Elsevier

Annals of Emergency Medicine

Volume 68, Issue 2, August 2016, Pages 181-188.e2
Annals of Emergency Medicine

Airway/original research
Hemodynamic Response After Rapid Sequence Induction With Ketamine in Out-of-Hospital Patients at Risk of Shock as Defined by the Shock Index

https://doi.org/10.1016/j.annemergmed.2016.03.041Get rights and content

Study objective

Ketamine is considered a stable induction agent for rapid sequence induction; however, hypotension rates up to 24% are reported. The shock index (shock index=pulse rate/systolic blood pressure [SBP]) may identify patients at risk of adverse hemodynamic change. We investigate whether SBP and pulse rate response to ketamine induction differ when patients are classified as being at risk of shock by their shock index.

Methods

We conducted a prospective observational study of electronically collected vital sign data from patients undergoing rapid sequence induction with ketamine. Patients were grouped into low shock index (shock index <0.9) or high shock index (shock index ≥0.9) preinduction. Pulse rate and SBP were compared between 3 minutes preinduction and for 3 measurements postinduction (3-minute intervals) by repeated-measures ANOVA. Proportions of patients developing hypotension or hypertension are also reported.

Results

One hundred twelve patients were enrolled (81 low shock index, 31 high shock index). Low shock index patients had increased SBP after induction (16 mm Hg; 95% confidence interval [CI] 11 to 21 mm Hg), whereas high shock index patients did not (2 mm Hg; 95% CI –4 to 7 mm Hg). Pulse rate in low shock index patients increased after induction (20 beats/min; 95% CI 16 to 25 beats/min) and remained elevated, whereas in high shock index patients a difference occurred at the second postinduction measurement only (15 beats/min; 95% CI 11 to 18 beats/min). More high shock index patients became hypotensive (26%; 95% CI 12% to 45%) than low shock index ones (2%; 95% CI 0% to 9%), whereas more low shock index patients became hypertensive (40%; 95% CI 29% to 51%) than high shock index ones (13%; 95% CI 4% to 30%).

Conclusion

After ketamine induction, high shock index patients exhibited blunted hypertensive responses and more frequent hypotension, whereas low shock index patients had sustained increases in pulse rate and SBP.

Introduction

Ketamine is considered a suitable drug for emergency intubation because of a catecholamine-mediated maintenance of blood pressure and pulse rate,1 in addition to its analgesic, amnestic, and bronchodilation properties. Whereas in normovolemic patients hypertension may occur,2, 3 early research in critically ill patients found ketamine to be occasionally associated with a reduction in mean arterial blood pressure and cardiac output,4, 5, 6 with hypovolemic patients potentially most at risk.7 Recent clinical studies of ketamine rapid sequence intubation report hypotension rates of 3.6% to 24%,8, 9, 10, 11, 12 which may be harmful because a systolic blood pressure (SBP) less than 90 mm Hg is associated with increased morbidity and mortality in trauma patients13 and an SBP less than 110 mm Hg has been advocated as hypotension in moderate to severe isolated traumatic brain injury.14 Similarly, in the setting of traumatic brain injury an SBP greater than 140,15 160,16 or 175 mm Hg17 is associated with worse outcomes, although the relationship between cause and effect is less clear.

Editor’s Capsule Summary

What is already known on this topic

Although sympathomimetic, ketamine can produce hypotension in patients with depleted catecholamine stores.

What question this study addressed

When ketamine is used for rapid sequence intubation, how do the resulting hemodynamics differ when patients with or without risk of shock are compared (as estimated by the shock index)?

What this study adds to our knowledge

In this observational comparison of 112 out-of-hospital adults, those without apparent shock generally exhibited the expected increases in blood pressure and pulse. These effects were blunted in patients with a high shock index, with 8 of these 31 experiencing hypotension.

How this is relevant to clinical practice

When ketamine is used for rapid sequence induction, hypotension and blunted sympathomimetic responses are more common when initial hemodynamics suggest possible shock.

