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Maintain Adequate Central Venous Oxygen Saturation

Maintain Adequate Central Venous Oxygen Saturation

Corresponding Bundle Element

In the event of persistent hypotension despite fluid resuscitation (septic shock) and/or lactate > 4 mmol/L (36 mg/dL) achieve central venous oxygen saturation (ScvO2) of > 70 percent.*

*Mixed venous oxygen saturation (SvO2) > 65 percent is an acceptable alternative.

Related Measures

Central Venous Oxygen Saturation Goal

Background

Goal-directed therapy represents an attempt to predefine resuscitation end-points to help clinicians at the bedside to resuscitate patients in septic shock. The end-points used vary according to the clinical study but attempt to adjust cardiac preload, contractility, and afterload to balance systemic oxygen delivery with demand. 

Two essential features of early goal-directed therapy include: 1) maintaining an adequate central venous pressure to carry out other hemodynamic adjustments; and 2) maximizing mixed or central venous oxygen saturation, discussed elsewhere.

Following the Sepsis Resuscitation Bundle, once lactate is > 4 mmol/L (36 mg/dL), or hypotension has been demonstrated to be refractive to an initial fluid challenge with 20 mL/kg of crystalloid or colloid equivalent, patients should then have their central venous pressure (CVP) maintained > 8 mm Hg and central venous oxygen saturation should be maintained > 70 percent.

These recommendations are consistent with the only trial to demonstrate a mortality benefit in early goal directed therapy using ScvO2 as one of it’s major end points, Rivers et al. (1)

Importance of Early Therapies

The resuscitation of severely septic individuals with lactate > 4 mmol (36 mg/dL) or in septic shock must start early.  It seems that the longer the resuscitation is delayed, the less likely a beneficial effect will be accrued. This makes sense, as the purpose of resuscitating a patient is to prevent further organ dysfunction and failure. If the resuscitation is delayed until after cellular dysfunction and death is present, then strategies designed to provide the cells with more oxygen are unlikely to be helpful. It is unclear however when the transition from reversible cellular dysfunction to irreversible cellular dysfunction occurs. At present, the only strategy that we can employ is to provide the resuscitation at the earliest stage possible.

Maintaining ScvO2

Techniques to maintain ScvO2 include two principal strategies.  In carrying out early goal directed therapy, if a patient is both hypovolemic and the hematocrit is less than 30%, it is appropriate to transfuse packed red blood cells provided that the fluid resuscitation has achieved a CVP > 8.  If CVP > 8 has not been achieved, additional fluid challenges are needed.  Once the decision to use blood products has been made, this may accomplish the dual purpose of 1) increasing ScvO2 due to increased oxygen delivery to ischemic tissue beds and 2) keeping the central venous pressure > 8 mm Hg for longer periods than fluids alone.

The second strategy involves attempting to improve the patient’s hemodynamic profile with inotropes.  Provided that the patient has been adequately resuscitated and the CVP is > 8 mmHg, it may be that cardiac output remains insufficient to meet metabolic needs of certain tissue beds despite an adequate circulating volume.  In some cases, cardiac output itself may be diminished due to sepsis induced cardiac dysfunction.  In these cases, dobutamine infusion (up to a maximum of 20 μg·kg-1·min-1) should be employed to increase oxygen delivery to the periphery and prevent further organ dysfunction due to hypoperfusion and ischemia.  If dobutamine infusion results in hypotension, norepinephrine should be used to counteract the vasodilatory effects of dobutamine.

Special Considerations

Evidence is not conclusive on attempting to maximize a patient’s cardiac index to surpranormal levels to overcome increased oxygen demand, abnormalities in oxygen extraction, and myocardial depression associated with sepsis. (2,3)  Therefore, a strategy of increasing cardiac index to achieve an arbitrarily predefined elevated level is not recommended.

Before attempting to use inotropes to maximize central venous oxygen saturation in mechanically ventilated patients, a higher target central venous pressure of 12 to 15 mm Hg is recommended to account for the presence of positive end expiratory pressure and increases in intrathoracic pressure.

Similar consideration to the above may be warranted in circumstances of increased abdominal pressure.

