Study Design

Reduced Quality Factors

0 = no serious, - = serious,

- - = very serious

Positive Quality Factors

0 = none, + = one, ++ = multiple

Dichotomous Outcome Summary

Non-Dichotomous Outcome Summary

Brief description

Overall Quality

High, moderate, low,
very low, none

No of studies

Study Type

RoB

Indirectness

Imprecision

Inconsistency

Large Effect

Dose-Response

Confounder

# Intervention with Outcome

# Control with Outcome

RR (95% CI)

Outcome: Surrogate markers of perfusion

5

EXP

0

- -

-

0

0

0

0

No studies were identified that directly compared outcomes among different hand positions in medium- to large-sized, keel-chested dogs undergoing chest compressions in lateral recumbency. All studies have indirect application.

Very low

Introduction

In dogs in lateral recumbency it is assumed that chest compressions performed directly over the anatomic location of the heart are more likely to directly compress the heart (cardiac pump theory), while chest compressions over the widest portion of the chest are more likely to increase the overall intrathoracic pressure (thoracic pump theory). Previous veterinary guidelines suggest hand placement directly over the heart in medium- and large-sized keel chested dogs.1 This question investigates whether chest compressions in medium- to large-sized, keel-chested dogs are better performed with hands placed over the widest part of the thorax or over the heart.

Consensus on science

For the most critical outcomes of favorable neurologic outcome, survival to discharge, and ROSC, we identified no studies addressing the PICO question.

Outcome 4: Surrogate Markers of Perfusion:

We found 5 experimental animal studies (very low-quality of evidence, downgraded for very serious indirectness and serious imprecision) that address the PICO question.2–6 No studies were found that directly compare chest compressions performed with hands placed over the heart versus hands placed on the widest point of the thorax; no studies were identified that directly compare how each of these methods affects intrathoracic pressure and blood flow. Five experimental studies were identified with some relevance for development of clinical guidelines. Four canine studies and 1 porcine study reported markers of perfusion using different approaches to chest compressions during CPR.2–6 A large degree of indirectness is present in all of these studies.

Direct cardiac compression has been shown to generate blood flow during CPR. One swine study documented that left ventricular position changes during chest compressions and that the proportion of the left ventricle that is being compressed correlates positively with cardiac output.3 Three of the identified studies showed that increases in intrathoracic pressure result in blood flow during CPR.2,4,6 One canine model of sternal chest compressions suggests that the thoracic pump mechanism is at play in these dogs and that intracardiac and intravascular pressures depend on fluctuations in intrathoracic pressure and not direct compression of the heart.[ 66] A study of manual CPR in dogs in supine position demonstrated that the thoracic pump mechanism prevails in this scenario (rather than direct compression of the heart), and that blood flow is generated in response to intrathoracic pressure changes.4 Another canine study showed that intrathoracic pressure changes can lead to closure of the mitral valve.6

A difference in the predominant mechanism of blood flow with different chest compression points during lateral chest compressions was supported by an experimental dog study evaluating mitral valve motion using transthoracic and transesophageal echocardiography in dogs weighing 18-26kg.5 With hands placed over the widest portion of the chest, the thoracic pump mechanism with the heart acting as a passive conduit seemed to prevail as demonstrated by non-opposing mitral valve leaflets, while with compressions directly over the heart, the mitral valve leaflets fully closed, supporting the cardiac pump theory.5 The chest conformation of the dogs in this study is not well described.

Moreover, this evidence suggests that blood flow in CPR can occur due to both changes in intrathoracic pressure and direct cardiac compression, and that hand placement over the thorax can impact which of these mechanisms predominates during chest compressions.

Treatment recommendation

We recommend performing chest compressions with hand placement over the heart in medium- to large-sized, keel-chested dogs (strong recommendation, very low quality of evidence).

Justification of treatment recommendation

Although no papers were identified to directly address this PICO question, evidence suggests that hands placed directly over the heart during chest compressions in lateral recumbency create a cardiac pump mechanism of blood flow and that when hands are placed in other locations, a thoracic pump mechanism predominates. In medium- to large-sized, keel-chested dogs it is generally assumed based on conformation that hand placement directly over the heart creates sufficient compression of the thorax to create a cardiac pump mechanism of flow; thus, hand placement over the heart is likely preferable in these dogs.

Knowledge gaps

There are no studies that evaluate outcomes among different hand placements for lateral chest compressions in medium- to large-sized, keel-chested dogs.