The out-of-hospital identification of shock is an ongoing challenge. Traditional vital signs perform poorly in predicting blood loss.18, 19 The shock index is an alternative measure and is calculated by dividing pulse rate by blood pressure. A shock index greater than 0.9 in the emergency department (ED) predicts increased mortality in trauma patients and the need for blood transfusion,20, 21, 22 as well as prolonged vasopressor use early in sepsis.23, 24 The exact cutoff for shock index varies between studies; however, a shock index of less than 0.7 is considered normal and values greater than 0.9 are associated with increasing risk of morbidity and mortality.21, 25 One of the advantages of the shock index is that it identifies individuals at risk whose blood pressure would be considered normal by other measures.26 A shock index of greater than 0.9 had been shown elsewhere to identify patients at risk of hypotension27 and cardiac arrest28 postinduction in the ED, with etomidate as the induction drug.

It would be useful to identify patients at risk of hypotension or hypertension when ketamine is used as an induction agent, as well as the frequency of these events. Consideration can then be made to reduce the dose of ketamine if the patient is at risk of hypotension, or add additional opiate if hypertension is likely to occur.

We performed a prospective observational study to investigate the hemodynamic response to out-of-hospital induction with ketamine in our patients. Our goals were to investigate the pattern of SBP and pulse rate change, as well as the proportion of patients developing hypotension and hypertension, and whether this differed in patient groups when divided by the shock index. Our primary outcome measure was the change in SBP and pulse rate between preinduction and 3 measurements after induction (taken at 3-minute intervals) in these groups, with the proportion of hypotension and hypertension in these groups as secondary outcomes.

Section snippets

Study Design and Setting

This prospective observational study was conducted between June 2014 and July 2015 at the Greater Sydney Area Helicopter Emergency Medical Service, New South Wales, Australia. This service provides a physician-paramedic team for out-of-hospital response. Ethical approval and consent waiver were granted by the Sydney Local Health District Human Ethics Committee.

Selection of Participants

We included patients undergoing out-of-hospital intubation when ketamine was used as the induction agent and excluded those younger than

Characteristics of Study Subjects

Patient flow is shown in Figure 1. Most of the 112 subjects were intubated for either severe head injuries or combativeness, with demographic characteristics similar between groups (Table 1).

Most patients were intubated within 2 minutes and first-pass laryngoscopy success was high (Table 2). The mean ketamine induction dose was slightly higher in the low shock index group (mean difference 0.2 mg/kg; 95% CI 0 to 0.4 mg/kg), whereas the total ketamine dose (preinduction plus induction) was

Limitations

Our principal limitation is that our study was observational and not randomized. Additionally, patient weight was estimated and not measured in accordance with actual practice. We relied on noninvasive blood pressure, not invasive blood pressure, which can be inaccurate, especially in patients with shock.32 However, invasive blood pressure is rarely used in the out-of-hospital environment. We had a number of patients with incomplete data who could not be studied.

We attempted to account for

Discussion

We set out to investigate whether the pattern of hemodynamic change in patients intubated with ketamine differed in patients without shock and those potentially with shock, as defined by the shock index. Although the overall rate of hypotension was low, we found that patients with a shock index greater than 0.9 had less overall change in SBP up to 9 minutes after intubation, but more episodes of hypotension, whereas those with a shock index of less than 0.9 had larger sustained changes in SBP.

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  • Cited by (0)

    Please see page 182 for the Editor’s Capsule Summary of this article.

    Supervising editor: Steven M. Green, MD

    Author contributions: MM, NK, CH, SW, CR, and BB conceived and planned the study. MM, NK, and SW designed the study and analysis. KH contributed to data collection. MM was responsible for ethical and site-specific approvals. MM and SW provided statistical analysis. MM drafted the article, and all authors contributed to its revision. MM takes responsibility for the paper as a whole.

    Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist.

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