Rivers’ et al Protocol

It is impossible to determine from the study which particular facet of the protocol was beneficial for the patients, so the protocol as a whole must be recommended.

Rivers et al. performed a randomized, controlled, predominantly blinded study in an 850-bed tertiary referral center over a 3-year period. This study was performed in the emergency department of the hospital and enrolled patients presenting with severe sepsis or septic shock who fulfilled two of the four systemic inflammatory response syndrome criteria in association with a systolic blood pressure of < 90 mm Hg after a 20 to 30 mL/kg crystalloid challenge or a blood lactate concentration of > 4 mmol/L (36 mg/dL).

The patients were randomized to receive six hours of standard therapy or six hours of early goal-directed therapy before admission to the intensive care unit. Clinicians who were subsequently involved in the care of these patients were blinded to the treatment arm of the study.

The control group’s care was directed according to a protocol for hemodynamic support. The aims of this protocol were to ensure that the patients had a central venous pressure of between 8 and 12 mm Hg, a mean arterial pressure of > 65 mm Hg, and a urine output of > 0.5 mL·kg-1·min-1. These goals were targeted with the use of 500-mL boluses of crystalloid or colloid and vasopressor agents as necessary. The patients assigned to the early goal-directed therapy group received a central venous catheter capable of measuring ScvO2. Their treatment aims were then the same as the control groups, except that they also had to achieve a ScvO2 of > 70 percent.

The patients assigned to the early goal-directed therapy group received a central venous catheter capable of measuring ScvO2. Their treatment aims were then the same as the control groups, except that they also had to achieve a ScvO2 of > 70 percent. This was achieved first by the administration of transfused red blood cells, then with positive inotropic therapy, and if this goal was then not achieved, by sedation and mechanical ventilation to reduce oxygen demand.

The study enrolled 263 patients equally between the two groups. There were no significant differences between the two groups at baseline. During the initial 6 hours of therapy, the early goal directed therapy group received more intravenous fluid (5.0 vs. 3.5 L, p < .001), red cell transfusions (p < .001), and inotropic therapy (p < .001). During the subsequent 66 hours, the control group received more red cell transfusions (p < .001), more vasopressors (p = .03), and had a greater requirement for mechanical ventilation (p < .001) and pulmonary artery catheterization (p = .04). This in part reflects the fact that the control group patients were relatively under-resuscitated initially, and this was noticed and thus acted on by clinicians later on in their treatment course. In-hospital mortality was significantly higher in the control group than in the early goal-directed therapy group (46.5 percent vs. 30.5 percent, p = .009). These differences were maintained through to 28 (p = .01) and 60 days (p = .03).

References

  1. Rivers E, Nguyen B, Havstad S, et al. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med. 2001;345:1368–1377.
  2. Gattinoni L, Brazzi L, Pelosi P, et al. A trial of goal-oriented hemodynamic therapy in critically ill patients. N Engl J Med. 1995;333:1025–1032.
  3. Yu M, Burchell S, Hasaniya N, et al. Relationship of mortality to increasing oxygen delivery in patients > or = 50 years of age: A prospective randomised trial. Crit Care Med. 1998;26:1011–1019.

Content adapted extensively from

  • Dellinger RP, Carlet JM, Masur H, et al. Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock. Crit Care Med. 2004;32:858-873.
  • Rhodes A, Bennett ED. Early goal-directed therapy: An evidence-based review. Crit Care Med. 2004;32(Suppl.):S448 –S450.

Tips

  1. Create a standardized protocol that includes a goal CVP > 8 for patients with lactate > 4 or hypotension not responding to initial fluid resuscitation (septic shock).
  2. Stress the importance of prioritization: initial fluid challenge as defined, followed by central line placement, followed by assessment of CVP; if CVP is low, the addition of PRBCs is appropriate if hematocrit is less than 30 percent and MAP remains < 65 mmg Hg, followed by further fluid challenges to keep CVP > 8.
  3. If your emergency department does not commonly perform these techniques, provide in-service training to emergency department personnel regarding CVP monitoring and the importance of leveling equipment relative to the patient’s heart.
  4. Do not wait for transfer to the ICU to initiate CVP monitoring.