopam, if available, in cardiovascular surgery patients at risk of AKI. Do not use fenoldopam for prophylaxis of contrast nephropathy.
- Use theophylline to minimize risk of contrast nephropathy, especially in acute interventions when hydration is not feasible.
- Do not use natriuretic peptides as protective agents against AKI in critically ill patients, while its use may be considered during cardiovascular surgery.
Hormonal manipulation and activated protein C
- Avoid routine use of tight glycemic control in the general ICU population. Use “Normal for age’’ glycemic control with intravenous (IV) insulin therapy to prevent AKI in surgical ICU patients, on condition that it can be done adequately and safely applying a local protocol which has proven efficacy in minimizing rate of hypoglycemia.
- Do not use thyroxine, erythropoietin, activated protein C or steroids routinely to prevent AKI.
Metabolic interventions
- All patients at risk of AKI should have adequate nutritional support, preferably through the enteral route
- Do not use N-acetylcysteine as prophylaxis against contrast induced nephropathy or other forms AKI in critically ill patients because of conflicting results, possible adverse reactions, and better alternatives.
- Do not routinely use selenium to protect against renal injury.
Extracorporeal therapies
- Use periprocedural continuous veno-venous hemofiltration (CVVH) in an ICU environment to limit contrast nephropathy after coronary interventions in high-risk patients with advanced chronic renal insufficiency
Prevention of acute kidney injury and protection of renal function in the intensive care unit
Expert opinion of the working group for nephrology, ESICM
Intensive Care Med. 2010 Mar;36(3):392-411
Low PPV can still be fluid responsive
Pulse pressure variation with respiration (PPV) predicts fluid responsiveness in mechanically ventilated patients. Because this is due to transmission of airway pressures to the vasculature, it is hypothesised that low tidal volume ventilation (or non compliant lungs, or both) results in less PPV even in fluid-responsive patients. This was confirmed in a study looking at the effect of airway driving pressure (Pplat – PEEP) on PPV. The study confirmed the positive predictive value of a high PPV, but some of those patients with a ‘low’ PPV (below a commonly accepted cut-off of 13%) were still fluid responsive, which was defined as a 15% or more increase in stroke index after a fluid challenge. In fluid responders with a low PPV, (Pplat – PEEP) was less than or equal to 20 cmH20.
Take home message: In mechanically ventilated patients, PPV values <13% do not rule out fluid responsiveness, especially when (Pplat – PEEP) was less than or equal to 20
The influence of the airway driving pressure on pulsed pressure variation as a predictor of fluid responsiveness
Intensive Care Med. 2010 Mar;36(3):496-503