Critical care

Critical care medicine is the "health care provided to a critically ill patient during a medical emergency or crisis".

Monitoring the critically ill patient

Respiration and oxygenation

PaO₂/FiO2 ratio (PF ratio)

${P/F\ ratio}=\left({\frac {PaO_{2}}{Fi0_{2}}}\right)\times 100$

• Normal is 500
• ARDS is < 200

This measure is easier to calculate. Comparative studies suggest it correlates better with pulmonary shunts than does the A-a gradient.

Alveolar-arterial oxygen (A-a) gradient (alveolar-arterial oxygen difference - AVO₂D)

${\mbox{A-a gradient}}={PAO_{2}}\ -\ {PaO_{2}}$

${PAO_{2}}={Fi0_{2}}*\left({760-47}\right)\ -\ {\frac {PaCO_{2}}{0.8}}$

• Normal is < 10 mm Hg

The A-a gradient is harder to calculate, but accounts for changes in respiration as measured by the partial pressure of carbon dioxide. However, this calculation relies on the respiratory quotient being constant in the prediction of alveolar CO₂ When compared to the PF ratio, the A-a gradient is found to correlate less well with pulmonary shunting.

Among outpatients with possible pulmonary embolism, the A-a gradient may be a better test.

An online calculator for the A-a gradient is at http://www.mdcalc.com/aagrad.

Central venous oxygen saturation (ScvO₂)

In patients with septic shock, maintaining the central venous oxygen saturation (ScvO₂) > 70% is a health care quality assurance measure for the Institute for Healthcare Improvement.

Mixed venous oxygen saturation (SvO₂)

In patients with septic shock, maintaining the mixed venous oxygen saturation (ScvO₂) > 65% is a health care quality assurance measure for the Institute for Healthcare Improvement that is an alternative to the central venous oxygen saturation.

The mixed venous pressure may be lower than the central venous pressure due to mixing with blood from the splanchnic circulation or carotid sinuses that has lower oxygen content.

Complications

Abdominal compartment syndrome

Abdominal compartment syndrome is associated with increased mortalty.

Medical error

Examining errors in administration of parenteral medications, a study found:

• 74 errors per 100 patient-days
• Independent risk factors were:
  • Patient complexity as measured by
    • number of organ failures
    • number of parenteral administrations
  • Work load as measured by
    • Larger intensive care unit
    • Increased ratio of patient turnover to the size of the unit
    • Number of patients per nurse
    • Occupancy rate of the unit

Preventing complications in the critically ill patient

Glucose control

Two clinical practice guidelines are available for patients with ; however, both of these guidelines were developed without broad representation of stakeholders. This may lead to overly aggressive clinical recommendations. In addition, these guidelines were published before the two recent negative trials.

The American Association of Clinical Endocrinologists (AACE) recommends the following target blood glucose levels:

• "Critically ill patients, between 80 to 110 mg/dL (grade A recommendation)"

The American Diabetes Association (ADA) states

• "Critically ill patients: blood glucose levels should be kept as close to 110 mg/dl (6.1 mmol/l) as possible and generally <140 mg/dl (7.8 mmol/l). (A) These patients require an intravenous insulin protocol that has demonstrated efficacy and safety in achieving the desired glucose range without increasing risk for severe hypoglycemia. (E)"

Evidence

Randomized controlled trials of tight glucose control in the critical care and perioperative care settings have produced mixed results. See Table.

