Shock Index: A Simple & Straightforward Evaluation
Shock, or inadequate oxygen delivery, is typically diagnosed with examination findings and measurements (eg, elevated heart rate, decreased blood pressure [BP]). The heart rate:systolic arterial BP ratio, known as the shock index (SI), is a simple, inexpensive shock measure, which could prove advantageous in recognizing occult shock when outward cardiovascular parameters appear normal. This study aimed to determine normal SI values in control patients and whether SI is higher in dogs with elevated lactate, a widely accepted indicator of shock. Data were compared among 3 groups: healthy dogs (n = 68), emergent dogs not in shock (n = 19), and emergent dogs in moderate to severe shock (n = 18). Dogs presenting in shock (based on plasma lactate levels >5 mmol/L) had a significantly higher SI than healthy dogs or emergent dogs not in shock. An SI >1 is a highly sensitive and specific indicator of a dog that will have biochemical evidence of shock, but these dogs typically also have overt clinical evidence of shock. Lack of data on SI determination in occult hypoperfusion, in which detection is likely to be most valuable, limited this study; however, the goal of introducing veterinarians to SI use was met.
Global Commentary
Clinicians need simple markers and procedures to identify dogs suspected to develop shock; these markers must be easy to obtain (especially in emergencies), repeatable, and not operator dependent. Lactate, considered one of the most useful biomarkers of shock, cannot be the sole criterion to detect early stages. Sidestream dark field microscopy allows real-time imaging of the microvasculature and has potential as an effective tool for monitoring microcirculatory changes associated with shock.1 However, this requires specific and expensive equipment and well trained clinicians. SI, on the other hand, is easily determined. In addition, noninvasive BP and heart measurement are routine when evaluating critical patients; thus, SI can be routinely calculated and followed and appears to be a promising parameter. Another study has proposed that SI may be an option for detecting early shock2; SI was significantly higher in a group of 38 dogs with hemorrhagic shock compared with 78 controls. SI was concluded to be used as an additional triage tool and should prompt further investigation for hemorrhage if values are >0.9. Their cut-off value is close to the that of the current study. Considering how easy SI is to obtain, ICU clinicians could begin to use and follow SI routinely.—Isabelle Goy-Thollot, DVM, PhD, EVECCS
Source
Evaluation of the shock index in dogs presenting as emergencies. Porter AE, Rozanski EA, Sharp CR, et al. JVECC 23:538-544, 2013.
Assessment of microcirculatory changes by use of sidestream dark field microscopy during hemorrhagic shock in dogs. Peruski AM, Cooper ES. AM J VET RES 72:438-445, 2011.
2. Assessment of shock index in healthy dogs and dogs in hemorrhagic shock. Peterson KL, Hardy BT, Hall K. JVECC 23:545-550, 2013.
This capsule is part of the Global Edition of Clinician's Brief