Haemodynamic changes during experimental tetanus toxicity in dogs

Survival in canine tetanus - retrospective analysis of 42 cases (2006-2020)

Objective

To define factors associated with survival in dogs with tetanus and to evaluate the prognostic significance of an established severity classification scheme.

Methods

Medical records of dogs with the clinical diagnosis of tetanus were retrospectively reviewed with regard to signalment, clinical signs, clinicopathological findings on admission, wound characteristics, complications, therapeutic measures, and survival to discharge. Based on the extracted data, dogs were graded according to a previously published 4-class severity scheme. Non-parametric tests were applied for comparisons between survival categories.

Results

Forty-two dogs fulfilled inclusion criteria, of which 32 survived. Of 10 non-survivors, 4 died and 6 were euthanised. Non-survivors were more often younger than 2 years of age (6/10 vs. 7/32 dogs, p = 0.023), had shorter duration of specific signs of tetanus (time from onset of typical signs to presentation) (2 vs. 4 days, p = 0.016), were prescribed less often antibiotics prior to presentation (p = 0.006), had higher tetanus severity grade (10/12 dogs in Class III or IV died, p < 0.001), more often received acepromazine (p = 0.009) and atropine (p = 0.012), and more often had hyperthermia (p = 0.005) and respiratory complications (pneumonia, laryngeal spasm; p = 0.008). Wound characteristics, the use of tube feeding, metronidazole, methocarbamol, magnesium and antitoxin were not significantly different between non-survivors and survivors.

Clinical significance and conclusion

Young dogs with a rapid course of severe generalized tetanus have a guarded prognosis. The previously described severity classification scheme proved valuable in predicting survival. Prospective multi-center studies are needed to clarify the prognostic significance of age, sedative usage and modified versions of an established classification scheme, including the presence of respiratory complications.

Risk factors associated with outcome in dogs with tetanus: 38 cases (1987–2005)

OBJECTIVE

To assess the clinical course of disease and risk factors associated with outcome in dogs with tetanus.

DESIGN

Retrospective case series.

ANIMALS

38 dogs with tetanus.

PROCEDURES

Data were collected from medical records of dogs with tetanus, including signalment; wound characteristics; initial clinical signs; severity of worst clinical signs; time to wound management, antimicrobial treatment, and antitoxin administration; and 28-day survival rate. Statistical analyses were performed to evaluate relationships between the potentially predictive variables and disease progression and outcome.

RESULTS

The 28-day survival rate was 77% (among 35 uncensored dogs). The most common initial clinical signs in affected dogs were ocular (n = 18) and facial (11) abnormalities. Nineteen dogs progressed to recumbency with severe muscle spasms, and 14 dogs had high or low heart rate or blood pressure values. Eight dogs died or were euthanized because of complications of tetanus. There was a significant association between younger age and development of more severe clinical signs. Furthermore, a significant inverse relationship between development of severe clinical signs and survival was identified. There was no association between earlier initiation of wound management, antimicrobial administration, or antitoxin administration and either progression of signs or 28-day survival rate. Wound type was not associated with 28-day survival rate.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that younger dogs with tetanus may be more likely to develop severe clinical signs. The prognosis for survival in dogs with tetanus is good if abnormalities in heart rate or blood pressure values do not develop.

Carotid chemoreceptor reflex in rats during experimental tetanus toxicity

The effects of stimulation of carotid body chemoreceptors on blood pressure, heart rate and ventilation were compared in normal rats and rats with local or generalised tetanus toxicity induced by injection of the toxin. Carotid chemoreceptor stimulation in an increase in blood pressure and a decrease in heart rate in both control and tetanus rats. However, while chemoreceptor stimulation resulted in increases in ventilation of 115% and 123% in normal rats and rats with local tetanus respectively, the increase in rats with generalised tetanus was only 29%. The experiments indicate that normal rats and rats with tetanus toxicity exhibit identical pressor and heart rate responses to stimulation of carotid chemoreceptors whereas the ventilatory response is attenuated in the tetanus rats.

The effects of induced hypoxia on the cardiovascular system in dogs poisoned with tetanus toxin

Tetanus toxicity was induced in dogs by injecting the toxin subcutaneously in the groin. On developing generalised toxic symptoms, these dogs were characterised by signs of increased sympathetic discharge to the cardiovascular system as evidenced by high basal values of blood pressure, heart rate and LV dP/dt max. Mild to moderate hypoxia induced by ventilation with 10% O2 in N2 had no appreciable effect on the cardiovascular variables. However, moderate to severe hypoxia induced by ventilation with 7% O2 in N2 further increased the sympathetic discharge to the heart and blood vessels resulting in increases in heart rate, LV dP/dt max and blood pressure. These responses were abolished by adrenergic blockers. The responses in the tetanus dogs were identical to those seen in dogs without tetanus toxicity. Atropine or moderate lactic acidaemia did not alter the responses to hypoxia. Beta-adrenergic blockers appear to be useful drugs in the control of tetanus patients who show evidence of increased sympathetic activity or who develop hypoxaemia.