Accurate and continuous measurement of oxygen deficit during haemorrhage in pigs

Objective

Haemorrhagic shock can cause organ failure and high mortality. Uncontrolled bleeding, a predetermined bleeding volume or blood pressure controlled bleeding are traditionally used to study haemorrhagic shock. These models are influenced by compensatory mechanisms preventing accurate knowledge about the severity of cellular insult. We describe the use of a method for continuous measurement of oxygen deficit during haemorrhage in pigs.

Methods

We defined a cumulative oxygen deficit of approximately 100 mL/kg as the primary endpoint for severe haemorrhage. For continuous assessment of oxygen deficit a metabolic monitor (Deltatrac™ II, Datex-Ohmeda Instrumentation Corp., Helsinki, Finland) was used. Data are presented as mean ± SD; ^*P < 0.05 was considered to be significant.

Results

17 out of 22 anaesthetised male pigs achieved a mean cumulative oxygen deficit of 106 ± 3 mL/kg (range: 95–117 mL/kg) by withdrawing an average blood volume of 47 ± 6 mL/kg over 1 h. Mean arterial blood pressure (MAP) fell from 83 ± 19 to 22 ± 7 mmHg (baseline versus shock), heart rate increased from 83 ± 7 to 147 ± 37 min⁻¹. Venous base excess changed from 4.8 ± 2.4 to −12.5 ± 3.4 mmol/L and venous lactate increased from 1.5 ± 0.4 to 13.3 ± 2.4 mmol/L after haemorrhage. Two pigs (11%) died during the haemorrhagic shock phase. The traditional method of assessing haemorrhage (measuring blood volume lost) showed only a poor correlation with heart rate (r = 0.3872; P = 0.1540), MAP (r = 0.3901; P = 0.1505), mixed venous oxygen saturation (svO₂; r = 0.0944; P = 0.7379) or cardiac index (CI; r = 0.2101; P = 0.4523). Cumulative oxygen deficit correlated significantly better with heart rate (r = 0.7175; P = 0.0026), MAP (r = 0.5039; P = 0.0556), svO₂ (r = 0.7084; P = 0.0031) or CI (r = 0.6260; P = 0.0125).

Conclusion

We describe a model to study haemorrhagic shock based on the cumulative oxygen deficit. We believe that the use of a metabolic monitor to measure oxygen deficit in our model represents an improvement on the current available methods to study the effects of haemorrhagic shock.     

Advantages and disadvantages of PET and SPECT in a busy clinical practice

The continued high utilization of rest-stress single-photon emission computed tomographic (SPECT) myocardial perfusion imaging (MPI) is supported by its known clinical benefits, established reimbursement, and wide availability of cameras and radiopharmaceuticals. However, traditional rest-stress SPECT protocols tend to be lengthy and inefficient, and the prevalence of equivocal studies continues to be a problem. The use of stress-only SPECT protocols in selected patients, and a new generation of ultrafast SPECT cameras have led to improved image quality, reduced dosimetry and shorter, more efficient MPI protocols. The utilization of positron emission tomographic (PET) MPI has been accelerated by the availability of radiopharmaceuticals that can be generated on-site, and by the availability of more PET cameras. Emerging evidence consistently demonstrates that PET provides improved image quality, greater interpretive certainty, higher diagnostic accuracy, lower patient dosimetry, and shorter imaging protocols as compared to SPECT. Importantly, PET imaging allows assessment of left ventricular function at peak-stress, and evaluation of microvascular function through the measurement of absolute myocardial blood flow at rest and at peak-stress. Wider utilization of PET MPI is hindered by a high cost of entry, high on-going costs, and an immature reimbursement structure.     

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