Selected randomized controlled trials of glucose control in critical care

Trial	Patients	Intervention	Comparison	Outcomes	Results		Authors' conclusions
					Intensive control	Control group
NICE-SUGAR 2009	6104 patients in medical and surgical ICU	Insulin drip targeting serum glucose of 81 to 108 mg/dl	Insulin drip targeting serum glucose of 144 - 180 mg/dl	Mortality at 90 days	27.5% *	24.9%	"intensive glucose control increased mortality among adults in the ICU"
Arabi et al 2008	523 patients in medical and surgical ICU	Insulin drip targeting serum glucose of 80 to 110 mg/dl	Insulin drip targeting serum glucose of 180 to 200 mg/dl	Mortality in the intensive care unit	13.5%	17.1	"Intensive insulin therapy was not associated with improved survival...and was associated with increased occurrence of hypoglycemia"
SepNet 2008	537 patients with severe sepsis	Insulin drip if needed to target serum glucose of 80 to 110 mg/dl	Insulin drip if needed to target serum glucose of < 200 mg/dl	Mortality in the intensive care unit	24.7%	26%	"intensive insulin therapy placed critically ill patients with sepsis at increased risk for serious adverse events"
Van den Berghe 2006	1200 patients in medical ICU	Insulin drip targeting serum glucose of 80 to 110 mg/dl	Insulin drip targeting serum glucose of 180 to 200 mg/dl	Hospital mortality	37.3%	40%	"Intensive insulin therapy significantly reduced morbidity but not mortality"
Van den Berghe 2001	1548 patients in surgical ICU	Insulin drip targeting serum glucose of 80 to 110 mg/dl	Insulin drip targeting serum glucose of 180 to 200 mg/dl	Mortality in the intensive care unit	4.6% *	8%	"Intensive insulin therapy...reduces morbidity and mortality"
Notes: * Significantly different from the control group.

Two of the trials in the Table suggested benefit (see green cells):

• Van den Berghe 2006. Although this trial concluded "intensive insulin therapy significantly reduced morbidity but not mortality among all patients in the medical ICU. Although the risk of subsequent death and disease was reduced in patients treated for three or more days" the trial stated "these patients could not be identified before therapy."
• Van den Berghe 2002. This trial has been criticized for the following reasons:
  

1. "The trial was stopped early for an unexpectedly large treatment effect, which can overestimate the efficacy of treatment or result in a false-positive finding;"
2. "The relative reduction in mortality for a decrease of 50 mg/dL in morning glucose levels seems biologically implausible and exceeds that for any other intervention in critically ill patients;"
3. "The mortality rate in the control group was much higher than that noted in tertiary care medical centers in the United States. On admission to the ICU, all patients received 200 to 300 g/d of intravenous dextrose followed by enteral or parenteral nutrition, an unusual practice considering the deleterious effects of parenteral nutrition; at least in part, the difference in outcomes between the 2 arms in this study might have reflected the harm of maintaining the control group as hyperglycemic rather than the benefit of strict glucose control in the intervention group."

Tight control may protect renal function.

Regarding intraoperative control of glucose, a randomized controlled trial concluded "the increased incidence of death and stroke in the intensive treatment group raises concern about routine implementation of this intervention."

Preventing anemia

Blood transfusion

There may not be a meaningful difference in outcomes between transfusing blood to maintain a hemoglobin > 7.0 g/dl versus a hemoglobin > 10.0 g/dl.

Erythropoietin

A randomized controlled trial reported "epoetin alfa does not reduce the incidence of red-cell transfusion among critically ill patients, but it may reduce mortality in patients with trauma. Treatment with epoetin alfa is associated with an increase in the incidence of thrombotic events."

Selective gastrointestinal decontamination

Systematic reviews conclude that selective decontamination of the digestive tract may reduce morbidity in critically ill patients although some randomized controlled trials have and others have not found benefit.

Preventing posttraumatic stress disorder

Light sedation (patient awake and cooperative) may be more effective than deep sedation (patient asleep, awakening upon physical stimulation).

Medical error in the intensive care

Regarding overlooked diagnosis among patients receiving artificial respiration in the intensive care, an autopsy study concluded "abdominal pathologic conditions--abscesses, bowel perforations, or infarction--were as frequent as pulmonary emboli as a cause of class I errors. While patients with abdominal pathologic conditions generally complained of abdominal pain, results of examination of the abdomen were considered unremarkable in most patients, and the symptom was not pursued."

Predicting outcomes of adult patients

Although there is much research into prognosing patients in intensive care, patients are not very confident in thei accuracy of prognoses.

Apache II score

The APACHE II is available at http://www.sfar.org/scores2/apache22.html.

SAPS II

• SAPS II
• SAPS II (expanded)

Coma

The FOUR (Full Outline of UnResponsiveness) score may be better than the Glasgow Coma Scale (GCS) in prognosticating patients in coma. The FOUR Score tests:

• eye response
• motor response
• brainstem reflexes
• respiration pattern